MEMOIRS 
OF THE 
BOSTON SOCIETY OF NATURAL HISTORY; 
VOLUME III. NUMBER VI. 
SOME OBSERVATIONS ON THE EMBRYOLOGY OF 
THE TELEOSTS. 
By J. S. KINGSLEY AND II. W. CONN. 
BOSTON: 
PUBLISHED BY THE SOCIETY. 
April, 1883. VI. Some Observations on the Embryology of the Teleosts. 
By J. S. Kingsley and H. W. Conn. 
Read March 15, 1882.1 
The following observations on the development of a marine bony fish were made 
at the Summer Laboratory of the Boston Society of Natural History at Annisquam, Mass., 
during the months of June, July and August 1881. Most of the facts here recorded have 
been witnessed by both authors and in the majority of cases have been repeated many 
times. The composition of this article is the work of Mr. Kingsley and when the pronoun 
“we ” occurs in the following pages it indicates the fact that both of us are responsible 
for the statements presented, the phenomena which were witnessed by Mr. Conn alone are 
indicated by the use of his name, while the “ I ” which will be frequently met in the course 
of the article indicates that Mr. Kingsley alone is responsible for the statement or interpre- 
tation presented. As.we separated soon after the conclusion of the observations herein 
recorded, it has fallen to.the lot of Mr. Kingsley to make the comparisons with the work 
of other authors; and the whole discussion of previous results, with the exception of a 
portion of the work of Oellacher, has been done by him. The bibliography which follows 
has been wholly the compilation of Mr. Kingsley and embraces only those papers which 
have been consulted during the preparation of this article. Nevertheless it is hoped that 
it may proye of use to other students of Vertebrate Embryology. I have adopted the 
method of referring to these various papers which is used by Dr. Mark in his valuable 
. memoir on the Maturation, Impregnation and Segmentation of Limax; viz: the name of 
the author followed by the date of the article in full faced type. Where two or more 
articles by the same author were published in the same year they have the additional 
letters a, b, c, etc. 
BIBLIOGRAPHY. 
Agassiz, Alexander E. R. * 
’76. The development of Flounders<American Naturalist, x, pp. 705-708 (1876). 
’77\ On the young stages of some osseous fishes. I. Development of the tail <Proceedings of the 
American Academy, xra, pp. 117-127, 2 pis. (1877). 
’77b. Sur le developpement des Pleuronectes < Journal de Zoologie vi, pp. 193-197 (1877). 
1 Owing to the long delay in the publication of this article 
I have had an opportunity to add extensively to it, having 
gone over much of the ground again during the summer of 
1882. The additions, however, will all appear as foot-notes 
each with the date 1882. For the opportunities enjoyed 
for pursuing my investigations I would return thanks to Pro- 
fessor Hyatt and Mr. Van Vleck for their kindness and the 
facilities afforded me during the two summers spent at 
Annisquam. 184 
KINGSLEY AND CONN 
78a. [Same title as 77a]. Abstract < Annals and Magazine of Natural History, Series v, Yol. i, pp. 419- 
421 (1878). 
78b. Embryology of the Gar Pike<Science News, i, pp. 19-20 (1878). 
’79a. On the young stages of bony fishes <Proc. Am. Acad. Arts and Sciences, xiv, pp. 1-25, pis. m-x 
(1879). 
' ’79b. The development of Lepidosteus<Proc. Am. Acad., xiv, pp. 65-76, pis. 5 (1879). 
’82. On the young stages of some osseous fishes. Part m<Proc. Am. Acad, xvn, pp. 271-303, 
20 pis. (1882). 
Aubert, Herman. 
’54. Beitrage zur Entwickelungsgeschichte der Fische<Zeitschrift fur wissenschaftliche Zoologie, Bd. 
v, pp. 94-109, pi. vi (1854). 
’56. (Same title as ’54] 1. c. Bd., vn, pp. 345-364, pi. xviii (1856). 
Balfour, Francis Maitland. 
’75. A comparison of the early stages in the development of Vertebrates <Quarterly Journal of 
Microscopical Science,-Yol. xv, p. 207, pi. x (1875). 
’76a. On the origin and history of the urogenital organs of Vertebrates <Journal of Anatomy and 
Physiology, x, pp. 17-48 (1876). 
’76b. On the development of the spinal nerves in Elasmobranch Fishes <Philosophical Transactions of 
the Royal Society, Yol. clxvi, pp. 175-195, pis. xvi-xviii (1876). 
’76c. [Abstract of 76b, same title] <Proceedings of the Royal Society, Yol. xxiv, pp. 135-136 (1876). 
’76d. On the development of Elasmobranch Fishes <Journ. Anat. and Phys., xi, pp. 377-411, 517-570, 
672-688, pis. xv, xvi, xxi-xxvi, xxix (1876). 
’77. [Continuation of 76d]<Z. c. Vol. xn, pp. 128-172, 416-490, 674-706, pis. v, vi, xv-xix, xxiv, xxv 
(1877). 
’78. A monograph of the development of Elasmobranch Fishes. London, Macmillan & Co., pp. xi, 
+295, pis. 20, (1878). 
’80. A treatise on Comparative Embryology. London, Macmillan & Co., Yol. i, pp. xi + 492 + xxn, 
(1880). 
’81. [Same] Yol. n, pp. xi + 655 + xxn (1881). 
Van Bambeke, Ch. 
’70. Recherches sur le d£veloppement du Pelobate brun (Pelobates fuscus, Wagl.)<M6m. Savants 
Etrangers Acad. Roy. Belgique, t. xxxiv, pp. 66, pis. 5, 1867 (1870). 
’75. Recherches sur l’Embryologie des Poissons osseux. Rapport de M. Ed. Van Beneden<Bulletin 
Acad. Roy. Belgique n, Serie, t. xxxix, pp. 75-84 (1875). 
’76. Recherches sur l’embryologie des Poissons osseux <Mem. Sav. Etr. Acad. Belg. xl, pp. iv + 66, 
pis. 3, (1876).. 
Baudelot, E. 
’73. Observations sur les structure et le developpement des nageoires’des Poissons osseux < Archives 
de Zoologie expeiumentale, t. n, Notes et Revue, pp. xviii-xxiv (1873). 
Van Beneden, Edouard. 
’70. Recherches sur la composition et la signification de l’oeuf [etc.] <Mem. Corn*. Acad. Belg. t. xxxiv, 
pp. 283, pis. 12, 1868 (1870). 
’75. (See Van Bambeke ’75). 
’78. A contribution to the history of the embryonic development of the Teleosteans < Quart. Journ. 
Micros. Science, xviii, pp. 41-57, 1 pi. (1878). 
Brooks, William Keith. 
’81. Alternations of periods of rest with periods of activity in' the segmenting eggs of Vertebrates 
<Studies from the Biological Laboratory of Johns Hopkins, Univ., Yol, n, pp. 117-118, pi. viii (1871). 
Bruch, C. 
’55. Ueber die Mikropyle der Fische<Zeitschrift f. wiss. Zool. vn, pp. 172-175, pi. ix (1855.) 
Calberla, E. 
’77. Zur Entwicklung der Medullarohres und der Chorda dorsalis der Teleostier und der Petromy- 
zonten<Morphologisch.es Jahrbuch, Bd. in, pp. 226-270, pis. xii-xra (1877). ON THE EMBRYOLOGY OF THE TELEOSTS. 
185 
Foster, Michael and Balfour, F. M. 
’74. The Elements of Embryology. 12° London, Macmillan & Co., pp. xix -f- 272 (1874J. 
Garlick, Theodatus. 
On the artificial reproduction of Fishes<Proc. Cleveland Academy i, pp. 86-91. 1854 (1874). 
Gensch, H. 
’80. Die Blutbildung auf dem Dottersack bei Knochenfisohen<Archiv f. Mikr. Anat. Bd; xix, pp. 144- 
146 (1880). 
Gotte, A; 
’78. Zur Entwickelungsgeschichte der Teleostierkieme<Zoologischer Anzeiger 1 Jahrg. No. 3, p. 52 
(1878). 
’73. Beitrage zur Entwickelungeschichte der Wirbelthiere. I. Der Keim des Forelleneies<Arch. f. 
Mikr. Anat. ix, pp. 679-708, pi. xxvn (1873). 
’78b. Beitrage zur Entwickelungsgeschichte der Wirbelthiere III. Ueber die Entwickelung der Central- 
Nervensystem<Arch. f. Mikr. Anat. xv, pp. 139-199, pis. vh-x (1878). 
Henneguy, L. F. 
’80. On some facts in regard to the first phenomena of the development of the osseous fishes <Annals 
and Mag. Nat. Hist., v Series, Yol. vi, pp. 402-404.(1880) (Extract Bulletin Soc. Philomath, de Paris, Apr. 
10, 1880). 
His, Wilhelm. 
’73. Untersuchungen fiber das Ei und die Eientwickelung bei Knochenfischen, 4° Leipzig, F. C. W. 
Vogel, pp. iv + 54, 4 pis. (1873). 
’75. Untersuchungen fiber die Entwickelung von Knochenfischen, besonders fiber diejenige des 
Salmens<Zeitschrift f. Anat. und Entwickelungeschichte, Bd. i, pp. 1-40, pis. i-ii, (1875). 
Hoffman, C. K. 
Zur Ontogenie der Knochenfische<Verh. der. k. Akad. v. Wetensch. xxi, pp. 167, pis. 7, (1881). 
Joly, N. 
’72. Observations on the metamorphoses of the bony fishes in general and especially on those of a 
small Chinese fish, of the genus Macropodia, recently introduced into France <Ann. and Mag*. Nati Hist, iv, 
x, pp. 463-465 (1872) [from Comptes Rendus Sept. 30, p. 766, 1872]. 
Klein, E. 
’72. Researches on the first stages of the development of the common trout, Salmo fario<Monthly 
Microscopical Journal, vn, pp. 192-200, pis. xvi-xvii (1872). 
’76. Observations on the early development of the common trout, Salmo fario.<Quart. Journ. Micro. 
Sci. xvi, p. 113, pi. vi, (1876). 
Kupffer, C. 
’68. Beobachtungen fiber die Entwickelung der Knochenfischen <Arch. f. Mikr! Anat., iv, pp. 209-272 
pis. xvi-xviii (1868). 
’65. Untersuchungen uber die Entwickelung des Harn-und Geschlechts-system <Archiv f. Mikr. Anat. 
i, p. 233 (1865). 
’66. [Same continued] <1. c. ii, p. 473 (1866). 
Lereboullet. 
’54. Resume d’un travail d’embryologie comparee sur le developpement du Brochet, de la Perche et 
de l’Ecrevisse<Annales des Sciences Naturelles, Zoologie, iv serie, i tome, pp. 237-289 (1854). 
’61. Recherches d’embryologie comparee sur le developpement de la Truite, du Lezard et du Limnee 
<Ann. Sci. Nat., iv, xvi, pp. 113-196, pis. ii-m (1861). 
’64. Nouvelles recherches sur la formation des premieres cellules embryonnaires<Ann. [Sci. Nat., v. ii 
pp. 5-41, pi: i (1864). . 
Muller, Johann. 
’54, Ueber zahlreiche Porencanale in der Eikapsel der Fische<Arch. f. Anat. u. Phys., pp. 186-190, 
pi. vm, F. 4-7 (1854). 
Oellacher, Josef. 
’72a. Beitrage zur Geschichte des Keimblaschen im Wirbelthiere<Arch. f. Mikr. Anat., vm, pp. 1-27, 
pi. i (1872). 
MEMOIRS BOST. SOC. NAT. HIST. VOL. III. 24 • 186 
KINGSLEY AND CONN 
’72b. Beitrage zur Entwickelungsgeschichte der Knochenfische, nacli Beobaehtungen am Bacbforelleneie 
<Zeitsch. f. Wiss. Zool., xxn, pp. 373. 
’73. [Continuation of 72b]<l. c. Bd. xxiii, pp. 1-115, pis. i-iv, (1873). 
Owsjannikow, Pit. 
’72. Ueber die ersten Vorgange der Entwickelung jn den Eien des Coregonus lavaretus <Melanges 
Biologiques Acad. Sf. Petersbourg, t. ix, pp. 198-212, 1 pi. (1872). 
’74. [Same] <Bulletin de Petersbourg, t. vn, pp. 225-235, 1 pi. (1874). 
Ransom W. H. 
’67a. Observations on the ovum of osseous fishes <Philosophical Trans. Roy. Soc., Yol. clvii, pp. 
431-501, pis. xv-xyii (1867). 
’67b. On the structure and growth of the ovarian ovum in Gasterosteus leiurus<Quart. Jour. Micr. Sc ., 
yii (New Series) pp. 1-4, (1867). 
Reichert, K. B. 
’56a. Ueber die Micropyle der Fischeier und fiber einen bisher unbekannten, eigenthtimliclien Bau 
des Nahrungsdotters reifer und befruchteter Fischeier < Arch. f. Anat. u. Phys., pp. 83-124, pis. ii-iv (1856). 
’56b. Uber die Mfiller-Wolff’schen Korper bei Fischembryonen und fiber die sogenannten Rotationen 
des Dotters im befruchteten Hechteie<l. c. pp. 125-143 (1856). 
’58. Beobachtungen fiber die ersten Blutgefasse und deren Bildung sowie fiber die .Bewegung des 
Blutesin derselbenbei Fischembryonen<Studien a. d. Physiolog. Institut zu Breslau, i, pp. 1-94, 1 pi. (1858). 
Reineck. 
’69. Uber die Schichtung des Forellenkeims <Arch. f. Mikr. Anat., v> pp. 356-366, pi. xxi, (1869). 
Ryder, John. A. 
’81a. Preliminary notice of the more important scientific results obtained from a study of the embry- 
ology of Fishes<Bulletin U. S. Fish Commission, i, pp 22-23, (1881). 
’81b. Notes on the development, spinning habits and structure of the four-spined stickleback, Apeltes 
quadracus.<l. c. pp. 24-29) (1881). 
’81c. Development of the Spanish Mackerel (Cymbium maculatum) <1. c. pp. 135-165, pis. i-iy [xiii- 
xiv] (1881). 
’81d. On the retardation of the development of the ova of the shad (Alosa sapidissima) with some 
observations on the egg fungus and Bacteria<1. c. pp. 177-190) (1881). 
’81°. A contribution to the development and morphology of the Lophobranchiates (Hippocampus 
antiquorum, the sea horse <1. c. pp. 191-199, pi. xvi, (1881). 
’82'*. Development of the silver gar (Belone longirostris) [etc.] <1. c. pp. 283-301, pis. xix-xxi, 1881 (1882) 
’82b. On the nuclear cleavage figures developed during the segmentation of the germinal disc of the 
salmon <1. c. pp. 335-339 pi. xvm, 1881 (1882.) 
Rudwaner, Josef. 
’76. Ueber die erste Anlage der Chorda dorsalis <Sitzungsberichte der k. k. Akad. zu Wien, Bd. lxixt, 
Abth. hi, pp. 159-165, 1 pi. (1876). 
ScHAPRINGER, ALOIS. 
’71. Ueber die Bildung des Medullarohres bei den Knochenfischen < Sitz. k. k. Acad. Wien., Bd. 
lxiv, Abth. m, pp. 653-656, (1871), 
Scott, W. B. 
’81. Beitrage zur Entwickelungsgeschichte der Petromyzonten<Morphologisches Jahrbuch,vn, pp. 101- 
172, pis. vii-xi (1881). 
Scott, W. B. and Osborn, Henry F. 
’79. On some points in the early development of the common newt < Quart.* Jour. Micr. Sci., xix, pp. 
449-475, pis. xx-xxi (1879). 
S. 
’65. Untersuchungen fiber die Entwickelung der Bachforelle<Sitz- der k. k. Akad. Wien, li Abth 2, pp. 
546-554, pis. i-ii (1865). 
Vogt, Carl. 
’42. Embryologie der Salmones<In Agassiz, Histoire Naturelle des Poissons d’eau douce de l’Europe 
centrale, 8° with folio atlas of plates, pp. 328, Neuchatel (1842). ON THE EMBRYOLOGY OF THE TELEOSTS. 
187 
The eggs on which we worked were obtained by surface skimming and were usually 
found in about equal abundance at day and in the evening, and as a rule were rather 
more abundant when the tide was coming in than when it was running out. One or two 
evenings however proved an exception to the rule, as once with about half an hour’s skim- 
ming we found over 700 eggs by actual count. This large number however was except- 
ional, one hundred or one hundred and fifty being near the average. 
The most numerous form of egg and the one on which our observations were principally 
made was perfectly spherical, about a thirtieth of an inch in diameter, and perfectly transpar- 
ent. The shell enveloping it (chorion of older authors) was extremely thin and only under 
high powers showing a double contour. A Tolies one-tenth objective revealed no traces of 
any structure in it, nor were there visible any pores such as exist in the egg shells of many 
Teleosts.1 The various preparations of carmine and liaematoxylin as well as the anilines 
very quickly stained the- shell, but a prolonged immersion in any staining fluid colored the 
contents of the egg but very imperfectly and very slightly, thus offering a striking contrast 
with the eggs of Merlucius which were studied at the same time by Mr. Van Vleck, and 
which stained easily and well. As our eggs obtained by skimming and were mature 
and fertilized, there existed between the shell of the egg and the egg proper a narrow 
space filled with a transparent fluid in which the yolk floats freely. This space is the 
breathing chamber of Ransom. The food yolk or deutoplasm comprises the greater por- 
tion of the egg over one side of which the formative yolk, or protoplasm, is spread as a thin 
layer. The deutoplasm is perfectly colorless, free from all oil globules or granules of any sort 
and of nearly the same refractive index as the salt water in which the eggs were kept, render- 
ing it an operation of some difficulty to pick the eggs out of the water in which they were 
kept, on account of their being nearly invisible. The protoplasm-was in the early stages 
relatively very small, composing less than a twentieth of the bulk of the egg. Like the 
deutoplasm it was perfectly free from granules or globules of oil or food-yolk but it was of 
a very pale straw-color and -was more refringent than the deutoplasm. With eggs of such 
transparence one could easily watch most of the changes going on, even in the interior of 
the egg, while it was on the stage of the micro&cope, thus affording in this respect a more 
favorable object than the egg of the trout which has been the subject of so much investi- 
gation in Europe. 
Upon the above described egg most of the observations were made which form the basis 
of this paper. When any other form is used the fact will be stated in the text. 
We greatly regret that we are unable to identify the eggs on which we worked,2 but all 
attempts to rear the young fish beyond a few hours after hatching proved futile. We tried 
keeping them at the ordinary temperature of the room, keeping them in an ice chest, 
and in breeding boxes, allowing a free circulation of water, or placed in the water from which 
the young were taken, but in vain. Mr Van Vleck had no better success with the young 
of Merlucius. 
From the numbers of eggs which we found we supposed that they must belong to some 
abundant shore fish, and the following observations may aid in approximating the species. 
The flounder (Platessa americcina) is, according to a letter to Mr. G. Brown Goode, a win- 
1 Conf. His. ’73 pi. ii. Aubert ’54 pi. vi, fig. 1. 
2 During the summer of 1882 I was able to identify the 
eggs, which turned out to be, as suspected, those of the Gunner 
(Ctenolabrus coeruleus.') 188 
KINGSLEY AND CONN 
ter spawning fish. The eggs of the smelt (Osmerus) are over twice the size of those on 
which we worked. The eggs of Merlucius, Microgadus, Motella, and possibly of all of the 
Gadidae have one or more conspicuous oil globules in the deutoplasm. The eggs of the 
Cunner (Ctenolabrus coeruleus) taken from the living fish, very closely resemble our 
specimens in size and appearance, and it seems to us that the probabilities are in favor of 
our eggs belonging to this species. 
On the other hand one would expect to find (if there be any correspondence between 
closely allied fish and their eggs which, with the possible exception of the Gadidae men- 
tioned above, has not yet been shownJ) a similarity between our eggs and those of the 
perch as described and figured by Lereboullet and Ransom. Lereboullet describes the 
egg of the European perch (’54 p. 241-242) as transparent vesicles containing “ glob- 
ules graiseaux et un grosse goutte huileuse” and also as agglutinated. These features 
were seen by us neither in the ovarian egg of the Ctenolabrus nor in the ripe, unsegmented 
egg which We studied. Neither were there present any filiform appendages. Ransom has 
given a separate description of the egg of the same species, but we saw none of the pores, 
the rythmic contractions, nor the micropyle2 which he figures and describes, nor any such 
tubes as he shows ( ’67a PI. XYI, fig. 26 etc.). The mode of development, especially in 
the early stages, is also far different from that of the perch as epitomized by Lereboullet. 
The other eggs upon which observations were made were: 
I. An egg of similar size and appearance 'with a large reddish colored oil globule in 
the deutoplasm. 
II. An egg of the same size with several reddish oil globules and a slightly granular 
protoplasm and deutoplasm. 
III. A larger egg, about a twentieth of an inch in diameter with one large oil globule. 
III. A large egg, about a fifteenth of an inch in diameter (twice that of our form) and 
like it in being perfectly transparent and in possessing no oil globule, though both its pro- 
toplasm and deutoplasm were slightly granular. In all of these eggs the relative amount 
of food and germinative yolk were about the same. 
These eggs all floated at or near the surface of the water and presented a marked con- 
trast to those of an Elasmobranch, Batrachian, Reptile or Bird (and which I have never 
happened to see mentioned as a characteristic of fish eggs) in* that the germinative 
'portion is invariably downward, or on the lower surface of the egg while the deutoplasm 
is uppermost. This peculiarity renders it very easy by inclining the microscope, to rotate 
the egg into almost any desired position with one exception : it does not permit us to 
obtain a surface view of the blastoderm. Nor could this be obtained by confining the egg, 
as the slightest pressure almost immediately killed it, rupturing the vitelline membrane and 
thus contracting the blastoderm so that nothing could be made out of it. The bad eggs 
always sank. 
1 Ryder’s papers should be consulted in this connection. 
2 During the summer of 1882 I was more fortunate, having 
twice seen the micropyle. This is shown in PI. xiv, figs. 1 
and 2. A shallow depression surrounds the micropyle which 
itself, when seen in optical section, is a funnel-shaped tube, 
its walls extending in some little distance beyond the rest of 
the egg membrane. Near the micropyle the membrane is 
thickened and in surface views is seen to be permeated by 
very minute tubes (or possibly only surrounded by punctae, 
though from what is known of other forms, the former view 
would seem the most probable). I did not see these tubes 
except very near the micropyle. The micropyle itself more 
closely approximates that of the Herring as figured by Hoff- 
man (’81, PI. i, fig. 9) than it does those of the more nearly 
related Julis and Crenilabrus as figured by the same author 
on his third plate. ON THE EMBRYOLOGY OF THE TELEOSTS. 
189 
The small size of the eggs and their great contraction in any hardening medium (osmic, 
chromic, and Kleinenberg’s picric acids, bichromate of potash and alcohol) prevented the cut- 
ting of any satisfactory sections though many attempts were made. It was also found very 
difficult to keep the eggs alive for twenty-four hours, and to these two causes must be 
attributed the fragmentary condition of these notes, of whose shortcomings no one can be 
more cognizant than the writer. Still in many ways, notably in witnessing the invagina- 
tion of the hypoblast and the formation of the notochord, the extreme transparence of 
the eggs rendered our information on these points far more satisfactory than any sections 
could have done, as every step of the process could be clearly seen. 
In the following pages the development of the egg will be taken up by stages, each of 
which is characterized by some prominent feature or by the appearance of some important 
organ. From the fact that the several portions of the body are undergoing development 
at the same time, a perfect chronological arrangement in treating of the subject cannot be 
maintained, but it is hoped that the general features may be followed* in nearly their 
proper order. 
These stages may be briefly indicated and epitomised as follows : 
I. The maturation of the ovum. We have been unable to obtain anything on this point 
in our eggs, but introduce some observations upon the eggs of the “ Old England Hake,” 
Merlucius. 
II. The phenomena of segmentation until the formation of the germ layers. 
III. The formation of the three primary layers, the segmentation cavity, the invagina- 
tion of the hypoblast, and the appearance of nuclei in the intermediary layer of Van 
Bambeke. 
IV. The formation of the notochord and neural cord. During this stage the invagina- 
tion is completed. 
V. The formation of the optic bulbs and the segmentation of the muscle plates into 
proto-vertebrae. During this stage the first appearance of what we call “Kupffer’s vesci- 
cle ” and what Balfour regards (’81 p. 61) as the post-anal vesicle, is seen. In the 
later portion of this stage the splitting of the mesoblast into somatoplure and splanchno- 
plure begins, while the epiblast in the cephalic region thickens to form the lens of the 
eye. 
VI. In this stage the ears and nasal pits make their appearance and undergo a portion 
of their development; the lens of the eye is segmented from the epiblast and the first 
traces of blood vessels were seen; the segmentation of the muscle plates still continues. 
VII. The heart and pericardial cavity begin to be differentiated and the former to 
beat. The blastoderm at this stage completely envelopes the deutoplasm and in subsequent 
stages will be spoken of as the yolk sac. The gills bud and the gill-arches and gill- 
arteries appear in the later portion of this stage. In this stage the first contractions and 
movements of the embryo are seen; simultaneously with the first beating of the heart. 
VIII. During this stage the development of the organs previously outlined progresses 
while the outgrowth of the tail and the formation of the anus are the new features. 
The fore and hind gut also become prominent and the lumen in the latter is readily seen. 
IX. This stage is characterized by the hatching of the embryo and is reached in from 
forty-eight to fifty-six hours after the first segmentation furrows make their appearance, a 190 
KINGSLEY AND CONN 
slight difference in time being noticeable with a change in the temperature. The yolk sac 
has rapidly decreased in size. 
X. The formation of the mouth, the complete disappearance of the yolk sac and the 
deposition of pigment in the eye. 
Though the processes above outlined and now to be described present many striking 
differences from those which are found in fresh water fishes, they are essentially similar, not 
only in all the eggs of the marine forms wliich-we have studied, but they also present many 
resemblances to those of other marine forms as described by Van Beneden, Haeckel, 
Kupffer and others, though seeming to indicate that there are two distinct types of 
teleost development, one for the fresh and the other for the salt water forms. However, 
we are not yet possessed of sufficient material on which to base any generalizations, since 
we know less about the development of the Teleosts than of any other Vertebrate type 
with the exception of some of the lower groups of the old class of fishes. 
The description which we give is purposely detailed and may be even prolix, and for 
these reasons : but few forms of marine fishes have been studied and so detailed observa- 
tions are necessary to serve as a basis for future comparison; the second is that our paper 
may be of more aid to American students who as a rule have no such facilities for consult- 
ing books as have their co-workers in the old world. Besides the works* of Alexander 
Agassiz, Drs. Brooks, Garlick, Lockwood, Putnam, Ryder, and Wyman, referred to in the 
bibliography, I do not know of a single paper by an American on the embryology of the 
Teleosts, while all papers embracing any original investigation on the embryology of the 
other Vertebrates will not exceed two dozen and of these fully one-half were not at their 
time of publication any contribution to knowledge. With such a poor showing surely any- 
thing which may incite to better work may be pardoned. 
I. Maturation of tiie Ovum. 
% 
We were unable to make any observations on the maturation of the eggs which we 
studied,1 nor to witness the phenomena connected with the impregnation, Jbut the following 
1 During the summer of 1882 eggs were taken from the liv- 
ing cunner some being fertilized and others not, and from 
the study of the latter I am able to add a little to the account 
of the maturation of the egg and to say a word concerning the 
formation of the polar globule in addition to the statements 
of the previous year. I would, however, state that it is barely 
possible that the supposed unfertilized eggs were in reality 
fertilized, as, for obvious reasons, I cannot say that there were 
no spermatozoa in the water in which they were kept. These 
eggs in general appearance have been described at the begin- 
ning of the second section of this article, and hence the 
description need not be repeated here. The features of 
maturation witnessed were a disappearance of the nucleus 
and of the strongly refractive globules; then the protoplasm 
began gathering itself together as shown in the figures 9, 10 
and 11. A slight constriction appears around the central por- 
tion of the protoplasm which, cutting down and-then in, sepa- 
rates the germinal portion of the egg from the yolk giving 
it eventually the shape of a button. It is to be noted that 
this operation does not include all of the protoplasmic portion 
of the egg, a thin layer (exaggerated in the figures) extend- 
ing down over the yolk and in all probibility giving rise to 
the intermediary layer. While this segregation of the pro- 
toplasm is taking place the aster appears, followed by the 
formation of the polar globule, This aster appeared, each 
time it was seen, as a true aster, not an ampliiaster, but this 
may be the result of the position of the egg, for were an 
ampliiaster viewed in the direction of the axis it would pre- 
sent this appearance. At the centre of the aster there 
appeared the polar globule in a manner almost exactly simi- 
lar to that so often described in the eggs of invertebrates. 
Once on rotating the egg the polar globule was actually 
witnessed in its passage through the micropyle as shown in 
figures 6 and 7, its connection with the egg being completely 
severed. At another time I saw a projection which I am 
inclined to regard as a polar globule attached to one of the 
resulting cells of the first segmentation (fig. 8, p. g ), but as 
the process of formation was not witnessed I am not positive ON THE EMBRYOLOGY OF THE TELEOSTS. 
191 
account of the changes undergone by the eggs of Merlucius may partially fill the gap. 
The eggs in question were taken from the fish and some were fertilized while others were 
not. We studied only the latter. Mr. Van Yleck spent his time on the development of 
the former, and it is sincerely to be hoped that he will soon publish his results in detail as 
many of them are very interesting and important. 
When first seen the proloplasm of the egg of Merlucius was collected at one pole (the 
lower) and covered about a third of the surface of the deutoplasm as a thin layer. At 
this time no nucleus was visible, though carefully looked for. Soon there appeared, at 
about the centre of the germinative disc, the well known aster so familiar to' embry- 
ologists (fig. 3). After about five minutes changes were noticeable in the aster; its 
rays grew shorter, were less distinctly defined, and finally the whole disappeared and no 
trace of the star could be seen. The length of time from the first appearance of this 
aster until its complete disappearance was thirteen minutes. Five minutes later the aster 
reappeared, this time at the centre of the outer surface of the germinal disc where during 
an interval of about ten minutes it presented the same appearance and went through the 
same changes as befc~e, at last disappearing as before leaving no trace of its former pres- 
ence. After twenty minutes more had elapsed it was again seen near the edge of the disc 
and on its outer surface, where after remaining in sight for about five minutes it again 
faded from sight. Several additional appearances and disappearances were witnessed but 
with no differences worthy of note and no further records were kept. These asters made 
themselves visible with comparative suddenness, while their disappearance was more 
gradual and is best described by the term “fading out Close watch was kept for the 
formation of polar globules but without success. 
The foregoing account is by Mr. Conn, but what interpretation to place upon the 
numerous appearances and disappearances of the aster I do not know. In another egg of 
the same lot I saw the following phenomena : 
The appearance of only one aster was noticed and this at the outer surface of the ger- 
minal disc and close to its outer margin. It was apparently composed of granules of pro- 
toplasm radically arranged. At the same time of its appearance slightly marked amoeboid 
movements of the whole protoplasmic area were seen and which were the most prominent 
in the neighborhood of the aster and which seemingly proceeded in a slow wave-like man- 
ner toward the aster as a centre from the circumference. This appearance was noticed for 
about five minutes, and as the time progressed the aster gradually faded from the sight as 
has been described above by Mr. Conn. After its disappearance two very small globules 
or granules were seen on the surface of the germinal disc in the exact spot formerly occu- 
pied by the aster (fig. 2). There exists in my mind considerable doubt as to whether 
these granules were the polar globules, arising chiefly from the following reasons: their 
very minute size, and also from the fact that neither by myself nor by Mr. Conn was there 
witnessed anything comparable to the amphiaster (Archamphiaster of Whitman) which 
of my identification. It may be that the exclusion of the 
polar globule from the egg is the normal method and this 
would account for the fact that it has so unfrequently been 
seen in the fishes. With the evidence of the present year I 
feel tolerably confident that the polar globule of the text 
(fig. 5 p. <7.) was in reality such. Hoffman (’81) gives an 
essentially similar account of the formation of the polar glob- 
ules and their extension from the egg and, more fortunate 
than I, saw all the stages of the operation, which were simi- 
lar to those described by Fol and others in the maturation 
of the eggs of the Invertebrata. He however does not appear 
to have seen the polar globules retained within the egg. 192 
KINGSLEY AND CONN 
accompanies the formation of the polar globule in the Invertebrates. The star was always 
single, nothing comparable to the “ Kern-platte ” was seen,1 and in my egg the elongate 
globules, arranged in the direction of their longer axes, marked the exact centre of the 
aster. Though watched for a considerable time no further changes were witnessed, and as 
the egg was not fertilized no segmentation could be expected. No other eggs of so 
early a stage were obtained. 
But two eggs were obtained by skimming before segmentation had commenced, the 
larger portion having the blastoderm well segmented indicating a development of from four 
to six hours. In one of these eggs which I found (fig. 4) the protoplasm was collected 
around one pole of the egg, imparting to it a very pale yellowish tinge and gradually 
fading out so that at about a third of the distance around the egg it was invisible. In 
this yellowish protoplasm the germinative vescicle or nucleus was visible and in these a 
single nucleolus. The egg measured .0375 in., the nucleus .0037 in., and the nucleolus 
.00055 in. Soon several strongly refractive bodies appeared in the nucleus, similar in appear- 
ance to, but smaller than the nucleolus. An unfortunate pressure of the cover glass then 
killed this egg, preventing any further observations upon it. 
Mr. Conn however found a single egg of the same species just as the first segmentation 
furrow was appearing. He describes the egg as essentially similar to the one which I had, 
the protoplasm extending down over the yolk in a similar manner. The nucleus, however, 
wras not visible. The segmentation furrow made its appearance at the centre of the sur- 
face of the protoplasm and gradually progressed outward and downward until the germinal 
portion of the disc was divided into two blastomeres. During the later stages of this seg- 
mentation the line of demarcation between the protoplasm and deutoplasm became more 
distinct, and at the close of the segmentation the protoplasm is gathered up at one pole of 
the egg as a thick two-celled cushion, as shown in figs. 12 and 13. These changes occupied 
about a quarter of an hour. 
We made more detailed observations upon the first segmentation of the eggs of Merlu- 
cius, but as Mr. Van Vleck is intending to publish on the development of this form we do 
not here relate our results, simply saying that they fully agreed with the description above. 
This segmentation we regard as the first segmentation of the egg. That of separation of 
protoplasm and deutoplasm cannot be considered as segmentation, since it is one of the 
features of the maturation of the egg and is accomplished befpre impregnation. 
It is to be noticed that in all the eggs which we studied all of the segmentation furrows, 
including the first, pass completely through the germinal area and in all the segmentation 
of the protoplasm of the egg is complete. Similar results were noticed by Van Beneden 
in the egg of an unknown Teleost, and by Haeckel in the egg of ? Motella. On the other 
hand (Ellacher, Strieker (Truttafario),Van Bambeke (Leuciscus), and Carl Vogt (Coregonus) 
describe the segmentation planes as at first passing only part way through the germinal 
disc. 
Returning to our original egg; from the stage with four blastomeres many observations 
were made and all features of segmentation were verified and re verified by both of us- 
II. Segmentation. 
1 See preceding note. ON THE EMBRYOLOGY OF THE TELEOSTS. 
193 
A description of the changes undergone by a single egg will be given in detail while the 
variations presented by others will be noticed as occasion demands. At the close of the 
section on segmentation, a tabulated account of a few eggs, all apparently of the same 
species, will be found, with the periods of time occupied in the various phenomena of 
segmentation. 
This egg with two blastomeres when first placed under the microscope had nuclei in 
each cell, though, judging from the analogies presented by the later stages as well as by 
the eggs of Merlucius at the same period of development, the nuclei probably did not 
reappear until some minutes after the first segmentation furrow was completed. Soon 
after this the nuclei disappeared, and in six and one half minutes afterward they were no 
longer visible, the first external features of cell division were noticed. A slight furrow 
appeared in the surface of each blastomere, their direction being at right angles to the 
original plane of segmentation (fig. 18). At first these furrows existed only at the junc- 
tion with the primary one and were also superficial. They then gradually extended out- 
wards and downwards from this place until in thirty seconds from their first appearance 
they had completely separated each blastomere into two. Two minutes later the nuclei 
reappeared. 
In some eggs, between the completion of the segmentation furrow and the reappearance 
of the nuclei in the four resulting blastomeres, marked amoeboid movements were observed. 
In other eggs from the same lot these movements were not noticed until the blastoderm 
had eight blastomeres. These amoeboid motions were very marked and similar ones were 
noticed in connection with each segmentation from the third onward. It is difficult to 
describe or illustrate these motions. Processes were sent out by the cells, and furrows 
appeared cutting into the blastomeres, conveying the impression, the first time that the 
phenomenon was witnessed, that the cells were about to divide-again immediately without 
the reappearance of the nuclei or the intervention of the usual period of rest. On the 
contrary, with the reappearance of the nuclei, or very soon after, these motions ceased 
and the blastomeres acquired their regular cellular appearance and an interval of rest inter- 
vened before further cell division began. 
As was mentioned above, the same amoeboid movements were witnessed at each seg- 
mentation and in all eggs studied, and, though we are by no means positive, it seemed to 
us that connected with these movements was an increase in the amount of protoplasm and 
that particles of the yolk or deutoplasm were taken into the blastoderm. Certain obser- 
vations which we made, but which are not easy to describe, seemed to admit of this and 
only this interpretation ; and the fact that the blastoderm grows, not only in superficial 
extent, but also in volume, shows that the amount of protoplasm is in some way increased 
and thus adds additional weight to the view which we have taken. On the other hand 
the fact that the cells, after they have reached a quiescent state and have regained their 
usual smooth contours, exhibited no traces of globules or granules of yolk as would have 
been expected with bodies of such different refractive indices, would seem to be against 
this idea. It may be, however, that the deutoplasm undergoes a gradual change, and that 
portions of it are transformed into the substance of the intermediary layer and that the 
nourishment of the cells is in turn derived from the intermediary layer. That this inter- 
MEMOIRS BOST. SOC. NAT. HIST. VOL. III. 194 
KINGSLEY AND CONN 
mediary layer contains a large proportion of protoplasm is shown by the free cell forma- 
tion which subsequently occurs in it, to be described farther on. 
It has been impossible to give any adequate representation of these amoeboid move- 
ments as they utterly surpass any efforts of the artist, but figs. 15 and 17 may serve 
to convey some slight idea of the appearances. Both are taken from blastoderms of eight 
cells. In fig. 17 only two cells are shown, each of which is about to segment while two 
processes are shown arising from one cell and uniting with the protoplasm of its neighbor. 
In this case the union was not broken until after the segmentation was completed. The 
other (fig. 13) represents an entire blastoderm of eight cells after the segmentation 
furrows are complete but before the reappearance of the nuclei. 
At the time of the reappearance of the nuclei in the blastoderm of four cells, grooves 
were noticed extending down from the blastoderm a short distance on the surface of the 
yolk (fig. 14); but they soon faded out, not lasting over four or five seconds. This 
phenomenon was noticed at two subsequent stages ; once when the blastoderm was composed 
of sixteen and once when of about sixty blastomeres. It may have occurred at other times 
but was not looked for ; in fact the times when it was seen were the result of accident, 
it being incidentally noticed while other changes were being watched. 
Concerning the internal features of the segmentation we regret that we can say nothing. 
Many times the nuclei of the blastoderm were carefully watched, but all that can be said is 
that they- gradually faded away from the sight, growing less and less distinct until at last 
they were invisible and had utterly disappeared before the segmentation of the protoplasm 
began. After the cells had divided the nuclei again became visible but rather more 
rapidly than they had disappeared. In this disappearance and reappearance there did not 
appear to be any change in the size of the nuclei, but rather their optical properties more 
and more approximated that of the surrounding protoplasm until at last the microscope 
was unable to differentiate them. At no time while the segmentation fissures were being 
formed were the nuclei to be seen. In vain we looked for those interesting features con- 
nected with cell division which have been described in such detail by Biitschli, Flemming, 
Klein, Peremeschko, Schleicher, Strasburger and others. Except in the case of the 
maturation of the egg of Merlucius described above, we have but twice seen anything in 
the eggs of Teleosts which in any way even approximated an aster, amphiaster or “ spin- 
del-kern” 4 Once asters were seen in a large proportion of the cells of a blastoderm com- 
posed of about one hundred segments. The other time a single aster was seen among 
the free yolk nuclei or rather, as I prefer to call them, the free nuclei of the intermediary 
layer. In both cases circumstances were such as to prevent any detailed observations 
upon them, while the little which was seen is of no value standing by itself and hence is 
not described. It is sufficient to say upon this point of internal features of segmentation 
that in the earlier stages of division nothing comparable to the phenomena I have seen in 
the eggs of other forms could be distinguished without the aid of reagents, which however 
do not readily penetrate the envelope of the eggs which are studied. The eggs of Mer- 
lucius afford in this respect a striking contrast, as in them Mr. Yan Yleck obtained by 
staining well marked spindel-kerne. 
1 The studies of 1882 require the modification of this state- 
ment for I was able several times to see these structures, they 
being well stained by a solution of carmine in acetic acid 
though they did not stain with the more common reagents. 
The appearance of both asters (b) and spindelkern or amphi- 
asters (x) sre shown in pi. 15, fig. 24*. ON THE EMBRYOLOGY OF THE TELEOSTS. 
195 
Returning to the egg whose segmentation we are discussing we have to note the suc- 
ceeding features of division and first the changes in going from four to eight cells. In six 
minutes after the appearance of the nuclei in the four blastomeres they again disappear as 
before, and fourteen minutes elapsed before any further changes Avere visible.* A 
depression then appeared at the middle of the inner margin of each cell and gradually 
extended outward and downward to the outer surface and to the yolk. These furrows 
were parallel to the first and at right angles to the second segmentation furrows and like 
them cut completely through the protoplasmic portion of the egg. The whole process of 
division occupied but a few seconds and the nuclei reappeared two minutes later and the 
blastoderm of eight cells was before us. 
In the egg Avhich formed the basis of this description the segmentation furrows appeared 
simultaneously in each of the four cells of the blastoderm and proceeded at nearly regular 
rates in all. Other eggs agreed with this, but still others (and they formed a large minor- 
ity) exhibited at this early period a heterochronous division, as in proceeding from four to 
eight blastomeres an intermediate stage was observed in which for a few moments the 
blastoderm consisted of six segments, two of the cells having divided slightly in advance 
of their fellows. In one egg which I studied three blastomeres divided some little time 
before tho fourth, the first three dividing simultaneously and the result was a blastoderm of 
seven cells. This egg presented also another peculiarity in that the nuclei reappeared at 
nearly the same moment of time in all of the cells and before the fourth had divided, 
and thus the seventh cell had two nuclei and only after the lapse of a minute and a half 
did this cell divide. 
It was at this time, when the egg has eight segments, that we noticed the first traces 
of Van Bambeke’s intermediary layer (figs. 21, 22, 23i). It was a very thin layer of pro- 
toplasm extending betAveen the blastoderm and the yolk and at this stage was without the 
thickened margins and the free nuclei which are present in the later stages. No traces of 
granulations or oil globules could be seen in it. We would not, however, by the forego- 
ing account, be understood to say that the intermediary layer made its appearance at this 
time, but merely that we first noticed it then. Of its time and method of origin we can 
say nothing except that it certainly was not present at the first segmentation of our eggs.1 
As will be seen further on Ave do not agree with Van Beneden in regarding this inter- 
mediary layer as the hypoblast, but I am inclined to believe that he is correct in his idea 
that the tail-like processes of the cells in Haeckel’s figure of an egg Avith two cells, in 
reality represent this intermediary layer. I also agree with the Belgian savant in his 
opinion that both Kupffer and Lereboullet observed this same intermediary layer, the 
statement of Kupffer to the contrary notwithstanding. Lereboullet ( ’54 p. 250) says 
“ II existe sous le blastoderm une membrane particuliere, distincte, composee de grandes 
cellules tres pales.; c’est d’elle que se formeront les organes abdominaux This agrees per- 
fectly (except in regard to the last portion, the destination of the layer) with the condi- 
tion of the layer in many of the fresh water fishes with numerous oil globules the “ gran- 
des cellules ” being either oil globules or vacuoles. But of this intermediary layer we 
will speak more at length further on. 
1I now think that this statement will have to be modified, 
as I regard the thin portions of protoplasm which are left 
extending down over the egg at the time of maturation 
(fig. 11), and which are also shown in fig. 12 extending out 
from the blastomeres, as the first traces of the intermediary 
layer, and the same investigations confirmed me in my beliet 
that the layer is largely produced by the change of deuto- 
plasm into protoplasm. 196 
KINGSLEY AND CONN 
At no time after eight blastomeres were reached did the segmentation proceed regularly, 
and with each succeeding segmentation the irregularity became more* and more marked 
until at last, at about that stage when the blastoderm should theoretically consist of sixty- 
four cells, every trace of regularity is lost and each cell divides entirely independently of 
its neighbors, the nuclei appearing in one just as they are disappearing in another, while 
a third is at the same instant dividing. In some eggs this irregularity is noticed at an 
earlier stage and is much more marked than in others, but in all it soon reaches such an 
extent that in any case it is difficult to ascertain when the theoretical segmentation is 
completed. 
We have now to describe the division of the blastoderm from eight to.sixteen cells. 
Nine minutes after the last mentioned reappearance of the nuclei, they again disap- 
peared almost simultaneously, but one or two seconds intervening between the times of the 
first and of the last. After this disappearance and before the division of the cells amoe- 
boid movements, similar to those which have been described were witnessed. The cells 
lost their regular outlines and their smooth contours and became lobulated and fur- 
rowed. Fig. 17 before referred to represents two cells from the blastoderm. While this 
amoeboid motion was in progress the segmentation furrows appeared. Fig. 18 will illustrate 
this division better than it can be described, the two interior cells divided first, then the 
other two, and lastly the four corner ones. The fissures in the second began before those 
in the first were completed and those in three before the segmentation of the second 
was accomplished. The complete segmentation occupied about two minutes. The planes of 
division were in general times at right angles with those of the preceeding segmentation 
and the result was a parallelogram with four cells on a side. The nuclei were again seen 
four minutes after the segmentation was complete and remained in sight for ten minutes. 
The amoeboid movements after this segmentation were very strongly marked and lasted 
for considerable time, and the cells did not attain their smooth contours until about the 
time when the nuclei vanished. The regularity of the parallelogram was far from being con- 
stant as frequently one or more cells would segment obliquely and the result would be 
more like that shown in fig. 19. 
From this point onward the segmentation in every egg studied by us was very irregular, 
and by various stages of 20, 21, 28, 29, and 30 cells the theoretical 32-celled blastoderm is 
obtained and a short period of rest (which was not timed but which could not have 
exceeded three minutes) intervened after which the segmentation proceeded but so irreg- 
ularly as to be beyond description. Figs. 20 and 21 will illustrate some of the later stages. 
In the following table are given the results of timed observations of the segmentation 
of several eggs. Several others were studied but without noting the intervals between 
the stages. The dash ( —) indicates that stage of development when the eggs were first 
noted and the figures the number of minutes since the last timed stage. 
l 
2 
3 
4 
5 
6 
7 
8 
9 
Nuclei disappear after first segmenta- 
tion (2 cells) .... 
7 
— 
— 
— 
— 
Second segmentation (4 cells) . 
6* 
7 
n 
10 
8 
Nuclei reappear ..... 
2 
3 
3 
Nuclei disappear .... 
6 
— 
— 
8 
6 
— 
7 
Third segmentation (8 cells) 
14 
18 
15 
10 
11 
— 
14 
4 
12 
Nuclei reappear..... 
2 
5 
6 
h 
4 
2 
Nuclei disappear .... 
9 
5 
5 
10 
10 
11 
10 
8 
Fourth segmentation (16 cells) . 
9 
10 
11 
7 
7 
12 
8 
Nuclei reappear 
2 
5 
4 
2 
9 
11 
4 
5* 
3 ON THE EMBRYOLOGY OF THE TELEOSTS. 
After this stage the segmentation is so irregular that it cannot be timed. 
From the above table, which is based on eggs of apparently the same species,1 it will be 
seen that there a considerable variation in the times which were required for the same 
changes in different eggs but nevertheless in many, well marked periods of rest alternat- 
ing with stages of activity, may be noticed. These periods of rest and activity have 
recently been commented upon by Dr. W. K. Brooks (’81) and have also been noticed by 
many of the older embrjmlogists in the eggs of other vertebrates and also in those of 
many invertebrata. I am of the opinion that these periods of (apparent) rest are thus to 
be explained, that at each one of them the deutoplasm, which I believe to have been taken 
up by the germinal area, is connected with protoplasm, and that while there is an interval 
of physical rest, the same time is one of chemical activity. There are several reasons for 
this belief, but before stating them I wish to obtain further evidence and make additional 
observations not only on the eggs of fishes but also on those of other animals. 
The phenomena of segmentation in the eggs of Teleosts have been several times 
described, and the accounts which we have presented to us agree in the main with what 
has been given above, though there are several points of more or less importance in which 
differences are to be noted. The first fact which we would discuss is that the planes of 
segmentation even at first pass through the germinal area, cutting it completely. This is 
in strong contrast with the observations of most writers and so far as we are aware occurs 
in the eggs of all marine teleosts. Every form which we studied presented this peculiarity 
and the description and figures of Haeckel1 and Van Beneden of the development of 
European marine teleosts. (It might here be remarked that the figures of Haeckel are 
highly idealistic and show many features which certainly do not exist in nature). On the 
other hand all writers describing the segmentation of the eggs of fresh water fishes agree 
in that the first cleavage planes pass but partly through the germinative disc, there 
remaining a portion next the deutoplasm (vitelline globe) which does not segment until 
much later. These facts are in strict accordance with the ideas of Balfour that eggs 
undergo total or partial segmentation according to the relative proportions of protoplasm 
and deutoplasm. In the eggs of fresh-water fishes besides the vitelline globe there is a 
large amount of deutoplasmic material scattered through the germinal area ; in the eggs of 
Merlucius there is a very slight amount in the same region, while in the eggs which we 
studied the protoplasm and deutoplasm appeared to be entirely distinct. 
According to Vogt (’42 p. 30) the segmentation furrows do not entirely cut through 
the germinal area of the eggs of Coregonus until a stage with eight blastomeres is reached. 
To Oellacher we must refer for the most detailed account of the segmentation of the eggs 
of fresh water fishes which has yet been published. His observations on the segmenta- 
tion of the eggs of Trutta fario (p. 395 et seq. pi. xxxiii figs. 18-20) agree essentially 
with those of Vogt but from their later date are much more valuable. He lays especial 
stress upon the fact that the cleavage furrows do not pass at first completely through the 
germinal portion, and in the later figures (1. c. figs. 22-26) he shows a layer of unsegmented 
protoplasm underlying the central cells of the blastoderm and continuous with the margin- 
1 These eggs as far as the microscope would show were 
identical, but there is a bare possibility that No. 4 which was 
slightly larger than the rest belonged to a different species. 
This would explain the great difference in time in certain 
changes which here are very much accellerated. 198 
KINGSLEY AND CONN 
al ones. At a later stage this lower layer of protoplasm becomes segmented. Aside 
from this difference, which is to be explained by the presence of quantities of yolk gran- 
ules, the external features of segmentation present no important differences from our 
results. 
The eggs of Merlucius although containing large numbers of deutoplastic globules in 
the germinal portion undergo a complete segmentation of the protoplasm as in that of 
the Cunner. There was to be noticed, however a very marked irregularity in the pro- 
cess of segmentation even from the very first. The blastomeres varied widely in size and 
the segmentation furrows progressed at varying rates and times in different portions of 
the germinal area. 
Though we found it impossible to obtain any satisfactory sections of our eggs, their 
perfect transparency enabled us to see, clearly and plainly, that even the first segmenta- 
tion furrow extended down to the vitelline globe and that the first two cells as well as 
the subsequent ones were entirely separated from each other. At no time was there an 
unsegmented basal portion of protoplasm except that presented by the intermediary layer 
and peripheral cushion of Van Bambeke. 
Kupffer mentions some marked irregularities in the eggs which he studied: in some 
the second segmentation furrow sometimes was eccentric or occasionally was even parallel 
to the first. We have seen nothing of this sort in the eggs which we studied. 
The theoretical segmentation of an egg is first two meridional furrows and then an 
equatorial one, but frequently this regularity is interrupted, in fishes noticeably so. If we 
interpret Haeckel aright, the equatorial furrow is the fourth to appear in the eggs of 
? Motella as he figures (fig. 58) a section of a blastoderm of sixteen cells and in it 
lower layer cells are seen. These figures however show in every line that they are 
wholly diagrammatic and could not have been drawn from either actual or optical sec- 
tions. In the eggs of the fresh water fishes it is at a somewhat later stage that the equa- 
torial furrow is formed and the lower layer cells produced, but even in eggs of the same 
species there does not appear to be much regularity. In our eggs lower la}?er cells did not 
appear until the blastoderm was composed of about a hundred blastomeres and even then 
they did not appear simultaneously in all parts. 
III. Formation of the Germinal Layers. 
In this section we have to consider the extension of the blastoderm over the yolk from 
the time of the appearance of the lower layer cells until the formation of the notochord 
and the neural canal. In it also will be discussed the differentiation of epiblast, mesoblast 
and hypoblast, and also the phenomena of invagination. Certain of the features here to 
be described belong in part to the next section, but from the fact that they are first 
noticed before the formation of the notochord they are best treated here. 
Until after the blastoderm has acquired a stage with about a hundred cells it consists, as 
before mentioned, of but a single layer, thus offering a marked contrast from the eggs of 
most fishes on which observations have been published. This simple condition of the 
blastoderm at this time was conclusively shown by optical sections in which the outlines of 
each cell could be readily traced with a power of a hundred and fifty diameters. ON THE EMBRYOLOGY OF THE TELEOSTS. 
199 
Soon after this number was reached, lower layer cells were noticed. We did not con- 
clusively settle the manner in which they arose but are inclined to believe that the greater 
portion arose from the already formed cell elements of the blastoderm while possibly a 
small proportion had their origin in the free nuclei of the yolk. With their formation the 
epiblast becomes differentiated and at first consists of a single layer of cells. These cells 
in vertical optical section are lens shaped while the lower layer cells are polygonal in out- 
line on account of their mutual pressure. 
At first the blastoderm fits as a cap over the yolk but soon by the proliferation of cells 
it acquires a lenticular shape and is seated in a concavity in the surface of the deuto- 
plasmic portion of the egg. At this time the intermediary layer (Parablast of Klein 
not of His) is plainly seen and its thickened margins (bourrelet peripherique of Tan 
Bambeke) is very conspicuous. Regarding the origin of this layer we have nothing new 
to offer. Its first appearance was not noticed either as to the exact stage or as to the 
method in which it arose.1 Neither was the time of its disappearance observed; it was 
visible until the blastoderm nearly covered the yolk. When first seen the layer was clear 
and transparent without any traces of granules, vacuoles, nuclei or cells, though at a later 
stage they were visible. The first observer who noticed this intermediary layer was Lere- 
boullet who saw it both in the pike (’54 p. 248) and perch (1. c., p. 250). He describes 
it in the latter as follows : “ II existe sous le blastoderme une membrane particuliere, dis- 
tincte, composee de grandes cellules tres pales ; c’est d’elle que se formeront les organes 
abdominaux”; and in speaking of the pike he says that the vitelline globules are changed 
to this layer. Almost all subsequent observers have seen this same layer and have added 
to our knowledge of it. Our discussion of their results will be taken up in connection 
with that of the germ layers with which it is intimately connected. 
At about the time of the differentiation of the lower layer cells as well as at later stages 
free nuclei were seen on the surface of the yolk. These nuclei were irregularly arranged, 
in fact no traces of any regularity could be discerned except that all were on the surface 
and now were to be seen on the interior of the yolk. (The term surface here embraces 
not only that portion which is in contact with the egg membranes but also that on which 
the intermediary layer rests). In the eggs of Merlucius at a slightly older stage similar 
nuclei were seen and around many of them, especially those nearest the blastoderm, the 
cell walls could be made out, the whole presenting an appearance somewhat similar to 
that given byKupffer (’68 p. 217 pi. xvi) in the eggs of Gasterosteus. These free nuclei 
and cells are not arranged with anything like the regularity of Kupffer’s figures. In the 
Gunner egg I watched the process of cell formation around these nuclei with some 
care. The nuclei nearest the germinal portion of the egg were the first to become the 
centres of cells and the formation of the cell boundaries took place in a corresponding 
direction, that is those portions of each cell wall nearest the blastoderm appeared first and 
these gradually extended themselves around the nuclei. The whole operation required 
over half an hour. In the Cunner but comparatively few of these free nuclei and 
resulting cells were seen.2 
1The observations of 1882 elsewhere detailed alter this 
statement slightly. 
2 In 1882 by staining, these free nuclei with all their accom- 
panying phenomena were seen and studied, fig. 24*, pi. xv, 
representing a portion of the blastoderm and the adjacent 
portion of the peripheral cushion; in the latter there being 
shown asters, amphiasters, and the process of outlining of the 
cells. 200 
KINGSLEY AND CONN 
As time passes the blastoderm gradually extends itself over the surface of the 
yolk until, at a later stage than that described in this section, it completely embraces it, 
thus forming the yolk sac. When about one-fourth of the surface of the yolk was thus 
covered, the segmentation cavity was first noticed. No observations were made regarding 
its mode of origin but it was doubtless by a lifting up of the blastoderm. In the earli- 
est stages its roof was formed by the epiblast alone, its walls of lower layer cells while its 
floor was formed by the yolk, or rather by the intermediary layer which rests upon the 
yolk. The floor at this time was perfectly free from nuclei or cells. At first the segmen- 
tation cavity is low, circular in outline, with its lateral margins about equidistant from the 
edge of the blastoderm. The blastoderm continues its extension over the yolk and 
increases rather more rapidly in one position of the margin than on the others, and at the 
same time the lower cells encroach upon the segmentation cavity from one side until the 
cavity becomes eccentric and is placed nearer one portion of the blastodermic margin than 
to the others. This pushing in of lower layer cells continues until the cavity acquires an 
arcuate or reniform outline. At this time free cells are numerous upon the floor of the 
cavity. 
This is the first opportunity we have for the orientation of the egg. The segmentation 
cavity is farthest from the portion of the blastodermic margin where the first outlines of 
the germ are to appear and so we may now speak of anterior and posterior portions of the 
blastoderm, the segmentation cavity is anterior and the embryonic area posterior. 
The invagination of the hypdblast now begins. As before stated we were unable to cut 
actual sections but the extreme transparence of the eggs rendered this almost a superfluity. 
Our observations on the invagination were made both by surface views and by optical sec- 
tions, the latter being in almost every respect equal to actual ones while from the fact that 
the steady progress of the invagination could be continuously watched in the living egg 
they presented advantages which no product of the section knife could equal. 
At all points of the margin of the blastoderm a single layer of cells may be seen push- 
ing themselves inward beneath the rest of the blastoderm and separated from the lower 
layer cells by a well defined line. Between this hypoblast and the yolk is still to be 
found the intermediary layer. The invagination progresses much more rapidly from the 
posterior or embryonic portion of the blastoderm than from any other portion of its mar- 
gin, and at the anterior portion more rapidly than at the sides. Fig. 22, pi. xiv, rep- 
resents an optical section on the median line of an egg in which invagination has just 
begun, while fig. 23 represents the same at a somewhat later stage. In this last figure 
the extent of the lateral invagination is shown by the shaded area. Fig. 24 gives a view of 
the lower surface of the same blastoderm showing the rates at which the invagination pro- 
gresses in different parts. (The dotted line indicates the plane on which the section 
described is taken.) The invagination continues until it forms a layer entirely separating 
the rest of the blastoderm from the yolk and intermediary layer. Its later stages and 
the phenomena accompanying it belong more properly to the next section. 
Our attention was not especially directed toward the origin of the mesoblast but we are 
of the opinion that it arises partly from the lower layer cells and partly from the hypo- 
blast. Whether it arises as two lateral plates, we know not, but at an early stage it forms a 
continuous layer extending across the embryonic area as shown in fig. 25. With ON THE EMBRYOLOGY OF THE TELEOSTS. 
201 
the progress of the invagination the segmentation cavity is encroached upon by the 
lower layer cells, its floor becomes covered with cells, some arising from the hypoblast 
while others apparently originate from the free yolk nuclei, and the cavity is shortly 
obliterated.1 
I admit that I am in doubt as to the part played by the intermediary layer and its 
resulting cells. As before mentioned a portion of the cells apparently enter into the 
floor of the segmentation cavity and are subsequently either embraced in the hypoblast of 
invagination or are crowded by it into a mesoblastic position. This however accounts for 
but a small proportion of the cells of the intermediary layer, and it seems to me probable 
that the hypoblast of invagination forms only the dorsal wall of the alimentary tract while 
the intermediary layer furnishes the ventral portion. This seems to be in full accord with 
the formation of the alimentary tract in other forms (e. g. Batrachia) where the ventral 
portion of the hypoblast is formed by yolk cells. 
Regarding the origin of the hypoblast in the Teleosts there seems to be a diversity of 
opinion. Henneguy (’80 p. 402-3) describes the invagination in the eggs of the perch and 
trout, the blastoderm being inflected at its margin and a line or fissure separating the 
sensorial [our lower layer cells] from the inflected portion. So far we agree with him. 
He however states that the epidermal layer is not inflected. In this he agrees with two 
of the figures of His (’75 pi. ii, figs. 2 and 3) but not with fig. 1. Our observations were that 
the epidermal layer of the epiblast alone is inflected. Balfour (’81, 57) says that the 
yolk cells form the hypoblast in the smaller Teleost eggs but that in the larger as in those 
of Elasmobranchs only a portion of the hypoblast has such an origin. We should con- 
sider our eggs as small. Kupfler with a doubt regards the cells as forming the hypoblast. 
Professor Yan Beneden in his researches on the eggs of an unknown Teleost (’78) arrives at 
widely different conclusions regarding the origin of the germ layers from those we have 
formed and we cannot reconcile his results with our observations. We have seen step by 
step, minute by minute, the progress of the invagination and it scarcely seems possible 
that any error of observation on this point can have crept in, especially as we witnessed 
the process many times. Yet Yan Beneden totally denies that in his Teleost any invagina- 
tion takes place. It would seem to me that he is wrong from the very start. On p. 52, 
he considers the egg before the appearance of (our) two segmentation spheres as follows: 
“ Directly after fecundation the egg of the osseous fish divides into two very unequal cells, 
very dissimilar, differing in constitution and significance; the one is a germ which seg- 
ments and from which the blastodisc is derived ; the other is formed by the deutoplasmic 
globe # * *. This cell is the origin’ of the endodermic layer of the future 
embryo.” To all of this I must express an emphatic dissent. The aggregation of the 
protoplasm at one pole of the egg and of the deutoplasm at the other cannot in any way 
be considered as a segmentation, nor can the deutoplasmic portion be considered as a cell. 
No one would think of regarding a centrolecithal egg, that of a Crustacean for example, 
as composed of two cells or the central portion as of a cellular character, yet the homology 
between the two eggs is easily shown. On the same page he explictly says that the germi- 
nal portion is the homologue of the ectoderm and the vitelline of the entoderm, a view 
1 Subsequent studies lead me to believe that this statement 
is an error and seem to confirm the idea of Ryder with regard 
to this cavity, though I must say that there appear many diffi- 
culties in connection therewith. 
MEMOIRS BOST. SOC. NAT. HIST. VOL. III. 202 
KINGSLEY AND CONN 
which is not warranted without considerable qualification. It must be understood that I 
am not criticising his observations on the free cell formation in the intermediary layer and 
in the yolk, nor do I deny that a portion of the hypoblast may arise from those portions. 
This free cell formation we have both witnesed in the eggs of several marine Teleosts and 
we are willing to accept his account of their formation but I do deny that the presence of 
these cells and nuclei can be addressed as evidence that the deutoplasmic globe itself can 
be considered as a cell and the complete homologue of the hypoblast. On p. 50 he con- 
siders that the hypoblast described by Haeckel, and which closely resembles in its structure 
and mode of origin that of our fishes, was in reality “ composed of cells derived from the 
intermediary layer.” It hardly seems possible that there should be in the eggs of teleosts 
such diverse methods of origin of the hypoblast and that in closely allied forms. Profes- 
sor Van Beneden following Haeckel regards his egg as probably belonging to one of the 
Gadidae, and with this opinion we are inclined to agree. The eggs of Merlucius and of 
Morrhua present a striking resemblance to those studied by Haeckel and Van Beneden, 
and if there be any relation between the characters of the eggs and of the fishes produc- 
ing them (a point on which we have but slight data) the eggs studied by both probably 
belonged to the Gadidae. Now as we have observed in an egg with a conspicuous oil globule, 
and as has been traced through with great care by our friend Mr. Van Vleck in the egg 
of Merlucius, the hypoblast arises exactly as we have described it above. 
It would thus appear that Van Beneden has been led into an error either of observation 
on his own eggs, or of interpretation of the results of Haeckel, regarding this point and we 
are inclined to believe that the former is the case, for the reason that it appears from inter- 
nal evidence presented by the article in question that he did not witness continuously the 
phenomena presented by his eggs. Still there remain certain statements which we can- 
not reconcile <with what we believe to be the facts of the case. For instance the statement 
on p. 56. “ The blastodisc remains all this time very sharply delimited inferiorly and in 
no part is there a passage from one to the other (from the upper portion of the blastoderm 
to the hypoblast). In no part have I found the slightest indication in favor of 
invagination.” 
In the earliest stages of the egg the intermediary layer is not present but it soon appears 
and acquires its maximum development about the time of invagination. It appears to 
arise by an elaboration of the food yolk into protoplasm. It consists in our eggs as in those 
of Van Bambeke and Van Beneden of a thin layer extending across the egg between the 
blastoderm and the food yolk, and having a thickened marginal welt. This welt extends 
down some distance over the yolk and it may be possible that the nuclei of the yolk men- 
tioned on p. 199 belong in reality to this extension of this layer. Klein (’72) describes this 
as a ring in the trout as he failed to find the portion extending across between the blasto- 
derm and yolk. 
Most observers have considered the mesoblast as arising as a continuous sheet in the 
Teleosts but Calberla claims that it is in two halves as in the Elasmobranchs. 
We found no traces of the segmentation cavity of Van Bambeke and judging from the 
irregularity of his figures we are inclined with others to regard it as a product of reagents 
or the section knife. The segmentation cavity of Von Baer which was found in our eggs 
is clearly homologous with that of other forms of animals. ON THE EMBRYOLOGY OF THE TELEOSTS. 
203 
IV. Notochord axd Neural Cord. 
The origin of the notochord in the Vertebrata has recently been the subject of some 
discussion, and though we cut no sections we endeavored to make such observations as 
would throw some light upon its source and the methods of its formation. All of our 
observations were made upon the living egg, and as we have in a single egg watched con- 
tinuously every step in the process, and have several times verified all of our results, we 
feel confident of their accuracy as far as our fish is concerned. To sum up our studies of 
this point on which we both agree, the notochord arises from the hypoblast, at first as a 
longitudinal median thickening of that layer and subsequently becomes segmented off and 
takes its place among the mesoblastic tissues. 
A detailed account of the evidence on which we base this statement will now be given. 
First an account will be presented of the changes witnessed in a view of the lower surface 
of the blastoderm and afterward a description of the phenomena observed in optical 
sections. 
Fig. 24 represents the under surface of the blastoderm at the earliest stage at which 
the notochord was seen in a flat view. The segmentation cavity (s)'posseses the arcuate 
outline before described while the shaded portion of the figure indicates the extent to 
which the invagination has extended. The embryonic area (ea) has encroached but slightly 
upon the cavity. Another sketch shows the same embryonic area on a larger scale.1 In 
the median line is seen the notochord extending not quite half way from the margin of 
the blastoderm to the anterior extremity of the embryonic area. Anteriorly the notochord 
is well marked and clearly differentiated from the surrounding tissues, while posteriorly 
this distinctness fades out until at last no line can be drawn separating the chord from the 
adjacent hypoblast. Anteriorly the cells of the notochord have the same polygonal out- 
line as have those of the hypoblast, but they are much smaller, indicating that rapid cell 
division is taking place. As we proceed in our examination, toward the hinder end of the 
notochord, we find the cells gradually increasing in size and approximating those of the 
lower germ layer in magnitude until at last no difference can be observed between them. 
Sometimes a sharp line may be seen cutting across the extreme end of the notochord and 
slightly in advance of the margin of the blastoderm and separated from it by a narrow 
strip of hypoblast, as frequently however this arcuate line was absent, but whether pres- 
ent or not we were never able to trace the notochord quite to the edge of the blastoderm. 
The margins of the chord at this stage were straight anteriorly but at the hinder end they 
diverged giving the whole a somewhat spatulate outline. This shape, resembling some- 
what the appearance of a paddle, the blade behind, was retained until a comparatively late 
stage in the development. 
At this stage, though the notochord was in a great portion of its length clearly and 
distinctly outlined, not a trace of cells could be seen extending across the ventral surface 
of the chord as would have been the case had it been of mesoblastic origin, for then the 
hypoblast would have extended over the lower surface. 
As the embryo increases in size the notochord becomes longer, apparently growing in 
both directions but much more rapidly posteriorly, keeping pace with the extension of the 
1 In drawing the plate this figure was inadvertently omitted. 
It is hoped that the description is sufficiently clear to be 
intelligible without it. 204 
KINGSLEY AND CONN 
blastoderm over the yolk. At the same time other changes may be noticed, in full accord- 
ance with the idea that the notochord arises from the hypoblast, though they are by no 
means the sole proof which we have to offer, “as will bo seen farther on. Near the 
anterior end of the chord, the cells of the hypoblast may be seen extending themselves 
across (on the under surface of) the notochord until these hypoblastic processes from either 
side meet and close in the chord. The formation of this bridge occupies but a few minutes 
and is first completed near the anterior portion, from which it progresses at the same time 
in both directions, reminding one of the closing up of the medullary groove in other ver- 
tebrates. It has been impossible to obtain any satisfactory sketch of this process as seen 
in a superficial view. The feature of the egg which has already been mentioned, the 
greater specific gravity of the germinal portion, readily permitted us to trace these various 
changes on the under surface of the blastoderm. 
Soon the cord is anteriorly entirely cut off from the hypoblast and closed in ; this process 
progresses more slowly posteriorly until finally the notochord is wholly separated from its 
parent layer and is entirely surrounded by mesoblastic tissues, but at what stage the sepa- 
ration is complete our notes and observations do not show. It is however before the for- 
mation of the optic lobes and pro to vertebrae. For a time the cells of the hypoblast can 
be distinguished by careful focussing extending across the notochord but soon they become 
so small that it is impossible to recognize them as such with the highest powers which it is 
possible to use in such investigations carried on upon the living egg. 
This cutting off and closing in of the notochord has been several times witnessed by 
both of us and it seems as if there were but little chance for errors of observation, but 
while this observation from the surface would show that the hypoblast plays a part in the 
formation of the notochord it does not conclusively prove that it is the whole source of 
the notochordal cells. So far as these already described observations go all three of the 
germ layers may play a part in its formation and there might be some truth in Rudwaner’s 
statement (’76 p. 161) that the notochord arises from the epiblast. We have however 
other evidence which proves to us conclusively that the hypoblast alone gives rise 
to the notochord. 
Returning to the invagination described above ; its later stages and its connection with 
the formation of the chorda dorsalis may now be described. These various steps have 
been constantly and consecutively watched by us both in several eggs, not only of the 
Cunner but in several other forms, as well as by Mr. Van Vleck in the eggs of Merlu- 
cius and there exists in the minds of us three not the slightest doubt of their general 
accuracy. 
In optical sections it was seen that the invaginated hypoblast was but a single layer of 
cells in thickness and at all times was separated from the overlying mesoblast by a well 
defined line. An optical section, transverse to the longitudinal axis of the embryo, was 
closely watched and at first the hypoblast was but a single layer of cells deep and every- 
where of uniform thickness. Soon a thickening was seen in the median line of the 
hypoblast, extending slightly into the mesoblast and also into the underlying yolk or 
intermediary layer. This thickening was dearly a part of the liypohlast and the meso- 
blast was in no way concerned in its composition, the line of demarcation between the 
two layers being as well defined as before. Gradually a sharp line appeared cutting the OR- THE EMBRYOLOGY OF THE TELEOSTS. 
205 
thickening away from the hypoblast (fig. 25) and succeeding this the hypoblast was seen 
to extend itself across beneath the now formed notochord (figs. 26—28 in just the man- 
ner which we were led to expect from our observations made from surface views. 
It is always difficult to make out cell limits in optical sections of eggs as small as those 
on which we worked and hence they are omitted in our drawings, but it was seen that in 
this notochordal swelling of the hypoblast that the cells were smaller than the adjacent 
portion of the layer just as was seen in the surface views. 
We would repeat and lay especial stress upon the fact that we witnessed, by constant 
and repeated observations on living specimens, every step in the formation of the notochord, 
from a hypoblast of but one cell in thickness until the chord was segmented off from its 
parent layer and eventually entirely enveloped by the mesoblastic tissues, and at no time 
did we witness the slightest appearance that could be regarded as evidence that any por- 
tion of the notochord was other than hypoblastic in its origin. The later history of the 
notochord will be treated under the respective sections of the development of the fish. 
Previous to Balfour’s first paper (Quarterly Journal of Micr. Science, 1874) all writers on 
vertebrate development had regarded the notochord as belonging not only in position but 
in its method of origin to the mesoblastic tissues. Dr. Balfour there and also in his com- 
plete monograph (’76b) showed that in the Elasmobranchs, at least, the notochord is a 
hypoblastic structure in its origin. Following him, Hensen, in a paper on the development 
of the rabbit, gives the same general account of the derivation of the chorda dorsalis with 
only such variations as might be expected in two diverse classes of Yertebrata. Calberla 
(’77) studying Petromyzon, Sygnathus andRana arrives at similar results and was the first 
to show that in the Teleosts the notochord is an endodermal structure. Rudwaner (’76) in 
a short paper also treats of the origin of the chorda dorsalis, but his article is of little 
value and his figures are evidently diagrammatic and do not represent the true state of 
affairs. He derives the notochord (p. 161) from the outer germ layer or epiblast. More 
recently Braun, in his paper on the development of Parrots in the Arbeiten a. d. zool. zoot. 
Inst, zu Wurzburg (the exact reference to which I have not at hand), still considers the 
notochord as of mesoblastic origin. All of these observers have worked with and studied 
sections and hence the discrepancy in their results. On the other hand our observations 
were made on the living embryo, and hence we saw the organ formed and did not have to 
call upon the imagination to fill up any gaps and also the sources of error in interpretation 
were eliminated. 
In the development of the neural canal the Teleosts present a marked contrast according 
to all observers with the other vertebrates in that it is first formed as a solid cord in 
which a lumen afterwards appears. 
At about the same time that the notochord was first seen the first appearances of the 
medullary folds were witnessed. Coincident with the invagination of the hypoblast the 
edge of the blastoderm increases in thickness and this thickening is most marked at the 
posterior margin in the median line forming what Balfour has called the tail swelling. When 
first noticed it presented much the appearance of the “ stage A ” of Dr. Balfour’s Elasmo- 
branch (’76b pi. vi, fig. A). This soon became elongate and more and more prominent until 
a broad shallow longitudinal furrow finally made its appearance dividing it into two lateral 
halves. These halves are the medullary folds and are low rounded ridges. With the 206 
KINGSLEY AND CONN 
increase in size of the blastoderm and the growth of the now outlined embryo, the folds 
anteriorly came closer and closer together and the medullary groove narrower and propor- 
tionally deeper. It then grew more and more shallow, its decrease in width also continu- 
ing until at last the groove was entirely obliterated. This groove is shown in fig. 28. 
As before mentioned it was very difficult to obtain surface views of the blastoderm and 
hence our surface observations on the closing in of the medullary folds have not that 
detail which we could wish. Were an egg so held that the blastoderm was uppermost, be 
the pressure never so slight, it almost immediately died and then contracted so that no con- 
secutive studies could be made. Enough, however, was seen to show that there was none 
of that infolding and direct formation of a neural canal which is so familiar in the other 
vertebrates. It was not seen whether the modified closing up took place near the middle 
and extended both ways or whether from the anterior end backward. From what we 
know of other forms the former would seem the more probable. 
Fig. 28 shows an optical section through the hinder part of an embryo of the 
stage shown in fig. 34. Here the medullary groove is shown broad and shallow, the noto- 
chord has been separated from the hypoblast but has not attained its later quadrate sec- 
tion but still retains the flattened outline ; the muscle plates on either side have not yet 
been differentiated from the mesoblast, while the hypoblast extends across immediately 
beneath the notochord and is not separated from it by any intervening mesoblast. In this 
optical section it was not possible to make out clearly the cell boundaries although the 
limits of the various germinal layers were readily made out as figured. 
As to the method in which the neural canal forms, whether in the normal way by an 
actual enclosing of a tube of epiblast cells, or as maintained by Calberlaby a lumen forming 
in the epiblast which is pushed down and not infolded, our observations will not allow us 
to decide, though I am inclined to believe that the latter is the method, and for this reason. 
The earliest optical sections of the neural cord do not show any traces of a medullary 
canal while at a later stage such a canal is found. The same is also true of the brain 
and the optic lobes. It will readily be seen that, if either of these methods be the true 
one, the canal so formed is perfectly homologous with the same structure in other verte- 
brates and hence the actual manner of its formation has not so much importance. It is 
however interesting to observe that there is the same formation of medullary folds in our 
fish as are found in other vertebrates, that they arise the same and only differ in the details 
of the formation of the canal. As was said above these medullary folds exist, but at no 
time did we see any closer approach to the formation of a closed tube by a longitudinal 
union of the summits of the neural folds than that shown in fig. 28. Still I am inclined 
to believe that a large hiatus in our observations may exist here. In a dorsal view 
of the tail of an embryo with about twenty protovertebrae a well-marked median line 
was observed which at the posterior extremity slightly broadens out into a groove, just as 
would be the case did the neural canal form as in other vertebrates. 
Not having witnessed the formation of the neural canal of course nothing definite was 
seen of a neurenteric canal of the same character as exists in the Elasmobranchs, Batra- 
chia and birds. In figure 30 which represents the first formation of the neural folds a 
slight notch is seen at the posterior margin of the blastoderm which afterward 
became much more marked. This notch arises in the same way and to my mind is ON TIIE EMBRYOLOGY OF THE TELEOSTS. 
207 
homologous with the canal connecting the neural and alimentary canals which has recently 
been demonstrated to exist in all vertebrates.’ An unfortunate accident occurred to the 
egg forming the subject of this figure and hence no consecutive observations were 
made upon it. No other eggs in such favorable conditions were found. In fig. 30 I have 
shown the medullary folds extending slightly farther over the deutoplasm than does the 
rest of the blastoderm, and between them the medullary groove, the epiblast of which of 
course forms the lining of the neural canal. Continuous with the epiblast which passed 
down into the notch between the medullary folds is the hypoblast which extends up the 
under surface of the blastoderm. Whether this notch eventually closes up leaving a tube 
connecting the neural and alimentary canals I do not know, but it seems impossible to 
escape the conclusion that it well represents the neurenteric canal of other forms although 
the enteric canal of the fish does not at this time have the closed condition which obtains 
in other forms. 
According to various observers, before the formation of the neural canal the epiblast 
separates itself into two layers, an outer or epidermal and an inner or nervous layer, the 
latter being confined more closely to the embryonic area. This differentiation we were 
not looking for and hence no allusion to it appears in the foregoing account of the for- 
mation of the neural cords ; whether it exists or not we cannot positively say though it 
probably does and was overlooked in our studies. According to those observers who 
make this distinction, the nervous layer forms the bulk of the neural canal and Cal- 
berla(’77) claims that a thin layer of epidermal cells penetrates into the nervous layer and 
eventually forms'the epithelial lining of the' neural canal, but Gotte (’78) denies this 
and Balfour studying Lepidosteus and the teleosts (’81) has not been able to confirm Cal- 
berla’s observations. It would however seem probable that Calberla is right though farther 
observations are necessary to settle the point. 
Schapringer (’71 p. 555) does not afford any information on this point, for he merely states 
that the medullary canal does not form in bony fishes, as in Birds, Batrachia and Mammals 
by a folding in of the medullary folds but through a process of separation on the inside. 
According to our observations the method of origin of the neural ridges has an almost 
exact parallel in that of the Elasmobranch as given by Balfour (’78) and also closely 
resembles Klein’s observations on the trout ’62 pi. 17, fig. 2. The figures of His, (’75) in 
text, and which are copied by Balfour, ’81 fig. 33, are greatly different from anything 
which we have seen as will be noticed on an inspection of our plates. 
Optic Bulbs and Protovertebrae. 
Shortly before the stages shown in figs. 29 and 32 the fore-, mid- and hind-brains are 
differentiated and almost immediately the optic lobes begin to be segmented off. At this 
time both the brain and the rudimentary lubes appear to be solid bodies without any 
internal cavity nor does there appear to be any trace of the neural canal in the spinal 
cord. A fissure appears on either side of the brain cutting off a portion which forms the 
optic lobe. This fissure begins above and behind and gradually extends forwards and 
downwards until at last but a slight connection is left, the rudimentary optic nerve (fig. 
36). The fissures progress until at last the nerve going to the right eye is connected only 
with the left side of the brain while the optic nerve of the left eye arises from the right 208 
KINGSLEY AND CONN 
side of the same central organ, the condition which obtains in the adult fish. During the 
differentiations thus described other changes take place, and before the stage represented 
in fig. 42 is reached the lumen in the brain, optic bulbs, and neural cord appears as shown 
in figs. 36 and 45. 
Synchronous with the differentiation of the regions of the brain, the mesoblast adjoining 
the notochord (fig. 32) becomes separated from the rest of the layer as the muscle plates, 
and with the separation of the optic bulbs the muscle plates are divided into protoverte- 
brae. The first of these protovertebrae to be formed is at about the middle of the body, 
and the fissures which limit it arise simultaneously. They begin close to the notochord 
above and progress outward and downward and at the same time slightly backward. 
From this central one the formation of the protovertebrae extends gradually in both direc- 
tions. At the same time the formation of pigment cells is seen. These arise as black 
dots and gradually increase and change their shape until at last they assume forms like 
those shown in fig. 51. 
Regarding the peculiar structure which from its first describer we may call Kupffer’s ves- 
icle I have but little to say. It first makes its appearance just before the stage shown 
in fig. 34 on the under surface of the posterior end of the embryo and rapidly increases in 
size until it acquires a diameter nearly equal to that of the fish. Of its subsequent fate 
our notes afford no information. Its first appearance is indicated by one or two small 
globules which soon are joined by others until an appearance like that of fig. 52 is seen. 
Very soon these globules unite and in two hours the vesicle has the appearance and 
relative proportion of fig. 53. Fig. 54 shows about the limit of its development and is 
reached'in about five hours from the first appearance of the minute globules. 
As mentioned above, this vesicle was first noticed by Kupffer (’68) and by him regarded 
as a rudimentary allantois. Balfour (’81) regards it as homologous with the terminal vesi- 
cle of the post-anal gut of Elasmobranchs. On the other hand Henneguy (’80) studying 
the perch thinks he saw an opening or traces of invagination of the vesicle and would 
homologize it with the primitive intestine of the Cyclostomi and Batrachia and its opening 
with the anus of Rusconi, a view which it seems to me is entirely unwarranted by the pre- 
vious growth of the embryo and by the method of origin and position of the vesicle as we 
have seen it. The view of Balfour seems much more probable. 
The epiblast over the optic lobe begins to thicken to form the lens of the eye when six- 
teen protovertebrae are outlined. This thickening increases until soon it acquires the 
character shown in fig. 49 and almost immediately the thickening begins to be segmented 
off and to make its way into a depression in the optic lobes and to acquire more and more 
of a spherical character as shown in figs. 55-57. The manner of the involution of the lens 
and the features connected with it have so often been described that it is unnecessary to 
repeat them here. 
At about this time the mesoblast begins to split into somatopleure and splanchnopleure. 
This splitting begins at the head end of the embryo and progresses regularly in every 
direction. This is a true splitting and not as suggested by Mr. Ryder in a letter to the 
author an apparent one. He interprets his observations as follows : the portion of the 
mesoblast which extends down over the yolk is that portion which eventually forms the 
splanchnopleure and that the somatopleure gradually extends down between this layer and ON THE EMBRYOLOGY OF THE TELEOSTS. 
209 
the epiblast, and he also (’81) regards the space into which the somatopleure thus forces 
itself as the remains of the segmentation cavity. So far as our eggs and our observations 
go there is not the slightest evidence in favor of either view, for the epiblast is everywhere 
in close connection with the mesoblast and nothing could be seen in the envelopes of the 
yolk which could in any way be interpreted as remains or derivations of the segmentation 
cavity, a cavity of which all traces are lost at an early stage in the development. In our 
eggs also there was a veritable splitting of the mesoblast as will be seen by an inspection 
of fig. 36.1 
From this point on my observations are exceedingly fragmentary and the account would 
best be confined to little more than the remaining figures, a course of procedure which 
will serve to connect the earlv stages with those of which Mr. Agassiz treats. 
In a side view, at first but two of the prominences of the brain are seen (fig. 33) but 
scon the third, the mid-brain, makes itself visible as shown in fig. 34, and at the latter 
stage we first find the traces of the pericardium and the heart (p. fig. 34). Of the origin 
of these portions of the anatomy I can say but little. It seems almost impossible to cor- 
relate the steps of their development with those found in other vertebrates. At first 
there appears a mass of mesoblastic tissue arising almost beneath the hind brain and pro- 
jecting into what has previously been regarded as the cavity produced by the splitting of 
the mesoblast (and therefore corresponding to the pleuroperitoneal cavity of other verte- 
brates) but which is regarded by Ryder as the segmentation cavity. (We shall return to 
this cavity further on). This mass of cells grows downward and when it comes in contact 
with the lower layer of cells (either hypoblastic or sphlanchnopleuric) a lumen appears, 
the primitive heart. At first this is a simple tube and indeed for a considerable time 
retains that character as shown in figs. 40 and 50. When the heart first begins to pul- 
sate the vibrations are very slow and frequently it ceases beating for some time and then 
begins again. Coincident with the first pulsations, which appear at a little later stage than 
that represented in fig. 43, the first motions of the embryo are seen, and consist of slight 
tremors of the whole body. At first the contractions of the heart produce no currents of 
blood nor in fact are any corpuscles to be seen. In the eggs of the cunner it is extremely 
difficult to trace the development of the circulatory system after this time, only slight and 
unsatisfactory views of portions being visible, while only once was I able to see anything 
whatever of the blood vessels of the yolk sac. Of the formation of the corpuscles nothing 
was seen nor were they visible until a comparatively late stage. 
We have seen in preceding pages the method of formation of the hypoblast of the ali- 
mentary tract by an invagination to which are possibly added cells from the intermediary 
layer. A portion of the hypoblast eventually forms a solid cord extending along beneath the 
body but of the exact mfethod we are not certain. This cord gradually grows forward and at 
intervals a lumen appears, as shown in fig. 33 me., the future cavity of the canal; this is shown 
again at a later stage in figure 42, which represents the hinder end of the mesenteron of a 
fish about as far developed as shown in fig. 43. Though the exact process of the closure of 
1 The investigations of 1882 which embraced these points 
lead me to regard Mr. Ryder’s conclusions more favorably, 
and though I am not ready to accept them wholly without 
some modification, the changes required are far less than those 
implied in the above paragraph which is based upon some 
erroneous interpretations. 
MEMOIRS HOST. SOC. NAT. HIST. VOL. III. 210 
KINGSLEY AND CONN 
the blastoderm was not seen, the writer feels confident that the posterior end of the alimentary 
tract arises in the normal way by an invagination of the epiblast to form the proctodeum 
(fig. 41) and that the division between the two portion breaks down, the result being as 
shown in figures 44 and 53. Ryder seems to regard this proctodeum as tjie neurenteric ca- 
nal. The steps between these two figures were all seen, but the formation of the anterior end 
of the canal was not witnessed. There are many points of the alimentary tract upon 
which additional information is needed: the manner of the formation of the mouth, the 
connection, if any exists, between the yolk sac and the stomach or intestine, and the rela- 
tions of what is here called the hypoblast of the yolk sac to that of the digestive portion. 
There are many points in connection with this latter which are absolutely unintelligible 
to me no matter how looked upon. In fig. 33 this layer is represented as extending beneath 
the embryo and nowhere united with the alimentary canal and together with another layer 
starting off on its course around the yolk. Now if this be the hypoblast from which the 
digestive tract arises, some connection would be expected between them though none has 
been found. 
The fins which are first seen in an egg about as far advanced as fig. 51, arise in the cun- 
ner as a simple outgrowth and not as a continuous lateral fold, as is found in many forms. 
The first skeletal elements appear as a small body at the base of the fin parallel to the 
body axis and it is not until considerable later that radial portions appear. This basal 
skeleton instead of appearing as a pair of rods as described by Ryder was rather a broad 
plate with a central opening, as if his rods had united at their extremities. The same 
feature was seen in Lophius. 
The remaining features of the development so far as I have clearly made them out can 
be seen from the plates, and my knowledge is too deficient to say more concerning them 
than will appear in the explanation of the figures. In about two days from impregna- 
tion, the fish hatches with a large yolk sac, which in four days more Jias almost entirely 
disappeared as shown in fig. 53. The time of hatching I cannot exactly state, in fact 
it varies considerably with the temperature. Eggs which were impregnated Friday 
morning at ten o’clock were found hatched Sunday at eleven A. m. (How much before that 
hour the actual hatching took place I cannot say). The act of hatching was often wit- 
nessed. The membrane of the egg, yielding to some violent struggles of the embryo 
bursts open and the young fish emerges usually head first. At the time of hatching the 
young fish is about a tenth of an inch in length and very slender in proportion. ON THE EMBRYOLOGY OF THE TELEOSTS. 
Explanation of Plates. 
a. anus. 
al. alimentary canal. 
ao. aorta. 
aud. auditory vesicle. 
b. blastoderm (in fig. 24* an 
aster.) 
be. buctus Cuvierii. 
ch. notocord. 
ea. embryonic area. 
/. fin. 
f. b. fore-brain. 
f. v. fin vein. 
g. gills or gill arches. 
h. or hy. hypoblast. 
ht. heart. 
h. b. hind-brain. 
i. intermediary layer (in fig. 
40 jugular vein.) 
j. jugular vein. 
1. lens. 
1. t. thickening of epiblast for 
lens of the eye. 
Iv. liver. 
mb. mid-brain. 
me. mesoblast (mesenteron in 
figs. 33 and 41. 
n. p. nasal pits. 
n. g. neural groove. 
o. eye. 
op. optic vesicle. 
o. g. oil globule. 
p. pericardium. 
pc. cardinal vein. 
p. g. polar globule. 
pr. proctodeum. 
p. t. protovertebrae. 
s. segmentation cavity. 
so. somatopleure. 
sp. splanchnojdeure. 
su. v. superior vertebra. 
s. v. sinus venosus. 
t. s. tail swelling. 
u. Kupffer’s vesicle. 
u. g. urogenital apparatus. 
y. yolk. 
y. s. yolk sac. 
PLATE XIV. 
Fig. 1. Micropyle of egg of Ctenolabrus in section. 
Fig. 2. Surface view of same with surrounding pore canals. 
Fig. 3. Merlucius the germinal disc above showing the archamphiaster of maturation. 
Fig. 4. Early egg of Ctenolabrus before maturation and impregnation. 
Fig. 5. Portion of germinal area of egg of Merlucius with probable polar globules. 
Fig. 6. Formation of polar globule and expulsion of same through the micropyle. 
Fig. 7. T he same a few seconds later; in these two figures the details of micropyle are omitted. 
Fig. 8. A polar globule attached to one cell of a blastoderm of two segments. 
Fig. 9-10-11. Three successive steps in the formation of the biscuit-like germinal area, shown in section, 
the shaded portion extending out from that region forming a portion of the intermediary layer. 
Fig. Ik. Result of first segmentation, the “tails” on either side the rudimentary “bourrelet peri- 
pherique.” . 
Fig. 13. Preparations for second segmentation. 
Fig. 14. Resulting four segments with the temporary furrows of the yolk. 
Fig. 15. Diagram of amoeboid motions in blastoderm of eight cells. 
Fig. 16. Blastoderm of eight cells showing a common irregularity. 
Fig. 17. Amoeboid appearance of two cells. 
Fig. 18. Preparation for dividing from eight to sixteen cells, showing irregularity in time of division. 
Fig* 19- Blastoderm of 16 cells. 
Fig. 20. Blastoderm of 24 cells. 
Fig. 21. Optical section through the edge of a blastoderm in a late stage of segmentation. 
Fig. 22. Beginning, and fig. 23, later stage of invagination of hypoblast. The upper shaded portion 
representing the epiblast and lower layer cells; s, the segmentation cavity, and the dark narrow line just 
beneath, the intermediary layer; the broad shaded portion shows the outline of the lateral invagination. 
The black line beneath A, the hypoblast, and e. a., embryonic area is possibly the segmentation cavity of 
Ryder. 
Fig. 24. Blastoderm of fig. 23 from above, showing the outline of the segmentation cavity, the line across 
shows the plane of the preceding section. 
PLATE XV. 
Fig. 24*. Cells from the margin of blastoderm; and beneath, free cell formation in peripheral cushion; 
amphiaster x, and an aster b, are shown and also a stage in the formation of cell walls. 212 
THE EMBRYOLOGY OF THE TELEOSTS. 
Figs. 25, 26 27. Three stages in formation of notochord shown in (optical) section. 
Fig. 28. Same at later stage. 
Fig. 29. Side view of embryo, etc., showing the blastoderm with (faintly) its thickened margin. 
Fig. 30. Oblique view of tail end of fig. 29, showing the neural groove, the tail swelling and the thick- 
ened margin of the blastoderm, the slight notch in the margin at t s may possibly represent the neurenteric 
canal. 
Fig. 32. Formation of optic lobes and protovertebrae; the apparent distortion of the figure is due to an 
attempt to represent the embryo in perspective. 
Fig. 33. Stage a little later than 32 showing optic lobe and mesenteron and a few of the anterior proto- 
vertebrae. 
Fig. 34. Still later with fore-, mid- and hind-brain differentiated and pericardial region forming. 
Fig. 35. Splitting of mesoblast into somatopleure and splanchnopleure. 
Fig. 36. Dorsal view of head a little later than fig. 34 with formation of the lens of the eye and the 
appearance of the lumen in the brain and optic vesicles. 
Figs. 37, 38, 39. Successive changes in appearance of notochord. 
PLATE XVI. 
Fig. 40. Heart and blood vessels in stage nearly corresponding with fig. 51, or shortly before hatching. 
Fig. 41. Relations of notochord, aorta, urogenital canal, mesenteron and proctodeum in hatched fish. 
Fig. 42. Lumen in mesenteron in embryo about like fig. 43. 
Fig. 43. Embryo with the lens of the eye, auditory vesicle and nasal pits well advanced. The blasto- 
derm has closed and the tail has begun to grow out. Kupffer’s vesicle was present but is omitted in the 
drawing. 
Fig. 44. Anal region in hatched fish. 
Fig. 45. Details of head in fig. 43. 
Figs. 46 and 47. Out-growth of liver in its earliest stage from the side and from beneath. 
Fig. 48. Anterior portion of fish two days old from beneath, showing anterior end of urogenital canal. 
The stomodeum and mesenteron have not yet met. H. W. Conn, del. 
Figs. 49 and 50. Fish of about four days. H. W. Conn, del. 
Fig. 51. Embryo of unknown teleost just before hatching; 
Fig. 52 and 54. Two stages in formation of Kupffer’s vesicle, u, seen in optical section. 
Fig. 53. Fish between four and five days old. Memoirs Boston Soc.Nat.Hist. Vol. Ill, 
Plate XIV. 
J.S. Kingsley, adnatlith. 
Printed. byA.Meisel. 
Kingsley on Embryology of Teleosis. Memoirs Boston Soc.Nat.Hisl. Vo], III 
Plate XV 
J.S. King-slay ad natlith. 
Printed byA.Meisel. 
Kingsley on Embryology of Teleosts. Memoirs Boston Soc.Nat.Hist. Vol. III. 
Plate XVI. 
J. 5. Kin si ay, ad nat.li ih. 
Printed byA.Meisel. 
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