BY THE SAME AUTHOR. 
GUIDE TO THE STUDY OF 
INSECTS, and a Treatise on those Injurious 
and Beneficial to Crops, for the use of Colleges, 
Farm-Schools, and Agriculturists. With fifteen 
Plates, and six hundred and seventy Wood-cuts. 
8vo, cloth, $5.00. 
LIFE HISTORIES OF ANIMALS, 
INCLUDING MAN ; or, Outlines of 
Comparative Embryology. Copiously illustrated. 
8vo, cloth, $2.50. LIFE HISTORIES 
OF 
ANIMALS, INCLUDING MAN 
OR 
OUTLINES OE COMPARATIVE EMBRYOLOGY 
BY 
A. S. PACKARD, Jr. 
v \ \ 
Author of “ A Guide to the Study of Insects,” etc 
NEW YORK 
HENRY HOLT and COMPANY 
1 8 76. Entered according to Act of Congress, in the year 1876, by 
A. S. PACKARD, Jr. 
in the Office of the Librarian of Congress, at Washington. 
PRINTED AT 
THE SALEM PRESS, F. W. PUTNAM & CO., 
Salem, Mass. TO THE 
MEMORY OF 
LOUIS AGASSIZ 
IN RECOGNITION 
OF 
THE IMPULSE HE GAVE TO THE STUDY OF 
C O MP A R A TIVE EMBRYOLOGY 
THIS LITTLE WORK 
IS GRATEFULLY DEDICATED 
► 
BY ( 
THE AUTHOR. PREFACE. 
These condensed biographies of animals have grown out of a 
series of notes made originally for the writer’s own information. 
It then occurred that what had been found useful to him might 
prove of service to others, and accordingly they were printed from 
time to time in the “American Naturalist” for 1875. 
These papers are now offered to the public after undergoing 
careful revision, and with the addition of the chapters on Mam- 
mals and Man. 
It is hoped that in their present form, they will be useful as 
containing the outlines of Comparative Embryology, forming a 
book of reference for teachers and advanced students, designed 
to supplement text books of zoology and comparative anatomy, in 
which little or nothing is said of the modes of growth of animals, 
especially of the surprising changes undergone before birth. 
The embryology of the leading groups of the animal kingdom 
is treated of without reference to a rigid classification, which it 
was not the intention of the author to present in this connection. 
A large number of the illustrations engraved especially for the 
work have been drawn as a labor of love by Mr. S. E. Cassino, of 
Salem. Due acknowledgments of the sources from which they 
are copied are made in the text. 
Peabody Academy of Science, 
Salem, Mass., Dec. 24, 1875. LIFE HISTORIES 
OF 
ANIMALS, INCLUDING MAN. 
I. THE MONERA. 
Structure and Habits. Haeckel, in 1868, applied to this group 
of organisms, which are doubtfully referred to the animal kingdom, 
the term Monera (from iJLovrjpyq, simple) in allusion to the extreme 
simplicity of their structure. “Their whole body,” he remarks, 
“ in a fully developed and freely moving condition, consists of an 
entirely homogeneous and structureless substance, a living parti- 
cle of albumen, capable of nourishment and reproduction.” They 
differ from the Amoebae, hitherto supposed to be as simple as any 
organism, in the want of a nucleus and of contractile vesicles. 
Moreover, they (as in Protamoeba) differ from the Rhizopodous 
Amoeba in being entirely homogeneous in structure, there being, 
as Haeckel observes, “no apparent difference between a more 
tenacious outer and a softer inner sarcode mass,” as is “percep- 
tible in most, perhaps in all, true Amoebae.” 
The motions of these Moners are effected by contraction of the 
homogeneous substance of the body, and by the irregular protru- 
sion of portions of the body, forming either simple processes 
(pseudopodia) or a net-work of gelatinous threads. The food is 
taken in after the manner of the Amoeba, the diatom, desmid or 
some protozoan being surrounded by the pseudopodia and gradually 
enfolded by the extremely extensible body, mass. 
The Monera are divided into two groups : 
1. Gymnomonera, comprising the genera Bathybius, Protobathy- 
bius, Protamoeba, Protogenes and Myxodictyum, which do not be- 
come encysted and consequently protected b}r a case. 
LIFE HISTORIES OF ANIMALS. 
1 2 
LIFE HISTORIES OF ANIMALS. 
2. Lepomonera, which become encysted and protected by a case, 
as in the genera Protomonas, Protomyxa, Vampyrella and Myxas- 
trum. 
The simplest form of all is Protamoeba, which is a simple mass 
Fig 1. 
of protoplasm without vacuoles (little cavities), which protrudes 
simple processes (pseudopodia) not ramifying or forming a net- 
work. Protogenes differs in protruding ramifying and anastomo- 
Bathybius. THE MONERA. 
3 
sing gelatinous threads, while Myxodictyum, the most complicated 
form, is made up of several simple Actinoplirys-like bodies, whose 
pseudopodia branch out and interlace, forming a net. 
Bathybius was first discovered by Prof. Wyville Thompson in 
1869 in dredging at a depth of 2435 fathoms at the mouth of the 
Bay of Biscay. He describes it as a “ soft, gelatinous, organic 
matter, enough to give a slight viscosity to the mud of the surface 
layer.” Thompson also adds that if a “little of the mud in which 
this viscid condition is most marked be placed in a drop of sea 
water under the microscope, we can usually see, after a time, an 
irregular net-work of matter resembling white of eggs, distin- 
guishable by its maintaining its outline and not mixing with the 
water. This net-work may gradually alter in form, and entan- 
gled granules and foreign bodies change their relative positions.” 
To this low Moner, Huxley has given the name of Bathybius Hcuck- 
elii (Fig. 1, with coccoliths embedded in the protoplasm, from 
Thompson’s “Depths of the Sea”). This Moner, adds Thomp- 
son, “whether it be con- 
tinuous in one vast sheet, 
or broken up into circum- 
scribed individual particles, 
appears to extend over a 
large part of the bed of the 
ocean.” It should be stated 
that Thompson and others 
do not believe that Bathy- 
bius is really an organic be- 
ing. Bathybius has been 
discovered at a depth of 
from fifty fathoms down- 
wards in the Adriatic Sea, 
by Oscar Schmidt. The 
Bathybius mud was detected by its yellowish gray color and its 
characteristic greasy nature. 
Fig. 2. 
Protobathybius Robesonii. 
Under the name of Protobatliybius Robesonii Dr. Bessels men- 
tions a Moner allied to Bathybius. I am indebted to Dr. Bessels 
for the following account and figure of it (Fig. 2, X 500 diame- 
ters) : “It is mainly distinguished from Bathybius by the absence 
of both the Discolithes and Cyatholithes. For this reason I take 
it to be an older form than Bathybius, whence the name given to 4 
LIFE HISTORIES OF ANIMALS. 
it. It consists of nearly pure protoplasm, tinged most intensely 
by a solution of carmine in ammonia. It contains fine gray gran- 
ules of considerable refracting power, and besides the latter a 
great number of oleaginous drops, soluble in ether. It manifests 
very marked amoeboid motions and takes up particles of carmine 
or other foreign substances suspended in the water in which it 
is kept. It hardly contained any foreign matter, except a fine 
sediment of limestone constituting the bottom of the sea. It was 
taken by means of a water bottle at a depth of ninety fathoms in 
Smith’s Sound, lat. 79° 30; N.” 
The Protogenes primordialis of Haeckel is a simple, shapeless 
mass of protoplasm, without vacuoles, but with over 1000 very 
fine pseudopodia, with numerous ramifications and anastomoses. 
The largest specimens are '04 inch in diameter. It is a marine 
form, found at Nice. It reproduces by fission. 
Myxodictyum is made up of several individuals, each one of 
which is like Protogenes, but with fewer pseudopods. M. sociale 
Haeckel, in the single specimen observed, formed a mass nearly an 
inch and a half in diameter, and was discovered in the Straits of 
Gibraltar. 
Protomonas amyli (Ckski) is a fresh-water, monad-like form, 
found by Cienkowski in Germany and Russia, and is from ‘08 to 
•20 inch in diameter. Protomyxa aurantiaca Haeckel has vacuoles 
in its simple, shapeless, orange-red body, and in the encysted 
condition is a globular jelly-like mass over half an inch in diam- 
eter. It occurred on empty shells of Spirula Peronii, floating 
about on the open sea, and driven in oil the coast of one of the 
Canary Islands. Vampyrella, as its name implies, is a jelly-like 
mass, which according to Cienkowski bores into the cells of con- 
fervae and other fresh-water algae, and sucks out their contents. 
Another species, V. vorax, engulfs diatoms, desmids and infusoria, 
drawing them into the interior of its body. 
The highest form among the Moners is Myxastrum radians 
of Haeckel, which forms a radiating ball of jelly of tough consist- 
ence from T2 to *20 inch in diameter. It has very tough, stiff' 
pseudopods. In the encysted condition it is nearly half an inch 
in diameter, and occurred on the beach of one of the Canary 
Islands. 
Development. In Protamceba and Protogenes, Haeckel tells ns 
we find the simplest possible mode of reproduction. They mul- THE MONERA. 
tiply by merely dividing into two portions, each part becoming 
an individual. 
The distinguished Russian microscopist Cienkowski has given 
an account of the mode of development of Protomonas amyli, 
which corresponds to that of the lowest algse, such as Protococcus 
(see Clark’s Mind in Nature, p. 136, Figs. 73-79) ; both repro- 
duce by spores; those of the animal Protomonas may be called 
“zoospores.” Fig. 3 (copied from Cienkowski) represents at 
A this moner during the formation of the zoospores ; B, a zoo- 
spore hatched out; C, D (A — D X 350 diameters), the Amoeba- 
like form it afterwards assumes. From these stages Cienkowski 
traced it to the encysted, or resting stage, E (y, food ; s, a pro- 
jection inwards of the cell-wall; x, moner-cyst X 450). This 
form lives in putrefying Nitellse. It should be observed that the 
Fig. 3. 
Development of Protomonas. 
cyst of this Protomonas, as in the true Monads studied by Cien- 
kowski, is composed of cellulose, while the granular contents be- 
come colored with chlorophyll. In these respects they are plants, 
but it should be remembered that cellulose is said to occur in the 
mantle of the Tunicates and various parts of Articulates and Ver- 
tebrates, while chlorophyll occurs in the Infusoria and Hydra. 
The course of development of Protomyxa has been observed by 
Haeckel. The orange-red contents of the ball or cyst (Fig. 4, 
A) of this moner, divided, after it had retracted itself from the 
hyaline capsular wall, into several hundred small, round, thor- 
oughly structureless, naked balls (Fig. 4, B). This process 
Haeckel regards rather as a “germ formation,” than a process of 
division or gemmation. These small globular masses of proto- 
plasm (a) are each drawn out into a long tail (cl), and issue from 6 
the cyst as “swarm-spores” (zoospores, Fig. 4, C a. d, c). 
These zoospores then assume an amoeba-form. These unite by 
twos or threes, or more, and form a new individual as at D, where 
two amoeba-like germs unite themselves by their anastomosing 
pseudopods and draw themselves over a Diatom (a), meet in the 
middle, and unite into one individual moner. Fig. 4, E, repre- 
sents a fully grown P. aurantiaca after having had a liberal diet 
of shelled Infusoria (E, a). From the central sarcode body the 
very strong, branching, tree-like pseudopods radiate, their outer 
LIFE HISTORIES OF ANIMALS. 
Fig. 4. 
Development of Protomyxa. 
anastomoses forming numerous crescent-shaped meshes. The vac- 
uoles extend into the larger pseudopods ; they first appear in the 
Amoeba stage after they begin to take food. 
This adult, Amoeba-like form becomes encysted in the manner 
thus described by Haeckel. “ To complete the natural history of 
the Protomyxa, it still remained only to observe the encysting of 
the adult form, the transition from the free moving plasmodia 
to the stationary red balls which had attached themselves to the 
Spirula shells near the latter. I succeeded in establishing this 
also. Two of the largest of the best fed plasmodia, which con- THE MONERA. 
tained very numerous vacuoli, and which had formed a very ex- 
tended sarcode net, with many branches and anastomoses, after 
some time began to slacken their extremely rapid currents, and to 
simplify their pseudopods. The silicious shells of the many dia- 
toms which had been absorbed were rejected, and the branches 
and twigs of the pseudopods were successively retracted. At last 
they drew back the main stems, which had everywhere become 
simple, into the central plasma-body, and the entirely homoge- 
neous sarcode body took the form of an irregular lump, and 
finally rounded itself into a regular ball. 
“ Now commenced the separation of the covering of the cyst, 
in which the sharply defined single outline of the orange-red 
plasma-balls passed into a perceptible, though certainly fine, 
double outline. A second, and then a third, concentric boundary 
line soon followed this, and then the proper concentric hyaline 
cyst-covering appeared somewhat quickly (in the course of a day) ; 
its layers corresponded with the above stated breaks of the sepa- 
rated gelatinous skin. At first a quantity of vacuoli were still 
perceptible in the plasma during the encysting process, which ap- 
peared and disappeared here and there, but visibly decreased in 
numbers ; and after the complete development of the cyst covering, 
no vacuoli could be any longer perceived in the orange-red plasma, 
now interspersed with numerous granules. The encysted plasma- 
ball was now no longer to be distinguished from those red balls 
whose transition to the mass of sporules I have above described. 
Thus was the cycle of the generation of the Proto my xa completed, 
and the course of its simple and remarkable life history estab- 
lished.” 
The phases may be thus summed up : — 
1. The free swimming flagellate state (sporule or zoospore). 
2. The creeping Amoeba state. 
3. The reticulated Rhizopod state. 
4. The encysted state. 
Somewhat similar is the development of Vampyrella spirogyrce, 
which penetrates into the cells of the fresh-water plant Spirogyra, 
and absorbs its protoplasm. Fig. 5, A, represents the adult, 
with its radiating pseudopods, and a large one in the act of boring 
into the walls of the plant. It then withdraws its pseudopodia, 
and assumes what Cienkowski calls the cell-state. During this 
period it is surrounded by a delicate membrane. The granular 8 
LIFE HISTORIES OF ANIMALS. 
contents divide into three portions, each of which becomes an 
Amoeba-like being (Fig. 5, B, showing one creeping out of the 
cell, x. C, D, E, the Amoeba-like stage). Finally one of these 
Fig. 5. 
Amoeba-like forms becomes encysted (Fig. 5, F, y, the food- 
granules ; t, cell-wall of the cyst). To sum up the life-history of 
Vampyrella as observed by Cienkowski, we have : — 
Development of Vampyrella. 
1. An Amoeba-stage. 
2. A cell-stage. 
3. A second Amoeba-stage. 
4. An encysted stage. 
So exactly does this mode of development parallel that of Col- 
podella pugnax described by Cienkowski, who regards it as a fla- 
gellate infusorian allied to Monas, that we doubt the naturalness 
of Haeckel’s division of Monera. Colpodella and in fact Proto- 
monas differ from the Monads (Flagellata) simply in having no 
nucleus. Whether this may not be found on further observation, 
or whether its absence or presence is so important as Haeckel 
thinks, future observation will show. We are now inclined to re- 
gard the Monera as a somewhat artificial group. It should be 
noticed that none of the other Moners have a “cell-state,” but the 
Amoeba-like organism becomes encysted at once after becoming 
fully fed. 
The development of Myxastrum radians of Haeckel is much like THE GREGARINIDA. 
9 
that of Protomyxa, but differs in some important respects. The 
cyst becomes filled with numerous conical portions, whose points 
rest towards the centre of the ball, while 
their rounded bases produce a mulberry- 
shaped outline externally. In the next 
stage these cone-shaped divisions have as- 
sumed a spindle shape, and each separate 
spore has developed a silicious covering 
(Fig. 6, A, a). When the spindle-shaped 
spore has been set free, the protoplasmic con- 
tents (b) slip out of the silicious shell (Fig. 
6, B, a), and assume an Amoeba form, with 
numerous radial pseudopods (Fig. 6, C), 
which in the fully formed Moner become as 
long as the diameter of the body. 
With the facts that have been presented, 
the question arises whether these moners are animals or vegetables. 
Structurally, and in their mode of development, the Monera would 
seem not to differ essentially from the lowest plants, such as the 
Myxomycetes and lowest Algae; but physiologically, or in what 
they do, they differ, as H. J. Clark (Mind in Nature, pp. 151,156) 
says of Amoeba, in taking in living organisms entire, digesting 
their protoplasm and rejecting the silicious coverings of the dia- 
toms or infusoria they have swallowed. The plants of corres- 
pondingly low organization on the contrary absorb only the ele- 
ments in an unorganized state. 
Fig. 6. 
Development of Myx- 
a strum. 
LITERATURE. 
Hceckel. Ueber den Sarcodekorper der Rhizopoden. (Siebold und Kblliker’s Zeits- 
chrift fUr natunvissenchaftliche Zoologie, xv. 1866.) 
Monograpbie der Moneren. (Jenaische Zeitschrift fiir Medicin und Natur- 
wissenschaft, iv. 1868. Translated in Quart. Journ. Microscopical Science, 1869.) 
Cienkowski. Beitrage zur Kenntniss der Monaden. Schultze’s Archiv fiir Micros- 
kopische Anatomie. Bd. 1. 1865. 
Huxley. On some Organisms living at great Depths in the North Atlantic Ocean (Ba- 
thybius. (Quart. Journ. Micr. Sc., viii. 1868.) 
II. THE GREGARINIDA. 
Structure and Habits. First discovered by Dufour, these para- 
sitic protozoans, with an organ, i. e., a nucleus, were considered as 
the lowest animals until the discovery by Haeckel of the still sim- 
pler Monera. It is now known that they pass through the Moner- 
state and attain a true Amceba condition, having an outer, clear- 10 
LIFE HISTORIES OF ANIMALS. 
muscular, and an inner, medullary or granular, layer, which are 
more distinct than in the Amoebae, and also a nucleus. In form 
they are more or less worm-like. They are parasitic, living in 
many types of animals, especially the insects and worms, and vary 
greatly in form. The largest species known is Gregarina gigantea 
(Fig. 7, after E. Van Beneden), which lives in the intestinal canal 
of the European lobster. It is worm-like, remarkably slender, be- 
ing -64 inch in length. It is, in fact, the largest one-celled animal 
known, and in size may be compared with the cells of some vege- 
tables ; in the animal kingdom it is only surpassed by the eggs of 
birds, which are really cells. In this organism an external, struc- 
tureless, perfectly transparent membrane, with a double contour, 
can be very clearly distinguished. It represents the cell wall of 
other cells. Beneath this outer wall is a continuous layer of con- 
tractile substance, by which these animals retain their form, not 
changing as in the Amoeba; it was first discovered in 1852, by 
Prof. J. Leidy. He showed that there existed under the cuticular, 
structureless membrane, a so-called muscular layer, which in con- 
tracting becomes longitudinally folded, so as to produce a marked 
striation. Van Beneden adds that in “the immense Gregarina of 
the lobster I have assured myself of the presence of, under the 
cuticle, a true system of muscular fibrillae, comparable to those of 
the Infusoria.” From this fact he places these animals above the 
Amoebae, which move by the simple contractility of their sarcode 
or protoplasm, a property of all animal and vegetable protoplasm 
generally. He therefore opposes the opinion of Haeckel that the 
Gregarina is an Amoeba, degraded by its parasitic life. 
The internal granular matter of the Gregarina is extremely 
mobile, like protoplasm generally. “ The whole cavity of the 
body is filled,” says Van Beneden, “with a granular matter formed 
by a viscid liquid, which is perfectly transparent. This holds in 
suspension fine granulations of a rounded form, which are formed 
by a highly refractive and slightly' }Tellow matter.” In this gran- 
ular matter the nucleus is suspended. The nucleus is surrounded 
by a membrane, and the cavity of the vesicle is filled by a homo- 
geneous, colorless and transparent liquid. This nucleus contains 
an inner vesicle, or nucleolus, which has the singular feature of 
spontaneously appearing and disappearing in a very short space 
of time. “If one of these Gregarinae of moderate size is ob- 
served, the nucleus is seen at first provided with a single nucle- THE GREGARINIDA. 
11 
olus, presenting some seconds later a great number of little 
refracting corpuscles, of very variable dimensions, which are also 
nucleoli. Some of these enlarge^chnsiderabl}7, whilst the primi- 
tive nucleolus diminishes in volume little by little, finally disap- 
pearing. The number of nucleoli varies at every instant.” These 
novel observations are considered of great importance b}7 Van 
Beneden as showing that the nucleolus of the Gregarina, and con- 
sequently the nucleoli of cells generally are sometimes, if not 
always, devoid of a membrane. And he draws the inference 
“that the nucleus of a cell is not necessarily a vesicle, and that 
Fite. 7. 
Development of Gregarina. 
contrary to the generally received opinion, a nucleus of a cell may 
be equally devoid of membrane,” though we may add that he saw 
it in the Gregarina of the lobster. Van Beneden distinguishes 
three kinds of motions in the Gregarinae. 1. They present a very 
slow movement of translation, in a straight line and without the 
possibility of distinguishing any contraction of the walls of the 
body which could be considered as the cause of the movement. 
It seems impossible to account for this kind of motion. 2. The 
next kind of movement consists in the lateral displacement of 
every part, taking place suddenly and often very violently, from a 12 
LIFE HISTORIES OF ANIMALS. 
more or less considerable part of its body. Then the posterior 
part of the body may be often seen to throw itself out laterally by 
a brusque and instantaneous movement, forming an angle with the 
anterior part. 3. Owing to the contractions of the body the gran- 
ules within the body move about. 
Development. The history of Gregarina has been worked out 
by Siebold, Stein, Lieberkuhn, and more recently by E. Van Bene- 
den. The course of development is as follows : the worm-like 
adult, G. gigantea (Fig. 7, K, n nucleus; L, two individuals of 
natural size), which is common in lobsters on the European coast 
in May, June and August, becomes encysted in September in the 
walls of the rectum of the lobster, the cysts (Fig. 7, A) appear- 
ing like “little white grains of the size of the head of a small 
pin.” When thus encysted the animal loses its nucleus, and the 
granular contents of the cyst divide into two masses (B), like the 
beginning of the segmentation of the yolk of the higher animals. 
The next step is not figured by Van Beneden, and we therefore 
introduce some figures from Lieberkuhn which show how the gran- 
ular mass breaks up into zoospores (called by authors “ pseudo- 
navicellm,” and by Lieberkuhn “ psorosperms” ) with hard shells. 
After the disappearance of the nucleus and vesicle, and when 
the encysted portion has become a homogeneous granular mass, 
this mass divides into a number of rounded balls (Fig. 7, C). 
These balls consist of fine granules, which are the zoospores in 
their first stage (Fig. 7, N). They then become spindle-shaped 
(O), and fill the cyst (Fig. 7, M), the balls having meanwhile dis- 
appeared. From these zoospores are expelled Amoeba-like masses 
of albumen (D, E) which, as Van Beneden remarks, exactly re- 
semble the Protamceba already described. This moner-like being, 
without a nucleus, is the young Gregarina. 
But soon the Amoeba characters arise. The moner-like young 
(Fig. 7, D, E) now undergoes a further change. Its outer por- 
tion becomes a thick layer of a brilliant, perfectly homogeneous 
protoplasm, entirely free from granules, which surrounds the cen- 
tral granular contents of the cytode (Haeckel) or non-nucleated 
cell. This is the Amoeba stage of the young Gregarina, the body, 
as in the Amoeba, consisting of a clear cortical and granular me- 
dullary or central portion. 
The next step is the appearance of two arm-like projections 
(Fig. 7, F), comparable to the pseudopods of an Amoeba. One THE GREGARINIDA. 
13 
of these arms elongates, and separating forms a perfect Gregarina. 
Soon afterwards the other arm elongates, absorbs the moner-like 
mass and also becomes a perfect Gregarina. This elongated 
stage is called a Pseudofilaria (Fig. 7, G). No nucleus has yet 
appeared. In the next stage (Fig. 7, II, n, nucleus) the body is 
shorter and broader, and the nucleus appears, while a number of 
granules collect at one end, indicating a head. After this the 
body shortens a little more (I, J), and then attains the elongated, 
worm-like form of the adult Gregarina (K). Van Beneden thus 
sums up the phases of growth :— 
1. The Moner phase. 
2. The generating Cytode phase. 
3. The Pseudo-filaria phase. 
4. The Protoplast1 (adult Gregarina). 
5. The encysted Gregarina. 
6. The spoi’ogony phase (producing zoospores). 
It seems evident that the mode of development of the Gregarina 
in part corresponds quite closely with the mode of growth of the 
Moners ; for example, it becomes encysted, i. e., sexually mature, 
produces zoospores (pseudonavicellse), and from these zoospores 
issues the young or larval form of the Gregarina. These zoospores 
abound in damp places and are devoured by insects and worms. 
After they are swallowed the shells burst and the Amoeba-like 
young are set free in the body of their host. 
It will be seen that there is here a total absence of sexual repro- 
duction. The Moner-stage arises by self-division of the contents 
of the cyst, a process analogous to the segmentation of the yolk 
of eggs ; and the Pseudofilarise arise by self-division of the young 
in the Moner-stage, i. e., by a budding process. 
LITERATURE. 
Dufour. Note suv la Gvegavine. (Annales des Sciences Naturelles, xiii. 1828.) 
Siebold. Beitriige zur Geschichte wirbellosev Thieve. 1839. 
Stein. Uebev die Natuv dev Gvegavinen. (Mullev’s Avchiv fiiv Anatomie. 1848.) 
Kolliker. Beitvage zuv Kenntniss niedeves Thieve. (Siebold und Kollikev’s Zeits- 
chvift 1. 1849.) 
Lieberkuhn. Evolution des Gvegavines. (Memoives couvonnes de l’Academie Royale 
de Bvuxelles, xxvi. 1855.) 
E. Van Beneden. On a New Species of Gvegavina to be called Gregarina gigantea. 
(Quavt. Jouvn. Micvoscopical Science, x. 1870.) 
Rechevches suv l’Evolution des Gvegavines. (Bulletins de l’Acad- 
emie Royale de Belgique, xxxi. 1871.) 
xThe Gregarinae and Amoebae constitute Haeckel’s group of Protoplasta. 14 
LIKE HISTORIES OF ANIMALS. 
Structure and Habits. We have almost anticipated a definition 
of the Rhizopoda, of which the Amoeba, or Protean animalcule, is 
the simplest form, by our frequent references to the “Amoeba- 
form” or “Amoeba-like” stages in the Moners and Guegarinas. 
The Amoeba is the starting point, the unit of the nucleated Pro- 
tozoa, the primitive, ancestral form to which the members of the 
subkingdom may be reduced. Until the Monera were discovered 
the Amoeba was regarded as the lowest possible animal. 
With the form of the Monera, a shapeless mass of protoplasm, 
changing each instant, throwing out threads or larger protrusions 
of the body, the Amoeba possesses 
a distinct organ, the nucleus, and 
its body mass is divided into a 
clear cortical and a medullary 
granular mass ; the outer highly 
contractile, the inner granular 
portion acting virtually as a stock 
of food. These granules, like the 
grains of chlorophyll in vegetable 
cells and Diatoms and Desmids, circulate in regular fixed cur- 
rents, according to H. J. Clark. (See Fig. 8, after Clark; the 
usual form of Amoeba diffluens Ehrenberg, magnified 100 diam- 
eters ; the arrows indicate the course of the circulating food. The 
head end is knobbed, and within free from granules.) We have 
then in Amoeba :— 
1. A nucleus, probably representing the nucleus and ovary of 
the Infusoria. 
2. A head and posterior end. 
3. A circulation analogous to that of the Infusoria. 
III. THE RHIZOPODA. 
Fig. 8. 
Amoeba. 
This animal, as we may justly call it, since it takes in living 
protozoans and rejects their shells, has the power of moving in 
a particular direction, one end of the body always advancing 
first; which indicates the rudiments of a nervous and muscular 
power; and can swallow, digest and circulate its food. Whether 
it gives out nitrogen and absorbs oxj'gen or not is unknown. It 
reproduces by self-division, and some allied forms by the produc- 
tion of monad-like, flagellate spores. 
The Amoeba is a fresh-water form, living on the stems and THE RHIZOPODA. 
15 
leaves of fresh-water plants. The late II. J. Clark, our most emi- 
nent microscopist, thus describes its habits in his “Mind in Na- 
ture.” “The three figures [8] represent the various forms which 
I have seen the same individual assume, whilst I had it under the 
microscope, as it crept over the water-plants upon which it is 
accustomed to dwell. The most usual form which it assumed is 
that of an elongated oval (A), but from time to time the sides of 
its body would project either in the form of simple bulgings (B), 
or suddenly it would spread out from several parts of the body 
(C), as if it were falling apart; just as you must have seen a drop 
of water do on a dusty floor, or a drop of oil on the surface of 
water ; and then again it retracted these transparent arms and 
became perfectly smooth and rounded, resembling a drop of slimy, 
mucous matter, such as is oftentimes seen about the stems of 
aquatic plants.” 
Pelomyxa (Fig. 10) is a fresh-water Amoeba-like form, but pro- 
vided with spicules. Under the name of Amoeba sabulosa Prof. 
Leidy describes2 a form which he thinks “is probably a member 
of the genus Pelomyxa,” and which is characterized by the com- 
paratively enormous quantity of quartzose sand which it swallows 
with its food. “The animal might be viewed as a bag of sand !” 
It is from one-eighth to three-eighths of a line in diameter, and 
was found on the muddy bottom of ponds in Pennsylvania and 
New Jersey. It is possibly Pampliagus mutabilis, figured by Pro- 
fessor Bailey in the “American Journal of Science and Arts,” 
1853. Another form resembling Greef’s Pelomyxa, and found 
by Professor Leid}r in a pond in New Jersey, is Deinamoeba 
mirabilis;3 its body bristles with minute spicules. He has also 
described in the same Proceedings (p. 88) Gromia terricola, which 
lives in the earth about the roots of mosses growing in the crev- 
ices of the bricks of the pavements of the streets of Philadelphia. 
He thus graphically describes this singular form. “Imagine an 
animal, like one of our autumnal spiders, stationed at the centre 
of its well spread net; imagine every thread of this net to be a 
living exten'sion of the animal, elongating, branching, and becom- 
ing confluent so as to form a most intricate net; and imagine 
every thread to exhibit actively moving currents of a viscid liquid 
both outward and inward, carrying along particles of food and 
2Proceedings of the Academy of Natural Sciences, Philadelphia, 1874. p. 86. 
31. c. p. 142. 16 
LIFE HISTORIES OF ANIMALS. 
dirt, and you have some idea of the general character of a 
Gromia.” 
A convenient division of the Rhizopods is into two groups, 
Foraminifera and Radiolaria. Schultze divides the former into :— 
1. Nuda, or naked forms, such as Amoeba and Actinophrys. 
2. Monothalamia, forming a one-chambered shell, but with the 
animal undivided, living in the simple hollow of the shell. Fresh- 
water forms are Arcella, Difflugia and Gromia, while Cornuspira 
is a marine form. 
3. PoJythalamia, with many-chambered shells ; all marine. The 
three divisions are represented by (1) Acervulina, (2) Nodosaria 
and (3) Miliola, Rotalina, Globigerina, Textularia, Nummulina, 
Polystomella, etc. 
The Rhizopods are divided by Haeckel into 1. Acyttaria, or the 
one and many chambered Foraminifera; 2. The Heliozoci, repre- 
sented by Actinospliairium (Actinoplirys) Eichhomii, or sun-animal- 
cule ; and 3. The Radiolaria. These last two groups he divides 
(a) into the Monocyttaria (represented by Cyrtidosphaera, Thalassi- 
colla and Acantliometra, etc.) and (b) the Polycyttciria, represented 
by Collozoum, Sphaerozoum and Collospliaera. Haeckel, who has 
studied these Radiolaria more than any one else, though Johannes 
Muller gave us the first definite information about them, says that 
“in the lower forms they are allied to the sun-animalcules and 
Foraminifera, but the higher forms are much more highly devel- 
oped. They differ from both the Actinoplirys and Foraminifera, 
in that the central part of the body is made up of many ceils, 
and is surrounded by a strong membrane. This closed, more or 
less spherical “central capsule” is surrounded by a slimy layer 
of protoplasm, from which thousands of very fine threads radi- 
ate, and often branch out and anastomose. Among them are 
scattered numerous yellow cells, which contain starch granules.” 
(Whether these yellow cells are parasitic organisms, or belong to 
the animal, is not yet known.) Most Radiolaria are provided with 
a highly developed silicious frame-work, like the outer shell of a 
nest of Chinese carved balls, the outer surface of which is studded 
with spines ; but both the form of the silicious box and the spines 
varies greatly, as may be seen by a glance at the accompanying 
plate, I4 (after J. Muller), illustrating the Polycystina. Some 
4 Explanation of the plate. Fig. 1, Tetrapyle octacantlia; Fig. 2, Haliomma ampliidis- 
cus; Fig. 3, Haliomma longispinum; Fig. 4, Haliomma hexacanthum; Fig. 5, Haliomma! PI. I. THE RHIZOPODA. 
17 
Radiolaria have a many chambered shell like those of the Poly- 
thalamia. 
While the Foraminifera live mostly at the bottom of the sea 
(some, however, occurring between tide marks) on stones and sea- 
weeds, creeping over sand and mud by means of their pseudopods, 
the marine Radiolaria for the most part float with outstretched 
pseudopods on the surface of the sea. They occur in countless 
numbers, but are usually so small that until 1858 they had been 
almost entirely overlooked by naturalists. The compound, or so- 
cial forms, such as Collosplioera, are nearly an inch in diameter, 
while most of the simple species cannot be seen with the naked 
eye. The Polycystina occur fossil in abundance at Barbadoes, 
Richmond, Va., and the Nicobar islands. 
Development. So far as is known Amoeba multiplies its kind only 
by the simplest mode of reproduction known, that of self-divis- 
ion. The following figure (9), copied from Haeckel, represents, 
Fig. 9. 
Amoeba sphserococcus 
highly magnified, Amoeba sphcerococcus, a fresh-water species with- 
out a contractile vesicle, in the process of fission; at B is the 
encysted Amoeba in its “resting stage.” It now consists of a 
spherical lump of protoplasm (d), in which is a nucleus (c) with 
its nucleolus (&) and the whole surrounded by a cyst or cell- 
membrane (a). It breaks the cell-wall and becomes free as at 
LIFE HISTORIES OF ANIMALS. 18 
LIFE HISTORIES OF ANIMALS 
A. Self-division then begins as at C, the nucleus doubling itself, 
until at Da and Db, we have as a result two individuals. 
In Pelomyxa, a higher form than Amoeba, we have according to 
Greef a production of ciliated zoospores. This form, described 
by Prof. Greef under the name of 
Pelomyxa palustris (Fig. 10, A, 
a, clear portion ; &, diatoms en- 
closed in the body mass), lives in 
the mud at the bottom of pools, 
and when first seen resembles 
little dark balls of mud *04--05 
inch in diameter. The body mass 
contains numerous vacuoles filled 
with water, and numbers of nu- 
clei and spicules. These nuclei 
and spicules have a dancing mo- 
tion, like the ordinary Brownian 
movements of molecules. There are also numerous hyaline, oval 
or rounded bodies which Greef calls “shining bodies,” and which 
originate from the nuclei. They increase by division within the 
body-mass of the Pelomyxa, becoming Amoeba-like bodies (Fig. 
10, B, n nucleus, c contractile vesicle) which issue in great num- 
bers from the parent-mass. These Amoeboid forms gradually pass 
into flagellate zoospores (Fig. 10, C) with a nucleus and con- 
tractile vesicle. It thus seems that the zoospores of this Rhizopod 
are produced without the animal becoming encysted. 
Fig. 10. 
Pelomyxa palustris. 
As regards the development of Actinophrys and the allied spiny 
forms, Greef thinks that besides being formed by direct self-division, 
there is a resting or encysted stage. “ The latter consists in the 
withdrawal of the sarcode body-mass from the inner boundary 
formed by the union of the bases of the radial spines, leaving a 
rather wide empty border, and its becoming invested by a double 
coat, viz., a firm inner one, when empty, dotted, as if perforated, 
and an outer hyaline one.” 
According to Schneider, Actinophrys Eichliornii undergoes di- 
vision ; the central mass divides twice or thrice. Then the alveo- 
lar cortical layer disappears, and each mass resulting from the 
self-division becomes enc}rsted. This process is undergone in two 
days. It remains encysted through the winter until the beginning THE EIIIZOPODA. 
19 
of Ma}r, -when the cyst drops off and a small Actinophrys with a 
number of nuclei appears. 
As an example of the reproduction of these forms by fission, 
we may cite the case of Gromia socialis, figured by Archer. He 
represents the body of a Gromia after having undergone a trans- 
verse self-fission, having in each portion a nucleus with its nucle- 
olus, the upper segment giving off branched pseudopodia as usual. 
Of the mode of development of the shelled Amoebae or Forami- 
nifera (Polytlialamia), numerous and often accessible as these 
animals are, we know but little. In fact, we have only the frag- 
mentary observations of Max Sclmltze, made in 1856, on a species 
of Miliola sent him from Trieste. He says that this Foraminifer, 
after remaining from eight to fourteen days in the same place on 
the side of the jar, became surrounded with a thin layer of brown- 
ish mud, so that the shell was lost to view. On the 15th of May 
he noticed that small, round, sharply defined bodies escaped from 
the brownish slimy mass, and after some hours as many as forty 
such bodies surrounded the Miliola. These round bodies were 
young Foraminifera in calcareous shells with one turn, but no inner 
walls, somewhat resembling Cornuspira, and with pseudopodia 
already like those of the adult. It is probable, therefore, that the 
shell of the young is formed within the parent. Sclmltze adds 
that the almost complete want of organic contents in the shell of 
the parent at this time, rendered it probable that the whole or 
greater part of its body had passed into those of the young. 
Of the mode of development of the Radiolaria, Prof. Cienkow- 
ski afforded, in 1871, the first definite information, lie states that 
“ J. Muller saw in the interior of an Acanthometra a swarming of 
small monad-like vesicles, which moved about for a time, and 
then changed themselves into Actinophrys-like structures. After- 
wards,” Haeckel saw, first, in Spliserozoids, “the contents of the 
capsules break up into many vesicles, and secondly, in Sphaero- 
zoum, he observed masses of vesicles which exhibited a vibratory 
movement.” Lastly, Schneider had noticed in Thalassicolla groups 
of amoeboid vesicles with movable flagellum-like processes. These 
facts rendered it probable, what Cienkowski has proved, that the 
Radiolaria reproduce by motile germs, i.e., zoospores. 
He studied the compound forms, such as Collosplisera and Collo- 
zoum, which are composed of aggregations of capsules (Fig. 11, A, 20 
LIFE HISTORIES OF ANIMALS. 
a capsule of a young Collosphsera without the latticed shell), held 
together by a common mass of protoplasm. These capsules are 
separated by a certain interval from one another, while the proto- 
plasm binding them together consists of alveoli (vesicles) of 
various sizes, between and on to which sarcodic threads and net- 
works are disposed. “I always found,” he adds, “the capsules 
supported on the surface of the alveoli, often lenticular, com- 
pressed, and enclosed by a radiating layer of protoplasm, which 
also spreads itself over the alveoli, and passed over continuously 
into the sarcodic envelope of neighboring capsules. Besides those 
alveoli which carry capsules, there are 
many smaller, which are free from cap- 
sules.” 
Collosphcera spmosa (Fig. 11, B) pos- 
sesses a fenestrated shell beset with small 
spines, which encloses a capsule with a 
protoplasmic investment. Fig. 11, B, a, 
indicates the problematical yellow cells. 
Fig. 11, A, indicates a young capsule of 
another spineless species, C. Huxleyi 
Mull. The young capsule of this species 
is naked, embedded, without any shell, in 
a radiated protoplasmic sheath, not emar- 
ginated by any sharply marked envel- 
ope. “In this stage they often divide 
themselves by fission into two halves. 
Not until maturer age does the capsule 
obtain a resisting membrane, and become 
enclosed in a fenestrated shell. 
The next change which takes place in 
the capsule is its division into a number 
of little spheroids. This process is accomplished in a single day 
in C. Huxleyi. These spheroids become monad-like bodies, filling 
the capsule with a mass of corpuscles having a tremulous move- 
ment, and which finally swarm out in all directions (Fig. 11, B) 
from the capsule as true zoospores (C). The capsules now die 
and break up. These zoospores are provided with two long cilia. 
In the interior are a few oil drops, and a little crystalline rod, 
which sometimes projects out of the body. 
Fig. 11. 
Collosphaera. 
“Among the swarms of swimming zoospores lay many motion- 21 
THE RHIZOPODA. 
less ones dispersed,” continues Cienkowski. “They were round 
or angular, with drawn-out points,” and one or more constrictions 
could be seen in them (Fig. 11, D). they were de- 
velopmental stages of the zoospores, obtained as they were in 
course of formation from the contents of the capsule.” Cienkowski 
observed the same process in Collozoum inerme, thus substanti- 
ating his observations on Collosplnera. 
In the Rliizopods, then, we know certainly two modes of repro- 
duction :— 
A. By self-division, as in Amoeba. 
B. By the production of zoospores, as in Pelomyxa and the 
Radiolaria. 
In the Radiolaria the following phenomena take place : — 
1. The capsule is filled with spheroids by a probable division of 
the contents of the capsule, as in the encysted stage of Monera 
and Gregarinida. 
2. The “out-swarming” of zoospores. 
LITERATURE. 
A. Naked Rhizopods. 
Auerbach. Ueber die Einzelligkeit der Amoeben. (Siebold and Kolliker’s Zeitschrift, 
1855.) 
Kolliker. Das Sonnenthierehen, Actinophrys sol. (Siebold and Kolliker’s Zeitschrift, 
1849. Translated in Quart. Journ. Micr. Science, 1853.) 
Clark. Mind in Nature. 1865. 
Archer. On some fresh-water Rhizopoda, new or little known. (Quart. Journ. Micr. 
Sc., 1869-71.) 
Schultze. Ueber den Organismus der Polythalamien nebst Bemei'kungen iiber die 
Rhizopoden in Allgeraeinen. 1854. 
Beobachtnngen ueber die Fortpflanzung der Polythalamien. (Miiller’s 
Archiv fill- Anatomie, etc. 1850.) 
Carpenter. Researches on the Foraminifera. (Philosophical Transactions of the 
Royal Society. London, 1856-7.) 
B. Foraminifera. 
C. Radiolaria. 
Muller. Ueber die Thalassicollen, Polycystinen und Acanthometren des Mittel- 
meeres. (Abhandlungen der K. Akad. Berlin, 1858.) 
Haeckel. Die Radiolarien. Eine Monographic, folio, 1862. 
Cienkowski. Ueber Schwarmerbildung bei Radiolarien. (Schultze’s Archiv fur Mik- 
ros. Anatomie, VII, 1871. Translated in Quart. Journ. Micr. Sc., 1871.) 
Schneider. Zur Kenntniss der Radiolarien. (Siebold and Kolliker’s Zeitschrift, 
xxi, 1871.) 22 
LIFE HISTORIES OF ANIMALS. 
We would not pass over certain forms doubtfully referred to 
the Protozoa, by Cienkowski, the only one who has studied them, 
and placed by Haeckel near the Diatoms and Desmids, in his 
IY. THE labyrinthula:. 
Fig. 12. 
Labyrinthula. 
kingdom “Protista,” but which may be provisionally located near 
the Rhizopods. These organisms were found by Cienkowski at 
Odessa beneath the seaweeds growing on the piles in the harbor. 
They are minute, orange-colored organisms, forming reticulated 
threads which enclose spindle-shaped nucleated bodies. Fig. 12, 
represents Labyrinthula macrocystis, highly magnified, with the 
single spindle-shaped bodies starting out from the mass on the 
left, and gliding over the “rope walk,” or framework of threads. 
This framework of cells, as Cienkowski, who studied its develop- 
ment, says, is to be “ considered as an exudation of cells, — as a 
peculiar fibrous jelly-like formation.” In this respect it resembles, 
he adds, the Palmellaceae, Conjugate, and Flagellate Algae in 
which a jelly-like substance is exuded to which the cells adhere. 
Cienkowski gives the following results of his investigations on the 
nature of these singular organisms, which we hope may be discov- 
ered in this country: 
1. They present masses of cells which enclose a nucleus, and 
which increase in number by division; they possess a certain de- 
gree of contractility, and now and then are covered with a cortical 
substance. THE FLAGELLATA. 
23 
2. These cells exude a fibrous substance, which makes a stiff, 
tree-like network, forming a branching framework. 
3. The cells leave the mass and glide in different directions 
along the framework to the periphery of the mass. The Laby- 
rinthula cells can only continue their peregrinations when sup- 
ported by this line of threads. 
Development. The moving cells unite in a new mass and be- 
come cysts, in which each cell is surrounded by a hard covering, 
the whole being held together by a rind like substance. 
After some time four small granules are formed from each cyst, 
which most likely become young Labyrinthula cells. 
He concludes that “these peculiar organisms bear no relation 
to any known group of beings of either of the organic kingdoms. 
They cannot be classed with the sponges, Rhizopoda, Gregarinae, 
or ciliated Infusoria, or with the algae or fungi.” 
CienTcowsH. Ueber die Ban und Entwicklung der Labyrinthuleen. (Schultze’s Ar- 
cliiv, 1867. Abstract in Quart. Journ. Micr. Science, 1867.) 
LITERATURE. 
V. THE FLAGELLATA. 
As with the Amoeba-stage of the lower Protozoa, so we have had 
anticipations of the Monads, as the Flagellata may be popularly 
styled, in the zoospores of the lower Protozoa and Monera. The 
monads in point of structure are scarcely more highly organized 
in their lowest forms than the spores of the algae and the zoo- 
spores of the other Protozoa, for which they are often mistaken. 
They are exceedingly minute, oval bodies, with a nucleus and 
contractile vesicle and one or two long whip-like cilia, whence the 
term Flagellata. 
The true monads have been studied by the late Professor H. J. 
Clark with more success than by any one else. Monas termo Ehr. ? 
is much like single individuals of Urella glaucoma Ehr.? (Fig. 13), 
though the body is shorter and more regularly oval. It is faint olive 
in color. The monads are provided with one or more flagella, or 
bristle-like cilia, situated in M. termo on the front near the beak- 
like prolongation of the body. In swimming the monad stretches 
out the flagellum, which “ vibrates with an undulating, whirling 
motion, which is most especially observable at its tip, and pro- 
duces by this mode of propulsion the peculiar rolling of the body, 
which at times lends so much grace to its movements as it glides 24 
LIFE HISTORIES OF AXIMALS. 
from place to place” (Clark). When the monad is fixed the flagel- 
lum is used to convey food to the mouth, which lies between the 
base of the flagellum and beak, or “lip,” as Clark calls it. The 
food is thrown by a sudden jerk and with precision, directly 
against the mouth. “ If acceptable for food, the flagellum presses 
its base down upon the morsel, and at the same time the lip is 
thrown back so as to disclose the mouth, and then bent over the 
particle as it sinks into the latter. When the lip has obtained a 
fair hold upon the food, the flagellum withdraws from its incum- 
bent position and returns to its former rigid, watchful condition. 
The process of deglutition is then carried on by the help of the lip 
alone, which expands latterly until it completely overlies the par- 
ticle. All this is done quite rapidly, in a few seconds, and then 
the food glides quickly into the depths of the body, and is envel- 
oped in a digestive vacuole, whilst the lip assumes its usual con- 
ical shape and proportions.” 
All the monads have a contractile vesicle. In Monas termo 
Clark observes that it is “so large and conspicuous that its globu- 
lar form may be readily seen, even through the greatest diameter 
of the body; and contracts so vigorously and abruptly, at the 
rate of six times a minute, that there seems to be a quite sensible 
shock over that side of the body in which it is embedded.” The 
contractile vesicle is thought to represent the heart of the higher 
animals. The reproductive organ may possibly, says Clark, be 
represented in Monas termo, by 
a “very conspicuous, bright, 
highly refracting, colorless oil- 
like globule which is enclosed 
in a clear vesicle” called the nu- 
cleus. This and other monads 
live either free, or attached by 
a slender stalk. As an example 
of the compound or aggregated 
monads may be cited Urella 
(Fig. 13), probably glaucoma of Elirenberg, of which an account, 
with accompanying figures, here reproduced, was published by 
Prof. A. II. Tuttle in the “American Naturalist,” vi, 286. Figs. 13, 
14 and 15 represent two, five, and about forty monads of this spe- 
cies, magnified 1000 diameters. Fig. 16 is an ideal section through 
a colony of this monad. Urella, as Tuttle observes, “probably 
Fiji 1\ 
Urella. 25 
THE FLAGELLATA. 
Fig. 14. 
A group of five Monads (Urella). 
Fig. 15. 
A colony of about forty Monads (Urella). 
Fig. 16. 
Ideal section through a colony of Ur ell as. 26 
LIFE HISTORIES OF ANIMALS 
finds its nearest ally in Anthophysa, differing from that genus 
principally in being free swimming instead of fixed upon a stalk.” 
The genera Chlamydomonas and Colpodella are represented at 
Fig. 20, B. A higher form than Monas is Codosiga (Fig. 17) in 
which the oval body is stalked and continued in front into a very 
high membranous bell-shaped collar. Other monads are certain 
human parasites, f.e., Cercomonas urinarius, C. intestinalis and 
Trichomonas vaginalis. 
The second family of monads are the Astasiaea. Here belong 
Astasia and Euglena (Fig. 18). The former genus is somewhat 
amoeba-like in the changes which it undergoes, its body, according 
to Clark, during its amoeboid retroversions becoming “contorted 
into a shapeless, writhing mass.” They have a conspicuous, red 
so-called “ eye-spot.” A similar organ occurs in the zoospores of 
some algae. 
The third family of Flagellata, the Peridinea, is represented by 
Heteromastix, Dysteria, Pleuronema, Peridinium and Ceratium. 
Clark observes that Heteromastix is a transitional form connect- 
ing the Flagellata with the Ciliata or true Infusoria. Dysteria is 
still nearer to the Infusoria. Clark describes it as a two-shelled 
infusorian, with the open space between the shells provided with 
“a row of closely set, large vibratile cilia,” with one larger than 
the others, the true flagellum. After a careful description of this 
organism he concludes that “in all the organization of this animal 
there is nothing which is not strictly infusorian in character. The 
jaw-like bodies are not confined to this alone, for there are quite a 
number of others which possess a similar apparatus at or near the 
mouth. Cliilodon has a complete circle of straight rods around 
the mouth. As for the pivot it is nothing but a kind of stem, such 
as exists on a larger scale in Stentor, or is more particularly spe- 
cialized in the pedestals of Epistylis, Zoothamnium, or Podo- 
phrya; and as counter to what we see in these last, I would state 
that there are certain of the Vorticellians closely related to Epis- 
tylis, which have no stem whatever, and swim about as freely as 
Dysteria.” 
The Monads are divided into three families, thus characterized 
by Claus in his “ Grundzuge der Zoologie : ” 
1. Monadina. Body small, rounded, naked or with a tough 
membrane; resembling the zoospores of algae, etc. 
2. Astasma. Bodj' naked and changeable like the monads, 
only bearing flagella. THE FLAGELLATA. 
27 
3. Peridinea. Body having, besides the flagellum, a row of 
cilia. 
Development. The common form of reproduction is by simple 
self-division. Clark describes this as he observed it in Codosiga 
pulcherrimus (Fig. 17, A). The act requires forty 
minutes. The first sign of fission is a bulging 
out of the collar, which becomes still more bell- 
shaped. The flagellum next disappears. Then 
marks of self-division appear in a narrow, 
slight furrow (Fig. 17, B, e), extending from 
the front half-way back along the middle of the 
bod}'. Meanwhile the collar, which had become 
conical, expands, and, most striking change of 
all, two new flagella appear. Then the collar 
splits into two (Fig. 17), and soon the two new 
Codosigas become perfected, when they split 
asunder, and become like the original Codosiga. 
Such is the usual mode of multiplication of the 
species in the monads. 
A second mode, that of becoming enc}Tsted, 
has been rarely observed. Carter, so far as we 
are aware, was the first to attempt to trace the 
life history of a monad. We copy the follow- 
ing figures from his memoir. Fig. A represents 
two Euglena viridis in conjunction ; n, the nu- 
cleus, c, contractile vesicle, and ?•, the red body ; 
B and C the same after the breaking up of the 
contents into the embryonic zoospores. The two Euglenm finally 
Fig. 17. 
Fission-ol Codosiga. 
Fig. 18. 
separate and each becomes spherical, encysted as at D. Fig. 18 
illustrates the mode of development in Euglena agilis. A repre- 
Development of Euglena viridis. 28 
LIFE HISTORIES OF ANIMALS. 
sents the adult Euglena, taken from the brackish water of marshes 
at Bombay; B, the resting stage, transverse division having taken 
place, and showing that the red body is not developed in the lower 
Fig. 19. 
Development of Euglena agilis. 
half; D, the same, with a quadruple longitudinal division, showing 
that the red body is equally multiplied ; E, linear development, 
probably by longitudinal division, as the red body is present in 
each cell. 
We copy a portion of the figures and account of the devel- 
opment of Colpodella pugnax as given by Cienkowski. Figure 
Fig. 20. 
20, A, represents this monad before taking food; B represents 
three Colpodellae in the act of absorbing the nucleus of a Chlamy- 
domonas; at C is a single Colpodella, without the nucleus, and 
much swollen anteriorly. Finally the Chlamydomonas is, as it 
were, eviscerated, nothing but the body walls being left. After 
this wholesale plundering of the contents of the Chlamydomonas, 
it then passes into a “cell” or encysted state, as at D (a, the mass 
of food, colored red). The contents of the cell then break up into 
a number of masses, as at E, which finally, as at F (the masses 
destined to change into zoospores), issue from the cyst in a mass 
surrounded by a thin membrane, which gradually disappears, when 
the free zoospores make off in every direction. G represents the 
encysted body of the monad, without the ball of food. He also 
shows that another unknown monad, a species of Bodo, and three 
species of Pseudospora also develop bj7 becoming encysted. 
Development of Colpodella. THE FLAGELLATA. 
29 
Messrs. Dallinger and Drysdale describe in two unknown mo- 
nads the process of encysting and the development of zoospores, 
the sarcode mass passing through a process resembling the seg- 
mentation of the egg into four, eight and many spheres, each 
sphere ultimately becoming a monad. The changes were noticed 
with greater fulness of detail in another unknown monad, Fig. 
21, A. When about to pass into the encysted stage it became 
amoeboid in its form, but still very active ; at the stage B, how- 
ever, it became spherical and quiet, and finally lost the flagellum, 
Ficr. 21 
Development of a Monad. 
and the contents suddenly divided into four portions, separated 
by a white cruciform mark or furrow. Then an intense activity 
pervaded the sarcode mass, “a sort of interior whirling motion” 
like the rushing of water “round the interior of a hollow glass 
sphere on its way to the jet of a fountain,” as indicated at C. 
This action lasted from ten to seventy minutes, when it stopped 
and the mass broke up into small embryonic zoospores, as at D, 
which began a “quick writhing motion upon each other, like a 
knot of eels.” After remaining in this state from seven to thirty 
minutes, they separated and swam away. Thus far they had 30 
LIFE HISTORIES OF ANIMALS 
passed through the ordinary mode of formation of young monads, 
but the authors noticed among the swarm of monads some much 
larger, and differing.from the others in being very granular towards 
the flagellate end. These fastened themselves upon one of the 
smaller common forms, Fig. 21, E, and finally absorbed it, a proc- 
ess certainly analogous to, if not identical with, conjugation. It 
then assumed a resting condition, as at F. The sphere then 
opened slowly and a glairy looking fluid poured out. On careful 
examination of this fluid, with powers of 2500 to 5000 diameters, 
seven hours after emission tiny dots, semitransparent and yellow- 
ish, appeared as at G. In an hour and ten minutes the dots ap- 
peared as at H ; after two hours more as at I. The sharp-pointed 
bodies at I became rounder, and from the pointed end a flagellum 
developed as at J, when they were ninety minutes older than at I. 
At this time “motion first showed itself; this, however, was not 
the motion usual to the monad, but a motion of horizontal vibra- 
tion from a through b and c, to d, and then back again.” It then 
swam away, became plump as in K and then was followed into 
the stages from A to E, the last figure (L) representing the com- 
plete monad, thus passing through two cycles of existence. 
Three modes of development in the Flagellata seem therefore 
established, as follows :— 
1. Simple fission. 
2. The production of monads by encysting. 
3. The production of monads by encysting and conjugation, 
with a resting stage and the production of excessively minute 
zoospores which grow, finally becoming normal monads. 
It will be seen that these methods of increase are paralleled by 
those observed in the Monera, the Gregarinida and the Rhizopoda. 
It appears that there is here nothing like a sexual development, 
unless we have something analogous to it in the conjugation (?) 
of the monads described by Dallinger and Drysdale, but which 
the}’ themselves do not call conjugation, merely confining them- 
selves to a statement of the facts observed by them. 
LITERATURE. 
Carter. Notes on the Fresh Water Infusoria of the Island of Bombay. (Annals and 
Magazine of Natural History, Aug. and Sept.. 1856.) 
Cienskowski. Beitrage zur Kenntniss der Monaden. (Schultze’s Archiv, 1,1865.) 
Clark. Spongise Ciliatte as Infusoria Flagellata. (Memoirs Boston Society of Nat. 
Hist.. 1867.) 
Dallinyer and Drysdale. Researches into the Life History of the Monads. (Monthly 
Microscopical Journal, 1874.) THE XOCTILUCiE. 
31 
YI. THE NOCTILUCiE. 
Tossed from one place to another among the Protozoa, we have 
now, thanks to the researches of Cienkowski, certain grounds for 
placing the Noctilucse near, if not among the Flagellata, from the 
resemblance of the zoospores to the monads ; while they seem to 
form a more higlity developed type. It thus appears that by a 
stud}" of the mode of growth of the Protozoa, as in the rest of the 
animal world, we can alone obtain correct ideas as to the affinities 
of the respective groups. 
The Noctiluca (Fig. 22) is a highly phosphorescent organism, 
so small as scarcely to be seen with the naked eye, being from -01 
to -04 inch in diameter. It occurs in great 
numbers on the surface of the sea. It has a 
nearly spherical jelly-like body, with a groove 
on one side from which issues a curved filament, 
used in locomotion. Near the base of this fila- 
ment is the mouth, having on one side a tooth- 
like projection. Connecting with the mouth is 
an oesophagus which passes into the digestive 
cavity, in front of which lies an oval nucleus. 
Beneath the outer skin oi firm membrane sur- 
rounding the body is a gelatinous layer, con- 
taining numerous granules. A network of granular fibres arises 
from the granular layer; these fibres pass into the middle of the 
body to the nucleus and digestive cavity. 
Fig. 22. 
Noctiluca miliaris. 
Development. Baddely had noticed a multiplication 1>3T division 
and reproduction by internal buds, and Bu >ch had 
observed round, transparent disks, of the same size, 
consistence and optical properties as the Noctilucae 
occurring among them, but could not determine 
what relations they bore to the former. It wis, how- 
ever, reserved for Cienkowski to trace the (develop- 
ment of monad-like zoospores in these reproductive 
bodies. Fig. 23 represents these zoospores.! They 
move about by a long flagellum. The tooth-like 
process (s) is thought by Cienkowski to be a rudi- 
mentary condition of the “whip” near the mouth of 
the adult Noctiluca. By keeping specimens in a drop of water on 
a thin glass which was placed over a moist chamber so as to ex- 
Fig. 23. 
Zoospores of 
Noctiluca. 32 
LIFE HISTORIES OF ANIMALS. 
elude all access of dry air to the water in which the animals were 
living, he was enabled to observe them for twelve hours. The 
stages he observed were — 
“ 1st. Noctiluca-like bodies, but without mouth or lash, and 
having a doubly spherical or so-called biscuit form, each partial 
sphere having a granular protoplasmic mass with fine branching 
rays, the two masses being connected more or less. 2d. The pro- 
toplasm connects so as to form a disk on one pole of the irregular 
double spheroid, which gradually becomes spherical, exhibiting 
three or four depressions at one pole. 3d. The formation of the 
disk is preceded by a segmentation of the entire mass of the pro- 
toplasm of the Noctiluca into two, four, eight, sixteen, etc. parts, 
after which the disk begins to grow up on the surface of the Noc- 
tiluca. 4th. The protoplasmic disk sends out stump}' processes 
which project from the surface of the spheroid and exhibit pecu- 
liar wriggling movements. 5th. The mass commences to divide 
into smaller pieces, the vesicle being now quite spherical. The 
commencement of this division was not directly observed, but later 
stages, in which clumps of protoplasmic matter were seen arranged 
at first in groups of eight; these, then, were followed carefully 
through their division into groups of sixteen irregular, oblong 
particles. These products of division appear like denser, sharply- 
defined masses or nuclei, lying in a less dense surrounding gran- 
ular plasma. 6th. The next stage was one of the first and most 
commonly observed, in which the protoplasmic disk, formed as 
above described, has become entirely split up into small oval bod- 
ies, each -016 millimetre long. The aggregated mass of these oval 
spores sometimes appears as a disk at one pole of a Noctiluca- 
like vesicle, or as a girdle passing round it. 7th. By high powers 
each oval particle is seen to have a terminal cilium, and whilst 
under observation many were seen to separate from the disk and 
swim about as free swarm-spores” (Fig. 23). 
Cienkowski also observed the fusion of two Noctilucge. “ The 
two animals place themselves with the two so-called ‘oral aper- 
tures’ close to one another, and through these a protoplasmic 
bridge is formed, which unites the nuclei of the two individuals. 
Later, at the points of contact, the outlines of the two Noctiluca- 
vesicles fuse, and thus the double-spheroid or biscuit-shaped blad- 
ders are formed. By further fusion the pinching in of the vesicle 
disappears from one side, so that the vesicle becomes more nearly 33 
spherical. Meanwhile the two nuclei become completely fused 
into one, retaining, however, their radiating threads and network, 
as in normal individuals. The cross-striped ‘ lashes ’ and the 
‘ teeth ’ of the two fused Noctilucas also disappear. All trace of 
the double origin of these ‘ copulated Noctilucse ’ may pass away 
by the disappearance of the fold on the surface, near to which the 
nucleus lies, and thus a Noctiluca vesicle is formed, which is al- 
ways larger than the normal Noctiluca, and seems identical with 
the bodies noticed by Busch, and also very probably identical 
with the biscuit-shaped and spherical Noctiluca vesicles in which 
Cienkowski has traced the formation of the swarm-spores. A 
direct observation of the formation of swarm-spores in the copu- 
lated forms Cienkowski was not able to obtain.” 
the noctiluca;. 
This fusion of two Noctilucai is not, however, essential for the 
production of zoospores, as they appear whether conjugation has 
occurred or not. When it does occur, however, it seems to be of 
a sexual nature. Conjugation, though by no means necessary, 
does frequently take place, and “as in the fusion of the zoospores 
of and the copulation of Actinoplirys, and others, 
leads to an augmentation of the mass of the protoplasm.” “ Zo- 
ospores,” he adds, “ occur in quite small Noctilucie, which cer- 
tainly could not be the product of the fusion of two individuals. 
Sometimes the zoospores develop very rapidly wdiilst still in the 
disk, and their protoplasm becomes differentiated into a nucleus 
and radiating threads.” Cienkowski considers that the zoospores 
of Noctiluca decide the systematic position which must be as- 
signed to this organism. It seems to him that they are animals 
of large dimensions belonging to the division of the Flagellata. 
A single mode of growth, therefore, occurs in Noctiluca, i.e. 
development from zoospores. 
Busch. Das Meerleuchten unci die Noctiluca (in Beobachtungen iiber Anatomie 
und Eutwicklung einiger wirbellosen Seethiere. 1851). 
Huxley. On the Structure of Noctiluca miliaris. (Quart. Journal Mic. Sci., 1855.) 
Qucitrefages. Observations sur les Noctiluques. (Annales des Science Nat., 1850, 
and Annals Nat. Hist., 1853.) 
Cienkowski. Schwarmerbildung bei Noctiluca miliaris. (Schultze’s Arcliiv, 1871. 
Translation in Annals and Magazine Natural History, 1871. See also 1872, p. 414.) 
LITERATURE. 
LIFE HISTORIES OF ANIMALS. 34 
LIFE HISTORIES OF ANIMALS. 
Though the term Infusoria has usually been applied to nearly 
all the Protozoa provided with cilia 
or flagella, it is now restricted to the 
highest division of the Protozoa. In- 
stead of an attempt to define the 
group, the following brief description 
of some of the well-known forms will 
perhaps best show how they differ 
from the Flagellata, with which they 
are most apt to be confounded. 
One of the simplest and most abun- 
dant forms is Paramecium. The ac- 
companying figure (24), copied from 
Clark’s “ Mind in Nature,” represents 
Paramecium caudatum, of Ehren- 
berg.5 This animalcule is a mass of 
protoplasm, representing, perhaps, a 
cell. In the body-mass are exca- 
vated a moutli and a throat leading 
to a so-called stomach or digestive 
cavity. Two hollows in the body 
form the contractile vesicles, and an- 
other cavity forms the reproductive 
organ. Prolongations of the body- 
mass form the cilia, which character- 
ize the Infusoria and give their 
name, Ciliata. No specialized tis- 
sues composed of cells exist in these 
organisms, and they are regarded as 
on the whole representing a single 
cell. Some authors, as Claparede, 
regard them as composed of several 
cells, but the whole animal, though performing functions nearly 
VII. THE INFUSORIA (CILIATA). 
Paramecium. 
B Fig. 24. A view from the dorsal side, magnified 340 diameters. H, the head: T, the 
tail; m, the mouth; m to <7, the throat; a, the posterior opening of the digestive cavity; 
cv1, the anterior and cv, posterior contractile vesicles; I, II, ill, the radiating canals of 
cv1; n, the reproductive organ; v, the large vibrating cilia at the edge of the vestibule. 
-After H. J. Clark. THE INFUSORIA. 
35 
as complicated as those of sponges, low worms and radiates which 
have bodies composed of many cells, should be regarded as made 
up of indifferent or unorganized sarcode or protoplasm, somewhat 
like that of the bodies of the embryos of the higher animals in 
their earliest stages. 
Paramecium has an elongated, oval body “ with one end (H) 
flattened out broader than the other, and twisted about one-third 
way round, so that the flattened part resembles a very long figure 
8.” In this form, as in Stentor (Fig. 25), as Clark remarks, “we 
have the mouth at the bottom of a broad notch or incurvation, 
and the contractile vesicle on the opposite side, next the convex 
back, whilst the general cavity of the body lies between these 
two.” The arrows in the figure represent the course of the par- 
ticles of indigo with which Clark fed his specimens, “ as they are 
whirled along, by the large vibrating cilia (v) of the edge of the 
disk, against the vestibule of the mouth.” During the circuit the 
food is digested, a mass of rejectamenta is formed near the protu- 
berance, a, which has appeared a short time before. This finally 
opens, allows the rejected matter to pass out and then closes over, 
leaving no trace of an outlet. This and other Infusoria seem, 
then, to have a definite digestive tract, hollowed out of the paren- 
chyma of the body. 
“The system,” says Clark, “which is analogous to the blood 
circulation of the higher animals, is represented in Paramecium 
by two contractile vesicles (cv, cv1, i, n, in), both of which have 
a degree of complication which, perhaps, exceeds that of any 
other similar organ” in these animals. When fully expanded they 
appear round, as at cv; but when contracted they appear, observes 
Clark, as “fine radiating streaks, and as the main portion lessens 
they gradually broaden and swell until the former is emptied and 
nearly invisible, and they are extended over half the length of the 
body. In this condition they might be compared to the arterial 
vessels of the more elevated classes of animals, but they would at 
the same time represent the veins, since they serve at the next 
moment to return the fluid to the main reservoir again, which is 
effected in this very remarkable way.” The contents of these ves- 
icles is a clear fluid. 
The reproductive organ in Paramecium is a small tube (n), only 
seen at the reproductive period when the eggs (n) are fully grown. 
Clark says that the eggs are arranged in it “ in a single line, one 36 
LIFE HISTORIES OF ANIMALS 
after the other, at varying distances.” It usually lies in the midst 
of the body, and extends from one-half to two-tliirds of the length 
of the animal. “According to 
Balbiani’s observations upon a 
closely allied species, when the 
eggs are laid they pass out from 
the ovary through an aperture 
near the mouth” (Clark). 
In the Trumpet animalcule 
(Fig. 25, Stentor polymorphic of 
Ehrenberg, after Clark6) we have 
a higher grade of development 
than in Paramecium, the animal- 
cule attaching itself at one end, 
and building up a slight tube in 
which it contracts when dis- 
turbed ; an anticipation in na- 
ture of the worm in its tube. 
Prof. Clark has studied in 
this animalcule certain circular 
bands within the edge of the 
disk, from which arise twelve 
very thin stripes (rr) which con- 
verge towards the mouth (m). 
These bands are evidently, he 
says, in close relation with the 
mouth and cilia, the most active 
organs of the animal, and he concludes that it is a nervous 
system. 
h Fig. 25. 
Trumpet Animalcule. 
The most complicated form of all among the Infusoria is the 
Vorticella, or hell-shaped animalcule. These animals are very com- 
mon on submerged plants and leaves, appearing to the naked eye 
like mould. Their motions, as they suddenly contract and then 
6“ Stentor polymorplius, magnified 130 diameters, expanded and bent slightly over 
towards the observer; the mouth, m, next the eye, and the dorsal edge in the distance. 
a, posterior end; sli, the tube enclosing a; c, the ciliated border of the disk (s); b, the 
larger, rigid cilia; cv, the contractile vesicle in the extreme distance, seen through the 
whole thickness of the body; cv1, ca2, the posterior prolongation of cv, in the distance; 
r, r1, the circular and radiating branches of the nervous system; n, n1, the reproduc- 
tive system, extending from the right side, at n, posteriorly, but towards the eye at n1 
(Clark). shoot out their bell, mounted on a long stalk, are very interesting. 
They form the most available and 
attractive infusoria for study and 
amusement. The throat is quite dis- 
tinct, while the nucleus is the most 
conspicuous organ of the body. The 
digestive cavity is “one vast hol- 
low,” in which the whole mass of food 
revolves in a determinate channel 
(Clark). In fact, so highly devel- 
oped are these Infusoria that they 
seem to anticipate certain low worms 
to which they bear a certain resem- 
blance, and indicate that the worms 
may have sprung either from the In- 
fusoria or early organisms like them. 
Biitschli claims to have discovered 
that lasso cells like those in the 
Hydra and jelly fishes are developed 
in a certain infusorium named by him 
Polyk rikos. 
The Infusoria may be divided into 
three groups; 1, represented by Pa- 
ramecium ; 2, by Vaginicola and 
Vorticella, and 3, by Acineta (Fig. 28, 
H). This latter form is not ciliated, 
the body is stalked and in front prolonged into slender suckers, 
each terminating in a mouth. At one time Stein supposed that 
the Vaginicola or Vorticella passed into an “ Aeineta-form,” but 
Claparecle disproved this and Stein retracted his opinion. 
THE INFUSORIA. 
Fig. 20. 
Fig. 27. 
Bell-shaped Animalcule, 
natural size; ancl one enlarged.7 
Development. The different modes of development among the 
Infusoria are still involved in doubt. The best observers have 
advanced theories that have appeared sound, and then revoked 
them. All agree, however, that the simplest and commonest mode 
of development is fission, a process analogous to the ordinary 
7 Fig. 26 “ Epistylis flavicans Ehr., a single, many-forked colony of bell animalcules, 
slightly magnified. Fig. 27, one of the animalcules magnified 250 diameters, p, the 
stem; d, the flat spiral of vibrating cilia at the edge of the disk; ms, the muscle; m to 
8, the depth of the digestive cavity; m, the mouth, g, g1. the throat; l, the single vibra- 
tory lash, which projects from the depths of the throat; cv, the contractile vesicle: n, 
the reproductive organ” (Clark). 38 
LIFE HISTORIES OF ANIMALS. 
self-division of the nucleus of eggs, and the primary mode of 
growth in both animals and plants, not involving the idea of sex. 
As a good example of fission, by which all Infusoria are sup- 
posed to multiply their kind, though some may at certain times 
reproduce from eggs, we may cite a case observed by Clark, the 
full account of which is given in his admirable “Mind in Nature.” 
He observed a Stentor polymorphus divide in two. The first 
change taking place is in the contractile vesicle, which divides into 
two distinct vesicles. The mouth of the new Stentor is formed in 
the middle of the under side, first appearing as a shallow pit, 
around which arises a semicircle of vibratile cilia. The new 
mouth deepens, the throat is hollowed out; all this taking place 
before any external sign of division appears. But in the course 
of two hours the body splits asunder, and two new individuals 
appear, each exactly like the other. 
In Vaginicola there is a modification of this simple process, 
Development of Vaginlcola. 
which is more like true gemmation or budding, and is accompanied 
by a process of encysting. Our figures of the mode of development 
are taken from a short paper by C. J. Muller. He first traced 
the fission of this infusorium (Fig. 28, A), which takes place in 
the following manner. After the animal has withdrawn within 
its case, and assumed a pear-shaped form, its cilia, meanwhile, 
apparently lost, a conical fissure appears at the base, and soon 
after “a wavy line of division shows itself at the upper extremity 
of the animalcule the two fissures enlarge and meet; pulsating 
vesicles become active on both sides of the line of fission, and 
cilia begin to grow out, until at the end of an hour, two separate 
animals are formed, which soon afterwards appear as in Fig. 28, B. THE INFUSORIA. 
39 
Now begins a new processj the production of a free swimming 
embryo. On one of the two Vaginicolas is developed “ a delicate 
ring or band at about one-tliird its length from the lower extrem- 
ity.” Then it contracts in its cell, becomes quiet (as in Fig. 28, 
C, D) and from the ring or band develops a new circle of cilia, 
the former ones having disappeared. It then swims off' as at Fig. 
28, E, darting about rapidly until it attaches itself to a piece of 
Conferva, as at Fig. 28, F. After some hours, perhaps twenty, 
a fringe of cilia begins to appear on the upper end, the old ones 
begin to be absorbed, and the tube arises, as at Fig. 28, G, and a 
new Vaginicola appears. Stein had some years previous made 
similar observations on Vaginicola crystallina Ehr., and thought 
he had traced their further development into a form resembling 
Acineta (Fig. 28, H), but this proved afterwards to be a young 
parasitic Acineta, a suctorial Infusorian. 
We have seen that Vaginicola passes through a resting stage, 
withdrawing into the case in which it lives, and being for a time 
inactive. Stein has shown that all the Vorticellinre k‘ at an earlier 
or later stage of their development become encysted, by drawing 
in their ciliated disk and contracting their bodies into a ball; at 
the same time secreting around themselves a gelatinous mass 
which solidifies into a firmer elastic covering.” Fig. 29, G, after 
Stein, shows a Vorticella thus enc}Tsted. After becoming thus 
encysted the interior becomes homogeneous, as in Fig. 29, H. 
From this cyst the Vorticelhe arise directly. 
Now a second mode of development, and the simplest, has been 
observed by Stein, i. e., that of monad-like young which result 
from the breaking up of the cyst. While examining a cyst Stein 
observed that it burst, and the free contents “ remained as a round, 
transparent limpid drop of jelly, of about the same diameter as 
the cyst, in which some thirty embryos, of the form of Monas 
colpoda or Monas scintillans, sailed about with varied and active 
motion, as if in a little ocean.” These embryos resulted from the 
breaking up of the band-like nucleus. This breaking up did not 
take place “ by successive acts of division, but in the nucleus, 
round disks become marked off contemporaneously, at the most 
distant points; whilst the intermediate substance of the nucleus 
becomes re-absorbed.” 
It thus seems that the Ciliata pass through a flagellate or monad 
condition. Stein regards the above described propagation by the 40 
LIFE HISTORIES OF ANIMALS. 
change of the whole inner enc}7sted body of a Vorticella into 
numerous embiyos, as the equivalent of the sexual propagation of 
the higher animals. We also quote Stein’s summary of the cycle 
of changes undergone by the Vorticella: “We may thus ideally 
arrange the different stages of development through which the 
Vorticellce pass ; the largest end their lives by becoming encysted ; 
the whole of the contents of their bodies then passes into em- 
bryos, to which the dividing germ-nucleus first gives origin. 
“ The embryos become fixed, develop from their posterior ex- 
tremity a stalk, which is at first not contractile, and gradually 
change their monad-like bodies into that of a common Vorticella. 
“As soon as this has taken place, their very much smaller size 
only distinguishes them from the perfect Vorticellae. Even in this 
imperfect condition they frequently multiply by continual division 
and in a subordinate degree by external gemmation. This power 
of multiplication in the imperfect state, however, is one of the 
most certain criteria that we have to do with an alternation of 
generations. * * * * Finally, the last generation become 
encysted, not to re-awake to an independent existence, but to 
break up into a swarm of embryos.” 
Let us now look at the development of Epistylis plicatilis as 
studied by Claparede. Fig. 29, A, represents an individual con- 
Fig. 29. 
Development of Epistylis 
tabling several embryos (B) and opposite the lower one on the 
right side is a projection, through which the embryo at IV has 
passed out. The specimen figured at B' is a fair example of the 
embryos of species belonging to six families of Infusoria, and THE INFUSORIA. 
41 
may, perhaps, serve as a typical example of most Infusoria at the 
time of birth. This young stage may, then, be contrasted with 
the embryos of the Flagellata, which are of a much simpler form, 
resembling the zoospores of the algre and lower Protozoa. 
The embryos of the Infusoria arise from the nucleus, which cor- 
responds to the ovary of the higher animals. The nucleus is a 
curved, oblongs oval body, represented in Figs. 29, A, n; 30, E. 
When the Epistylis is about to reproduce its young, the nucleus 
sends off a portion which enlarges until it assumes the appearance 
indicated by Fig. 29, C. It has become round, and contains a cen- 
tral, granular mass, from which the embryos arise. At Fig. 29, D, 
is a globular mass, detached from the nucleus, and containing sev- 
eral embryos in the first state of development. Fig. 29, E, repre- 
sents the embryos provided with a circle of cilia, and nearly ready 
to swim about freely. Claparede did not watch their further devel- 
opment, but thought it probable that they grew directly into the 
Epistylis form. 
What is the meaning of conjugation in the Infusoria is not 
clearly understood. Whether it is analogous to sexual union is 
not certainly known, but it is now thought by Balbiani that the 
smaller individuals found conjugating with the larger are males, 
and he even thinks that some Infusoria contain spermatozoa. 
Fig. 29 represents an Epistylis conjugating, each one provided 
with two buds ; the bud of the individual on the left is conjugated 
with that of the individual on the right hand. Epistylis also 
passes through encysted stages as indicated at Fig. 29, G and II. 
The same mode of development was observed by Claparede in 
Fig. 30. 
Development of Urnula. 
a parasite of the Epistylis, i. e., Urnula epistylidis (Fig. 30), 
which, besides reproducing by fission, also produces ciliated 42 
LIFE HISTORIES OF ANIMALS. 
young. Fig. 30, B, e, represents the ciliated young within the 
body of the parent, B ; Fig. 30, C, the free swimming ciliated 
young. In another specimen Claparede observed the interior of 
the body subdivide into several masses, as at Fig. 30, D. These 
masses increase in size and become filled with a number of small 
corpuscles, with active movements, which finally press through the 
walls of the Urnula. These are probably spermatozoa, as Stein 
considers Urnula as the male of Epistylis, contrary to the opinion 
of Claparede, who regarded it as a Rhizopod, though its ciliated 
young is, in the light of later studies, sufficient to prove that it is 
a ciliate infusorian. 
As to the sexuality of the Infusoria, Balbiani has advanced the 
idea that they are in reality hermaphrodite, the nucleus repre- 
senting the ovary, and the nucleolus the testis, the latter produc- 
ing bodies which he regards as spermatozoa. Claparede regards 
this view as well founded, as it had already been suggested b}r 
himself, Lieberkiihn, J. Muller and Stein that certain Infusoria 
contained spermatic particles, found not only in the nucleolus, but 
also in the nucleus, into which they had penetrated from the nu- 
cleolus. This has been observed in Paramecium, where, as Clap- 
arede quotes as Stein’s opinion, “ Fecundation having been accom- 
plished, these zoosperms disappear, and the nucleus then divides 
in a manner comparable to the segmentation of the egg into a 
certain number of segments, or reproductive bodies, destined each 
to give rise to an embr}ro. The Infusoria, then,” adds Claparede, 
“ are androgynous.” 
It appears, also from the observations of Balbiani, that the 
Infusoria, as Stentor, Paramecium, Vorticella, etc., have true 
eggs, each egg consisting of “two hollow membranous spheres, 
the smaller being enclosed within the other, and separated from it 
by a considerable interval.” The smaller vesicle he regards as 
the germinal vesicle, and the larger as the vitelline membrane. 
After the fecundation, “at the end of four or five days, the devel- 
opment of the eggs is complete, and each, with the aid of re- 
agents, displays in a very distinct manner its characteristic ele- 
ments, namely, vitelline membrane, vitellus, germ-vesicle and 
germ-spot.” Butschli, however, it should be stated, denies that 
Infusoria produce spermatozoids which fertilize the nucleus. As 
to the development of the Acinetae, self-lission is in them very 
rare, while conjugation is very frequent. THE SPONGES. 
43 
There are, then, two modes of development among the Infusoria 
(Ciliata) : — 
1. By fission. 
We have, then, for the first time among the Protozoa, if the 
observations of Balbiani be correct (though this is denied by 
good observers), truly sexual animals, producing true eggs and 
spermatic particles. The same animal reproduces both by fission 
and by the production of ciliated embiyos. Most of them before 
producing embryos undergo fission. This is comparable to the al- 
ternation of generations among the Hydroids, Aphides, etc. 
2. By production of internal ciliated embryos arising from eggs. 
Elirenberg. Die Infusionsthiere als volkommcne Organismen, 1838. 
Dujardin. Infnsoires, 1811. 
Stein. Infusionsthiere anf ihre Entwicklungsgescliichte untersucht. 1854. 
Untersuchungen iiber die Entwickelung der Infusorien. (Wiegmann’s Archiv. 
1849.) 
Der Organismus des Infusorien. 1867. 
Clnpare.de und Lachmann. Utudes sur les Infnsoires et les Rhizopodes (Memoires 
de I’Institut National Genevois, 1858-61). 
Balbiani. Recherches sur les I’henomenes sexuels des Infnsoires. (Brown-Sequard’s 
Journal de la Physiologie. 1831. Translated in Quart. Journ. Micr. Science. 1862.) 
Clarlc. Mind in Nature. 1865. 
Everts. Untersuchungen an Yorticella nehulifera. (Siebold and Kolliker’s Zeits- 
chrift, 1873.) 
LITERATURE. 
VIII. THE SPONGIA1 (PORIFERA). 
We now come to animals whose bodies are composed of numer- 
ous cells, and which produce true eggs, sometimes even with a thin 
calcareous shell, and genuine sperm cells. The embryo sponge 
arises from eggs which undergo a total segmentation of the }'olk. 
The free swimming larva later in its life becomes fixed, loses its 
external cilia, but retains its cellular walls, now composed of two 
layers, which are supported by silicious or calcareous needles or 
spicules developed in the inner layer. 
To regard such an organism as a Protozoan, or even to compare 
it with a compound Radiolarian such as Sphaerozoum, with its sili- 
cious spicules and aggregations of one-celled organisms, would 
not seem warranted. We have, in fact, in the light of the anatomi- 
cal investigations of Lieberkulin, Carter and Clark, and the com- 
bined anatomical and embryological studies of Haeckel, Metsch- 
nikoff and Carter, no grounds for leaving them among the Pro- 
tozoa. Indeed, one of the most striking illustrations of the value 44 
LIFE IIISTOIUES OF ANIMALS. 
of a knowledge of the early history of an organism is afforded 
by the embryology of the sponge. Haeckel’s discovery that the 
larval sponge is a planula, though not homologous with the em- 
bryo polype or jelly-fish, enables the naturalist to at once decide 
that the sponge is not a Protozoan, but belongs to a type only less 
highly organized than the lower polypes, and with more analogy 
to the Radiates than the Protozoa. 
If, under the guidance of the results of the studies of Lieber- 
kiihn, Carter, Clark, and particularly of Haeckel and Metschnikoff, 
Fig. 31. 
Fig. 32. 
Axinella polypoidCs. 
Axinella, With a parasitic 
polype, 2-3 natural size. Af- 
ter Schmidt. 
we examine the structure of a sponge, we shall find that in its 
simplest form it is a hollow, vertical cylinder, fastened by its base, 
with the mouth opening upwards from a central gastro-vascular 
cavity, with ciliated epithelial cells lining the cavity, and possess- 
ing a surprising degree of individuality. There are usually sev- 
eral mouths, and the cavity usually opens into a labyrinth of 
chambers connected b}r passages through the cellular tissue ; these 
round chambers being lined with ciliated epithelial cells. This THE SPONGES. 
45 
body is supported by a basket-work of interlaced needles of silica 
or lime, developed in the inner layer of cells of the larva. 
Such, in brief, is the sponge. Does the fact that in the sim- 
plest, immature forms, we have quite a regular body-wall and a 
single cavity, compel us to range the sponges side by side and in 
the same natural division with the potypes and jelly-fishes, in the 
Fig. 35 
Fig. 33. 
Tethilla polyura. After Schmidt 
Hyalonema boreale. Nat. 
size; with part of stem 
enlarged. After Lov6n. 
typical forms of which the central cavity acts as a true stomach 
and the outlet surrounded with tentacles acts as a mouth ? Metsch- 
nikoff has shown that it would seem to be a violation of the 
existing principles of classification to place together animals so 
unlike. The sponges apparently represent a class lower than, but 
possibly equivalent, systematically, to the polypes and jelly-fishes. 
Currents of water, created by the cilia and bearing along parti- 46 
LIFE HISTORIES OF ANIMALS. 
cles of food, enter through the system of mouths, and when the food 
is absorbed by the cells of the inner lining, they pass out through 
the larger openings. Both the larger and smaller “mouths” are 
capable of opening and closing. 
The eggs and sperm cells are scattered at irregular intervals 
among the cells composing the body-walls; the spermatozoa are 
Fig. 34 
Pheronema Anna3 and spicules. After Leidy. 
in some species developed in “mother” cells, as in many of the 
higher animals. 
The sponges are by Hseckel regarded as closely allied to the 
Hydroid polypes, members of the Coelenterates, a division formed 
by Leuckart, including the polypes and acalephs. His reasons 
are based on the fact that the sponges are made up of two layers 
of cells (ectoderm and entoderm, or outer and inner layer) sur- 
rounding a central cavity, and that both reproduce by eggs and 
spermatozoa, and pass through a Gastrula (“planula”) stage. THE SPONGES. 
47 
Fig. 30, 
Fig. 37. 
Hyalonema with parasitic polypes, 
embedded half its length in the 
mud. After Gray. 
Hyalonema Sieboldii (5 nat. size). 
After Schulze. 48 
L1FE HISTORIES OF ANIMALS. 
Gegenbaur and some English naturalists have endorsed this 
view. Haeckel goes so far as to state that the only character ex- 
Fig. 38, 
Fig. 39. 
Corbitella, f natural size. After Liitken 
Tuba labyrinthiformis, | natural size. 
After L'utken. 
eluding tlie sponges from the Coelenterates is the want of lasso 
cells,8 but we have seen that the true Infusoria possess them. 
8 Eimer claims to have found true lasso cells in Reniera, a sponge observed by him at 
Capri; but Carter attributes their presence to a parasitic polype which he detected in 
this sponge. Eimer on other grounds claims that he has discovered a sponge which 
affords a passage into the Hydroids. “ In an Esperia,'in another silicious sponge allied 
to Myxilla, and in a horny sponge, the surface is studded with small chitinous tubes, 
which are external prolongations of a similar investment of the whole channel-system, 
becoming, however, more delicate below, and finally passing into a sarcode-like con- 
dition; each of these tubes is inhabited by a retractile, sac-like body, provided with 
ectoderm, a muscular layer, and entoderm, with thread cells, and with 6-12 long, un- 
branclied tentacles, with cilia and thread cells; below, they pass successively into the 
common sponge-substance, and generally lie four in each channel, each, however, with THE SPONGES. 
49 
Metschnikoff has, however, shown that there is no true homology 
between the sponges and Radiates. 
The sponges are divided into (1) the Myxospongice, represented 
by Ilalisarca; (2) the Fibrospongice, or the silicious sponges, rep- 
resented by Axinella (Fig. 31, A. polypoides; 32, another species 
of Axinella), the fresh water Spongilla; Thethya; Tethilla (Fig. 
33, T. polyura) ; Pheronema (Fig. 34, P. Annce and spines) ; the 
glass sponges, such as Hyalonema (H. boreale, Fig. 35, from the 
Fig. 40. 
Dactyocalyx pumicea. After Liitken. 
Arctic Ocean ; Fig. 36, H. Sieboldii; Fig. 37, another Hyalonema, 
anchored in the mud by its silicious threads) the Venus flower 
basket, or Euplectella aspergillum from the Philippines ; the Tuba 
(Fig. 38, T. labyrintliiformis) from the West Indies; the Corbi- 
tella from the Moluccas (Fig. 39) ; and Dactyocalyx (Fig. 40, D. 
pumicea9) from the West Indies. The third division of sponges 
comprises the calcareous sponges (Calcispongice), represented by 
the Sycon (Sycandra ciliata, Fig. 41), a common little white 
sponge found on our shores, and in the North Atlantic generally. 
its own special chitinous tube. In other sponges (Reniene) these polypoids were found 
in a lower stage of evolution, with short or absent tentacles, thread-cells present or 
wanting, no muscular layer, chitinous investment sometimes strongly developed, an- 
nular and projecting — in other instances reduced to a delicate, almost sarcode-like 
membrane, or almost totally wanting. The idea of parasitism is, according to the 
author, quite out of the question; the ‘ polypoids ’ lie constantly regards as the true 
nutritive zooids of the sponge, and the sponges in which they occur in a more rudi- 
mentary shape as intermediate forms, leading to the great majority of sponges without 
nutritive zooids of any kind.” Liitken in Zoological Record for 1872. London, 1874. 
9 This and Figs. 31-33, 35-41 were kindly loaned me by Dr. C. F. Liitken, of the Royal 
Zoological Museum at Copenhagen. They are from the Tidsskrift for Populajre Frem- 
stillinger af Naturvidenskaben. 1871. 
LIFE HISTORIES OF ANIMALS. 50 
LIFE HISTORIES OF ANIMALS. 
Development. Lieberkiihn made the astonishing discovery, con- 
firmed by Haeckel, that sponges were really hermaphrodite animals 
reproducing by eggs and sperm cells developed 
in the same individual sponge. Haeckel showed 
that they were probably developed from the inner 
(endodermal) layer of cells forming the body, 
being simply modifications of these endodermal 
cells, much as the eggs of the higher animals are 
modified epithelial cells. Fig. 42, from Haeckel, 
shows one of these cells (of Sycortes quadrangu- 
lata) with several spermatozoa mingling their 
protoplasmic contents with the protoplasm of the 
egg itself. 
The endodermal cell transforms into an egg, 
according to Haeckel, in the following manner. 
At first provided with a “collar” and flagellum 
much as in the Codosiga figured on page 27, it 
begins to draw these in until they disappear; then a nucleus (nu- 
cleolinus) appears within the nucleolus of the cell. The egg soon 
becomes detached from the body wall, and 
moves about, sometimes penetrating into the 
exoderm, or “emigrating, in the oviparous 
species, from the ‘ stomach * to be fecundated 
abroad.” 
“ The spermatozoa are apparently devel- 
oped through repeated divisions of modified 
endodermal cells; the ‘ head ’ is formed by 
the ‘ nucleus,’ the tail by the protoplasm 
of the minute sperm-cells.” 
After fecundation of the egg, it begins to 
undergo self-division, splitting into two, 
four, eight, sixteen, etc., nucleolinated cells (Fig 43, total seg- 
mentation of eggs of Halisarca), 
the process being exactly as in 
the eggs of nearly all the higher 
animals including man. This 
stage of segmentation, like the 
mulberry mass of the egg after 
segmentation in the higher ani- 
mals, Haeckel terms the Morula stage (from its likeness to the mul- 
berry, Morus; see Fig. 43, after Carter). The cells of the 
Fig. 41. 
Sycandra ciliata, a 
calcareous sponge 
enlarged. After 
Schmidt. 
Fig. 42. 
Fusion of spermatic parti- 
cles with egg of sponge. 
After Haeckel. 
Fig. 43. 
Segmentation of egg of sponge. 51 
Morula afterwards become separated into two kinds, a few re- 
maining round, the majority becoming long and prismatic, and 
provided each with a cilium (flagellum), by means of which it 
swims about and looks like a “planula” or larval jelly-fish. 
This stage Hmckel consequently calls the “Planula” stage. 
The next step is the formation of a “ stomach” or internal 
cavity in the body of the ciliated larva. This stage Haeckel calls 
Gastrula. Fig. 44, from Ilfeckel, represents the gastrula of 
Leuculmis echinus, as seen in optical section, the outer layer (ec- 
THE SPONGES. 
Fig. 44. 
toclerm) being composed of long prismatic, nucleated cells (ex) 
provided with a lash, while the cells (en) of the lining (endoderm) 
of the cavity are much larger and rounder.10 After swimming 
about for a time it becomes fixed bj’ the end of the body to some 
object, the« cavity finally opening out by a mouth. The external 
cilia now disappear, and others become developed in the cells lin- 
ing the interior of the cavity.11 Afterwards the true sponge char- 
Larva of a Sponge (gastrula). 
10Metschnikoff shows that this “entoderm” is really an invaginated portion of 
Ilacckel’s “ectoderm.” 
11 Metschnikoff observed on the contrary that the ciliated external cells are with- 
drawn in the process of growth and line the cavity. 52 
LIFE HISTORIES OF ANIMALS 
acter of the organism is revealed. The bod3T-wTall becomes per- 
forated with pores, which open into the general cavity of the body, 
while currents of water are maintained b}r means of the cilia, and 
flow out through the so-called mouth. This is the “ Proto- 
spongia” state, and when spicules of silex or lime are developed 
to strengthen the walls of the body, the 3roung sponge is termed 
by Haeckel, the “ Olynthus.” 
Thus, following the course of development as Haeckel supposed 
to be the case with the calcareous sponges, for he, as Metschnikoff 
remarks, did not actually observe the stages after the formation 
of the ciliated larva, we obtain a very clear idea of the typi- 
cal structure of the sponge. I cannot do better than emplojr the 
condensed account of the discoveries of Haeckel given b}r Dr. 
Liitken in the “Zoological Record” for 1872, with a few correc- 
tions taken from Metschnikoff’s paper. The Olynthus, the sim- 
plest type of the sponge, is a “ cylindrical, clavate or pyriform, 
etc., tube, closed at the extremity by which it is affixed, commonly 
open by a ‘ mouth ’ at the other; the body-wall, enclosing the 
‘gastric’ cavity, is a thin membrane composed of the two layers 
named above—the ‘syncytium’ or exoderm [Metsclinikoff’s inner 
layer] a mass of sarcodine with nuclei, the cells of which are so 
completely fused together that the original cellular structure 
cannot be made visible through any chemical reaction; if torn 
mechanically, the fragments will, whether containing one or more 
or no nuclei, take the shape of Amoebae and walk about. In this 
layer12 the spicula are developed, chiefly of three types — simple, 
3-radiate and 4-radiate, anchor-shaped spicula are rare (Syculmis 
synapta, anchoring the animal in the mud bottom) ; the stellate 
spicula sometimes occurring are foreign bodies, belonging origin- 
ally to Didemnia (Ascidiae). The spicula are invested with a 
delicate sheath of condensed sarcodine; they contain an axial 
filament, and are composed of concentric layers, like the sili- 
cious spicula; chemically they are composed partly of Co2, CaO, 
partly of an organic substance (‘spiculin’). The endodermal 
cells are, like certain flagellate Infusoria, provided wkh a collar 
and flagellum; they contain a ‘nucleus’ (with ‘nucleolus’), 
and often one or two contractile ‘ vacuola’ (water drops) ; 
though without ‘mouth,’ they both ‘drink’and ‘eat,’ or receive 
12 Metsclmikoff shows that the spicules really arise from the inner layer. TIIE SPONGES. 
into their interior, not only fluid, but also minutely diffused solid 
matter (e. g., carmine), probably through the soft exoplasm be- 
tween the collar and flagellum. Liberated artificially, they also 
assume amoeboid shapes and motions. On the endodermal cells 
devolve the whole of the nutritive (digestive, respiratory and 
secretory) functions ; and there can be little doubt that both eggs 
and spermatozoa are modified endodermal cells.” 
Hieckel did not observe the development of the larva, his gas- 
trula, into the young sponge. This gap has been filled by Metsch- 
nikoff. He observed the course of development in Sycon ciliatum 
(Fig. 45) from the segmentation of the yolk, through the larval 
state, up to the time when the sponge is fixed and the spicules are 
Fig. 45. 
Development of a Sponge (Sycou ciliatum). 
well developed ; in fact, through nearly every important stage in its 
life. By making a section through the sponge he found eggs and 
embryos in different stages of development in springtime. The 
total segmentation occurred as Haeckel describes. Metschnikoff, 
however, observed that a small “ segmentation-cavity ” appeared 
in the egg (Fig. 45, A, c) which soon disappeared (Fig. 45, B). 
As a result of the process of division, a roundish embryo appears, 
which is made up of a large number of small cells. lie was un- 
able to study the mode of origin of the germ-layers. The free- 
swimming larva (Fig. 45, C) is an oval body, made up of two 
sorts of cells : those which are small, long and ciliated, and cer- 
tain large round ones, much fewer in number. The first form a 54 
LIFE HISTORIES OF ANIMALS. 
sort of arch, with a hollow in the middle, around which a large 
number of very fine brown pigment corpuscles are collected. 
The next change of importance is the disappearance of the cavity, 
the upper or ciliated half of the body being much reduced in size. 
Then the large round cells of the hinder part are united into a com- 
pact mass, leaving only a single row. The ciliated cells are gradu- 
ally withdrawn into the body cavity. Fig. 45, D, shows this process 
going on. At this period also the larva becomes sessile, and now 
begins the formation of the sponge spicules, which develop from 
the non-ciliated round cells. Metschnikoff calls attention to the 
fact that at this early stage the Sycon passes through a phase 
which is persistent in the genus Sycyssa. The layer of ciliated 
cells are gradually withdrawn into the body cavity, until a small 
opening is left, surrounded with a circle of cilia. These cilia 
finally disappear, and a few more spicules grow out, and meanwhile 
the opening disappears. In the next stage (represented at D) a 
considerable (gastrovascular) cavity appears, which may be seen 
through the body-walls. At this time, by soaking the specimen 
in acetic acid, the body of the sponge was seen to consist of 
two layers, the inner layer of ciliated cells forming a closed sac, 
enveloped in the spicule-generating layer (representing the ento- 
derm). At this time no moutli-opening was formed, though three- 
pointed spicules had appeared. 
It results from Metschnikoff s observations that the body of the 
larval sponge is composed of two primary germ-layers, an “ento- 
derm” and “ectoderm,” the two germ layers about which we shall 
hear much more hereafter. 
The observations of Carter, made on several additional species 
both of sUicious and calcareous sponges, confirm the results of 
Metschnikoff as to the later history of the larval sponge, and those 
of Haeckel as to the mode of segmentation of the egg. Our Fig. 
43, A (copied from Carter), shows the total segmentation of the 
yolk in Halisarca lobulctris into two portions ; these portions farther 
subdivide, as at Fig. 43, B, until an immense number of small 
embryonic cells are produced. 
Carter observes that the embryos may be found at all seasons, 
from March through the summer. These observations are not dif- 
ficult to follow out. We have, by tearing apart a species of Sy- 
candra (or Sycon) perhaps S. cilicita, which grows on a Ptilota, 
found the planula much as figured b}r Haeckel, Metschnikoff and THE SPONGES. 
Carter, and any one can with patience and care observe the life 
history of the marine sponges. 
It seems, then, that the life history of the sponges consists of 
the following stages :— 
1. Fertilization of a true egg by genuine spermatozoa; both 
eggs and sperm cells arising from the inner germ-layer. 
2. Total segmentation of the yolk, or protoplasmic contents of 
the egg. 
3. A ciliated embryo. 
4. A free swimming “ planula ’’-like larva, with two germ-layers. 
The plauula becomes sessile, spicules are developed in the hinder 
end of the body, afterwards a gastro-vascular cavity appears, con- 
stituting the 
5. Gastrula stage. 
6. A mouth and side openings appear and the true sponge char- 
acters are assumed. 
LITERATURE. 
Lieberkilhn. Znr Entwickelungsgeschichte der Spongillen (Muller’s Archiv, 1850.) 
O. Schmidt. Die Spongien des Adriatisches Meeres. Leipsig. 1802-60. 
Clark. Spongife Ciliata; as Infusoria Flagellata. 1807. 
Hceckel. Die Kalkschwamme. Eine Monograph. 2 vols. and atlas. Berlin, 1872. 
Metschnikoff. Zur Entwickelungsgeschichte der Kalkschwamme. (Siebold and KOI- 
liker’s Zeitschrift. (Feb., 1874.) 
Carter. Development of the Marine Sponges, etc. (Annals & Mag. Nat. Hist., Nov 
and Dec., 1874.) 56 
LIFE HISTORIES OF ANIMALS. 
IX. THE HYDROIDA. 
The animal next higher in structure than the sponge is the 
curious Protohydra discovered by Greef among diatoms and sea- 
weeds in the oyster park at Ostend. It is regarded by Greef as 
the marine ancestral form of the Coelenterates (Hydroids, Jelly 
fishes and Actiniae). It is the simplest possible radiate form }’et 
discovered. As the form of the fresh-water Hydra is familiar, 
Protohj'dra may be best described as similar to that, except that 
it is entirely wanting in tentacles. Like Hydra it is made up of 
two layers (an ectoderm and endoderm), with a mouth and stomach 
(gastro-vascular cavity). Nothing is known of its history, though 
Greef is positive that it is not a young Actinia. His interesting 
and detailed account was published with excellent illustrations in 
Siebold and Kolliker’s “Journal of Scientific Zoology” in 1869. 
The next higher form is the fresh-water Hydra, which is com- 
monly found on the under side of the leaves of aquatic plants. 
There are two varieties of Hydra vulgaris apparently common to 
the fresh waters of the old and new world. They are viridis and 
fusca. This well known animal is the simplest form of the divis- 
ion of radiates known as Hydroids. The somewhat club-shaped 
body consists of two layers, the inner (endoderm) lining the gen- 
eral cavity of the body, which serves both as mouth and stomach 
and for the circulation of the nutritive fluid, and is called the gas- 
trovascular cavity. The mouth is surrounded with eight tentacles, 
which are prolongations of the body-wall and are hollow, commu- 
nicating with the body cavity. 
Such is the general structure of the Hydra. In the ectoderm 
are situated the lasso-cells or nettling organs, being minute barbed 
filaments coiled up in a cell-wall. From Kleinenberg’s recent 
researches on the Hydra it appears that there are scattered irregu- 
larly through the endodermal lining of the body-cavity isolated 
ciliated cells. They do not form a continuous lining membrane, 
and thus bear an interesting analogy to the ciliated cells of the 
sponge. While the endoderm forms a simple cell-layer, the outer 
layer (ectoderm) is more complex, as just within an external 
simple layer of large cells is a multitude of smaller cells, some of 
them being thread or lasso cells, while still within are fine muscu- 
lar fibxillse which form a continuous layer. The large cells first THE HYDROID A. 
57 
named end in fibre-like processes, which alone possess contractil- 
ity and are thought by Kleinenberg to be motor-nerve endings. 
These large cells, from combining the functions of muscle and 
nerve, are termed “ nervo-musele cells.” The little cavities be- 
tween the large endodermal cells and the muscular layer which 
lies next to the endoderm is filled with small cells and lasso- 
cells, forming what Kleinenberg calls the interstitial tissue. From 
this tissue are developed the eggs and spermatozoa. 
The organization of all the hydroids and even Lucernaria and 
the larger jelly-fishes (Discophora) is based on the plan of the 
Hydra. They all have a simple body-cavity, but no true alimen- 
tary canal surrounded by a perivisceral cavity. This is the dis- 
tinguishing character of the Coelenterates. In the jelly-fishes, the 
often complicated water vascular system of canals are simpty 
passages leading out from the axial gastro-vascular cavity. If we 
place a jelly fish in the same position as the Hydra, i.e., with the 
tentacles directed upwards, the general homology between the 
parts can be clearly traced. In the Hydroids, such as Sertularia, 
etc., the ectoderm is surrounded by a chitinous sheath, secreted 
from this layer. While in Hydra the young bud out from the side 
of the body, in the Hydroids the young are developed on a sepa- 
rate stalk from the barren or nutritive stalk or “zooid.” The in- 
dividual Hydroid is thus subdivided into a reproductive and a 
nutritive zooid. The reproductive zooids seldom or never take in 
food, but are nourished by the nutritive zooids, the two zooids 
being connected by a common creeping stem called the “coenosarc.” 
The Anthozoa or sea anemones and coral polypes differ from 
the Hydroids and Medusae in having the stomach open at the 
bottom into a second and larger cavity communicating with the 
radiating chambers. In the Ctenophorse there is a decided ap- 
proach in the complication of the body to the Echinoderms. The 
radiated structure so clearly shown in the lower forms is here in 
part subordinated to the bilateral arrangement of parts; they 
have a right side and a left side. They also differ in the mouth 
opening into a wide digestive cavity, enclosed between two verti- 
cal tubes, uniting at the end of the body, where the stomach forms 
a reservoir for the gastro-vascular tubes ramifying throughout the 
body. They move by a peculiar apparatus consisting of bands of 
comb-like flappers. Not detaining the reader with a definition of 
the subdivisions of the Coelenterates we shall be content with 58 
LIFE HISTORIES OF ANIMALS. 
giving the following tabular view of the lowest subdivision of 
Radiates:— 
CCELENTERATA. 
Acalephs or Hydrozoa. 
1. Hydroida. a. Jlydriform (Hydra, Hydractinia, Tubularia, Sertularia) 
b. Siphonophora (Velella, Agalma, Physalia). 
2. Calycozoa (Lucernaria). 
3. Medusm or Disccpliorce (Aurelia.) 
Anthozoa (Actinia, Cerianthus, Astra3a, Alcyonium, Gorgonia and Renilla). 
Ctenophorae (Beroe, Cydippe, Cestum). 
Development of Hydra and the Hydroids. Ehrenberg first showed 
that the Hydra reproduced by eggs which become fertilized by 
spermatic particles. Kleinenberg describes the testis, which is 
lodged in the ectoderm and which develops tailed spermatozoa like 
those of the higher animals. They arise, as in other higher ani- 
mals, from a self-division of the nuclei of the testis-cells. There 
is a true ovary formed in the same interstitial tissue of the ecto- 
derm, consisting of a group of cells, which differ entirely in their 
mode of formation from the ovaries (gonophores) of the marine 
Hydroids, which are genuine buds. 
It thus seems that Hydra is monoecious or hermaphrodite, i. e., 
the sexes are not distinct. The egg of Hydra originates from the 
central cell of the ovary ; thus confirming the opinion now gener- 
ally held that all animals as a rule arise from a simple cell. After 
the egg-cell has escaped from the ovary through the ectoderm, it 
still holds on by a narrow point to the sides of the Hydra, where 
it is fecundated by the spermatic particles discharged into the 
surrounding water from the testis. 
Fecundation is succeeded by a true segmentation of the egg. 
The .young Hydra thus passes through a true “Morula” stage.13 
There is an outer layer of prismatic cells, forming the surface of 
tlie germs, and surrounding the inner mass of polygonal cells. At 
first none of these cells are nucleated, but afterwards nuclei ap- 
pear, and it is an important fact that these nuclei do not arise 
from any preexistent egg-nucleus. 
The next step is the formation of a true cliitinons shell, envel- 
oping the germ or embryo. After this Kleinenberg asserts that 
the cells of the germ become fused together, and that the germ is 
like an nnsegmented egg, being a single continuous mass of proto- 
plasm. Allman remarks that “as this phenomenon does not occur 
13Hereafter we shall often use Haickei’s convenient term “Morula,” instead ol 
“ stage of segmentation of the egg,” for the sake of brevity. THE HYDROIDA. 
59 
in other Hydroids it can have no general significance for the 
development of the order.” 
The remaining history of Hydra is soon told. In this proto- 
plasmic germ-mass there is formed a small excentric cavity; this 
is the beginning of the body cavity, which finally forms a closed 
sac. Allman remarks on this discovery of Kleinenberg’s that “ it 
is clear that the formation of a body cavity by invagination of the 
walls [f. e., ectoderm] with the significance which Ivowalevsky 
has assigned to it in other animals, does not exist in and 
just as little will it be found in any other hydroid.” It will be 
seen farther on that in certain medusae, Ivowalevsky has discov- 
ered that the digestive cavity is formed by the invagination of the 
ectoderm, and we have seen (p. 54) that Metznikoff declares 
that the ciliated cells lining the gastro-vascular cavity in the embryo 
of the sponge are the originally external ciliated cells of the pla- 
nula withdrawn into and lining the body cavity. 
After several weeks the germ bursts the hard shell and escapes 
into the surrounding water, but is still surrounded* by a thin inner 
shell. After this a clear superficial zone appears, and a darker 
one beneath, which is the first indication of the splitting of the 
germ into the two definitive germ-lamellae, common to all animals 
except the one-celled Protozoa. 
The embryo soon stretches itself out, a star-shaped cleft appears, 
which forms the mouth. The tentacles next appear. The animal 
now bursts open the thin inner shell, and the young Hydra appears 
much like its parent form. 
There is, then, no metamorphosis in the Hydra; no ciliated pla- 
nula. The adult form is thus reached by a continuous growth. 
It will be seen, to anticipate somewhat, that the Hydra, ex- 
actly as in the vertebrates, including man, arises from an egg 
developed from a true ovary, which is fertilized by a true tailed 
spermatic particle ; that the egg passes through a morula stage; 
that the germ consists of two germinal layers, while from the 
outer layer, as probably in the vertebrates, an intermediate or 
nervo-muscular layer is formed, which Allman thinks is the homo- 
logue of the middle germ-lamella of the vertebrates, supposed 
to have originally split off from the ectoderm. Allman even 
regards the chitinous shell of the germ of Hydra as the equivalent 
of the epidermis of vertebrates, being a provisional embryonic 
organ in Hydra, but permanent in vertebrates. 60 
LIFE HISTORIES OF ANIMALS. 
In all the marine Hydroids, which are more complex in their 
individualism than Hydra, the sexes being separate, the eggs and 
spermatic particles are thought by Allman to be developed from 
the endoderm. But E. Van Beneden has on the other hand shown 
that the eggs in Hydractinia are exclusively developed from the 
endoderm, while the spermatic cells arise from the ectoderm. 
The simplest form next to Hydra is Hydractinia, in which the 
individual is differentiated into three sets of zooids ; i.e., a, hydra- 
like, sterile or nutritive zooids; b and c, the reproductive zooids, 
one male and the other female, both being much alike externally, 
having below the short rudimentary tentacles several spherical 
sacs, which produce either male or female medusae. These 
medusa buds or closed generative sacs are fundamentally like 
the free medusae in structure. The marine Hydroids, then, are 
universally dicecious, and usually each colony is either male or 
female. 
A rather more complicated form is the common Coryne mirdbilis. 
Fig. 46 shows the hydrarium with its long tentacles (t) and a the 
medusa buds, Fig. 47 its free medusa. Tubularia is a higher form, 
and allied to the latter is still another form, Corymorpha pendula 
(Fig. 48. After Agassiz). 
Figs. 49-53 (after A. Agassiz) represent quite fully the life his- 
tory of another Tubularian, Bougainvillia superciliaris. Fig. 49 
represents the hydrarium, with the sterile zooids provided with long 
tentacles, and the medusa buds of dilferent ages. Fig. 50 shows 
a bud still more enlarged, with the proboscis (manubrium) just 
formed, and knob-like, rudimentary tentacles. In an older stage 
(Fig. 51) the proboscis is enlarged and the tentacles lengthened, 
while the depression at the upper end indicates the future opening. 
In Fig. 52 the appendages of the proboscis are plainly indicated, 
the tentacles are turned outwards. Shortly after this the 
breaks loose from its attachment and swims around as at Fig. 58. 
How do the zooids first arise? This leads us to speak of the sim- 
plest mode of reproduction in the Hydroids, which is by budding. 
The object of sexual reproduction, i. e., by eggs and spermatozoa, 
throughout the animal and plant world, is by bringing the germ or 
portion of protoplasm of one individual, which is an epitome 
potentially of its physical and psychical nature, to mingle with 
that of another of the same species, so that the offspring may 
combine the qualities of both parents, and not deteriorate. The THE HYDROIDA. 
61 
species can be reproduced simply by budding, but the result would, 
if maintained for a number of generations, in the end prove disas- 
trous to its integrity. Nature abhors self-fertilization. So that 
while, as in these Hydroids, the zooid form may be produced by 
budding, yet the time comes when the individuals of one colony 
must mingle their reproductive elements with those of a remote 
colony, through the medium of the water. By this mode of repro- 
Fig. 47. 
Fig. 46. 
Fig. 48. 
Polypite of Coryne mira- 
bilis, with a bud below 
a, and medusa bud, 
(gonophore) above. «, 
much enlarged. After 
Agassiz. 
Cory morph a. 
Free medusa of Co- 
ryne thrown off 
from the gono- 
phore. Natural 
size. After Agas- 
siz. 
duction new colonies are also set up. On the other hand budding 
or gemmation has for its object the extension of the colony of 
nutritive and reproductive zooids. This alternation of budding 
with sexual generation or “ alternation of generations,” or “parthe- 
nogenesis,” is first met with in the Hydroids, and we shall find it 
often recurring in the higher animals when needed to meet some 
special exigency of the species. 62 
LIFE HISTORIES OF ANIMALS. 
Fig. 49. 
Fig. 51. 
Fig. 52. 
Medusa bud of 49, farther ad 
vanced. 
Fig. 50. 
Medusa bud with the tenta- 
cles turned out. Magni- 
fied. 
Hydrarium of Bougainvillia, mag- 
iiifled. 
Medusa bud of 49. 
Fig. 63. 
Medusa of Bougainvillia. Magnified. After A. Agassiz. THE IIYDIIOIDA. 
63 
Budding begins as a slight protrusion of the basal portion (coe- 
nosarc) of the colon}7, which then becomes spherical and finally 
club-shaped, as in Fig. 46, until it assumes the form of a zooid. 
It remains permanently attached in all the Hydroids except in 
Hydra, where it breaks off and bears a free individual. In some 
species of Tubularia the heads of the zooids successively drop off, 
and are renewed. 
Multiplication by fission has only been observed in one case, in 
the medusa of Stomobrachium, observed by Kolliker at Messina. 
In this the pendent stomach divided in two, becoming doubled, 
which was followed by a vertical division of the umbrella, sepa- 
rating the animal into two independent halves. These again sub- 
divided, and Kolliker thinks this process went on still farther. 
The second mode of generation, i. e., by eggs and spermatic 
particles, have been observed in many marine Hydroids. As in 
the Hydra, the eggs, after being fertilized, pass through a morula 
stage, and finally the germ becomes surrounded by a blastoderm, 
as in Hydra, formed of long prismatic cells directly comparable 
with the zone of blastodermic cells of insects, and many other 
animals, including the mammals. The germ elongates and finally 
escapes from the ovisac (gonophore) of the parent as a ciliated 
“ planula,” a term first applied to it by Dalyell. 
Now how do these planulas become converted into hydras, and 
through them into medusae ? A glance at the accompanying figures 
will give the main points in the life history of a not uncommon 
Hydroid found on our shores, a Melicertum allied to Campanu- 
laria (Fig. 57). We are indebted to Mr. A. Agassiz (Seaside 
Studies in Natural History) for the following facts and illustra- 
tions regarding its history. After keeping a number of the Meli- 
certum in a large glass jar for a couple of days at the time of 
spawning, he found that the ovaries, at first filled with eggs, 
became emptied, and that the planulae, at first spherical and after- 
wards pear-shaped (Fig. 54) swam near the bottom of the jar, and 
soon attached themselves by the larger end to the bottom of the 
jar (Fig. 55). “Thus their Hydroid life begins; they elongate 
gradually, the horny sheath is formed around them, tentacles 
arise on the upper end, short and stunted at first, but tapering 
rapidly out into fine, flexible feelers; the stem branches, and we 
have a little Hydroid community (Fig. 56), upon which, in the 
course of the following spring, the reproductive calycles contain- 
ing the medusae buds will be developed.” 64 
LIFE HISTORIES OF ANIMALS. 
Fig. 54. 
Fig. 56. 
Planula of 
Melicertum. 
Fig. 55. 
Cluster of Planulae 
just attached to the 
ground. 
Polypites of Melicertum 
developed from the plan- 
ulae; greatly magnified. 
Fig. 57. 
Melicertum campanula, seen in profile. Natural size. After 
Agassiz. THE IIYDROIDA. 
65 
Coming now to the Portuguese man-of-war (Physalia, Fig. 58), 
which have so much occupied the attention of the best naturalists, 
it would seem at first well nigh impos- 
sible to trace their relationship with 
the ordinary Hydroids. A Physalia 
may, howrever, be compared to a fixed 
colony of Hydractinia or Coryne, for 
example. Each Physalia is either 
male or female, and consists of four 
kinds of zooids ; viz., nutritive and re- 
productive, with medusa buds, which, 
by their contractions and dilatations 
propel the colony onward; and the 
“feeders,” a set of digestive tubes 
which nourish the entire colony. 
The Siphonophores (as observed by 
Gegenbaur, Ivowalevsky, Haeckel and 
Metschnikoff, in Agalma and several 
other genera) arise from eggs which 
pass through a morula stage, into a 
ciliated planula, whose body consists 
of an ectoderm and endoderm. The 
gastro-vascular cavity in the Siphono- 
phores, as in the lower Hydroids so 
far as observed, is formed by a fold 
of the endoderm, while, as we shall 
see farther on, in the Discophorous 
jelly fishes it is formed by an infolding 
of the ectoderm. 
The further development of Nanomia, a Siphonophore native to 
our northern shores, from the larval state, has been described and 
figured by Mr. A. Agassiz. To use nearly his own words, the 
Nanomia consists, when first formed, of an oblong oil bubble, 
with but one organ, a simple digestive cavity. Soon between the 
oil bubble and the cavity arise a number of medusa buds, though 
without any “proboscis” (manubrium), as these medusa buds, 
called “ swimming bells,” are destined to “ serve the purpose of 
locomotion only, having no share in the function of feeding the 
Fig. 58. 
Pliysalia arethusa; from Ten- 
ney’s Zoology. 
LIFE IIISTOKIES OF ANIMALS. 66 
community.” After these swimming buds, three kinds of Hydra- 
like zooids arise. In one set the Hydra is open-mouthed, and is 
in fact a digestive tube, its gastro-vascular cavity connecting with 
that of the stem, and thus the food taken in is circulated through- 
out the community. These are the so-called “ feeders.” The 
second set of Hydras differ only from the “feeders” in having 
shorter tentacles twisted like a corkscrew. In the third and last 
set of Hydras the mouth is closed, and they differ from the others 
in having a single tentacle instead of a cluster. Their function 
has not 3ret been clearly explained. Gradually new individuals are 
added, until a long chain of Hydroids is formed, which move 
gracefully through the water, with the oil globule uppermost, 
which serves as a float and is identical with the large-crested 
“float” of the Physalia. 
LIFE HISTORIES OF ANIMALS. 
Finally, the higher Hydroids, such as AEginopsis, iEgineta, 
Cunina and Lyriopehave been found by. Muller, Agassiz, McCrady, 
Leuckart, Gegenbaur, Fritz Muller and others, to develop directly 
from eggs and pass through a metamorphosis as medusa}. During 
the past year (1874) Metschnikoff has published, with many fig- 
ures, an account of the development of Geryonia, Polyxenia 
(AEgineta) and AEginopsis. 
In these animals the egg passes through a morula stage; an 
outer layer of cells (blastoderm) splits off from the morula, form- 
ing the ectoderm and entoderm. The embryo, then, as in Polyx- 
enia, passes through a ciliated planula stage. The embryo may 
remain spherical, as in Geryonia, or as in Polyxenia and JEgin- 
opsis, the body of the planula becomes greatly elongated and 
bomerang-shaped, and from each end are developed the first two 
tentacles, then others, and after a slight metamorphosis the adult 
form is attained. 
Tlie life history of the Hydroids comprises, then, the following 
phases in development:— 
1. a. Origin of young Hydra by budding. 
b. Origin of embryo from egg fertilized by spermatozoa. 
2. Morula stage. 
3. Planula (?Gastrula) stage. 
4. Hydra-like form, attached. , 
5. Medusa, free and discharging eggs. THE medusa;. 
67 
Gegenbaur. Versuch eines Systemes der Medusen (Siebold and Kolliker’s Zeitschrift. 
1&57). 
McCrady. Gymnophthalmata of Charleston harbor (Proc. Elliott Soc. N. H., i, 1859). 
L. Agassiz. Contributions to the Natural History of the United States, vols. 3 and 4, 
1860 and 1862. 
Allman. Keport on the Present State of our Knowledge of the Reproductive System 
in the Hydroida. (Rep. Brit. Assoc. Adv. Sc., 1863.) 
Clark. Mind in Nature. 1865. 
A. Agassiz. Catalogue of the Acalephse of North America. Mus. Comp. Zool., 1865. 
E. C. and A. Agassiz. Seaside Studies in Natural History. Radiates. Boston, 1871. 
Kleinenberg. Hydra, ein Anatomisch-entwicklungsgeschichliche Untersuchung. 
Leipzig, 1872. (Abstract, with notes by Allman in Quatr. Journ. Micr. Science, 1874.) 
Metschnihoff. Studien ueber die Entwickelung der Medusen und Siphonophoren 
(Siebold und Kolliker Zeitschrift, 1874). 
LITERATURE 
X. THE MEDUSA] (Discophorse). 
Passing by the Lucernaria, beautiful and interesting, but of 
whose early development we know nothing, we come to the common 
larger jelly-fishes of our shores, which differ from the bell-shaped 
hydroid medusae in their usually larger size and solid disk, as well 
as in the larger number and greater complication of the water 
tubes, which ramify and interbranch along the under side of the 
disk; and in carrying their eggs in pouches. In our common 
Aurelia Jlavidula there are four of these large pouches occupying 
the centre of the disk. 
The life history of the Aurelia, which we will select as an ex- 
ample of the mode of development of this group, since it is best 
known, is far less complicated than that of the Hydroids. The 
ciliated planulae may be found in the egg pouches of the female 
Aurelia during the last of summer. Soon 
after the ectoderm and entoderm are 
formed, a mouth is developed, and a gas- 
tro-vascular cavity is formed by the invag- 
ination of the ectoderm, as stated by Mets- 
chnikoff, and they then pass into a gastrula 
(planula) stage (Fig. 59, Gastrula of a 
form allied to Aurelia ; a, mouth ; 6, gastro- 
vascular cavity ; c, ectoderm ; d,entoderm 
after Metschnikoff), with a mouth and 
large digestive cavity. After swimming about for a while they fix 
Fig. 59. 
Gastrula of an Aurelia-like 
Medusa. 68 
LIFE HISTORIES OF ANIMALS. 
themselves to some object at the bottom of the sea and soon a 
pair of tentacles begin to develop, and then two more, until not 
more than sixteen are developed. When of this hydra-like form 
(Fig. 60 a, young; &, older, after A. Agassiz) it is called a “ Scy- 
phistoma,” having originally, as well as the Strobila and Fphyra, 
Fig. 61. 
Fig. 60. 
Scyphistoma of Aurelia, at differ- 
ent ages. Magnified. 
Strobila of Aurelia. 
been mistaken for and described as an adult animal under that 
name. 
After assuming tins scypliistoma condition, transverse constric- 
tions appear at regular intervals, dividing the column, as it were, 
into a pile of saucers; the edges rise, tentacles bud out, and the 
animal assumes the form seen in Fig. 61 (after Agassiz). The 
uppermost disk becomes detached, the rest 
separate one after the other and float away in 
the form of an “ Ephyra” (Fig. 62, after A. 
Agassiz) and after some weeks assume the 
aurelia or adult condition (Fig. 63). The gi- 
gantic Cyanea arctica, which attains a diam- 
eter of from three to five feet across the disk, 
as Agassiz remarks, is produced from “a hy- 
droid measuring not more than half an inch when full-grown.” 
On the other hand there are several exceptions known to this 
mode of development, a few growing directly from the egg, with- 
out passing through a hydra, or scypliistoma stage. Such is the 
large Pelagia, as observed by Krohn. Mr. A. Agassiz has ob- 
Fig. 62. 
Ephyra of Aurelia THE MEDUSAS. 
served the same fact in Campanella pacliy derma, a minute jelly 
fish. 
The Discophores, then, develop in two ways :— 
A. Directly from the egg (Pelagia and Campanella). 
Fig. 63. 
Atirelia flavidula. After Agassiz. 
B. From bydra-like young arising from eggs (Aurelia and 
Cyanea) and presenting the following phases of growth :— 
1. Egg. 
2. Morula (?) 
3. Planula (Gastmla). 
4. Scyphistoma. 
5. Strobila. 
6. Ephyra. 
7. Aurelia (adult). 
LITERATURE. 
Nearly the same as for the Hy droids. 70 
LIFE HISTORIES OF ANIMALS. 
XI. THE ACTINOZOA. 
The sea anemones and coral polypes are more highly developed 
than the Hydroids, since the mouth opens into a double digestive 
cavity, which is supported for its whole length by the six primary 
curtains or septa. The second and lower half of the cavity en- 
larges greatly, and communicates with the general cavity of the 
body, the upper portion being entire, tubular, and forming a sort 
of throat opening into the proper digestive cavit}’. In the Hy- 
droids, the digestive cavity, it may be remembered, is simply hol- 
lowed out of the body cavity and is a more primitive affair than 
that of the Actinozoa. 
While in the Hydroids also the ovaries hang outside the body 
cavit}r, in the true polypes they are attached to the septa or walls 
of the radiating chambers, so that the eggs, when ripe, drop down 
into the body cavity, whence they pass out through the mouth, or, 
as observed by Lacaze-Duthiers in the coral polypes, through the 
tentacles. The chambers between the septa correspond to the 
water canals, or chymiferous tubes of the Hydroids. The so- 
called mesenterial filaments attached to the septa are excretory 
glands supposed to be renal in their nature. 
In the coral polypes the coral is secreted in the chambers, so that 
there are soft partitions alternating with the limestone ones. The 
tentacles which surround the mouth vary greatly in number. They 
are hollow, each communicating with a chamber. 
The polypes are divided into (1), the Aetinoids (Zoantharia) 
which either secrete no limestone, as in the sea anemones, or form 
a coral stock, as in the coral polypes, and have an indefinite num- 
ber of tentacles, and (2), the Halc}'onoids, in which the tentacles 
are eight in number. Such are the sea fans (Gorgonia) and Hal- 
cyonium, which does not secrete a coral stock. 
Development. Nearly all the Actinozoa increase by budding, 
new individuals arising at the base of the large ones. In Zo- 
anthus the young grow out in stolons branching from the parent 
polype. The life history of a polype from the egg is soon told. 
Naturalists are indebted to the magnificent memoirs of Lacaze- 
Duthiers for a full biography of not only several genera of sea 
anemones (Actinia mesembryanthemum, Bunodes and Sagartia) 
but also of the Gorgonia, Halcyonium, red coral, and the Astro- 
ides, a Mediterranean form (Fig. 65). THE ACTINOZOA. 
71 
The young sea anemone develops without any metamorphosis, 
directly into the adult condition. Lacaze-Duthiers could not 
determine by actual sight how fecundation of the egg takes place, 
or whether the egg passes through a morula stage or not, though 
he infers, with every reason, that this stage, ?. e., the segmentation 
of the egg contents, takes place in the ovary. The ovaries and 
spermaries are in the Actinia situated in the same individual; the 
eggs are oval, while the spermatic cells are of the usual tailed 
form. The fecundated egg in the state in which it was first seen 
by Lacaze-Duthiers was oval, and surrounded 
by a dense coat of transparent conical spinules. 
He was soon able to detect the presence of the 
two primitive germinal layers, the ectoderm 
and endoderm. Fig. 64 (from Metschnikoff) 
illustrates the relation of the embryonal layers 
in the larva of another polype which he calls 
“kaliphobenartige Polypen larve a, primitive 
opening into the gastro-vascular cavit}7, b; c, 
ectoderm; d, entoderm ; e, body cavity), show- 
ing that the walls of the digestive cavity are 
formed by the entoderm ; and Metschnikoffs figure shows that the 
embryo polype has a greater resemblance to the embryo starfish 
of the same age than the acalephs. 
Fig. 64. 
Ciliated larva (gastrula) 
of a Polype. 
Two lobes next appear within the body, these subdivide into 
four, eight and finally twelve primitive lobes. This stage is rep- 
resented by the corresponding stage of the coral (Fig. 66, B). Not 
until after the twelve primitive lobes are fully formed do the ten- 
tacles begin to make their appearance. When the first twelve 
tentacles have grown out, twenty-four more arise, and so on, until 
with its increasing size the actinia is provided with the full number 
peculiar to each species. The preceding remarks apply to Actinia 
mesembryanthemum, but Lacaze-Duthiers observed the same 
changes in two species of Sagartia and in Bunodes gemmacea. 
Turning now to the stony corals we will give more fully the 
sequence of events in the life of a coral builder of the Mediter- 
ranean, the Astroides calycularis, so faithfully narrated by La- 
caze-Duthiers. Fig. 65 taken from Tenney’s “Manual of Zool- 
ogy” illustrates this coral in various stages of expansion. 
He studied this coral ou the coast of Algiers, and found that 
reproduction took place between the end of May and July, the 72 
LIFE HISTORIES OF ANIMALS. 
young developing most actively at the end of June. Unlike Ac- 
tinia, which is always hermaphrodite, this coral is rarely so, but 
the polypes of different branches belong to different sexes. 
As in the other polypes, including Actinia, the eggs and sper- 
matic particles rupture the walls of their respective glands situ- 
ated in the partitions. As in Actinia, Lacaze-Duthiers thinks 
the fecundation of the egg occurs before it leaves the ovary, when 
also the segmentation of the yolk must take place. Unlike the 
embryo Actinia, the ciliated young of the coral, after remaining 
in the digestive cavity for three or four weeks, make their wray out 
into the world through the tentacles. “ Many times,” says Lacaze- 
Duthiers “have I seen the end of the tentacle break and let out 
Fig. 65. 
the embryo.” The appearance of the embryo, when first ob- 
served, was like that in Fig. 66, A, an oval, ciliated body with a 
small month and a digestive cavity. This may be called the gas- 
trula, adopting Haeckel's phraseology. 
Coral polype (Astroides calycularis) expanded. 
The gastrula changes into an actinoid pol}Tpe in from thirty to 
forty in confinement, after exclusion from the parent, but in 
nature in a less time, and it probably docs not usually leave the 
mother until ready to fix itself to the bottom. 
Before the embryo becomes fixed and the tentacles arise, the 
lime destined to form the partitions begins to be deposited in 
the endoderm. Fig. 66, C, shows the twelve rudimentary septa. 
These after the young polype, or “actinula” (Allman), has be- 
come stationary, finally enlarge and become joined to the external THE ACTINOZOA. 
73 
walls of the coral now in course of formation (Fig. 66, C, c) 
forming a groundwork or pedestal on which the actinula rests. 
D represents the young polype 
resting on the limestone pedestal. 
In the experience of Lacaze-Du- 
tliiers it happened that the embryo 
polype which had been swimming 
about in his jars for 
about a month, sud- 
denly, within the 
space of three or four 
hours after a hot si- 
rocco had been blow- 
ing for three days, 
assumed the form of 
small disks (Fig. 66, 
B), divided as in the 
Actinia into twelve small folds forming the bases of 
the partitions within. 
The tentacles next arise, being the elongation of 
the chambers between the partitions, six larger and 
elevated, six smaller and depressed (Fig. 66, D). 
The definitive form of the coral polype is now as- 
sumed, and in the Astroides it becomes a compound 
polypary. 
The singular floating young Edwardsia, originally 
described under the name Ai'achnactis, has been 
found by Mr. A. Agassiz to be the early swimming 
stage of Edwardsia, a worm-like Actinian, which, 
like Halcampa albida (Fig. 67), lives in the sand or mud, unat- 
tached to any fixed object. 
Kowalevsky has lately found that the Cerianthus, a gigantic 
Actinia which lives in a tube in the mud at great depths, has a 
free swimming early stage like Edwardsia. 
The following is a summary of the changes undergone by the 
polypes so far as known :— 
1. Egg fertilized by true spermatozoa. 
2 ? Morula. 
Fig. 66. 
Fig. 67. 
Development of a coral polype, Astro- 
ides ealycularis. After L.-Duthiers. 
Halcampa al- 
bida. 
Note. — Figs. 63, 67, 73, 74 and 76, 'were kindly loaned by Frofessor Verrill, from 
his Report on the Invertebrates of Vineyard Sound. 74 
LIFE HISTORIES OF ANIMALS. 
3. Gastrula. 
4. Actinula, with twelve primitive tentacles (in the Actinoids). 
5. Adult actinia or polype. 
LITERATURE. 
Lacaze-Duthiers. D£veloppment des Coralliaires (Lacaze-Duthiers’ Archives de Zo- 
ologie Experimentale, etc. 1872,1873). 
XII. THE CTENOPHORAE. 
These beautiful animals derive their name Ctenophorae, or 
“comb-bearers,” from the vertical rows of comb-like paddles, situ- 
ated on horizontal bands of muscles, which serve as locomotive 
organs, the body not contracting and dilating as in the true jelly 
fishes. In their organization they are much more complicated 
than any animals of which we have yet spoken, as it has been 
shown by the two Agassizs that they have a true digestive cavit3% 
passing through the body cavity, with a posterior outlet, and orig- 
inating in the same manner as in the Echinoderms. From this 
alimentary canal are sent off chymiferous tubes which “ correspond 
in every respect with the water tubes of the Echinoderms” (A. 
Agassiz). The rows of paddles are intimately connected with the 
chj’miferous tubes, so that the movements of the body are in di- 
rect relation with the act of breathing. Moreover these animals, 
while in the disposition of the organs following the radiate plan 
of structure, are also more truly bilateral than any of the lower 
classes of radiates. The sexes are united in the same individual; 
the ovaries in Idyia are on one side of the main chymiferous tube, 
and the spermaries on the other, both being brilliantly colored. 
Referring the reader for farther details to Mr. A. Agassiz’s “Sea 
Side Studies,” where these animals are described and illustrated 
with sufficient detail for the general reader, we will now turn to 
their mode of growth, under the guidance of the same author, 
whose recent richly illustrated memoir, with others by Kowalevsky 
and Fol leave but few gaps to be filled by future observers. 
Development. Agassiz states that the Ctenophorae are readily 
kept in confinement, and from twelve to twenty-four hours after 
they are captured lay their eggs, either singly or in strings, or, 
as in Idyia, in a thick slimy mass. The Ctenophorae of our 
eastern coast spawn from late in July through August and Sep- 
tember. “The young brood developed during the fall, comes to THE CTENOPHOR.E. 
the surface again the following spring as nearly full-grown Cteno- 
phorm, to lay their eggs late in the summer.” Fortunately the 
eggs are so transparent that in some forms (Pleurobrachia and 
Bolina) the embryology can be studied, not only in the egg but 
also through nearly all the earlier stages of the larva. 
Selecting Pleurobrachia as an example of the mode of growth, 
we find that as in Idyia the egg consists of two layers, i.e., an 
inner yolk mass and an outer, thin, finely granular layer surrounded 
by a transparent envelope. The inner mass acts merely as a nu- 
tritive mass, while the outer is the true embryonic layer, which 
builds up the body at the expense of the central nutritive mass. 
No nucleus nor nucleolus has been observed by Agassiz in the 
eggs of any Ctenophone, after they are once laid, until late in the 
stage of segmentation. The egg divides into four and again eight 
spheres of segmentation, each of which has, like the egg, origi- 
nally an outer and inner mass. In a second stage of segmentation 
small cells arise which surround the original eight large cells. 
From these small cells (the blastoderm) the external organs are 
destined to arise, while the larger cells form a yolk mass out of 
which the internal organs arise. 
The embryonal layer is next formed, then the outer wall by “the 
gradual encroachment of the actinal cells over the whole of the 
yolk mass.” Finally, the mouth (actinos- 
tome) of the germ is formed, and after- 
wards the digestive cavity, which results 
from an invagination of the outer embry- 
onic layer (ectoderm). Fig. 68 (after 
Metschnikoff) represents the larva of a 
Cydippe ; a, primitive opening; b, gastro- 
vascular cavity; c, ectoderm; d, endo- 
derm ; e, interspace corresponding to the 
body cavity of the larva of the polype. The development of the 
chymiferous tubes is succeeded by that of the locomotive flappers, 
eight or nine pairs in each row appearing before the young leave 
the egg, and of the fringed tentacle, which attains a great length 
after the young is hatched. 
Fig. 68. 
Gastrula of Cydippe. 
Finally the definitive form of the Pleurobrachia is attained 
before it leaves the egg, as seen in Fig. 69 (£, tentacles ; e, eye- 
speck ; c, c, rows of locomotive flappers ; d, digestive cavity ; 
greatly magnified after A. Agassiz). 76 
LIFE HISTORIES OF ANIMALS. 
Fig. 70 shows the young Pleurobraehia swimming about in 
the egg just before hatching, and in Fig. 71 (after A. Agassiz), 
we see the young after hatching 
(magnified) with nearly the same 
form as the adult; / indicates the 
funnel leading to the anal opening, l, 
the lateral tubes, and c c c' c1 the rows 
of locomotive flappers. The remain- 
ing changes are slight, and there is 
not even a slight metamorphosis, the 
body simply becoming spherical and 
the tentacles increasing enormously 
in length. In Bolina and its allies, 
as A. Agassiz states, “the morpho- 
logical changes are very great, and it would indeed puzzle the 
most accurate systematist to recognize in the early stages of some 
of the Mnemidm the young of well known genera. We cannot 
say that there is a metamorphosis in the ordinary sense of the 
word, as supposed by Gegenbaur, but there certainly are remark- 
Fig. 69. 
Young Pleurobrachia still in the 
egg. 
F;g. 71. 
Fig. 70. 
Young Pleurobrachia 
swimming in egg 
ready to hatch. 
The same alter hatching. 
able changes, such as the almost total suppression of the tentacu- 
lar apparatus, the development of auricles, of lobes, with their 
complicated winding chymiferous tubes, which alter radically the 
appearance of the Ctenophorse at successive periods of growth, 
and present between the younger and the older stages differences 
usually considered as of great systematic value.” THE ECHINODERMS. 
The summary of stages is very brief, the Ctenophore passing 
through three phases t— 
1. Egg stage. 
2. Morula state. 
3. Gastrula state. 
4. Adult form, assumed before hatching. 
I.ITERATURE. 
A. Agassiz. Catalogue of North American Acalephas-. 1805. 
Kowalevsky. Entwickelungsgeschichte der ftippenquallen. Acad., St. 
Petersbourg, x, No 4.) 
Fol. Ein Beitrag zttr Anatomie und Entwickelung einiger Rippenquallen. (Siebold 
and Kblliker’s Zeitschrift, 1S69.) 
A. Agassiz. Embryology of the Ctenophor-ae. (Memoirs Arner. Acad. Arts and 
Sciences, x, No. 3,1874.) 
XIII. THE ECHINODERMS. 
The Echinoderms (starfishes, sea ui’chins and sea cucumbers) 
are far more complicated than the Coelenterates, having a true ali- 
mentary canal passing through the general cavity of the body. 
In them for the first time among the Radiates appears a well devel- 
oped nervous system. Not -only do the young exhibit a bilateral 
symmetry, but in the higher forms, as the spantangoid sea urchins, 
Fig. 72. 
Pendacta frondosa. (From Tenney’s Zoology.) 
this is quite well marked ; and there is a dorsal and ventral side. 
Still, in the generality of the forms, the radiated plan of structure 
is remarkably adhered to, the body as distinctly made up of sphse- 
romeres, or wedge-shaped sections of the body, as the worms are 
of segments (arthromeres). In this and other respects, as well 
as the form of the larvae, there is a remarkable parallelism be- 
tween the worms and echinoderms. 78 
We will briefly review some of the anatomical features of the 
Echinoderms, in order to understand their complicated mode of 
growth. 
LIFE HISTORIES OF ANIMALS. 
The stomach and intestinal canal either pass straight or in a 
spiral course through the body, as in the sea urchins (Fig. 92) and 
Holothurians (Fig. 72), and open out at the opposite end ; or, as 
in the Antedon (Comatula), the anal opening is situated near the 
mouth, while in the Ophiurans (Fig. 74) and Luidia and Astro- 
pecten, low starfishes, the undigested food is rejected from the 
mouth. In the starfishes and Holothurians, the alimentary canal 
opens into five voluminous caecal appendages. These are wanting 
in the Ophiurans, and there are but two in Astropecten. They 
are in connection with the complicated 
water tubes, which consist of a canal 
surrounding the mouth and sending 
branches out into the rays of the star- 
fishes in communication with the loco- 
motive organs or suckers, called am- 
bulacra. The water fills the tubes 
through a duct leading from the sieve- 
like plate, situated in the dorsal 
(abactinal) portion of the body. Near this duct is the pulsating 
tube, the so-called heart. 
Fig. 73. 
Hooks and Plates ot Synapta. 
The Echinoderms are further distinguished by the body walls 
secreting calcareous plates, often 
forming a solid limestone shell, as 
in the sea urchins; or the plates 
are smaller and movable as in the 
starfishes, or as in the sea cucum- 
bers they are microscopic, buried 
in the skin ; sometimes, as in the 
Synapta forming anchor-like hooks 
and small plates (Fig. 73). 
The sexes are as a rule distinct. 
In Opliiura squamata and Synapta 
they are united in the same indi- 
vidual. The ovaries and testes 
are gland-like masses situated at 
the base of the arms in the starfishes, or between the ambulacra 
in the sea urchins. The ovaries are red or yellow, the male glands 
Fig. 74. 
Sand star (Ophiopholis aculeata). THE ECHINODERMS. 
79 
whitish. In the Ophiurans the eggs and spermatozoa pass out of 
the body through little holes between the plates on the under side 
of the body. In those starfishes in which the alimentary canal 
is a blind sac, the eggs are emptied into the body cavity ; but 
how they pass out is unknown. In some starfishes they escape 
through certain (interradial) plates on the back. In the Echi- 
noids they make their exit from between the ambulacra. In the 
Holothurians, however, there is a duct leading from the generative 
gland opening out near the mouth, between the tentacles. The 
eggs are usually round, and minute ; the spermatozoa of the usual 
tailed form. Fertilization takes place in the water. 
Remembering that there are five well-marked divisions of 
Echinoderms, i.e., Crinoidea, Opliiuroidea, Asteroidea, Echinoidea, 
and Holothuroidea, we will now review some of the main points in 
the mode of development of the respective orders. 
Development of the Crinoids. While we know nothing of the 
mode of development of the true Pentacrinus and Rhizocrinus, 
the lineal descendants of the Crinoids of the earlier geological 
ages, we have quite full information regarding the life-history of 
the Antedon, which is for a part of its life stalked, and is in fact 
a true crinoid. 
The following account is taken (sometimes word for word) from 
Professor Wyville Thompson’s researches on the Antedon rosaceus 
of the British coast. The ovaries open externally on the pinnules 
of the arms, while there is no special opening for the spermatic 
particles, and Prof. Thompson thinks they are “discharged by the 
thinning away and dehiscence of the integument.” The ripe eggs 
hang for three or four days from the opening like a bunch of 
grapes, and it is during this period that they are impregnated. 
The egg then undergoes total segmentation. Fig. 75, A, represents 
the egg with four nucleated cells, an early phase of the mulberry 
or morula stage. After the segmentation of the yolk is finished, the 
cells become fused together into a mass of indifferent protoplasm, 
with no trace of organization, but with a few fat cells in the centre. 
This protoplasmic layer becomes converted into an oval 
whose surface is uniformly ciliated. The mouth is formed, with 
the large cilia around it, before the embryo leaves the egg. When 
hatched, the larva is long, oval, and girded with four zones of cilia, 
with a tuft of cilia at the end, a mouth and anal opening, and is 
about *8 millimetre in length. The body cavity is formed by an 80 
LIFE HISTORIES OF ANIMALS. 
inversion of the primitive sarcode layer which seems to corres- 
pond to the ectoderm. 
Within a few hours or sometimes daj’S, there are indications of 
the calcareous areolated plates forming the cup of the future cri- 
noid. Soon others appear forming a sort of trellis work of plates 
and gradually build up the stalk, and lastly appears the cribriform 
basal plate. Fig. 75, B, c, represents the young crinoid in the 
middle of the larva, whose body is somewhat compressed under the 
covering glass. Next appears a hollow sheath of parallel calca- 
reous rods, bound, as it were, in the centre by the calcareous 
plates. This stalk (B, c) arises on one side of the digestive 
Fig. 75. 
Development of a Crinoid (Antedon 
cavity of the larva, and there is no connection between the body 
cavity of the larva and that of the embiyo crinoid. 
Two or three days after the appearance of the plates of the 
crinoid, the larva begins to change its form. The mouth and di- 
gestive cavity disappear, not being converted into those of the 
crinoid. The larva sinks to the bottom resting on a seaweed or 
stone to which it finally’' adheres. The Pentacrinus is embedded in 
the former larval body (the cilia having disappeared), now consti- 
tuting a layer of sarcode conforming to the outline of the Antedon. 
Meanwhile the cup of the crinoid has been forming. It then 
assumes the shape of an open bell; the mouth is formed, and five 
lobes arise from the edges of the calyx. Afterwards five or more, 
usually fifteen tentacles, grow out, and the young Antedon appears THE ECHINODERMS. 
81 
as in Fig. 75, C (after Thompson). The walls of the stomach then 
separate from the body-wall. The animal now represents the pri- 
mary stage of the crinoids, that which is the permanent stage in 
the Pentacrinus and its fossil allies. The Antedon, however, in 
after life separates from the stalk and moves about freely. 
Development of the Starfish. We will select as a type of the 
mode of development of the starfishes, that of the common five 
finger, Asterias (Fig. 76), as worked out with great thoroughness 
Fig. 76. 
Asterias. 
by Mr. A. Agassiz, and given in the “Seaside Studies.” The 
accompanying illustrations are taken from this work and the orig- 
inal memoir, through the kindness of the author, whose descrip- 
tion is here freely used. 
Fig. 77 shows the transparent spherical egg, enclosing the ger- 
minative vesicle and dot, and Figs. 78, 79, illustrate the segmen- 
tation of the yolk into two and eight and more cells, enclosing a 
central cavity. After this the embryo hatches and swims about as 
a transparent sphere (Fig. 80). A depression (Fig. 81, ma) then 
begins to appear, the body elongates, and this depression forms 
an inversion of the outer wall of the body (ectoderm), constitut- 
ing the body cavity (d, Fig. 82 ; oc, being the provisional mouth- 
LIFE HISTORIES OF ANIMALS. 82 
LIFE HISTORIES OF ANIMALS. 
opening, afterwards becoming the anal opening; at this time, how- 
ever, serving both for taking in and rejecting the food). From 
the upper extremity of the digestive cavity next project two lobes 
(w, w', Fig. 83 ; m, mouth). These separate from their attachment 
and form two distinct hollow cavities (w, wl, Fig. 84; a, d, c, di- 
gestive system; u, vibratile chord; m, mouth). Here begins the 
true history of the young starfish, for these two cavities will de- 
velop into two water-tubes, on one of which the back of the star- 
fish, that is, its upper surface, covered with spines, will be devel- 
oped, while on the other, the lower surface, with the suckers and 
Fig. 77, 
Fig. 78 
Fig. 79. 
Fig. 80 
Free swim- 
ming germ. 
Egg of Starfish. 
Segmentation of yolk. 
Fig. 81. 
Fig. 82. 
Fig. 84. 
Fig. 83. 
The same, 
older. 
Mouth of Gastrula. 
Gastrula. 
Larva. 
tentacles, will arise. At a very early stage one of these water 
tubes («?', Fig. 85) connects with a smaller tube opening outwards, 
which is hereafter to be the madreporic body (b, Fig. 85). Almost 
until the end of its growth, these two surfaces, as we shall see, 
remain separate and form an open angle with one another; it is 
only toward the end of their development that they unite, enclos- 
ing between them the internal organs, which have been built up in 
the meanwhile. 
“At about the same time with the development of these two 
pouches, so important in the animal’s future history, the digestive 
cavity becomes slightly curved, bending its upper end sideways THE ECHIXODERMS. 
83 
till it meets the outer wall, and forms a junction with it (m, Fig. 
86 ; o, digestive cavity). At this point, where the juncture takes 
place, an aperture is presently formed, which is the true mouth. 
The digestive sac, which has thus far served as the only internal 
cavity, now contracts at certain distances, and forms three dis- 
tinct, though connected cavities as in Fig. 85, viz., the oesoph- 
agus leading directly from the mouth (m) to the second cavity or 
stomach (cl), which opens in its turn into the third cavity, the ali- 
mentary canal. Meanwhile the water-tubes have been elongating 
till they now surround the digestive cavity, extending on the other 
side of it beyond the mouth, where they unite, thus forming a 
Fig. 87. 
Fig. 85. 
Fig. 86. 
Profile view of Larva. 
Larva. 
Y-shaped tube, narrowing at one extremity, and dividing into two 
branches toward the other end, Fig. 87.14 
“On the surface where the mouth is formed, and very near it on 
either side, two small ones arise, as v in Fig. 84 ; these are cords 
consisting entirely of vibratile cilia. They are the locomotive or- 
gans of the young embryo, and they gradually extend until they 
respectively enclose nearly the whole of the upper and lower half 
of the body, forming two large shields or plastrons (Figs. 87, 88). 
The corners of these shields project, slightly at first (Fig. 87), 
but elongating more and more until a number of arms are formed, 
stretching in various directions (Figs. 88, 89) 15 and, by their con- 
Larva with arms developing 
14 Fig. 87 a, anus; c, intestine; e' e" e’" e4 e5 e6, arms; o, oesophagus. 
10 Figs. 88,89, side view of 88. Adult larva, so-called Brachiolaria, lettering the same 
in all the figures; t, tentacles of young starfish; //, brachiolar appendages; r, back of 
young starfish. Fig. 90, t', odd tentacle. 84 
stant upward and downward play, moving the embryo about in the 
water” (A. Agassiz). 
Having reached the Brachiolaria stage, the body of the future 
starfish begins to develop. On one of the water-tubes (w1) the 
tentacles of the future starfish arise as a series of'lobes (t) ; while 
LIFE HISTORIES OF ANIMALS. 
Fig. 88, 
Full grown larva of Starfish, or Brachiolaria. 
on the opposite water-tube (tv), arise a number of little calcare- 
ous rods, which afterwards form a continuous net-work; r indi- 
cates the back of the young starfish. The larva now shrinks and 
drops to the bottom and attaches itself there by means of the 
short arms (//', Fig. 88). The starfish now absorbs the larva, and THE ECHINODERMS. 
85 
appears of an oval form with a crenulated edge, and soon reaches a 
stage indicated by Fig. 90. (Fig. 91, the same seen in profile). 
In this stage it remains probably two or three years before the 
arms lengthen and the 
adult form is assumed. 
The development of the 
Ophiurans is much like that 
of the starfish, with some 
characters of the embryo 
sea urchin. The larva of 
the sand star (Ophiura) 
is called a Pluteus, and is 
remarkable for the great 
length of two of the arms. 
Development of the Echi- 
noids. The researches of 
Mr. A. Agassiz, who has 
given us a very complete 
history of the common sea 
urchin of the northern e 
shores of the United States 
in his “Revision of the 
Echini,” will be our guide 
in these studies. The 
earlier stages of develop- 
ment were obtained by 
artificial fecundation of 
the egg during February. 
The early embryonic 
stages are much as des- 
cribed in the starfishes, the 
process requiring but a few 
hours. The embryo when hatched is like that of the starfish at 
the same period (Fig. 80) and then it passes into the gastrula 
stage (Fig. 93, lettering the same in all the figures as in those of 
the starfish) the digestive cavity being formed by an inversion of 
the ectoderm. “The embryo, in escaping from the egg, resembles 
a starfish embryo, and it would greatly puzzle any one to perceive 
any difference between them. The formation of the stomach, of 
the oesophagus, of the intestine, and of the water tubes takes 
Fig. 89. 
Fig. 88 seen in profile. 86 
LIFE HISTORIES OF ANIMALS. 
place in exactly the same manner as in the starfish, the time only 
at which these different organs are differentiated not being the 
same. In figure 94 we see the begin- 
ning at w and w1 of the water tubes 
arising as pouches sent off from the di- 
gestive cavity, and T-shaped rudiments 
of the limestone rods (r), so character- 
istic of the larva of the sea urchin are 
now visible.” 
Fig. 95 represents the larva well 
advanced towards the pluteus stage. It is now in the tenth day 
after fecundation.16 The arms are now well marked, and the “ vi- 
bratile epaulettes” appear. When the larva is twenty-three days 
Fig. 92. 
Common Sea Urchin (Echinus). 
Fig. 90, 
Fig. 91. 
Young Starfish seen in profile. 
Young Starfish seen from the back. 
old, the rudiments of the five tentacles of the sea urchin appear, 
the first one on the left water tube. The arms have increased in 
length, until in the full-grown larva, now called the pluteus (Figs. 
96, 97, the same seen sidewise), the arms with the calcareous rods 
supporting them are of great length, opening and shutting like the 
rods of an umbrella; while the sea urchin growing within lias 
concealed the shape of the digestive cavity of the larva, and the 
spines are so large as to conceal the tentacles. 
16Fig. 95, e-e’T arms; v-v\ vibratile chord, w w , earlets, water tubes; aodc, digestive 
system; r-r"' solid rods of the arms; m, mouth; b, madreporic opening. Fig. 96, /, 
brachilar appendages. THE ECHINODERMS. 
87 
The pluteus, a nomadic stage of the echinus, is as Mr. A. 
Agassiz states “ a scaffolding in which the future sea urchin plays 
but a secondary part, and is composed of two open spirals, the 
one to form eventually the complicated abactinal system (the in- 
terambulacral and ambulacral plates), the other to form the water 
system, and holding between them the digestive cavity and 
other organs of the pluteus, which as yet appear to have no con- 
nection whatever with the spines of the future Echinus. Yet to- 
wards the end of the nomadic pluteus life a few hours are sufficient 
to resorb the whole of the complicated scaffolding, which has been 
the most striking feature of the Echinoderm, and it passes into 
Fig. 95. 
Fig. 93 
Fig. 94. 
Development of the Pluteus of the Sea Urchin 
something which, it is true, we could hardly recognize as an 
Echinus, yet has apparently nothing in common with its former 
condition.” 
From this time the body of the pluteus is absorbed by the 
growing sea-urchin ; the spines and suckers of the latter increasing 
in size and number with age, and by the time the larval body has 
disappeared the young Echinus is more like the adult than the 
starfish at the same period in life. Fig. 98 (££, tentacles; s',s"', 
spines) represents the sea urchin very soon after the resorption of 
the pluteus. 
In after life the young sea urchin with its few and large spines 
resembles Cidaris and a number of allied forms, showing that 88 
LIFE HISTORIES OF ANIMALS. 
these genera, which appeared earlier geologically than our common 
Echinus (Fig. 92, Strongylocentrotus Drobachiensis), are lower in 
development. 
Development of the Holothuroids. Of the development of our 
Fig. 96. 
native sea cucumbers our knowledge is exceedingly fragmentaiy, 
and for nearly all that we do know of the mode of growth 
of these animals in general, we are indebted to the elabo- 
Pluteus of the Sea Urchin. THE ECHINODERMS. 
89 
rate researches of the distinguished J. Muller. He figures the 
earliest stage of the larval Holothurian, which he calls an “Auric- 
ularia.” The course of de- 
velopment is much as in 
the starfishes. The earliest 
stage known resembles 
that of the starfish repre- 
sented by Fig.82. It then 
passes through a stage re- 
presented Fig. 85, when 
the mouth and digestive 
tract is formed, and again 
a stage analogous with Fig. 
87. The Auricularia when 
fully grown, is cylindrical, 
annul ated, with four or 
five bands of cilia, usually 
with ear-like projections, 
whence its name Auricu- 
laria. Before it becomes 
fully formed the young 
Holothurian begins to 
grow near the side of the 
larval stomach, the cal- 
careous crosses appear 
and the tentacles of the 
future Holothurian bud 
out. The ear-like projec- 
tions disappear, the Auri- 
cularia becomes cylindri- 
cal, and is now called the 
“ pupa.” The Auricularia 
is gradually absorbed and the young Holothurian strikingly re- 
sembles a worm. In this pupa stage, in certain transparent 
forms observed by Muller, the intestine of the embryo Holothurian 
could be observed twisted on itself, with the mouth surrounded by 
tentacles. The only observations published on our native Holo- 
thurians are those of Mr. A. Agassiz, on Cuvieria, our large red, 
heavily plated sea-cucumber, which inhabits stony bottoms in deep 
water. The young are of a brilliant vermilion. In the earliest 
stage observed by Mr. Agassiz (Fig. 99 Z, “pupa;” g, tentacles) ; 
Profile view of 96. 
Fig. 97. 90 
LIFE HISTORIES OF ANIMALS. 
the “ pupa” or second form of the Auricularia is very large and 
the tentacles do not project beyond the body, as they afterwards 
do (Fig. 100) when the Auricularia is nearly absorbed by the grow- 
ing Holothurian. In a succeeding stage the tentacles begin to 
branch, where before they were simple and knobbed. At this time 
the cesophagus, stomach, intestine and anus are developed, and 
there is a ring of limestone rods and crosses around the mouth. 
The madreporic body (&) has not yet been drawn within the body. 
Fig. 98. 
The young Echinus. 
Finalty, the Auricularia becomes wholly absorbed, the tentacles 
are much branched and capable of retraction within the body ; the 
tegument secretes limestone plates, the suckers are developed in 
the ambulacral rows and the adult form is attained without import- 
ant changes. Fig. 72 represents a common sea-cucumber of our 
coast. 
Some holothuvians, as well as starfishes and ophiurans, as ob- 
served by Mr. A. Agassiz, undergo their larval (i. e., Pluteus, 
Brachiolaria and Auricularia) phases of development above 
described without leaving the parent, in pouches held over the 
mouth of the parent, making their escape in a form approaching 
that of the adult. THE ECHINODERMS. 
91 
Metschnikoff lias made some valuable comparisons between the 
ciliated embryos of the Coelenterates and Echinoderms, and shows 
that the primitive bod}r-cavity of 
the former is not homologous with 
the peritoneal cavity (t. e., the space 
in which the digestive canal hangs) 
of the Echinoderms. He also shows 
that while the primitive body cavity 
of the Coelenterates remains perma- 
nently as the digestive tract, in the 
Echinoderms it is temporary and 
embryonic. Metschnikoff, on embry- 
ological grounds (a view which the 
structure of the adult animals con- 
firms), thinks that there is the same 
similarity between the Coelenterates 
(Acalephs and Ctenophorae) and 
Echinoderms, as between the higher 
worms (Ilirudinese, Gephyrea and 
Annelides), and the Crustacea and 
Insects. 
Reproduction by fission as in the Actiniae and jelly fishes very 
rarely occurs in the Echinoderms. An Ophiuran deprived of all 
Fig. 101. 
Larva of Cuvieria. 
Fig. 99. 
Fig. 100. 
its arms will reproduce them by budding, and Lutken shows that 
certain starfishes divide in two spontaneously, having three arms 
Development of a Holothurian (Cuvieria). on one side and three on the other, while the disk looks as if it 
had been cut in two by a knife, and three new arms had then grown 
out from the cut side. 
Echinoderms as a rule, then, are reproduced alone by eggs and 
sperm cells. After fertilization of the egg they pass through : 
1. Morula stage. 
2. Gastrula stage. 
3. A larval, temporary stage (Pluteus, Brachiolaria, Auricu- 
laria), the earliest phase of these larvae being a Cephalula. 
4. The Echinoderm grows from a water tube of the larva, 
finally absorbing the latter, whose form is often materially 
changed during the process. It thus undergoes a true metamor- 
phosis, in a degree comparable with that of some insects. 
LIFE HISTORIES OF ANIMALS. 
LITERATURE., 
J. Muller. Abhandlungen iiber die Metamorphose der Ecliinodermen. (K. Ak- 
ademie der Wissenschaften. Berlin, 1848-1855). 
A. Agassiz. On the Embr3’ology of Echinoderms. (Memoirs Amer. Acad. Arts and 
Sci. ix, 1864.) Revision of the Echini, Part iv. (111. Cat. Mus. Comp. Zool. vii, 1874J. 
Wyville Thompson. On the Embryology of Antedon rosaceus. (Philosophical Trans 
actions, London, civ. 1865). 93 
THE LAMELLIBRANCHIATA. 
Having gone thus far along the track leading from the moners 
to man, wre come to where the road branches in several directions. 
The path from the Protozoa to the sponges, from the sponges to 
the polypes, and from the polypes to the Ctenopliorse, and through 
them to the Echinoderms, though at times devious and readily 
lost, yet in the retrospect is more easily followed than those lying 
before us. In fact there is no single track leading directly from 
the lowest to the highest animals. We have to follow distinct 
lines of development, and, after toiling up one ascent, find that it 
ends abruptly, without bringing us very near the goal. We then 
have to retrace our steps, return to the old fork in the road and 
essay a new path. For example, following up the line of mollusca, 
we come to the cuttlefishes with their well developed eyes and cir- 
culatory apparatus, nearly as complicated as those of fishes. If we 
follow the ascidian line of development, trace immediately in 
their larval condition a chorda dorsalis and a relation of rudi- 
mentary organs which bear a striking analogy to those of Amplii- 
oxus, the lowest vertebrate. Again, in studying the Brachiopods, 
we follow a line of life which leads us to forms such as the Lingula, 
which combines Annelid characters with remarkable features of 
its own. If after traversing these paths wre take up the long and 
devious route which leads from the non-segmented worms through 
the Rotifers up to the leeches and Annelides, to the Crustacea 
and Insects, we shall then reach animals which in many respects 
are only inferior to the vertebrates, and in complexity of organiza- 
tion, in their morphology and in their psychological endowments, 
are on the whole, superior to any other invertebrates. 
XIY. THE LAMELLIBRANCHIATA. 
What is this initial point from which these lines diverge? It is a 
larval form having a bilateral, cylindrical bod3r, sometimes annu- 
lated, divided into a preoral and postoral region, i. e., a head and 
hind body, with a ciliated crown, often a whip-lash or tuft of 
bi’istles, with a mouth, a usually curved alimentary cavity, and 
anus opening often near the mouth. This stage is seen in the 
young Echinoderm, such as the earliest stage of the Auricularia 
or Bipinnaria condition, as represented by Fig. 85 on page 83 ; or 
in the Veliger state of the young mollusk; in the young worm, 
whether the “ Actinotrocha” of the Sipunculus, or “Tornaria” of 94 
LIFE HISTORIES OF ANIMALS. 
Balanoglossus, or “Mesotrocha” of a higher annelid, or even in 
the young Rotifers. For such a form the term Ceplialula may be 
proposed in allusion to the fact that a cephalic region is indicated 
in this state, the Gastrula being a simple sac with the head end 
not differentiated from the opposite extremity. Let the reader 
compare the gastrula of the sponge (Fig. 44) with the Cepha- 
lula of the Trochus (Fig. 121, B) and he will detect the difference 
between the two stages. This stage is thus named simply to give 
emphasis to the fact that it is a form common at one stage in 
their life-history to several entirely different classes of animals, 
radiate, articulate and molluscan, independently of any theoret- 
ical considerations. I will only say that the Cephalula bears an 
analogous relation to these classes, as the Planula to the Radiates, 
the Nauplius to the Crustaceans, or the Leptus to the Insects. 
We shall see in our future studies of the life-histories of the 
different classes of invertebrate animals, how often this Cephalula, 
with its ciliated crown, recurs. 
No one has ever given a thoroughly satisfactory definition of 
the type of Mollusca, and we shall certainly not attempt one here. 
It may be said, however, that they are in their early stages, and 
in nearly all (except the Gastropoda, in which the visceral or ab- 
dominal end is asymmetrical), in adult life bisymmetrical animals 
bearing usually an external or internal shell (sometimes the shell 
is larval and deciduous), with the under lip converted into an or- 
gan of locomotion, the large fleshy foot. The nervous system 
consists of three pairs of ganglia usually surrounding the oesoph- 
agus, sending nerve-threads in irregular directions to the different 
organs. 
The Mollusca usually have a well developed heart, more so than 
in the Crustacea and Insects, situated dorsally and consisting 
usually of a ventricle and two auricles. The respiratory organs 
depend or project from the mantle or tegument, and are permeated 
by a net-work of blood-vessels. A large number have an “odon- 
tophore” or “lingual ribbon, a band of teeth rolled up in the 
mouth. The mollusks are neither radiate nor segmented as in the 
Articulates or Vertebrates, though certain larvae are indistinctly 
annulate as in that of Chiton. 
The Tunicates, Polyzoa and Brachiopoda are not regarded as 
Mollusks, both on anatomical and developmental grounds, the 
reasons being given in the chapters treating of them. THE LAMELLIBRANCHIATA. 
95 
For a further discussion of the characters of the mollusks as 
compared with the worms the reader is referred to Prof. Morse’s 
memoir “ On the Systematic Position of the Brachiopoda.”17 
The following tabular view of the mollusks is copied from Geg- 
enbaur’s “Principles of Comparative Anatomy.” For further in- 
formation the reader is referred to Wood ward’s “Manual of the 
Mollusca.” 
I. Lamelt II5RAN chiata. 
1. Asiphonia (Ostrsea, Anomia, Pecten, Mytilus, Area, Unio). 
2. Siphoniata (Chaina, Cardium, Cyclas, Yenus, Tellina, Mactra, 
Solen, Pholas, Teredo). 
II. Ceptialophora. 
1. Scaphopoda (Dentalium). 
2. Pteropoda. 
Thecosomata (Hyalea, Cleodora, Clireseis, Cymbulea, Tiede- 
mannia). 
Gymnosomata (Pneumodermon, Clio). 
3. Gastropoda. 
Heteropoda (Atlanta, Carinaria). 
Opisthobranchiata (Bulla, Aplysia, Doris, Glaucus, iEolis). 
Prosobranchiata. 
Cyclobranchiata (Patella, Chiton). 
Ctenobranchiata (Paludina, Neritina, Buccinum, Purpura, 
Murex, Fusus, Conus, Oliva, Strombus, Haliotis). 
4. Pulmonata (Lymnseus, Physa, Planorbis, Helix, Bulimus, Limax). 
III. Cephalopoda. 
1. Tetrabranchiata (Nautilus). 
2. Dibranchiata. 
Decapoda (Spirula, Sepia, Loligo). 
Octopoda (Octopus, Argonauta). 
MOLLUSCA. 
Development of the Lamellibranchs. It is only within a com- 
paratively few years that we have learned anything of the mode 
of growth of our commonest bivalve mollusks. To this day the 
life history of the common clam or qualiaug is a mystery. The 
early stages of the oyster are only partially known. We know 
much less about the early stages of the common sea mussel; while 
the history of the fresh-water mussel (Unio) sketched roughly in 
1831 by Carus, is still fragmentary. For the first definite knowl- 
edge of the metamorphoses of the Lamellibranchs, we are indebted 
to the distinguished Swedish observer Loven, who gave between the 
years 1844 and 1849, a series of sketches more or less complete of 
17 Proceedings of the Boston Society of Natural History, Yol. xv, 1873,8vo. pp. 60. 96 
LIFE HISTORIES OF ANIMALS. 
a number of marine forms. To him and to Sars, the famous Nor- 
wegian zoologist, who made the first sketch of the mdtamorphoses 
of the Gastropods, we are indebted for our earliest and most val- 
uable facts in the life-history of the mollusks. Before this, some 
larval mollusks were regarded as infusoria by Ehrenberg. 
Of the mode of development of the oyster, the lowest lamelli- 
branch, the first information was supplied by Lacaze-Dutliiers 
(1854-5), supplemented by the recent (1874) observations of 
Salensky. While some lamellibranchs, such as the Unio, are bi- 
sexual, the oyster is hermaphroditic. The eggs, which are yellow, 
after leaving the ovary are retained among the gills. A single 
oyster may lay 2,000,000 eggs. The spawning time of the oyster 
in Europe is from June to September. During their development 
the eggs are enclosed in a creamy slime, growing darker as the 
“sprat” (the term applied to the young oysters) develops. 
The course of development is thus: after the segmentation of 
the yolk (morula stage), the embryo divides into a clear peripheral 
layer (ectoderm), and an opaque inner layer containing the yolk 
and representing the inner germinal layer (endodenn). A few fila- 
ments or large cilia arise on what is to form the velum or the 
future head. The shell then begins to appear at what is des- 
tined to be the posterior end of the germ, and before the di- 
gestive cavity arises. At this stage the two-layered germ is said 
by Salensky to represent the planula of the sponge. The digest- 
ive cavity is next formed (gastrula stage), and the anus appears 
just behind the mouth, the alimentary canal being bent at right 
angles. Meanwhile the shell has grown enough to cover half the 
embryo, which is now in the “Veliger” stage, the “velum” being 
composed of two ciliated lobes in front of the mouth-opening, and 
comparable with that of the gastropod larvae. The young oyster, 
as figured by Salensky, is directly comparable with the Veliger of 
the Cardium (Fig. 102). 
We have, then, three stages of growth in the oyster, (1) the 
morula, (2) the gastrula (with the digestive cavity as yet unde- 
veloped and, (3) the veliger with an alimentary canal and a head 
and hind body (cephalula). This is an epitome of the mode of 
development of most of the lamellibranchiate mollusks whose em- 
bryology is known. Soon the shell covers the entire larva, only 
the ciliated velum projecting out of an anterior end from between 
the shells. In this stage the larval oyster leaves the mother and THE LAMELLIBRANCIIIATA. 
97 
swims around in the water, the cilia of the velum keeping up a 
lively rotary motion. In this state Lacaze-Duthiers observed it 
for forty-three days, without any striking change in form, except 
that the velum increased in size, and the auditory vesicle appeared, 
containing several otoliths, which kept up a rapid motion. But 
still the gills and heart were wanting. Of its further history we 
know but little, except that it becomes fastened to some rock and 
is incapable of motion. The oyster is said by the appearance of 
its shell, to be three years in attaining its full growth, but this 
statement needs confirmation. 
The most complete life history of a bivalve mollusk is that of 
Cardium (0. pygmceum), the cockle shell, as described by Loven. 
The egg of this shell is spherical, the yolk being surrounded by 
a layer of white protoplasm, much as in the eggs of vertebrates. 
The process of fertilization was observed by Loven, who saw the 
spermatic particles of the usual form, i.e. with a head and long tail, 
to the number of a dozen penetrating through the envelopes of 
the egg out toward the yolk. Following the morula condition the 
embryo consists of two layers, an outer peripheral clear mass like 
the “white” of an egg (ectoderm), and a central dark mass, re- 
garded by later observers as equivalent to the inner germinal 
The embryo now becomes ciliated on its upper surface 
and already rotates in the shell. On one side of the oval em- 
bryo is an opening or fissure ,18 on the edges of which arise two 
tubercles which eventually become the two “sails” of the velum. 
This probably represents the gastrula stage, and the embryo 
already shows a tendency to become bilateral. The next step 
is the differentiation of the body into head and hind body, i.e. 
an oral (cephalic) and postoral region. Out of the middle of 
the head grows a single very large cilium, like the whip-lash of 
the Flagellata, the so-called flagellum (Fig. 102 A,Ji; v, velum). 
The shell (Fig. 102 B, sh) and mantle (mt; ml, muscle) now begin 
to form. From the inner yolk-mass are developed the stomach, the 
two liver lobes (li) on each side of the stomach (t), and the intes- 
18 Tliis primitive opening, the mouth, appears both in Cardium and Grenella, accord- 
ing to Loven’s figures and descriptions, long before the shell begins to form. It is thus 
not a secondary formation, as Salensky insists, but a primary invagination of the ecto- 
derm. The embryo is therefore properly a gastrula. It will be remembered that in 
the oyster on the contrary the shell begins to form before the mouth-opening appears. 
The young oyster at the stage immediately succeeding the morula is, then, a planula; 
the Cardium and Crenella, a gastrula. This exception does not warrant us in denying a 
gastrula state to the Lamellibranchs as a class, as Salensky does. 
LIFE HISTORIES OF ANIMALS. 98 
LIFE HISTORIES OF ANIMALS 
tine (i). The mouth (m), which is richly ciliated, lies behind the 
velum, the alimentary canal is bent nearly at right angles and the 
anus opens behind and near the mouth. The velum (Fig. 102, v) 
really constitutes the upper lip, while a tongue-like projection (Fig. 
102, B /) behind the mouth is the under lip, and is destined to 
form the large unpaired “foot,” so characteristic of the mollusks. 
In a stage previous to this, when the shell only partially covers 
the animal, the veliger may be compared with the veliger of Trochus 
(Fig. 121, B) and a remarkable resemblance be traced, the velum, 
the bent alimentary canal and the foot being almost identical. 
The shell arises as a cup-shaped organ in both bivalves and uni- 
valves, but the hinge and separate valves are indicated very early 
in the lamellibranchs. The earliest phase of the veliger stage 
Fig. lOL 
Development of Cardium. Alter Lov^n 
(trochosphere) indicated at Fig. 102 A, in which a cephalic and 
abdominal region is demarked, may be compared with profit by 
the reader with the embryo infusorian with its cup-shaped body 
and its crown of cilia, or with the larval Polyzoan or even the larval 
Brachiopod to be hereafter figured. At the stage represented by 
Fig. 102, B, the stomach is divided into an anterior and posterior 
(pyloric) portion. The liver forms on each side of the stomach 
an oval fold, and communicates In’ a large opening with its 
cavity; while the intestine elongates and makes more of a bend. 
The organ of hearing then arises, and behind it the provisional 
eyes, each appearing as a vesicle with dark pigment corpuscles 
arranged around a refractive body. The nerve ganglion (m) 
appears above the stomach. The two ciliated gill-lobes, now 
appear, and the number of lobes increases gradually to three or TIIF. LAMKLLIBRANCHIATA. 
99 
four. The foot grows larger, and the organ of Bojanus, or 
kidney, becomes visible. The shell now hardens; the mouth 
advances, the velum is withdrawn from the under side to the 
anterior end of the shell. In this condition the veliger remains 
for a longtime, its long flagellum still attached, and used in swim- 
ming even after the foot has become a creeping organ. Latest 
of all appears the heart, with the blood-vessels. 
Upon throwing off the veliger condition, the velum contracts, 
splits up and Loven thinks it becomes reduced to the two pairs 
of palpi, which are situated on each side of the mouth of the ma- 
ture Jamellibranch. The provisional eyes disappear, and the eyes 
of the adult arise on the edge of the mantle. 
The mode of development of Crenella marmorata is nearly 
identical with that of Cardium. The Crenella is dioecious, the 
females being known by their reddish ovaries, the males by their 
white sexual glands. In this genus, however, there is no egg- 
c.apsule, and no “white” enveloping the yolk. 
All that we know of the development of the common muscle 
(Mytilus edulis, Fig. 103. after Morse) is from studies made by 
Lacaze-Duthiers on the shores 
of the Mediterranean. The 
larval forms were not discov- 
ered. The young about £mm in 
length were found swimming 
at ebb tide on the surface of 
the water. The shell at this 
stage is like a Crenella, and 
there are four long gill lobes, 
which arise from the outer la- 
mella of the inner gill. 
The fresh water bivalves pass through entirely different phases 
of development from the marine forms. The eggs of Cyclas have 
no shell, no “ white” and no yolk skin ; they are few in number, 
from one to six existing in unequal degrees of development in 
broad cavities fdled with a nutritive fluid, and hanging free from 
the base of the inner gill. The velum is either absent or very 
slightly developed, and the shell begins to develop at two widely 
separated initial points on the mantle, according to Leydig. 
Fifr. 10 > 
Common Mussel. 
The fresh water mussels (Unio, Fig. 104, after Morse, and Ano- 
donta) represent another mode of development. In their embryo 100 
LIFE HISTORIES OF ANIMALS. 
the velum is wanting or exists in a very rudimentary state. I he 
mantle and shell are developed very early. They live within the 
parent fastened to each other by their byssus. The shell (Fig. 
105) differs remarkably from that of the adult, 
being broader than long, triangular, the apex 
or outer edge of the shell hooked, while from 
different points within project a few large, long 
spines. So different are these young from the 
parent that they were supposed to be parasites 
and were described under the name of Oloclii- 
dium parasiticum. They are found in the pa- 
rent mussel during July and August. The eggs have a shell, 
“white,” and yolk skin and a micropyle. The embryo rotates, 
Tig. 105. 
Young Unio. 
Fig.104. 
Unio moving through the sand with the siphons expanded. 
and remains a month in the egg. When hatched, great numbers 
still remain among the gills in a mass of slime, and during this 
time the shell thickens, grows rounder and somewhat longer. 
The history of the ship worm (Fig. 106, Teredo navalis Linn.) 
is one of great interest both from a practical and scientific point 
of view. To the eminent French naturalist, Quatrefages, we are 
indebted for its life history. Its general development up to the 
time of the larval stage is much like that of the o}Tster. The 
egg has no shell. After fertilization it undergoes total segmenta- 
tion (Fig. 107, A). The two germinal layers appear as usual, the 
velum arises much as in the embryo oyster, there being no lash, as 
in the Cardium, but scattered cilia. Swimming about in this state 
the embryo would be mistaken for an infusorian. In forty-eight 
hours after life begins, the cilia begin to disappear and the germ THE LAMELLIBRANCHIATA. 
101 
sinks to the bottom. A deep fissure now separates the germ into 
halves; meanwhile the mantle and shell hive grown, and when 
Fig. 106. 
five clays and a half old the germ appears as in Fig. 107, B, the 
shell almost covering the larva. Soon after this the velum be- 
comes larger, and then decreases, the gil’s arise, the auditory sacs 
develop, the foot grows, though 
not reaching to the edge of the 
shell, and the larva can still 
swim about free in the water. 
When of the size of a grain of 
millet, it becomes spherical, 
as in Fig. 107, C, brown and 
opaque. The long and slender 
foot projects far out of the 
shell, and the velum assumes 
the form of a swollen ring on 
which is a double crown of cilia. 
The ears and eyes develop more, and the animal alternately swims 
with its velum, or walks by means of the foot. At this stage 
Quatrefages thinks it seeks the piles of wharves and floating wood 
in which it bores and completes its metamorphosis. The further 
changes must be very great before it assumes the adult form of 
the ship worm with its long body, but these stages have not been 
observed. Keferstein, however, says that Vrolik saw in July the 
The Ship Worm.19 After Verrill 
Fig. 107. 
Development of the Ship Worm. 
19 Fig. 106, c, collar; p, pallets; t, siphonal tubes; s, shell; /, foot. After Verrill. Re. 
port U. S. Fish Commissioner. Fig. 107, v, velum; /, foot. After Quatrefages. 102 
LIFE HISTORIES OF ANIMALS. 
larvae swimming about on the coast of Holland, and some by the 
middle of the month had bored into the wood and attained the 
adult Teredo form, though still very small, while others in Sep- 
tember still retained their larval, veliger shape. It requires about 
three weeks for them to complete their metamorphosis. Verrill 
states that the Teredo navalis on the coast of New England “pro- 
duces its young in May, and probably through the greater part or 
all of the summer.” Quatrefages says that the Teredos die during 
the winter succeeding their birth. 
Keferstein tells us that some lamellibranehs attain their growth 
in one year. The fresh water mussels (Unio and Anodonta) are 
thought to live from ten to twelve years, while Tridacna gigantea 
probably lives from sixty years to a century. 
The time of spawning usually takes place in summer. The 
edible mussel (Mytilus edulis) and different species of Venus 
are found with eggs and embryos among the gills from March till 
May, on the coast of Holland and France, while Pliolas and Pan- 
dora and most other genera breed from July until September. On 
the Sicilian coast, according to Poli, Mya and Solen breed early 
in spring; Pholas, Chama, Venus, Donax, Anomia, Tellina and 
Mactra in summer; Mytilus edulis from October to December. 
We have seen that the Lamellibranclis pass through a true 
veliger stage, and we shall soon see that their larval forms are 
directly comparable with the veliger state of most Cephalopliora. 
In after life the “head” of the bivalve, i.e. the oral and preoral 
part of the body, which was fully half as large as the body in 
the veliger, diminishes greatly in size and importance, becoming 
finally merged with the postoral region and represented simply 
by the palpi and foot, the mouth-opening being situated at or 
near the extremity of the body, so that the old term Acephala 
well indicates the want of a cephalic region as compared with 
the large and well developed head of the snails (Cephalophora) 
and cuttle-fishes (Cephalopoda). 
The summary of changes is usually as follows : 
1. Egg fertilized by tailed spermatic particles. 
2. Morula. 
3. Gastrula. (Observed in a very few cases.) 
4. Veliger (Cephalula). In Unio and Cyclas wholly or mostly 
suppressed. 
5. Adult Lamellibranch. THE CEPHALOPHORA. 
LITERATURE. 
.7. E. Cams. Enttvicklung von Unio und Anodonta. (Nova Acta Phys. Med. Leo- 
pold. 1831). 
S. Loven. Development of Marine Lamellibranchs. (Ofversigt af Kong. Vetensk. 
Akad. 1844-1849. Wiegmann’s Archiv, 1849. See also Keferstein’s abstract in Bronn’s 
Classen and Ordnungen der Thierreichs, vol. iii.) 
A. de Quatrefages. Anatomie et Embryologie de la Teredo. (Annales des Sciences 
Nat. 1848-50.) 
Lacaze-Duthiers. Development of various Lamellibranchs. (Annales des Sc. Nat. 
1854,1855). 
O. Schmidt. Entwickelung von Cyclas. (Muller’s Archiv, 1854). 
F. Leydig. Cyclas; Anatomie und Entwickelung. (Miiller’s Archiv, 1855). 
W. Sal en sky. Bemerkungen iiber Haeckel’s Gastraea-Theorie, with three drawings 
of the embryo oyster and very brief description. (Wiegmann’s Archiv, 1874). 
The Cephalophora include not only the Gastropods (snails and 
whelks) but more aberrant forms such as the swimming Pteropods 
XV. THE CEPHALOPHORA. 
F:g. 103. 
Fig. 109. 
Helix in its natural position, creeping. 
Trivia, a Gas- 
tropod. After 
Stearns. 
and the Dentalium, etc. The term indicates the presence in the 
adult of a well formed head, as distinguished from the acephalous 
clams. Not only is there a head, but the eyes are restricted to 
the most anterior part of the preoral region, being, as in the 
snail, borne on extensile tentacles, whereas in the bivalves, such 
as the pecten, the eyes are scattered on the edge of the mantle 
along the entire body. The adult animal is not symmetrical, the 
mantle containing the viscera being thrown on one side. The foot 
is greatly enlarged, forming the entire under side of the animal, 
as in the snail (Fig. 109). The shell is usually external, spiral and 
asymmetrical, or cup-shaped. 104 
LIFE HISTORIES OF ANIMALS. 
The tooth shell, or Dentalium, is the lowest of its class, and its 
life history is one of much interest. For the following facts we 
are indebted to the memoir of Lacaze-Duthiers. The sexes are 
distinct. It breeds from the beginning of August until the middle 
of September. After fertilization by the spermatic particles, which 
Lacaze-Duthiers saw penetrating into the egg, the yolk undergoes 
complete segmentation (A). At the end of this time the embryo 
swims about by means of tufts of fine cilia (Fig. 110, B), and a 
pencil of large cilia in front. * It then lengthens and is provided 
with seven bands of cilia, and the larva is remarkably worm-like 
Fig. no. 
Development of Dentalium. 
(C). When two da}rs old the mantle secretes a small shell (a) at 
the end of the body. The ciliated bands now approach and form 
a swollen ring, or ciliated crown, the velum, as in fig. 110, D, z. 
At this time the shell is median, unpaired and situated on the back 
of the larva. The lobes of the foot next arise. Fig. 110, E, re- 
presents the young Dentalium, after leaving the larval state, and 
when thirty-five days old. The three-lobed foot protrudes from 
the shell now enclosing the animal, the rudimentary tentacles 
(E, cl) are visible, as well as the submsophageal nerve-ganglia 
(E, J) and the digestive canal (E,/, f") and liver (/'). After this, 
the change into the mature form is slight. THE CEPHALOPHORA. 
105 
The winged sea-snails (Pteropods) are beautiful creatures found 
floating on the high seas. With their large, ciliated velum and 
rudimentary foot the}7 represent the Veliger or larval condition of 
the Gastropods. There is scarcely a more strikingly beautiful and 
strange object in nature than the Spirialis with its large heavily 
ciliated velum, which may be caught in our harbors with the tow- 
ing net and compared with the young veligerous gastropods often 
captured in the same net. 
The egg of Cavolinia undergoes total segmentation, and before 
the large yolk-spheres are absorbed, the spherical embryo swims 
about like a larval infusorian with a crown of cilia. It may now 
be called a Trocliosphere. Soon the larva assumes a conical form 
Fig. 112 
Fig. 113. 
F g. 111. 
Fig. 111. 
Pteropod larva 
Larval Nudi- 
brancb. 
Sty] iola vitrea. 
iEolis, a Nudi- 
branch. 
and subsequently the velum greatly expands. Afterwards the 
Cavolina, with its projecting foot, assumes a form much like the 
veliger of Trochus (Fig. 121, B). Fig. Ill (after Gegenbaur) re- 
presents a singular Pteropod veliger after the velum has disap- 
peared, consisting of three distinct ciliated segments, like a 
Fig. 112, after Verrill, represents an adult Pteropod, Styliola vitrea, 
enlarged three times, with the wings of the velum. 
Bulla, JEolis and Doris, represent the Opistliobrancliiate or 
naked mollusks, which either, as in the two latter genera, have no 
shell, with the gills arranged singly or in tufts on the back, or 
possess a white shell, as in Bulla, the bubble shell. Fig. 113 (from 
Verrill’s Report), represents JEolis. Fig. 114 20 (after Schultze) 
20Fig. 114, d, foot; s, nautilus-like deciduous shell; v, velum. 106 
LIFE HISTORIES OF ANIMALS. 
represents the young Tergipes, a naked sea-slug allied to Doris, 
with its lai-ge ciliated velum and foot, the animal being partly 
surrounded by a large shell (.s). This shell is finally dropped 
with the other deciduous larval organs, the gills grow out from 
the back and the soft elongated body of the adult nudibranch, (as 
this animal is called,) is finally attained. It is a singular fact, 
discovered by Sars, that in the egg-capsules of Dendronotus as 
many as six embryos develop side by side. 
We will now more carefully study the course of development of 
a Bulla (Acera bullata) as given by Langerhans. 
In this animal the yolk of the egg subdivides into two spheres 
of segmentation, one being much smaller than the other and dif- 
fering in color. Each of these two cells subdivides into similar 
halves. The two larger cells then remain passive, while the 
smaller form a mass of nucleated cells which in two or three da}Ts 
form a layer surrounding the central, inactive yolk cells. On the 
fifth daj’ arises the first indication of the shell, and on the same 
day is developed a furrow, the primitive mouth, which separates 
the cephalic end from the postoral extremity. On the seventh 
day appear the rudiments of the organ of hearing, and on the day 
after, the operculum. On the ninth day the phaiynx, stomach and 
intestine begin to develop. On the fifteenth day 
the otolites are seen in the ear. The liver is next 
formed, and a few days after the eyes and nerve 
ganglia, when the larva hatches. 
With the mode of development of Chiton, a cj’clo- 
brancliiate Gastropod, Loven has made us ac- 
quainted. The larva leaves the egg oval in 
form, with a ciliated ring in the middle of 
the body and a long tuft of large cilia on 
the head. Afterwards it becomes annu- 
lated, as in Fig. 115 (after Loven) and two 
eye specks appear.* Its resemblance to a 
worm larva is now remarkable. It soon settles down into a quiet 
life as a Chiton (Fig. 116, C. ruber, represents a species found 
on our shores, from VerriH’s Report, after Morse), and the lime- 
stone plates correspond to the primitive larval rings. 
Of the mode of development of the other marine univalve shells 
(Prosobranchiate Gastropoda), I cannot do better than avail my- 
self of the recent papers of Dr. Salensky. Ilis studies were made 
Fig.115. 
Fig. 116. 
Chiton. 
Veliger ofCliiton. THE CEPHALOPHORA. 
107 
on shells living in the Black Sea, but we have species of Calyptrrea 
and Troches on our own coast. 
Calyptrcea sinensis lays its eggs in pear-shaped capsules at- 
tached to the same mussel or stone on which it lives. The young 
of the same brood develop at the same time. Development be- 
gins with the total segmentation of the yolk. After it divides 
into eight cells the blastoderm forms, which consists of a single 
layer of cells, the result of the subdivision of the first four spheres 
of segmentation, which grow over and envelop the yolk spheres, 
thus forming the two germinal layers (ectoderm and endoderm). 
The'cells of the outer layer multiply and form the blastoderm, 
from which the skin, mantle and external organs, as well as the 
walls of the mouth arise, while, as in the articulates, the aliment- 
ary canal with its dependencies, the liver, etc., arise from the pe- 
riphery of the 3rolk cells, the central mass being absorbed. 
As soon as the blastoderm is formed, a heap of cells arise and 
the ectoderm pushes in at a spot which becomes the ventral 
side of the body. This is the primitive mouth. The anterior 
part of this cellular heap is the first indication of the “head- 
vesicle,” which becomes a provisional organ well developed in 
the larva, and is also seen in the embryo fresh-water snails (Pul- 
monata). The sides of the primitive mouth form the two “ sails” 
of the velum or swimming organ, so characteristic of the larval 
mollusks, and which was first noticed by Forskal, who wrote on 
animals just a century ago. Finally, the posterior edge of the 
infolding, which is also at first a little mass of cells, is the first 
indication of the foot. The whole surface of the embryo is now 
covered with cilia, and by their movement 
the embryo with its fellows, rotates in its 
capsule. 
The next change consists in the growth 
and differentiation of the parts already 
sketched out. The germ of the foot extends 
backwards, the mouth-opening deepens and 
becomes tube-like, the first indication of 
the pharynx (Vorderdarm). The next most 
important change is the presence of a layer of cells between 
the outer and inner germinal layers, which is called the middle 
germ layer, with cells very unlike the outer layer, from which are 
developed the muscles of the foot and head as well as the heart 
Fig. 117. 
Veliger of Calyptrsea. 108 
LIFE HISTORIES OF ANIMALS. 
itself. Salensky thinks that this middle layer arises from the 
outer. It appears first on the ventral side of the embryo. The 
germ is now of the form indicated b}r Fig. 117 (ce, ectoderm; 
'ce, middle layer, the }rolk spheres representing the inner la}Ter, 
or endoderm ; ra, mouth ; -u, velum ; /, foot. After Salensky). 
The next important chapter in the life history of the Calyptraea, 
is the appearance of the mantle, which arises as a disk-like thick- 
ening of the outer germ-layer on the back of the embryo. In the 
middle of the disk the shell grows out as a cup-like cavity which 
is connected only around the edge with the mantle, but is free in 
the centre. The ears or auditory vesicles next appear, which, like 
the eyes, begin as an infolding of the outer germ-layer. 
Up to this time the entire body has been symmetrical. Along 
the longitudinal axis of the body are the foot, the head-vesicle, 
the germ of the alimentary canal, and on each side a lobe of the 
velum. The alimentary canal, now further developed, begins to 
curve to the left, and as the shell grows, the visceral sack, or post- 
oral portion of the body, hangs over on one side. Not until the 
organs of sense appeared, the ears with their otolites, and the eyes 
with their pigment cells, did Salensky discover any trace of a 
nervous system, and then it was not the cephalic, but the ganglion 
of the foot which first arises as 
a mass of nerve cells from the 
ectoderm. 
Fig. 118 (after Salensky) re- 
presents the asymmetrical larva 
with the shell enveloping a large 
part of the body, and the velum 
(v) and foot (/) well developed. 
The larval head forms a third 
of the whole body and is still 
ciliated. The temporary 
larval heart (/i), a large oval 
vesicle, is situated on the right side of the back of the embryo, 
between the head and anterior edge of the mantle, in quite a dif- 
erent position from that of the adult heart, which afterwards arises 
as a new organ. The larval heart contracts rhythmically sixty 
times a minute. This is an entirely different organ, says Salensky, 
from the pulsating vesicle or “heart” seen by Duben and Koren 
in Purpura (Fig. 119, P. lapillus and egg capsules, from Verrill’s 
Fig. 118. 
Veliger of Calyptraea farther advanced. THE CEPIIALOPIIORA. 
109 
Report) and Buccinum, or tlie contractile vesicle found by Semper 
in Ampullaria, Cyprcea, Murex and Ovulum, or the dorsal vesicle 
of the Pulmonates (snails). There is, 
however, a similar larval heart in Nassa. 
At this stage also appears the primi- 
tive kidney (Fig. 118, A;), also a deciduous 
organ, the permanent, adult kidney aris- 
ing in another part of the body far be- 
hind the larval heart. It resembles the 
primitive kidneys of the snails (Pulmo- 
nates), and appears first as a sort of 
necklace consisting of four yellowish cells, situated next to the 
lar val heart. 
Fig. 119. 
Purpura and Egg Capsules. 
Meanwhile the more the posterior part of the body grows, the 
larger and more spiral becomes the shell, until the helmet shape 
of the adult is approached. At this stage also the gill-cavity 
appears, but there is as }ret no trace of the gill itself. 
In a succeeding stage the foot has increased in length, the 
spire of the shell has begun to topple over as it were and fall 
on one side like a skull cap, and now the adult heart (the peri- 
cardium being formed first), and permanent kidney and gills grow 
out. The gills originate from the ectoderm. It is not until this 
period that the end of the intestine and anal outlet is formed. 
The provisional larval organs now begin to disappear, the ceph- 
alic vesicle (larval head) grows smaller, the primitive 
kidneys disappear. Of the larval visceral organs only 
the heart remains which, though smaller, still pulsates. 
It now rests under the mantle in the branchial cavity. 
There are now two gill-leaves, and finally the perma- 
nent heart is formed. The further changes consist in 
the perfection of all these organs and the development 
of the shell into the helmet shape of the adult. Fig. 
120 (after Morse) represents the common Calyptraia 
striata of our own coast. We have seen that the usual five stages 
have been undergone, i.e. the egg, morula, gastrula (not so well 
marked as in the pond snail, Fig. 122), veliger and adult. 
The metamorphoses of Troclms represent another t}?pe of de- 
velopment in the Gastropods, which illustrate points less clearly 
wrought out in the Catyptrsea. 
The eggs of Trochus varius are very small, spherical, and laid 
Fig. 120. 
Calyptraea 
striata. 110 
LIFE HISTORIES OF ANIMALS 
in masses of jelly on sea weeds. The morula, or mulberry mass, 
forms as usual. The blastoderm arises from a few small 
clear spheres of segmentation situated at one pole of four prim- 
itive dark morula cells. The four vitelline or primitive cells, 
instead of remaining passive as in Calyptraea, subdivide, as well 
as the blastodermic cells. The egg now becomes flattened at 
one pole and slightly pointed at the other, the latter being the 
anterior end. 
In six hours after development begins, the outer layer begins 
to form, and the first organ to arise is the velum, which at first 
consists of a swollen ciliated ring on the anterior end of the em- 
bryo. This stage (Fig. 121, A, v, velum, after Salensky) is equiv- 
alent to the trochosphere (Lankester) of the pond snail. It will 
thus be seen that the development of Trochus is now very dif- 
ferent from that of the Calyptraea, where the velum, head-vesicle 
and foot arise simultaneously. A little later the mouth and oesoph- 
agus arise. Salensky remarks that the Prosobranchiate Gastropods 
as a rule develop like Trochus. In Vermetus, however, according 
to the observations of Lacaze-Duthiers, the velum does not arise 
in the form of a ciliated crown, but as a paired organ. Salensky 
adds, however, that in other respects there is a strong analogy 
in Calyptraea to Vermetus and Buccinum and Purpura, which 
develop like the former mollusk, having a similar larval heart and 
primitive kidneys, though the mode of development of the exter- 
nal organs is almost wholly unknown. There are thus five gen- 
era of Prosobranchiate Gastropods which develop as in Calyptraea, 
all belonging to the suborder Ctenobranchiata. 
On the other hand, Paludinci vivipara, Neritina. Jluviatilis, and 
certain Pteropods (Tiedemannia neapolitana, Cavolinia gibbosa) 
and a Ileteropod (Pterotrachea) are provided, as in Trochus, with 
a ciliated crown, the first organ lying behind the primitive mouth. 
“A good starting point,” adds Salensky (whom we have in reality 
been quoting all along), “for the comparison of the development of 
Trochus and allied forms, with that of other animals, consists in 
this stage (Fig. 121, A). A cursoiy glance at the illustration will 
convince one that this condition of the Trochus embryo is simi- 
lar to the larva of some Annelides. Examples of such Annelid 
larvae may be seen in some Sabellidae (e. r/., Dasychone lucuUana) or 
Spio (S. fuliginosus). The latter in escaping from the egg have 
a more or less oval body consisting of two layers, its only organ a ciliated crown on the anterior part of the body. The idea of an 
analogy between the Mollusca and Annelid larva has already been 
suggested by Gegenbaur. Still more strongly does it follow from 
these facts, that in the Annelides, as surely as in the Mollusks, the 
mouth-opening, with the pharynx, arises immediately after the for- 
mation of the ciliated crown and somewhat behind the same. Im- 
mediately after the formation of the rudimentaiw pharynx arise 
the characteristic organs of the two types : in the Annelides the 
bod}' segments with their appendages ; in the Mollusks the foot, 
shell and two velar lobes.” 
THE CEPHALOPHORA. 
Salensky then compares the development of Trochus with the 
Rotifer, Brachionus, and finds some striking analogies. Ilis facts 
we shall present hereafter in describing from his memoir the life- 
history of a rotifer. 
In the second period of development of Trochus, the true Vel- 
iger state is entered upon. The mantle and shell are formed much 
as in Calyptraea. The body is now 
flattened, and the ciliated crown 
projects very slightly. The shell 
(s) has grown considerably. 
Fig. 121, B, after Salensky, repre- 
sents this stage. The pharynx (cl) 
arises through a tube-like invagina- 
tion of the outer germ-layer, behind 
the ciliated crown (v). At the 
same time behind the mouth arises 
a projection, which indicates the beginning of a foot (/). Within 
the foot, as well as in the anterior part of the body, may be no- 
ticed the middle germ-layer, which arises as a layer of cells be- 
tween the outer and inner germ-layer. 
Fijf. 121. 
Larval Trochus. 
In the following stage the form of the larva is somewhat 
changed. The shell begins to unroll spirally on the under side of 
the body. The velum grows more than the middle portion of the 
head, and the lateral lobes become larger. The operculum also 
arises on the posterior portion of the foot. 
Coming now to the mode of development of the Pulmonate 
mollnsks (fresh-water and land-snails), we find that the aquatic 
forms undergo a complete metamorphosis, while in the land-snails 
there is no metamorphosis, and they are hatched in nearly the 
same form as the adult. 112 
LIFE HISTORIES OF AXIMALS. 
The life history, particularly the earlier stages, of the common 
pond snail (Limnceus stagnalis) of Europe has been worked out with 
much care by Prof. Ray Lankester, his observations confirming 
those of Lereboullet, Poucliet and others so far as they extended. 
The eggs of Limnaeus are deposited in June on the under side 
of water-plants, in capsules enclosing one, rarely two eggs, and 
surrounded by a mass of jelly. After seg- 
mentation the Gastrula (Fig. 122, m, mouth ; 
ec, ectoderm ; en, endoderm) is formed, the 
primitive digestive cavity or mouth result- 
ing probably from an infolding of the ecto- 
derm. Lankester believes that this orifice or 
mouth is temporary, the mouth of the adult 
being a later production. The primitive 
mouth closes as the embryo enters on the 
Veliger state, in the earliest stages of which the embryo is oval 
and surrounded by a ciliated ring, much as in the larval Trochus 
(Fig. 121, A). This state is called by Lankester the “Trocho- 
sphere.” A definite Veliger stage is finally attained ; the foot is 
large and bilobed, the mantle and shell then arise and the larva 
soon passes into the definite molluscan condition, with a shell, 
creeping foot, mantle-flap and eye-tentacles. The young snail 
hatches in about twenty days after life begins. 
Fig. 122. 
Gastrula of the Pond 
Snail. 
Professor Lankester confirms the suggestions already made by 
Gegenbaur, Morse and Salensky regarding the resemblance of the 
larval mollusks to 3Toung w orms. He remarks also that both the 
Trochosphere and Veliger forms are “ well known and character- 
istic of various groups of Worms and Echinoderms, and the latter 
is seen in its full development in the adult Rotifera, and in the 
larval Gasteropoda and Pteropoda. The identity of the velum of 
larval Gasteropods, with the ciliated disks of Rotifera, seems to ad- 
mit of little doubt, and it wrould be well to have one term, e. g., 
velum, by which to describe both. The Trochosphere is the ear- 
lier, more or less spherical form in which the velum is represented 
by an annular ciliated ridge, and which is sometimes (e. (/., Chiton) 
provided with a polar tuft of long cilia. 
“The cell, polyblast (morula), gastmla, trochosphere, and vel- 
iger phases of molluscan development are not distinctive of the 
molluscan pedigree; belong to its prse-molluscan history. 
The foot, shell-gland, and the odontophore are organs which are THE CEPHALOPHORA. 
113 
distinctively molluscan — the last characteristic of the higher Mol- 
lusca only — the other two of the whole group, and their appear- 
ance must- be traced to ancestors within the proper stem of the 
molluscan family tree. The foot is essentially a greatly devel- 
oped lower lip.” 
We would add that the Molluscan as well as Annelid Trocho- 
sphere may be directly compared (morphologically, not histolog- 
icall}7) with the embryo Infusoria (see Fig. 28, E, p. 38) and the 
ancestry of the Mollusca as well as the Vermes should, as Haeckel 
declares, be traced back to the Infusoria, perhaps the parent- 
forms of the entire animal world above the Protozoa. 
The usually hermaphroditic Cephalophora, as a rule, to sum up 
the different phases of their metamorphosis, pass through the fol- 
lowing stages: 
1- Egg. 
2. Morula. 
3. Gastrula. (sometimes suppressed?). 
4. Veliger (the earliest substage being the Trochosphere, which 
passes into the generalized Cephalula form ; or, restricted to the 
mollusks, the Veliger stage). 
5. Adult mollusk, with foot, shell and often lingual ribbon 
(odontophore). 
LITERATURE. 
Snrs. Development of Nudibranchs. (Wiegmann’s Archiv, 1837,1840,1845). 
Pouchet. positive de l’Ovulation spontange, etc. Paris, 1847. 
Leydig. Ueber Paludina vivipara (Siebold and Kolliker’s Zeitschrift, 1850). 
Koren and Danielssen. Bidrag til Pectinibranchiernes Udviklingshistorie. Bergen, 
1851, 1856. (Wiegniann’s Archiv, 1853). 
Kolliker and Gegenbnur. Entwickelung von Pneumodenmon. (Siebold and Kolli- 
ker’s Zeitschrift, 1853). 
Gegenbctur. Untersuchungen ueber Pteropoden und Heteropoden. Leipzig, 1855. 
Clciparede. Anatomie und Entwickelungsgeschichte der Neritina fluviatiHs. (Miil- 
ler’s Archiv. 1857). 
Lacaze-Duthiers. Histoire de l’Organization, du Development, etc., du Dentales. 
(Annales des Sciences Nat. 1858). 
Lereboullet. Recherehes d’Embryologie comparee sur le Development de la Truite, 
du Lezard et du Limnee. (Annales des Sciences Nat., 1862). 
Salensky. Beitrage zur Entwicklungsgeschichte der Prosobranchien. (Siebold 
and Kolliker’s Zeitschrift, 1872.) 
Langerhans. Zur Entwickelung der Gastropoda Opisthobranchiata. (Siebold and 
Kolliker’s Zeitschrift. 1873). 
Lankester. Observations on the Development of the Pond Snail. (Quart. Journ. 
Microscopical Science, 1874.) 
Fol. Etudes sur le D6veloppment des Mollusques (Pteropods). (Archiv. Zool. 1875.) 
Consult also Keferstein, the author of vol. 3 of Bronn’s Classen und Ordnungen der 
Thierreichs; 1862-66; and papers in different journals of Alder and Hancock, Carus, 
Krohn, Lacaze-Duthiers, Loven, Miiller, Reid, Schmarda and Semper. 
LIFE HISTORIES OF ANIMALS. 114 
LIFE HISTORIES OF ANIMALS. 
XVI. THE CEPHALOPODA. 
Development of the Cephalopoda. Though the homologies of the 
Cephalopods with the Cephalophora, particularly the Pteropods, 
are quite direct, yet the cuttlefishes differ greatly in their mode of 
growth, particularly in the embryological stages. AVhile the work 
of Kolliker on the development of the Cephalopods is a classic, yet 
I shall here avail myself in part of Ussow’s more recent work. 
His observations, made at Naples, are based on two species of 
Sepia, Sepiola, Loligo and Argonauta argo, and they agree so 
well in their embryology, that the following description answers 
for all. In the partial segmentation of the yolk, Ussow, as Kolli- 
ker before him, was reminded of the same process in the eggs of 
birds and the turtle. It begins on one side of the yolk; a primi- 
tive furrow arising, which is intersected at right angles by a second 
furrow forming four divisions, afterwards eight, until finally a one- 
layered germinative disk (blastoderm) is formed on a portion of the 
surface of the egg, on the second day after development begins. 
The inner germ-layer then arises, which farther splits into two 
sub-layers (the outer of which is the dermo-muscular, and the 
inner the intestino-fibrous). 
In the second period of development, that of the production of 
organs, the blastoderm covers the entire yolk. The mantle be- 
gins to form, next the rudiments of the eyes arise from the ecto- 
derm, and the mouth appears. The embryo is now like a convex 
disk, or rather a hollow hemisphere. 
On the 10th day the gills, funnel, arms and anal tubercle make 
their appearance, the germ of the gills arising from the dermo- 
muscular sub-layer of the middle germ-lamella. 
On the 11 tli day the rudiments of the auditory organs, the 
pharynx and salivary glands arise, as well as the anal orifice, and 
on the succeeding day the auricles of the heart, the pericardium 
arising afterwards. The walls of the aorta and of the larger arte- 
ries and veins, with the offshoots of the latter (the so-called 
kidneys), are developed from the cells of the middle lamella, 
which become elongated and arrange themselves in rows. On 
the 13th day the ink-sac develops, and the liver. The intestinal 
tract originates from the primitive invagination of the outer 
germ-layer (ectoderm) as in Amphioxus, Ascidia, some Coelen- THE CEPHALOPODA. 
115 
terates, the Brachiopoda, Vermes, etc. As to the mode of origin 
of the nervous sj’stem, Ussow says “I have been compelled to 
Fig. 123. 
Development of the Cuttle, Fish. 
give up forever the hope of finding any resemblance to its de- 
velopment in the Vertebrata, Tunicata, Annulosa and Mollusca.” 
All the ganglia of the Cephalopoda originate 
from more or less compact thickenings of the 
middle germ-lamella (dermo-muscular sub-layer), 
as in the peripheral ganglia of the vertebrates. 
Ussow was unable to trace the origin of the 
genital glands, as they do not arise until, after 
the animal is three days old, and he could not 
keep his specimens alive beyond this period. 
Now returning to Kolliker’s memoir for our 
information regarding the later stages, Fig. 123, 
A (m, mantle ; 5, branchial processes ; s, siphonal 
processes; a, mouth; e, eyes; 1-5 rudimentary 
arms, after Kolliker) represents the disk-like em- 
bryo resting on the surface of the yolk ; B, a side 
view of the embryo when farther advanced (y, 
yolk sack; 7t, head), and C the same still older, 
the yolk sac still smaller, the contents having 
been partially absorbed. Soon after this the 
body and arms grow longer, and the animal 
moves about in its shell. 
For our information regarding the still later 
history of our native cuttle fishes we are indebted to the observa- 
tions of Prof. Verrill, from whose report on the Invertebrates of 
Egg Capsule of Lo- 
ligo Pealii. 116 
LIFE HISTORIES OF ANIMALS. 
Fig. 126. 
Fig.125. 
Fig. 128. 
Fig. 127. 
Development of a Cuttlefish. After Verrill. THE CEPHALOPODA. 
117 
Vineyard Sound, in Prof. Baird’s U. S. Fish Commission report, 
these cuts are taken. Fig. 124 represents the egg-capsule of 
Loligo Pealii. Fig. 1251 represents the young of the same cuttle 
fish, with the yolk sac (y). Fig. 126 represents the same farther 
advanced, while Fig. 127 gives an idea of the same after hatching, 
the yolk having been completely absorbed. Another species of 
cuttle fish {Loligo pallida) is represented by Fig. 128. 
Such is the usual mode of development of the cuttle fishes. But 
in an unknown form probably over three feet in length, as its mass 
of eggs was thirty inches long, the mode of development is entirely 
different. The growth of the embryo is greatly accelerated, and 
immediately after segmentation it assumes a state analogous to 
the Trochosphere of other mollusca. To Grenacher’s beautiful 
Fig. 130 
Fig. 129. 
Development of an unknown Cuttlefish 
memoir we are indebted for the fol'owing facts regarding the 
life-history of this cuttle fish, whose adult form is unknown; he 
studied the eggs found floating in the Atlantic ocean, and was un- 
able to raise it to maturity. After partial segmentation, the 
process being indicated by from five to eight radiating streaks, 
on the surface of the yolk, the embryo assumed the form indi- 
cated by Fig. 129, which represents the blastoderm growing 
around the under pole of the yolk mass and approaching the 
anterior end, where there is a swollen, ciliated band (v) appar- 
ently identical with the velum of the Trochosphere of the lower 
mollusca. This is an interesting point, as Grenadier adopts 
Loven’s opinion that the arms of the Cephalopods represent and 
xFig. 125 a, a", a'", a"", the right arms belonging to four pairs; c, the side of the 
head; e, the eye;/, the caudal fins; h, the heart; m, the mantle in which the color- 
vesicles are already developed and capable of changing their colors; o, the interna- 
cavity of the same; s, siphon. The letters in Fig. 126 are the same (after Veri-ill). 118 
are homologous with the velum of the lower mollusks, particularly 
the Pteropods, and not with the foot as commonly urged. 
This spherical stage is also remarkable for the early appearance 
of the mantle, with the contractile pigment cells (chromatophores). 
It will be seen that the entire egg is, as in the lower mollusks, 
converted directly into the embryo. The embryo soon elongates, 
the mantle grows, the eyes and arms bud out, and the form of the 
adult is rapidly sketched out as in Fig. 130 (m, mouth ; a, a', a", 
arms; /, inner and outer funnel-layer; mt, mantle, the dotted line 
ending in a chromatophore ; h, ear ; g, optic ganglion ; e, eye. 
We thus have in the embryology of this form, which seems 
not very different from Loligo (as may be seen in a more advanced 
stage figured by Grenacher not reproduced here), a mode of de- 
velopment much more like the lower mollusks than was before 
suspected. 
Of the embryology of the fossil Tetrabranchiate Ceplialopods 
(the Ammonites, etc.) we know from the beautiful researches of 
Professor Hyatt that the shell in Ammonites as well as Goniatites 
begins as a minute globular sac; in Nautilus this sac “ is not re- 
tained, but traces of its former existence are apparent on the 
apex of the first whorl, in the form of a scar or cicatrix.” 
Summarizing the known facts regarding the living, dibranehiate 
Ceplialopods, we have eggs and spermatic particles developed in 
separate sexes, the egg passing through the following phases. 
1. Partial segmentation, analogous to that of Vertebrates. 
2, a. Trochosphere (?) or germ developing on the surface of the 
yolk and gradually absorbing it, the Gastrula state suppressed ; 
or, as is more usually the case (&), the adult form is directly at- 
tained without passing through a morula or gastrula state. 
LIFE HISTORIES OF ANIMALS. 
LITERATURE. 
Xdlliker. Entwickelungsgeschichte der Cephalopoden. Ziirich, 1844. 
Hyatt. Embryology of the Tetrabvanchiates. (Bulletin. Mus. Comp. Zool. 1872). 
Lankester. Development of the Cephalopoda. (Annals and Mag. Nat. Hist. 1873, 
and Quart. Journ. Micr. Sc. 1875). 
Grenacher. Zur Entwickelungsgeschichte der Cephalopoden. (Siebold and Kolli- 
ker’s Zeitschrift, 1874). 
Ussow. Zoologico-Embryological Investigations. (Annals and Mag. Nat. Hist. 
1875). 
Consult also the writings of Van Beneden, Metschnikoff, D’Orbigny, G. & F 
Sanberger, Barrande and Verrill. THE PLATYELMINTHES. 
119 
XVII. THE PLATYELMINTHES. 
Returning from our journey through the subkingdom of the 
Mollusca, we will follow the path leading from the Worms up to 
the Insects. The lowest worms are far more simple in structure 
than the lowest mollusks. Indeed in organisms like the Vortex, 
for example, we have forms which serve as a point of departure, 
ancestral forms, from which the entire animal world above the 
Infusoria may have been originally derived. 
The division of worms is now so vast and unwieldy that it 
seems impossible to give a general definition of it, and in the 
present state of science it may be unnecessary. The group em- 
braces all grades of development from simple ciliated forms like 
the Vortex, Prostomum and Macrostomum, which are scarcely 
more complicated than the ciliated infusoria, differing chiefly in 
having genuine cells composing the tissues, up to animals like the 
earth worms and nereids which are in some respects as high if not 
higher than the Crustacea and insects. 
Claparede in his “ Beobachtungen,” etc., says that “the Rhab- 
docoela have interested me on account of their undeniable passage 
to the ciliated Infusoria. I am truly of Agassiz’s opinion that 
many so-called Infusoria may be simply Turbellarian larvae ; al- 
though at first opposed to this opinion I afterwards expressed my 
views as to the near relationship of the Infusoria as well with the 
Rhabdocoela as the Dendrocoela. Thus as Trachelius ovum forms 
an evident connecting link between the Infusoria and Dendrocoela, 
so are the early stages of the Rhabdocoela often scarcely to be 
distinguished from the Infusoria. In man}7 cases one is in doubt 
whether he is dealing with a young Turbellarian worm or a ciliate 
Infusorian.” He then describes an Infusorian-like worm in which 
the mouth opens by a pharynx into a broad body and digestive 
cavity, with no anal opening. There is thus no digestive cavity 
separated from the body cavity. There are no other organs 
except an otolite. This is evidently an immature form, but 
none the less closely allied structurally to Paramecium and 
Trachelius. 
It should also be remembered that among the worms are many- 
synthetic types which, as regards some organs, remind us of other 
groups of animals. For example the Rotifers recall the lower 120 
LIFE HISTORIES OF ANIMALS. 
Crustacea, and are by some naturalists regarded as such ; the 
Planarians have been considered by Girard as mollusks, the 
Polyzoa and Brachiopods are still regarded as mollusks by emi- 
nent naturalists, and there are very few who do not place the 
Tunicates among the latter. On the other hand the Echinoderms 
are regarded as worms by some, and Amphioxus has been called 
a worm. Indeed if any one has any prejudices regarding fixed 
t3rpes in nature, and would learn how regardless of preconceived 
zoological systems the actual state of our knowledge of the lower 
animals must lead one to become, let him study the animals now 
placed among the “Worms.” 
Leaving out of consideration the lowest forms, almost without 
organs, and many parasitic forms, as a general rule the worms 
are bilateral, segmented animals with the nervous cords either sep- 
arate or united by commissures, and resting on the floor of the 
body under the alimentary canal, which usually (when present) 
passes directly through the middle of the body. There is in the 
Annelides a dorsal and ventral blood-vessel, the circulatory appar- 
atus being closed and more highly developed than in the Crustacea 
and Insects, Limulus excepted. In the lower worms (Platyel- 
minths, Nematelminths, Acanthocephali and Rotatoria) there is a 
complicated system of excretory tubes, thought by some anato- 
mists to be analogous with the water-vascular system of Radi- 
ates. 
The organs of locomotion are, when present, simple bristles as 
in the earth-worm; or there are besides lateral prolongations of 
the walls of the body forming paddle-like flaps, as seen in the 
higher Annelides, such as Nereis, etc. 
We are now concerned with tracing the mode of development 
of some of the typical forms belonging to the different subdivis- 
ions, the general relations of which may be seen in the following 
tabular view, which is taken from Gegenbaur’s “Principles of 
Comparative Anatomy,” with the addition of the Brachiopoda, 
which he still retains among the Mollusca. The Onychophora, 
represented by Peripatus, are also omitted, as since the publica- 
tion of Gegenbaur’s work, Peripatus has been proved the re- 
searches of Mr. Moseley to be a tracheate insect, for in the young 
genuine tracheae exist, though they disappear in the adult, or at 
least have not been discovered. 121 
THE PLATYELMINTHES. 
VERMES. 
I. Platyelminthes. 
TurbeUaria (Vortex, Prostoraura, Planaria). 
Trematoda (Distoma, Monostomum). 
Cestoda (Taenia, Bothriocephalus). 
Ncmertina (Nemertes). 
II. Nematelminthes. 
Nematodes (Strongylus, Ascaris). 
Gordiacea (Gordius, Mermis). 
III. (Sagitta). 
IV. Acanthocephali (Echinorhynclius). 
V. Rotatoria (Brachionus, Rotifer). 
VI. Polyzoa (Alcyonella, Flustra, Lepralia). 
VII. Brachiopoda (Lingula, Terebratulina). 
VIII. Tunicata (Appendicularia, Ascidia, Pyrosoma, Doliolum, Salpa). 
IX. Gephyrea (Sipunculus). 
X. Annulata (Hirudo, Balauoglossus, Lumbricus, Serpula, Nereis). 
To the Platyelminthes belong the Flat Worms, Flukes and Tape 
Worms. These are flat-bodied ciliated worms without lateral ap- 
pendages, usually with hooks or suckers. They are usually her- 
maphroditic. 
Development of the Turbellaria. These lowest of worms, in 
which there is no true stomach and intestines, but a simple short 
blind digestive sac leading from the mouth and 
pharynx, are known to multiply by fission, the 
body dividing into two. They also possess ovaries 
and male glands, and reproduce from eggs. We 
are not acquainted with the life-history of the 
Rhabdocoelous forms, such as Vortex, Prostomum, 
etc., except that we know that they produce eggs 
and spermatic particles. In Prostomum, an orbic- 
ular form, the yolk cells are formed in a gland 
(vitellogene) distinct from the true ovary or germ- 
forming gland (germogene). As an example of 
reproduction by fission may be cited the singular 
Catena quaterna Schmarda, which occurs in fresh 
water at the Cape of Good Hope. Fig. 131 repre- 
sents two individuals in partial division, and a chain of four indi- 
viduals, natural size. This form reminds us of the tape worm, in 
which the joints remain permanently attached. We know nothing 
Fig. 131. 
Catena quaterna. 122 
LIKE HISTORIES OF ANIMALS. 
further regarding the history of Catena except that it has been 
found as indicated in the figure here reproduced from Schmarda. 
Among the Dendrocoela, or Planarians, and in fact in the flat 
worms generally, fission takes place. If we cut the common fresh 
water Planarians into several pieces, each piece will become a 
perfect worm. 
All the fresh water flat worms are born as infusorian-like cili- 
ated bodies which attain maturity without any metamorphosis. 
As an example of the mode of development of a Planarian worm, 
may be given the history of Planocem elliptica discovered by 
Girard in Boston and Beverly harbors. The spawning time lasts 
from the middle of May until the middle of June, the eggs being 
deposited in a thin viscid band on stones and sea weeds. The 
egg undergoes total segmentation in four or five days after. A 
ciliated blastoderm begins to form around the yolk mass, and be- 
fore the embn'o leaves the egg it assumes the larval shape, being 
an infusorian-like form, with a caudal flagellum. There are no 
internal organs except two eye-specks. 
In eight or ten days after the larva begins to revolve in the egg, 
and after it has hatched, it stops swimming about and becomes 
a “mummy-like body” which Girard calls a “chrysalis.” In this 
condition, which apparently corresponds to the encysted state of 
the flukes, it floats about in the water. Here Girard’s observa- 
tions came to an end. Whether in this resting stage it is swal- 
lowed by some other animal, and becomes a parasite before 
resuming its active life, remains to be seen. 
The later history of Planaria angulata has been traced by Mr. 
A. Agassiz. “ On examining,” he says, “ a string of eggs, mistaken 
at first for those of some naked mollusk, I was surprised to find 
young Planarhe in different stages of growth with a ramifying 
digestive cavity, somewhat similar to that of adult specimens, but 
showing besides, one distinct articulation for each spur of the 
digestive cavity. The eyes were well developed, and when the 
young became free, the articulations were still distinct.” In the 
youngest specimen (Fig. 13*2) observed, the body w*as almost 
cylindrical, while as seen in Fig. 133, the body has become con- 
siderably flattened. The fact that before attaining maturity the 
Planarian is articulated is very significant, showing that these 
low worms, non-segmented in maturity, should not be excluded 123 
THE PLATYELMINTHES. 
from the class of worms, and that the terms “bilateral, articulate” 
applies as well to the lowest division (though with many ex- 
ceptions) of worms as to the true 
Annelides. 
The Turbellaria then, so far as 
our limited knowledge extends, de- 
velop (a) by fission, (6) from eggs 
fertilized by sperm cells, and pass 
through the following stages, not, 
however, all observed in a single 
species. 
1. Morula. 
2. Infusorian-like stage. 
3. A quiet, encysted (?) stage (Girard’s Planocera). 
4. Articulated stage observed in one species (Agassiz’s Pla- 
naria angulata). 
5. Adult, ciliated, not segmented. 
Fig. 133. 
Fig. 132. 
Young Planaria. 
Development of the Trematodes. The flukes are parasitic 
worms, with a sucking disk in the centre of the body by which 
they attach themselves on or within the body of their host. The 
fluke or “liver worm” (Distoma hepaticum) lives in the liver of 
the sheep and of man. The fishes and snails are much infested 
by them, nearly each species having its distinct kind of fluke. 
The adult flukes are not ciliated, the alimentary canal ends in a 
blind sac, and the sexes are united in the same individual. 
For the mode of formation of the egg of the Trematodes, and 
the embryonic history of certain forms, the student is referred to 
Leuckart’s “ Menschlichen Parasiten” and E. Van Beneden’s 
beautiful “Researches.” E. Van Beneden has shown that the 
development of the Trematodes begins by subdivision of the 
germinative cellule or nucleus. The nucleus and nucleolus then 
divide and the “ protoplasmic body.” The yolk, 
however, remains entirely independent of this division, and serves 
as nourishment for the other cells forming the body of the 
embryo. 
From Van Beneden’s observations, it appears that the eggs of 
the lower flukes as a rule undergo total segmentation, and the 
young are hatched either oval, ciliated, Infusorian-like, without 
anv organs, not even eye-specks, as in Distoma and Amphistoma; 
or as in the higher Trematodes, as shown by the elder Van 124 
Beneden, the development is direct, the embryo passing directly 
into a form like the adult. 
LIFE HISTORIES OF ANIMALS. 
For the further history of the fluke we will turn to Steenstrup’s 
famous work “On the Alternation of Generations,” wherein is first 
related the strange history of these animals. While the flukes 
were well known, as well as the tadpole-like Cercaria, it was not 
known before the publication of Steenstrup’s work in 1842, that 
the Cercariae were the free larval forms of the Distom®. The 
Cercaria ecliinata, first described by Siebold, is like a Distoma ex- 
cept that the body is prolonged into a long extensible tail. This 
tail, says Steenstrup, is formed of several membranes or tubes 
placed one within the other, of which the outermost is a very 
transparent epidermis, under which is a tolerably thick membrane 
furnished with transverse muscular fibres or strice, and between 
each pair of these transverse fibres is placed a globular vesicle 
which appears to be a mucous follicle or gland ; the innermost 
tube is opaque and of firmer consistence, it contains the longitu- 
dinal muscular fibres, and is usually reticulated on the surface. 
Through the centre of these tubes there passes a slightly narrower 
canal, which becomes very small towards the extremity of the 
tail. The existence of the same layers in the body itself of the 
Cercaria, can easily be demonstrated ; but the transversely striated 
layer is here not so much developed. This description of the 
Cercaria will remind one of the tadpole-like larva of the Ascidians. 
The apparent homology in structure of the tail of the Cercaria 
with that of the Ascidian larva as figured by Kupffer, is striking. 
This similarity may be seen if the reader will compare fig. 7, 
Tab. ii, in De la Valette St. George’s “Symbol®,” representing 
a stage in the development of Cercaria Jlava into Monostomum 
flavum. The author figures a row of cells on each side of a 
central cavity through which passes what is regarded as pos- 
sibly a nerve. Whether this is not as much a chorda dorsalis 
and spinal nerve as those parts regarded as such in the Ascidian 
larva, is a subject for future investigation. But in other respects 
the position of the mouth, the sense-organs, as well as the form 
of the body strikingly recall the Ascidian larva, so much so that 
it gives strong confirmation to the opinion that the Ascidians are 
worms, and that they and the Trematodes have possibly originated 
from allied forms. In another species, Cercaria ocellata, the tail 
has a lateral fin ; and in still another species figured by J. Muller THE PLATTELMINTHES. 
125 
on the same plate (Cercaria setifera) unaccompanied by any de- 
scription, the tail contains an axial row of large cells, with a row 
on each side reminding one of the embryo of the Ascidian, with 
its axial row of cells (the germ of the chorda dorsalis) and the 
Fig. 134 
Development of Distoma. 
cells on each side ; moreover the tail is provided with nineteen 
pencils of long hairs, each pair arising from a distinct segment, 
so that in one larval Trematode at least, 
the annulated structure of the body exists, 
as well as in the larval Planaria. 
Returning now to Steenstrup’s narrative, 
he tells us that these “Echinate Cercai’iae 
(Fig. 134, A, parent nurse; e, germs; a, 
nurse; B, larva), are found by thousands, 
and frequently by millions in the water, 
in which two of our largest fresh-water 
snails, Planorbis cornea and Limnceus 
stagnalis, have been kept.” After swim- 
ming about in the water some time they 
fix themselves by means of their suckers (B, s) to the slimy slvin 
of the snails, in such numbers that the latter look as if covered 
with bits of wool. 
The Cercaria by contracting its body and violent lashing of the 
tail forces its way into the body of its host, loses its tail, and then 
resembles a mature Distoma. By turning about in its place and 
secreting a mucus, a cyst is gradually formed, with a spherical 
shell. This constitutes the “pupa” state of the Cercaria, first 
Fig. 135. 
Development of Monas- 
tomum. 126 
LIFE HISTORIES OF ANIMALS. 
observed b}7 Nitzsch and afterwards by Siebold. Steenstrup 
thinks that the Cercaria casts a thin skin. In this state the body 
can be seen through the shell of the cyst, as in Fig. 134, C, where 
the circle of spines embedded around the mouth is seen.1 The 
encysted Cercariae remain in this state from July and August until 
the following spring ; and during the winter months in snails kept 
in warm rooms, they change into Distomas (Fig. 134, D) the ma- 
ture fluke differing, however, in some important respects from the 
tailless larvae. In nature they remain from two to nine months in 
the encysted state. 
“Now,” asks Steenstrup, “Whence come the Cercariae?” Boja- 
nus states that he saw this species swarming out from the “king’s 
yellow worms,” which are about two lines long and occur in great 
numbers in the interior of snails. From these are developed the 
larval Distomas, and Steenstrup calls them the “nurses” of the 
Cercariae and Distomata. They exactly resemble the “parent 
nurses” (Fig. 134, A) and like them the cavity of the body is filled 
with young, which develop from egg-like balls of cells. Steenstrup 
was forced to conclude that these nurses originated from the first 
nurses (Fig. 134) which he therefore calls “parent-nurses.” Here 
the direct observations of Steenstrup on the Cercaria ecliinata came 
to an end, but he believed that the parent-nurses came from eggs. 
The link in the cycle of generations he supplied from the observa- 
tions of Siebold, who saw a Cercaria-like young (Fig. 135, B) 
expelled from the body of the ciliated larva of Monostomum 
mutabile (Fig. 135, A, a, nurse developing from ciliated larva; m, 
mouth ; 6, eye specks). Steenstrup remarks that “ the first form of 
this embryo is not unlike that of the common ciliated progeny of 
the Trematoda, as they have been known to us in many species 
for a long time, from the observations of Mehlis, Nordmann and 
Siebold, and it might at first sight be taken for one of the poly- 
gastric infusoria of Ehrenberg, which also move by cilia; whilst 
in the next form which it assumes the young Monostomum bears 
an undeniable resemblance to those animals which I have termed 
‘nurses’ and ‘parent nurses’ in that species of the Trematoda 
which is developed from the Cercaria ecliinata” 
Thus the cycle is completed and the following summary of 
1 Other figures by Steenstrup and other authors show the form of the encysted Cer- 
caria very distinctly, but in the figure given above only the spines are distinctly repre- 
sented in the plate from which this is copied. THE PLATYELMINTHES. 
127 
changes undergone by the lower Distomas present as clear a case 
of an alternation of generations as seen in the jelly fishes. 
1- Egg. 
2. Morula. 
3. Ciliated larva. 
4. Cercaria (parent nurse, Proscolex) producing 
5. Cercaria (nurse, scolex). 
6. Encj’sted Cercaria (Proglottis). 
7. Distoma (Proglottis). 
The Cercaria echinata, living in snails which are eaten by ducks, 
have been shown by St. George to develop into the adult Distoma 
in the body of that bird. It is generally the case that those Dis- 
tomas which pass through an alternation of generations live in 
the larval state in animals which serve as food for higher orders. 
Thus the Bucephalus of the European oyster passes in the en- 
cj'sted state into a fish (Gasterostomum), which serves as food for 
a larger fish, Belone vulgaris, where the cysts of the same worm 
occur. 
Distoma hepaticum, the liver fluke, sometimes occurring in man, 
is thought by Dr. Willemoes-Suhm to begin its existence as Cer- 
caria cystoj)hora, parasitic on a species of Planorbis. 
Steenstrup. On the Alternation of Generations. 1842. Translated by G. Busk, 1845. 
De la Valette St. George. Symoolae ad Tremalodum Evolutionis Historiam. Berlin, 
1855. 
Leuckart. Die Menschlichen Parasiten. Leipzig. 18(i8, incomplete. 
E. Van Beneden. Reeherches sur la Composition et la Signification de l’Oeuf. Brux- 
elles, 1870. 
LITERATURE. 
Development of the Cestodes. In the tape worm there is no ali- 
mentary canal, the liquid food being absorbed from the juices of 
its host through the walls of the body. The head is armed with 
suckers, hooks or leaf-like soft appendages, while the body is sub- 
divided usually into a great number of segments, each containing 
an ovary and male gland. While the Turbellaria possess a pair 
of nerve-ganglia, the Cestodes are not known positively to possess 
any trace of a nervous system. 
E. Van Beneden shows that the egg is formed by two glands, 
one of which (the germogene) forms the nucleus and nucleolus, 
while the other (vitellogene) forms the yolk. Development begins 
very probably as in the Trematodes, by multiplication by division 
of the nucleus (germinative cell). In the eggs of Taenia bacil- 128 
LIFE HISTORIES OF ANIMALS. 
laris E. Van Beneden saw the nucleus subdivide ; afterwards the 
cells are arranged in two layers, and the outer layer 
is thrown off (this probably corresponding to the am- 
nion of insects and Crustacea) ; the central mass 
forms the em- 
bryo, and soon 
the three pairs 
of hooks arise 
as in Fig. 136. 
Three struc- 
tureless mem- 
branes are secreted around 
the embiyo, which then 
hatches. The embryo of 
Bothriocephalus is provided 
with a ciliated membrane, 
which corresponds to the 
first blastodermic moult of 
the embryo Taenia, which 
is not ciliated. 
Now taking up the history 
of the human tape worm, 
Tcenia solium (Fig. 1371), 
the eggs eaten by the hog 
are developed in its body 
into the larval tape worm 
(scolex) called in this spe- 
cies, Cysticercus celluloses, 
(Fig. 138; Fig. 139, head 
enlarged). The head with 
its suckers is formed, the 
body becomes flask-shaped 
(Fig. 138, Cysticercus) ; the Cysticerci then bury themselves in the 
liver or the flesh of pork, and are transferred living in uncooked 
pork to the alimentary canal of man. The body now elongates, 
Fig. 136. 
Fig. 137. 
Embryo of 
Tania. 
Common Human Tape worm. 
1 Tania solium. A, the worm natural size; h, head; a, 309th joint; b, 448th; c, 569th; 
d. 680th; e, 768th; /, 849th; g, 855th joint and last blit one. This worm was-10 feet 9 
inches long. B, a separate joint (Proglottis) showing the ovary with its outlet o; the 
same joint contains a testis, too minute to show iu the figure. Fig. 168, Cysticercus 
celluiosce. the larval tape worm, a, circle of hooks; b, suckers; c, wrinkled neck; d, 
sac filled with fluid. This and Fig. 166 and 169 from Weinland. THE PLATYELMINTHES. 
129 
and new joints arise behind the head until the form of the tape 
worm is attained, as in Fig. 137 (after Weinland). 
Now we shall see how the eggs are distribute. The hinderd 
joints become tilled with eggs and then break off’, becoming inde- 
pendent animals comparable with the “parent-nurses” of the Cer- 
carias, except that they are not contained in the body of the 
Taenia (as in the Cercaria), but are set free. The independent 
joint (Fig. 137, (/,) is called a “proglottis.” It escapes from the 
alimentary tract, and the eggs set free are swallowed by that nn- 
Fig. 139. 
Fig. 138 
Cysticercus. or 
larval Tape 
worm. 
Head of Cysticercus enlarged, showing the suck- 
ers (S) and circle of hooks. 
clean animal, the pig, and the cycle of generations begins anew. 
We thus have the following series of changes which may be com- 
pared with the homologous series in the flukes : 
1- Egg. 
2. Morula. 
3. Double-walled sac (Planula?). 
4. Proscolex, free embryo with hooks, surrounded by a blasto- 
dermic skin. 
5. Scolex (Cysticercus, larva). Body few-jointed. 
6. Scolex (Taenia). Body many-jointed. 
7. Proglottis (adult). 
P. J. Van Beneden. Les Vers Cestoide«. Brussels. I860. 
. Memoire sur les Yers Intestinaux. Paris. 1858. 
LITERATURE. 
LIFE HISTORIES OF ANIMALS. 130 
LIFE HISTORIES OF ANIMALS. 
Si-hold. Ueber die Band- und Blasenwiirmer. Leipzig. 1854. 
Wiinland. An Essay on the Tapeworm* of Man. lsf>8. 
Compare also the works of Lcuckart, Klichenmeister, E. Van Beneden and Cobbold. 
Development of the Nemerteans. In the development of some 
of these worms we are reminded of the mode of growth of the 
Eehinoderms, while in others the larvae attain the adult condition 
by gradual development. In no order of animals, perhaps, is 
there a greater range of variation in the mode of development 
than in these curious worms. 
The simplest mode of growth is that described by Dieck in Ce- 
phalotlnix, where the ciliated larva, after passing through a morula 
and plannla1 stage (being a two-layered sac, but not a gastrula) 
leaves the egg and undergoes no metamorphosis, the young worm 
having no body cavity. In the Nemertes larva of Desor there is 
a body cavity, but the larva is still an infusorian-like being, and 
attains maturity by direct growth. Another Nemertean (N. corn- 
munis') has been found by Barrois to have a somewhat more com- 
plicated mode of growth than in the larva of Desor. The first 
stages of development are like 
those of the larva of Desor, the 
morula passing, as he claims, 
into a ciliated “gastrula” state 
in the egg, the body cavity being 
formed by invagination of the 
outer layer of cells, but the ani- 
mal after shedding an amnion 
leaves the egg in the Nemertes 
form, and there is no free swim- 
ming stage. 
Now we come to those Nemer- 
teans in which there is a very 
complicated metamorphosis. J. 
Muller had described an animal 
caught with the towing net which he called “Pilidium.” Busch 
had suspected that a Nemertes came from the Pilidium, and Leuc- 
Fig. 140. 
Pilidium with the Neniertes growing in it. 
1 The inner lining of the pianola arises before the body cavity is formed, by a differ- 
entiation of a second inner cell-layer, as occurs in other worms, zoophytes, etc. Dieck 
evidently l.mits the term gastrula to a two-layered sac. with a bo<ly cavity formed by 
the invagination of the ectoderm Lai kester's “gastrula” includes any embryo with 
a two-layered sac and a primitive cavity. Dieek’s pianola is like 11 seckel’s planula of 
the sponge, the cavity being formed during the segmentation of the egg. THE PL AT YELMINTIIES. 
131 
kart and Pagenstecker proved it. Our figure, taken from flic 
drawings of these two last named authors, shows the singular Pili- 
dium, and the planarian-like Nemertes with the eye-specks (Fig. 
140, e), growing in it. How the worm originates in the body of 
the Pilidium, and how the latter arises, have lately been fully shown 
by Metsehnikoff, and to his memoir we are indebted for the 
strange history of the mode of development of these worms. 
He followed the development of the Pilidium from the egg, 
which undergoes total segmentation, leaving a segmentation-cav- 
ity. The next occurrence is the separation of a one-layered cili- 
ated blastoderm, the ectoderm, which invaginates, forming the 
primitive digestive cavity, from which the stomach and oesophagus 
are formed. The larva is now helmet-shaped, ciliated, with a long 
lash (flagellum) attached to the posterior end of the body. 
After swimming about on the surface of the sea awhile, the 
Nemertes begins to grow out from near the oesophagus of the 
Pilidium. On each side of the base of the velum (v) of the Pilid- 
ium appear two thickenings of the skin, one pair in front, the other 
behind; these thickenings push inwards, and are the germs of the 
anterior and posterior end of the future worm. The anterior pair 
become larger than the posterior; the part of the disk next to the 
oesophagus thickens; at the same time the alimentary canal of 
the Pilidium grows smaller and only a narrow slit remains. The 
disks now divide into two layers, the outer much thicker than 
the inner. A new structure now arises, a pair of vesicles near the 
hinder pair of disks; these are the “lateral organs” of the future 
worm. Soon the anterior pair of disks unite and the head of the 
worm is soon formed, when the elliptical outline of the flat worm 
is indicated, and appears somewhat as in Fig. 140 (i, intestine 
of the worm). The yolk mass, with the alimentary canal of the 
Pilidium, is taken bodily into the interior of the Nemertes, the 
Pilidium skin falls off, and the worm seeks the bottom. 
Metsehnikoff discovered five other species of Pilidium, and 
thinks this mode of development is not an uncommon occurrence. 
This manner of development is directly comparable with that of 
the echinoderm from the Pluteus. 
To show the wide range of metamorphosis existing in the Ne- 
merteans, we may cite the case of a Narecla studied by Mr. A. 
Agassiz, and whose earl}'' stages are like those of the higher 
Annelides; in fact so much so that Milne-Edwards and Claparede 132 
FIFE HISTOIUES OF ANIMALS. 
Fig. 141. 
Fig. 142. 
Fig. 144. 
Fig. 143. 
Fig.145. 
Fig. 146. 
Development of a Nemertean worm. After A. Agassiz. THE PLATYELMINTIIES. 
133 
associated “the larva of Loven” (which Mr. Agassiz has traced 
without any doubt to the Nemertean worm) with that of Polynoe, 
a representative of the highest family of Chmtopod worms. _ In 
the first stage (Fig. 141, a, anus; c, intestine; m, mouth; o, 
oesophagus; s, stomach ; e, e3re-speck; v, ciliated ring) the larva 
is not ringed ; this figure may be compared with figure 85 on p. 
83 to show how much alike the worm and Echinoderm larvae 
appear. The new rings are formed between the anal rings and the 
older anterior rings, as in annelid larvae, and in fact in the em- 
bryos of the Insects and Crustacea. Figs. 142 and 143 represent 
the ringed larva. “A number of rings make tlieir appearance at 
once, and are the more distinct the nearer they are placed to the 
mouth.” The worm now greatly elongates, more segments are 
added and it appears as in Figs. 144 and 145, with the ciliated 
crown, the small short tentacles and eyes. The worm now swims 
about slowly' and creeps over the bottom, and is nearly a quarter 
of an inch long. It will be observed that the larva differs from 
those of other Annelides, as Mr. Agassiz states, in the absence of 
“feet, bristles or appendages of any7 sort, except the two tentacles 
of the head ; and, were it not for these, it would seem as if the 
young worm were the larva of some Nemertes-like animal.” Fig. 
146 represents the worm over four months after the stage rep- 
resented by Fig. 145 ; the articulations have disappeared and a 
month later the head is separated from the body7 by a neck, the 
tentacles disappear, the body is flattened, and the Nemertes 
(Polia) form is attained. 
It is thus interesting to know that the young Echinoderm (Fig. 
85), the young mollusk (Fig. 121 B), and the young Nemertean 
worm pass through a similar free-swimming Cephalula stage. We 
shall see farther on that the young Balanoglossus and the true 
Annelides pass through a similar phase. The changes through 
which the Nemertean worms pass are the following, though it 
should be borne in mind that different species pass through dif- 
ferent cycles of growth, some exhibiting no metamorphosis, the 
stages being more or less condensed in the embryo state. 
1. Egg. 
2. Morula. 
3. Planula (or Gastrula?), hatching as a 
4. Ciliated Infusorian-like larva, or a 
5. Pilidium or a Cephalula. 134 
G. Nemertes (a) budding out from the Pilidium, or (b) arising 
b}’ direct growth from the Ccphalula. 
LIKE HISTORIES OF ANIMALS. 
LITERATURE. 
Loren. Jakttagelse ofver Mctamorfos hos en Annelid. (K. Vet. Akad. Ilandlingnr. 
Stockholm, istO. Translated in Avchiv luer Naturgesclnchte, 1842, and Annales des Sc. 
Nat. 1842.) 
JJexi.r. Emhryologie von Xeniertes. (Muller’s Arcliiv, 1848.) 
l.euckart and t’aycnsticher. Untersuchungcn ucber niedere Seethicrc. (Muller’s 
Arclnv. 1858 ) 
A. Af/asAz. On the young stages of a few Annelides. (Annals Lyceum of Natural 
History. New York, 18tM>.) 
Met sclurikoff. Entwickclung dor Echinodermen und Ncmertinen. (Memoircs Acad. 
Imp. Sciences. St. 1’etershourg. 18<>9.) 
Merle. Heitrage zur Entwickeiungsgeschiclite der Nemertinen. (.Jcnaischc Zeits- 
chi’ilt liir Naturwissenschalt. 1874.) 
XVIII. NEMATELMINTI1ES Wound worms, Thread worms, Hair 
worms.) 
There is little of interest in the development of the ordinary round 
worms, which whether 
free or parasitic are of 
the usual form, as shown 
in the Enstrongylns. 
The mode of develop- 
ment of all these worms 
so far as known is very 
uniform. Development 
begins in three ways: 
(1) usually the egg un- 
dergoes total segmenta- 
tion ; others (2), as in 
Ascaris dentata and Oxy- 
uris ambigua, do not 
show any trace of seg- 
mentation, and (3) in 
Cucullanus elegans there 
is no yolk, the nucleus 
absorbing all the vitel- 
line matter which is lim- 
pid and transparent (E. 
Van Beneden). The 
germ consists of a single 
row of cells bent on it- 
self somewhat as in Fig 149, which represents a little more ad- 
Fig. 117. 135 
THE CH.STOGNATIII. 
van cod state in Sagitta, and there arc a few cells representing the 
entoderm. The Nematode may he said therefore to pass through 
an incomplete gastrula condition. 
T he adult form is rapidly assumed 
in the egg. Fig. 14JS, after J. Wy- 
man. represents the young of Eu- 
stron(/f/lus papillosus in the egg, 
and the worm just after hatching. 
Fig. 14 7, «, several mature worms 
coiled up in the brain of the snake 
bird; b, female; c, head much enlarged; cZ, end of the body; e, 
male ; /, the end of its body, after Wyman.) 
The Trichina spiralis is the author of the terrible disease called 
triehiniasis or trichinosis. The young worms exist in the flesh of 
the hog, where they become encysted, and if swallowed by man, 
the cysts are dissolved during digestion, and the young worms are 
set free in the intestinal canal. From here the young bore in all 
directions in the body, and becoming encysted cause the flesh to 
look as if spiinkled with white sand. 
The development of the hair-worm (Gordius and Mermis) is 
quite complicated, as the young are parasitic, tadpole-shaped, liv- 
ing in the bodies of insects, especially grasshoppers, in whose 
bodies the mature worms are found coiled up. M. Yillot is now 
publishing an account of the mode of development of these 
worms in a monograph appearing in Lacaze-Duthiers ‘-Archives,” 
but not yet completed. These worms are oviparous, laying ex- 
ceedingly numerous, minute eggs agglutinated together, forming 
long white strings. The young of one genus live in the aquatic 
larvae of flies and were afterwards found by Villot in the mucous 
layer of the intestines of fishes. 
The diacious round worms pass without metamorphosis through 
a morula, and a condensed gastrula state (not so well marked as 
in Sagitta) in the egg, assuming the adult form before hatching. 
In the hair-worms there is a well marked metamorphosis. 
Fig. US. 
Development of a Round worm. 
LITERATURE. 
Claparecle. De la Formation et de la fecondation des (Eufs chez les Vers Nema- 
todes. Genfeve, IS5!). Compare also papers by Bagge, lteichert, Siebold, Nelson, 
Schneider, Perez, E. Van Bcnedcn, Biitscltfi and Villot. 
This singular worm .bad been referred to the Crustacea by same, 
XIX. CH7ETOGNATHA (Sagitta). LIFE HISTORIES OF ANIMALS 
to the mollusca by Forbes, and even to the vertebrates by Meiss- 
ner. Its development and structure, however, show that it is 
nearly related to the Nematodes. The mouth is, however, armed 
with six pairs of bristles; and a double-fin-like expansion of the 
sides and ends of the body gives it a slightly fish-like shape. This 
fin-like expansion is seen in the Cercaria, and the young ascid- 
ian, and is of little morphological importance. It swims on the 
surface of the water, not seeking the bottom or living parasiti- 
cal ly. 
Development of Sagitta. This animal is a hermaphrodite, and 
the eggs may he found in August well developed. Its develop- 
ment has been studied by Gegenbaur and 
Kowalevsky, by the latter in great detail. 
The egg undergoes total segmentation, a 
segmentation cavity being formed and the 
blastoderm invaginating exactly as in the 
Nematodes. This results in the formation 
of a gastrula-condition (Fig. 149) in which 
the infolding of the blastoderm leaves a 
well marked primitive body-cavity. Soon 
at the opposite end of the body another 
cavity (the permanent mouth) forms, which deepens and connects 
with the primitive body-cavity (a) ; this closes up at the posterior 
end, and the true digestive canal is formed. The embryo is oval, 
but soon elongates, and the adult Sagitta form is attained before 
the animal leaves the egg. 
The phases of development are, then, as follows : 
1. Morula. 
2. Gastrula (well marked, but not ciliated and free). 
3. Adult Sagitta. 
Fig. 149. 
Gastrula of Sagitta, 
LITERATURE. 
Gegenbaur. Ueber die Entwickelung der Sagitta. Halle, 1857. 
Kowalevski/. Embryologische Studien an Wiirinen und Artliropoden. (Memoirs 
Acad. Imp. Sciences. St. Petersburg, 1871 ) 
XX. ACANTHOCEPHALI. 
The Echinorhynchus (Fig. 150, head, afte • Owen); 151, the 
same, with the proboscis retracted (a, oral pore ; 55, protractile 
muscles; cc, retractile muscles; from Owen), a singular worm, THE ACANTHOCEPIIALI. 
137 
without a, mouth or alimentary canal, hut with a large proboscis 
armed with hooks, evidently lives by imbibition 
of the fluids of its host. It is a not uncommon 
parasite of fishes. Fig. 152 represents an al- 
lied ( ?) form (Koleops avguilla) described by Dr. 
Lockwood, who found it in the eel (American 
Naturalist, vi, 1872). 
Development of Echinorhynchus glgas. Schnei- 
der has given the only account we have of the 
early stages of this worm. “ The ova of this 
worm are scattered upon the ground by the pigs. 
Here they are eaten by the larvae of Melolontlia 
vulgaris (a beetle allied to our June beetle), and 
thus arrive at their further development. The 
ova burst in the stomach of the larva, and the embryos contained 
Koleops. 
Fig. 150. 
Fig. 151 
Head of Ecliinorhynchus. 
in them can then penetrate, by means of their spines, through the 
intestine into the body cavity of the larva; here they become de- 
veloped, and again reach the intestine of the pig by the agency of 
the larva. 
“The larvae infested with Echinorhynchi live on until their meta- 
morphosis into cockchafers When the embryos have 
arrived at the body cavity of the larvae of Melolontha, they re- 
main for some days unaltered and capable of motion ; they then 
become rigid, acquire an oval form, and envelope themselves in a 
finely cellular cyst, which is formed of the connective tissue of 
the larva. The skin of the embryo, with its circlet of spines at 
the anterior extremity, con inues at first to be the skin of the 
growing larva; and it is only at a later period, when the forma- 138 
LIFE HISTORIES OF ANIMALS. 
tion of the hooks commences, that it is thrown off, when it forms 
a second cystic envelope. The embryo, or rather the larva, pro- 
ceeding from it, divides very soon into two layers, a thick dermal 
layer and an inner cell-mass, from which the other organs origi- 
nate.” The ovaries and testes are produced at a very early stage. 
Schneider. On the development of Echi iorlu/nchus gijnx. tSitzungsberieht der 
Ohcrhessisehcu Oesellsclndt lilr Natur und lie Ikundc. 1871. Translated in Annals and 
Mag. Nut. Hist., 1871.) See also a paper by Leuckart, 1873. 
LITERATURE. 
XXI. ROTATORIA. 
The Rotifers, by some eminent naturalists regarded as Crus- 
tacea, are shelled worms, related to the flat-worms in many re- 
spects. The body consists of sev- 
eral segments, and the sexes are 
very unlike, the small males hav- 
ing the organs more or less rudi- 
mental, with no alimentary canal. 
Like the lower worms they have a 
set of tubes excretory in their na- 
ture and perhaps respiratory, cor- 
responding to the water vascular 
tubes of the Radiates, but with 
fine ciliated infundibuliform ori- 
fices comparable with the seg- 
mental organs of the Brachiopods 
and higher worms : also a pair of 
teeth in the pharynx, as in many 
worms. The anus is situated on 
the back a the base of the tail. 
'Sometimes the digestive canal 
ends in a blind sac. The distinc- 
tive organ is the retractile, eiliated, paired organ which may be 
called the velum. Fig. 1531 from H. J. Clark, represents Squa- 
iKiff. 15 . 
A Rotifer. 
1 Squamilla oblonga, magnified 200 diameters. From freshwater. A view from be- 
low; shell or carapace (•s, s1, s2); s, the anterior transverse edge of the carapace; s1, 
the anterior, and .s2, the posterior coiners of the carapace; s8, the border of the oval, 
flat area which occupies the lower face of the carapace; lb. i he cilia hearing velum of 
the head; t, the fork of the tail (f1); m, the mouth; j. jaws; j1, muscles which move.?; 
st. stomach; cv, the contractile vesicle, or heart of the aquiferous circulatory system; 
cv1, cv2, the right, and cr8, cv*. the lelt aquiferous circulatory vessels; eg, eg1, eg2, two 
largely developed young. —Clark’s “ Mind in Nature.” THE ROTATORIA. 
139 
mella ohlonga of Ehrenberg, found in this country. It is closely 
allied to Brachionus. 
Development of the Rotifers. The sexes are distinct. The fe- 
males lay both summer and winter eggs, the former being un- 
fertilized, like the summer eggs of the Cladocera (Daphnia). The 
Rotifers live in damp places in water and revive after being 
nearly dried up for a long time. Dr. Salensky has been the first 
to give a complete sketch of the life-history of a Rotifer, Brach- 
ionus urceolaris. 
The eggs of Brachionus are attached by a stalk to the hinder 
part of the body of the female. The following remarks apply to 
the female eggs, which are quite distinguishable from the mascu- 
line ones. The eggs undergo total segmentation, and the outer 
layer of cells resulting from subdivision form the blastoderm, 
when the formation of the organs begins. The first occurrence is 
an infolding of the blastoderm (ectoderm) forming the primitive 
mouth, which remains permanently open, the mouth not opening 
at the opposite end as in Sagitta, but the entire development of 
the germ is as in Calyptraea, as Salensky often compares the ear- 
liest phases of development of the Rotifer with those of that mol- 
lusk. The “trochal disk,” or velum, as we may call the ciliated 
disk of the Brachionus, arises as in certain mollusks, as a swell- 
ing on each side of the primitive infolding. Behind the primitive 
hole appears another swelling, which becomes the “foot” or tail. 
There is soon formed at the bottom of the primitive infolding a 
new hole or infolding, which is the true mouth and pharynx, while 
a swelling just behind the mouth becomes the under lip. 
Soon after, the two wings of the velum become well marked, and 
their relation to the head is as constant as in Calyptraea. The 
foot becomes conical, larger, and the termination 
of the intestine and anal opening is formed at 
the base. 
The internal organs are then elaborated ; first 
the nervous system, consisting of but a single 
pair of ganglia arising from the outer germ-layer 
(ectoderm). Soon after the sensitive hairs arise 
on the wings of the velum. 
Fig. 154 shows the advanced embiwo, with the 
body divided into segments, the pair of ciliated 
wings of the velum (v), and the long ta,il (t), At this time the 
Fig.154. 
Brncliionus nearly 
ready to hatch. 140 
LIFE HISTORIES OF ANIMALS. 
shell begins to form, and afterwards covers the whole trunk, but 
not the head. 
The inner organs are developed from the inner germ-layer (en- 
doderm), which divides into three leaves, one forming the middle 
part of the intestine, and the two others the glands and ovaries. 
The pharyngeal jaws arise as two small projections on the sides of 
the primitive eavit}\ 
The male develops in the same mode as the female. The Roti- 
fers, so far as can be judged from one species, seem to develop in a 
manner quite unlike other worms, and in the earliest phases much 
as in some Gastropods, the mode of their embryology not throwing 
much light on the affinities of the group, which is of doubtful posi- 
tion, though with more of the characters of worms than Crustacea. 
The young pass through a morula state, and the embryo directly 
attains the mature form in the egg. 
LITERATURE. 
Salensl-y. Beitrage zur Entwicklnngsgeschiclite der Brachioitvs urceolaris. (Siebold 
and Kolliker’s Zeitschrift, 1872). Compare also the papers of Huxley, Leydig, Cohn, 
Gosse and Nageli. THE POLYZOA. 
141 
XXII. THE POLYZOA. 
The Polyzoa or moss animals derive their common name from 
their resemblance to aquatic mosses. For example, the freshwater 
Fredericella Walcottii (Fig. 155, after Ityatt) would easily be mis- 
Fig. 155. 
Fig. 156. 
Sea mat. 
Fresh water Polyzoon. 
taken for moss growing on a submerged stick. The marine species 
have smaller cells and form mat-like encrustations, as in Membrani- 
pora (Fig. 156, cells enlarged) ; or as in Myriozoum subgracile 
Fig. 157. 
Branching Marine Polyzoon. 
(Fig. 157), they form a coral-like branching mass. On magnifying 
these cells when the animal is alive and extended from its cell, 
each polypide, as it is called, appears with its crown of tentacles 142 
LIFE HISTORIES OF ANIMALS. 
somewhat like a Sabellid worm. This crown of tentacles surrounds 
the mouth, which leads by an oesophagus into the throat and a 
stomach, the latter bent so that the intestine beyond ends very 
near the mouth ; the polypide is thus bent on itself within the cell 
(cystid) and its body is drawn in and out by muscles. Attached 
to the end of the fold of the stomach is a cord (funiculus) holding 
the ovary in place; this cord extending back to the end of the 
cystid, as we may call the cell. 
Allman regards the polypide and cystid as separate individuals. 
Now in confirmation of this view we have the singular genus Lox- 
osoma, wlrtch is like the polypide of an ordinary Polyzoan, but 
does not live in a cell. On the other hand, we know of no cystids 
which are without a polypide (Nitsehe). 
The affinities of the Polyzoa to the worms are quite decided. 
In the Phoronis worm, which is allied to Sipuneulus, we have the 
alimentary canal flexed, and the anus situated near the mouth. 
The Polyzoa have but a single pair of nerve ganglia, and in some 
cases a tubular heart. The fresh-water species are the higher, 
and are called Phylactohemata; the marine species are termed 
Gymnolannata. All the Polyzoa are hermaphrodite, the ovaries 
and male glands residing in the same cystid, the testes being situ- 
ated near Ihe bottom, while the ovary is attached to the walls of 
the upper part of the cell (ItoUeston’s Forms of Animal Life). 
Reproduction is both sexual and asexual (or by budding). 
Development of the Polyzoa.— Remembering that the cyslids 
stand in the same relation to the polypides as the hydroids to the 
medusae, as Nitsehe insists, we may regard the polypides as sec- 
ondary individuals, produced by budding from the cystids. The 
large masses of cells forming the moss animal, which is thus a 
compound animal, like a coral stock, arises by budding out from a 
primary cell. The budding process begins in the endocyst, or 
inner of the double walls of the body of the cystid, according to 
Nitsehe, but according to an earlier Swedish observer, F. A. Smitt, 
from certain fat bodies floating in the cystid. 
Nitsehe has observed the life-history of Flustra membranacea. 
H e has traced the budding of one cell or zooeciurn (representing 
the cystid individual) from another. During this process the poly- 
pide within decays, leaving as a remnant the so-called “brown 
body,” regarded by Smitt as a secretion of the endocyst and germ 
of a new polypide. After the loss of its first polypide, it can pro- TI1K POLYZOA. 
143 
duce a new one by budding from the endocyst on the side of the 
stomach. In Loxosoma, young resembling the adult bud out like 
polyps. 
Nitsche does not regard this budding process as an alternation 
of generations, but states that in Polyzoa of the family Vesicu- 
lariidae, this may occur, as in them some cystids form the stem, 
and others (the zooecia) produce the eggs. 
The Polyzoa produce winter and summer eggs, the winter eggs, 
called statoblasts, being protected by a hard shell. Fig. 158, after 
Fig. 158, 
Egg of Pectinatclla magnillca. 
Hyatt, represents the winter egg of Pectincitella magnified, with 
spines. These winter eggs crowd the zooecia, and may be found 
in them after the polypides have decayed. 
Grant first described the ciliated young of the Polyzoa. The 
Swedish naturalists, Loven and Smitt, have described 
the development of the young Jjejpmlia pallasiana, 
which, after passing through a true morula condition, 
issues from the egg as a flattened ciliated sphere with 
a single band of larger cilia surrounding one end. 
Our figure (151)) is copied from Claparede’s memoir, 
and represents the larva of Bugula avicularia imme- 
diately after escaping from the egg. After swimming 
about for a while as a spherical ciliated larva, with a bunch of 
larger cilia (flagellum) at one end, it elongates, looses its cilia and 
Fig. 159. 
PoTvzoon 
larva. 144 
LIFE HISTORIES OF ANIMALS 
flagellum, and soon the polypide grows inside, the stomach and 
tentacles arise, and finally the polypide is formed. 
In conclusion, the Polyzoa increase (a) by budding, (b) by 
normal eggs and winter eggs. In reproducing from eggs the 
young passes through : 
1. Morula state. 
2. Trochosphere, much as in certain worms and mollusks, attain- 
ing the 
3. Adult condition (zooecium). 
LITERATURE. 
Smitt. Bidrag till Kannedomen om ITafs-Bryozoernas utveekling. 
Om Hafs-bryozoernas utveckling och Fettki'oppar. (Ofversigt af K. Vet. 
Akad. Forh. 1805.) 
Nitsche. Beitrage zur Anatomie und Entwickelungsgeschichte der phylactolamen 
Siisswasserbryozoen. (Archiv fiir Anat. u. Phys. 1868.) 
Beitrage zur Kenntniss der Bryozoen. (Siebold und Kdlliker’s Zeitsclirift, 
1871.) 
Clapare.de. Beitrage zur Anatomie und Entwicklungsgeschichte der Seebryozoen. 
(Siebold und Kolliker’s Zeitschrift, 1870.) 
Coueult also papers by Grant, Loven, Huxley, Hyatt and Hincks. 
XXIII. THE BRACHIOPODA. 
While the Brachiopods have been regarded by many as closely 
related to the Polyzoa, there are many features, as insisted on by 
Prof. Moi •so, which closely ally them to the Chaetopod worms. In 
his treatise “On the sjstematic Position of the Brachiopoda,”1 
Morse has given conclusive reasons for removing them from the 
mollusks and placing them among the worms, and even, in his 
opinion, among the Chaetopods, the highest division of worms, 
lie thus, after giving the anatomical facts in his view sustaining 
his position, concludes that ancient Chfetopod worms culminated 
in two parallel lines, on the one hand, in the Brachiopods, and 
on the other, in the fixed and highly cephalized Chmtopods. 
On the other hand Mr. A. Agassiz, swayed b}r their relationship 
to the Polyzoa, remarks that “the close relationship between 
Brachiopods and Bryozoa cannot be more fully demonstrated than 
by the beautiful drawings on PI. v., of Kowalevsky’s history of 
Thecidium. We shall now have at least a rational explanation of 
the homologies of Brachiopods, and the transition between such 
types as Pedicellina to Membranipora and other incrusting Bry- 
ozoa, is readily explained from the embryology of Thecidium. In 
1 Proceedings of the Boston Society of Natural History, xv, 187-5. THE BRACHIOPODA. 
145 
fact, all incrusting Bryozoa are only communities of Brachiopods, 
the valves of which are continuous and soldered together, the flat 
valve forming a united floor, while the convex valve does not 
cover the ventral valve, but leaves an opening more or less orna- 
mented for the extension of the lophopliore.”1 
In his first paper on the “Earlier Stages of the Terebratulina” 
Morse had shown the same relationship between the young Braeh- 
iopod and the Pedicellina. 
The two commonest forms on our coast are the Terebratulina 
septentnonalis, found attached to stems or shells in the seas of 
New England, while the Lingula pyrimidata (Fig. 160, A, with the 
peduncle perfect, retaining a portion of the sand tube; B, showing 
the valves in motion, the peduncle broken and a new sand case be- 
Fig. 160. 
C 
B 
A 
Lingula pyrimidata. After Morse 
ing formed ; C, the same with the peduncle broken close to the body, 
after Morse) is common in sand between tide marks, from North 
Carolina to Florida. It is usually free, but sometimes attached. 
Development of the Bracliiopods. The life-liistory, from the 
time that it leaves the egg until it attains maturity, of our com- 
mon lampsliell, Terebratulina septentrionnlis, has been told by Prof. 
Morse. Before his account appeared our knowledge was ex- 
tremely fragmentary. Morse believes that in all the Braclnopods 
the sexes are separate. The eggs (Fig. 162, A), he says, as in the 
Annelida, when arrived at maturity, escape from the ovaries into 
the general cavity of the body, and are thence gathered up by 
the segmental organs, or oviducts, and discharged into the sur- 
rounding water. Whether they are fertilized after they leave the 
1 Amer. Journ. Sc. and Arts, Dec., 1874. 
LIFE HISTORIES OF ANIMALS. 146 
LIFE HISTORIES OF ANIMALS. 
parent or before, is not settled. In a few hours after they are 
discharged the embryos hatch and become clothed with cilia. The 
earliest stages of the egg of Bracliiopods before the larva hatches, 
were studied by Kowalevsky after the publication of Morse’s re- 
searches. The Russian zoologist observed in the egg of The- 
cidium the total segmentation of the yolk (also observed in Tere- 
bratulina by Morse), until a blastoderm (ectoderm) is formed 
around the central segmentation cavity, which contains a few cells. 
The similar formation of the blastoderm was seen in Argiope, 
but not the morula stage. After this the ectoderm invaginates 
and a cavity is formed, opening externally by a primitive mouth. 
The walls of this cavity now consist of an inner and outer layer 
(the endoderm and ectoderm). This cavity eventually becomes 
the digestive cavity of the mature animal. After this the devel- 
opment goes on as previously described by Morse, Kowalevsky’s 
discoveries confirming those of the former observer. 
Iii Terebratulina Morse observed that the oval ciliated germ 
became segmented, .dividing into two and then three rings, with a 
tuft of long cilia on the an- 
terior end (Fig. 1G1, A). 
In this stage the larva is 
quite active, swimming rap- 
pidly about in every direc- 
tion. 
Soon after, the germ 
looses its cilia and becomes 
attached at one end as in Fig. 161, B (c, cephalic segment; th, 
thoracic segment; p, peduncular or caudal segment). The tho- 
racic ring now increases much in size so as to partially enclose 
the cephalic segment, as at Fig. 161, C. The form of the Brachi- 
opod is then soon attained, as seen in Fig. 161, D, in which the 
head (c) is seen projecting from the two valves of the shell (th), 
the larger being the ventral plate. 
Fig. 161. 
Larval stages of Terebratulina. 
The hinge margin is broad and slightly rounded when looked at 
from above; a side view however, presents a wide and flattened 
area, “as is shown in some species of Spirifer, and the embryo for 
a long time assumes the position that the Spirifer must have as- 
sumed.” Before the folds have closed over the head, four bundles 
of bristles appear; these bristles ai*e delicately barbed like those 
of larval worms. The arms, or cirri, now bud out as two promi- THE BRACHIOPODA. 
147 
nences, one on each side of the mouth. Then as the embryo ad- 
vances in growth the outlines remind one of a Leptama, an ancient 
genus of Brachiopods, and in a later stage the form becomes 
“ quite unlike any adult Brachiopod known.” 
The deciduous bristles are then discarded, and the permanent 
ones make their appearance, two pairs of arms arise, and now the 
shell in “ its general contour recalls Siphonotreta, placed in the 
family Discinidse by Davidson, a genus not occurring above the 
Silurian.” No eye spots could be seen in Terebratulina, though 
in the young Thecidium they were observed by Lacaze-Duthiers. 
The young Terebratulina differs from Discina of the same age in 
being sedentary, wThile, as observed by Fritz Muller, the latter 
“swims freely in the water some time after the dorsal and ventral 
plates, cirri, mouth, oesophagus and stomach have made their 
appearance.” Discina also differs from Terebratulina in having a 
long and extensible oesophagus and head bearing a crown of eight 
cirri or tentacles. Regarding the relations of the Brachiopods 
with the Polyzoa, Morse suggests that there is some likeness be- 
tween the embryo Brachiopod, and the free embryo of Pedicellina. 
Fig. 162, B, represents the Terebratulina when in its form it re- 
calls Megerlia or Argiope. C represents a later Lingula-like stage. 
“It also suggests,” says Morse, “in its movements the nervously 
acting Pedicellina. In this and the several succeeding stages, 
the mouth points directly backward (forward of authors), or away 
Fig. 162. 
Later stages of Terebratulina. 
from the perpendicular end (D) and is surrounded by a few cili- 
ated cirri, which forcibly recall certain Polyzoa. The stomach and 
intestine form a simple chamber, alternating in their contractions 
and forcing the particles of food from one portion to the other.” 
Figure 162, E, shows a more advanced stage, in which a fold is 
seen on each side of the stomach ; from the fold is developed the 148 
LIFE HISTORIES OF ANIMALS. 
complicated liver of the adult, as seen in E, which represents the 
animal about an eighth of an inch long. The arms (lophophore) 
begin “to assume the horse-shoe-shaped form of Pectinatella and 
other high Polyzoa. The mouth at this stage begins to turn to- 
wards the dorsal valve (ventral of authors), and as the central lobes 
of the lophophore begin to develop, the lateral arms are deflected as 
in F. In these stages (G) an epistome1 is very marked, and it was 
noticed that the end of the intestine was held to the mantle by an 
attachment, as in the adult, reminding one of the funiculus in the 
Phylactolaemata” (Potyzoa). Turning now to Kowalevsky’s me- 
moir, he shows, according to Mr. A. Agassiz, that the larvae of 
Brachiopods are strikingly like those of the Annelides. “The 
homology between the early embryonic stages of Argiope with 
well known Annelid larvae is most remarkable, and the resem- 
blance between some of the stages of Argiope figured by Ivowa- 
levsky and the corresponding stages of growth of the so-called 
Loven type of development among Annelides is complete. The 
number of segments is less, but otherwise the main structural 
features show a closeness of agreement which will make it diffi- 
cult for conchologists hereafter to claim Brachiopods as their 
special property. The identity in the ulterior mode of growth 
between the embryo of Argiope and of Balanoglossus, in the 
Tornaria stage, is still more striking. We can follow the changes 
undergone by Argiope while it passes through its Tornaria stage, 
if we may so call it, and becomes gradually, by a mere modifica- 
tion of the topography of its organs, transformed into a minute 
pedunculated Brachiopod, differing as far from the Tornaria stage 
of Argiope as the young Balanoglossus differs from the free swim- 
ming Tornaria. In fact, the whole development of Argiope is a 
remarkable combination of the Loven and of the Tornaria tj'pes 
of development among worms.” 
At the close of liis first memoir Morse again insists on the close 
relationship of the Brachiopods and Polyzoa; these views, taken 
with his later views as to the close relationship of Lingula with 
the Chsetopod worms, show how intimately the Polyzoa and Brach- 
iopods are bound together with the Annelides. 
1 The free lip seemed to perform all the functions pertaining to the epistome in the 
higher Polyzoa, and we find it on the inner bend of the arms, as in the Polyzoa, though 
not occupying the same homological position in regard to the flexure of the intestine.” 
Early Stages of Terebratulina, p. 34. THE BRACHIOPODA. 
149 
It will be seen that neither in the Polyzoa nor Brachiopods are 
there any true molluscan characters, nothing homologous with the 
foot, the shell gland or odontophore. The Brachiopods should in 
our opinion be, perhaps, united with the Polyzoa and form a group 
lower but sub-parallel with the Annelides. The Brachiopods, from 
the facts afforded by Morse and others, have neither such a nervous 
system or respiratory or circulating organs, or an annulated body, 
as would warrant their union with the Cluetopods. Morse has 
fully proved that they are a synthetic type, combining the features 
of different groups of worms, and this fact apparently forbids their 
being regarded as a group of Chcetopods. Looking at the subject 
from an evolutional point of view, we should be inclined to regard 
the Brachiopods and Polyzoa as derived from common low vermian 
ancestors, while the Clnetopod worms probably sprang indepen- 
dently from a higher ancestry. 
To sum up, the Brachiopods pass through :— 
1. A morula state. 
2. A free swimming, ciliated Gastrula condition, formed by in- 
vagination of the ectoderm. 
3. Free swimming larval annulate Cephalula stage, combining 
the characters of the larva of Nareda, and of Tornaria the larva 
of Balanoglossus. 
Morse. On the Early Stages of Terebratulina septentrionalis. (Memoirs Boston Soc. 
Nat. Hist., 1869.) 
. Embryology of Terebratulina. (Memoirs Bost. Soc. Nat. Hist., 1873). 
Kowalevsky. Investigations upon the Development of Braehiopoda, Moscow, 1874. 
With papers by Oscar Schmidt, Lacaze-Duthiers, F. Miiller and McCrady. 
LITERATURE. 150 
LIFE HISTORIES OF ANIMALS. 
XXIV. THE TUNICATA. 
Like the Polyzoa and Bracliiopods, the Ascidians may be said 
to be worms in disguise. The singular test easily confounded 
with the mantle of mollusks, the excurrent and incurrent orifices 
like those of the clam, led naturalists to regard them as low shell- 
less mollusks, but the structure of more important organs, and 
the mode of development of these animals, so unlike that of mol- 
lusks, has led some of our leading naturalists (Gegenbaur, Haeckel 
and Ussow) to decide that they should be placed among the 
worms ; while so high an authority in zoology as Prof. Oscar 
Schmidt regards them as not only not mollusks, but as the imme- 
diate vermian ancestors of the vertebrates, and as forming a dis- 
tinct group of animals which he terms Pro-vertebrata. 
One of the most important characters indicating the true affini- 
ties of the ascidians, is the sieve-like pharynx, a prolongation of 
the digestive canal, resembling that of Balanoglossus. The ner- 
vous system, like that of many low worms consists of a single 
ganglion, and not a chain of them surrounding the oesophagus as 
in the mollusks. In the tad-pole like Appendicularia, which re- 
sembles the larval ascidians, there is a chain of caudal ganglia 
from ten to eighteen in number, united by means of a nerve sent 
out from the ganglion in the head. Moreover the heart is a sim- 
ple tube like that of some articulates. Besides the vermian char- 
acters there are some remarkable larval organs which suggest an 
affinity with Amphioxus and the lower vertebrates. It would thus 
seem that except in the more secondary external, superficial char- 
acters there is no good reason for the prevalent 
opinion that ascidians are mollusks. 
At first sight the typical ascidians look like any- 
thing but worms. Fig. 1G3 (from Verrill’s Report) 
represents Molgula Manliattensis, of the natural 
size. It looks like a double-necked bottle when 
the two orifices are thrust out. The viscera are 
enclosed by a thick test or tunic, whence the name 
of the class, Tunicata. This test is rendered 
tough and dense by the presence of cellulose, a substance secreted 
usually by vegetable cells, and very rarely found in animals. 
There are two orifices, the most anterior corresponding to the 
Fig. 1C3. 
Molgula. THE TTJNICATA. 
151 
mouth, and the posterior leading into the anus. The alimentary 
canal is much bent on itself. The opening of the pharynx is sur- 
rounded by a fringe of tentacles, arising from the peritoneum or 
lining membrane next to the outer test. The capacious pharynx 
is perforated with slits, and serves as a respiratory cavity compar- 
able with that of the worm, Balanoglossus. At the bottom of this 
respiratory sac opens the true mouth, which communicates by an 
oesophagus with the stomach, while the intestine is twisted so that 
the anus opens near but posterior to the mouth. There is a ner- 
vous ganglion on the dorsal side of the body situated at a point 
between the two external orifices, sending threads to the two 
openings in the test and the pharynx. The heart is a short tube 
open at both ends. Its action may be beautifully seen in the 
transparent Perophora of our coast. The current of blood is 
momentarily reversed, so that each end becomes, as Huxley re- 
marks, “alternately arterial and venous.” 
Such in general terms is the structure of a typical simple 
ascidian as wrell as the compound ascidians, and the Pyrosoma 
and Salpa. The aberrant Appendicularia is, as has been observed, 
provided with a tail, and resembles the tailed young of the higher 
ascidians. 
The ascidians are, for the most part, hermaphrodites, the ovary 
and testis being lodged in the same individual. 
Development. While Milne-Edwards discovered that the larvae 
of certain ascidians were tad-pole like, Kowalevsky, in 1866, 
studied the development of the ascidians and threw a flood of 
light on their history. The following account is an abstract of 
his classic memoir. The early stages of most ascidians is typified 
by the mode of growth of Phallusia mamillata Cuv., while the 
mode of growth from the free swimming larval period to the adult 
was traced in Ascidia intestinalis. Kowalevsky’s discoveries were 
confirmed by Kupffer and others, while exceptional modes of de- 
velopment were pointed out by Lacaze-Duthiers and also Kupffer, 
who found that the larvae of Molgula have no tail. 
While some ascidians, such as Perophora, increase by budding, 
creeping by stolons along the fronds of sea-weeds, the common 
method of reproduction is by eggs and sperm cells. The eggs of 
Phallusia and the ascidians consist of a yolk, not protected by a 
yolk-skin, but surrounded by a layer of jelly containing yellow 
cells. 152 
LIFE HISTORIES OF ANIMALS. 
After fertilization by the sperm cells, which enter the substance 
of the egg tail-foremost, the yolk undergoes total segmentation. 
The next step is the invagination of the ectoderm, a true Gastrula 
state resulting. Fig. 164, A (after Kowalevsky), represents the 
Gastrula; h, the primitive digestive cavity ; a, the primitive open- 
ing, which soon closes ; and c, the segmentation-cavity or primitive 
body-cavity. After this primitive opening (a) is lost to view, 
sometime before the embiyo lias reached the stage B, another 
cavity («) appears with an external opening. This cavity is 
Fig. 164. 
Embryo Ascidian 
formed by a union of two ridges which grow out from the upper 
part of the germ. This is the central nervous system, and in the 
cavity are subsequently developed the sense-organs. We thus 
see, says Kowalevsky, a complete analogy in the mode of origin 
of the nervous system of the ascidians to that of the vertebrates, 
the nervous cavity, where the embryo is seen in section, being 
situated above the digestive cavity in both types of animals. 
The next important stage is the formation of the tail. The pear- 
shaped germ elongates and contracts posteriorly until of the form in- 
dicated at Fig. 164, B (i, pharynx ; t, epithelium forming the body- 
wall). At this period appears the axial string of nucleated cells, 
called the chorda dorsalis, as it is homologous with that organ in 
Amphioxus and the embryo of higher vertebrates. The nervous 
system consists of a mass of cells extending halfway into the 
tail and directly overlying the chorda, but extending far beyond 
the end of the latter as seen in the figure. The nerve-cavity (B, n) 
after closing up forms the nerve-vesicle, a large cavity (Fig. 165, a) 
in which the supposed auditory organ (e) and the supposed eye (a) 
arise; this cavity finally closes, and the sense-organs are indicated TIIE TUNICATA. 
153 
b}1 certain small masses of pigment cells in the fully grown ascidian 
larva. 
As the embryo matures, the first change observed in the cord is 
the appearance of small, highly refractive bodies between the cells. 
Between the neighboring cells soon appear in the middle minute 
highly refractive corpuscles which increase in size, and press the 
cell-contents out of the middle of 
the cord. After each reproduc- 
tive corpuscle grows so that the 
central substance of the cell is 
forced out, it unites with the oth- 
ers, and then arises in the mid- 
dle of the simple cellular cord a 
string of bodies of a firm gelati- 
nous substance which forms the 
support of the tail. After this co- 
alescence the substance develops 
farther and presses out the pro- 
toplasm of the cells entirely to 
the peripheiy. The cord when 
complete consists of a firm ge- 
latinous substance surrounded 
by a cellular sheath which is 
formed of the remains of the 
cells originally comprising the 
rudimentary cord. The cells ly- 
ing under the epithelial layer 
form a muscular sheath of which 
the cord (Fig. 165, c) is the sup- 
port or skeleton. 
The alimentary cavity arises 
from the primitive cavity (Fig. 
164, A, h) ; whether the primitive 
opening (Fig. 164, A, a) is closed 
or not, Kowalevsky says is an 
interesting question. According to analogy with many other ani- 
mals it probabty closes. In Sagitta, Phoronis, Limnseus, Echinus 
and others, we know that the opening which remains after the first 
invagination becomes the anus. 
Fig. 105. 
Larval Ascidian. 
The larva hatches in from forty-eight to sixty hours after the 154 
LIFE HISTORIES OF ANIMALS. 
beginning of segmentation, and is then of the form indicated by 
Fig. 165 (copied with some additions and omissions from Kupffer’s 
figure, being partly diagrammatic). This anatomist discovered 
in the larva of Ascidia canina, which is more transparent than 
Kowalevsky’s Phallusia larva, not only a central nervous cord 
overlying the chorda dorsalis and extending well into the tail, 
while in the body of the larva it becomes broader, club-shaped 
and surrounds the sensitive cavity (a), but he also detected three 
pairs of spinal nerves (s) arising at regular intervals from the 
spinal cord (h, h') and distributed to the muscles (not represented 
in the figure) of the tail; Kupffer calls / the middle and g the 
lower brain-ganglion. The pharynx (6), or respiratory sac, is now 
very large ; it opens posteriorly into the stomach and intestine (i) ; 
x represents one of the three appendages by which the larva 
fastens itself to some object when about to change into the adult, 
sessile condition; t indicates the body-wall, consisting of epi- 
thelial cells. 
We will now, from the facts afforded us by Ivowalevsky, trace 
the changes from the larval, free-swimming state to the sessile 
adult Ascidia, which may be observed on the New England coast 
in August. After the larva fastens itself by the three processes 
to some object, the chorda dorsalis breaks and bends, the cells 
forming the sheath surrounding the broken axial cord. The mus- 
cular fibres degenerate into round cells and fill the space between 
the chorda and the tegument, the jelly-like substance forming a 
series of wrinkles. With the contraction and disappearance of 
the tail begins that of the nerve-vesicle, and soon no cavity is 
left. The three processes disappear ; the pharynx becomes quad-; 
rangular; and the stomach and intestine are developed, being bent 
under the intestine. A mass of cells arises on the anterior end be- 
neath the digestive tract, from which originate the heart and peri- 
cardium. In a more advanced stage two gill-lioles appear in the 
pharynx, and subsequently two more slits, and at about this time 
the ovary and testis appear at the bottom, beyond the bend of the 
alimentary canal. The free cells in the body-cavity are trans- 
formed into blood cells, and indeed the greater part of those which 
composed the nervous system of the larva are transformed into 
blood corpuscles. Of the embryonal nervous system there re- 
mains a very small ganglion, no new one being formed. The THE TENICATA. 
155 
adult ascidian form meanwhile has been attained and the very 
small individuals diflfer for the most part only in size from those 
which are full-sized and mature. 
It will be seen that some highly important features, recalling 
vertebrate characteristics, have occurred at different periods in the 
life of the embryo ascidian. Kowalevsky remarks that “the 
first indication of the germ, the direct passage of the segmenta- 
tion cells into the cells of the embryo, the formation of the seg- 
mentation cavity, the conversion of this cavity into the body 
cavity, and the formation of the digestive cavity through invag- 
ination— these are all occurrences which are common to many 
animals and have been observed in Ampliioxus, Sagitta, Phoronis, 
Echinus, etc. The first point of difference from other animals in 
the development of all vertebrates is seen in the formation of the 
dorsal ridges and their closing to form a nerve-canal. This mode 
of formation of the nervous system is characteristic of the verte- 
brates alone, except the Ascidians. Another primary character 
allying the Ascidians to the vertebrates, is the presence of a 
chorda dorsalis, first seen in the adult Appendicularia by J. 
Muller. This organ is regarded by Kowalevsky to be functionally, 
as well as genetically, identical with that of Ampliioxus. This 
was a startling conclusion, and stimulated Professor Kupffer of 
Kiel to study the embiyology of the ascidians anew. He did so, and 
the results this careful observer obtained, led him to fully endorse 
the conclusions reached by Kowalevsky, particularly those regard- 
ing the unexpected relations of the ascidians to the vertebrates, 
and it would appear from the facts set forth by these eminent ob- 
servers, as well as Metschnikoff, Ganin, Ussow and others, that the 
vertebrates have probably descended from some type of worm re- 
sembling larval ascidians more perhaps than any other vennian 
type, though it is to be remembered that certain tailed larval Dis- 
tomse appear to possess an organ resembling a chorda dorsalis, 
and farther investigation on other types of worms may lead to 
discoveries throwing more light on this intricate subject of the 
ancestry of the vertebrates. At any rate, it is among the lower 
worms, if anywhere, that we are to look for the ancestors of 
the vertebrates, as the Coelenterates, Echinoderms, the Mollusks, 
Crustacea and Insects, are too circumscribed and specialized 
groups to afford any but characters of analogy rather than affinity. 156 
LIFE HISTORIES OF ANIMALS. 
For example, the cuttle fish, with its “bone” and highly devel- 
oped eye, is far more remote from the lowest fish, Ampliioxus, than 
the Appendicularia or larval Ascidia. 
Not all Ascidians have tailed larvae; three species of Molgula 
have been found to have no tailed young and to attain maturity 
by direct growth. The jToung have five temporary, long, slender 
processes. Now as in other types of animals, as we have already 
seen, some forms have a metamorphosis and others attain the 
adult condition by direct growth. Professor Kupffer tells us that 
in Ascidia ampulloides, as observed by Van Beneden, the young 
has a tail, a chorda dorsalis and pigment spots, which are want- 
ing in the young of several species of Molgula, but it has the 
five long, deciduous appendages ob- 
served in young Molgulae. Among the 
compound Ascidians, Botrjdlus and Bo- 
trylloides have tailed young, while in 
other forms there is no metamorphosis. 
Besides the normal mode of reproduc- 
tion, from eggs, it was discovered by 
Cliamisso, in 1819, that the singular 
Salpa reproduced by budding; that in 
other words there was an alternation of 
generations, there being a sexual, soli- 
tary individual which gives rise by bud- 
ding to chains, or aggregations of simple 
individuals, which reproduce by eggs. 
The startling announcement of the poet- 
naturalist, “ that a Salpa mother is not 
like its daughter or its own mother, but 
resembles its sister, its granddaughter and its grandmother,” was 
combated at first, but stated to be true by Sars, Krohn and 
others. Mr. W. K. Brooks however, claims that the solitary 
females produce chain ! of males by budding, and discharge an 
egg into each male before the birth of the latter, the eggs being 
impregnated while the males are undeveloped. After the embryos 
have been discharged from the bodies of the males, the latter grow 
Fig. 1G6. 
1 Fig. 219. Salp • Cabotii, an individual from a mature chain, three-quarters view 
enlarged; a posterior or anal opening; b, anterior or branchial opening; c, processes 
by which the individuals of the chain were united; h, heart; n, nervous ganglion; 
o, nucleus; r, gill. After A. Agassiz, from Terrill’s Report. THE GEPHYREA. 
157 
up, become sexually mature and discharge their spermatic parti- 
cles into the water, by which they are carried to the eggs within 
the bodies of the males composing the younger chains. 
The Tunicates undergo, then, the following changes: 
1. Morula state, or total segmentation of the yolk. 
2. Gastrula. 
3. Free-swimming tailed larva (or as in Molgula, no metamor- 
phosis). 
4. Adult, reproducing sometimes by budding (Parthenogenesis). 
LITERATURE. 
Chamisso. De Animalibus quibusdam e classe Vermium, etc. Berlin, 1819. 
Milne-Edwards. Observations sur les Ascidies composees des Cotes de la Manche. 
Paris, 1841. 
Kowalevsky. Entwickelungsgeschichte der einfachen Ascidien. (Mem. Acad. St. 
Petersburg. X. No. 15. I860). 
Kupffer. Die Stammvenvandtschaft zwischen Ascidien und Wirbelthieren. 
(Schultze’s Archiv flir micr. Anat., vi, 1870). 
. Zur Entwickelung der einfachen Ascidien. (Schultze’s Archiv. viii, 1872). 
Consult also papers by Sars, Krohn, Huxley, Leuckart. Vogt, Lacaze-Duthiers, 
Ussow and W. K. Brooks. (Proceedings Bost. Soc. Nat. Hist., 1870.) 
XXV. GEPIIYREA (Sipunculus). 
There are two points of interest connected with these singular 
worms, i. e., the fact that they were formerly associated with the 
Holothurians, and that their free-swimming Actinotrocha larva so 
closely resembles the young Echinoderms. The Sipunculus usu- 
ally lives in broken shells, building out the mouth with a tube of 
sand; the anus is situated near the mouth, while in Priapulus it is 
situated at the end of the body. In none of these worms are 
there bristles, or indications of segments, and they in their gen- 
eral appearance with their tentaculated mouth, resemble certain 
Holothurians, as Synapta. Most of these worms are bisexual, 
Sipunculus however, or at least certain species of the genus, being 
hermaphroditic. 
Development. The free-swimming larva of Sipunculus was first 
discovered and named “ Actinotrocha” by J. Muller. It is re- 
lated closely in form to Echinoderm larvae, as well as to the Pili- 
dium and other larvae of the Nemertian worms. The fully grown 
larva is much like the larval Nemertian noticed on p. 132, fig. 141, 
the disposition of the digestive canal being the same, while on 
the head is a large umbrella-like expansion, and behind the mouth 
and on the end of the body is a c bated baud and twelve arm-like 158 
LIFE niSTORIES OF ANIMALS 
projections, like those in certain Ecliinoderm larvm. In all re- 
spects the Actinotroclia is a true Ceplialula. 
We will now, with Metschnikoff, follow the life-history of the 
Actinotroclia. The earliest stage he observed was when the larva 
had a transparent, ciliated bod}', with an umbrella-like expansion 
on the head, covering the mouth region, while the end of the bod}' 
was truncated. The young at this stage was much like a Plioronis 
larva. Soon four projections arise at the end of the body, and 
twelve long, arm-like projections grow out by the time the larva 
becomes mature. 
When the larva is about to transform into the Sipunculus, the 
end of the intestine bends up, opening outwards near the mouth. 
The umbrella is gradually withdrawn into the mouth, so that 
finally only a crown of short tooth-like projections surrounds the 
mouth. Finally the whole umbrella disappears in the oesophagus, 
is actually swallowed, while the arms on the end of the body 
are absorbed and disappear, and the end of the intestine projects 
far out from the body behind the mouth. By this time the Sipun- 
culus form is clearly indicated, the body being long and slender 
and the mouth surrounded by a crown of short tentacles, and the 
anal opening is withdrawn within the head. The change from the 
free-swimming larva to the sedentary worm is effected in a very 
short time. 
The Sipunculus, then, so far as its history is known, passes 
through a Cephalula stage before transforming into the adult 
worm. 
LITERATURE. 
Muller. Archiv fill- Anatomie, p. 103,1846. 
Metschnikoff. Ueber die Metamorphose einiger Seethiere. (Siebold und Rolliker’s 
Zeitschrift, p. 244, 1871.) 
Consult also papers by Wagener, Krohn, Schneider, Rowalevsky and Claparfede. 
XXVI. ANNUL AT A. 
The life-history of Balanoglossus, a peculiar worm found in fine 
sand along our whole coast from Cape Ann to Beaufort, North 
Carolina, is one of singular interest. Its free swimming larva was 
regarded by Muller, who discovered and called it Tornaria, as the 
young of some starfish. Later studies by eminent naturalists only 
seemed to confirm this opinion, until in 1869 Metschnikoff sug- 
gested that it might be the larva of the worm, first described 
under the name of Balanoglossus, or whale’s tongue, by Delle THE ANNULATA. 
159 
Cliiaji, and Mr. A. Agassiz fully confirmed the suggestion, giving 
an account of the intermediate stages between the larval and adult 
condition. 
The Tornaria (Fig. 1671 after A. Agassiz) seems in many re- 
spects like some cchinoderm larvse, differing from any yet known, 
however, in having an organ, the so-called heart (/t) situated at 
the base of the canal leading from the water system to the dorsal 
pore. The water system is very fully developed. Mr. Agassiz 
says that the natural position of Tornaria in the water while mov- 
ing, is usually with the eye-specks uppermost. “They revolve 
quite rapidly upon their longitudinal axis, and at the same time, 
Fig. 167. 
Fig. 1G8. 
Balanoglossus 
(immature). 
Tornaria, or young Balano- 
glossus. 
inclining this axis, advance by a motion of translation, or revolve 
upon either of the extremities as a fulcrum. Previous to the 
transformation of Tornaria it is quite transparent; the brilliant 
carmine, violet or yellow pigment-spots are closely crowded along 
the broad belt of anal vibratile cilia, as well as smaller spots on 
the longitudinal bands of smaller cilia. The eye-specks are black 
and extremely prominent. The large and powerful cilia of the 
broad anal belt move comparatively slowly, more like the cilia of 
the embryo of mollusks, as has already been observed by Muller.” 
The Tornaria soon throws off its disguise of a young Ecliino- 
derra, and now begins its strange transformations. Previous to 
i«, anus; ft, branch of water system leading to dorsal pore, d; e, eyespeck; g, 
gills; ft, heart; i, intestine; m, mouth; m', muscular band from eye to water tube; o, 
oesophagus; s, stomach or alimentary canal; w, lappet of stomach; u', anal band of 
cilia; w, water system. LIFE HISTORIES OF ANIMALS. 
any other change two gills develop from the round bag-shaped di- 
verticula of the rasophagus, and afterwards three more pairs of gill- 
slits arise, somewhat as in the young Ascidian. Agassiz then re- 
marks that the “ passage of Torn aria with the young Balano- 
glossus is very sudden, taking place in a few hours; but unlike 
the transition from the Pluteus into the Echinoderm, there is no 
resorbition of any portion of the larva.” The body lengthens, 
the proboscis is indicated and assumes much of the form of 
the adult, the four pairs of gills are well developed, the cilia drop 
off first, the longitudinal bands and finally the transverse ones, 
and then the collar becomes well marked. The young worm, for 
it rapidly assumes the adult Balanoglossus likeness, though much 
shorter proportionally, now instead of swimming “ creeps rapidly 
over the bottom by means of its proboscis, which acts as a sort of 
propeller taking in water at the minute opening of the anterior 
extremity of the proboscis, and expelling it through an opening 
on its ventral side immediately in front of the mouth.” 
Fig. 1G8, after Agassiz, represents the youngest stage found in 
the sand, but it differs from the adult simply in the shorter body 
and less distinct development of the collar, with fewer gills and 
other unimportant points of difference. 
There is considerable difference of opinion regarding the affini- 
ties of this worm. On first digging it out of the sand at Beaufort, 
N. C., it seemed to us a most anomalous form, the large soft pro- 
boscis, the singular gills, and the absence of setiform feet, appa- 
rently forbidding its relationship to the true Annelides. Yet its 
true position appears to be between the leeches and setiferous An- 
nelides, with some Nemertian analogies. The reader can choose 
between the opinion of Gegenbaur that this worm is the type of 
an order equivalent to the Annelides, or a true Annelid allied to the 
Terebrellidse, Clymenidm and allied Annelides, as suggested b}' 
Metschnikoff and Kowalevsky; or that of A. Agassiz who regards 
it as the type of a family intermediate between tubicolous Annel- 
ides and Nemertians.” 
Turning now to the lowest Annulata, the leeches, in which there 
are no bristles or gills, while each end of the body terminates in a 
sucker, it has been found by Rathke and Kowalevsky that their 
embryology is nearly identical with that of the earthworm, in 
which there are bristles. In the leeches the sexes are united in 
the same individual, except in the genus Malacobdella. The eggs 161 
TIIE ANNULATA. 
after fertilization undergo total segmentation. There is a primi- 
tive band much as in insects, and the adult form is attained before 
the animal is hatched. There is no metamorphosis. So with the 
earthworms. Kowalevsky studied the mode of development of 
two species. As nothing has heretofore been known of the life- 
history of so common a creature we will delay a moment to learn 
the results of the Russian naturalist’s observation. The eggs of 
the European Lumbricus agricola were laid while the worm was in 
confinement in January and February. They were laid in nu- 
merous capsules, sometimes as many as fifty eggs in a capsule, 
though usually only three or four embryos were to be found in a 
capsule. The egg-capsules of Lumbricus crubellus were found in 
dung. They were much smaller and contained but one egg. 
Segmentation is total, and after the embryo-cells are arranged 
in two layers, the innermost layer (endoderm), invaginates and 
forms a primitive cavity. The embryo at this time seems, then, 
not to correspond to the gastrula condition of other worms, al- 
though as in other worms, the Aseidians, Insects and Vertebrates, 
there are two primitive germ-lamella;. Later in embryonic life, 
a primitive band like that of insects (which will be described 
farther on), rests on the outside of the yolk, as in the leach (Ilirudo 
medicinal is). Finally, the form of the earthworm is attained 
before it breaks through the egg-shell, and it hatches without un- 
dergoing a metamorphosis, in a condition differing but slightly 
from that of the adult worm, so familiar to us, the body being pro- 
portionately shorter and thicker near the middle. 
We now come to the sea worms, or Annelides, in which there 
are external gills and often a complicated locomotive apparatus, 
consisting of fleshy oar-like projections from the body, and strong 
bristles. They have free-swimming larvae, which by a complicated 
metamorphosis, comparable with that of the Nemertian worms, 
attain the adult worm-condition. 
A singular type is Phoronis, which lives in a membranous tube 
attached to rocks, and recalls strikingly the appearance of a Poly- 
zoan, as it has a true lophophore and the intestine opens externally 
near the mouth. It is in fact a connecting link between the Annel- 
ides and the Polyzoa. Its life-history as told by Metsclmikoff is 
nearly identical with that of Sipunculus. 
We will now in a fragmentary way study the mode of develop- 
ment of certain typical Annelides, beginning with the lower forms. 
LIFE HISTORIES OF ANIMALS. 162 
LIFE HISTORIES OF ANIMALS. 
The common Spirorbis spirillum (Gould) whose minute nautilus- 
like shells cluster on the common Fueus of our coast, lays its eggs 
Fig. 170. 
Fig.171 
Fig. 169. 
Egg of 
Spirorbis. 
Larva of Spirorbis. 
Older larva of Spirorbis. 
in strings formed of two rows (Fig. 169, after A. Agassiz), and 
laid on the sides of the 
body within the shell. The 
young ciliated embryos may 
be seen in the eggs, the 
eye-spots being very dis- 
tinct. Fig. 170 (this and 
Figs. 171, 172, after A. 
Agassiz) represents the em- 
bryo just after hatching. 
It will be seen that it is 
already far advanced before 
leaving the egg, and 
siz thinks that the free- 
swimming life of the larva 
does not last more than 
from eight to ten hours, as 
“it frequently happens dur- 
ing a night that the smooth 
sides of the vessel are com- 
pletely covered with small 
limestone tubes, formed by 
the young Spirorbis hatched the evening before.” Fig. 170 repre- 
sents the young Spirorbis soon after its escape from the egg, 
Fig. 172, 
Young Spirorbis THE ANNULATA. 
163 
having only one tentacle (() developed on the right side. In a 
succeeding stage (Fig. 171) the opercular tentacle (to) which is 
destined to act as a door to the hole of the cell, begins to grow 
out, and there are two pairs of bristles. Shortly after this the 
young Spirorbis hatches, and before building its limestone tube 
assumes the form indicated by Fig. 172, in which there “are nine 
rings,” with tentacles nearly as branching as those of the adult, 
and a well formed operculum which with advancing age loses all 
trace of its former tentacular nature.” The subsequent changes 
are very slight. * 
The metamorphoses of the other sea worms are well marked, 
and the larval forms present a great variety of shapes. As a 
rule, perhaps, the eggs undergo total segmentation, and the em- 
bryo leaves the egg in the Cephalula condition, the head-end 
being large and full, with the alimentary canal more or less flexed. 
In some cases, as in TerebreUides Stroemii Sars, observed *>y 
Willemoes-Sulnn, the young leaves the egg as a Trochosphere, 
(“Atrocha” of Claparede and Metschnikoff, who observed the 
same stage in Lumbriconereis ?) like 
that of certain mollusks and the Poly- 
zoa, being spherical, with a long, ce- 
phalic tuft of cilia, two eye-spots, and a 
zone of cilia, but without any bristles. 
Others, as in Leucodora, are similar, but ,.3 
provided with a few long set;e, which act r" 
as oars. 
The early stages of the embryo have 0 
not yet been studied,' so that we are not 
in possession of any certain knowledge 
regarding the development of the em- 
bryonal membranes and the presence or absence of a gastrula 
condition. 
Fig. 173. 
Young Polydora. 
Soon after the larva leaves the egg, branches of bristles appear 
and the body is divided into segments. Fig. 173 (this and Figs. 
174, 175, 176, 177, 178, after A. Agassiz) represents an advanced 
larva of Polydora. Fig. 174 and 175, illustrate the early stages 
of Nerine. 
The early stages of Phyllodoce metadata are indicated by figures 
176, 177, 178. The subsequent changes are not important, con- 
sisting chiefly of the addition of a great number of segments and LIFE HISTORIES OF ANIMALS 
the growth of smaller bristles. IIow the adult forms appear may 
be known by a glance at the accompanying figures of certain sea 
worms of our coast described and figured by Prof. Verrill, from 
Fig. 175 
Fig. 174. 
Young Nerine. 
Older Nerine 
whose reports the figures are taken. Fig. 179, represents Cly- 
menella torquatci, 180, Euclione elegans, and fig. 181, a not un- 
common and very elegant worm, Cirratulus grandis. 
Besides the normal mode of reproduction by eggs, certain 
Fig. 170. 
Fig. 177. 
Young 
Phyllodoce. 
Side view of 
Fig. 229. 
Advanced young 
of Phyllodoce. 
worms reproduce by self-division or budding; sucli are Nais, 
Sabella, Filograna, Protula, Syllis, Autolytus, and others. In the 
latter worm as well as in Syllis there is, according to A. Agassiz, THE ANNULATA. 
165 
an alternation of generations, an asexual form giving rise to male 
and females, while these sexual and asexual forms are so unlike 
each other as to pass for different species and even genera. 
The Annulata, then, to sum up what is known of their life- 
Fig. 179. 
Fig. ISO. 
Clymenella tor- 
quata. 
Euchone elcgans. 
history, besides reproducing by budding and parthenogenetically, 
usually kiy eggs, and pass through the following stages: 
1. Morula state. 
2. (not observed). 
3. Atrocha or Troehosphere. 
4. Cephalula 
5. Adult. 
Milne-EiJwarcls. Observations sur le Development des Annelides. (Ann. Se,. Nat. 
Ill, 145, 1815). 
Sars. Zuv Entwickelung der Annelidcn (Archiv lur Naturg. T. i, 11, 1845). 
Busch. Beobaclitungen ueber Anat. und Entwickelung einiger Wirbelloser Tbiei’e. 
Berlin, 1851. 
Rathke. Beitriige znr Entwicklungsgeseliichte der Ilirndineen. Leipzig, 18G2. 
LITERATURE. LIFE HISTORIES OF ANIMALS. 
A. Agassiz. On alternate Generations in Annelides. (Jour. Bost. Soc., N. II. vii, 
18(52.) 
Clapare.de. Beobachtungen ueber Anat. und Entwicklungsgeschichte Wirbelloser 
Tliiere, etc. Leipzig. 186:1. 
and Metsclinilcoff. Beitrage zurKenntniss der Entwickelungsgeschielite 
der Chaetopoden. (Siebold and Kolliker’s Zeitsehrift, 1S68). 
Compare also tlie writings of Loven, A. Agassiz and Kowalevsky. already cited, and 
papers by Krohn, Leuckart and Pagens.teclier, Frey and Leuckart, Scluiltze, J. and 
Max. Mtiller, Busch and Willemocs-Suhm. 
Fig. 181. 
Oirratulus grandis. THE CRUSTACEA. 
167 
Having left the worms, we come now to a more circumscribed 
group of articulated animals, in which the jointed body is protected 
by a more or less dense tegument. Moreover there are attached 
to the bod}’ jointed appendages, serving as feelers, jaws or legs. 
The barnacles, water fleas, shrimps and crabs are tolerably fa- 
miliar forms, and therefore we will not pause to discuss the anatomy 
and classification of these animals, merely premising our account 
of their development with the following tabular view of the main 
divisions of the group : ' 
XXVir. THE CRUSTACEA. 
CRUSTACEA. 
SUBCLASS I. 
SUBCLASS II. 
Decapoda (Lobsters and Ciabs). 
Tetradecapoda (Sow Bugs, Beach 
Fleas). 
Neraeiad/E (Shrimp-like forms). 
PhyllopodA (Leaf-footed Shrimps). 
Cladocera (Water-fleas). 
Ostracoda (Bivalved Water-fleas). 
Copepoda, including Sipiionostoma. 
Cirripedia including Rhizocephai.A 
(Barnacles). 
Trilobita. 
Merostomata (King Crab). 
Development of the Barnacles. Before we turn to the life-his- 
of the barnacles, let us look for a moment at the mode of 
development of those strange parasites, the Rhizoeephala, whose 
larval feet become by a retrograde process of development con- 
verted into long irregular root-like extensions which ramify in the 
body of their host. The animal itself, as it adheres by means of 
its root-like feet to the under side of the abdomen of the crab on 
which it lives, would be readily mistaken for a large wart or 
sausage-like bunch. This shapeless mass is the mature Rhizo- 
cephalon, apparently the last term in the series of degradational 
forms so numerous among the lower Crustacea. This sac-like body 
is filled with eggs. 
After total segmentation the embryo rapidly grows and hatches 
in an oval form with no distinct head, but with an oval shield-like 
disk covering the insertion of the three pairs of jointed swimming 
feet, ending in long bristles which aid in locomotion. This larval 
Rhizocephalon is comparable with the young of the water-fleas or LIFE HISTORIES OK ANIMALS. 
copepods, called “Nauplius’ (see also Fig. 203), but differs 
from them in the shield-like expansion of the body, and in the 
presence of a distinct abdomen ending in a movable caudal fork. 
But however well developed is the body generally, the young root- 
barnacles, as we may term them, have no mouth, or so far as 
known, stomach or intestine, so that after swimming about freely 
for a few days, they change into the “pupa” state, in which they 
bear a remote resemblance to the bivalved Ostracodes. 
The broad shield of the larva has now become folded together 
like the covers of a pamphlet, enclosing the body of the pupal 
root-barnacle. The foremost limbs (to avail ourselves of Fritz 
Muller's description in his “Facts for Darwin”) have become 
transformed into very peculiar adherent feet (prehensile antennae 
of Darwin). From the ends of these feet grow out two filaments 
which are possibly, as Muller suggests, the “commencements of 
the future roots.” The two following pairs of feet are rejected, 
six pairs of forked swimming feet have meanwhile grown out on 
the abdomen, while the tail ends in two short appendages. These 
pupae are also mouthless and soon attach themselves by means of 
their adherent feet to the abdomens of crabs and hermit crabs. 
The other feet drop off, the fihwnents grow down into the body of 
their host, entwining around the intestine or ramifying through 
the liver. “The onty manifestations of life which persist in these 
non plus ultras in the series of retrogressively metamorphosed 
Crustacea, are powerful contractions of the roots, and an alter- 
nate expansion and contraction of the body, in consequence of 
which water flows into the brood-cavity and is again expelled, 
through a wide orifice” (Muller). 
Such is the ordinary history of a Peltogaster or Sacculina, but 
Mr. Darwin tells us of another form (Cnjptophialas minutus) 
which undergoes the larval state in the egg, hatching in the pupa 
condition, while another form (a species of Peltogaster?) also 
leaves the egg in the pupa form. 
The barnacle has a somewhat similar life-history. It passes 
through a stage of total segmentation of the yolk and hatches as 
a Nauplius-like free-swimming larva, but differs from the llhizo- 
cephalus larva in having a mouth, stomach and intestine, while 
the body is covered by a triangular shield, the anterior corners of 
which are prolonged into horns, while the posterior angle extends 
beyond the tail, the forked abdomen hanging down below this TIIE CRUSTACEA. 
long spine. The anterior feet (corresponding to the anterior an- 
tenme) are simple, while the two pairs of posterior feet are forked, 
ending in long bristles. 
These well armed creatures swim vigorously about on the sur- 
face of the water for a season, moulting several times before as- 
suming the bivalve, pupal condition. 
The pupa is almost identical in appearance with the bivalved 
Sacculinn, having no mouth, and with a similar arrangement of 
limbs, except that no filaments are developed on the anterior pair 
of limbs, and they possess a pair of compound e}res. 
The pupal condition is so much alike in the two groups, as 
stated by Fritz Muller, that we scarcely see why they should be 
separated as different groups, as Muller is disposed to regard them, 
but prefer to consider them as subordinate groups of Cirripedia. 
The shield of the bivalved “ pupal ” barnacle becomes converted 
into the multivalued barnacle, the solid shell of the latter, as in 
the true sessile barnacles; becoming so unlike the thin valves of 
the pupa, that, as is well known, even Cuvier supposed them to 
be mollusks, though there were the jointed feelers and the articulate 
plan of the nervous cord as witnesses of their crustacean affini- 
ties. The swimming feet of the larval barnacle become the long 
slender “cirri,” which serve to draw in the food, creating currents 
setting in towards the mouth. Strange as is this retrograde 
development, we shall see it paralleled among the fish lice. 
To sum up, the barnacles and root-barnacles, which are her- 
maphrodites, except in one family (Abdominales) pass through the 
following stages of development: 
1. Morula. 
2. Nauplius or larva. 
3. A bivalved “pupal” stage. 
4. Adult retrograde condition. 
Thompson. Zoological Researches and Illustrations. I. i. 1S28-29. 
Burmeister. Bcitriige zur Naturgeschiclite tier Rankenl'iisser. Berlin, 1834. 
Darwin. A monograph of the subclass Cirripedia. 2 vols. London, 1851-54. 
Muller, Fritz. Die llliizocephalen. (Archiv fiir Naturgeschiclite, 1862.) 
Van Benedcn, E. Recherches sur 1’ des Crustacea. III. (Bulletin de 
l’Acad. Roy. Belgique, 1S70.) 
LITERATURE. 
Development of the Copepods. As the true Copepocls and their 
allies, the fish-lice or Siphonostomatous Copepods, travel the same 170 
LIFE HISTORIES OF ANIMALS. 
developmental road until the -larval stage is completed, the early 
stages here described apply to the species of both groups. The 
embryonic development, however, is very simple. The sexes are 
distinct, and the females (Fig. 182, Cy- 
clops quadricomis, after Clark) in many 
cases swim about as seen in the figure, 
with a sac of eggs attached to each side 
of the body. 
The embryo in those species of Cope- 
pods which have been examined, is formed 
in the following manner, as observed by 
E. Van Beneden. 
The egg undergoes total segmentation, 
resulting in a layer of blastodermic cells 
surrounding the yolk. These cells in- 
crease in length on one side, forming the 
blastodermic disk, or “ primitive streak.” 
On the ventral surface of this disk, viz., 
the side pointing outwards, the three pairs 
of limbs arise simultaneously, and the 
Nauplius (or larva) directly hatches, its 
body being more or less oval and rounded. 
In this simple condition, with no sepa- 
ration of the body into a head-thorax or 
abdomen, and with a simple unpaired eye 
and a labrum, it swims about. Its 
farther transformations can be traced by any one who will take 
the pains to keep these water-fleas in aquaria. 
Before the larval Copepod leaves the egg it moults twice; the 
first is the “blastodermic skin” secreted by the blastodermic cells, 
and exuviated before the limbs bud out. This blastodermic moult, 
comparable to the serous membrane of Arachnides and the true 
insects, has been observed by Van Beneden to be the larval mem- 
brane of Gammarus, and he has recognized it as surrounding the 
embryo of Sacculina, Lcptomera, Caprella, Nebalia and Crangon. 
The second or Nauplian moult takes place after the larval form 
is attained, but before the embryo hatches. The skin peels off 
when the appendages are of a certain length and before they are 
jointed. 
Fig. 182. 
Cyclops. 
At the moment of birth, saj-s Van Beneden, the appendages 171 
are distinctly jointed and provided with simple or branched bris- 
tles. The alimentary canal is distinct, so is the eye; and the 
nerve-ganglion is recognizable while the blood circu- 
lates in the body-cavity. 
While most Copepods leave the egg in this per- 
fected, Nauplius condition, the embryo Anchorella and 
Hessia, according to the researches of Van Beneden, 
pass through a Nauplius state in the egg ; then three 
pairs of abdominal feet grow out, and an abdomen, 
consisting of five well marked segments, is differenti- 
ated from the cephalothorax. This stage is called the 
cyclopian stage by Van Beneden. Now this embry- 
onic stage of the Lernoeans, or fish lice, corresponds 
to the stages undergone by the free swimming young 
of Cyclops and other Copepods. 
The Nauplius of Cyclops in growing to maturity 
elongates, while mouth-appendages, abdominal seg- 
ments and appendages arise after successive moults, 
until the adult form is attained. 
In the parasitic genera, the larva is either a Nau- 
plins, as in Achtheres and Chondracanthus (in Actheres 
the young has but two pair of appendages) or, as in 
Anchorella and others, a cyclops-like being, which 
after swimming around for awhile fastens 
itself by its appendages to the gills of 
some fish. Then begins the race be- 
tween the organs of vegetative and ani- 
mal life, the former far outstripping the 
latter. As in the Lernaea of the cod the 
appendages grow deep into the flesh of 
its host like' twisted and gnarled roots, 
while the shapeless sac-like body is, as -• 
in the Sacculina, a simple sac filled with 
eggs. Or the body is still without seg- 
ments, as in Lerneonema radiata (Fig. 
183, from Verrill’s Report) and ends in 
two attenuated ovaries ; or as in Adheres 
Carpenteri, Fig. 184 (from Hayden’s Re- 
port), which lives on trout, the deformation is less, and the body 
is divided into a head and abdomen, the latter in the female bear- 
ing two egg-sacs. 
THE CRUSTACEA. 
Fig. 183. 
Fish Louse. 
Fig. 184. 
Fish louse. 172 
LIFE HISTORIES OF ANIMALS. 
To recapitulate the changes undergone by the Copepods in 
attaining maturity, they pass through the following phases of 
development: 
1. Morula. 
2. Nauplius. 
3. Cyclopian (in certain genera embryonic) stage. 
4. Adult Copepad, in some forms being a degraded more or less 
amorphous parasitic condition. 
Nordmavn. Mikrographische Beitriige zur Naturgescliichte der Wirbellosen Thiere. 
Beilin, 1832. 
Claus. Ueber den Bait mid die Entwicklung einiger parasitischer Crustaceen. 
Cassel, 18.18. 
Van Bencden, E. Recherclies, IV. (Bull. Acad. Bruxelles, 1870.) See also Fritz 
Miiller’s Facts for Darwin. Translation. London, 1809. 
LITERATURE. 
Development of the Ostracodes and Cladocera. Of the life-his- 
tory of the bivalved Ostracodes we only know from Claus’ studies 
Sida. 
that “the youngest stages are shell-bearing Nauplins forms.” It 
seems evident that these creatures undergo no metamorphosis. 
Of the development of the Cladocera, such as the fresh-water 
Daphnia and Sida (Fig. 185, from Hayden’s Survey) we have 
more certain knowledge. The eggs are borne by the females in 173 
so-called brood-cavities on the back under the shell. The females 
bring forth two sorts of eggs, i.e., the “summer eggs,” which are 
laid by asexual females, the males not appearing until the autumn, 
when the females lay the fertilized “winter eggs,” which are sur- 
rounded b}’ a very tough shell. 
Dolirn observed the development of the embiyo in the summer 
eggs. At first the embiyo has but three pairs of appendages, 
representing the antennae and two pairs of jaws. It is thus com- 
parable with the Nauplius of the Copepods, and thus the Cladocera 
may be said to pass through a Nauplius stage in the egg. 
Afterwards more limbs grow out, until finally the embiyo is 
provided with the full number of adult limbs, and hatches in the 
form of the mature animal, undergoing no farther change of form. 
TIIE CRUSTACEA. 
LITERATURE. 
Dolirn. Untersuclmngen ueber Bau und Entwieklung der Arthropoden. Leipzig, 
1870. 
Development of the King Crab (Limulus). Here we must turn 
aside from the true Crustacea to study the development of the 
king crab, so unlike in its organization to the normal Crustacea, 
and remarkable for being an ally of the trilobites. 
Fig. 18G. 
Fig. 1S7. 
Unlike most Crustacea the female king crab buries her eggs in 
the sand between tide marks, and there leaves them at the mercy 
of the waves, until the young hatch. The eggs are laid between 
the end of May and early in July, and the young are from a month 
to six weeks in hatching. 
After fertilization the yolk undergoes partial segmentation, 
much as in the insects. When the primitive disk is formed (much 
as in the spiders and certain crabs) the outer layer of blasto- 
Embryo of King Crab. 174 
LIFE HISTORIES OF ANIMALS. 
dermic cells peels off soon after the limbs begin to appear, and 
this constitutes the serous membrane (Fig. 186, am) which is like 
that of insects. 
Then the limbs bud out, the six pairs of cephalic limbs appear 
at once as in Fig. 186. Soon after the two basal pairs of abdomi- 
nal leaf-like feet arise, the abdomen becomes separated from the 
front region of the body, and the segments are indicated as in L ig. 
187. A later stage is signalized by the more highly' developed 
dorsal portion of the embryo, an increase in size of the abdomen, 
and the appearance of nine distinct abdominal segments. The 
segments of the cephalothorax are now very clearly defined, as 
also the division between the cephalothorax and abdomen, the 
Fig. 188, 
Fig. 18!) 
King Crab shortly before hatching; trilobitic stage. 
latter being now nearly as broad as the cephalothorax, the sides 
of which are not spread out as in a later stage. 
At this stage the egg-shell has split asunder and dropped 
off, while the serous membrane has increased in size to an unusual 
extent, several times exceeding its original dimensions and is filled 
with sea water in which the embryo revolves. 
At a little later period the embryo throws off an embryonal 
skin, the thin pellicle floating about in the egg. Still later in the 
life of the embryo the claws are developed, an additional rudi- 
mentary gill appears, and the abdomen grows broader and larger, 
with the segments more distinct; the heart also appears, being a 
pale streak along the middle of the back extending from the front 
edge of the head to the base of the abdomen. 
Just before hatching the head-region spreads out, the abdomen THE CRUSTACEA. 
175 
being a little more than half as wide as the cephalothorax. The 
two compound eyes and the pair of ocelli on the front edge of 
the head are quite distinct; the appendages to the gills appear on 
the two anterior pairs, and the legs are longer. 
The resemblance to a Trilobite is most remarkable, as seen in 
Figs. 188 and 189. It now also closely resembles the fossil king- 
crabs of the Carboniferous formation (Fig. 190, Presticichia ro- 
Fig. 190. 
Fig. 191. 
Prestwichia. 
Euproops. 
tundatus, 191, Euproops Dance, from Worthen’s Paleontology of 
Illinois). 
In about six weeks from the time the eggs are laid the embryo 
hatches. It now differs chiefly from the previous stage in the 
abdomen being much larger, scarcely less in size than the cephalo- 
thorax ; in the obliteration of the segments, except where they 
are faintly indicated on the cardiac region of the abdomen, while 
the gills are much larger than before. The abdominal spine is 
very rudimentary ; it forms the ninth abdominal segment. 
The reader may now compare with our figures of the recently 
hatched Limulus, that of Barrande’s larva of Trinucleus ornatus 
(Fig. 193, natural size and enlarged). One will see at a glance 
that the young Trilobite, born without any true thoracic segments, 
and with the head articulated with the abdomen, closely resembles 
the .young Limulus. In Limulus no new segments are added after 
birth; in the Trilobites the numerous thoracic segments are added 
during successive moults. The Trilobites thus pass through a LIFE HISTORIES OF ANIMALS. 
well marked metamorphosis, though by no means so remarkable 
as that of the Decapods and the Phyllopods. 
The young swim briskly up and down in the jar, skimming 
about on their backs, by flapping their gills, not bending their 
bodies. In a succeeding moult, which occurs between three and 
four weeks after hatching, the abdomen becomes smaller in pro- 
portion to the head, and the abdominal spine is about three times 
as long as broad. At this and also in the second, or succeeding 
moult, which occurs about four weeks after the first moult, the 
Fig. 102 
Fig. 11)3, 
Larva of a Trilobite. 
young king crab doubles in size. It is probable that specimens 
an inch long are about a year old, and it must require several 
years for them to attain a length of one foot. 
The stages of growth, to recapitulate, are as follows : — 
1. Peripheral or partial segmentation of the yolk. 
2. No true Nauplius stage, but the six legs appear simulta- 
neously. 
3. Trilobitic stage. 
4. Adult Limulus form attained before hatching. 
Larva of Ihe Kin,a; Crab 
Packard. The Development of Limulus Polyphemus. (Memoirs Boston Society of 
Natural History. 1872.) 
Consult also papers by Lockwood, Dohrn, and E. Van IJeneden. 
Development of the Phyllopods. We will now return to the true 
Crustacea, and trace the mode of growth of the leaf-footed forms, 
beginning with Limnadia (Fig. 548, L. Agassizii Packard, in Hay- 
den’s Report), a form with whose development we are acquainted. 
LITERATURE. 177 
THE CRUSTACEA. 
These shelled crustaceans live in pools which often dry up in 
summer. The eggs after leaving the oviduct are arranged above 
the back under the carapace, where they remain for one or two 
days in midsummer, or for several days during September. The 
eggs of the European L. Hermanni are irregular in form and en- 
closed in a solid calcareous shell composed of two valves. So 
thick is the shell that Lereboullet was unable to study the devel- 
opment of the embryo. 
The young are hatched in from five to ten da}Ts after the expul- 
sion of the eggs from under the carapace. The freshly hatched 
larva is a nauplius, with the body rather long and with two pairs 
of appendages bearing bristles, the anterior pair being forked; 
there is a single eye in the middle of the head and an enormous 
labrum. Lereboullet states that the larvae “ have a great resem- 
Fig. 194. 
Limnadia Agassizii. 
blance with the larvae of other branchiopod Crustacea, among oth- 
ers with those of Branchipus and Artemia. But the larvae of these 
two genera have antennae, which are wanting in the larvae of Liin- 
nadia, while also the larvae of Artemia have no labrum.” About 
the beginning of the second or third day, the two halves of the car- 
apace begin to grow out from the sides of the base of the abdomen. 
They finally unite over the back forming a sort of a hinge, and at 
length enclose the body, with the exception of the head and extrem- 
ity of the abdomen. When the creature is fully grown, the head 
and tail are entirely covered by the shells of the carapace. I have 
found the young of L. Agassizii about half a line in length in a 
pool on Penikese Island early in August. The pool a few days 
after dried up, and the young met the fate so common to these 
Phyllopods, but the eggs, protected by their solid calcareous cov- 
LIFE HISTORIES OF ANIMALS. LIFE HISTORIES OF ANIMALS. 
ering, undoubtedly withstand the desiccation for over one year, 
and thus the species is preserved. 
The larval development of Apus (Fig. 195, A. oequalis Packard, 
in Hayden’s Report) has been studied by Zaddach. We know 
nothing of the embryology of this animal. I have, however, been 
able to discover that the blastodermic skin, like that of Limulus, 
consists of a single layer of moulted cells. Zaddach represents 
the chorion, or egg-shell, as splitting apart just as in Limulus, and 
Fig. 195. 
Fig. 196. 
Brine Shrimp, Artemia. 
the embryo surrounded by an inner membrane, which is the blas- 
todermic skin. 
The young breaks out of its blastodermic skin in the nauplius 
form, with two pairs of appendages. After a moult a third pair is 
added and the larva appears as in Fig. 197, b. The numerous 
foliaceous feet, to the number of sixty, are added during subse- 
quent moults. 
Of the embryological development of Branchipus and Artemia 
(Fig. 196, A. gracilis, after Verrill) we also know nothing. The 
Apus ajqualis. THE CRUSTACEA. 
179 
young is hatched in a nauplius condition (Fig. 197, a) but with 
three pairs of limbs. I have observed a similar nauplius-brood in 
the Artemia fertilis of Great Salt Lake. 
As in Apus, new pairs are added at sub- 
sequent moults until the adult form is 
attained. Siebold has shown that the 
summer broods of females reproduce bjr 
budding, as is probably the case in Lim- 
nadia and also Branchipus and Artemia, 
the males not appearing until towards 
autumn, though I have found males of 
Artemia fertilis in great abundance in 
Great Salt Lake late in July. Fig. 198 
represents Branchipus (Branchinectes) 
Coloradensis (Packard, in Hayden’s Re- 
port), the female being distinguished by 
the short clasping antennre, and the long 
egg-sac at the base of the abdomen. 
The Phyllopods, then, with whose embryological development we 
are not acquainted, after hatching pass through a nauplius stage, 
and the adult condition is attained after a number of moults. 
Fig. 197. 
Larva of Apus; a, Artemia. 
Joly. Histoire d’un petit Crustace (Artemia salina), etc. (Annales des Sc.Nat., 1840.) 
Zaddach. De Apodis cancriformis Anatome et Historia Evolutionis. Bonn. 1841. 
Lereboullet. Observations sur la Generation et le D4veloppement de la Limnadia 
Hermanni. (Annales des Sc. Nat., 1866.) 
LITERATURE. 
Development of Nebalia. A great degree of interest attaches 
to the life-history of this animal, which is not uncommon in deep 
water off our coast. It is a relict of a group still older than the 
king crab, being represented in the primordial rocks by Hymeno- 
caris, and in lower Silurian strata by Discinocaris and Peltocaris, 
and in the upper Silurian by Ceratiocaris and other forms, gigantic 
in size (some of them being about seven inches long) compared 
with the recent Nebalia, which is about half an inch in length. 
Nebalia is regarded by Metschnikoff as a Decapod; it may be re- 
garded at least as a connecting link between the Phyllopods and 
Decapods, and as a prophetic type preceding, in paleozoic time, the 
introduction of the mesozoic Decapods. 
Judging by the plates of Metschnikoff’s memoir, for the text is 
written in Russian (a sealed language to us), the early develop- 180 
LIFE HISTORIES OF ANIMALS. 
ment of Nebalia is apparently identical with that of Oniscus, as 
studied by Bobretzky, and probably all the Tetradecapods, and 
also with that of perhaps the majority of the Decapods. As in 
Oniscus the segmentation is partial, the blastodermic cells arising 
from the subdivision of a polar cell, finally forming a blastodermic 
disk consisting of a few large cells. At first but three pairs of 
appendages arise; these corresponding to the two pairs of an- 
tennae, and the third to the mandibles. At this period the abdo- 
Fig. 198. 
Branchinectes Coloradensis, and front view of head of the male 
men is distinct from the cephalothorax, but on the whole the em- 
bryo may be said to pass through a nauplius stage. 
Then the two pairs of maxillae and two pairs of feet arise si- 
multaneously, the abdomen increases considerably in length, when 
the ten other pairs of foliaceous feet spring forth. Meanwhile 
the bivalved carapace grows out from behind the eyes, covering 
the cephalothorax and base of the abdomen. The young hatches 
soon after the shield is developed and the further changes are but 
slight. 
The Nebalia, then, in brief, passes through the following stages : 
1. Partial segmentation of the yolk. 
2. Nauplius stage (in the egg). 
3. Larval form like the adult; with no metamorphosis. 
LITERATURE 
Metschnikoff. The History of the Development of Nebalia. (In Russian.) St. Pe- 
tersburg, 1868. 
Development of the Tetradecapods. Much good work has been 
done since the days of Rathke, on the mode of growth of the fresh THE CRUSTACEA. 
181 
and salt water sow-bugs, etc. (Isopods), and the beach fleas (Am- 
phipods). The development of the Asellus aquaticus of Europe 
has been studied by E. Van Beneden. He found that the seg- 
mentation of the yolk is partial; that after a blastodermic moult 
the two pairs of antennae are formed before the mandibles and 
maxillae, the embryo passing through a Nauplius phase. At this 
time the embryo moults again. Like all Tetradecapods the young 
hatch in the form of the adult, there being no metamorphosis. Per- 
haps the most careful study of the embryology of the higher Crus- 
tacea, with the improved means of examination instituted mainly 
by Kowalevsky, is that of Oniscus murarius, a sow-bug, by Dr. 
N. Bobretzky, a student of the eminent Russian zoologist. The 
following is an abstract of his paper. The egg is provided with a 
chorion and yolk skin. The first change after fertilization is the 
origin of the formative or original blastodermic cells, which arise 
at one pole of the egg. As a result of the self-division of the 
single primitive blastodermic cell, there arises a disk corresponding 
to the primitive streak of other articulates, consisting of a single 
layer of large spheres of segmentation. It thus appears that the 
segmentation is partial. 
Before one-half of the surface of the egg is covered, the middle 
and inner germ-layers are indicated by a mass of cells in the con- 
cavity of the outer layer, resulting from the division of certain cells 
of the outer layer. This primitive mass is the first indication of 
the innermost (third) and middle la3Ters. The third or inner layer 
consists of large cells mingled with the yolk cells, among which 
they press. (He finds this to be the case also in Crangon and 
Palsemon.) There are, then, three germ-layers as in the verte- 
brates. 
The primitive disk, or streak, then forms by the cells of the 
outer layer assuming a cylindrical form. The first indication of 
the intestine is an invagination of the hinder end of the primitive 
band. A larval skin, like that of Asellus and other Crustacea, 
arises when the first traces of the appendages appear. Bobretzky 
finds that, contrary to Kowalevsky’s opinion, the inner germ-layer 
in the Crustacea agrees with that of vertebrates. Soon after the 
imbs grow out, a cross-section shows that it is due to a bulging 
out of the outer germ-layer, the cavity being filled with cells of 
the middle layer. Now appear the first indications of the liver, a 
layer of large cells forming the liver sac. After the appendages 182 
LIFE HISTORIES OF ANIMALS. 
appear, the nervous cord arises as a thickening of the outer layer 
on the ventral side of the primitive band, and consists of three or 
four layers of roundish cells. Fig. 199 (this and Fig. 200, after 
Bobretzky) is a transverse sec- 
tion of an embryo in nearly the 
same stage as the embryo Am- 
phipod (Fig. 201) ; d, indicates 
the intestine, and 7, the two lobes 
of the liver; g, a transverse sec- 
tion of the nervous cord, and /*, 
the walls of the body (hypoder- 
mal layer). The opening of the 
liver into the intestine is shown 
in another section made and 
drawn by Bobretzky. 
One of the most difficult prob- 
lems to solve in the embryology 
of the Arthropods is the origin of the large intestine. It is 
known that it arises out of the yolk sac, but how and where it 
takes its origin remained without an answer. “After I had as- 
certained,” says Bobretzky, “in the Astacus and Palsemon the 
peculiar relation of the intestino-glandular cells to the yolk, I 
could, in these Crustacea, follow step by step the origin of the epi- 
thelium constituting the walls of the large intestine. This 
epithelium first appears in the liver sac.” He found the same 
mode of origin in Oniscus. The next step is the disappearance 
of the yolk, while the large intestine is fully 
formed, but there is as yet no communication 
with the stomach, there being a double wall of 
cells shutting off the large intestine. 
The heart is the last to be formed ; it arises 
from the middle layer, though Bobretzky was 
unable to study its early development. Fig. 
200 is a transverse section of the body show- 
ing the viscera; h, indicates the heart; 7/p, hy- 
podermal layer, or body wall; m, muscular 
wall of the intestine ; e, epithelial lining of the 
intestine ; p, the dividing wall between the heart aud the intestine ; 
l, the two lobes of the liver; g, ganglion, the clear space being 
filled with the fine granular substance of the ganglion. Nothing 
Fig. 199. 
Section of Embryo Sow-bu; 
Fig. 200. 
Section of advanced 
embryo Sow-bug. THE CRUSTACEA. 
183 
has been said of the development of* the external parts. The two 
antennae in Oniscus and Asellns are the first to bud out (Nau- 
plius stage) and then the remaining appendages of the head and 
thorax appear together, and subsequently the abdominal feet are 
formed. The abdomen is curved up and backwards, while in the 
Amphipods it is bent beneath the 
body, as in Fig. 201, and this is 
really, as Fritz Muller observes, the 
only important difference between 
the embryos, at an early stage, of 
the two groups. The embryo Isopod 
at the time of hatching closely resem- 
bles the adult, there being no meta- 
morphosis. ' 
The development of the Amphi- 
pods or beach fleas, is nearly identical 
with that of the Isopods. The eggs 
of certain species undergo total seg- 
mentation, while those of other species of the same genus (Gam- 
marus) partially segment, as in the spiders, and in a less degree 
the insects, showing the slight importance to be attached to this 
matter, and that Haeckel's term Morula when used for the total 
segmentation of Crustacea is of little significance, how much it 
may be in the lower animals. It should be borne in mind that it 
has been used in the present work mainly as a convenient term to 
avoid circumlocution. 
Fig. 201, after Muller, represents the embryo of a Coropliium, 
magnified ninety diameters, in which all the limbs are developed. 
Summary of changes: — 
1. Segmentation of the }rolk partial, or total (Morula). 
2. Nauplius state in the egg. 
3. Larva hatching in the form of the adult with the full number 
of feet; no metamorphosis. 
Fig. 201. 
i : 
Embryo of an Amphipod. 
h, head; a'a’, antennse; y, yolk; m, 
mouth-jjarts. 
LITERATURE. 
Van Beneden, E. L’ Oeuf. Brussels, 1870. 
. Recherches sur l’Embryologie desCrustacea,I. (Bull. Acad. Bruxelles, 1869.) 
Dolirn. Die embryonale Entwickelung des Asellus aquaticus. (Siebold and Kolli- 
ker’s Zeitschrift, 1867.) 
. Zur Morphologie, Reisebemerkungen aus Taurien. Leipzig. 1837. 
Rathke. Untersuchungen ueber die Bildung und Entwickelung der Wasser-Assel 
(Asellus aquaticus). Leipzig, 1832. 
Bobretzky. Zur Embryologie des Oniscus murarius. (Siebold and Kolliker’s Zeits- 
chrift. 1874.) 184 
LIFE HISTORIES OF ANIMALS. 
Development of the Decapods. When we come to the stalk-eyed 
Crustacea, such as the shrimps and crabs, we are introduced to 
a group of animals in which there is a most striking metamor- 
phosis, as first shown by Thompson. The life history of a Deca- 
pod is full of interest and significance, as the phases which some 
present from the larval stage up are as varied and astonishing as 
the biography of any animal known. In the group as a whole, 
we have species in which the metamorphoses are attended by 
great detail and complexity of form, the animal shifting its garb 
as if an actor with many parts to perform in the drama of life, 
while in its co-species these phases may be mostly suppressed, and 
the few it does undergo, rapidly assumed and discarded within 
the narrow compass of the egg-shell. 
One Decapod, the shrimp Penmus, studied by Fritz Muller, on 
the coast of Brazil, is an exception to all other stalk-eyed Crus- 
tacea in hatching as a true nauplius, and then by a complicated 
series of metamorphoses assuming the zoeal and finally adult life. 
On the other hand, there is the common lobster, or fresh water 
craw fish, in which the free nauplius and zoea stages are sup- 
pressed, being undergone in the egg, and which hatches in nearly 
or quite a similar form to the fully grown animal. Between these 
stages there are all grades in other Crustacea. 
As regards the development of the embryo, there is in those 
species which undergo a metamorphosis, a quite similar mode. 
The yolk so far as known (Seyllarus, Astacus, etc.) undergoes 
partial segmentation : no case of a total division is as yet known. 
After the formation of a short round primitive streak, or band, 
the limbs arise. In several cases observed by Dohrn, the three 
anterior pairs of limbs, namety, the two antennse and the mandi- 
bles were developed simultaneously and before the others appear. 
The embiyo may with truth, then, as Dohrn states, be said to pass 
through a nauplius condition in the egg, as much as a mammal 
passes through a fish-like stage. He observed this nauplius-stage 
in the embryo of Seyllarus, Pandalus and Galathea. I have ob 
served it in Lupa, hastuta at Charleston, S. C., and in Libinia ca- 
nal icul at a. It is not improbable that most crabs pass through a 
nauplius state in the egg. As if in proof of the supposition that 
this is a (rue nauplius in embryo, we have the fortunate discovery, 
by Fritz Muller, of the fact that a Brazilian shrimp (Penoeus, allied 
to P. setiferus of Florida) leaves the egg “with an unsegmented 
ovate body, a median frontal eye, and three pairs of natatory feet, 185 
THE CRUSTACEA. 
of which the anterior are simple, and the other two biramose; in 
fact, in the larval form, so common among the lower Crustacea, 
to which O. F. Muller gave the name of Nauplius. No trace of 
a carapace ! No trace of the paired eyes ! No trace of masticating 
organs near the mouth which is overarched by a helmet-like hood !” 
Let us, with Muller, follow the subsequent history of this young 
shrimp. After passing through the nauplius condition (Fig. 202) 
it acquires several pairs of appendages (maxillae and maxillipedes), 
but as yet no true legs. It is now a typical zoea (Fig. 203) hav- 
ing two compound eyes, a carapace and a jointed body. The next 
Fig. 202. 
Nauplius, or larva, of a Shrimp. 
important step is the appearance of the five pairs of thoracic feet, 
and soon the mature form of the prawn is attained. 
Most true Decapods, namely, the shrimps and crabs, are hatched 
as zoeae (Fig. 204, after Thompson, represents the zoea of Car- 
emus mamas), and swim about awhile in this state, the swimming 
feet being the antennae and jaws and foot jaws, which afterwards 
acquire their special functions. 
Now one species of the genus Alphcus, observed by the writer at 
Key West, is hatched in a more advanced condition ; in what may be 
called a super-zoeal state, namely, it possesses not only five pairs 
of thoracic feet, but also five pairs of swimming, biramose abdom- 
inal feet, with the characteristic large claw! Here we have a sup- 186 
LIFE HISTORIES OF ANIMALS. 
pression of a true zoeal free swimming condition, just as we have 
seen to be the case in all the other groups of the animal kingdom, 
where one species may be born in an extremely imperfect condi- 
tion, and another, even of the same genus, in a very perfect state, 
the intermediate phases being rapidly assumed and as rapidly 
discarded in the embryo. 
A less extreme case is that of the lobster, which hatches without 
abdominal feet, but still with well developed thoracic legs. The 
Fig. 203. 
Zoea of the same Shrimp. 
larva is super-zoeal. The most extreme case, namely of an entire 
absence of a metamorphosis, is the cray-fish (Astacns and Cam- 
barns), which hatches exactly in the form of the parent. 
These facts are paralleled by the metamorphoses of the insects, 
where the terms “larva” and “pupa” are exceedingly arbitrary, 
the larval bee or fly attaining maturity only after a series of sur- 
prising changes, while the larval grasshopper simply differs from 
the adult in having no wings. THE CIIUSTACEA. 
187 
Crabs breed all through the spring and summer. At Charleston, 
S. C., on the 12th of April, I found the eggs 
of the edible crab, Lupa hastcota, containing 
embryos in all stages of development from 
the nauplius to the zoea. The fiddler crabs 
(Gelasimus pugncix) at Fort Macon, N. C., 
during the middle of May, carried eggs in 
which the polar cells, or formative cells of 
the blastoderm, were present, while others 
contained zoeoe, with the two claws alike, 
and it is probable that the strange inequality 
in size of the claws in these animals does 
not show itself until after one or more 
moults. 
The development of the lobster has been 
studied with much care by Prof. S. I. Smith. 
The lobster breeds between April and November. Fig. 2051 rep- 
resents the embiyo just before hatching. After hatching it swims 
Fig. 20L 
Zoea of a Crab. 
Fig. 205. 
Embryo of the Lobster. 
around with only the thoracic feet. After moulting, the abdominal 
1 Fig. 258. Embryo some time before hatching, removed from the external envelope 
and shown in a side view, enlarged 20 diameters, aa, dark green yolk mass still un- 
absorbed; b, lateral margin of the carapax marked with many dendritic spots of red 
pigment; c, eye; d, antennula; e, antenna;/, external maxilliped; g, great cheliped 
which forms the big claw of the adult; h, outer swimming branch of the same; i, the 
four ambulatory legs Avith their exopodal branches; k, intestine; l, heart; m, bilobed 
tail/seen edgewise. After Smith. 188 
LIFE HISTORIES OF ANIMALS. 
feet arise. After a second moult it is half an inch long and loses 
Fig. 206. 
Zoea of the Common Crab. 
Fig. 207. 
Megalops of the Common Crab. 
its formerly Mysis-like appearance and closely resembles the adult. THE INSECTS. 
189 
Soon after this it leaves the surface of the water and seeks the 
bottom. Specimens three inches long are quite like the adult. 
Besides the zoea stage, many crabs pass through a stage inter- 
mediate between the zoea and adult. This is called the Megalops 
stage, as it was supposed to be an adult animal and described 
under this term, just as early observers mistook the Nauplius and 
Zoea for adult Crustacea. Fig. 206 (this and 207 after Smith) 
represents the zoea of the common Crab (Cancer irroratus) in the 
last stage just before it changes to the megalops condition, and 
Fig. 207 the megalops of the same, magnified thirteen diameters. 
In two cases, Eriphia spinifrons, and a species of Gecarcinus, or 
the land crab of the West Indies, there is no metamorphosis, the 
young being like the adult. 
Summary of the life-history of the Decapods: 
1. Partial segmentation of the yolk. 
2. Nauplius stage; either free swimming or undergone in the 
egg- 
3. Zoea stage ; sometimes suppressed. 
4. Megalops stage; in many crabs; in a few cases no meta- 
morphosis. 
5. Adult. 
LITERATURE. 
Rathke. Untersuchungen ueber die Bildung und Entwickelung des Flusskrebses. 
Leipzig, 1829. 
Thompson, J. V. On the double Metamorphosis in the Deoapodous Crustacea. 
(Phil. Trans. London, 1835.) 
Muller. Facts for Darwin. 1869. 
Dohrn. Untersuchungen ueber Bau und Entwicklung der Arthropoden. (Siebold 
and Kolliker’s Zeitschrift. 1870. Jenaischer Zeitschrilt. V. 1871.) 
Smith. The Metamorphoses of the Lobster and other Crustacea (in Baird’s Report 
on Fish and Fisheries, U. S. 1873). 
With papers by Thompson, Rathke and Claus. 
XXVIII. THE INSECTA. (Tracheata.) 
Under the term Insecta may be included the three groups of 
Myriopods, Arachnids and true six-footed insects, or Hexapoda. 
All differ from the Crustacea in having, as a rule, for there are ex- 
ceptions among the mites, a distinct head, separate from the tho- 
rax, and in breathing by internal air-tubes (tracheae) instead of 
external gills. Without spending any time in describing the 
metamorphoses of the winged insects, accounts of which may be 
found in any entomologica' work, we will briefly describe their 
embryological development, from sources less generally accessible. 190 
LIFE HISTORIES OF ANIMALS. 
Development of the Myriopods. Though Newport’s classical 
memoir on the development of Julus will be found useful for the 
post-embryonic stages, the indefatigable Metschnikoff has recently 
cleared up the embr3rological development of these animals, so that 
we are now in possession of a life-history of these creatures, the 
early phases of whose existence had thus far eluded the scrutiny 
of embryologists. 
We will now follow Metschnikoff in his studies, beginning with 
the history of a Polydesmus-like form, Strongylosoma Guerinii, 
an inhabitant of the island of Madeira. The eggs were laid dur- 
ing a period extending from February to the end of May. Before 
ovipositing the female buries herself in the earth one or more 
inches below the surface, then depositing one or two hundred eggs 
in the manner of several other Myriopods. The eggs are spherical, 
yellowish-white, and from 1-3 mm. in diameter. 
The egg undergoes total segmentation, the process beginning in 
six or eight hours after it is laid, and ending on the fourth or fifth 
day. By this time the primitive band rests on the outside of one- 
half of the egg. A furrow next arises (compare Fig. 218 a of the 
Podurid, Isotoma) on each side of which the primitive ridges 
afterwards swell up. The two germ-layers now arise, the inner 
originating in a small mass of cells on each side of the furrow. 
The antennae bud out, and subsequently three additional pairs, 
namely, the mandibles, the second maxillae (the first pair wanting 
in the Chilognaths as in the Poduridae) and the first pair of legs ; 
and now the two ends of the body meet over the yolk as in the 
Podurids, the head touching the tail. 
The brain is now formed from the outer germ-layer (ectoderm), 
the mouth and anal opening also being formed by an invagination 
of the same outer layer, the inner la}Ter constituting ultimately 
the muscular walls of the digestive tract, while the epithelial lin- 
ing of the large intestine also arises from the inner germ-layer. 
By the fifteenth, or early on the sixteenth, day the “boring 
apparatus,” a chitinous point by which the embryo cuts open the 
shell, appears on the head. The legs now assume their form, the 
fourth and fifth pair belonging to a single segment. The embryo 
now moults, the skin forming a cuticle enveloping the embryo 
after the shell splits asunder. The nervous cord arises from the 
middle portion of the upper germ-layer, though the division of the 
layer into an epidermal and nerve-laj'er has not yet taken place. THE INSECTS. 
191 
By the sixteenth, the chorion is cut through by the point of the 
egg-shell breaker, when it splits apart, and the embryo thus remains 
covered by this membrane until the larva is ready to creep about, 
a curious fact first observed in Julus by Newport. 
By the seventeenth day nine or ten true segments are formed, 
and the appendages begin to show articulations, while beneath 
the skin, the fourth, fifth and sixth pairs of feet arise as little sacs, 
opening in the middle line of the body. The two stigmata arise 
as a fine tube with a small opening on the basal end of the third 
pair of feet, the walls of the tube (trachea) being due to an in- 
pushing of the outer germ-laj’er. The epidermis is now well de- 
fined and the nervous cord is isolated from the skin, while on the 
nineteenth, or last day of embryonal life, the hairs arise over the 
body. The embryo would now easily be mistaken for a Podurid, 
so remarkable is the resemblance, owing to the similar number of 
body-segments, and the large head, wanting in both animals the 
true maxillfE. 
On the twentieth day the larva breaks through the membrane, 
and the head is clearly separated from the body. The larva closely 
resembles the young Julus, being as yet cylindrical, and having 
but nine rings besides the head. 
In Polydesmus complcmatus of the Madeira islands, the egg also 
undergoes total segmentation, but the embryo develops more fap- 
idly, being by the fifth day covered with a membrane. 
Meanwhile the antennae have appeared, and on the sixth 
day five additional pairs of limbs bud out, namely, the 
mandibles, second maxillae (labium) and three pairs of 
legs. There is no shell breaker, the shell bursting, how- 
ever, on the tenth day.. The mandibles are very large, 
almost covering the labium. The larva is cylindrical, 
the body (the head excepted) consisting of seven seg- 
ments. 
The development of the singular Polyxenus lagurus, 
a little short creature with the body covered with fasci- 
cles of hairs, was observed by the Russian embryologist 
in Switzerland. 
The egg undergoes total segmentation, but the blastoderm is 
restricted to one pole of the egg, being disk-like. The antennae 
and mouth-parts arise as in the foregoing genera, but the three 
pairs of legs appear simultaneously. Metschnikoff found amoe- 
Fig. 208. 
Polydes- 
mus. 192 
LIFE HISTORIES OF ANIMALS. 
boid bodies, like those in the mites, moving about in the egg, 
having previously separated from the blastoderm. 
We now come to the developmentof the Thousand-legs (Fig. 209) 
which was first studied by Newport. Our skilful Russian embryol- 
ogist, with all the advantage of modern means of inves- 
tigation, and possibly by observing more transparent 
eggs than those studied by the famous English zoolo- 
gist, has thrown a flood of light on the embryonic 
stages of a species (Julus Morelettii) observed by him 
in Madeira. The eggs were laid in November, rarely 
in the spring, and not at all in the summer, being de- 
posited in rounded masses under the surface of the 
earth, as in the other Chilognathic myriopods. They are 
oval, dirty greenish white, with the shell unfortunately 
more opake than in the other genera mentioned. Here, 
also, as in the others, the segmentation was total, a 
thing not known to occur in the Hexapods (the Pod- 
urids excepted), and rarely in the Arachnids, chiefly in 
the mites. The primitive band arises on one side. 
There is a blastodermic moult, like that of many Crus- 
tacea, and corresponding to the “ deutovum ” of certain Acari. 
The two germ-layers were observed to arise as in the other 
genera, while the three cephalic appendages (antennae, man- 
dibles and second maxillae) appear as in the other Myriopods. 
The shell splits, as first observed by Newport, 
and the retort-shaped embryo remains enveloped 
in the blastodermic skin, remaining connected 
with the chorion by a fine structureless mem- 
brane. By this time four additional pairs of 
limbs, like little buds, are visible under the lar- 
val skin, which is homologous with that of the 
Isopods. The head is free from the thorax, and 
the body composed of eight segments. The 
embryo before hatching is as in Fig. 210 (after 
Newport), there being no feet on the third ring 
from the head. This, however, is not apparcn ly 
a fact of much morphological importance, as in 
Geophilus the embryo has a pair of feet on each body segment. 
In the figure, a indicates the rudiments of the new limbs, and 6, 
the six new rings growing out from between the penultimate and 
last ring of the body. 
Fig. 209. 
Julus. 
Fig. 210. 
Larva of Julus. THE INSECTS. 
193 
Metschnikoff discovered in all the embryo Myriopods studied by 
him certain paired bodies which he names “ primitive-vertebrae- 
like bodies.” He has also noticed them in the scorpion, the Pha- 
langitis, Araneids, Mysis and some other Crustacea, Termes and 
several Oligochete worms. 
When we turn to the embiyologv of the Poduridae we shall see 
how much alike those insects and the Chilognaths are in the mode 
of development of the embryo, and should also bear in mind the 
fact that the Poduras also have but a single pair of maxillae, while 
Scolopendrella is half insect and half Myriopod. The conclusion 
that the Myriopods are a subclass of the class of insects is thus 
based on morphological and embryological grounds. 
A later paper of MetschnikofFs gives us, for the first time, the 
life-history of Geophilus, one of the centipedes or Chilopod 
Myriopods. He found that the yolk undergpes a total segmenta- 
tion, and the primitive band surrounds one-half of 
the yolk. In the next stage observed the antennae 
and three pairs of jaws were developed (for there are 
besides the mandibles, two pairs of maxillae, like 
those of insects, in the centipedes) besides twenty- 
three segments. The anal opening was situated in 
the unsegmented end of the body. In the next stage 
the primitive band is much longer than before, and 
the head and tail approach nearer to each other, 
while there are now from forty-four to forty-six body 
segments, most of them bearing rudimentary appen- 
dages, though there are none as yet on the end of the 
body. In a succeeding stage the head is much larger, 
the body longer and curved over the yolk, while the 
egg-shell breaker is situated on the second maxilla. 
In a following stage the body is still more elongated 
and the joints of the antennae appear. The embryo now slips out 
of the split shell, the body being very long and cylindrical, not 
yet flattened as in maturity (Fig. 211 represents an American 
Geophilus), while the feet are not jointed, and resemble the ventral 
cirri of annelides. 
Fig.211. 
Geophilus. 
We see, then, that the centipedes (Chilopoda) differ from the 
thousand-legs (Chilognaths) in the month-parts being of the same 
number as in insects, and that the young are born with a pair of 
feet on each of the three segments behind the head, while the 
LIFE HISTORIES OF ANIMALS. 194 
LIFE HISTORIES OF ANIMALS. 
larva is provided with nearly the full number of feet on the rest 
of the body, there being no metamorphosis. The body, at first 
cylindrical, afterwards becomes flattened. Thus the centipedes 
may be said in some degree to pass through a Julus condition, 
and at all events, both morphologically and embryologically, the 
centipede is a more highly developed creature than the thousand- 
legs, a view we have always taken, but felt was rather based on a 
priori conceptions than on a sure basis of facts, now happily af- 
forded by the beautiful researches of Metschnikoff. To sum up 
the phases of development of the Myriopods we have, then: — 
1. Morula stage. 
2. A hexapod larva (Leptus form) as in the Thousand-legs; or, 
as in the Centipedes, there is no metamorphosis, the young being 
like the parent. 
3. Adult. 
Newport. On the Organs of Reproduction, and the Development of the Mvriopoda. 
(Phil. Trans. 1841.) 
Metschnikoff. Embryologie der doppelt flissigen Myriapoden (Chilognatha). (Sie- 
bold and Kdlliker’s Zeitschrift. 1874.) 
. Embryologisches ucber Geophilus. (Siebold and Kdlliker’s Zeitschrift. 1875.) 
LITERATURE. 
Development of the Mites. Coming now to the mites and spi- 
ders, we find some peculiar features in the life-history of the 
former which deserve attention, though space compels us to be 
brief at the risk of being obscure. Most mites pass through a 
metamorphosis, some undergoing striking changes within the egg. 
For example, the Atax Bonzi, which is a parasite on the gills of 
fresh water muscles, first hatches in an oval form enveloped in 
a membrane (deutovum). From this “deutovum” is developed a 
six-footed larva. In this second larva state it is free, moving over 
the gills of the mussels, finally boring into the flesh of its host to 
undergo its next transformation. Here the young mite increases 
in size and becomes round. The tissues soften, the limbs are 
short and much larger than before, the animal assuming an em- 
bryo-like appearance, and moving about like a rounded mass in 
its enclosure. After a moult it assumes the so-called “ pupa- 
state.” During this process the limbs grow much shorter and are 
folded beneath the bod}’, the animal being immovable, while the 
whole body assumes a broadly ovate form, and looks like an em- 
bryo just before hatching, but still lying within the egg. 
Iii the genus Myobia, a parasite of the European field-mouse, THE INSECTS. 
195 
there is not only a “deutovum,” but also what Claparede calls a 
“ tritovum-stage,” there being two stages with distinct embryonal 
membranes before the six-legged free larval state is assumed, the 
larva when hatching having thrown off two membranes, as well as 
the egg-shell. Certain bird-mites pass through four stages to 
reach the male condition, while the females pass through as many 
as five before attaining sexual 
maturity. Fig. 212 illustrates 
the six-legged larva of the tick, 
which is simply a large mite. The 
eggs of the mites either undergo 
total segmentation or a partial 
one, as in the spiders. 
The water-bears or Tardigrades 
are born with four pairs of legs, 
not undergoing any metamorpho- 
sis. Not so, however, with cer- 
tain worm-like mites, which by 
their parasitic life lose all resem- 
blance to other mites and are 
often mistaken for intestinal worms. I refer to the Pentastoma 
and Linguatula. Here the metamorphosis is backwards, the3roung 
after passing through a morula condition, being born as short, 
plump, oval mites, provided with boring horny jaws, but with only 
two short rudimentary legs. 
Finally, we come to those problematical forms, the sea-spiders, 
or Pycnogonidae, which are often referred to the Crustacea, whose 
has been so faithfully studied by Dr. Dohrn. The 
3*olk undergoes total segmentation, and the 3Toung are hatched 
with three pairs of legs, which after moulting attain in some spe- 
cies an extraordinary length. 
To sum up, then, certain mites pass through either: — 
1. A Morula state, or the yolk only partially divides. 
2. Sometimes one or two embryonal stages (deutovum and 
tritovum). 
3. A six-legged larval state. 
4. Eight-legged “ pupal” state. 
5. Adult. 
Fig. 212. 
Tick and Six legged Young. 
Claprtrede. Studien an Acariden. (Siebold and Kolliker’s Zeitschrift. 1868.) 
Leuckart. Bau nnd Entwiekelungsgeschichte der Pcntastomen. Leipzig und 
Heidelburg. 1860. 
LITERATURE. 196 
LIFE HISTORIES OF ANIMALS. 
Bohrn. Untersuchungen ueber Bau und Entwicklung der Arthropoden. Heft. I. 
1870. 
Consult also papers by Dugfes, Doyfere, MUller, Van Beneden, Robin and others. 
Development of the False-scorpions (Fig. 213). Some most un- 
expected features occur in the life-history of these little tailless 
scorpion-like creatures, which are found 
living under the bark of trees, and under 
stones, etc. The female runs about in 
early summer pressing the eggs to the 
under side of its body by means of its 
claws or nippers. 
Here, as in most mites, the segmenta- 
tion of the yolk is total. The blastoderm 
forms, and then a singular feature ensues, 
namely, the collection of an albuminous 
substance between the egg-shell and the 
blastoderm, increasing the size of the egg 
very materially and containing small bodies ; suggesting an em- 
bryonal membrane, though MetschnikofF does not regard it as 
truly such. Soon the blastoderm becomes two-layered. 
Fig. 213. 
False-scorpion. 
Next arise the rudiments of the two large claws, before any other 
limbs appear ; at the same time a huge projection forms on the 
head, with indications of muscular .bands. This strange appear- 
ance is merely a sort of temporary upper lip. At this time the end 
of the body is conical and curved beneath the abdomen. In this 
imperfect stage the embryo sheds a skin and then breaks through 
the delicate egg-membrane, becoming free, though the larva, kan- 
garoo-like, is still attached to the under side of the mother Cheli- 
fer, where it remains until it has completed its metamorphoses', 
though of course it derives no nourishment from its mother. 
Now the embryo-larva is nearly as long as broad, with the sin- 
gular hood-like upper lip, and the rudiments of the first pair of 
feet directly behind the enormous rudimentary nippers. Within 
are no signs of a digestive sac or any other organs, simply a mass 
of yolk cells. 
In the second larva-state the body is broader than long, the 
“ upper lip ” diminutive in size, and the mandibles and four pairs 
of legs are present. Here also, as in the scorpions and the spi- 
ders, four pairs of deciduous, abdominal feet appear (such as our 
author has also seen in Phalangium and Forfieula). There are 
now seven segments in the abdomen. 197 
THE INSECTS. 
The larval skin is after a while ruptured, and the insect deserts 
its parent, in a form like that of the mature animal. 
It will thus be seen that the first larva of Chelifer is comparable 
with that of certain low mites, but very different from the Scor- 
pion, its nearest alty, the segmentation of the yolk being total, as 
in most mites, the sea spiders, Pentastoma and the Tardigrades, 
while the larval condition is on a still lower plane of!existence 
than the Nauplius of the lower Crustacea. The false-scorpion 
differs in its mode of growth much more from the spiders, the 
scorpion and other Pedipalps, than the harvest-man (Phalangium), 
Phrynus or the Acarina. 
The harvest-men, or daddy-long-legs, as the researches of 
Metschnikoff and Balbiani show, develop as in the spiders, differ- 
ing from them only in the want of a provisional post-abdomen and 
the relatively smaller abdomen. 
The false-scorpions pass through, then :— 
1. A Morula stage. 
2. Hatching in the first larval state, with but one pair of ap- 
pendages (maxillae). 
3. Second larval state, with all the limbs present, but envel- 
oped in a larval skin. 
4. Throwing off the larval skin, becoming free and with the 
form of the adult animal. 
LITERATURE. 
Metschnikoff. Entwicklungsgeschichte des Chelifev. (Siebold and Kolliker’s Zeits- 
chrift fUr wissens. Zoologie. Leipzig, 1871.) 
Development of the Scorpions, etc. (Pedipalps). In a beautiful 
memoir by Metschnikoff on the embryology of the scorpion we 
have full details regarding the embryonic life of this animal, which 
brings forth its young alive early in summer; being one of the 
very few viviparous insects known. His studies were made on 
three species of Scorpio found in southern Europe. The females 
are big with young at the end of spring or early in summer. I 
have observed this to be the case with the scorpion of the Florida 
Keys. 
The earliest phases of development' take place in the follicles of 
the ovary. The blastoderm is formed out of a few polar cells just 
as in the higher Crustacea (Isopods and Decapods). It is at first 
a round disc, which eventually splits into two germ-layers. Soon 198 
LIFE HISTORIES OF AXIMALS. 
it becomes oval, the larger end being the head-end. The next 
step is the formation of a primitive longitudinal furrow, and after- 
wards of two transverse creases dividing the germ into three por- 
tions, the anterior the head, the middle portion the thorax and 
abdomen, and the third, the so-called post-abdomen. 
The egg now leaves the follicle and descends into the oviduct. 
The head grows broader, and by this time the germ is subdivided 
into twelve segments, from which the appendages next bud out. 
The month may be discerned, the claws are indicated, the post- 
abdomen is folded on the body and the nerve-ganglia may be de- 
tected arising from the outer germ-layer. The embryo is now sur- 
rounded by a membrane composed of two layers of quite dissimilar 
cells. 
A singular feature, also noticeable in other Insecta, is the pres- 
ence of six pairs of deciduous abdominal feet, which directly assume 
the form of horizontal plates, each with a terminal button, which 
finally disappear, the four pairs of stigmata taking their place ; 
the second pair, however, become converted into the comb-like 
tracheal gills, so that it is evident that the latter are exvaginate 
stigmata. The germ (primitive band) is now broader, and the limbs 
have a more definite outline and are jointed, while the head is 
narrower than before, assuming the shape of that of the adult. 
Metschnikoff claims that there are three germ-layers in the 
Scorpion, homologous with those of the vertebrates. 
A summary of the chief events in the development of the scor- 
pion is as follows : 
1. Partial segmentation of the yolk, the embryo developing 
within the oviduct. 
2. The young is brought forth by the mother, in a form exactly 
like the adult, and about half an inch long, about a dozen being 
produced in a season. 
LITERATURE. 
Rathlce. Zur Morphologic. Reisebemerkungen ans Tanrien. 18:J7. 
Metschni/coff. Embryologie des Scorpions. (Siebold and Kdlliker’s Zeitschrift. 1870.) 
Development of the Spiders. From the life-history of one spider 
we may learn that of all, as there is much uniformity in the mode 
of development of all those species whose growth has been yet 
observed. The eggs are laid usually in silken cocoons. All un- 
dergo partial segmentation of the yolk, which is surrounded by THE INSECTS. 
199 
a blastoderm, which thickens on one side forming the primitive 
band, eventually becoming marked off into rings or zones, as in 
Fig. 211. 
Fig. 215. 
Fig. 21G. 
Development of the Spider. After Clapar&le 
Fig. 214. The primitive band elongates, new segments appear 
(Fig. 215), until finally the germ appears, when drawn as if spread 
out, as in Fig. 216. Besides the rudi- 
ments of the two pairs of head-appen- 
dages (i.e., the mandibles and maxillae) 
and the four pairs of legs, there are at 
first four, as in figure 216, and subse- 
quently six pairs of deciduous abdomi- 
nal feet, as in the Scorpion and two 
other species of tracheate insects. 
Soon the mouth-parts and legs grow 
longer, and the embryo spider lies on 
the surface of the yolk as seen in Fig. 
217. Finally, the head, originally dis- 
tinct from the thorax, becomes soldered 
to the thorax; the eyes appear and the 
animal is rapidly perfected, the spider being hatched in a form 
like the adult, differing only in size and its paleness of color; the 
changes in after life being almost imperceptible. All spiders, 
then, so far as known :— 
1. Undergo in the egg state a partial segmentation of the yolk, 
and 
2. Are hatched in the adult form, having no metamorphosis. 
Fig. 217. 
Advanced embryo of the Spider 200 
LIFE HISTORIES OF ANIMALS. 
LITERATURE. 
Herold. De Generatione Araneavum in Ovo. Marburg, 1824. 
Claparede Reelierches sur l’Evolution des Araign4es. Utrecht, 1832. 
Development of the true Itisects. While the history of the winged 
insects before hatching is much the same in the different orders, 
there are some exceptional modes of development possessing a 
high degree of interest on account of the resemblance to the mode 
of embryonic growth of still lower animals. First I will give an 
epitome of the changes observed by myself within the egg of a 
Fig. 218. 
Fig. 219. 
Fig. 220. 
Fig. 221. 
Development of a Poduran 
Poduran. The eggs were not studied until after the formation of 
the blastoderm, but Ulianin of Moscow has ascertained that the 
eggs of certain Podurids undergo total segmentation, in this fea- 
ture, as indeed in some of the other phases of embryonic life, 
closely resembling the Myriopods. Fig. 218 shows the primitive 
band infolded at a, as in the Myriopod germ. A more advanced 
stage (Fig. 219) shows the rudimentary appendages (1-3,1-111) the 201 
THE INSECTS. 
second maxillae or labium, not being present. (It will be remem- 
bered that a pair of maxillae are also wanting in the Thousand- 
legs.) The next change is the clos- 
ure of the body-walls over the yolk, 
and the appearance of the rudiments 
of the “ spring.” By this time the 
serous membrane is formed, being a 
tough membrane enveloping the 
germ. In a succeeding stage the 
intestine is formed and the rudi- 
ments of the antennae and legs have 
greatly increased in size. Still later, 
the appendages begin to show traces 
of joints. In a later period (Fig. 220, 221 a) the head is quite 
Fig. 222 
Platygaster. 
Fig. 223. 
Development of Platygaster. 
separate from the rest of the body, the antennae (at) are of much 
the same shape as in the larva, while the upper lip (labrum) and 
clypeus are clearly indicated, and the spring (sp) is fully formed. 
Soon after, the “finishing touches” are, as it were, put on, and 
the mandibles and maxillae (md and mx) are withdrawn within the 202 
LIFE HISTORIES OF ANIMALS. 
head, when the embryo throws off the chorion and serous mem- 
brane and runs about in a lively way. 
Coming now to the true winged insects, we are met with a very 
exceptionable mode of development, observed by Ganin in certain 
species of minute ichneumon flies, some of them egg-parasites. 
The ovary of Platygaster (Fig. 222) differs from that of most other 
insects in that it is a closed tube or sac. Hence it follows that at 
every time an egg is laid, the egg- 
tube is ruptured. The egg is a single 
cell. Out of this cell (Fig. 223 A, a, 
arise two other cells, but the central 
cell (a) gives rise to the embryo, 
which as seen at jB, g, originates from 
the nucleus of A, a, while the circle 
of cells, b, form an equivalent to the 
serous membrane or blastodermic skin 
of other insects and Crustacea. The 
germ farther advanced, as in (7, g, 
reminds us of the embryo of certain 
low worms. D and E are successive 
stages in the growth of the provis- 
ional larva (Fig. 224, m, mouth; at, 
antennae ; md, mandibles ; d, decidu- 
ous organs). In this condition it 
clings to the inside of its host by 
means of its temporary hook-like jaws 
(md) moving about like a Cestodes 
embiyo. The nerves, blood vessels 
and air tubes are wanting, while the 
alimentary canal is simply a blind sac, 
remaining in an unorganized state. 
It then passes into the second larval state (Fig. 225) like that of 
the ichneumon flies, and the remaining changes into the pupal and 
winged state are as usual. 
Fig. 224. 
First larva of Platygaster. 
In Polynema, the larva in its first stage is very small and mo- 
tionless, and with scarcely a trace of organization, being a mere 
flask-shaped sac of cells. After five or six days it passes into a 
worm-like stage, and subsequently into a third stage (Fig. 226, tg, 
three pairs of abdominal tubercles destined to form the ovipositor ; 
l, rudiments of the legs; fk, portion of the fatty body ; at, rudi- THE INSECTS 
203 
ments of the antennae; jl, imaginal disks or rudiments of the 
wings). 
Fig. 225. 
Fig. 226. 
Second larva of Platygaster 
Third larva of Polynema, 
Fig. 227. 
Development of Egg-parasites. 
The larva of Ophioneurus is at first of the form indicated by 
Fig. 227, E. It differs from the genera already mentioned, in 204 
LIFE HISTORIES OF ANIMALS. 
remaining within its egg-membrane, and not assuming their 
strange forms. From the non-segmented, sac-like larva it passes 
directly into the pupa state. 
The development of Teleas is like that of Platygaster. Fig. 
227, A, represents the egg; B, C and D, the first stage of the 
larva, the abdomen being furnished with a series of bristles on 
each side. B represents a ventral, C a dorsal, and D a profile 
view ; at, antennae ; md, mandibles ; mo, mouth ; 6, bristles ; m, 
intestine ; sw the tail, and id the under lip or labium. Not until 
the beginning of the second larval stage is the primitive band 
formed. 
In all the other insects whose earty stages have been studied, 
there is a remarkable uniformity, all travelling nearly the same 
developmental road until just before hatching, when they assume 
the characteristics belonging to the larval forms of their respec- 
tive orders. For example not until very late in emlnyonic life 
do the germs of a bee, a bug, a beetle or a fly, or even a dragon 
fly, differ in any essential point. 
We will, then, give a general and brief account of the mode of 
growth of the germ, not dwelling on the metamorphoses of in- 
sects. The egg after fertilization shows the first sign of the new 
life thus originated by the appearance of a few polar cells; these 
multiply and surround the egg with a single layer, thus forming 
the blastoderm. The segmentation of the yolk is thus peripheral 
and partial. On one side of the egg the blastodermic cells elon- 
gate, forming a thickening, called, the primitive streak or band, 
which in some insects sinks into the }’olk. By this time the se- 
rous membrane (s) has moulted and envelopes the germ and yolk. 
The germ soon splits into an outer (ectoderm) and inner la}'er 
(endoderm) and then sheds the true am- 
nion, which as in vertebrates, peals off from 
the primitive band or germ, and acts as a 
protective membrane. 
In Fig. 228 (after Kowalevsky), repre- 
senting a transverse section of the embryo 
of a Sphinx, we see the relation of parts. 
The primitive band has sunk into the yolk which is surrounded by 
the serous membrane (s) or blastodermic skin (formerly, but erro- 
neously termed the amnion). The primitive band is seen to be 
formed of two layers, h, the outer, and m, the inner. In the 
Fig. 228. 
Section of Sphinx embryo. THE INSECTS. 
205 
outer is subsequently formed the nervous cord and air vessels, 
while from the inner arise the digestive canal and its glands and 
the organs of circulation. The amnion (am) envel- 
opes the germ. From the ventral side of the primitive 
band bud forth the appendages of the head, the thorax, 
and as in the embryo caterpillar, the ten pairs of ab- 
dominal legs, i.e., one to each ring, a portion of which 
disappear before it hatches, no caterpillar having more 
than five pairs of prop-legs. Fig. 229 (after Kowal- 
evsky) represents the primitive band of the Sphinx, 
with the four pairs of head appendages (c, upper lip; 
at, antennae ; md, mandibles ; mx, mx' first and second 
maxillae), and the three pairs of thoracic legs (l, l' l") 
succeeded by the ten pairs of abdominal legs. The 
observer will notice that all the appendages, whether 
of the head or thorax or hind-body, are alike at first, 
being simple outgrowths of the outer germ-layer. 
When in a more advanced stage, as seen in the ac- 
companying figure (230, am, serous membrane ; db, 
amnion ; vk, forehead) of the embryo louse, the an- 
tenn® are longer than the mouth-parts, 
and the legs are still larger. Afterwards 
those features characterizing the differ- 
ent orders of insects appear, and shortly 
before hatching we can ascertain to 
what group the embiyo belongs. 
As regards the development of the 
internal organs, the nervous s}-stem is 
the first to show itself, the alimentary 
canal is next formed, and the stigmata 
and air-tubes arise as invaginations of 
the outer germ-layer. The development 
of the salivary glands precedes that of 
the urinary tubes, which, with the geni- 
tal glands are offshoots of the primitive 
digestive tract. Finally the dorsal ves- 
sel is formed. Fig. 231 (after Kow- 
alevsky) is a transverse section of the 
embryo bee; g, is a nerve ganglion; i, 
the alimentary canal; m, muscular bands running to the heart (h) ; 
Fig. 229. 
Sphinx em- 
bryo. 
Fig. 230. 
Embryo of the'Louse. 206 
LIFE HISTORIES OF ANIMALS. 
d is a gland, and t, indicates the trachea, its mode of origin being 
illustrated on the left side of the figure where it is seen in com- 
munication with a stigma or air-hole (s). 
So far as we know (the Thysanura and certain minute ichneu- 
mons excepted) there is in the winged insects a remarkable uni- 
formity in their mode of development, 
and it is difficult to determine what em- 
bryological characters may be set down 
as distinguishing even the different orders, 
but they will probably be found, if any- 
where, in the form of the advanced em- 
bryos. 
A summary of the most important 
events in the life-history of insects is as 
follows :— 
1. Peripheral (partial) segmentation 
of the yolk (in the Podune a true Morula 
condition). 
2. Larva hatched in the form of the adult (in Aphis and Mi- 
astor producing young alive), but wingless, and undergoing an in- 
complete or complete metamorphosis. 
3. Pupa (in a species of Chironomus producing young). 
4. Adult, usually winged, sometimes propagating asexually. 
Fig. 231. 
Section of advanced Sphinx 
embryo. 
Herold. Disquisitiones de Animalium vertebris carentium in Ovo Formatione. 
Frankfurt a Maine. 1835-38. 
Kolliker. Observationes de prima Inscctorum Genesi. Turici, 1842. 
Zaddach. Untersuchung ueber die Entwickelung und den Bau der Gliederthiere. 
Berlin, 1854. 
Leuckart. Die Fortpflanzung und Entwickelung der Pupiparcn nach Beobach- 
tungen an Melophagns ovinus. Halle, 1858. 
Huxley. On the Agamic Reproduction and Morphology of Aphis. (Phil. Trans. 
London, 1859.) 
Weismann. Die Entwickelung der Dipteren im Ei. (Siebold and Kiilliker’s Zeits- 
chrift, xiii, 18(i4.) 
Metschniknff. Embryologische Studien an Insecten. (Siebold and Kolliker’s Zeits- 
clirift, 1866.) 
Melnikow. Beitrage zur Embryonalentwicklung der Insekten. (Archiv fur Natur- 
geschiclite, 1869. 
Brandt. Beitrage zur Entwicklungsgeschichte der Libelluliden und Hemipteren, 
etc. (Memoires Acad. Imp. St. Petersburg, 1869.) 
Ganin. Ueber die Embryonalhulle der Hymenopteren und Lepidoptereu Embry- 
onen. (Memoii es Acad. Imp. St. Petersburg, 1869.) 
. Beitrage zur Erkenntniss der Entwickelungsgeschichte bei deni Insekten. 
(Siebold Zeitschrift, 1869.) 
Consult, also, papers by J. Miiller, S. Wagner, Van Grimm, Balbiani, Dohrn and 
Packard. 
LITERATURE. THE LEPTOCARDII. 
207 
XXIX. TIIE LEPTOCARDII (Amphioxus). 
In the adult Amphioxus, we behold a vertebrate without a true 
back bone, but a dorsal cord like that of certain larval Ascidians ; 
with no brain, no true heart, but with a vascular system resembling 
that of worms; with primitive kidneys like the segmental organs 
of worms, and with the front end of the alimentary canal perforated 
with gill-slits, like those of Ascidians and the Balanoglossus worm 
rather than vertebrates. Viewing the body it has no 
true head as in fishes, nor appendages supported by bony axes, like 
the fins and arms or legs of vertebrates. Yet on making a section 
of the body, the relation of the chief anatomical organs is on the 
vertebrate plan, a nerve-cavity being situated above the digestive 
cavity, the vicarious back bone, or chorda dorsalis, separating the 
two cavities. 
It will thus be seen that the line separating the vertebrates from 
the rest of the animal kingdom is in a degree artificial, and that 
the beings most like the ancestors of the present vertebrates are 
to be looked for in some lower branch. 
Development of Amphioxus. Again when we study the develop- 
ment of Amphioxus, we shall find, that while there are important 
points in which the embryology of this animal differs much from 
that of the higher vertebrates, still, as observed by Balfour, “all 
the modes of development found in the higher vertebrates are to 
be looked upon as modifications of that of Amphioxus.” 
For the life-history of the laneelet, we turn to Ivowalevsky’s 
classical memoir. He found the eggs issuing in Maj' from the 
mouth of the female, and fertilized by spermatic particles likewise 
pouring out from the mouth of the male. The eggs are very small, 
0.105 millimetres in diameter. The eggs undergo total segmenta- 
tion, exactly as in the sponge, the ascidian, the mammal, and 
even as in man, and leaving a segmentation cavity which becomes 
the body-cavity. 
The blastoderm now invaginates and the embryo swims about as 
a ciliated gastrula, comparable with that of the sponge, or Sagitta 
(Fig. 140). The body is now oval, and the germ does not differ 
much in appearance from a worm, starfish, snail or ascidian in the 
same stage of growth. No vertebrate features are yet developed. 
Soon the lively ciliated gastrula elongates, the alimentary tube 
arises from the primitive gastrula-cavity, while the edges of the 208 
THE LOWER VERTEBRATES. 
flattened side of the body grow up as ridges which afterwards, as 
in all vertebrate embryos, grow over and enclose the spinal cord. 
By this time the transverse muscular bands appear. 
By the time the embryo is twenty-four hours old it assumes the 
form of a ciliated flattened cylinder, with both ends much alike. 
It is now somewhat like the Ascidian embryo (Fig. 164, 73, n), 
there being a nerve-cavity, the nerve-tube, with an external open- 
ing, which afterwards closes. 
The vertebrate character, namety, the emlnyonic back bone 
{chorda dorsalis) has now appeared, and extends to the front end, 
beyond the end of the brain, instead of being confined to the pos- 
terior portion of the body as in the Ascidians (Fig. 164, 73, x). 
In the next stage observed by the Russian embryologist, the 
Amphioxus-form was attained, the body being compressed and 
deeper in the region of the mouth, though there is no true head. 
The first gill-opening now appears, the mouth having previously 
been formed, and afterwards twelve such openings appear; the 
pharynx is thus provided with ciliated slits, as in the Ascidians, 
the Balanoglossus ; and, on the other hand, all embryo vertebrates. 
The embryo lancelet is still ciliated, but these swimming-hairs 
disappear eventually and the young animal seeks the bottom and 
burrows finally in the sand. When the larval Amphioxus is still 
very small, the body is not symmetrical, the mouth is far on one 
side, and on the lower edge is a circle of external filaments sur- 
rounding the mouth, comparable with the fringe of filaments of 
the Ascidians, the clam or certain worms. 
It seems to result from these and other facts, not here presented, 
that while the Amphioxus is a low, embryonic vertebrate, which 
graduates into the fishes through the lamprey and Myxine, the 
early history of Amphioxus unmistakably points back to worm- 
like parents; and on the other hand that of the vertebrates indi- 
cates their descent from an Amphioxus-like ancestor. 
Briefly recapitulating the chief events in the life of the lancelet, 
we find the following well marked stages : 
1. Morula. 
2. Gastrula (ciliated). 
3. Ascidian-like larva. 
4. Adult. LITERATURE. 
Kowalevski). Entwickelungsgeschichte des Amithioxus (Memoircs de 
l’Acad. Imp. des Sciences de St. Petersbouvg, 1867). THE PISCES. 
209 
XXX. THE PISCES. 
Development of the Sharks and Skates (Selachians). These 
fishes are either oviparous or viviparous. The dog-fish brings 
forth her young alive, while the skates and many sharks lay square 
eggs with a tough horny shell (Fig. 232, after Wyman). The yolk 
is not enelosed in any membrane like the vitelline membrane of 
birds, but lies freely in 
a viscid albumen filling 
the egg-capsule. 
We will now, in order 
to make out a tolerably 
complete life-history of a 
Selachian, condense Bal- 
four’s account of the early 
stages of the dog-fish 
(Mustelus), and close 
with the latter stages of 
the skate, as given by 
the late Professor Wy- 
man. The blastoderm or 
germinal disk is a large 
round spot darker than 
the rest of the 3rolk and 
marked off from the rest 
of the egg by a dark 
line (really a shallow 
groove). Segmentation 
occurs much as described 
in the bony fishes, rep- 
tiles and birds. The upper germ-layer (epiblast) arises much as 
in the bony fishes, the Batrachians and birds, while the two inner 
germ-layers are not clearly indicated until a considerably later 
stage. The segmentation-cavity is formed much as in the bony 
fishes. There is no invagination of the outer germ-layer to form 
the primitive digestive cavity and anus of Rusconi, as in Amphi- 
oxus, the lamprey, sturgeon and Batrachians, but the Selachians 
agree with the bony fishes, the reptiles and birds, in having the 
alimentary canal formed by an infolding of the innermost germ- 
layer, and with no anus of Rusconi, the digestive tract remaining 
¥ig. 232. 
Egg of the Skate. 
LIFE HISTORIES OF ANIMALS. 210 
LIFE HISTORIES OF ANIMALS. 
in com muni cation with the j’olk for the greater part of embryonic 
life by an umbilical canal. This 
mode of origin of the digestive 
cavity, Balfour regards as second- 
ary and adaptive, no “gastrula” 
(Hgeckel) being formed as in Am- 
phioxus, etc. The embryo now 
rises up as a distinct body from 
the blastoderm, just as in other 
vertebrates, and there is a medul- 
lary groove along the middle line, 
and by the time this has appeared 
the middle and inner germ-layers are clearly indicated. After this 
development goes on much as in the chick. 
At this time the embryo dog-fish externally resembles the young 
trout; the chief difference is an internal one, the outer germ- 
layer not being divided 
into a nervous and epi- 
dermal sub-layer as in 
the bony fishes. 
The next external 
change is the division 
of the tail-end into two 
caudal lobes. The no- 
tochord arises as a rod- 
like thickening of the 
third germ-layer, from 
which it afterwards en- 
tirely separates, so that 
the germ, if cut trans- 
versely, would appear 
somewhat as in the em- 
bryo bird (Fig. 251). 
Now the protovertebrae arise, and about this time the throat 
becomes a closed tube. The head is now formed by a singular 
flattening-out of the germ, like a spatula, while the medullary 
groove is at first entirely absent. The brain then forms, with its 
three divisions into a fore, middle and hind brain. Soon about 
twenty primitive vertebrae arise, and by this time the embryo is 
very similar, in external form, to any other vertebrate embryo, and 
finallv hatches in the form of the adult. 
Fig. 233. 
Embryo Skate. 
Fig. 231. 
Fig. 235. 
Side view of head of 
Fig. -231. 
More advanced em- 
bryo Skate. THE PISCES. 
211 
Not so, however, with the skate (llaia bcitis) as it presents an 
additional chapter in its life-history, 
discovered by Professor Wyman. 
Fig. 233 (this and those following 
after Wyman) shows the 3’oung 
skate resting on the large yolk-sac. 
It is eel-shaped, the dorsal (c) and 
(eZ) anal fins extending to the end 
of the tail as in the eel. Fig. 234 
represents a more advanced embryo, 
showing at a and b the pectoral and 
ventral fins, and at cZ, the temporary 
anal. Fig. 235 is a side view of the 
same enlarged (a. first branchial 
fissure, largest at its outer end; 
this enlarged portion corresponds with the future spiracle ; 6, the 
inner end ; the first arch is in front of the fissure; b', the second 
fissure, in front of which is the second arch, bearing a fringe ; c, 
nasal fossa; tZ, projection of the optic lobes ; e, cerebral lobes.) 
Soon after, the embryo skate becomes shark-shaped, as in Fig. 
236, while Figs. 237 and 238, represent a lateral and dorsal view 
of the embryo (/;, facial disk ; a, pectoral; c, ventral fin ; e, gill- 
Fig. 2:>6. 
Shark-shaped embryo Skate, 
Fig. 237 
More advanced embryo of Skate. 
fringes). There are at first seven branchial fissures, the most 
anterior of which is converted into the spiracle, which is the ho- 
mologue of the Eustachian tube and the outer ear-canal; the 
seventh is wholly closed up, no trace remaining, while the five 
others remain permanently open. 
Fig. 239 represents tlie newly hatched skate, when the form of 
the adult is closely approached (a, yolk-sac in the cavity of the 212 
LIFE HISTORIES OF ANIMALS. 
abdomen, connecting with the intestine, 6; c, embryonic portion 
of the tail, which disappears in the adult (Wyman). 
A condensed summary of the chief events in the life of a Se- 
lachian, is as follows :— 
1. Partial segmentation of the germinal disk. 
2. The embryo arises as a distinct body from the germinal 
disk (the “gastrula” condition being suppressed). 
Fig. 269. 
Fig. 238. 
Dorsal vicw.of Fig. 290 
Newly-hatched Skate. 
3. The cmbr3’o appears like that of an\’ other vertebrate, until 
finally 
4. The shark or skate form is assumed just before birth, or 
hatching from the egg. 
5. The skates pass through a shark-like form, before attaining 
the adult shape. 
LITERATURE. 
Wyman. Observations on the Development of Raia batis. ('Memoirs Amer. Acad. 
Sc., 1864). THE PISCES. 
213 
liambelce. Recherches sur le Developpment dn Pelobates fuscus (Memoires couron- 
nes Acad. Belgique, 34, 1870.) 
Balfour. A preliminary Account of the Development of the Elasmobranch Fishes. 
(Quart. Jour. Slier. Science, 1874.) 
Development of the bony Fishes. During their reproductive sea- 
son, the bony fishes, such as the stickleback, salmon and pike, 
are more highly colored than at other times, the males being es- 
brilliant in their hues, while other secondaty sexual char- 
acters are developed. The female deposits her eggs either in 
masses at the surface of the water, as in the cod and goose fish, 
or at the bottom on gravel or sand as in most other fishes, the 
male passing over them and depositing his “ milt ” or spermatic 
Fig. 210. 
Fig. 241, 
The same as Figs. 241, 242, 
243, before the egg-shell 
has burst. 
Embryo Blenny seen 
in front. 
Fig. 242. 
Fig. 213. 
The same as Fig. 241. 
seen in profile from 
the right side. 
The same as Fig. 241 > 
seen in profile from 
the left side. 
particles. The egg has a thin transparent shell, and the 3’olk is 
small, covered with a thick layer of the “ white.” 
The eggs after fertilization undergo partial segmentation, the 
primitive streak, notochord, nervous cord and brain developing 
much as described in the section on the embryology of birds. 
That the embryo before us is a' fish is soon determined by the 
absence of an amnion and allantois, and by the fact that the germ 
lies free over the yolk like a band. Figs. 240, 241, 242, 243 (cop- 214 
LIFE HISTORIES OF ANIMALS. 
ied by Agassiz 1 from Rathke), represent an advanced stage of the 
embryo Blenn}7 (Zoarces viviparus) in various positions, with the 
eyes, gill-arches, fins and vitelline network of blood vessels on 
the outer surface of the yolk sac. 
In the*pike the heart begins to beat about the seventh day, and 
by this time the alimentary canal is marked out. The primitive 
kidnej’s are developed above the liver. The air-bladder (probably 
the homologue of the lungs of higher vertebrates) arises as an 
offshoot opposite the liver from the alimentary canal, and the gall- 
bladder is also originally a diverticulum of the intestine. The 
urinary bladder in the fish is supposed to be the homologue of the 
allantois of the higher vertebrates. The principal external change 
is the appearance of the usually large pectoral fins. 
The embryo pike hatches in about twelve days after develop- 
ment begins and swims about with the large yolk bag attached, 
and it is some seven or eight days before the young fish takes 
food, living meanwhile on the yolk mass. The perch hatches in 
twelve days after the egg is fertilized, and swims about for eight 
or ten days before the yolk is absorbed. The vent opens in the 
pike four da\rs, and in the perch six days, after hatching. The 
gills gradually develop as the yolk is absorbed. 
The tail in most bony fishes (the Gadidae excepted, according 
to Owen), is heterocercal as in the maturer sharks, but subse- 
quently after the fish has swam about for a while and increased in 
size it becomes homocercal or symmetrical. The scales are Ihe 
last to be developed. 
In the large size of the pectoral fins, the position of the mouth, 
which is situated far back under the head, the heterocercal tail, the 
cartilaginous skeleton and uncovered gill-slits, the embryo salmon, 
pike, perch, etc., as Owen observes, manifest transitory characters 
which are permanent in sharks (Selachii). 
A summary of the changes undergone in the bony fishes is as 
follows : 
1. Segmentation partial. 
2. A gastrula-condition in the lamprey and sturgeon, but not 
in the bony fishes (trout, etc). 
3. The embryo arises as in any other vertebrate. 
iThe Structure and Growth of Domesticated Animals,” 20th Ann. Report of the 
Secretary of the Massachusetts Board of Agriculture. Boston, 1873. These and Figs. 
253-203, 266, were kindly loaned by Mr. C. L. Flint, the Secretary. TIIE AMPHIBIA. 
215 
4. Adult form attained at the time of hatching or birth, in the 
viviparous species; certain forms undergoing slight metamor- 
phosis. 
Vogt. Embryologie des Salmones (in Agassiz, Hist. Nat. des Poissons d’Poau douce 
de l’Kuroiie Ccntrale.) Neucliatel, 1842. 
Lereboullet. Kecherches d’Embvvologie Comparee snr le Developpement des Bro- 
chet, de la i'erche, etc. (Annates des Sc. Nat. Paris, 1855 ) 
(Ellricher. Beitrage zur Entwicklung der Knoclienflsche, etc. (Siebold and Kdili- 
ker’s Zeitschrift, 1873, ’74.) 
Kowalevsky, Owsjnnnikoff, unit Wagner. Entwickelung der Store (Sturgeon. Bulle- 
tin Imp. Acad. St. Petersburg, xiv, 1873.) 
Witli the writings of Kupffer, Gotte, Ray Lankester and Owsjannikoff. 
LITERATURE. 
XXXI. THE AMPHIBIA. 
Development of the Amphibia. Passing by the Dipnoa (Cera- 
todus, Protopterus and Lepidosiren) of whose development we as 
3’et are totally ignorant, and the Simosauria, Plesiosauria and 
Ichthyosauria, we come to the salamanders and toads and frogs, 
or Amphibia. The early history of the extinct Archegosaurus, 
Dendrerpeton and Labyrinthodonts died with them, and we can 
only predicate from the imperfectly known structure of the adult 
forms that their young possibly developed in a manner like that 
of the living batracliians. 
As in the Ashes the batracliians are most highly colored during 
the breeding season. The males of certain newts acquire the 
dorsal crest and a broader tail-fin, aiding in the process of fecunda- 
tion (Owen), and other secondary sexual features are added, es- 
pecially to the male during the reproductive season. After an 
imperfect sexual union the salamanders deposit their eggs on the 
leaves of aquatic plants. The eggs of the toad are laid in long 
strings, those of the frog in Inasses. In these creatures each egg 
is fertilized as it is extruded, and the egg then swells greatly, the 
yolk appearing as a dot in the large jelly-like mass surrounding it. 
Until we have a detailed embryology of the Amphibians, studied 
in the light of the newer school of embryology, the reader must 
be content with the following summary of Owen’s account. 
The segmentation of the egg in the Amphibia is total, the pro- 
cess beginning usually about three hours after impregnation in 
the frog, and lasting twenty-four hours. The primitive streak, 
the notochord and nervous system then arise as in other craniated 
Vertebrates. After the appearance of the branchial arches, the 
gills begin to bud out from them, finally forming the larger gills 216 
LIFE HISTORIES OF ANIMALS. 
of the tadpole. The embryo now rests on the large yolk sac, 
much as in the embryo fish, but this is entirely absorbed before 
the embryo leaves the egg. Before the yolk-sac is absorbed a 
communication opens between the alimentary canal and the 
branchial cavity in the head (bucco-branchial cavity of Owen), 
“and this opens externally on the lower part of the head by a 
vertical fissure, on each side of which a small protuberance buds 
out, forming a special organ of adhesion — a pair of temporary 
cephalic limbs.” (Owen.) Now the gills having got their growth, 
the remnant of the yolk enclosed by the abdominal walls, and 
the tail well developed, the tadpole bursts its egg membrane and 
swims about freely. In Italy, Rusconi found that the tadpoles 
hatched in four days, in England they hatch in five days, and the 
period may be prolonged to four weeks by cold weather. It is a 
common sight in Maine to see frogs’ eggs laid in ponds still con- 
taining ice and snow. 
The tadpole is much less developed than the larval fish or any 
other vertebrate ; the intestine is not }ret formed, and in other im- 
portant characters it is lower in organization than the freshly 
hatched fish. It is also a vegetarian, eating decaying leaves ; the 
mouth is small and round, the alimentary canal is remarkably long, 
the intestine coiled up in a spiral, the mouth is small, destitute of 
a tongue and the beak unarmed with teeth. “About the middle 
period of aquatic life the true or permanent kidneys begin to be 
formed from and upon the primordial ones; and the basis of the 
ovaria, or testes, may now be discerned. The oviduct is soon 
distinct from the ureter; but the testes retain the same excretory 
duct as the kidneys; their vasa deferentia communicate with re- 
tained caeca of the primordial kidneys before penetrating the later 
glands ; the upper or anterior ends of the first remain for some 
time behind the heart.” (Owen.) 
“ Soon after the external gills have reached their full develop- 
ment they begin to shrink, and finally disappear; but the branch- 
ial circulation is maintained some time longer upon the internal 
giils; these consist of numerous short tuft-like processes from the 
membrane covering the cartilaginous branchial arches; they are 
protected by the growth of a membranous gill-cover, which, as the 
external branchiae are absorbed, leaves only one small external 
orifice, by which the branchial streams, admitted by the mouth, 
continue to be expelled. The chief distinction between the fully THE AMPHIBIA. 
217 
developed branchial circulation in the Batrachian larva and that of 
the fish consists in the presence of small anastomosing channels, 
between the branchial artery and vein of each gill, proximad of the 
gill itself. The tongue makes its appearance when the fore limbs 
are developed.” 
The vertebra* of the tadpole are biconcave, but in the change to 
the adult are converted into cup-and-ball joints, by ossification of 
the substance of the cavities, and its coalescence either with the 
fore (Pipa) or back (Rana) part of the centrum. The remarkable 
changes in the hyo-branchial apparatus and the skull are described 
by Owen. 
The accompanying figures (from Tenney’s Zoology) represent 
the external changes of the toad from the time it is hatched until 
the form of the adult is attained. The tadpoles of our American 
toad, as observed in the European toad by Owen, are smaller and 
blacker in all stages of growth than those of the frog. The tadpole 
is at first without any limbs (Fig. 244) ; soon the hinder pair bud out. 
After this stage (Fig. 245) is reached the body begins to diminish 
in size. The next important change is the growth of the front 
Fig. 246. 
Fig. 245. 
Fig. 244. 
Fig. 247. 
Fig. 248. 
Metamorphosis of the Toad. 
legs and the partial disappearance of the tail (Fig. 246), while 
very small toads (Figs. 247 and 248), during midsummer, may be 
found on the edges of the pools in which some of the nearly tail- 
less tadpoles ma}T be seen swimming about. When the tadpoles 
are hatched late, the gills are often retained through the winter, 
as large tadpoles of frogs are often found in pools by breaking 
through the ice. It is three years, according to Owen, before the 
Amphibia are capable of breeding. 
“ In the newts (Triton) the gills are in three pairs, larger and 
more complex than in the frog; the fore limbs are the first to 218 
LIFE HISTORIES OF ANIMALS. 
emerge, and the gills persist long after the hind limbs are devel- 
oped.” (Owen). While as a rule the eggs of newts or salaman- 
ders are laid in the water, the red-backed salamander lays its eggs 
in damp places on land, though the young 
are provided with gills. Fig. 249 (after 
Iloy) represents the young of Amblystoma 
lurida on the tenth day after hatching, the 
lower figure the natural size of the freshly 
hatched young. In the Surinam toad and 
Hyla of the island of Mauritius there is no 
metamorphosis, the young hatching with the form of the adult. 
The Siredon or Axolotl of Mexico, according to Dumeril, lays 
eggs, though a larva, while, 
as in the Axolotl, the lar- 
va of Amblystoma mavor- 
tium, originally described 
as an adult animal under 
the name of Siredon liche- 
noides (Fig. 250, from Ten- 
ney’s Zoology) has been 
found by Professor Marsh 
to drop its gills and assume its adult form when brought to the 
sea level, its original habitat being the lakes situated in the Rocky 
Mountains at an altitude of 4500 - 7000 feet. 
Fig. 249. 
Larval Salamander. 
Fig. 250. 
Sircdon or larval Salamander-. 
Professor Owen lias well summed up the wonderful changes 
undergone in these metamorphoses, which are nearly paralleled 
by those of the vegetarian larval gnat with biting jaws and gills 
into the blood-sucking volant, air-breathing fly; entirely new 
organs replacing the deciduous ones of the larva, and the body 
in attaining maturity being made over anew. “ In the metamor- 
phoses of the Batrachia,” says the distinguished comparative 
anatomist, “we seem to have such process carried on before our 
eyes to its extremest extent. Not merely is one specific form 
changed to another of the same genus ; not merely is one generic 
modification of an order substituted for another, the transmuta- 
tion is not even limited by passing from one order (Urodela) to 
another (Anoura) ; it affects a transition from class to class. The 
Fish becomes the Frog ; the aquatic animal changes to the terres- 
trial one ; the water-breather becomes the air-breather ; an insect 
diet is substituted for a vegetable one. And these changes, more- THE AMPHIBIA. 
219 
over, proceed gradually, continuously, and without any interrup- 
tion of active life. The larva having started into independent 
existence as a fish, does not relapse into the passive torpor of the 
ovum to leave the organizing energies to complete their work un- 
troubled by the play of the parts they are to transmute, but step 
by step each organ is modified, and the behavior of the animal 
and its life-sphere are the consequence, not the cause, of the 
changes.” 
“The external gills are not dried and shrivelled by exposure to 
the air, nor does the larva gain its lungs by efforts to change its 
element and inhale a new respiratory medium. The beak is shed, 
the jaws and tongue are developed, and the gut shortened, before 
the 3Toung Frog is in a condition to catch a single fly. The em- 
bryo acquires the breathing and locomotive organs—gills and com- 
pressed tail—while imprisoned in the ovum ; and the tadpole ob- 
tains its lungs and land-limbs while a denizen of the pool; action 
and reaction between the germ and the gelatinous atmosphere of 
the yolk, or between the larva and its aqueous atmosphere, have 
no part in these transmutations. The Batrachian is compelled to 
a new sphere of life by antecedent obliterations, absorptions and 
developments, in which external influences and internal efforts 
have no share.” 
While the passage we have quoted is an attack against La- 
marckianism, we do not see but that in a long course of genera- 
tions of the ancestors of the present species of amphibians, the 
metamorphoses may have become gradually established, finally be- 
coming the normal history of each individual; the changes of the 
individual epitomizing the successive steps in the collective life- 
history of the entire group of Amphibians. That changes in the 
physical surroundings induce important modifications of structure 
is seen in the exceptional mode of metamorphosis of the Surinam 
Pipa, or the Hyla of Mauritius, and on the other hand, in the 
prematurity of the axolotl, which near the level of the sea drops 
its gills, while from four to six thousand feet above the sea it re- 
tains its gills and even produces young. 
To recapitulate, we have the following stages of development 
in the Amphibia: 
1. Morula (segmentation total). 
2. The embryo develops as in the bony fishes. 
3. Young with external gills hatching with a fish-like form, but 220 
LIFE HISTORIES OF ANIMALS. 
much less advanced in internal organization; or, rarely, hatching 
in the adult form, the metamorphosis being suppressed. 
4. Larval forms retained as in the Menobranchus, Siren, Meno- 
pona and salamanders ; or dropped, as in the toad and frog. 
Swammerdam. Biblia Naturas. 1737. 
Reichert. Vergleieh. Entwickelungsgeschichte der nackten Amphibien. 1838. 
Rusconi et Configliacht. Histoire Nat. Developpeinent et Metamorphose de la Sala- 
tnandre terrestre. Pavia, 1854. 
Schultze. Observaticnes nonnirllae de Ovorum Ranarum Segmentatione, 1863. With 
papers by Provost and Dumas, Newport, Horne, Dumeril and Marsh. 
LITERATURE. 
XXXII. THE REPTILIA. 
Development of the Reptiles. We now come to study the em- 
bryology of those vertebrates in which there is an important 
embryonal membrane, the amnion, developed, besides an allan- 
tois. The early stages of the reptilian embryo are so much like 
those of the bird that the reader is referred to the account of 
the development of the chick for a more complete histoiy of the 
early phases of embryonic life in the reptiles. 
As with birds, the eggs are enormous in size, and like those of 
the ostrich they are laid in the sand, where they are left by the 
parent to be hatched by the warmth of the sun. 
Professor H. J. Clark, in his “ Mind in Nature,” tells us that of 
all eggs those of turtles are by far the most easily preserved in a 
healthy state during the time of incubation. “All that is required 
to obtain them is to collect a number of turtles in early spring, 
before May, and keep them enclosed in some shady spot where 
they can have easy access to water and soft earth, and to feed them 
well with fresh herbage, such as plantain-leaves, lettuce, beet- 
leaves, etc., etc., and in the course of time, usually in May and 
June, they may be caught, at early dawn, digging holes in the 
earth with their hind legs, and depositing therein their brood of 
eggs, and then covering them up.” 
The lizards, snakes, and crocodiles, lay their eggs in sand or 
light soil, the iguana in the hollows of trees, while certain lizards 
and snakes are viviparous. Agassiz has discovered the extraor- 
dinary fact that in turtles fecundation does not appear to be an 
instantaneous act, resulting from one successful connection of the 
sexes, as it is with most animals, but “ a repetition of the act, thrice 
every year, for four successive years, is necessary to determine THE REPTILIA. 
221 
the final development of a new individual, which may be accom- 
plished in other animals by a single copulation.” From the same 
source we learn that Chrysemys picta does not lay its eggs 
before the eleventh year. Our other turtles probably lay their 
eggs from the eleventh to the fourteenth year, according to the 
species. The operation takes place in the month of June, both at 
the north and south, climatic differences not seeming to have any 
effect upon this particular function. 
Before segmentation of the yolk, the nucleus, or germinal vesicle, 
undergoes self-division. According to Agassiz and Clark “ this 
takes place, at least to a certain extent, without the influence of 
fecundation within a year, but at the same time has been seen only 
in those eggs which have been expelled from the ovary. Finally 
they become the original cells, “ the primitive embryonic cells ” en- 
gaged in the composition of the different organs of the body. In 
the bony fishes, according to (Ellacher, the germinal vesicle is 
ejected bodily from the germinal disk, and Foster and Balfour 
think this fate awaits that of the birds. In insects the germinal 
vesicle is supposed to undergo self-division and form the nuclei 
of the cells of the blastoderm. 
The segmentation of the yolk has been fully observed in Glyp- 
temys insculpta. “The process of segmentation is not so 
regular, and there does not seem to be alwaj’s, in the beginning, 
a symmetrical halving of the embryonic area, as has been observed 
among birds ; but in other respects it resembles what takes place 
within the eggs of the latter animals, and finally results in shap- 
ing out the embryonic disk.” Agassiz and Clark, from whom we 
have quoted, think, however, that, from certain phenomena ob- 
served by them, the whole mass of the yolk becomes segmented. 
The formation of the primitive streak, the amnion, allantois, 
and chorda dorsalis, are much as observed in the chick, and for 
an account of the early stages of the embryo reptiles, the reader 
is referred to the chapter on the embryology of birds. The lungs 
arise as hollow sacs projecting from the sides of the throat; the 
liver is a thickening of the same membrane from which the stom- 
ach is formed, while the reproductive glands ‘‘arise in intimate 
connection with the posterior end of the intestine.” 
By the time that the heart has become three-chambered, the 
vertebrae have reached the root of the tail, the eyes have be- 
come entirely enclosed in complete orbits, and the allantois begins 222 
LIFE HISTORIES OF ANIMALS. 
to grow. Soon after, the embryo turns upon its axis, and always 
rests on its left side. The nostrils may now be recognized as two 
simple indentations at the end of the head, and at first are not in 
communication with the mouth, but soon a shallow furrow leads 
to it. 
The shield begins to develop by a budding out laterally of the 
musculo-cutaneous layer along the sides of the body, and the 
growth of narrow ribs extending to the edge of the shield. “The 
feet, or rather paddles, of the lower forms of turtles, the Chelon- 
ioidce, do not remain in a partially undeveloped state, as might be 
expected from what is observed among other vertebrates, but un- 
dergo what may be called an excess of development; the bones 
of the toes becoming very much elongated, and the web—which 
remains soft among some turtles with moderately elongated toes, 
— is hardened by the development of densely packed scales, so 
that the whole foot is almost as rigid as the blade of an oar. At 
this time the embryo of Chelydra serpentina snaps at everything 
which touches it.” 
Of the development of the Saurians, or lizards, we have no com- 
plete account. The advanced embryo of the lizard, as figured by 
Owen (443), is like that of the turtle without its shell. 
As regards the development of snakes, Owen, deriving his in- 
formation from Rathke’s work, tells us that in the oviparous 
snakes (Natrix torquata) the embryo partially develops before the 
egg is laid, while the young hatches in two months after the egg is 
deposited. By this time the amnion is perfected, “the head is 
distinct, and shows the eye-ball and ear-sac; also the maxillary 
and mandibular processes. The allantois is about as large as the 
head.” The long trunk of the serpent grows in a series of de- 
creasing spirals, and when five or six are formed, the rudiments of 
the liver and the primordial kidneys are discernible.” At the 
latter third of embryonic life the right lung appears as a mere 
appendage to the beginning of the left. 
A summary of the changes in the egg undergone by the reptiles 
is as follows : 
1. Segmentation partial, possibly total (morula?). 
2. The embryo develops much as in the bony fishes until the 
embryonal membranes appear. 
3. Formation of an amnion. 
4. After the alimentary canal is sketched out, the allantois buds 
out from it. « THE AYES. 
223 
5. The shield of the turtle develops and the reptilian features 
are assumed. 
6. The embryo hatches in the form of the adult. 
LITERATURE. 
Rathlce. Entwickelungsgeschichte der Natter. Konigsberg, 1837. 
. Entwickelung tier Schildkroten. Braunsschwieg, 1848. 
. Ueber die Entwickelung und den Korperbau der Krokodile. 180G. 
Agassiz and Clark. Embryology of the Turtles in Agassiz’s Contributions to the 
Natural History of the United States, II, part iii. Boston, 1857. 
XXXIII. THE AYES. 
Development of Birds. So much alike are all the living species 
of birds that the embryology of a single kind is in all probability 
a type of that of the others. The development of the domestic 
fowl has been studied in more detail than any other vertebrate, 
since it is eas}T to hatch the eggs artificially, and from their large 
size they can be examined more readily than the eggs of fishes. 
Our account of the embryology of birds will be taken from the 
admirable history by Foster and Balfour in their “Elements of 
Embryology,” and we shall freely use their work, often quoting 
them, word for word, where it is not possible to farther condense 
their language. 
The eggs of the hen are fertilized in the upper extremity of the 
oviduct, whether before or after the “ white” of the egg is depos- 
ited is unknown, but at any rate before the shell is deposited 
around the “ white.” * 
First day. As the first result of impregnation the germinal 
vesicle disappears, probably being, judging from the analogy of 
the bony fishes, bodily ejected from the germinal disk. Then be- 
gins the process of segmentation of the yolk, which goes on at 
about the time the shell is formed. Segmentation is partial, being 
restricted to the germinal disk of the ovarian egg ; the result is 
the formation of the blastodermic disk, which is the beginning of 
the embryo, resting on the upper surface of the yolk and appear- 
ing as a pale round spot seen in the freshly laid egg. This blas- 
toderm at first consists of two layers of cells, the upper made up 
of nucleated cells, and the lower of irregular rounded massss 
called “ formative cells.” 
Now begins the marking out of the embryo, which develops in 
the “a?ea pellucida ” a transparent rim (encompassed by the 
“ area opaca ”) surrounding the blastoderm. The first step is the 
origin of an inner germ-layer, the two others having previously 224 
LIFE HISTORIES OF ANIMALS. 
arisen, so that we now have the three germ-layers found in all 
vertebrates and in some invertebrates. From the outer laj’er 
(epiblast) arises the tegument and walls of the body, with the 
nervous cord; while from the second (mesoblast) are formed 
the heart and the vascular system or blood-vessels, and the stom- 
ach and intestines. The third and innermost layer is called 
the “ hypoblast.” By the sixth or eighth hour these three mem- 
branes become definitely established. The middle layer now 
thickens and thus causes the appearance known as the “ primitive 
streak,” along the middle of which runs the depression known as 
the “primitive groove.” In front of the primitive groove appears 
the “ medullary groove,” and below it the notochord or u chorda 
dorsalis ” originates from the cells of the middle layer. This 
notochord (Fig. 251, ch) lies directly beneath the medullary tube 
Fig-25h 
Section of an embryo Hen. 
(mr) and between the outer and third germ-layer in the form of a 
flattened circular rod. The blastoderm is now folded anteriorly 
like the letter S ; this is called the “ head-fold,” and soon after 
the “tail-fold” is formed in a similar way. These two folds meet 
in the middle, thus forming the body of the embryo. 
Next the primitive groove and streak disappear as the sides of 
the medullary groove rise up, when they finally meet, forming the 
neural tube, or hollow in which the nervous cord is developed. 
About this period the first pair of protovertebne make their 
appearance. They arise from the mcsoblast as two cubical masses 
(Fig. 251A, u w) lying one on each side of the notochord. Two 
more pairs appear behind the first pair before the first day is 
1 Fig. 251; dd, third or inner germ-layer (darmdriisenblatt or hypoblast); ch, chorda 
dorsalis or notochord; uw, primitive vertebrae, or protovertebrae; uwh, cavity in the 
protovertebra?; no, primitive aorta; ung, Wolffian duct; sp, split in the middle-germ 
layer, the beginning of the pleuro-peritoueal cavity (mesoblast) by which it is divided 
into two layers, the lower layer (df) the splanchnopleure (or davmfaserblatt), the upper 
layer (hpl) being the somatopleure (hautplatt), the two layers unite at nip (Kblliker’s 
mittelplatt); mr, medullary tube (riickenmark); li, outer germ-layer (liornblatt or 
epiblast). THE AVES. 
225 
ended. “ Out of the protovertebrae are formed not only the per- 
manent vertebrae, but also the superficial dorsal as well as certain 
Fig. 252. 
Early stage of a Vertebrate (Fowl). 
other muscles and the spinal nerves. The pair of protovertebrae 
first formed corresponds not with the first cervical vertebra of the 
adult chick, but rather with the third or even fourth; for though 
LIFE HISTORIER OF ANIMALS. 226 
LIFE HISTORIES OF ANIMALS. 
the majority of the protovertebrae are formed regularly behind the 
first pair, two or even three pair may make their appearance in 
front of it” (Foster and Balfour). 
Fig. 251 (from Kolliker) is a cross section through an embryo 
chick of the second magnified 90-i00 times, showing the rela- 
tions of the medullary tube, chorda dorsalis and protovertebrae. 
Meanwhile the middle layer has split into two layers ; the upper 
(or outer) leaf is called the “ somatopleure,” so-called from its 
giving rise to the body walls, while the lower (or inner) leaf is 
called the “ splanchnopleure,” as it is destined to form the ali- 
mentary canal, and the liver and other glands originating from the 
digestive cavity. 
The amnion next arises from certain folds of the somatopleure. 
As the embryo thickens and sinks into the yolk two folds grow 
out of the head and tail end respectively (Fig. 252, 2, ks and ss). 
These finally meet and coalesce on the fourth day over the back 
of the embryo, forming the amniotic cavity (Fig. 252, 3, ah) in 
which the embryo lies. The fluid which fills this cavity is called 
the amniotic fluid. 
The allantois arises as an appendage of the alimentary canal, 
budding out at the hinder end of the embryo. It finally grows 
(as in Fig. 252, 4, al) so large as to curve over the embryo, serv- 
ing as a foetal respiratory organ.1 
Second Day. By the time the embryo is thirty hours old the 
outlines are bolder, more distinct and the tissues firmer, so that 
1 Fig. 252. Five schematic figures showing the development of the foetal egg-mem- 
branes, where in all except the last the embiyo is represented as if seen in longitudinal 
section. 1. Diagram of egg with zona iiellucida, blastoderm (a,i) germinal disk and 
embryo. 2. Egg with the first traces of the yolk sac (d) and amnion (ks, ss and am). 
3. Egg with the amnion uniting and forming a sac; the allantois (al) budding out. 4. 
Egg with the villi of the serous membrane (sz); the allantois larger; embryo with 
mouth and anal opening. 5. Egg in which the vascular layer of the allantois lies close 
to the serous layer and has grown into the villi of the same, constituting the true cho- 
rion (ch). Yolk sac much smaller, about to be drawn into the cavity of the amnion. 
d, yolk-skin; d’, villi of the yolk-skin; sh, serous membrane: sz, villi of the serous 
membrane; ch, chorion (vascular layer of the allantois) chz, true villi of the chorion 
(arising from the projections of the chorion and the sac of the serous membrane); am, 
amnion; ks, head-fold of the amnion; ss, tail-fold of the amnion; ah, cavity of the am- 
nion ; as, sheath of the amnion for the navel string; a, the first beginning of the embryo 
arising from a thickening of the outer layer of the blastoderm a'; m, thickening form- 
ing the germ in the middle layer of the blastoderm (m'), which at first only reached as 
far as the germinal disk, and afterwards forms the vascular layer of the yolk-sac (df) 
which connects with the intestino-muscular layer (darmfaserblatte); st, sinus termi- 
nalis; dd, intestino-glandular layer (darmdrusenblatt) arising out of a part of i, the 
inner layer of the blastoderm (afterwards the epithelium of the yolk-sac; kh, cavity of THE AVES, 
227 
the whole blastoderm can be removed from the egg wdth much 
greater ease than before. The head-fold has now become more 
prominent than before. The nerve-tube, at first of uniform thick- 
ness dilates anteriorly forming the first cerebral vesicle, and the 
second and third cerebral vesicles successively form; the proto- 
vertebrae increase rapidly, and soon the embryonic chick presents 
the appearance of the embryo rabbit of nearly the same age. 
The alimentary canal commences as a cxd cle sac, closed in front 
but widely open behind, situated below the anterior end of the 
medullary tube. The heart originates also in the head-fold at 
about the time the protovertebrae are formed, and the rudiment is 
situated below the fore gut or rudiment of the alimentary canal; 
by the end of the first half of the second day it is flask-shaped, 
with a slight bend to the right. “ Soon after its formation the 
heart begins to beat, its at first slow and rare pulsations beginning 
at the venous and passing on to the arterial end.” Its movements 
begin before the cells of which it is composed are differentiated 
into muscle or nerve-cells. To provide channels for the fluid 
pressed out by the contractions of the heart; the heart divides into 
the two primitive aortae, and connects with other embryonic tem- 
porary arteries and veins. Meanwhile in the vascular area and 
area pellucida, the arteries, capillaries and veins rapidly develop, 
and blood disks arise as amoeba-like cells separating from the adja- 
cent cell-mass of the mesoblast (middle genn-layer), while the 
vessels are contemporaneously forming; the red blood corpuscles 
not being true cells, but nuclei. The first half of the second day 
ends with the rise of the rudiment of the Wolffian duct. “ It is 
important to remember that the embryo of which we are now 
speaking is simply a part of the whole germinal membrane, which 
is gradually spreading over the surface of the yolk. It is impor- 
tant also to bear in mind that all that part of the embryo which is 
in front of the most anterior protovertebrae corresponds to the 
future head, and the rest to the neck, body and tail. At this 
the blastoderm, which afterwards becomes ds, the cavity of the yolk-sac; dg, passage 
way of the yolk; al, allantois; e, embryo; r, original space between the amnion and 
chorion, tilled with albuminous fluid; vl, anterior body-wall in the region of the heart; 
hh, cavity of the heart without the heart itself. 
In Figs. 2 and 3, the amnion is for the sake of clearness represented as situated too 
far away from the embryo; so also the cavity of the heart is drawn too small and the 
embryo too large, since except in Fig. 5, they are only drawn diagrammatically. These 
and Figs. 251, 264, 265, 267 and 268 are from Kblliker’s Entwickeluugsgeschiclite des 
Menschen und der hoheren Thieve. 228 
LTFE HISTORIES OK ANIMALS. 
period the head occupies nearly a third of the whole length of the 
embryo” (Foster and Balfour). 
In the second half of the second day, among the most important 
changes are the appearance of the second and third cerebral vesi- 
cles, the optic vesicles, while the “ first rudiment of the ear is 
formed as an involution of the epiblast on the side of the hind 
brain or third cerebral vesicle.” 
Third day. This day is one of the most eventful, as the rudi- 
ments of so many important organs now first appear. First, the 
embryo, now almost completely enveloped by the amnion, turns 
around so- as to lie on its left side. The heart, originally formed 
under where the brain is destined to lie, moves backward into the 
trunk, and by this time (the third day) the neck has been formed, 
in which appears the four branchial fissures, the most anterior 
being formed first. It is these temporary fissures which corres- 
pond to the branchial fissures of Amphioxus. “ On account of 
this resemblance—in fact by some assumed as an identity both in 
form and function—the fissures have been called by embryologists 
the branchial fissures (compare Fig. 235) and the vessels [passing 
between them] the branchial aortas, the former corresponding with 
the passages between the gills of fishes, and the latter with the 
vessels which supply the gills with blood” (Clark’s Mind in Na- 
ture, p. 311). 
in fact the embryo bird in some respects is now as far advanced 
in organization as the Lancelet, and majr be rudely compared with 
that animal, though the incipient neck, head and brain are features 
which the Lancelet lacks. 
The e3re commences as a lateral outgrowth of the fore brain, 
in the form of a stalked vesicle subsequently converted into the 
optic nerve, while the lens is formed by an involution of the skin 
of the body (outer germ-layer) over the front end of the optic 
vesicle. The ear is also at first simply an involution of the outer 
germ-layer (epiblast) forming a pit, or “ otic vesicle,” which is 
destined to form the internal ear, containing the bones and other 
parts of the inner ear. The nose begins as two shallow pits 
formed by the sinking in of the outer germ-layer. Each of these 
pits is situated next to the olfactory vesicles (afterwards nerves), 
but at first there is no connection between the pits and the nerves 
as between the pits and the mouth, the latter not being yet formed, 
since it arises afterwards as an extension inward of the cleft be- 229 
THE AVES. 
tween the first branchial folds and its branch, as the jaws or max- 
illae arise from the first fold, the upper jaws being two branches of 
the fold, the fold itself being the under jaw, while a lozenge- 
shaped cavity between the fold and its branches becomes the 
mouth. 
Meanwhile, for all the changes in the different organs are going 
on contemporaneously, the vesicles or lateral expansions of the 
nerve-tube appear, the vesicles of the cerebral hemispheres devel- 
oping, whilst the separation of the hind-brain into the cerebrellum 
and medulla oblongata takes place. The digestive cavity is during 
the third day also, differentiated into the fore-gut and liind-gut, 
the former farther subdividing into the oesophagus, stomach and 
duodenum, and the hind-gut into the large intestine and cloaca. 
The lungs arise as two pocket-like appendages of the alimentary 
canal immediately in front of the stomach; while the liver is 
originally two diverticula, and the pancreas a single offshoot, from 
the duodenum. 
Fourth day. With a decided increase in size by this day, the 
amnion becomes more distinct, and the allantois is visible. The 
wings and legs now appear as flattened conical buds arising from 
the “Wolffian ridge,” a low ridge running from the neck to the 
tail, those forming the wings being scarcely distinguishable from 
the rudimentary legs. 
The olfactorj7 grooves appear at this time and the partition 
heretofore existing between the mouth and throat is absorbed and 
disappears. 
The protovertebrae have, by this time, increased in number from 
thirty to forty. The upper portion (muscle-plate) having previ- 
ously separated to form the muscles inserted in the skeleton (epi- 
sketal muscles of Huxley), has left the remainder of each proto- 
vertebra as a somewhat triangular mass, the upper angle of which 
grows up and meets its fellow in the median line above, thus 
enclosing the nerve-canal. On the lower side each protovertebra 
sends out a similar growth enclosing the notochord. “ While the 
inner portion of each protovertebra is thus extending inwards 
around both notochord and neural canal, the remaining outer por- 
tion is undergoing a remarkable change. It becomes divided into 
an anterior or praeaxial, and a posterior or postaxial segment. 
The anterior, which is the larger and more transparent of the two, 
is the rudiment of the spinal ganglion and nerve, while the pos- 230 
LIFE HISTORIES OF ANIMALS. 
terior, which remains more particularly connected with the exten- 
sions round the neural canal and notochord, goes to form part of 
the permanent vertebra. In this way each protovertebra, having 
given rise to a muscle-plate, is farther subdivided into a ganglionic 
rudiment, and into a mass which we may speak of as a ‘ primary ’ 
vertebra, consisting as it does of a body or mass investing the 
notochord, from which springs an arch covering in the neural 
canal.” (Foster and Balfour.) The conversion of the primary ver- 
tebrae or membranous vertebral column into the permanent verte- 
brae is “ complicated by a remarkable new or secondaiy segmenta- 
tion of the whole vertebral column,” so that “ each permanent 
vertebra is formed out of portions of two consecutive protoverte- 
brae. Thus, for instance, the tenth permanent vertebra is formed 
out of the hind portion of the tenth protovertebra, and the front 
portion of the eleventh protovertebra, while its arch, now attached 
to its front part, was attached to the hind part of the tenth proto- 
vertebra.” (Foster and Balfour). 
By the sixth day the notochord begins to diminish, and disap- 
pears by the time the bird is hatched, while by the twelfth day the 
ossification of the bodies of the vertebrae commences, the process 
beginning in the second or third cervical, and thence extending 
backwards. The ribs begin as a downward growth from the ex- 
terior of the vertebrae, becoming by the sixth day separate from 
the bodies of the vertebrae. 
Between the eightieth and one hundredth hour of incubation 
the permanent kidneys arise, and previous to this the sexual 
glands have arisen out of the middle germ-layer, from the germinal 
epithelium lying at the upper end of the pleuroperitoneal cavity. 
In this epithelium may be seen certain large cells, the primordial 
ova, which are at first seen in male as well as female embryos, so 
that in early stages it is impossible to distinguish the sexes. Be- 
tween the eightieth and one hundredth hour, however, the pri- 
mordial ova disappear in those embryos destined to be males, 
while they enlarge and multiply in the female. “The large nu- 
cleus of the primordial ovum becomes the germinal vesicle, while 
the ovum itself remains as the true “ ovum.” The testes begin 
to arise on the sixth day. 
Fifth day. This period is signalized by the further growth of 
the allantois, and by the appearance of the knee and elbow, and of 
the cartilages which precede the formation of the bones of the THE AVES. 
231 
digits and limbs; as well as by the formation of the primitive 
skull, with the development of the parts of the face, and the 
formation of the anus. 
The cranium, from the researches of Rathke, Parker and others, 
is formed from the middle germ-layer, and in the fourth day is 
simply membranous; after that time the tissue composing it be- 
comes cartilage. After the fourth day the primitive skull consists 
of two portions, *.e., a sheet of cartilage ensheatliing the noto- 
chord from its anterior end to the first vertebra. “ This sheet of 
cartilage forms an unsegmented continuation of the vertebral bod- 
ies. It is to be considered as the most anterior portion of the 
axial skeleton, in which the segmentation has become obliterated ; 
and as such is equivalent not to one, but to a (hitherto not cer- 
tainly determined) number of vertebrae.” (Foster and Balfour. 
For the farther changes in the development of the skull the reader 
is referred to Parker’s memoir on the Development of the Skull 
of the Common Fowl, or the excellent, illustrated abstract in 
Foster and Balfour’s “ Elements.”) 
Not until the sixth day are distinct bird-characters developed. 
Hitherto it would be almost impossible to distinguish the embryo 
from a reptile or mammal. During the sixth and seventh day the 
wing and foot assume a bird form, the crop and intestinal coeca 
make their appearance, “the stomach takes the form of a gizzard, 
and the nose begins to develop into a beak, while the incipient 
bones of the skull arrange themselves after the avian type. . . . 
From the eleventh day onwards the embryo successively puts on 
characters which are not onty avian, but even distinctive of the 
genus, species and variety.” By the ninth or tenth day the 
feathers originate in sacs in the skin, these sacs by the eleventh 
day appearing to the naked eye as feathers, the sacs however re- 
maining closed as late as the nineteenth day, though many are an 
inch in length. ' 
The nails and scales begin to appear on the thirteenth day. 
“By the thirteenth day the cartilaginous skeleton is completed, 
and the various muscles of the body can be made out with toler- 
able clearness. Ossification begins, according to Yon Baer, on the 
eighth or ninth day by small deposits in the tibia, in the meta- 
carpal bones of the hind-limb, and in the scapula. On the eleventh 
or twelfth day a multitude of points of ossification make their ap- 
pearance in the limbs, in the scapular and pelvic arches, in the 232 
LIFE HISTORIES OF ANIMALS. 
ribs, in the bodies of the cervical and dorsal vertebrae, and in the 
bones of the head, the centres of ossification of the vertebral 
arches not being formed till the thirteenth day.” 
While the blood is at first aerated by the allantois, and there is 
a partial double circulation of the blood ; as soon as respiration 
begins a completely double circulation is formed. 
After the sixth day muscular movements of the embryo proba- 
bly begin, but they are slight until the fourteenth day, when the 
embryo chick changes its position, lying lengthways in the egg, 
with its beak touching the chorion and shell membrane, where they 
form the inner wall of the rapidly increasing air chamber at the 
broad end. On the twentieth day or thereabouts, the beak is 
thrust through these membranes, and the bird begins to breathe 
the air contained in the chamber. Thereupon the pulmonary cir- 
culation becomes functionally active, and at the same time blood 
ceases to flow through the umbilical arteries. The allantois shriv- 
els up, the umbilicus becomes completely closed, and the chick, 
piercing the shell at the broad end of the egg with repeated blows 
of its beak, casts off the dried remains of allantois, amnion and 
chorion, and steps out into the world.” (Foster and Balfour). 
A brief summary of the changes undergone by the developing 
chick will be seen to be nearly identical with that of reptiles : 
1. Partial segmentation of the yolk. 
2. The embryo develops much as in the bony fishes until the 
embryonal membranes appear. 
3. Formation of an amnion. 
4. After the alimentary canal is sketched out, the allantois buds 
out from it. 
5. The avian features appear from the sixth to the tenth day. 
6. The embryo leaves the egg in the form of the adult, and like 
the reptile, is at once active, feeding itself. 
LITERATURE. 
Harvey. Exercitationes anatomic® de Generatione Animalium. London, 1651. 
Malpighi. De Formatione Pulli in Ovo. London, 1672. 
Haller. Sur la Formation du Coeur dans le Poulet. London, 1758. 
. Elementa Phy3iologi®, Liber xxix. 1766. 
Wolff. Theoria Generationis. Halle, 1759. 
J’ander. Dissertatio inauguralis sistens Historiam Metamorphoseos quam Ovum 
incnbatum prioribus quinque diebus snbit. Wurzburg, 1817. 
. Beitrage zur Entwickelungsgeschichte des Hiihnchens im Eie. WUrzburg, 
1817. 
Purlcinje. Symbol® ad Ovi Avium Historiam. Yratislav, 1825. THE MAMMALIA. 
233 
Von Baer. Ueber Entwicklungsgeschichte der Thiere. Konigsberg, 1828. 
Reichert. Das Entwicklungsleben im Wirbelthierreich. Berlin, 1810. 
Erdl. Die Entwicklung des Menschen und des IlUhnchens im Ei. Theil 1. Leipzig, 
1845. 
RemaJc. Untersuchungen fiber die Entwicklung der Wirbelthiere. Berlin, 1855. 
Parker. On the Development of the Skull of the Common Fowl (Phil. Trans, clvi, 
1. London, 1866.) 
Foster and Balfour. The Elements of Embryology, Vol. i. London, 1874. 
With the works of Coste, Allen Thompson and others. 
XXXIY. THE MAMMALIA. 
That fishes, amphibious reptiles and birds should lay eggs, 
seems quite in the course of nature, but that a mammal should 
grow from an egg appeared incredible to Haller, who in 1778 
publicly disputed Degraef’s discovery, six years previous, of the 
egg of the rabbit. That all mammals grow from eggs was fully 
proved by Von Baer in 1827, while Coste, Valentin and Jones in 
1834 and 1835, showed that the mammalian egg is homologous 
with the eggs of the lower vertebrates. 
The ovarian egg of a mammal, such as the rabbit, is shown at 
Figs. 253, 254 and 255. It is exceedingly minute, from the small 
Fig. 253. 
Fig. 254. 
Fig. 255. 
Ovarian egg of rabbit. Mag- 
nified 125 diameters. 
Ovarian egg of rabbit, freed 
of the cells which surround 
the zona pellucida in Eig. 
253. Magnified 125 times. 
The germinative vesicle 
shines through the yolk as 
a light spot. 
The same ovarian egg of 
the rabbit as in Fig. 254, 
opened with a needle. 
The yolk with the ger- 
minative vesicle and 
dot are flowing out. 
Magnified 125 times. 
quantity of yolk-substance in it; but in the duck bill (Monotremes) 
the egg is quite large, with more yolk-matter, being from two- 
and-a-half to three lines in diameter; while in the kangaroo, the 
egg is a tenth of a line in diameter. 234 
LIFE HISTORIES OF ANIMALS. 
Development of the Mammals. As in the Amphioxus and the 
Amphibians, the egg undergoes total segmen- 
tation. Fig. 256 represents the egg of the dog 
surrounded by the cells which partly conceal 
the zona pellucida, with the spermatic particles 
swimming just within. Fertilization (a pro- 
cess apparently identical with that seen in 
the egg of the sponge, Fig. 42,) having been 
effected, the yolk subdivides as seen in Figs. 
257-263, and the mulberry state (Morula) is 
soon assumed. 
To relate how the blastoderm divides into 
two germinal layers and afterwards into three, how the primitive 
Fig. 256. 
Egg of Dog fertilized 
by the spermatic parti- 
cles seen in the zona 
pellucida. 
Fig. 257. 
Fig. 258. 
Fig. 259. 
Fig. 260. 
Fig. 261. 
Fig. 262. 
Fig. 203. 
Different Stages of segmentation of the yolk in the Egg of the Dog. 
streak, the notochord, and the sides of the medullar}- groove which 
rise up and enclose the spinal cord, and the protovertebne appear, 
would be but a repetition of the account of the mode of devel- 
opment of the chick. About the end of the first day, the germ THE MAMMALIA. 
235 
appears as in Fig. 264,1 which represents the embryo rabbit when 
slightly over a line in 
length. At this time 
the amnion surrounds 
the head-end of the 
primitive band as if 
with a hood ; the three 
primary divisions of the 
brain, into fore, middle 
and hind brain, are now 
well marked, and im- 
mediately after this 
stage the blood vessels 
arise, forming* the vas- 
cular network permeat- 
ing the germinal disk, 
on which the embryo 
rests, the heart being 
at first a simple tube, 
afterwards twisted and finally dividing into the two auricles and 
Fig. 284. 
Embryo rabbit, about one day old, 
Succeeding changes, including the formation of the gill-slits, 
limbs and tail are exactly as those represented by Fig. 267 and 
268 of the human embryo, and correspond to similar phases of 
the fishes, amphibians, reptiles and birds. By the twenty-fifth 
day the embryo dog appears as in Fig. 265, and soon after this 
period the distinctive mammalian features are brought out, when 
finally the characters peculiar to dogs appear. At the time of its 
birth the young mammal is usually of large size, as compared 
with its parent, as in the cat, dog and monkey; but in the duck- 
bill (Ornithorhynchus), the young is only one inch and two lines 
in length, naked, and in nearly as helpless a condition as the young 
marsupial. 
The young marsupials are very small and embryonic in form 
when born. The opossum, whose period of gestation is from 
twenty to twenty-six days, brings forth helpless young which are 
1 Fig. 264. Germinal disk and germ of a rabbit about one day old, seen from the 
back, a, edge of the head-end of the amnion; b, fore-brain; c, lateral expansion of 
the same, or primitive eye-vesicle; d, middle, e, hind-brain. There are eight proto- 
vertebrse, between which is situated the spinal cord. Enlarged ten times. Copied from 
Bischoff, by Kblliker. 236 
LIFE HISTORIES OF ANIMALS. 
naked, and only eight-tenths of an inch in length from the mouth 
to the end of the tail. The kangaroo (Macropus major), an ani- 
mal as large as a calf, and whose period of gestation is thirty-six 
days, produces young which measure only an inch from the mouth 
to the root of the tail. On the other hand the whales at birth are 
Fig. 2G5.i 
remarkably large and mature in form. The remaining mammals 
(Didelphia), besides the chorion and amnion, which are discarded 
at birth, are, in the embryo condition, provided with an important 
Embryo dog, twenty-five days old. 
1 Fig. 2G5, front view of the embryo of a dog at the end of the twenty-fifth day, mag- 
nified twice. The embryo seen sideways would appear as in Fig. 268, but has been 
straightened out and enlarged, with the anterior ventral wall removed, so that the ven- 
tral cavity appears more capacious than in nature, and the heart seems to lie exposed. 
a, nasal cavities; b, eyes; c, lower maxillae (first gill-arches); d, second gill-arches; e, 
right,/, left auricle; g, right, li, left ventricle; i, aorta; k, liver-lobes with the cavity of 
the vena omphalo-mesenterica between them; l, stomach; m, intestine, united by a short 
narrow yolk-canal with the yolk-sac n ; o, Wolffian body; pp, allantois; q, anterior, r, 
hinder extremities. Copied by Kolliker from Bischoff. MAN. 
237 
organ, the placenta, or after-birth, a development of the allantois, 
serving as an organ of respiration as well as to nourish the foetus, 
and carry off its effete products by means of the maternal circu- 
lation. 
The Mammals, then, as a rule, pass through the following 
stages : — 
1. Morula. 
2. Remaining stages as in the birds, until the mammalian char- 
acteristics appear. 
8. Adult form at birth ; or subembryonic, as in the duck bill and 
marsupials. 
LITERATURE. 
Barry. Researches on Embryology. (London Phil. Trans., 1838-10.) 
Bischoff. Entwicklungsgeschichte des Kanincheneies, Hundeeies, Meerschwein- 
chens, und Rehes. 1842-51. (Four separate works.) 
Owen. Comparative Anatomy and Physiology of Vertebrates. Vol. lii, London, 1868. 
Absolutely identical in his mode of embryonic growth with the 
placental mammals, man’s developmental history until shortly be- 
fore birth, is probably but a repetition of that of the rabbit or dog. 
Like his blood relations, the lower mammals, he derives his origin 
from a minute sac of protoplasm, which is at first, as in the eggs 
of all animals, like a Moncr, having no nucleus. It then becomes 
nucleated and nucleolated like any egg, and is of an inch in 
diameter (Fig. 2661). 
XXXV. THE BIMAN A (Man). 
This egg, on contact with several sperm cells, likewise simple 
sacs of protoplasm, immediately undergoes segmentation, probably 
(though this point has not yet been proved) ex- 
actly as in the dog and even in the sponge, and 
indeed in animals of all grades. A blastodermic 
disk, from which originates the primitive streak, 
which subdivides into the two primitive germ- 
layers, comparable with the two-layered sac of 
the free swimming embryonic Amphioxus, next 
arises, and from it are formed the nervous cord 
and notochord (Ascidian stage) and protovertebrse. 
He next attains a stage of development that may be compared 
Fig. 266. 
Human Egg. 
1 Fig. 266. Ovarian egg of a human female, cut open. The yolk has escaped whole 
and in it the germinative vesicle and germinative dot are seen as a lighter spot. Cop- 
ied from Bischoff. Magnified one hundied times. 238 
LIFE HISTORIES OF ANIMALS. 
with that of the adult Amphioxus. After the brain appears he is 
like a young shark or fish, lie next reaches the stage (Fig. 267 
characterizing the embryos of 
all amphibians, reptiles, birds 
and beasts, when the rudi- 
ments of the four limbs ap- 
pear. The amphibian char- 
acter, the want of an allantois, 
is now dropped, and develop- 
ment advancing, he rises to a 
level with the reptiles, birds 
and mammals, the allantois 
now having formed (Figure 
2682). When five weeks advanced the characters separating man 
from the ordinary mammals 
begin to appear, and at this 
time when compared with the 
embryo dog of the twent}’- 
fifth da}T, the head is seen to 
be higher on the crown, owing 
to the greater development of 
the brain, and the tail is pro- 
portionately shorter. Imme- 
diately after this, the hinder 
extremities lengthen, the head 
enlarges in the cerebral region 
and the human form is clearly 
indicated by the seventh week, 
the subsequent changes con- 
sisting in the remodelling of the outlines, in which it passes 
through a generalized ape-like figure, until the human form is 
shaped out. At birth he casts off the amnion, chorion and pla- 
Fig. 267. 
Human embryo, third week. 
Fig. 268. 
Human embryo, fourth week. 
1 Fig. 267. Human embryo at the end of the third or beginning of the fourth week, 
enlarged, a. amnion; 6, yolk-sac; c, first gill-arch, or lower jaw; e, second gill-arch, 
behind which are two others with gill-slits between them; f, indications of the arms; 
g, primitive ear-vesicle; /t, eyes; i, heart. Compare figure of the embryo skate (Fig. 
225). 
2 Fig. 2(58. Human embryo of the fourth week, a, amnion, partly removed on the 
back; b, yolk-sac; b', yolk canal; c, under jaw or first gill-arch ; d, prolongation of the 
first gill-arch destined to form the upper jaw; e, e', e”„ second and fourth gill arches; 
f, primitive ear-vesicle; g, eyes; h, fore, i, hinder limbs; k, navel-string with a portion 
of the amnion; l, heart; m, liver. This and Fig. 267, from Kolliker. MAN. 
239 
centa, and enters the world helpless, naked and toothless, not at- 
taining full maturity until from the fifteenth to the twentieth year. 
During this time he undergoes a partial metamorphosis, discarding 
temporary organs, such as the first set of teeth, the first set of 
eye-lashes, and undergoing important changes of the external 
form of the body as well as of the internal organs. 
In giving our summary of the life-history of man, we will enter 
a little more in detail than in the other vertebrates. It will be 
seen that the embryonic life of man is almost an epitome of the 
animal kingdom, beginning with characters common to the moners 
and the worms, and ending with the vertebrates. The stages which 
he passes through are, then, as follows: 
1. A minute mass of protoplasm, like a moner. (Compare 
Protomonas, Fig. 3A.) 
2. Egg stage. (Compare Fig. 42.) 
3. Morula stage. (Compare Fig. 43.) 
4. A suppressed gastrula stage ? at least a two-layered sac, as 
in Fig. 252, 1. (Compare Fig. 44.) 
5. Ascidian stage with a notochord. (Compare Fig. 164, B). 
6. Amphioxus stage, having no brain or skull, but with gill- 
slits. 
7. Fish stage, with brain and skull. 
8. Reptile stage, having an amnion and allantois. 
9. Mammal stage, with a placenta. 
10. Quadrumanous stage, like the tailless apes. 
11. Man. 
KolliJeer. Entwickhuigsgeschiclite des Menschen, etc. Leipzig, 18G1. 
Pouchet. Trait4 du Developpmeut de l’Homme et des Mammifaires. Paris, 1843. 
Hasckel. Anthropogenic. Entwickelungsgeschichte des Menschen. Leipzig, 1874. 
LITERATURE INDEX. 
Acanthocephali, 136. 
Acanthometra, 19. 
Accra, 106. 
Acineta, 39. 
Adheres, 171. 
Actinia, 70. 
Actinophrys, 18. 
Actinotrocha, 157. 
Actinozoa, 70. 
ASginopsis, 66. 
Allantois, 226. 
Alpheus, 185. 
Amblystoma, 218. 
Amnion, 226. 
Amoeba, 14,17. 
Amphibia, 215. 
Amphioxus, 207. 
Amphipods, 183. 
Anchorella, 171. 
Anemone, Sea, 70. 
Annelides, 161. 
Annulata, 158. 
Antedon, 79. 
Apus, 178. 
Arachnactis, 73. 
Area opaca, 223. 
pellucida, 227. 
Argiope, 148. 
Argonauta, 114. 
Artemia, 178. 
Ascidians, 150. 
Asellus, 181. 
Asterias, 81. 
Astroides, 71. 
Atax, 194. 
Aurelia, 67. 
Auricularia, 89. 
Axinella, 49. 
Axolotl, 218. 
Balanoglossus, 158. 
Barnacle, 167. 
Bathybius, 3. 
Birds, 223. 
Blastoderm, 199, 204, 209, 223. 
Bougainvillea, 62. 
Brachionus, 139. 
Brachiopoda, 144. 
Brain, 229. 
Branchial Assures, 228. 
Branchipus, 178. 
Bugula, 143. 
Bulla, 106. 
Calyptraea, 107. 
Cardium, 97. 
Catena, 121. 
Cavolinia, 105. 
Cephalophora, 103. 
Cephalopoda, 114. 
Cephalula, 94, 96, 133,158. 
Cercaria, 124. 
Cerianthus, 73. 
Cestodes, 127. 
Chaetognatha, 135. 
Chelifer, 196. 
Chiton, 106. 
Chlamydomonas, 26. 
Chorda dorsalis. 
Chrysemys, 221. 
Ciliata, 34. 
Circulation, 232. 
Cladocera, 172. 
Codosiga, 27. 
Coelenterates, 56. 
Collosphaera, 19, 20. 
Collozoum, 19, 21. 
Colpodella, 26, 28. 
Copepods, 169. 
Corophium, 183. 
Coryne, 60. 
Crab, 187. 
Crab. King, 173. 
Cranium, 231. 
Crenella, 99. 
Crinoids, 79. 
Crustacea, 167. 
Ctenophor®, 74. 
Cuttle Ash, 114. 
Cyanea, 68. 
Cyclops, 170,171. 
Cydippe, 75. 
Cysticercus, 128. 
Daphnia, 172. 
Decapods, 184. 
Deinamoeba, 16. 
Dentalium, 104. 
Discophora, 67. 
Distoma, 124. 
Dog, 234, 236. 
Ear, 228. 
Earth worm, 161. 
Echinoderms, 77. 
Echinoids, 85. 
Echinorhynchus, 136. 
Edwardsia, 73. 
Ephyra, 69. 
Epistylis, 37, 40. 
Euglena, 27. 
Eye, 228. 
Fishes, 209. 
Fish lice, 169,171. 
Flagellata, 23. 
Flat worm; 122. 
Fluke, 123. 
Flustra, 142. 
Foraminifera,.16. 
Frog, 215, 217. 
Gastrula, 51, 71, 75. 
Geophilus, 193. 
Gephyrea, 157. 
Germ-layers. 
Gill-slits, 228. 
Gregarina, 9. 
Gromia, 15,19. 
Halcampa, 73. 
Haliomma, 16. 
Halisarca, 54. 
Hyalonema, 49. 
Hydra, 56, 58. 
'241 242 
INDEX. 
Hydractinia, 60. 
Hydroida, 56. 
Idyia, 75. 
Infusoria, 34. 
Insects, 189. 
Isopods, 180. 
Isotoma, 200. 
Julus, 192. 
Kidneys, 230. 
Labyrinthula, 22. 
Lamellibranchiata, 93. 
Leech, 161. 
Limnadia, 176. 
Limulus, 173. 
Lingula, 145. 
Liver worm, 123. 
Lobster, 187. 
Loligo, 114. 
Louse, 205. 
Lumbricus, 161. 
Lupa, 184. 
Lymnseus, 112. 
Mammals, 233. 
Medusas, 67. 
Melicertum, 63. 
Miliola, 19. 
Mite, 194. 
Molgula, 150. 
Mollusca, 93. 
Monad, 23, 29. 
Monas, 23. 
Monera, 1. 
Monostomum, 124. 
Morula, 50. 
Mussel, 99, 100. 
Myobia, 194. 
Myriopods, 190. 
Mytilus, 99. 
Myxastrum, 4, 8. 
Nanomia, 65. 
Nareda, 131. 
Matrix, 222. 
Nauplius, 168, 184. 
Nebalia, 179. 
Nematelminthes, 134. 
Nemerteans, 130. 
Nerine, 163. 
Newt, 215. 
Noctilnca, 31. 
Nose. 
Notochord, 152, 154, 224. 
Oniscus, 181. 
Ophioneurus, 203. 
Ophiusa, 78. 
Ostracodes, 172. 
Oyster, 96. 
Pamphagus, 15. 
Paramecium, 34. 
Pelomyxa, 15, 18. 
Peltogaster, 168. 
PenEeus, 184. 
Pheronema, 49. 
Phoronis, 161. 
Phyllodoce, 163. 
Phyllopods, 176. 
Physalia, 65. 
Pilidium, 130. 
Planaria, 122. 
Planocera, 122. 
Planula, 51, 63. 
Platyelminthes, 119. 
Platygaster, 202. 
Pleurobrachia, 75, 76. 
Pluteus, 87. 
Podura, 200. 
Polycystina, 17. 
Polydesmus, 191. 
Polydora, 163. 
Polykrikos, 37. 
Polynema, 202. 
Polythalamia, 16. 
Polyxenus, 191. 
Polyzoa. 141. 
Proglottis, 129. 
Proscolex, 129. 
ProtamcEba, 2. 
Protobatliybius, 3. 
Protogenes, 4. 
Protohydra, 56. 
Protomonas, 4, 5. 
Protomyxa, 5. 
Protovertebras, 224, 229. 
Pteropods, 105. 
Pycnogonidse, 195. 
Rabbit. 233. 
Radiolaria. 16. 
Reptiles, 220. 
Rhizopoda, 14. 
Rotatoria. 138. 
Rotifer, 138. 
Roundworm, 134. 
Sacculina, 168. 
Sagitta, 135. 
Salamander, 217. 
Salpa, 156. 
Scolex, 128. 
Scorpion, 197. 
Scorpion, false. 196. 
Scyphistoma, 68. 
Sepia, 114. 
Sharks, 209. 
Ship worm, 100. 
Sida, 172. 
Siphonophora. 65. 
Sipunculus, 157. 
Siredon, 218. 
Skates, 209. 
Skull, 231. 
Snail, 103. 
Snake, 222. 
Sphinx, 204, 206. 
Spider, 198. 
Spirorbis, 162. 
Sponge, 43. 
Squamella, 138. 
Starfish. 81. 
Statoblast, 143. 
Stenfcor, 36. 
Stomobrachium, 63. 
Strobila, 68. 
Strongylosoma, 190. 
Sycandra, 49, 54. 
Sycon, 49, 53, 54. 
Tadpole, 217. 
Tape worms, 127. 
Tardigrade, 195. 
Teleas, 204. 
Terebratulina, 145. 
Terebrellides, 163. 
Teredo, 100. 
Tethilla. 49. 
Tetradecapods, 180. 
Tetrapyle. 16. INDEX. 
243 
Thalassicolla, 19. 
Thecidium, 146. 
Thethya, 49. 
Thread worm, 134. 
Tick, 195. 
Toad, 217. 
Tornaria, 158. 
Trematodes, 123. 
Trichina, 135. 
Trilobite, 175. 
Trochosphere, 112. 
Trochus, 109. 
Tuba, 40. 
Tunicata, 150. 
Turbellaria, 121. 
Turtle, 220. 
Unio, 100. 
Urchin, Sea, 85. 
Ureila, 24. 
Urnula, 41. 
Vaginicola, 38. 
Vampyrella, 4, 7. 
Veliger, 96, 107, 112. 
Vermetns, 110. 
Water hear, 195. 
Wolffian bodies, 235. 
Worms, 119. 
Zoea, 185. 
Zona pellucida, 226, 234.