Surgeon General's Office %* ^VTfW%3\) r"^V 'ffiT^Y ^W)'P A. 33 MX XA -^ C flKr Hsi 7fc//rn, No. .£.£. *V6 -----—--- - "/•"-N V MIND IN NATURE; THE ORIGIN OF LIFE, AND THE MODE OF DEVELOPMENT OF ANIMALS. HENRY JAMES ^LARK, A.fe., B.S. ADJUNCT PROFESSOR OF ZOOLOGY IN HARVARD UNIVERSITY, CAMBRIDGE, MASS. MEMBER OF THE AMERICAN ACADEMY OF ARTS AND SCIENCES, BOSTON, MASS.; OF THE BOSTON SOCIETY OF NATURAL HISTORY; CORRESPONDING MEMBER OF THE AMERICAN MICROSCOPICAL SOCIETY OF NEW YORK, ETC., ETC. " La Daissance des etres organises est done le plus grand mystere de l'economie organique et de toute la nature; jusqu'a present nous les voyons se developper, mais jamais se former." Cuvier, Regne Animal, 1829. OVER TWO HUNDRED ILLUSTRATIONS. 7J ;:; i/.>l»'* NEW YORK: D. APPLETON AND COMPANY, 443 and 445 Broadway. 18 05. QH C55Sw, Entered according to Act of Congress, in the year 1865, by D. Appleton and Company, In the Clerk's Office of the District Court of the United States for the Southern District of New York. RIVERSIDE, CAMBRIDGE: STEREOTYPED AND PRINTED BY H. O. HOUGHTON AND COMPANY. PREFACE. The following chapters comprise the substance of a course of public lectures which were delivered by the author in the hall of the Lowell Institute, in Boston, Mass., during the months of February and March, 1864. Since that time a considerable amount of matter has been added, chiefly in the form of notes; and some alter- ations have been made in the sequence of the subjects, during which it has been found necessary to arrange the chapters in such a way that they do not correspond with the original succession of the lectures. To obviate any difficulty, however, which might arise from the fre- quent references to previous lectures, care has been taken to mention the page upon which the subject alluded to may be found. Although these lectures were originally given to the public in a popular form, it must not be supposed that they were altogether based upon what was already known to the scientific world; on the contrary, no small proportion of the facts and ideas promulgated herein are claimed by the author to be original with himself. In this respect the attention of naturalists is invited to the following subjects. The structure of Bacterium termo. The organization of Vibrio baccillus. The theory of the eo-g. The polarity and bilaterality of the egg. The eel- iv PREFACE. lular structure of Actinophrys. The relation of vitality to the various degrees of organic complication. The re- lation of the egg to secondary causes. Anatomy of Polypi The nervous system of Infusoria. The individu- ality of Hydro-Mednsce, Strobiloid Medusas, and the lower Invertebrata. The peculiar mode of reproduction of the hydroid genus Rhizogeton. Monstrosity and reproduction by budding. The typical animal. The relation of the five grand divisions to the typical animal. The typical form of Protozoa and Zoophyta. Polarity of animals. The so- called radiation of Zoophyta. A new form of ciliated Infusoria, Heteromastix. The digestive system of Infusoria. The longitudinal axis of Echinodermata. Anatomy of the apodous holothurian, Caudina. Investigation of the structure of Loligopsis, in reference to the dorsal and ventral sides of Cephalopoda. The relation of the spinal marrow to the vertebral axis. The development of the tentacles in Tuhdaria. The bilaterality of Tubu- laria. The structure of the scyphostoma of Aurelia. The subsidiary layer of the vertebrate embryo. In this con- nection the author would also request, especially of the younger naturalists, the perusal of the "IVote on Sdentific Property" on p. 37, and also the note on p. 304. A large proportion of the figures which were used to illustrate the lectures are reproduced in this volume; and, beside these, numerous others are introduced in order to meet the requirements of the additional matter and the notes. At least two thirds of these were taken from the original drawings of the author, and the rest were almost invariably selected from the first authori- ties. In the latter case, the name of the original author is given at the end of the description of the figure. PREFACE. • v Whenever possible, figures of American animals were selected in preference to those from foreign sources. When an object is magnified, the amount of enlarge- ment is stated to be so many diameters, e. g. 250 diam. i. e. 250 times the diameter of the natural size. HENRY JAMES CLARK. Cambridge, Mass., September, 1865. CONTENTS. PART FIRST. THE ORIGIN OF LIFE. CHAPTER I. PA 08 THE OLD AND THE NEW DEVELOPMENT THEORY. --CHEMICAL AFFINITY AND THE PRINCIPLE OF LIFE, OR THE ORGANIC AND INORGANIC FORCES. — THE LOWEST ORGANIC BEINGS. — SPONTANEOUS GENERATION ... 8 CHAPTER II. WHAT SPONTANEOUS GENERATION PROVES. --THE EGG IS THE LOWEST PHASE OF ANIMAL LIFE.--THE EGG A BIPOLAR ANIMAL.--THE EGG CON- TRASTED WITH THE LOWEST FORMS OF ADULT BEINGS. — THE EGG AS RELATED TO SECONDARY CAUSES........28 CHAPTER III. THE OLD APHORISM, " OMNE VIVUM EX OVO," NOT STRICTLY CORRECT. — THE ORIGIN OF INDIVIDUALS BY BUDDING AND SELF-DIVISION . . 64 CHAPTER IV. THE REGENERATION OF LIVING ORGANISMS AFTER PARTIAL DESTRUCTION. — THE PERSISTENCY OF VITALITY DURING DECOMPOSITION.— THE RELA- TION OF SECONDARY CAUSES TO THE GREAT PRIMARY CAUSE.--ANIMALS PRIMARILY CREATED IN AN ADULT STATE......88 CHAPTER V. SPONTANEOUS GENERATION AND REPRODUCTION BY BUDDING AND FISSIGEM- MATION MOST FREQUENT AMONG THE LOWEST RANKS OF ANIMATE BEINGS. —ALL ANIMALS ALIKE IN THE EARLIKST STAGES. --MAN AND MONAD ARE AT ONE TIME A MERE DROP OF FLUID .... 109 vm CONTENTS. PART SECOND. THE FIVE GREAT ANIMAL GROUPS. CHAPTER VI. pacu THE IDEAL TYPES.--ALL ANIMALS BILATERAL......H« CHAPTER VII. THE DISTINCTION BETWEEN ANIMALS AND PLANTS.-- THE PSEUDO-INFUSO- RIA, THEIR PLANT-NATURE. — THE PLANT-LIKE INFUSORIA . . . 181 CHAPTER VIII. THE PHYTOZOA, OR PLANT-ANIMALS. — THEIR RELATION TO UNDOUBTED ANIMALS 153 CHAPTER IX. THE SYMBOLICAL ANIMAL. —THE PROTOZOA....... 158 CHAPTER X. ZOOPHYTA........•.....177 CHAPTER XI. MOLLUSCA............... 195 CHAPTER XH. ARTICULATA.............214 CHAPTER XIII. VERTEBRATA.............226 CHAPTER XIV. THE DISTINCTNESS OF THE FIVE GRAND DIVISIONS.....236 CHAPTER XV. THE MIMETIC FORMS OF DIVERSE TYPES OF ANIMALS.....248 CHAPTER XVI. THE TRANSITIONS AMONG THE SUBORDINATE TYPES OF THE FIVE GRAND DIVISIONS.............254 CONTENTS. IX PART THIRD. THE MODE OF DEVELOPMENT OF ANIMALS CORRESPONDS WITH THE TYPE OF THE GRAND DIVISION TO WHICH EACH ONE SEVERALLY BELONGS. CHAPTER XVII. PA0« THE SEGMENTATION OF THE EGG. — THE EMBRYOLOGY OF PROTOZOA, ZOOPHYTA, MOLLUSCA, ARTICULATA, AND VERTEBRATA .... 283 INDEX..............317 PART FIRST. THE ORIGIN OF LIFE. PART FIRST. THE ORIGIN OF LIFE. CHAPTER I. _t£E OLD AND THE NEW DEVELOPMENT THEORY. — CHEMICAL AFFINITY AND THE PRINCIPLE OF LIFE, OR THE ORGANIC AND INORGANIC FORCES. —THE LOWEST ORGANIC BEINGS. —SPONTANEOUS GENERATION. No doubt most of you have heard of what is called the " Development Theory," and have been led, in the course of your various readings, to believe that its doctrines have such a tendency as might induce one finally to exclude from the mind every idea of the interposing hand of the Creator, in the origination, development, and growth of living creatures. It is true that this is one of the various forms of the develop- ment theory; arid the one which, more than any other, is promi- nent in the minds of men at large throughout the world. It is that form of the development theory which teaches that all things originated through physical forces, which operate according to what are called physical laws ; the laws of elec- tricity, magnetism, chemical affinity, &c.; laws which have been said to administer themselves. There was a time when this idea may be said to have raged among the philosophic portions of the community ; but although the heat of the fever has abated at this time, still there is a cer- tain tendency to relapse, if not into the old stage, at least into another no less dangerous form of it, which is this. Admitting, say the advocates of this theory, that in the beginning the Creator made all things living by a direct act of his own hand, yet after that, in order that the universe might 4 THE OLD AND THE NEW go on in the course which he had set it upon, he established certain laws which should act as independent rulers of the forces of nature, competent to influence the origin, the development, and growth of all things, without any further interposition of his power. This is indeed the most insidious form in which Materialism has attempted to make its first approaches to the citadel of our belief in a ruling Providence. It acknowledges the primary interposition of the Great First Cause, but eventually would make it seem possible that his power can be made to operate in such a way that his very existence is not necessary ; for, say they, why should he continue to exist, if the laws which he has established can control the work for him ? And now then, so much being allowed, the next step in the fallacy is in this guise. It being admitted that these forces are competent to perform all the offices of a Creator; they being equally powerful to create and to destroy, to determine the movements of this mighty uni- verse or to originate new ones; all this being admitted, why, then, are they not equally powerful and omnipresent as a Crea- tor ; what is there not in them that a Creator possesses; if noth- ing, then why may they not have given rise to their own exist- ence, or have existed eternally; in fine, what more is needed to constitute them a Great First Cause ? Your ready answer no doubt will be that the revelation de- clares the existence of a God! Truly ! And it is this revelation which satisfies a large portion of the community; but then there is still a great body of readers and thinkers, inquiring minds, who would like to know more about the manner in which the Creator manifests himself. What did the King of Israel mean they ask, when he said, " The heavens declare the glory of God; and the firmament showeth his handy work ? " I hope in the course of these lectures to be able to answer this question to your fullest satisfaction. In doing this, it is my design to proceed in an argument to prove that there is a power at work in the universe which possesses foreknowledge; the design of a forecasting, foreordaining mind, — a thinking, intel- DEVELOPMENT THEORY. 5 ligent, animate being; such a combination of powers that no form of physical law could possibly be conceived to represent. He must be a bold metaphysician indeed, who could assert such a possibility! It seems to me that it would be tantamount to declaring an utter impossibility to be possible. The form of the argument which I wish to introduce for your consideration is identical, up to a certain point, with just such a one as would be advanced to prove the prevalence of indepen- dent physical law as a controlling power ; but beyond that point I hope I shall be able to show that it may be used as evidence of a thoughtful design to produce a succession of events, or a combination of contemporaneous, interdependent phenom- ena.* I have chosen for the subject of this course of lectures a somewhat comprehensive field, namely, that of the origin of life and the mode of development of animals, because I do not wish to be limited in what I have to say to a simple narration of the mode of putting together the organization of animals. I have purposely used the term " putting together " here, because that is the general idea of the way in which an organized being is brought into existence. You have been led to think so by various means. In " Paley's Philosophy," a work so extensively * In the succession of beings from a lower to a higher type, and a consenta- neous greater degree of complication, we have the strongest proof of an intel- ligent being, designing, ordaining, and controlling. The laws of the older physicists were not claimed to be derived from an intelligence; they were deemed to exhibit the necessary operations of matter upon matter; but when we see that these laws have an order, and, as they are understood at the present day, a rate of succession in their operations, which have the stamp of thoughtful- ness impressed upon them, it is impossible not to discover that they do not work of their own accord, but are controlled by a creative forethought and design. If the product of these causes was a heterogeneous mixture of beings, with no rela- tion whatever among themselves, then one might more plausibly claim that the so-called physical causes had produced living creatures. As it is, though, we have before us animals allied to each other by progressive relations, which finally, if we follow them up, end in the highest forms of life at the present day, from having begun with the lowest and ascended. What mere non-intelligent causation could produce the like ? 6 CHEMICAL AFFINITY AND used in our schools and colleges, the animal frame is compared to a watch with all its interdependent wheels and pulleys, which can be put together after all the parts have been manufactured separately. In our institutes of instruction we have very little or nothing of the physiology of growth and development taught, because the text-books are devoted to an enumeration of the organs of the adult body; and as the movements of the animal frame are illustrated by mechanical contrivances, pulleys, levers, and the like, the digestion by chemical forces, and the circula- tion by mechanical propulsion, it is very natural that scholars should grow up with the idea that the human frame is moulded upon a mechanical contrivance. This is of what I would totally disabuse your minds. Al- though there may be a certain degree of truth in it, yet it is in such a small proportion to what is commonly received to be the truth, that I would rather, for the present purposes, you had never heard of such a thing as an organized being, for then your minds would not be diverted, by any preconceived ideas, from the argument which I am about to lay before you. I beg, therefore, that you will allow me to lead you on, unrestrainedly, step by step, in the new path which I have laid out for the pres- ent occasion. In the preparation of these lectures I have revised the whole history of the origin of life, and of the mode of development of animals, as it is understood at the present day. I have commenced with the lowest and simplest forms of life; those obscure manifestations of a living existence, immediately upon, or rather just this side of the confines of mere chemical association. The characteristics of these I have careiully bal- anced between the probabilities of life on the one hand, and of mere existence without life on the other. This no doubt seems to you like a mystery; and so it is, in a measure at least; and I would, certainly, rather that it might so appear at the outset, than that it should be involved in your minds with any of the mechanical ideas of which I have spoken, when referring to Paley's work. VITAL AFFINITY. 7 All living beings, whether animals or plants, are composed, essentially, of four chemical elements, Carbon, Hydrogen, Oxy- gen, and Nitrogen, which are combined in various proportions. It would be very natural to suppose after this statement that these chemical combinations are such as you see exhibited every day around you; such as are called the natural chemical affin- ities, which exist, for instance, between the gases of which the air is composed, or the acids, chloroforms, alcohol, salts, crystals, &c, &c. But this is not so! Although I am well aware that it is getting to be the general opinion, among organic chemists and physiologists, that the inorganic and organic affinities ap- proximate each other, and may eventually turn out to be, among themselves, mere degrees of difference; yet, even with such an idea in view, it is not incorrect to say that it is in direct opposi- tion to natural chemical affinity that organized beings exist. There is another principle or affinity which is not commonly recognized in our daily experience; it is the principle of life, or vital affinity, which binds together the chemical elements in certain forms or groups, which are nowhere known but in or- ganized, living beings. Between these two kinds of affinities, then, — the natural chemical affinity on the one hand, and the vital affinity on the other, — there is a constant struggle, the one to counteract the operations of the other. Perhaps this question may arise in your minds, as it has with me, namely, Why should inorganic chemical affinities be called the natural affinities, any more than those which are exhibited by organic life ? Is not one as extensive in its influence as the other, and does not the vital affinity, in assimilating material for organized bodies, tend just as much to decompose bodies held together by the natural chemical affinities, as in the reverse way ? I cannot anticipate what may be thought of this ques- tion by the physical causists, those who maintain that life, organized bodies, originate through the operations of physical agencies, or in other words, the natural chemical affinities. Can the latter transform themselves into vital affinities ? It may be so, if the two differ from each other only in degree. 8 INORGANIC BODIES AND But to return to our proposition, which is that all living beings are composed of four chemical elements, and these ele- ments are held together by the principle of life. We cannot go behind the veil to see the ultimate condition of this principle; — it must remain, like the principle of gravity, of electricity, and many other things, a partially unexplained phenomenon; — suffice it for our purpose that we consider it perhaps as fully understood as is ordinary chemical affinity. A drop of water is composed of two elements, Oxygen and Hydrogen, represented by O H, which are held together by ordinary or natural chemical affinity. Common hartshorn or ammonia is composed of two elements, namely, Nitrogen and Hydrogen, in these proportions, N H3. Alcohol is composed of three elements, namely, Carbon, Hydrogen, and Oxygen, represented by C4 H6 O2, in the pro- portions indicated by the figures, and these also are held together by natural chemical affinity. This is easily understood. It is a very simple proposition. Now, in place of this so-called natural chemical affinity, sub- stitute in your minds that other kind of affinity which I have called the vital affinity, and apply it to these selfsame chemical elements, Carbon, Hydrogen, Oxygen, and Nitrogen, C H O N, and you have an organized being, a plant or an animal. We may have on one side of a line, life, C H O N, and on the other side the same elements, C H O N, but in different proportions, representing the absence of life, which is death, and between them, circumstances * which determine the conditions of these elements, whether they shall exist in one combination or an- other. Organiclife=CHON,circumstances,Inorganicbodies = C HON. Without reflection this might seem like the exchange of one chemical compound for another, and not the substitution of life for death, or the substitution of the vital affinity in place of natural chemical affinity; but nevertheless it is true that so * Thus, for instance, flesh or blood is composed of C48 H39 N6 O15, and when these decay and putrefy, Carbonic Acid (C 02), Water (H O), and Ammonia (N H3), are the result. ORGANIC LIFE. 9 closely do these two affinities approach each other in the range of their actions, that there is on the one hand the drop of resin, gum, or mucus, held together by the natural chemical affinity, and on the other hand, there are certain living beings so exceed- ingly simple in structure that they may be compared to a drop of gum or mucus, but from, which they are distinguished by being held together and animated by the affinity which is called the principle of life. These creatures are so simple that under the most powerful microscopes of the present day they appear like drops of gum or starch, and in fact they would not be rec- ognized as living beings,— I mean to say, in the most literal sense, that they could not be distinguished from the gum-drop— did they not move, and take in food, even living animals as a prey, which they digest in the most simple manner. The creatures to which I refer are commonly known as the Protean animalcules, on account of their changeable form. This diagram (fig. 1) represents the one which is called by scientific men, Amoeba. The three figures repre- FigTi. sent the various forms which I have seen the same individual assume, whilst I had it under the microscope, as it crept over the water-plants upon which it is accustomed to dwell. The most usual form which it assumed is that of an elongated oval (A), but from time to time the sides of its body would project either in the form of simple bulgings (B), or suddenly it would spread out from several parts of the body (C), as if it were falling apart; just as you must have seen a drop of water do on a dusty floor, or a drop of oil on the sur- face of water; and then again it retracted these transparent arms and became perfectly smooth and rounded, resembling a drop of slimy, mucous matter, such as is oftentimes seen about the stems of aquatic plants. But what gave character to this Fig. 1. Amoeba diffluens. Ehr. The Protean animalcule. 100 diam. A, B, C, the three attitudes of the same individual, a, the head. The arrows indi- cate the course of the circulating food.—Original. 10 THE LOWEST FORMS unstable globule, in all its changes of form, was that it invari- ably progressed with a certain part of its body forward ; and upon close examination I found that this part had a peculiar appearance which distinguished it from the rest of the body, that is, it was covered with little knobs (a), and the interior was perfectly clear and transparent, with not the least trace of mo- tion to be discovered therein. This I shall call the head. This was in marked contrast with what was to be seen in the other part of the body, for there were the most unmistakable signs of life, exhibited not only by the activity of the numerous particles of food, but by the regularity with which they circulated in cur- rents, having a fixed direction. The arrows which I have intro- duced in the figures (A B) will indicate the trend of these streams. Constantly and invariably the currents of food passed backwards along the sides of the body to the posterior end, and there uniting in a single stream, turned their course toward the head, passing along the middle line of the body, and again turned off right and left backwards along the sides. Nothing could be more wonderful than this sight; not a sign nor trace of any interior organization which could be supposed to direct these currents; all was as clear as crystal, excepting the circu- lating particles; and they seemed as if impelled by magic. To increase this almost unavoidable illusion, there was another phenomenon which was connected with the movements of the circulation, which I could not explain to myself for some time; I mean, that, with the exception of the head, the whole of the body seemed to be gradually sliding on itself, and turning over, end for end. This I knew could not be strictly true; and yet the deception to the optical senses was perfect, even after I had discovered the cause of it. This is akin to what every one must have observed whilst sitting in the cars at a station, when a passing train gives to the one you are in the appearance of moving; and this cannot be banished from the impression until the eye is cast upon some fixed object. The illusion in the case of the Amoeba was derived from the fact that the particles of food, as they passed backward along the sides of the body, OF ANIMATE BEINGS. 11 pressed so closely to its surface as to project it more or less, and thus they appeared to be a part of the body itself. The food, which may be either a living animal or plant, is evidently in- troduced into the body at any point, simply by being adhered to by the viscous surface, and gradually engulfed in the trans- parent sarcode, as this sort of structureless animal-tissue has been called. Now what I wish particularly to draw your attention to, in this somewhat minute description of the Amoeba, is that so ex- ceedingly simple a structure should perform such a variety of acts. It creeps and changes its form, which indicate a muscular power; and seeing that one end of the body always precedes the other, it is fair to draw the inference that this muscular power is under the directing control of at least a certain degree of nervous sense. And again the introduction, circulation, and digestion of food, and the final rejection of the harder indigest- ible parts of the prey, all point unquestionably to a function which is proper to animals and not to plants. There can be no doubt, then, that this particle of slime-like matter, which is called Amoeba, is an animal in the fullest sense of the term. These other three diagrams (figs. 2, 3, 4,) are intended to illustrate the manner in which the complication of the organization is brought about, as we rise from the lowest forms of life, as represented by the Amoeba, through the gradually more elevat- ed types to the highest in this peculiar group of beings. The first step in this advance is made by the addition of a covering, of such a IfH-flfil f°rm in this case as to restrict the prolongation of the protrusile parts of the body to one re- gion. In the figure before us, which is that of a Difflugia, (fig. 2,) the body is enveloped in a globular or pear-shaped membranous sac (a) Fig. 2. Difflugia prolei/ormis. Ehr. 100 diam. A view from above, look- ing down upon the top of the shell, a. b, the pseudopodia, projecting from before and behind. The arrow indicates the flow of the granulated fluids of the body. — Original. 12 THE LOWEST FORMS to which angular grains of sand are adherent. This has been secreted, or rather excreted by the surface portion of the animal, and the minute fragments of sand are stuck on by some un- known process. At one side of the sac there is an aperture, through which alone the body can protrude. This is not to be seen in the figure, because it is on the opposite side of the shell to that which is here represented. From this aperture the body sends out processes (b) similar to those of Amoeba; but they appear to have a more definite character, and a seemingly more especial office than in that animal. These pro- cesses have been called pseudopodia, i. e. false feet, by which name I shall designate them hereafter. Owing to their ex- ceeding transparency, the pseudopodia, as they stretch out over the surface upon which the animal creeps, remind one of water spreading in streaks over glass, and sending off little branches, here and there, sideways. Sometimes only a single pseudopod is stretched out, and waves gently from side to side as if feeling for something. One cannot help but admire the caution with which this seems to be done, for after reconnoitering awhile the other pseudopodia come forth. There would seem to be good rea- son to believe that the animal really does exercise at least an instinctive caution, from the timidity which becomes apparent when it is disturbed ; for instantly, and as if with a sudden jump, the body darts toward the ends of the pseudopodia, and the latter being contracted in the act, are then drawn into the shell. The leap thus made is owing to the fact that the contraction of the pseudopodia is more rapid than the loosening of their hold, and consequently they drag the whole body toward the point of at- tachment. I mention this phenomenon particularly that I may draw your attention to the rapidity of the muscular contraction which is ex- hibited in the act. We are apt to suppose that a low degree of organization has a correspondingly low vitality; and this is true to a certain extent; but we are not justified in supposing it to be in exact parallelism with the organic grade of the animal for OF ANIMATE BEINGS. 13 here is one instance among many others in which the muscular action of a scarcely organized body is as rapid as in the most highly perfected types of animals. The circulation of the fluid and granular contents of the body is more active than in Amoeba, but it does not appear to' be at all different in kind or of a more complicated nature, although it seemingly is so because it has the appearance of being con- fined in more restricted channels, as it passes along the slender pseudopodia; but these channels are mere hollows with as in- definite boundaries as in Amoeba. From this we may infer that it is not by a general advance of the whole organization that the upward steps, in the develop- ment of types, are made; but here and there one organ after another is either added, or more and more specialized in its functions, until, by insensible grades, the highest type of organ- ization within each group is attained. In this other figure, (fig. 3,) which represents an animal which I kept by hundreds in my marine aqua- rium for eighteen months, the advance in grade is made by a simple compli- cation of the covering of the body ; * merely by elongating and coiling the dormitory of the little creature, so as to resemble the spiral shell of some of the snails. The pseudopodia (b) are exceedingly trans- parent, pointed, and so excessively slender toward their tips that it requires the best powers of the microscope to see them ; but yet, upon the least disturbance, these frail threads retract their length down to almost nothing, with a lightning-like rapidity; even while you are looking at them there is a sudden shock, and they are gone ! How* slight indeed is the degree of organization required in which to manifest some of the most active powers of vitality! Almost within a step we have the dazzling complication of the Fig. 8. Cornuspira planorbis. Schultze. 50 diam. Represented as it crept over the glass side of the aquarium, a, the shell; b, the pseudopodia, par- tially extended backward over the surface of the shell. — Original. 14 THE HIGHEST RHIZOPODA. inorganic crystal, revelling in glittering angles of such definite proportions and relations that an infinite design shines forth at every turn; and yet the simple faculty of self-determinative motion stamps upon the almost shapeless mass of the Amoeba a character by which the mind, as it were instinctively, places it at a far more elevated status than the attractive mineral. There is but one more figure which I shall introduce to your notice, as I think that the animal which it is intended to illus- trate represents within itself the highest tendencies of organi- d zation that may be found in the group of Rhizopods. This animal, (fig. 4,) which was called by Schultze, its dis- coverer, Rotalia Veneta, is to be found crawling over the slimy mud among the lagoons of Venice. From point to point along the turns of the spiral shell (b, c, d) there are transverse partitions, Fig. 4. which divide its cavity into as many chambers, but do not shut them off from one another entirely, as there is left a passage-way from one to the other, through which the soft parts of the animal connect with each successive one, from the central globular chamber (c) to the broadest and last formed one (d) at the edge of the shell. The pseudopodia (a) are not restricted in their egress to the single aperture at the termination of the shell, as in the last animal, but they project from all parts of the body through fine pores in the shell, as you see in the figure. It is not necessary, however, that you should infer that the food, whether animal or vegetable, is of necessity very minute in order to be introduced within the shell; for I must tell you that the digestion may go on outside as well as within, and that it is done in quite a simple manner. The pseudopodia, as I have told you, are mere prolongations of the body, and the circulation of nutrient particles extends to their Fig. 4. Rotalia Veneta. Schultze. 72 diam. a, the pseudopodia, projecting in every direction through the pores of the shell; b, the transverse partitions; c, the original, primary chamber; d, the last chamber. — From Schultze. SPONTANEOUS GENERATION. 15 very tips. When, therefore, any living thing is seized upon, it is at once enveloped in a glairy mass (a), which is formed by the pseudopodia fusing their sides together; and in this temporary stomach the nourishment is extracted from the victim, and car- ried in the circulation to the main part of the body. I think this will suffice to show you what is the extent of the duties which these simple creatures perform. It is true that their functions are not very complicated, but yet they are far more so than any one, knowing their simplicity, would suspect them to be capable of. Were you to imagine these chemical elements, Carbon, Hy- drogen, Oxygen, and Nitrogen, (C H O N,) to be united in the most simple manner, in order to form some animate creature, you could hardly produce a more lowly organized being than these self-same Amcebas which I have illustrated here. They are, in truth, among the lowest of all animals known. While we are engaged upon this part of our subject, it would seem to be most fitting to introduce here a description of some experiments which were made to ascertain under what condi- tions these rudimentary forms of life may originate. I will refer to only one set of experiments, because they seem to be, by far, the most satisfactory of any that have been made. In July, 1862, Professor Jeffries Wyman, of Harvard Univer- sity, Cambridge, Mass., published, in the " American Journal of Science," a paper whose title runs thus, — " Experiments on the formation of Infusoria in boiled solutions of organic matter, enclosed in hermetically sealed vessels, and supplied with pure air." I propose now to make some extracts from that paper, and illustrate what is therein stated by these diagrams. After some preliminary remarks, Professor Wyman proceeds thus : — " In order that the reader may understand what precautions were taken, we shall first describe the manner in which the ex- periments were performed." " (1.) In some instances (as in Expts. i. to v., vii. to xi., xiii. to xv., xxix. and xxx. inclusive) they were prepared as in fig. A. 16 SPONTANEOUS GENERATION. The materials of the infusion were put into a flask, and a cork a, through which was passed a glass tube, drawn to a neck at b, was pushed deeply into the mouth of it. The space above the cork was filled with an adhesive cement d, composed of resin, wax, and varnish. The glass tube was bent at a right angle, and inserted into an iron tube e, and cemented there with plaster of Paris c. The iron tube was filled with wires/, leaving only very narrow passage-ways between them. " (2) Others (as in Expts. vi., xii., xvi. to xxiii., and xxxi. to xxxiii. inclusive) were prepared as in fig. B, in which the joining at a, fig. A, is avoided, and the iron tube is cemented directly into the mouth of the flask, the neck of which is drawn out at b, to render the sealing of it easy; otherwise the conditions are the same as in fig. A. " (3.) In other experiments (as in Expts. xxiv. to xxviii., and xxxiv. to xxxvii. inclusive) the flask, fig. C, was sealed at the ordinary temperature of the room, and submerged during the period of the experiment in boiling water. This was the method followed by Needham and Spallanzani, and has the merit of eliminating all suspicions of error which might be supposed -to arise from some imperfections in the joinings. " In the first and second methods, the solution in the flask ia boiled, and at the same time the iron tube filled with wires is SPONTANEOUS GENERATION. 17 heated to redness. While the contents are boiling the steam formed expels the air from the flask; when the boiling has con- tinued long enough, the heat is withdrawn from beneath the flask, and, as the steam condenses, the air again enters through the iron tube, the red heat of which is kept up, so that all organ- isms contained in the air are burned. In both methods the flask is allowed to cool very slowly in order that the entering air may be as long as possible in passing through the iron tubes, and thus the destruction of its organic matters insured. When cold, the flasks are sealed at b, figs. A and B, with the blowpipe. " In experiments xxix. and xxx., a glass tube filled with as- bestos and platinum sponge was used instead of the iron tube filled with wires. " The time during which the infusions were boiled varied, as will be seen by the records, from fifteen minutes to two hours, and the amount of infusion used was from one twentieth to one thirtieth of the whole capacity of the flask, the object being to have the materials exposed to as large a quantity of air as pos- sible. " In the account which follows, especial mention is made, in most instances, of the time of the formation of the 'film? This is always the first indication which can be had, without opening the flasks, that minute organisms are developed; it is in fact made up entirely of them, as has been proved by repeated ex- aminations with the microscope. "After the flasks were prepared they were suspended from the walls of a sitting-room, near the ceiling, where they were ex- posed to a temperature of between 70° and 80° F. throughout the day and nearly the same during the night. " Expt. xii. (B.) * March 13th. The juice of an ounce of beef, to which was added 10 cub. cent.f of urine and 40 c. c. [cubic * " The figure [letter] in brackets following the number of the experiment indicates which of the three modes of preparing the experiment was made use of." f Cubic centimetres. A centimetre is about equal to -J of an inch, and there- fore a cubic centimetre is equal to the cube of £ of an inch, which is jfa of a cubic inch. 2 18 SPONTANEOUS GENERATION. centimetres] of water, was boiled 20' [20 minutes] in a bolt- head and hermetically sealed. A film formed on the fourth, and the flask was opened on the eleventh day, when there was a distinct rush of air outwards. Large numbers of Bacteriums (fig. 6, a, b, c, d) were found, also small spherical bodies, (fig. 5, a,) with ciliary motions and oval bodies like Kolpoda, contain- ing what appeared to be Bacteriums; one of these Kolpoda-like bodies moved with cilia. (Fig. 5, c, d.) " Expts. xvi., xvii., xviii., xix., (B,) March 20th, were made with juice of beef and water in flasks of 550 cub. cent, capacity ; d Fig. 5. a, a group of Monads ; minute spherical bodies, constantly agitating, as if moved by the vi- brations of thread-like appendages (cilia) ; 6, Vibrio rugula. 500 diam. A very common thing in all decaying fluid matter, forming a sort of scum at a Fig. 5. certain period of the decomposition. Seen with the lower powers of the microscope, the scum appears to scintillate all over its surface ; and if higher powers are applied, this phenomenon is found to be due to the rapid whirling motion of these minute, curved, moniliform (bead-like) strings, as they shoot, with greater or less velocity, backward and forwards across the vision. Their curved form produces the appearance of a screw or spiral as they vibrate in their path through the fluid, and the alternate appear- ance and disappearance of the highly refractive bead-like grains has the effect of sudden flashes of light, or scintillations. When there are only four or five beads in a string, the velocity of their movements is almost inconceivable, and their structure cannot be ascertained until they stop to change or reverse the whirl, and return upon the path in which they came. Most frequentlv, however, there are six or eight beads in a string; and in this condition, although their speed is less than that of the shorter ones, yet they swim very rapidly; but as the string is found to be longer, so do we see also that the motion is proportion- ately slower; and finally we may meet with those very long ones which wind their way with the leisurely undulations of a snake. c, d, " Kolpoda-like bodies," seen in Expt. xii. The presence of movable cilia on a body is the most indubitable evidence that it is in a living condition ; but whether it is an animal or plant must be determined by its internal structure. Professor Wyman's unpublished figures, from which these two were copied, by his kind permission, do not indicate an animal any more than a vegetable nature. They would seem to be allied to those extremely low forms of life, whose position either in the animal or vegetable kingdom is to be hereafter determined by more searching investigations than have thus far been made. SPONTANEOUS GENERATION. 19 xvi. was boiled 15', the film formed on the second day and the flask was opened on the ninth. Vibrios were found in abun- dance, (fig. 5, b,) of different lengths, some of them moving with great rapidity, xvii. was boiled 30/, the film was formed on the third, and the flask was opened on the ninth day. Vibrios were found in great numbers, some of them bending and extending themselves rapidly. Some minute spherical bodies were also seen, having the kind of motion which results from vibrating cilia, though none of these were detected, xviii. was boiled 15', the fluid having been previously filtered; the film formed on the third, and the flask was opened on the eighth day: the organ- isms found were the same as in xvii. xix. was boiled one hour. The film formed on the second, and the flask was opened on the twenty-fourth day. The infusion had a slightly putrid odor, and contained Vibrios and Bacteriums. " Expts. xxix., xxx. (A,) February 17th. In both of these the contents of the flasks were solutions of sugar and gelatine in water, to which fragments of cabbage-leaves were added. The air was introduced through a Bohemian glass tube, filled with asbestos and platinum sponge, and heated to redness. The ma- terials were boiled 30'. In xxix. the film was formed on the Fig. 6. Bacterium (Zoogloza) termo. a, a group mag- nified 500 diameters ; b, c, d, magnified 3500 diam. When seen as at a, they appear like minute, oval, brilliantly refracting granules, dancing in a constant zigzag, some- thing like a swarm of mosquitoes vibrating in a sunbeam. They never move in a direct course, but ever hover about the same spot; in this respect imitating the spores or seeds of certain aquatic plants. By the application of a *'"&• ®* higher power of the microscope we may recognize their shape more distinctly. Most frequently they were found, as at b, simple guitar-shaped bodies with a dark oval centre, and excessively transparent ends; but now and then one or two of them were enclosed in an exceedingly transparent envelope, as at c and d, which appeared like a halo around them. In this condition they resembled some of the jointed Vibrios. The transparent gelatinous envelope is eminently characteristic of certain kinds of mould, growing in damp places. — Original. (See fig. 8.) 20 SPONTANEOUS GENERATION. twenty-ninth, and the flask was opened on the thirty-ninth day. The solution was found to contain Bacteriums, and cells filled with them. In xxx. the film was formed on the seventh day, and Bacteriums were found on the twenty-third, when there was a slight odor of putrefaction. " Expts. xxxi., xxxii., xxxiii. (B.) March 24th. 30 grains of sugar, 20 c. c. of beef-juice, 158 c. c. of water, were divided into three parts, and each part put into a flask of 550 c. c. capacity, and boiled 15'. No film was formed in either of them, xxxiii. was opened on the thirtieth day; ferment cells (fig. 7) and some Fig. 7. Fig. 7. Torula Cerevi- siai. Yeast - plant. Mag. 500 diam. Original. From fi new yeast. In all fluid fermentations, in yeast, and among decomposing fluid matter, what are called " ferment-cells " are found in greater or less abundance. It is in such conditions that this lowly organized member of the vegetable kingdom finds its proper basis for origin and develop- ment. Where it is abundant one may have all stages of growth represented at one time in the field of the microscope, as they are illustrated from a to f, in this cut; and by watching for a few hours the whole process of cell multiplica- tion from a to /may be seen. The little spherical granulated cell at a is about j^g-g of an inch in diameter; but it was originally much smaller, for it may be traced from excessively transparent globular bodies, with soft, delicate outlines, not more than l0^0ft of an inch in diameter. As it progresses in development, one side of the cell bulges out, as at b; and this bulging grows until another cell is formed like the one at c; then the first cell, increasing in size, (c?,) develops another cell-like body, (rfi,) called the nucleus, in its fluid contents, whilst the second cell sends out a bulging process, which eventually becomes a third cell. In this way a single string of cells is formed ; but quite as frequently the primary cell develops a new cell from two different points, as at e; or even three cells are developed from the primary one, (see the largest cell at /,) and, each of these secondary cells developing a cell from its sides, produce together the irreg- ular branching form, which we have here represented as the perfect " yeast- plant" (/). It is well known now, however, that this is not its perfect state. Under favorable circumstances, the yeast-plant, so-called, rises to the surface of the fermenting fluid, and clinging to the side of the vessel, allows its growing SPONTANEOUS GENERATION. 21 filaments of a doubtful vegetable appearance were found, xxxii. was opened on the forty-second day, and contained ferment cells and monads (fig. 5, a). An escape of gas took place when the flask was opened, xxxi. was opened on the forty-third day, and found to contain ferment cells in large numbers, in different stages of cell multiplication; as in xxxii., there was an escape of gas. " Expt. xxxiv. (C.) March 27th. Juice of mutton, in a her- metically sealed flask, was boiled 5' in a Papin's digester, under a pressure of two atmospheres.* A film formed on the fourth day. It was opened several days later, in the presence of Professor Gray, and found to contain Vibrios, (fig. 5, b,) and Bacteriums, (fig. 6,) some of them moving with great rapidity. " Expt. xxxv. (C.) The same as the preceding, and boiled in Papin's digester 10' and under the pressure of five atmospheres.! No film was formed. The flask was opened on the forty-first day. Monads, (fig. 5, a,) and Vibrios, (fig. 5, b,) were found, some of the latter moving across the field. No putrefaction ; the solution had an alkaline taste. "Expt. xxxvi. (C.) March 28th. Beef-juice was filtered and boiled, as in the preceding experiment, 15', under two atmos- pheres. Opened on the forty-first day, and no evidence of life was found. When the end of the flask was heated, previously to opening, it collapsed. "Expt. xxxvii. (C.) March 28th. The same as the preced- ing; boiled 15' under five atmospheres. Opened on the forty- first day, and no evidence of life was detected. branches to project into the air. The emergence from its fluid habitat is the beginning of another stage in its growth ; and in fact it could not otherwise per- fect its development. In course of time, then, its branches become a tangled mass of white threads and bristling points. This is the condition in which it is known as "white mould"; or, when the bluish or greenish spores (seeds) are ripened, on the ends of the bristling points, " blue mould." * Two atmospheres are equal to 250.52° Fahrenheit, or about 38° above boil- ing point. The pressure of five atmospheres is equivalent to 307.5° Fahr., or about 95° above the boiling point. 22 SPONTANEOUS GENERATION. " We have here a series of thirty-three experiments, prepared in different ways, in which solutions of organic matter, some of them previously filtered, have been boiled at the ordinary press- ure of the atmosphere for a length of time, varying from 15 minutes to 2 hours, and exposed to air purified by heat. " In many instances, a solution like that in the sealed flasks, and boiled for the same length of time, was exposed to the ordi- nary air of the room, in an open flask. Although the same forms were found in the two, they appeared much more rapidly in the open than in closed vessels, and the contents of the for- mer soon became putrid, while those of the others, at the time of opening, were mostly not, and in a few instances only slightly so. " We have, in addition, four experiments: namely, xxxiv., xxxv., xxxvi., xxxvii., made under increased pressure, and sealed by the third method; xxxiv. and xxxvi. were boiled 5' and 15' respectively, under two atmospheres, and xxxv. and xxxvii., un- der five atmospheres for 10' and 15' respectively. Evidence of life, consisting of Monads and Vibrios, was found in xxxiv. and xxxv., but none in the others. " The result of the experiments here described is, that the boiled solutions of organic matter made use of, exposed only to air which has passed through tubes heated to redness, or enclosed with air in hermetically sealed vessels and exposed to boiling water, became the seat of infusorial life. " The experiments which have been described throw but little light on the immediate source from which the organisms in ques- tion have been derived. Those who reject the doctrine of spon- taneous generation in any of the forms in which it has been brought forward, will ascribe them to spores contained either in the air enclosed in the flask, or in the materials of the solution. " Those who advocate the theory of spontaneous generation, on the other hand, will doubtless find, in the experiments here recorded, evidence in support of their views. While they admit that spores and minute eggs are disseminated through the air, they assert that no spores or eggs of any kind have been actually SPONTANEOUS GENERATION. 23 proved by experiment to resist the prolonged action of boiling water. As regards Vibrios, Bacteriums, Spirillums, etc., it has not yet been shown that they have spores ; the existence of them is simply inferred from analogy. It is certain that Vibrios are killed by being immersed in water, the temperature of which does not exceed 200° F. We have found all motion, except the Brownian, to cease even at 180° F. We have also proved by several experiments that the spores of common mould are killed, both by being exposed to steam and by passing through the heated tube used in the experiments described in this article. If, on the one hand, it is urged that all organisms, in so far as the early history of them is known, are derived from ova, and therefore from analogy we must ascribe a similar origin to these minute beings whose early history we do not know, it may be urged with equal force, on the other hand, that all ova and spores, in so far as we know anything about them, are de- stroyed by prolonged boiling: therefore from analogy we are equally bound to infer that Vibrios, Bacteriums, &c, could not have been derived from ova, since these would all have been destroyed by the conditions to which they have been subjected. The argument from analogy is as strong in the one case as in the other." On the 4th of August, 1863, Prof. Wyman put into my hands, for examination, the contents of a sealed flask which he had just opened, and which was prepared according to the method (B) on the 22d of July previous, i. e. thirteen days before. I directed my attention particularly to the structure of the Bacteriums, (fig. 8, a, b,) which floated in immense numbets throughout the fluid. Ordinarily, the central part of the guitar- shaped body is occupied by a dark oval mass, as I have described it in fig. 6, but in this examination, by the help of an immensely Fig. 8. a, b, Bacterium (Zooglcea) termo. Duj. 3500 diameters. Two of the most diverse forms, with a granulated centre and transparent ends. — Original. c, d, Spirillum. Spiral thread-like bodies oftentimes seen among decaying sub- stances in fluids. They whirl with great velocity. — Original. 24 SPONTANEOUS GENERATION. magnifying lens,* that gave me a power equal to 3500 diameters, I found that this centre was composed of a number of granular bodies, (fig. 8, a, b,) but the ends of the Bacterium were, like those in fig. 6, very transparent ; and, moreover what gave additional character to these bodies, one end was always much more delicate than the other, at times so excessively faint as to be scarcely discernible. What induced me, among other things, to believe that these bodies were in a peculiar stage of growth, was, as Prof. Wyman had noticed at the same time, that they did not move, as they are ordinarily observed to do. From the foregoing observations it is clear that the Bacteriums, found in the sealed flasks, are of a more elevated nature than the simple granules which go by the name of Monads; in fact, they are even more highly organized than the Vibrio, which is essentially nothing more than a string of Monads moving in concert. Finally, I will add, in confirmation of what I have said in regard to Bacterium, that a German observer, Cohn,f has shown that the Bacterium termo is merely one of the stages of growth of a kind of mould which he has called Zooglcea termo. In one of Prof. Wyman's flasks, containing some slivers of beef, sugar, and water, which he had prepared, according to the method marked (B), and boiled 20' on the 2d of Sept., 1864, and which I opened, at his request, on the 25th of Oct., 1864,1 found large numbers of Bacterium termo oscillating very lively. These I have illustrated and described under fig. 6. The moniliform Vibrio (fig. 5, b,) was seen only here and there ; but there abounded another form of Vibrio, which, when seen with a mag- nifying power of only 300 diameters, might be mistaken for the moniliform Vibrio; if, however, they were magnified with a good lens, 500 diameters, their true outlines would become ap- parent. In order to get as clear a conception of their form and nature as possible, I subjected them to the searching scrutiny of * One of Tolles's -fe of an inch objectives, made for me with particular refer- ence to the study of the minuter Infusoria and the early stages of cellular de- velopment. f See Cohn, Acta Academiae Naturae Curiosorum, 1854* vol. XXIV. pars i. p. 119, and PI. xv. fig. 9. SPONTANEOUS GENERATION. 25 a h of an inch lens. With this power, of 3500 diameters, I made out distinctly that the Vibrio bacciltus, (fig. 9,) as it is called, consists of a series of little rods which are joined end to end by a delicate mem- n brane; or rather, I might say, that they are en- sheathed in a tubular membrane, with sufficient space between the successive rods to allow them h to double upon each other. Although they are represented here under a lower amplification,— only 2000 diameters, — yet I think it is sufficient ' to show the manner in which they are connected with each other. Their movements are very much like those of Vibrio rugula, but still they have a method of progression which is eminently characteristic, for such minute bodies, when seen with the highest magnifying powers. I know of nothing so apt to compare them with, when in motion, as a jointed toy-snake vibrating. The effect is most striking when one of the longest, many-jointed specimens moves across the field of the microscope with a sort of disjointed action, as if each rod held an independent course in one common stream. Some- times a considerable portion of the end of the sheath was empty and collapsed, (fig. 9, c,) and in this condition, being quite flexible, it was difficult to persuade one's self that it was not a vibrating cilium, as it waved from side to side during the undu- lating progress of the chain. This, as well as the moniliform Vibrio, is generally considered to be allied to certain aquatic, filamentous plants, common in our streams and ponds, which are known as Oscillatoria. Now it is true that in these experiments of Professor Wyman, the matter which was introduced into the flasks was not reduced to its separate chemical elements C, H, O, N, but rather to the fluid state. This is the condition of animal and vegetable sub- stances when in a decomposed state ; and when such large numbers of animalculae, identical with those which have just Fig. 9. Vibrio baccillus. Ehr. 2000 diameteis. a, b, c, three individuals in various attitudes of flexion whilst in motion. —Original. 26 SPONTANEOUS GENERATION. been described, develop in the putrid mass. If left to the action of time the whole fluid would eventually resolve itself into the ultimate chemical elements C, H, O, N, (see pages 7 and 8); but this was not desirable in these experiments. Under these decomposing conditions we may see one of Nature's modes of reproducing or rather generating new forms of life by spon- taneity. Professor Wyman has since been so kind as to show me some other experiments which prove that these same bodies which are developed in the sealed flasks, are killed at a point far below that of boiling water. He placed large quantities of each kind, viz: Vibrios, Bacteriums, Kolpodas, &c, each in a separate test tube, and each tube with a thermometer in a water-bath, and applying heat to the bath, he examined, from time to time, as the temperature was raised, portions of each set with the micro- scope. Some of the animalculae survived the heat up to 125°, and others up to 130°, but in no instance did any of them live when the temperature was raised to 150°, which is sixty-two degrees below boiling, 212.° You will recollect that in all of the experiments with the sealed flasks, the fluid was raised to the boiling point, 212°, and in some of them it was raised still higher, in one case to 250°, which is 38° above boiling, or 100° above the temperature at which these animalcules can live. In another instance the flask was heated to 307°, which is 95° above boiling, or 157° above what these creatures can live in. The fact that the experiments with the sealed flasks proved,— if anything can be proved beyond the reach of change or im- provement,— that beings with motion, undoubted living beings, were produced where life could not possibly have existed pre- viously, is a sufficient basis for the further assumption that still higher forms could arise from these. That is to say, if, under the conditions arranged in the sealed flasks, living beings, either animals or plants, of the lowest degree arise, there is nothing illogical in assuming that from these lowly organized, animate bodies somewhat higher and more complicated beings may originate. Keeping these exoeriments in view let us now return SPONTANEOUS GENERATION. 27 to the Amoebas and their protean congeners, Difflugia, Cornu- spira, &c. Calling to mind now what I have said about the extreme simplicity of the lowest animate forms, the Amoebas, Difflugias, and the like, let us turn to an examination of the lowest condi- tion of life in which any animal, whether high or low, can exist. I mean the egg-state. 28 THE ORIGIN OF THE THEORY OF CHAPTER II. WHAT SPONTANEOUS GENERATION PROVES. —THE EGG IS THE LOWEST PHASE OF ANIMAL LIFE. - THE EGG A BIPOLAR ANIMAL. — THE EGG CONTRASTED WITH THE LOWEST FORMS OF ADULT BEINGS. — THE EGG AS RELATED TO SECONDARY CAUSES. At the end of my last lecture I announced that I would next take up the consideration of the egg of animals, as that is the phase in which all animals, at one time, are in the lowest possible condition of life. Before I proceed to do this, however, I wish to preface it with some remarks upon the theory of spontaneous generation, which may serve not only as a recapitulation of what I have already said upon that subject, but will, I hope, make more clear to your minds the object for which the experiments in the sealed flasks were instituted; and it will at the same time lead in a direct line to the consideration of what may be the relation of the egg-condition, of all animals, to the adult state of the lowest forms of animate beings. When geologists first announced that the earth contained the remains of animals and'plants, which, from the nature of the action of physical causes, and the position in which these fossils were found, demonstrated that they belonged to a period, or series of periods, anterior to the creation of man, the assertion was received, by what was then called the " Church Party" in England, with an expression of horror, that scientific men should attempt to support atheism by the palpable evidence of scientific facts ! Without stopping at the present time to show how this holy horror was finally, and in the process of time, changed to an enthusiastic and religious advocacy of this geological theory, I will merely state the fact, and then pass on to the result of this general recognition and admission of the existence of a pre- Adamite world. Having made this admission, it became evident at the same. time that a series of creations had been going on previously to SPONTANEOUS GENERATION. 29 the origination of the present race of beings on the globe; and out of the contemplation of this idea arose the question as to whether the Creator has not continued to exercise the creative faculty at all times, even to the present day. They recognize the Creator's controlling hand when they see the child resembling the parent; it is not blind chance to them that like comes from like; there must be some reason for this, and the reason they give is that the Creator is continually active in the administration of his laws. If, therefore, he is visibly present in the operation of one series of acts, it may be that he still continues to carry on another series, which we know he has at some time in the remote past begun. At some unknown, distant period, animals originated through creative influence on this globe. Now, then, the question arose in this form, namely, did all ani- mals, which have appeared from the beginning, originate by birth from the first created ; or is this only one mode of continuing their presence on the earth, and has the Creator also constantly repeated his original creation through all time, even until now ? This question arose from various reasons, and among others, because observers had noticed the fact, that, when a pond or stream, or a whole tract of country, dries up, as oftentimes happens in the summer months, as a natural consequence, all the animals and plants in it, which are dependent upon water for their existence, die for want of their natural element; but when the rains of autumn have refilled these streams and ponds, the aquatic ani- mals appear again. This some observers accounted for by sup- posing that the eggs and seeds of these animals and plants were constantly floating in the air, and were washed down by the rains, and thus the ponds became restocked with life; but other ob- servers disputed the fact that there were seeds and eggs floating about in the air, or insisted that they were in such small numbers that they could not possibly account for the sudden appearance of such large quantities of living creatures in these ponds ; and therefore they propounded the idea that they originated there exactly in the same way as did the first aquatic animals that originally began life in the rivers and ponds of this globe; that is, they were created there. 30 PRIMARY AND CONTINUED CREATION. In support of this theory they sought to contrive some way by which they might construct artificial ponds which should be shut off from the surrounding air, and therefore no floating or flying seeds or eggs, if they really existed, could gain access to these isolated waters. There have been several contrivances set up which were destined to carry out this plan, and among others, the one which I have already described to you. The various kinds of fluids, such as beef-juice, mutton-juice, sugar-water, ammonia, gelatine, &c, which were introduced in the different experiments, were for the purpose of furnishing a diversity of conditions and food for the creatures which might originate therein, and also to imitate the decomposed contents of stagnant pools and ditches; the heat which was applied to the flasks was to kill all life that might be in the fluid ; and the air was allowed to enter the flasks, as they cooled down, through red-hot tubes, in order that whatever seeds or eggs there were floating in the air might be killed by the heat, and the air then would be pure. In the hermetically sealed flask, C, (p. 16,) the air and the fluid are sealed up before heating, so that after boiling in the Papins digester, this little world within the glass cools down without the least possible chance of communication with anything ex- ternal to it. Under these circumstances, the advocates of the continued creation of animals to the present day, claim, that, if living creat- ures do appear in these isolated pools in the flasks, they must have originated there without the previous intervention of a parental form, because all life had previously been extinguished by the heat. From this, then, they argue, that, when the dried-up pools and streams are refilled by the autumn rains, the animals which appear therein originate on the spot, in the same way as did the first animals that peopled this world. As I said before, at the end of my last lecture, the fact that the experiments with the sealed flasks proved that motile beings, undoubted living beings, originated where life could not by any means have existed previously, is a sufficient basis for a further assumption that still higher forms could arise from these. Keep- ing in mind now what has been said about the extreme sim- THE EGG-PHASE OF ANIMALS. 31 plicity of the lowest animate forms, the Amoeba, Difflugia, and others like them, let us turn to a consideration of the lowest con- dition of life in which any animal, whether high or low, can exist. I mean the egg-state ! Let us compare this preliminary, scarcely organized, low form or state of life which we find in the egg, with these gum-drop like beings, as I have called the Amoebas, Difflugias, &c. In the first place we must consider what an egg is, and under what conditions it originates and exists. Originally, that is when beginning to form, an egg is a very minute aggregation of fluid matter,— more simple even than the Vibrios and Bacteriums of the sealed-flask experiments of Dr. Wyman, — and yet this fluid is gradually transformed into mi- nute granular bodies, the yolk-granules so called, and these in their turn eventually become cells, and by combining form a living, sentient being. Now when we turn to the lowest animals, such as Amoeba, Difflugia, Rotalia, &c, we find among them those which are nearly or fully as simple as the eggs which they themselves lay. In the latter instance, the egg, in order to become an adult, merely changes its form without developing into an ap- preciably more complicated state. Those un- doubted animal infusoria, such as Paramecium (fig. 96), Stentor (fig. 30), Epistylis (fig. 95), Pleuronema (fig. 90), &c, arise from eggs which are not such as might answer fully to the theoretical egg of physiologists. Balbiani (Journ. Phy- siol., 1861, IV.) found that the egg of Spirostomum (fig. 10, A) and Stentor (fig. 11) is a mere cell, without any other sign of the characteristic nucleus-like Fig. 10. Spirostomum teres. Clap. 150 diam. View of the lower side, showing the narrow oblique furrow which passes from the mouth, m, to the end of the body ; c, tubular contractile vesicle; e, eggs. A, one of these eggs more highly magnified. — From Balbiani. Fig. 11. The egg of Stentor cceruleum. Ehr. 500 diam. The central clear space is all that represents the germinal vesicle. — From Balbiani. Fip. 10. Fig. 11. 32 THE ESSENTIAL CHARACTERISTICS vesicle, the so-called germinal vesicle, than a clear spot in the midst of the yolk granules. Were it not for the subsequent development of these, Balbiani could hardly have determined their true nature. If, therefore, such simple cells are really eggs, we must of neces- sity form a new diagnosis of the characteristics of the theoretical or typical egg; and that I have, for one, been long inclined to do. For the last five or six years I have felt that my studies were leading me to look upon the relations of the various regions of the egg as those of degrees, which shade off, the one into the other. Our ideas of an egg have been heretofore based upon the structure of the eggs of the higher animals, instead of upon what is common to all eggs. For instance, some eggs of the higher animals (fig. 12) have a germinal (or Purkinjean) vesicle ; within that a germinal spot (or Wagnerian vesicle), and within the last a nucleolus ; all equally and sharply defined, like so many hollow concentric spheres, each and every one hav- ing its peculiar, characteristic feature. Under this guise one would hardly suspect the true relations of these parts to each other. But these I will explain presently. In the eggs of some other animals (fig. 13) there are but two of these concentric vesicles, (namely, the Pur- kinjean p, and the Wagnerian w,) the in- nermost one being absent. Again there are those which have but one vesicle: for Fig. 12. The egg of the Sow. 166 diam. Natural size ^ of an inch. The next to the outer circle forms the boundary of the yolk. The small circle at the upper side is the germinal or Purkinjean vesicle ; the oval spot is the germinal dot or Wagnerian vesicle ; and the central spot is the nucleolus. — From Thompson. Fig. 13. Egg of the Rabbit. 166 diam. z, the "zona pellucida" or yolk envelope; y, the yolk; p, the Purkinjean (germinal) vesicle ; w, the Wagnerian vesicle or nucleolus. — From Coste. Fig. 12. Fig. 13. OF AN EGG. 33 instance that of Laomedea, (fig. 14,) a kind of Hydra. Finally, we come to the lowest degree, in whieh, as I have already described, the egg (figs. 10, 11) is a mere cell with a light spot in one part of the yolk. The eggs of Amoeba are also in the same condition as the last. In this Fig. 14. case the parent of the egg is as simple in structure as the egg itself. What, then, are the characteristics of an egg ? If the sharply defined, concentric vesicles of the most complicated eggs are not to be found everywhere, but on the contrary we see all grades of definiteness and number as regards these apparently special bodies, we must come to the conclusion that each vesicle is not restricted within its own boundaries, even though its out- line may have the appearance of a wall which would seem to be intended to shut off direct communication with the outside. I think that the most straightforward solution of this problem is, that the germinal vesicle, — which is always present in some form, either sharply defined, or, as I have shown, as a mere transparent spot at one side of the egg, — is simply an expression of the concentration of albuminous matter at one pole; whilst at the opposite, or, as one might call it, the negative pole, we have the mass of yolk. That this is so, is demonstrated by the process of develop- ment of the egg from its inception to its completion ; and as the egg is a cell, and the type of all cells, its mode of genesis is typical of all free-cell development. This I will illustrate by a series of ideal figures (figs. 15, 16, 17, 18) of the progressive stages of development of the theoretical egg; such a one as would, in the progress of growth, pass through all the conditions in which the egg has been known to exist in various animals. As I have already said, the egg in its inception is a minute aggregation of fluid matter; but this drop of fluid has not a homogeneous, uniform density throughout; on the contrary, it Fig. 14. Egg of Laomedea amphora. Ag. 125 diam. The Purkinjean vesicle is filled with transparent, coarse granules. — Original. 3 34 THE MODE OF DEVELOPMENT makes its first appearance in the egg-bearing organ, the ovary, in the form of an indefinitely bounded globule, with a greater degree of transparency on one side than on the other (fig. 15). This diversity in the degree of refraction between the two sides is owing to the difference in the nature of the constituents of the globule; on one side the substance is pure albumen (alb.), whilst on the other there is a certain amount of oleagi- nous material (ol.) opposed to the albumen. Their boundaries, however, are not definitely marked; on the contrary, they insen- sibly mingle with each other toward the centre of the egg, and it is this indefiniteness that renders the aspect cloudy. Presently the difference in the opposing features becomes stronger and more easily discerned; the albuminous portion grows denser (fig. 16, alb.) and more decided in character, whilst the oleaginous substance (ol.) assumes a peculiar kind of refraction, totally dif- ferent from that of the albumen; and in the meanwhile the egg attains to a more clearly defined outline, and grows larger. Soon, now, and while the egg is yet very minute, the albuminous substance (fig. 17, alb.) w alb. vs. becomes more concentrated toward one side of the egg, and assumes an appreciably definite outline (p), but not as yet perfectly globular. At the same time there is initiated within this con- creted mass a similar condensation (w) at one side. Coincident, usually, with this, the egg, having continued to increase in size, becomes very clearly defined in contour, and the superficial portion develops into a more or less densely accreted envelope, which bears the name of vitelline sac (vs.). The aim of all these pro- Figs. 15, 16, 17, 18. Theoretical eggs, representing the process of develop- ment from the inception to completion, alb. the albuminous pole; ol. the oleag- inous pole; vs. the vitelline or yolk envelope; p, the Purkinjean (germinal) vesicle; w, the Wagnerian vesicle, or germinal dot. — Original. OF THE TYPICAL EGG. 35 cesses becomes now rapidly apparent, for soon we find that the albumen has clearly defined itself as a separate mass, (fig. 18,) apart from the yolk (ol.), and its superficies has condensed into a well-marked envelope, which constitutes the germinal vesicle (p), whilst the condensation, going on within it at the last stage, has resulted in the formation of a clearly estab- lished agglomeration (w) with a distinct wall Fig is around it, which is usually called, together with the contents, the germinal dot, or sometimes the Wagnerian vesicle. Outside of this field of operations, and antagonistic to it in character, the yolk (ol.) has its peculiarities, in physiognomy, refraction, density, opacity, and color, according to the kind of animal in which the egg develops; all tending to demonstrate that it is under a different formative influence from that of the albumen, at an opposite pole, we might say, from the latter.* We may, therefore, define an egg to be a globular accretion of two kinds of fluids, albumen and oil, which are always situated at opposite sides or poles ; but, at the point where they meet, there are various degrees of separation, from the most sharply defined line down to the most indefinite boundaries when they are more or less mingled with each other. In the earliest stages of all eggs, these two poles shade off into each other; but whilst some do not develop-above this condition, there are others which, as we have seen, take on a higher form of specialization; and in this latter case the concentric vesicles of the egg would seem to bear the character of special organs. The eggs of all birds, as I have reason to know from almost innumerable observations, possess not only this high degree of specialization in the albuminous region, but exhibit, to an extraor- * To such an extent is this antagonism, between the oleaginous and albuminous components of the ogg, carried out in some of the worms, — e.g. Taenia (fig. 44), Planaria (fig. 47), Prostomum (fig. 19), — that the oleaginous portion, or yolk, of the egg is developed in a different part of the body from where the albuminous material originates: and it is not until a certain period that these two are brought into proximity to each other to form a single egg. In this figure 36 THE OLEAGINOUS AND ALBUMINOUS dinary extent, a species of organization in the yolk, such as is observable in no other class of animals. This is as conveniently phi r2 (fig. 19) it may be seen that there are three separate organs necessary to the formation of the egg, namely, the yolk-bearing (vitelligenous) organ (vi), which generates the oleaginous substance; the albumen- bearing (germigenous or germ-forming) organ (ov), in \ph which the albumen originates and develops into ger- minal vesicles; and the womb (uterus) (ut),into which the germinal vesicles descend and where they are each separately enveloped in a portion of the yolk, which pours into the uterus in certain quantities as it is needed, and there forms, with the germinal vesicle, a perfect egg (w). The uterus then forms a shell about the egg, and it is ready to be laid. In other worms, for instance, the Round-worm (Ascaris), the formation of the yolk and that of the albumen are carried on in comparative proximity to each other, but yet in dif- ferent parts of the same organ, and after a while the germinal vesicles (albumen) pass into the yolk (oil) bearing part of the organ, and are there enveloped separately with a quantity of yolk, and the egg is completed. This same process is known to take place in certain Insects; for instance, the common cricket (Acheta), &c. Again, in Spiders, the diversity of local origin is still less than in the last; the germinal vesicle is developed, in a saccular body, to a certain extent, and then the yolk grows about it. Finally, we may find, as in the clams (Venus), &c, the ger- minal vesicles scattered through a mass of yolk, which in process of time is broken up into groups or con- cretions, each one of which becomes connected with a germinal vesicle, and surrounded by an envelope which forms a kind of vitelline sac. Fig. 19. Prostomum lineare. (Est. Natural size about 1-1^'" (line) long. View of the lower side, o, mouth; ph, the first part, and pM, the second part of the throat; v, vl, the stomach; n1, the central part of the nervous system, consisting of a large ganglion on each side of the throat, joined by an inferior commissure, n ; m\ the sucking disc, a sort of prehensile apparatus ; /, vs, pe, ga, the male portions of this double organization; the female reproductive organs are, vi, the yolk-bearing organ, ov, the germ-forming organ, and ut, the womb, at present occupied by a single egg, w; rs, accessory fertilizing receptacle; R, R, the exterior openings of the water canals, r, r, H, r\ r% A— From Schultze. Fig. 19. POLES OF THE EGG. 37 demonstrated in the egg of the common domestic fowl as in that of any bird.* If a per- ol «»i c p y a <*i fectly fresh egg (fig. 20) is boiled hard and allowed to cool, at least until it may be d, handled comfortably, and the shell (s) and white (a, a1) carefully s peeled off, the yolk (ol) will remain as a perfectly distinct Fig. 20. Fig. 20. Longitudinal section of a freshly laid Hen's egg, which has been boiled, s, the shell; a, a1, the spirally wound layers of the " white "; ch, the innermost layers of the "white" (albumen) twisted into cords, chalazoz, which serve as axles, upon which the yolk swings and revolves, whenever the egg is rolled over, so as to keep the side with the white spot, cicatricula (c). uppermost; y, y1, the outline of the yolk mass; ol, the concentric layers of yolk; i-, t1, the more fluid-like part of the yolk; p, remnant of the germinal vesicle; c, the cicatricula. — Original. * In my investigations of the character of the yolk of Turtles, a group of reptiles which produce eggs most closely allied in character to those of birds, I found an approximation to what occurs in the eggs of the latter. See my observations to this effect in Agassiz's " Contributions to the Natural History of the United States," vol. n. 1857, p. 479, section V.; and note 1, p. 480, note 2, p. 481; also Plate IX., figs. ll-llh, and Plate IXd, fig. 2, with the descriptions of the figures. Note on Scientific Property. It may, perhaps, surprise some of the readers of this volume, upon turning to the " Contributions" mentioned in the above note, not to find my name upon the title-page of the volumes which contain the subjects referred to therein. This is no fault of mine, but of the editor of the series, Professor L. Agassiz. In a little pamphlet entitled, "A Claim fur Scien- tific Property," I have published, with somewhat of detail, my claim to a part of the substance of the second, third, and fourth volumes, and a right to have my name upon the title-page of such volumes. It was well understood between Prof. Agassiz and myself, as the result of several conversations, that my share in the investigations should be clearly and distinctly set forth, so that I, in com- mon with him, should be held responsible for the facts, ideas, theories, &c, as far as the language so expressed them; and in accordance with this understand- 38 THE ORGANIZATION OF spheroidal ball (y, yl). It will be noticed, then, that there is on one side of the yolk a light spot (c). Taking this spot as a guiding point, and keeping it uppermost, the yolk should be cut into, a short distance, at the side, in such a direction as would divide it into halves, were the knife pressed through so as to strike the middle of the white spot. As the pressure of the knife flattens and smooths over the cut surface so as to obscure ing, the term, we, was used as representative of our combined authorship, and the term, J, whenever Prof. Agassiz wished to hold himself alone responsible for anything said. And to keep the distinction always clear, when I myself in turn was the sole authority, my name was mentioned in connection with it, either in a note (vol. in. p. 237; vol. iv. pp. 41, 44), or in the body of the text (vol. iv. pp. 61, 209, 237). In fact, so large a proportion of some of the volumes was the result purely of my own work that I ought to have been represented as the sole authority where the term, we, was used ; but as long as I was led to believe that I should share it with Prof. Agassiz, I was content to let it appear so. So clear, indeed, is my own individuality impressed upon these portions which I claim, both in the nature of the microscopic work and the style of the language, a totally different idiosyncrasy from that of Prof. Agassiz's, that, even as much as two years before I had published my " Claim " in the pamphlet above mentioned, European naturalists referred to the investigations as mine. This could hardly be otherwise, as every working naturalist knows how such work is done, espe- cially with the microscope ; and he is fully aware, too, that it cannot be delegated to another to be done for him. The original authority must be the one who sits over the microscope day after day, and month after month ; and when he takes his pen in hand to describe what he has seen, and what he thinks of it, the very character of the language shows that he who writes has seen and elaborated and thought of what is written; and his fellow-naturalists will recognize him in spite of all the efforts of any one who may be so unscrupulous as to attempt to assume the credit through any carefully studied arrangement of the title-page, and the appearing to give due credit in an ingenuous preface. Naturalists do not look to the preface to ascertain who is the author, but to the body of the work itself; and any such subterfuge is quickly detected by them. Credit given in a preface, and nowhere else, can only affect and influence the popular reader, who knows nothing of and can judge nothing of the merits of the work. How, and by what representations, I was led to allow this wrong to accumulate in the third and fourth volumes, cannot be entered into here, nor, unfortunately for myself, the facts connected with the matter so easily proved, since the greatly lamented death of one who, could he speak now, might reveal altogether too much for the comfort and effrontery of the one who has done me this great wrong. " Con- scientia insanafrons aeneus." THE EGG OF BIRDS. 39 what it is desirable to see, the gash should be only sufficient to give a directing tendency, which may be followed up by care- fully pulling apart the yolk with the fingers. The structure of the interior will explain for itself why the yolk splits more readily through the white spot than at right angles to that axis. It is impossible, even with the most prolonged boiling, or immer- sion in spirits, to harden that part of the yolk which extends from the white spot (cicatricula) (c) to the centre (v) of the spheroid, and consequently there is the least cohesion along that line, and therefore the split takes place most readily in that direction. These same peculiarities, which I have and am about to describe, exist in the egg just before the white and the shell are deposited around it, but the characters are not quite so strongly marked as in the laid egg; and for this reason I have chosen the latter for the better purposes of demonstration, and that you may repeat the observation for yourselves. The prin- cipal feature, to which I wish to draw your attention, is the arrangement of the yolk in concentric layers (ol), which are alternately dark and light, from the centre to the circumference. These layers, as you will observe, do not form perfectly closed circles, but on the side next the cicatricula bend outwardly and terminate at the circumference. They might be compared to a set of vases placed one within the other, the central one (v, v1) containing the uncoagulated fluid which extends from the cica- tricula (c) to the centre. In the egg, before it has the shell and white deposited around it, the germinal vesicle would then be found just at the mouth of the central vase (v, vl); but at this stage there is a mere trace of it, in the form of a clear area (p) just beneath the cicatricula (c). In specimens of birds' eggs, preserved in spirits, the more highly oleaginous nature of the darker layers is particularly well demonstrated, as the latter assume in that condition a dark orange hue, and the oil oozes out in large quantities at the surface of the fissure, and floats off in drops. The popular idea of an egg includes the " white," which is merely an accessory, like the shell, and really has no direct 40 THE PROGRESSIVE DEVELOPMENT relation to the organization of the egg. The concentric, spiral layers (a, a1) of the white are the result of several successive deposits in the tube (oviduct) through which the egg passes, with a boring motion, in order to reach the outer world. Now, as is well known, there are animals which in a full- grown condition are so lowly organized as to correspond in this respect to the early embryonic stages of some of the higher animals, — for instance, a fish in the degree of development of its various organs is comparable to the embryonic state of a horse, sheep, or any of the quadrupeds, — why may we not then have embryonic eggs which correspond to the earliest stage of the more highly developing eggs ? Such, probably, is the state and relations of the eggs (figs. 10, 11) of Balbiani's Spirostomum and Stentor, when compared with those of Laomedea (fig. 14), the Rabbit (fig. 13), and Sow (fig. 12). From this latter point of view, then, we may look upon the egg as theoretically a bipolar aggregation of albuminous and oily substances, and which eventually exhibits a more or less elevated degree of animality; sometimes attaining to an eminent status, as when it develops into the most highly organized animals, and in other instances not rising above a very low degree, hardly beyond the egg-stage, properly speaking. In the latter category Amoeba is found, and in fact all Rhi- zopoda, as you have already been made aware of (p. 9). But let us go on a little further and see how, as we ascend the scale of being, the animal organization proceeds to develop be- yond that degree of simplicity which obtains in the egg. The Sponge is a fair example of those forms which stand, in a transitionary condition, between the Rhizopoda and the next group of animals above them ; and we will therefore take it to il- lustrate the first step in the progress toward a higher state of organization. Although it is difficult to determine whether Sponges are single or compound individuals, it does not affect the question of their relations to the Rhizopoda. That they are undoubtedly above the latter cannot be disputed when we con- sider that they have a higher degree of specialization, not only OF PROTOZOA. 41 in the various functions which they perform, but in the actual differentiation of the various parts of the body. The common sponges of commerce, as they come to us for our daily use, would not help us much to understand their nature; it is only after an attentive study of their living forms, in their native ele- ment, water, that one may comprehend the character of those parts of the dried sponge which are not destroyed by the process of preparation to which they are subjected, before they are brought into market. It is a very easy matter to obtain living sponges, because they abound on our rocky coasts, and in our fresh waters. The sponges of commerce, of which there are apparently several species, are not native ; nor can any of those which grow about us be used for the purposes to which the foreign sponges are adapted; but yet as far as their nature and general structure are concerned, the native ones are fully ade- quate to illustrate the group. The sponge which I have pic- tured here (fig. 21) is a com- mon occupant of our ponds and streams, most frequently adher- ing to and growing on the stems of aquatic plants, or forming low Fig. 21. prominences on the surface of stones. It is readily detected by a whitish brown color and bristly surface, and may be found from an almost invisible size to the dimensions of the fist, and in shape either perfectly globular, or oval, or elongated, so as to assume the shape of the stem on which it grows; or, as I have said, as a low prominence, like a bristling wart, on the stones in brooks, or at the side of the pond. It is only when placed in a glass jar and held up to the light, that, with the help of the microscope, its peculiarities are revealed. After the specimen under observation has recovered from the shock of the removal and expanded again, the first thing that strikes the eye is a more Fig. 21. Siphydora echinodes, nov. gen. et sp. 10 diam. A tresh-water sponge, s, the emptying conduit; p, the superficial interstices, forming a part of the anastomozing channels, and the points of ingress for the water.— Original. 42 THE PROGRESSIVE DEVELOPMENT or less elongated, finger-shaped, transparent body (s) which pro- jects from one side. If this is watched attentively, even with a common pocket-magnifier, it will be found to be a hollow tube; and minute particles may be seen passing in streams through the tube, outwards, into the surrounding water. If now, using a much higher magnifier, the surface of the sponge, at the bases of the groups of bristles, be closely examined, there may be de- tected from time to tirr\e the expansion of a minute aperture (p), and the passage of particles of matter inwardly. In this way a constant current is kept up, from without to the interior, through these numerous minute apertures ; and by a system of variously united canals, the fluid and the included floating matter are transmitted through the body of the sponge and poured into one main channel, and from there they pass into the projecting trans- parent conduit (s), and finally make their exit from its terminal aperture. By this process the sponge obtains its food. The circulation, wThich is at times fitful, is produced by the vibration of minute cilia which cover the interior of the anastomozing tubes, and by the occasional contraction of the whole body. In the latter case the particles of loose matter within the canals are ejected with considerable violence. The body consists of a soft, highly extensile and contractile, transparent, filmy substance, in which groups of bristles (spiculae), of a horny nature, are im- bedded at irregular intervals, and through which the channels, which I have mentioned, run in every direction. The color is due to numerous granules which lie within its substance; other- wise it would be perfectly glassy in hue; as it really is at the surface, and in the digitiform emptying conduit. Although I have applied the best and highest powers of the microscope to the most transparent and clearest portions of the body, and to the conduit (s), I have not been able to make sure that there is a cellular structure in the soft tissue. It is true that occasionally I have detected in the conduit what appeared to be a decided cellular tissue, consisting of distinctly nucleated, closely packed, polygonal cells, but at other times I could not see the least trace of such ; nor have other observers been more fortunate than my- OF PROTOZOA. 43 self; so that in this respect sponges have as low a type of tissues as the Rhizopods. But yet you must have seen, that, as I said at the beginning of this description, the sponges have a degree of specialization, of parts of the organization, that at once stamps them as of a higher order of beings than the Amoebas and their congeners. In addition to what may be found in the Rhizopods, we have in the Sponges distinct channels of circulation, vibratile cilia giving a direction to these currents, particular inlets and as definite an outlet for the passage of food; and in some of the peculiar forms, the spicules are arranged according to definite patterns about the inlets and the outlet, thus adding an element of gradation, while subserving the needs of an already distinctly specialized function. The group of beings to which the next animal, that I shall in- troduce to your notice, belongs, is one that in a certain sense is more directly allied to Rhizopods than to Sponges, on account of the mode of life which is prevalent among the members. But what distinguishes the Actinophryians, as this group is called, from the two foregoing is that they, at least some of them, have a distinct cellular structure ; and yet, though the cells are very distinct, they exhibit a low state of development, as low perhaps as could possibly obtain without failing to be genuine cells. In other respects the nature of the organization is very much like that of Rhizopods. Still, from another point of view, the Actino- phryians might be called a peculiar group of Sponges ; in fact, there are some forms among them that are as yet in an un- decided position, in the opinions of naturalists, as to whether they are members of the latter or the former group. The truth of the matter is, they form a transition from the one to the other, of such insensible gradations that it is impossible to determine where the one group ends and the other begins. It is on this account, therefore, that out of these innumerable gradations I can only present for your consideration those forms, in the progress- ing scale of development, which exhibit such features as mark a distinct step in the elevation of animal organization. 44 ACTINOPHRYS. This figure (fig. 22) represents the internal structure of Acti- os vc Fig. 22. nophrys, the typical genus of this group. It abounds in still waters and ditches, from whence it may be collected and pre- served alive by skimming the surface of the soft silt, and deposit- ing it, for observation, in a glass jar of clear water taken from the same spot. Even to the naked eye it is visible as a distinct, white, glistening spot, apparently about as big as a pin-hole. Un- der a moderate magnifier it resembles a small sun with greatly prolonged rays. It is on this account that one of the species has been called Sol. Although, as we shall see presently, capable of moving parts of its locomotive apparatus with great rapidity, it progresses at a very slow pace, balancing itself on the tips of its rays (ps), which project from all sides of the body. In fact, it is so sluggish that it may be handled, with a great deal of freedom, without inducing it to retract its pseudopodia (ps), as its rays are called. Notwithstanding that the pseudopodia are capable of being totally contracted, so as not to leave a trace of Fig. 22. Actinophrys Eichornii. Ehr. 130 diam. A view of the interior, as if it had been cut open at the middle, ps, the pseudopodia acting as organs of locomotion and for prehension ; r, living prey, a Rotifer, just caught; r*, another Rotifer in the process of engulfment; cv, the contractile vesicle, one of the cells of the outer layer. — Original. ACTINOPIIRYS. 45 their presence, they possess a power not only of extending to a great length, but also of rendering themselves so rigid that a few of them can sustain the whole weight of the body. As a gen- eral thing they project from the body in perfectly straight lines, and move so slowly as to appear like stiff bristles, rather than what they really are. By a close and patient examination, however, one is not long in coming to a conclusion that these apparently sluggish creat- ures are not only animals, but at times very active and power- ful. These particulars are better understood when the intimate structure of the Actinophrys is under consideration than by any other process of observation. We will therefore proceed to in- vestigate the basis of its organization, as it is exhibited in its cellular tissues. The most comprehensive view of its structure, that it is desirable to take, is that in which we get what is called a sectional view, as if a section of the body, next the eye, had been cut away and the interior exposed to the sight. This is done by placing the glasses of the microscope so as to get a view of the interior, whilst all those parts nearer to the eye are out of focus, and consequently not defined so as to form a distinct picture. The figure before us is a sectional view, so deep that the body is as it were cut into halves. By it we get an insight of the re- lations of the cells to each other, and to the pseudopodia; in fact every part of the organization may be seen at a glance. Under a low magnifying power the body appears as if it were a mere globule of gum-like or mucous matter, with numerous closely set cavities hollowed in its substance; but a closer examination, with good lenses of a higher power, will detect a distinct cell- wall about each cavity. Where the cells lie close together the neighboring walls appear as one; but at other points, which are numerous, the cells are separated by the interstitial mucous sub- stance, (cytoblastema, cell-generator,) and there the wall may be seen to have a very appreciable thickness. This is a very im- portant point to determine, because by this feature alone the Actinophryians are to be estimated as more highly organized than those groups, the Rhizopods and Sponges, which possess a 46 ACTINOPIIRYS. mere mucous tissue. In the latter case we see the lowest possible grade of organic tissue, whilst in the former it is spe- cialized so as to present two distinct forms, namely, the mucous form, (cytoblastema,) and the cells which have been generated in it. At once, then, you will see that the organic functions are dis- tributed not only in different regions of the body, — as we have already observed among the successively rising members of the Rhizopod group,— but among two distinct sets of tissues. In the former groups everything is performed by a body that is all cytoblastema, but in this group the cytoblastema has generated cells which assist in performing the functions of the organiza- tion. Moreover the cells are differentiated so as to present two distinct features among themselves ; thus we have an outer layer of cells (cv, r1), which are much larger than those within, and they are disposed quite methodically in a single layer all over the body ; and within, the smaller cells are united, without apparent regularity, so as to form a sort of core. In the inter- stices of both kinds of cells there is a universally pervading cytoblastema, which also at certain points has a specialization of its own substance. I refer to its prolongation, from between the cells of the outer layer, into those attenuated, bristling bodies which I have spoken of as pseudopodia (ps). It is a notable fact that although the cytoblastematous sub- stance overlies the whole body, exterior to the larger cells, yet it never projects, in the form of pseudopodia, as if in prolongation of the cells, but invariably alternately with them. Notwithstanding the simple structure, or rather structureless character, of the pseudopodia, they at times exhibit a rapidity of motion equal to that of the most highly organized muscle. This is most frequently seen in connection with the seizure of living animals for food. Minute creatures of almost every kind are a prey to this far-reaching Briareus. The moment that any mov- ing body comes in contact with one of the pseudopodia,— as for instance the little Rotifer, a shrimp-like animal, which I have represented here (/•), —it becomes as it were glued to it, and ACTINOPHRYS. 47 stupefied; the pseudopodium then either gradually retracts, or, as I have frequently seen, suddenly, and as if it were a rubber thread under high tension abruptly cut loose at one end, jerks the prey toward the body. At the same time the neighboring pseudopodia bend over the victim and form a sort of cavity (r1) about it, and then the surface of the body rises on each side and gradually engulfs the living morsel, which by this time shows but little signs of life. In a short period it is passed through the cortical layer of cells to the interior, and there undergoes diges- tion in a fluid which seems to be generated, in a cavity between the cells,'for each special body that is introduced. As yet we have not arrived among those animals which possess a distinct mouth, but the food is introduced at any point of the body which corresponds to the interspaces of the cells ; and likewise when the digestible parts of the prey are extracted, the refuse is ejected at any spot in the circumference. There is also a tendency toward a circulation of fluid, most especially exhibited in the pseudopodia ; but it is more apparent than real, and requires the most careful scrutiny to detect the actual state of things. The minute transparent granules that more or less abound in the cytoblastema, and particularly in the pseudopodial prolongations (ps), are the only means by which we are enabled to descry the movement of this tissue at any particular point; and as they are borne along in dilations, extensions, or retractions of the various regions of this glairy substance, they appear to be floating in streams of .fluid, whereas their motions are really limited to the extent of the expansibility or contractility of the cytoblastema. There is, however, in certain parts of the body, a more re- liable exhibition of an incipient fluid circulation. Among the large cells of the cortical layer, one or two of them (cv) exhibit a tolerably regular but slow expansion and dilatation, like the diastole and systole of the so-called heart, or contractile vesicle, of the higher Infusoria, which I shall speak of presently. In what manner these vesicles are connected with the clear fluid with which they fill themselves, when they expand, or through 48 THE DIFFERENCE BETWEEN ORGANIC what channels they expel it, when they contract, has not been discovered ; although in all probability it is strained through the cell-wall. Such are a few points of the structure of this marvellous creat- ure. For hours I have watched it with an ever increasing interest, and when I left my microscope I could only feel that but a beginning had been made in the investigation of its varied functions. Indeed, I hardly know where to stop in the enumer- ation of the rapidly accumulating differentiations of organs and the specializations of functions. We have scarcely arrived in the midst of creatures which possess barely such a sufficiency of struc- ture of an organic nature as would enable us to distinguish them from inorganic bodies, before we light upon, I might almost liter- ally say, numerously appointed functions, each devoted to a sepa- rate work. This, no doubt, teaches us that we are not to look to any peculiar and absolute form of combination of the chemical elements, Carbon, Hydrogen, Oxygen, Nitrogen, by which we may distinguish the organic from the inorganic kingdom of na- ture. The variously performed functions of the extremely simple Amoeba gave us the hint toward this conclusion; and now the but little more highly organized Actinophrys more than redoubles the impression upon our minds, that it is a power or force, or, as I have stated in the beginning of these lectures, a principle of life, — whatever that as yet uncomprehended principle may be, — that constitutes the vitality of the organic being, and distin- guishes it from the inorganic thing. The most highly organized creature, even man, is no more an animal, as distinguished from the mineral, than Amoeba is; for no one will pretend to say that when he existed in that em- bryonic condition, the egg-state, which is as simple in structure as the Amoeba, that he was any the less animate, that he was any the less an organic being, than when in an adult state. The more highly elevated and the infinitely more numerous functions of man are not any addition to, but merely so many variables of, the simple principle, vitality; alike as potential to vivify the Amoeba as the Man; but no further removed from the AND INORGANIC BODIES. 49 principle that rules the mineral, in the most highly complicated, than in the most lowly organized beings. Doing away, then, with the idea of the necessity of a more or less complicated structure for a medium in which to exhibit the principle of vitality, as distinguished from the inanimate, we can readily imagine that a living being could be possible, were it no more complicated than a drop of water; and when we come to this conclusion, we have but to call to mind the initiatory stages of the animal, in its egg-form, to realize this thought in its per- fection. The most infinitesimal drop of fluid, that is potentially an egg, is as truly so as the most complicated, and likewise as cer- tainly an animate being, as on the day that commences its career as a -wanderer over the earth, whether in the waters as a fish, or on land as a quadruped, or in an erect position, a Man. Man or Monad, the mighty oak or the slimy mould of our cellars, are alike the medium for the exhibition of the principle of vitality; nor can we say how simple that body ought to be which might not be subjected to the dominion of this power. But let us return from this digression, and see, if possible, whither the group of Actinophryians will lead us, if we pursue the investigation of the successively higher forms. I will stop but a moment to point out two or three of the characteristic features of one of the Polycystinae, (fig. 23.) a very peculiar group of animals, which stands related to the three groups which I have already discussed; to the Rhizopods, like Cor- nuspira (fig. 3) and Rotalia (fig. 4), it is allied by its thread-form pseudopodia (fig. 23, ps), which are projected through the apertures of a shell; to the Sponges Fig. 23. Lithocampe tropeziana. J. Miiller. Nat. size, T^'" (line) long. A mitre-shaped shell enclosing an Actinophrys-like body. Marine, ps, the pseudo- podia projecting in every direction through the pores of the shell. — From J. MiUkr. 4 50 ZOOTEIRA. it is more distantly related through a group of sponge-like creat- ures called Acanthometrae, which combine in their organization spicules, resembling those of Sponges, and a perforated net-work- like shell, similar in conformation to that of many of the Poly- cystinae; to the Actinophryians (fig. 22) it so closely approxi- mates that it might be called an Actinophrys, with a stony net- work thrown over it. The most direct line, by which we may pass from Actinophrys to the higher Infusoria, is through the mediation of a very singu- lar creature which was discovered, by Dr. Strethill Wright, on the coast of Scotland, jp* near Edinburgh, and to which he gave the name of Zooteira religata (fig. 24). It is, as he says, " an Actinophrys mounted on a contractile pedicel." At times its pseudo- podia (ps) are extended into extremely at- tenuated threads, and at others they are " all thickened or clubbed at their extremi- ties." This figure (fig. 24) represents them in the latter condition, and the tubular stem (s) so expanded as to render its net- like character (n n1) very conspicuous. The axis of the stem is occupied by a " muscular band " (m), along the centre of which fluid was seen to circulate on one occasion. The whole animal can retract itself into the gelatinous sheath (sh) which surrounds its base. Its mode of catch- ing its prey and engulfing it is precisely like that of Actinophrys. The next animal that I shall draw your attention to, although it is not directly and closely related to Zooteira, is, however, in Fig. 24. Zooteira religata. Strth. Wright. Magnified considerably. A stalked Actinophryian. h, the head; ps, pseudopodia; s,%tem; n, nl, net-like threads of the interior of the stem; m, the hollow muscular band in the axis; sh, the sheath. — After Strth. Wright. Fig. 24. PODOPHRYA. 51 Borne respects similar to it, and stands in the course of the tran- sitions toward the highest In- fusoria. It is called Podoph- rya (fig. 25). I introduce it here principally because, in its adult state, its character and ./' habits are strikingly like those of some of the Rhizopods; for instance, it seizes its prey with its globe-tipped feelers (/), and through them sucks the juices of the victim. The same we have seen is done by some of the Rhizopods which live in a perforated shell, (p. 14.) In its *"'*• 25- embryonic state (fig. 25, A, B) it is evidently a close ally to those higher Infusoria which move by vibrating cilia, and, like them, the young (B) exhibit in the arrangement of the cilia an obliq- uity which points to the spiral type of conformation, which, as I shall show hereafter, is at the base of the organization of Protozoa. What chiefly gives it a rank above those Protozoa which we have already taken note of, is the definite character of its contractile vesicle (cv), and the reproductive organ (n); both of which can scarcely, if at all, be distinguished from the corre- sponding organs of the highest Infusoria. In Podophrya, the contractile vesicle (cv) is readily distinguishable from the rest of the tissues ; nor is it, as in Actinophrys, likely to be mistaken for one of the ordinary cells of the body, as it is differentiated in such a manner that its physiognomy is peculiar to itself, and it seems like an isolated cavity in the midst of the animal. With regular precision it slowly contracts to an almost invisible point, and then expands to its former rotundity, and again and again repeats the systole and diastole, with ever-recurring, evenly marked intervals. Fig. 25. Podophrya Cyclopum. Clap. 300-350 diam. /, the globe-tipped feelers; cv, contractile vesicle ; n, the reproductive organ. A, B, the young in different stages of development.— After Claparede. 52 THE EGG IS THE FIRST STAGE And so I might go on upwards, from one kind of creature to another, showing point by point the gradual increase in the com- plication of animal organization, until I arrived at the highest forms, even at Man himself, who, of all animals, departs most from that degree of simplicity which we find in the egg. But it will be more proper to trace these gradations, in full, in another part of my subject. It does not necessarily follo*w here, from what I have said, that there is a serial relation from the lowest to the highest animals ; that is another thing. I simply mean to assert that the various degrees of complication are not suddenly marked off, with gaps between them, but that the idea of differ- entiation has been carried out gradually. My present object is merely to impress upon your minds the fact that there is no sud- den transition from the condition of an egg to that of an animal, taken in its usual sense. Being thus preoccupied with the idea that there are animals (Amoeba, Actinophrys, etc.) as simple as some eggs, or even more simple than others, you are prepared for the assertion that an egg is not to be looked upon as a distinct body, which preex- ists the animal, but rather that it is the animal itself, from the moment when it begins to form in the ovary of its parent. The egg is merely the first stage of growth of an animal, and it is not separated from the succeeding phases, any more than these latter are from each other. From this, and what has already been told you preceding this, you may draw the inference that there is a perfect parallelism between the development of an animal from the earliest or egg- stage to the adult, and the successive degrees of grade from the lowest to the highest animals, within a group. Now, in regard to the point of origin of the egg, the fact that it is formed within a parent rather than in the outer world is per- haps only a difference of degree ; for although some eggs are re- tained by the parent until after the egg-stage is passed, in fact until the time when the young is able to move about and take care of itself when born, as in our common quadrupeds, yet even here there is a marked difference among the successively OF THE GROWTH OF ANIMALS. 53 lower ranks, and a more or less corresponding decrease in the de- gree of dependence of the young upon the parent; for instance, in the duck-billed quadruped, or Ornithorhynchus, (fig. 26,) the young are born while yet in a far inferior state of development to that of the young of the horse, or cow, or dog, when born. The young of the kangaroos Fib- 26- and opossums, of which there are many species, are hardly more advanced when born than the young Duck-mole. But there are vertebrates which in a descending scale are for a less and less time retained; the eggs of birds are laid, that is, subjected to the influence of surrounding external causes, at a time when there is scarcely a trace within them of the so-called germ, which from this period is altogether dependent upon one of the phys- ical agencies, heat, for its development. Still lower in the scale we find the eggs of frogs and toads, and some kinds of fishes, are laid before they can hardly be said to have become fully formed as eggs. And so we might go on, pointing out instances of this decreasing degree of dependence, until we find the egg expelled from the parent at such an early stage as to be dependent upon physical agents during a large part of its period of growth; for instance, it is dependent upon temperature, or moisture, or dryness, or light, or some form of physical help, exactly as are spontaneously generated bodies, or as those developed in the sealed flasks. Fig. 26. Ornithorhynchus paradoxus. Blum. Natural size, " as large as a cat." The Duck-bill quadruped, or Duck-mole. Inhabits Australia. — After Bennet. 54 THE MULTIPLICATION OF INDIVIDUALS CHAPTER III. THE OLD APHORISM, " OMNE VIVUM EX OVO," NOT STRICTLY CORRECT.—THE ORIGIN OF INDIVIDUALS BY BUDDING AND SELF-DIVISION. Having thus shown to you that there are among adult ani- mals those which are as simple as the lowest forms of eggs, and that eggs are merely one stage, and that the earliest, of animal life ; and having demonstrated that the so-called egg is left more or less dependent upon physical causes for its growth, in some cases almost altogether independent of the influence of the par- ent, and consequently in like proportion dependent upon phys- ical agency for its growth, there seems to be but one step left to bring us to that condition of things under which the animal-egg may arise altogether independent of a parent! This idea may seem at first startling and unnatural, so accus- tomed are we to look upon all animals as direct developments from maternal parents. Yet there are numerous instances, well known, and acknowledged as such, by all naturalists, of in- dividuals which originate in such a way that they may be truly said never to have been born ; that is, they have never passed through or existed in an egg-state or condition. Now, in order that this may not seem to be an incidental assertion, but that it shall appear to you in its true light, which is, that an individual is not always derived directly from a pre- liminary egg-phase, I shall illustrate the phenomena by a pretty full description of the various modes of reproduction otherwise than those which take place through the means of ovarian ges- tation. There are, in the first place, two apparently well-marked kinds of individuals which originate by budding: the one is an in- dividual in the truest sense, a complete, independent organ- ization, and the other is as fully complete in all its parts, BY THE BUDDING PROCESS. oo but at the same time lives in common with others like itself, and forms what is called a compound individual. Between these two kinds there are, however, all possible gradations; but as it is not germane to my purpose to describe them, I merely mention the fact, for the sake of future reference, and then pass on to what is most pertinent to our subject. The strictly independent individual is one in which all the parts of the organization, which belong to animals of this or that particular group, are fully represented in a single body. To com- mence with a most familiar instance, I will draw your attention to the animal which is represented here (fig. 27). It is known by the name of Hydra, and belongs to the same type of animals, namely, the Zoophytes, as the jelly-fishes, corals, star- fishes, &c, but is one of the simplest of them all, in every respect. It is to all intents and purposes a simple elon- gated sac (s), with slender, hollow prolongations (t) ar- ranged around its mouth. These prolongations, which vary in number from five to eight, are called the ten- tacles, and are used as feel- ers, and for the purpose of seizing the food, which is mostly living animals, and conveying it to the mouth. Fig. 27. Hydra fusca. Trembly. 14 diam. The Fresh-water Hydra, with two young (a, c) budding from it. b, the base, attached to a piece of stick ; .«, the digestive cavity ; t, tentacles of the adult; tl, tentacles of the young. — Orig- inal. Fig. 27. The latter opens at the end of the 56 THE BUDDING OF HYDRA. little conical eminence at the base of the prehensile organs (t). The opposite end (b) of the body is closed, and slightly expanded in the form of a disc, by which it attaches itself to various ob- jects, such as pond-lilies, duck-weeds, or even to the sides of stones on the margins of lakes. At certain seasons very few individuals are to be found which are not in the condition which we have represented here, that is, having either one, two, or three younger individuals (a, c) growing out from each single adult. The process of this kind of reproduction is very clear: the bud begins in the form of a simple bulging from the side of the sac-like body ; it increases by a mere prolongation, as if the wall were puffed out in the form of a hollow cylinder with a rounded end, and presently minute processes rise around this end, and produce a form such as stands out from the body on our left (a). We have, now, all that is essential to the new individual, but in a rudimentary condition. To attain to perfection, then, the cylinder elongates, as represented on our right, (c,) and the minute processes, the tentacles, simply develop into thread-like bodies, (t1,) -whilst the rounded end becomes more prominent and conical, and a perforation appearing therein, a mouth is formed. In this condition the little creature is prepared to seek its own prey. Its independence is finally accomplished by a gradual constriction of the base of the new body, at the point where it is attached to the old stock, until it finally, as it were, cuts itself off. From this time, it is as purely an individual as the one from which it budded, and, like that, it reproduces its own like- ness, and apparently without limit as to numbers. Sometimes this occurs before the young stock is detached from the primary one, and in this way a numerous colony is produced, which has all the physiognomy of a minute branching water-weed. To heighten the deception, some species of Hydra are green, and in their most expanded state, with the tentacles spun out to excessively fine threads, they resemble tufts of green silk waving backwards and forwards under the influence of varying currents. Finally, however, the whole ramified mass scatters into numerous branchlets, and each individual pursues its own independent course. THE SEA-ANEMONE. 57 Now it is remarkable that the proportion of individuals which are produced in this way is so great, when compared with the number of those which arise directly from eggs ; and one might almost say that the latter process is the exceptional one, and the former the normal mode of reproduction. Another instance of the budding of independent individuals among the Zoophyta is exemplified in the common Sea-Anem- one, or Animal-flower, so-called. This is a much more highly organized animal than Hydra, although it belongs to a group which, as a whole, is more simple in structure than that of which Hydra is a member. The latter is classed among the jelly-fishes, " sea-blubbers," " sting-bladders," &c, but the former is one of the Coral group. The body of the Sea-Anemone, which we have represented here (fig. 28), under the name of Metridium marginatum, has the appearance of a cylinder cut straight across at each end, and at both of these points covered by a membrane. One end (A) is bordered by an undulating fringe (a) of numerous short finger-shaped tentacles, and the other extreme (P) is more or less broadened like the base of a pillar, Fig. 28. Metridium marginatum. M. Edw. \ natural size. A Sea-Anem- one attached to the shell (b) of a mussel. From Boston harbor. A, the anterior end; P, the posterior end; a, the fringed disc, covered by pointed feelers, and pierced by the scalloped, oblong mouth ; c, d, e,f, young budding. — Original. 58 THE SEA-ANEMONE. !• The Privet Hawk-Moth. Natural size. A longitudinal, sectional view, an, antennae, or feelers; hd, the head, or first joint of the body; th, the thorax, consisting of the 2d, 3d, and 4th rings; b to b1, the eight rings of the abdomen; /, the base of the legs; p, the tubular proboscis; gl, the gullet; st, stomach ; cr, crop; i, intestine; a, posterior end of i; h, h1, h?, 120 THE CLASSIFICATION OF CUVIER. is divided by transverse folds into a certain number of rings, (th, b to V)." In his fourth grand division, Zoophyta, — or Radiates, as he frequently calls them, — in which he includes not only starfishes, sea-urchins, jelly-fishes, and corals, but also intestinal worms, and infusoria, "the organs are arranged like rays around a centre," or, as he expresses it in one place, (vol. in. p. 218, ed. 1829-30,) " along two or more lines going from one pole to the other As a general thing, naturalists have accepted the divisions of Cuvier; but there is a diversity of opinion in regard to the limits of these divisions. Some accept them in the same sense as the heart; sg, superior nerve ganglion of head; g, g1, ganglions of the thorax; c, nervous collar; n, main abdominal nerve; g% g%, g*, ganglions of » ; ov, ovary; d, oviduct; o, exterior aperture of d. — From Newport. Slightly altered. Fig. 54. Caudina arenata. Stmp. Natural size. A longitudinal, semi- diagramic view of a common Trepang of our coast, t, t1, the four-pronged, anchor-shaped feelers of the head; /,/*, the stave-like, calcareous, forked pieces of the buccal ring; g, the anterior end of the intestine; g1, the first bend of the same; <72, the second bend of the same; g%, the posterior or cloacal region of the intestine; g\ posterior aperture of the same; rt, rt1, rft, the respiratory branches; m, the madreporic body; mc, the madreporic canal; r, the aquiferous ring; aq, the aquiferous canals going from r to the space (aq3) at the base of « THE FIVE GROUPS OF ANIMALS. 121 Cuvier presented them, or even in a more stringent sense, making each grand division an absolute circumscription within itself. Others look upon these four groups, or rather five groups, — since the Protozoa (Infusoria) are regarded at the present day as a distinct division from the Zoophyta, — as so many sub- divisions which have more or less intimate relations with each other; as if they were the components of a vast cloud which is divided into five masses, having their edges mutually merged into each other. In a certain accordance with this idea of the mutual relations of the five divisions of the animal kingdom, I have constructed these diagrams (figs. 55 to 64), to illustrate the corresponding positions of the organs in the typical forms.* the feelers (t) ; aq*, aq2, aq*, aq5, aq®, aq1, the longitudinal aquiferous canals running close to the under surface of the skin; h, hl, the heart; c, the ribbon- like nervous collar; ov, ov1, ov2, the reproductive organ; o, the external aper- ture of ov. — Original. * It may be objected here that some of the animals in these diagrams are placed upside down, in order to bring the organs into corresponding position in all of thein; but I would ask, then, do animals have any definite relation to up and down ? Which, for instance, is the back among the Zoophytes ? The Holothurians (Trepangs, fig. 54) creep on the side exactly opposite to that on which the Sea-urchins do ! The latter creep in the position which the diagrams (figs. 57, 58,) represent, i. e., heart downwards. Among the Mollusca, the Cuttle-fish and Squid (ch. xr., fig. 124) swim usually backwards, and with the back downwards. Now these comprise a large group among Mollusca. Another considerable group among Mollusca, the so-called Nucleobranchiata, allied to Conch-shells, swim rapidly in the sea back downwards. Many kinds allied to the clams live in holes in the sand and mud, with the head downwards, and others, like the oyster, rest on the side! Among Articulata, who can say which is the back of those intestinal worms (the Tape-worms, fig. 44) which live on the juices of the stomach of various animals ? Even among the Insects, in which back and front seem to be most distinctly marked, the Notonectas, water-bugs, invariably swim back downwards. Of the Vertebrates, the Halibuts and Flounders creep and swim on the side. The Bats rest all day hanging by their hind legs, head downwards. The Sloths, a curious group of quadrupeds, always move among the branches of the trees, where they constantly live, back downwards, hanging from the limbs by their long claws. Now if it should be urged that the Sloths nevertheless have what is to them their terra firma next the lower side of the body, we would ask, why 122 THE IDEAL TYPES OF THE m net- ma Fiff. 56. h mat h Fig. 55. c nc2 nc c nc1 h ma Fig. 57. en 91 nc /7a nc2 ma c en nc1 G 9 h Fig. 62. then does the Notonecta invariably keep his back in one direction, i. e., down- wards, when his terra firma, the water, is all around him ? This is enough to show that the matter of up and down has nothing whatever to do with the rela- tive position of the organs of animals. FIVE GREAT ANIMAL GROUPS. 123 Now if you will call to mind what I have said in regard to the nature of the connection of these groups with each other, when I compared them to clouds which are more or less merged into each other at their margins, you will understand me when I tell you that these diagrams not only represent the type or symbolical form of each group, but also exemplify the tendency of one group to merge into another. What the meaning of this tendency is, I will make apparent in good time. Thus, the Protozoa (figs. 55, 56) have an irregular, hardly defined, digestive cavity, (m, ma, ma1, a,) on one side of which is a hollow, (h, h,) which beats like a heart. The nervous system, according to the most recent researches, (see p. 64,) is a layer of nerve-cells, or threads, (nc, nc1,) which lie just beneath the surface of the body. In Zoophyta, (figs. 57, 58,) the intestine (m, ma, a) is more evident as a canal than in Protozoa, and, among the highest, the heart (h) is a distinct tube which runs along one side of the body, whilst the nervous system, (en, g, g1, g2, c, nc, nc1, nc2,) although disposed around the body in an apparently diffuse manner, has its principal parts so regularly posited as to stand in perfect symmetry with the other organs ; thus it has two ganglions, (g, g,) one on each side of the heart, (h,) one also on each side (g1,g2) above, and one directly on the median line, (en,) Figs. 55, 56, longitudinal and foreshortened views of an ideal Protozoan ; figs. 57, 58, the same of a Zoophyte; figs. 59, 60, the same of a Molluscan ; figs. 61, 62, the same of an Articulate; figs. 63, 64, the same of a Vertebrate. The corre- sponding parts of the organization are lettered alike in all. — Original. 124 THE IDEAL TYPES OF THE all of which are united by nervous threads (c) into a ring, which is often called the nervous collar. In Mollusca, (figs. 59, 60,) there is, as before, a distinct intestine (m, ma, a) in the centre, but the heart (h), as a general thing, is more concentrated than that of the Zoophyta, and the ner- vous system (en, g, g1, g2, c, ga, nc, nc1, nc2) preponderates on the side opposite to the heart (h), whilst there is one or more gangli- ons (g) next to it. All of these ganglions are united by nervous threads (c) into an irregular circle about the body. The Mollusca were considered by Cuvier as next in rank to the highest animals, the Vertebrata; and such is the opinion of the most eminent of all his successors, Richard Owen. The reason is obvious; for the Mollusca, especially that group of them which comprises the Cuttle-fishes and Argonautas and Nautilus, have an organization which in part is more nearly related, in complicity and kind, to the Vertebrates, than is that of any of the other grand divisions. I have said that the Molluscan organization is, in part, superior to that of all others below Vertebrates; for anatomical investi- gations of later years, and observations upon the intelligence of Insects, have led many naturalists to look upon Articulata as parallel with Mollusca in point of rank. Let us see what is the tendency among them as regards the nervous system, the ruling power of life. In Articulata, (figs. 61, 62,) the intestine, (m, ma, a,) still in the centre, is bordered on one side by the heart, (h,) as in previous groups, and on the opposite side we find the nervous system, (en, g, c, nc, nc1,) nearly altogether concentrated along a median line, and showing a strong advance toward the head, but on the side next the heart (h) a single ganglion (g) which is united to the main group by a nervous ring (c). The tendency to con- centrate the life-giving system toward the head is illustrated by the longitudinal section. In the Vertebrata, (figs. 63, 64,) we have the highest degree of concentration of the nervous system, (en, g, c, c1, nc, nc}). The main group of nerves is massed as a single chain, (en, nc,) — still with traces of a double character, as in Articulata, — and FIVE GREAT ANIMAL GROUPS. 125 this chain is on one side of the intestine, opposite to the heart (h), but yet one of the ganglions, that of the sense of taste, (g,) one of the chief senses, is placed on the opposite side of the intestine, and next the heart. The position of the internal skeleton is rep- resented by a line (ch, ch1, ch2) running between the main nerve- trunk (en, nc1) and the intestine (m, a). I know some naturalists would object that the Mollusca, Articulata, and Zoophyta cannot correspond, in the nervous system, with the Vertebrata, because the first three have a ner- vous ring or collar, (c,) and the brain is on the opposite side to the nervous cord ; but this, upon careful comparison, will be found to be not true ; for, in the first place, the Vertebrata do have as distinct a nervous collar (figs. 63, 64, c) as some Mol- lusca, and secondly, one of the principal senses, taste, is centred in a ganglion (g) which is reached from the main nerve by this collar of nerve-threads which passes around the intestine exactly in the same way as in Mollusca and Articulata. Moreover, in regard to the position of the so-called brain in Mollusca and Articulata not corresponding to that in Vertebrata, I would say that in the Mollusca the position of the sense-ganglions varies, but in the highest of them, the Cuttle-fishes, the ganglion for the eye holds almost the same relation to the main trunk as does the corresponding organ in Vertebrata; and in the Articulata, the position of the eye-ganglion also varies, for although among Insects it is on the opposite side from the main nerve, yet among a large group of Worms, the Nemertians, the ganglion from which the optic nerve springs is on the same side as in the Ver- tebrates. Between these two extremes of position there are all grades. As to the objection raised by those who claim that the verte- bral column, or bone of the back, is the distinguishing feature of Vertebrata, I would say that when we refer to certain fishes, such as Lamprey eels and the Sturgeons, we find the backbone represented by a mere gristly cord, and in other fishes (Myxine, Ammocoetes) a cord of interlaced fibres in place of vertebrae. Yet in several respects these fishes are far more highly organized 126 THE IDEAL TYPES OF THE than the so-called bony-fishes; their brain is of a higher order; their circulatory and respiratory system is also superior ; and the organs of reproduction are not only higher, but approach closely to those of reptiles. So we see that the bony nature of the ver- tebrae is not the essential characteristic of Vertebrates ; it is the presence of some longitudinal mass, either bone, or gristle, or interlaced fibres, or a mere jelly-like string, as in Amphioxus, (fig. Fig. 65. 65, v, v\) which is intended to separate the main nervous cord from the rest of the organs ; it is the presence of this ideal, as I may call it, that constitutes the characteristic of Vertebrates. In other words, it is an ideal axis materialized. From this you may judge that in considering typical forms of life, it is the relation and not the nature of a substance which is to be taken into account. Relation should be the ruling standard. Accordingly, therefore, we see in the Protozoa, (figs. 55, 56,) the Fig. 65. Amphioxus lanceolatus. A diagramic figure of the Lancelet. Nat- ural size. /, the head ; v, v1, the notochord, or vertebral column; vs, the sheath of v, v1; be, the buccal cirrhi; j, the buccal ring at the entrance to the mouth ; I, II, oval bodies projecting freely into the buccal cavity; g1, entrance to the throat or branchial cavity; g, posterior end of the same, and entrance to the in- testine proper (i) ; bo, the lateral branchial openings; i1, posterior end of i; Iv, Iv1, appendage to i, opening into it at Iv1; h, the heart; h1, Ifl, the anterior blood- vessels ; W, branches from h*, supplying I, II; A4, Jfi, the dorsal artery; h$, the abdominal vessel; b, the upper, and b1, the lower point of junction of the branchial vessels (br) with the dorsal (h*, W) and ventral (h1, h*) vessels; ac, abdominal cavity; ap, abdominal pore; nr1, the anterior, and nr, the posterior end of the main nerve or spinal marrow ; ns, sheath of nr, nr1; o, the eye ; n, the olfactory nerve; nv, the facial nerves; ov, the reproductive organ. — From Owen. FIVE GREAT ANIMAL GROUPS. 127 nervous system, although formless, holding a certain position in reference to the other organs. In Zoophyta, (figs. 57, 58,) it is more collected, and arranged symmetrically, in reference to right and left, and above and below. In Mollusca, (figs. 59, 60,) it is more concentrated toward the side opposite the heart. In Articulata, (figs. 61, 62,) the concentration is still further carried out; and finally in Vertebrata, (figs. 63, 64,) the nervous system attains its highest confluence not only toward the median line opposite the heart, but also in its tendency toward a head. Now it is a remarkable fact, that, as we trace the arrangement of the systems of organs from the lowest to the highest groups, we find the tendency is, in one sense, to carry out the idea of polarity, which we see in the egg, to its strongest expression. Thus, among the lower animals, the egg has the two poles (page 34, fig. 15) not distinct, since the opposing oil (ol) and albumen (alb) merge more or less into each other; but among the higher, (page 35, fig. 18,) the two poles, yolk (ol) and germ vesicle (p) are very marked. So it is in regard to the organs of animals; for the lowest of them, as I have shown, gradually differentiate the opposing sides, the nervous and the digestive, until, as we rise to the highest forms, we find the digestive system, or, as the heart is a part of it, the nutritive centre corresponding to the yolk, and the nervous centre corresponding to the albumen, or germinal-vesicle pole. When we draw a line from one of these poles to the other, whether we do it in the lowest or the highest animals, we divide the body exactly into right and left; that is to say, we find that all animals are double, even man. The brain of man is double; one half may be taken away altogether, without affecting the mental functions, as certain diseases have shown. The experiment of removing one half of the brain has been tried successfully on dogs, rabbits, and pigeons, and these animals did not lose their usual mental powers. The paralysis of one side of a man's body, whilst the other half retains its powers of motion, shows that the spinal cord is also double, like the brain. The duplicity of this system 128 BILATERALITY. among the lower animals is much more apparent thah in the higher. Such an arrangement of the organs of the body is called Bilaterality ; and, as you see by these diagrams, (figs. 55 to 64,) bilaterality is the basis upon which the animal structure is erected; and whatever modification there may be of this feat- ure, this type of form, such a modification is subordinate to the type. Perhaps some of you will call to mind the starfishes and sea- urchins, which you may have read about in books as being formed upon a plan which is called radiate, like the spokes of a wheel, or the divisions of an orange. It has been represented that these so-called Radiates differ essentially from all other animals, because their organs are not arranged upon the plan of bilaterality ; and that whatever appearance of bilaterality — for its presence is admitted in a certain sense — there is in them, is of secondary importance. Now as the Radialists, as I may call them, have admitted, nay, have even claimed, that there is the appearance of bilaterality among Zoophytes (Radiates), let us see what we can add to this acknowledgment. Let us refer for a moment, without intending to anticipate what I may say hereafter, to the earliest forms that have appeared on our globe; and, to make the case the more decisive, to what were probably the only representatives of their class at one time. This figure (fig. 66) represents the body of one of the Crinoids, a Hemicosmites, which lived in the earliest geological age. It belongs to the same class as the trepangs, such as Caudina (fig. 54) and the starfishes (chap. x. figs. 109,110); but, unlike them, it is attached at the end (fig. 66, s) opposite the mouth (m) to a stern. The principal feature is the snout- like protrusion (m), at the end of which is the mouth. From our knowledge of the course of the intestine Fig. 66. Hemicosmites. Natural size. A fossil Encrinite, without its stem. m, the proboscis; a, the aperture to the posterior end of the intestine; o, the BILATERALITY. 129 of the living Crinoids, it has been agreed among naturalists that the small aperture, which is in the slight prominence (a) near the mouth, is the posterior terminus of the digestive canal. Taking, now, the two opposite extremities of this canal as the extreme points of a line, we may project that line, as a plane, through the body toward its stem, so as to divide the Crinoid into right and left portions. There is not anything about the animal which militates against this method of topography; and at the same time I would say that there is not the least rudi- ment of radiation in the disposition of the components of this body. There are traces, that is, scars on each side of the pro- boscis (m), where it is thought that arms were attached ; but these are as definitely arranged in regard to right and left as are the arms of a cuttle-fish or squid (chap. xi. fig. 124). There are other kinds of Crinoids whose arms are much more conspic- uous for their right and left arrangement than those of Hemi- cosmites.* What then do you suppose would have been the decision of a naturalist had he lived at that time, — far down at the bottom of the Silurian period, — at the period of the first appearance of life upon the earth ? He certainly would never have thought of such a thing as a radiate type ; simply because there is nothing in these animals to suggest such an idea. I might also refer you to the embryonic or earliest stages in the growth of Zoophytes, and you would see there also that the radiate character is either very feebly represented, or altogether absent, whilst the bilateral feature stands out prominent; but I cannot at present go into many details, as that would anticipate what you will hereafter aperture of the reproductive organ; p, the plates of the shell; s, the point of junction of the shell with the stem. —From Pictet. * For the benefit of those who may object that the ovarian opening (fig. 66, o) of Hemicosmites is unsymmetrically placed, and therefore is out of relation with the bilateral plane, I would propose, as an answer, to show on the same score, that the worm Bonellia (chap. xn. fig 126) is not a bilateral animal, inas- much as the aperture of its reproductive organ is a little on one side of the me- dian line ; or that a man is not a bilateral creature, because he uses his right hand more than his left. 9 130 BILATERALITY. learn, when we come to the history of the mode of development of these animals. But let us turn aside awhile toward the margins of these five grand divisions or groups, where the clouds, as I have said, merge into each other, and see if this idea of distinct types can be maintained. ANIMALS AND PLANTS. 131 CHAPTER VII. THE DISTINCTION BETWEEN ANIMALS AND PLANTS. — THE PSEUDO-INFUSORIA, THEIR PLANT-NATURE.— THE PLANT-LIKE INFUSORIA. In the consideration of this matter, I come now to the explana- tion which, in a previous lecture, I promised to give you in regard to the meaning of the " merging of the clouds " of the five grand divisions. You will recollect that I stated that although some considered the five grand divisions as so many distinct groups, yet an equally large class of naturalists looked upon these di- visions as so many subdivisions which have more or less inti- mate relations with each other, as if they were the components of a vast cloud which is divided into^ye masses, having their edges mutually merged into each other. Now I think that you will best comprehend the meaning of these relations, as to whether they are those of consanguinity, or ideal, when I have explained the relations of the classes or minor groups of each grand divis- ion. There are two distinct considerations to be held here: the one is whether these five grand divisions are related in the same sense as are the classes of each division, or whether they have a different relation, and what that relation is. Now, as this distinction is based upon the very foundation of the animal kingdom, I must go back to first principles, and, as you will see presently, to the investigation of a different kind of life characteristics from those which were concerned in the dis- cussion of the "principle of life^ as I termed it in a previous lecture (p. 7). In that lecture I pointed out the distinction which exists between organized bodies, whether animals or plants, on the one hand, and unorganized bodies, mineral and chemical, on the other. But now we will take up the matter of the distinctive characters between organized life as manifested in one form, the 132 THE DISTINCTION BETWEEN] animal, and organized life as manifested in another form, the plant. In beginning a description of the Animal Kingdom, the first question that arises is, " What is an animal ? " By what char- acters do we distinguish the animal from the plant? To the generality of people it would seem as if the question would be answered as soon as asked. No one, say they, would confound a man with a tree ; a fish with a sea-weed ; a coral with a mush- room, or a sponge ; but to show at once how soon the very dif- ficulty would be plunged into, by instituting such a running comparison, I will tell you that the sponge has been, for years, the centre of controversy as to its animal or vegetable nature. The common, every-day acquaintance with the sponge would not help one to distinguish it from certain kinds of corals which I could produce. There are also other species of sponges which are filled with limestone; and they cannot be distinguished from certain corals except by the closest scrutiny of the naturalist, and sometimes in the fossil state the separation is impossible. This is only one out of many instances of the kind; and that you may fully appreciate the hesitation of naturalists, of all faiths, in determining the limits between the animal and vegetable kingdoms, I will illustrate certain phenomena which occur where the uninitiated would least suspect. From the early days of the microscope, when it was looked upon rather as a marvellous sort of plaything, up to the time, about 1826, when Ehrenberg began his researches upon the more minute organisms, all those infinitesimally small moving bodies which were seen by the earliest observers in various kinds of fluids, whether water from the ocean, or streams, ponds, stagnant pools, ditches, or decomposing fluids, such as old milk, or in sour paste, or starch, &c, were believed to be Infusorial animals. Notwithstanding that Vaucher, as early as 1803, had seen that certain of these minute moving bodies burst forth from the interior of one of the common fresh-water plants (Confervae), and developed into fixed stems and branches, like those of the plant ANIMALS AND PLANTS. 133 from which they emerged ; I say that in spite of this strong hint, it was not until Ehrenberg had excited the marvel of the scientific world by his disclosures of the complicated organisms of many of these moving atoms, and had stirred up a lively and some- times rather too caustic criticism upon the correctness of his observations, and by this means had brought the microscope into use as a scientific instrument, whose tremendous power as an engine of progress, along the great road of science, I believe is but half suspected,—not until Ehrenberg had given this impulse, and there finally appeared in the field a class of observers who devoted themselves to the elucidation of the nature and relation of the so-called Infusorial animalcules, — that it was suspected that anything but animals were comprised in this group. Finally, from the year 1843 to 1850, among other observers, Thuret was the most active in throwing doubts upon the an- imality of certain of the so-called Infusoria, which were classed together from their similarity, as here represented (figs. 67 to 72). Fig. 67. Protococcus pluvialis. A zoospore. 1000 diam. c, cell-wall; g, granular contents; e, transparent region; n, nucleus; I, I, vibrating lashes. — Original. Fig. 68. Saprolegna ferax, in different stages of growth. 500 diam. n1, body of the zoospore; I, vibrating lash of the same ; n, n2, p, three successive degrees of development. — Original. Fig. 69. Chlamidomonas pallida, n. sp. 500 diam. c, the pair of contrac- tile vesicles. — Original. 134 THE DISTINCTION BETWEEN Fig. 70. Fig. 72. Unless I were to point out their differences, you could not dis- tinguish the true Infusorians from the false ones. Which they are, respectively, I will explain presently. Thuret discovered that the seeds (spores) of certain marine (Algae) and fresh-water (Confervas) plants have attached to them peculiar threads, or cilia, with which they move; and he also pointed out their resemblance to the published figures of certain so-called Infusorial animals. To prove what is the real character and relations of these cil- iated spores, he spent a number of years in the investigation of the mode of reproduction of a large number of different kinds of water-plants, such as are commonly called sea-weeds and pond-weeds. The process which Thuret adopted, in order to carry out his proofs to perfection, although laborious, was the only one that could be successful. At first he watched the grad- Fig. 70. Heteromita fusiformis, n. sp. 500 diam. c, the contractile vesi- cle ; I, the anterior probocis-like vibrating lash ; I1, the trailing lash. — Original. Fig. 71. Heteromastix proteiformis. Nov. gen. et sp. 500 diam. A, an in- dividual fully extended; e, the red eye-spot; I, the anterior lash; I1, the pos- teriorly trailing lash; cl, the group of vibrating cilia. B, a contracted individual; P, same as I; cl1, same as cl. — Original. Fig. 72. Euglena spirogyra. Ehr. 300 diam. e, the eye-spot; I, the vi- brating lash. — Original. ANIMALS AND PLANTS. 135 ual changes which the contents of the plants pass through in the formation of their spores, and then he doubled the proofs by tracing the growth of these self-same spores into branching plants. Subsequent researches have confirmed the observations of Thuret, and have also carried that delicacy of distinction, which he introduced, to the highest degree of critical comparison. Moreover, it was in following out these elaborate examinations that observers have come across some of the most important physiological facts that this century has produced. One of these facts is this: that within the boundaries of a simple circle, a series of phenomena are exhibited which consti- tute the components of a whole life, of origin, growth, and reproduction. The physiology of life, in this case, is reduced to, or more properly speaking, it does not rise above the simplest form of operation and manifestation. This I think you will fully comprehend from a description of the life characters of one of the lowest organized of all plants. It is closely related to, if not identical with, the famous " Red- snow plant." In one of its states of existence it is frequently to be found not only in water, but also in damp places; and dur- ing the winter, in some localities, it gives a red color to the snow upon which it grows. The whole plant is a mere microscopic globule, so small indeed that a single one would escape the eye, but when congregated in vast numbers they make themselves visible by their color. This little globe consists of a thick, trans- parent, delicate shell or coat, (fig. 73, c,) which is filled with a red- dish or brownish yellow granular mass (gig1). The latter is most frequently found divided into two portions, (g, g1,) each one of which contains a comparatively large brownish red globule, or nucleus (n, n1) as it is called. In this condition the plant is known to be commencing a series of changes which result in its total metamorphosis into new individuals. The manner in which this is brought about is in this wise. When it is sub- jected to the action of water, the transparent envelope (which is the homologue of the stem of the thread-form aquatic plants, 136 THE SNOW-PLANT. the Confervae) swells to a larger size, (fig. 74, c,) and the two granular masses, (g,) increasing in transparency, become grad- ually tinted with a light green, whilst one end of each changes to a clear transparent area (e) totally devoid of granules, and the nucleus (n, n1) enlarges considerably, and at the same time loses all of its color.* Frequently before these changes occur the two granular masses of the primary stage (fig. 73, g, g1) divide again, each doubling itself and its nucleus, and then the changes of their color and of the nucleus, which I have just described, occur. In this figure (fig. 75) the four masses, (g,) the future spores, have already assumed their final shape, and the narrower end Figs. 73 to 79. Profococcus pluvialis. The successive phases of growth of the plant from the resting stage to maturity, c, the cell-wall; g, g\ the granular cell contents ; n, n1, the nucleus; e, e1, the transparent end of the cell; e2, the transparent centre ; I, the vibratory lashes. — Original. * It is barely possible that the nucleus disappears as the transparent space develops. THE SNOW-PLANT. 137 (e, e1) is as pointed, transparent, and clear as in the later stages, but the nucleus (n, n1) is as yet quite dark. This teaches us that the changes do not go on with similar steps in each individ- ual, but yet all tend toward one end, which we find illustrated here (fig. 76). Each spore has developed, from the transpar- ent end, (e, e1,) a pair of thread-like bodies, (/, I,) of equal thickness throughout, which are in constant motion, writhing and lashing about as far as the increased size of the parent-cell (c) will allow. Plunging now with the microscopic probe within the green mass, we find its interior to be still more largely occu- pied by a transparent space (e2) than in the first change (fig. 74, e) which we took note of; and moreover it is evident that this transparency is in direct continuation with the clear area at the pointed end, (fig. 76, e, e1,) where the vibratory lashes (I) are attached. In this condition the spores are set free by the burst- ing or dissolving away of the parent-cell (c), and allowed to swim off through less restricted habitats than they have hereto- fore occupied. There is no definite aim to these movements, but each spore seems to lead a sort of indeterminate, roving life, following in an irregular line the lead of the constantly twirling double lashes. In process of time there appears a thin, transparent film (fig. 77, c) on the surface of the ever-active spore; at first it is very indistinct, and the outline is indefinite, more like a halo than a sharp, light contour, but gradually it assumes greater prominence and apparent .solidity, (fig. 78, c,) and finally it stands off from the surface of the green contents, a firm, clear, sharply defined wall, (fig. 79, c,) with all the characteristics of that of the par- ent, excepting thickness. There is at the same time another equally significant phenomenon of growth that appears during the formation of the spore-wall. Within the granular mass a faint spot (fig. 77, n) looms out of the darkness, and, gradually growing more intense and bright, becomes quite conspicuous; then it elongates (fig. 78, n) and assumes an oblong form with a constricted middle; and lastly it undergoes the process of self- division, and the two resultants (fig. 79, n, n) become the most 138 THE MODE OF DEVELOPMENT noticeable features of the perfected spore, by their strong, brill- iant, oil-like, refractive powers. This is the beginning of the end, of the completion of the cycle of development; already the preparatory step has been taken for the partition of the granular mass, by the self-division of its nucleus, and all that is required to bring it to the perfect state, the one with which we started, is a falling away of the vibratory cilia, (fig. 79, /,) the thickening of the cell wall, (c,) the self-division into two of the granular contents, (g,) and then the development is perfected; the off- spring has become the image of the parent-plant (fig. 73). Here we have within this little space an eternal circle of the incomings and outgoings of life; so simple in its manifestations, and yet so intensely vital; so determined toward a particular end, that one, after the contemplation of these phenomena, in- stinctively inquires, what chance is there now to comprehend the physiological actions and reactions of the highest and most complicated of those beings which manifest life ? This question the physiological anatomist has held as a problem for the last twenty-six years, dating back to the time when the botanist Schleiden and the physiologist Schwan, in 1838, gave to the world the results of their studies upon the growth of the cells of plants and animals. Ever since that time, our ideas in regard to the high complicity of the functions of life, among the elevated classes of animals and plants, have been changing, and verging toward a more simple philosophy. In short, life, in- stead of being that long and often-represented etitangled mesh of complications and puzzling manifestations, stands now, in the mind of the thoughtful, laboriously investigating physiolo- gist, as a unity. Perhaps you can best realize this idea if I call to mind the great simplicity in the administration of medi- cine to the sick at the present day, as compared with the com- plicated operations through which the human frame was com- pelled to pass not many years ago. For this you may thank the student who scarcely more than a quarter of a century since bent patiently over his microscope from early morn till setting sun, watching, with almost suspended breath, the little transparent OF CONFERVA. 139 sphere which eventually became a universe of attractions for the whole circle of scientific minds. Thuret's task in the investigation of the mode of growth and reproduction of the simplest branching water-weeds, was to show what is the nature of the apparent increase in the complicity of the progressively more elevated forms. The first and simplest step in this way is exhibited by a very common green sea-weed which is called Bryopsis (figs. 80, 81). Notwithstanding that it differs so much, to all appearances, from the snow-plant, and seems to be much more complicated than that, yet in reality it is scarcely more elevated in rank than the little globule whose de- velopment we have just followed Fig. 80. through. It has made an initiatory step, however, toward a higher status by a differentiation of its whole into stem and top, and by assuming the form of the more highly or- ganized aquatic plants; although the organization is rendered none the more complicated by the manner in which this is done. This you will readily comprehend if I suppose, for instance, that the globular cell of the snow-plant were so plastic that you could stretch it out into a long tube, and then draw out the sides of the tube into numerous parallel, finger-like -projections (like fig. 80, a); you would still have a single cell, with a single cavity within it, and therefore in reality no more complicated than before. Such is the condition of Bryopsis. The process of re- production is the same as in the snow-plant; the whole contents become changed into lively, moving spores, (fig. 81, B, C,) each furnished with from two to four vibrating cilia. The entire Fig. 81. Fig. 80. Bryopsis plumosa. A young plant from our coast, a, the pinnules or lateral projections. — Original. Fig. 81. Bryopsis hypnoides. a, the aperture of a pinnule like a of fig. 80; B, C, zoospores, one with two, and the other with four vibratory cilia, magnified 330 diameters. — From Thuret. 140 THE MODE OF DEVELOPMENT plant does not, however, dissolve at once in order to allow the ripened spores to escape, but an aperture (fig. 81, A, a) is formed in the side of the finger-like projections, through which the young glides forth to a freer life. This it enjoys for a few hours, and then commences its career as a fixed plant. I will not now describe the process of transformation into this latter condition, but reserve it until we come to one of those plants in which I have myself watched the development through all its changes. The most clearly defined step that is taken toward a higher rank, is exhibited by the partitioning of the cavity of the single plant into several chambers. This we have in the sea- weed, of which a portion is delineated here (fig. 82, A). It is called Cladophora. These three cavities, separated from each other by these double diaphragms, (c,) have each an aperture, (a, a1,) through which the spores (B) are escaping. The whole plant, which branches considerably, is made up of similar cells, in all of which, Thuret says, spores are developed, and from which they event- Fig. 82. ually escape. The entire plant, from top to bottom, becomes a mass of seeds. It is merely a branching string of one-celled plants, each one of which is formed in the likeness of the snow-plant, Protococcus. What, in addition to its vibrating lashes, renders the zoospore all the more like cer- tain of the Infusoria, is a red spot in the clear space at the pointed end. This has been mistaken for and identified with the eye-spot of certain animalculae, such as Euglena, (fig. 86,) &c.; but Thuret has shown it to be a mere globule of oily mat- ter, and that, moreover, it is not always present, or is more or less indistinct. The next decided advance in rank is exhibited by those plants Fig. 82. Cladophora glomerata. Ktz. A, three of the joints or cells from the end of the branch of a plant; a, lateral apertures; a1, terminal aperture; c, transverse partition ; s, young plants germinating within the cell of the par- ent; B, a zoospore magnified 330 diameters. — From Thuret. OF CONFERV.E. 141 in which the reproductive process is confined to one part of the organism ; that is, certain regions are specialized and devoted to a different office from that of the other merely vegetative portions, and by this specialization a reproductive organ is produced. Commonly, this organ is the terminal cell of the plant among the lower grades of sea-weeds and their fresh-water relatives. The one which I have represented here, (fig. 83, A,) in its natural size, grows like a white mould over dead flies and other insects which may happen to fall in the water. You may very readily raise it in a few days by throwing „ b some flies into a jar of water, and letting it stand quiet in a nA warm place, when a white film of fine threads gradually makes its appearance all over the de- caying body of the insect. These threads, if examined soon after they become clear- ly visible, will be found to be mere tubes with a sharp point at the free end, and a broad base where attached. After a while their tips lose their transparency and become whitish. If now they Fig. 83. are examined, it will be found that this part of the plant is partitioned off from the rest, as in this figure, (fig. 83, B,) and the contents are little yellowish, globular bodies crowded together as close as they can lie. Presently this whole mass begins to be agitated, and the globular bodies tremble from an apparently invisible cause, reminding one of a commu- Fig. 83. Saprolegna feraxf A, a group of plants growing on a dead fly; B, the tip of a plant magnified 250 diameters; a, its terminal aperture; s, zo- ospores ; C, zoospores just escaped from the plant. — Original. Fig. 84. Saprolegna feraxf Same as fig. 83. Various stages of growth after the escape of the zoospores; A, a ripe zoospore; n1, its body; /, its vi- bratory lash. B, the first stage of the plant-growth; n, its nucleus. C, sec- ond stage; n2, its nucleus. D, the young plant just attaching itself; p, the basal end. 500 diam. — Original. 142 THE MODE OF DEVELOPMENT nity of bees when swarming; then the cell which confines them seems to be convulsed, and swells and stretches now and then, until finally the end (a) bursts open, and the swarming globules (C) are ejected in a body by the contracting cell. Occasionally a few are left behind, (s,) and commence to develop within the parent-cell. I wish particularly to draw your attention to the form of the spores (fig. 83, C, and fig. 84, A) of Saprolegna, on account of their resemblance to certain Infusoria. Compare the zoospore, (fig. 84, A,) with its eye-spot-like nucleus, and its single * vibrating lash (I) attached at the bottom of a notch at one side, with the Euglena, (fig. 86,) and you will not wonder that the spores of sea-weeds have been mistaken for animalcules. It was no difficult matter in this case to prove that they were the genuine seeds of the plant from which they came, and not its parasites; for in an hour and a quarter after they were set free, and during which time I watched them constantly, they began to stop their roving, and settling down upon terra firma with a sort of side way motion, as if trying to wedge themselves into some hollow, they became globular, and insensibly lost the vibratile cilium by what appeared to be a process of deliquescence. In the course of two or three hours after this, one side of the globule began to show distinct signs of growth by a slight pro- tuberance, (fig. 84, B,) and consentaneously a distinct trace of a cell-wall appeared upon its surface, in the same way as we have seen it develop in the snow-plant (p. 137). In time the protuber- ance lengthens so as to give the young plant a pear-shaped figure, (C.) and then, continuing to elongate, it becomes tubular in form, (D,) and, the rounded end at the same time growing comparatively narrower, the whole soon assumes the shape of the parent stock. It is not necessary to watch the growth of a spore through all its phases up to the full-grown state, as every step beyond what I have depicted here can be found exemplified * As these spores have not the two terminally attached cilia which Thuret figures, it would seem that this plant must be not only specifically but generi- cally distinct from Saprolegna ferax. OF ALG^E. 143 in a group of plants, upon placing the whole colony under the microscope. We have already had before our eyes two methods by which plants rise from a lower to a higher rank, namely, by the formation of distinct cells in a continued series, and by the specialization of parts for a particular function. The complication is still fur- ther increased by the development of cells in a lateral direction, so as to form a leaf-like plant. The common, light green, parch- menty sea-weed, TJlva, everywhere upon our rocky coast known under the name of green Dulse, or Laver, is an example of this kind; and the olive-colored, or brown, leather-apron-like sea- weed, Laminaria, exemplifies the increase of growth of cells, not only longitudinally and transversely, but at right angles to the latter direction. In this whip-cord- like plant, (fig. 85, A,) known in science as Chor- da, which is very common in rocky bays, the lateral growth of cells is such as to produce a round figure, from slender base to tapering tip. The spores (B, C) resemble those of Saprolegna, but have a red eye-spot. According to Thuret's observations, they are developed in the superficial cells of the cord This, I think, will suffice to il- lustrate the tendencies of the march of develop. ment from the lower toward the higher forms of plant-life, as contrasted with a similar procedure among the inferior grades of animal life, which I have described to you in a former lecture (pages 9 to 14). But let us now turn again more particularly to the supreme result of these investigations, which was to show that certain kinds of so-called Infusoria were not animals but plants. Here, then, was a new set of phenomena to be investigated by the physiologist. Zoologists said at once that the fact that a body moved from place to place was no longer a criterion of its animality ; nor could they fall back upon another fact, which Fig. 85. Chorda flum. A, a plant; B, C, zoospores, magnified 330 diameters. -B, C,/rom Thuret. Fig. 85. 144 THE PLANT-LIKE was so long a strong basis, and apparently invincible, namely, that vibratile cilia are indubitable indications of an animal nature in the body which possesses them, for we have seen how active those cilia are which are attached to the spores of the lowly organized plants. They also said that the red " eye-spot" — as Ehrenberg believed it to be, and consequently deemed it a nerve of sense, — had also lost character, and was reduced to a mere globule of oily matter which was sometimes present in, and sometimes absent from, the rapidly changing contents of the flitting, spasmodic spores. It is true, however, that certain un- doubted animals, Euglena (fig. 86) for instance, also have this red, eye-like spot; but its presence in spores of plants deprives it of all character as a mark of distinction unless accompanied by other diagnostic features. Casting about from point to point, endeavoring to find some safe foundation upon which to raise a firmer and more lasting framework, naturalists came to the conclusion to settle down upon contractility as one reliable character, and the absorption of food as another, and probably the more trustworthy; but both were far beyond suspicion, as was then thought. Let us see, now, what proofs of animality we may derive from some of the infusoria which most resemble the sea-weed-spores. I will take, for ex- ample, one of the most familiar and common of the animalcules ; it is known under the name of Euglena, or the Eye-animalcule, (fig. 86). The resemblance in char- acter to the spore of Saprolegna is heightened by the fact that the vibratile cilium (fig. 86, I) of the Euglena, like that of the former, emerges from a notch near the narrower end, and moreover there is close to it a nucleus-like spot; but the latter in Euglena is red, and is known as the red eye-spot (e). The spores of Cladophora (fig. 82) and Chorda (fig. 85), you will recol- lect, also have a red spot near the vibratile lashes; Fig. 86. Euglena spirogyra. Ehr. 300 diam. The Eye-animalcule, e, the red eye-spot; I, the vibratory lash. — Original. INFUSORIA. 145 so that the matter of color does not affect anything in this com- parison. So far, then, the argument holds good for their close relationship; but when I assure you that the Euglena as fig- ured here is only one of the many forms which the same individual may assume from moment to moment, and that you may see it change before your eyes, almost as quick as thought, from this elongate figure (fig. 86) to one like this pear-shaped infusorian (fig. 88, B), and that in the next sec- ond it is stretched out and pointed at each end like a spindle, as in this figure, (fig. 88, A,) and, in the midst of these vari- ous elongations and contractions, exhibits an extreme de- gree of flexibility, at times fairly doubling itself up end to end, as you would fold a strip of india-rubber, you cannot fail to appreciate the marked diversity of character between the two objects in question. How far this distinction goes, we will not stop to discuss until we have seen these other kinds of infusorians. The separation apparently grows wider yet when we learn that Euglena takes in food in the form of solid particles, and stores them away in globular cavities, sometimes called the digestive vacuoles. There is still another peculiarity among these spore-like Infusoria which does not find its parallel in the sea-weeds. I refer to the contractile vesicle. I was fortunate in obtaining another infusorian, Chlamidomonas, (fig. 87,) which resembled the spores of some of the sea- weeds so closely, not only in form and actions, but also in size, which in the doubly ciliated spores is very minute, that, were it not for one almost inconspicuous character, I should certainly have taken it for the colorless spore of some water-weed, or of something like the snow-plant. That charac- ter was exemplified in its double contractile vesicle (c). These vesicles appeared and disappeared alternately, or sometimes both together, with considerable rapidity, and yet, notwithstanding Fig. 87. Chlamidomonas pallida, n. sp. 500 diam. c, the pair of contrac- tile vesicles ; I, the vibratory lashes. — Original. 10 146 THE PLANT-LIKE their minuteness, when once recognized, it was an easy matter to see that they had the physiognomy and habit, as I might say, of the contractile vesicles of well-known infusorians. We have now noted three diagnostic features in the Infusoria which we did not observe in the plant-spores; but let us go on still further with the animals for the purpose of getting a broader basis of comparison; one that will aid us in discovering the nature of the differences between the developmental process, from the lower to the higher ranks, of the Infusoria, and the corresponding process in the sea-weeds. Here is an infuso- rian (fig. 88) from fresh water, which, although it has a pretty strong re- semblance to Euglena, |B heightened by the pres- ence of a red eye-spot, (e,) will be found, upon investigation, to possess some additional and de- cidedly different charac- ters. In the first place, F>g-88- it has two vibrating lashes, (I, I1,) which differ remarkably among themselves both in position and character. One of them is always carried in front like a sort of proboscis, (I,) and in fact it seems to have the office of such an organ, like that of the elephant, to feel and to take hold of objects. I must confess that I was struck with aston- ishment at the apparent intelligence with which the infusorian extended and twisted and turned and felt about with this ex- traordinarily muscular organ. Never did an elephant seem to use his trunk with more thoughtfulness. With like control did the animal also use the other lash, (I1,) always keeping it turned Fig. 88. Heteromastix proteiformis, nov. gen. et sp. 500 diam. A, an indi- vidual fully extended; e, the red eye-spot; /, the anterior lash; I1, the poste- riorly trailing lash ; cl, the group of vibrating cilia; B, an under-side view of a contracted individual; P, the same as I / cl1, the same as cl. — Original. INFUSORIA. 147 back along its body; so that it formed a kind of movable keel, when the little creature glided through its watery element, or was used to sway it from side to side, or oftentimes to raise it up on its tail by forming a prop, as we see it in this other figure (fig. 88, B). The motory or propelling power, on the other hand, is restricted, at least in the greatest measure, to another kind of vibratile cilia. These are very short, and are crowded to- gether in great numbers in a broad furrow or depression, (cl, cP,) which extends over half the length of the body, along its infe- rior, middle line. When the body is turned over, and the ante- rior end retracted and swelled out sideways, the furrow becomes quite conspicuous, (fig. 88, B,) and the extent of the group of minor cilia is easily ascertained. They are very minute and in constant motion, propelling the body backwards and forwards, up and down, to the right or left, according as it is steered by the trailing lash which extends along its length. Thus it is, that, although similar in form, a diversity of functions is laid upon these three kinds of cilia that amounts to the most marked spec- ialization, through the simplest means ; in fact, so simple that the eye cannot detect them in any form beside that of proportion and position, and certainly not in the intimate structure of these bodies. The whole body, too, possesses a flexibility and exten- sibility scarcely inferior to its cilia ; at one moment it is darting through the water, sharp as a lance at both ends, and at the next it is as round as a ball, or worming its way through tortuous passages with every possible degree of flexure short of actually tying itself into a knot. When, now, I turn your attention to one of the next succeed- ing higher forms, this one here, (fig. 89,) for instance, Ceratium, some of you may perhaps recognize in the one which we have just studied a transition from those, like Chlamidomonas (fig. 87) and Euglena (fig. 86), which have but one kind of vibratory lash to those which possess two forms of such organs special- ized to the highest degree. In this new subject the smaller cilia (fig. 89, w, w1) are methodically disposed in a linear series along the edge of the circumambient annular furrow which 148 THE PLANT-LIKE INFUSORIA. Fig. 89. separates the two parts of the mi- nutely sculptured shell (t, t1). It is in this animal that, as we ascend from the lower to the higher kinds of Infusoria, we find for the first time a disposition of the cilia which prevails so generally among the aristocrats of their class. I need but to remind you of the Stentor, which I described when speaking of the self-division of Infusoria (p. 62, and fig. 30) and other an- imals. The habits of the Cerati- um, whilst swimming, correspond to the arrangement of these cilia : it progresses with a spinning mo- tion, boring its way through the fluid by being whirled, like a wheel on its axis, by means of the transverse vibrating motion of the belt of cilia, whilst its double proboscis (I, ll) plays the part of a tactile organ. I will detain you here with but one more example of the pro- gressive series, simply that the investigation shall have fairly entered the bounds which include the true, so-called ciliated Infu- soria. You would hardly suspect at first glance that this oval figure here (fig. 90) possessed any configurative relationship to the trumpet-shaped Stentor (fig. 30) ; but yet, the young (fig. 91) of the latter, when placed beside this, Pleuronema, cannot fail to strike you with its resemblance to it (compare figs. 90 and 91). I hope hereafter to prove to you conclu- sively that the similarity is based upon an idea of form which is common to both of them, and, in F'g- 90. fact, to all Protozoa. PLEURONEMA. 149 What I wish now to show in the Pleuronema is the triple, or I might say even the quadruple, diversity of the vibrating cilia, or in other words, a quadruple specialization of one type of organs, by their manifold offices ranking their possessors above those of their class which attain to a less degree d of complicity in this respect. The most prominent of these cilia are those which are Fjg- yl- arranged in longitudinal rows (fig. 90, cl) over nearly the whole extent of the body, and which most frequently are seen in a quiet state, projecting far out from the surface like so many fine, rigid bristles. In fact, the motions of this animal are so lightning-like in rapidity that I have never seen this form of cilia except when the body is in a quiet state, and therefore I judge that, as they do not move then, they are the principal organs of locomotion. There is on the right side a group of much more heavily built cilia, (mc,) which project from the pblique furrow in which the mouth (m) is set. They are more particu- larly devoted to producing currents in which the particles of food may be brought to the mouth. We see, also, projecting from the forward end of the oblique furrow, and near the ante- rior edge of the mouth, (m,) one of those proboscis-like lashes (I) which are so characteristic of the lower, ciliate Infusoria; but yet it would not seem to have the same office as in the latter, since it is usually held in this position, apparently as rigid as if it were a wire; and only now and then does it move, by a sudden Fig. 89. Ceratium cornutum. Clap. 300 diam. A marine infusorian, cov- ered by a reticulated shell (testa), t, t1, the two halves of the testa; h, the horns of t; I, the vibratory lashes ; ll, base off; w, w1, transverse rows of vibrat- ing cilia ; c, the contractile [?]vesicle. — From Clapare'de. Fig. 90. Pleuronema instabilis, n. sp. 1000 diam. From fresh water, m, the mouth; st, the food gathered in one mass, mc, large cilia in the vestibule of the mouth ; /, the single vibrating lash projecting from m; cl, vibratory cilia cov- ering the body in rows ; si, the posterior, and si1, the anterior saltatory cilium ; cv, the contractile vesicle; n, the reproductive organ.—Original. Fig. 91. Stentor polymorphus, Ehr. 300 diam. A very young individual, turned upside down to compare with fig. 90. d, edge of the oblique furrow; cv, the contractile vesicle. — From Clapare'de. 150 THE CRITERION OF DIVERSITY jerk, and disappears in the oblique furrow ; probably acting there in concert with the other cilia in the introduction of food into the mouth. The fourth and last kind of cilia which I have to speak of are two excessively faint, very long, and quite large, bristle-like filaments (si, si1) which project from each end of the body. The straight one (si1) always precedes when the creature is in motion, and the curved one (si) is attached a little to the left of the posterior end of the body. Both are always rigid when the animal is not in motion, — but yet there can be no doubt that they are flexible, for at times they disappear suddenly, and prob- ably are bent under the body. What their office is I cannot say, but conjecture, from their resemblance to what are called the sal- tatory bristles of other infusorians, that they are used as accessory means of sudden propulsion, or leaping,— a habit which seems to be the most frequent mode of leaving any point at which the creature has fairly come to a stand-still. The contractile vesicle (cv) lies close to the forward end of the body, and corresponds in activity to the vivacity of the motions of the latter. It con- tracts every ten seconds, and with more vigor than any other that I know of. It is very conspicuous, as it is two thirds of the time in an expanded state; and disappears and reappears like the sudden closing and opening of a large eye. I have alreadv indicated the position of the mouth as being near the broader anterior end of the oblique furrow, but again speak of it here in order to make the description of the digestive system complete. From the mouth (m) the food passes directly into the general cavity without going through any throat, and most frequently combines in large masses (st). The presence of a reproductive organ, which we find here (n) in the form of a clear, colorless, globular body, when added to all the other systems which I have mentioned, puts this animal in the condition of a fully organized, ciliated infusorian; and would seem to give us full warrant for believing it to be the culmination of a progressive development, whose tendency is to pass through such forms of animate organ- ization as we have just been tracing in the successively more and more complicated creatures whose images are before us. BETWEEN ANIMALS AND PLANTS. 151 But now, to go back to the lowest of them, the spore-like forms, let me recall, in a word, what are the animal-like character- istics of their organization. They are, contractility of the body, the pulsation of an organ called the contractile vesicle, and the introception of food, — none of which have been recognized in the spores of any of the aquatic plants which most resemble these infusorians in external conformation. Now this would appear to settle the confusion which had mingled such a mass of heterogeneous material; and the zoolo- gist, on the one hand, would be enabled to draw his inferences without fear of imposing upon animals those characteristics which, on the other hand, the botanist might claim for the special objects of his study. But it would seem to be a vain hope, and the work of the physiologist and the microscopist has but just begun ; for to this day there remains a doubt as to , the gelatinous envelope of the colony; t to t5, the U-shaped double row of feelers; lp, the U-shaped arms; m, the mouth ; I, the lip of m; oe, the throat; st, the stomach; st1, the bottom of st; sft, the anterior end of st; cl, the valvular passage from st to the last division (cl to an) of the intestine ; an, the posterior opening of the intestine ; ac, the abdominal cavity, in which the arrows indicate the circulating currents ; g, the nervous ganglion ; r to r1, the retractor muscles of the head; s, the statoblasts, or so-called winter-eggs, in various stages of development from / to s ; f the posterior end of the funiculus, attached to the side of the body ; s1, the anterior attachment of the reproductive organ. — Original. Fig. 119. The same as fig. 118. A foreshortened view of the head, with the body in the distance. The letters as in fig. 118, and in addition, c, the mem- brane which passes from the base of one feeler to the other; the arrows indicate the direction of the currents of the circulating fluid in the U-shaped arms; lp\ end of lp. — Original. OF BRYOZOA. 197 that is, at the toe of the shoe, and from the convex and concave curves of the U a row of hollow fringes (t to i5) projecting about in the same direction as the first tube, and you have the outlines of the general cavity of this animal. All three of these parts are in open communication with each other; and it is here only that the fluids, or rather fluid, of the body circulates. There is nothing that otherwise resembles a circulatory system. If, now, the U be divided right and left into halves, the line which sepa- rates them may be projected in the form of an imaginary plane so as to divide also the first tube, which is the body proper, into halves. This we will designate as the axial plane ; and you will find that the arrangement of the organization is in reference to this plane. Going back to the U, now, there is to be seen between the outer (t3, t5) and inner (fi) rows of fringes, and immediately opposite the toe of the horse-shoe, a round aperture (m) half covered by a sort of lid (/). This is the mouth. From it the intestinal canal projects into the depths of the body cavity, and then doubles upon itself, and terminates (an) not far from the beginning, without deviating either to right or left from the axial plane. A knife passed along this plane would split the digestive system, from end to end, into halves. The throat (as) extends about one fourth of the length of the body, and is shut off from the stomach (st) proper, except during the passage of food, by a sort of valve (st2) which projects like a ring between them. The stomach (st, st1) occupies the next two fourths of the general cavity, and preserves the same narrow proportions which obtain in the throat; i. e., it is a mere thick-walled tube. In- stead, however, of being continued directly from the furthermost point of its backward reach, it opens at its mid-length (at cl) into a thick tube, which passes forward and debouches (an) at the surface of the body, on the side next the two limbs of the U, and about opposite to the mid-length of the throat (ce). All that has ever been discovered of the nervous system of Bryozoans is a small, double-oval, or broad, heart-shaped mass, (g,) which trends transversely to the bilateral plane, and is situated 198 THE ORGANIZATION close to the anterior end of the throat, on the side facing toward the limbs of the U, and therefore in the interspace between the anterior (m) and posterior (an) ends of the digestive canal. From this there are a few nervous threads which pass, in part, right and left into the fringed arms, and otherwise into the throat near the mouth. The reproductive system (s,f) is attached to the wall of the general cavity, on the side opposite to the nervous centre, (g,) and consists of a more or less elongated mass within which the eggs of various sizes are imbedded. The animal has the power of withdrawing into itself by what is called invagination; like the sliding of the tubes of a telescope one within the other, or more properly, like the inver- sion of the finger of a glove upon itself. This is accomplished by the aid of two long, complex muscles (r, r1) which extend, one on each side, from the head to the bottom of the sheath (ek, ek1) which encloses the organization. The sheath of the species before us is peculiar on ac- count of its jelly-like character; and as the Up individuals live in a community, which has \bd arisen by the budding of one from the other, their combined sheaths form a large tremu- lous mass, oftentimes six inches in width, covering submerged sticks and the stems of aquatic plants in slow streams and pools. The sheath of most of the Bryozoa is more elongated than the one we have be- fore us, and usually of a parchmenty, horny, or eoralline nature. This other figure (fig. 120) represents one, Fredericella, which possesses a parchmenty sheath, (ek, tu,) and whose crown of tentacles (t, t1, t2) is a nearly perfect circle, but still shows a trace of that prepon- Fig. 120. Fredericella regina. Leidy, MSS. 25 diam. A profile view of one of the individuals of a branching, compound, fresh-water Bryozoan. tu, the parch- Fig. 120. OF BRYOZOA. 199 derance toward the nervous (neural) side (g) which is so largely developed in the one which I have just sketched out. So slight indeed is this obliquity, from front to back, of the tentacular crown of Fredericella, that it seems almost like an accidental one-sidedness; but an attentive examination of any number of individuals will reveal the unvariableness of this character, and always in symmetrical relation to right and left; although not so strikingly prominent in this respect as in Pectinatella. Among the asymmetrical forms of Mollusca, and one of the most lowly organized of the series, is the familiar Oyster. Although so comparatively simple in its structure, there are numerous intermediate stages of organization between it and the Bryozoans, some of which, from their peculiar interest, I would be glad to lay before you ; but I must, from want of time and space, content myself with the illustration of a sketch here and there, along the line of upward progress, of such as are most serviceable for our immediate wants. The irregular, ragged out- line, and unsymmetrical shape of the Oyster (fig. 121), would hardly lead one to suspect the unity of relationship to right and left which reigns in its organization. That it has a definite right and left, and that too always corresponding, the first to the flat, and the latter to the deeper hollowed shell, is easily demonstrated, and without entering into the minuter details of its structure. Having separated the flat valve from the animal, keep it in posi- tion with the right hand, and hold the hollowed valve (sh1) in the left hand, both so disposed that the thicker part or beak (sh) of the shells is turned from the body and their edges project in a menty exterior tube common to the whole colony; ek, the thinner transparent part of tu immediately about the body of the contained individual; t, t1, fi, the slightly oblique single circle of feelers ; c, the calyx, a scalloped membrane which joins the bases of the feelers ; /, the lip at the front of the mouth ; ce, the throat; st, the stomach ; sfl, the bottom of st; sft, the anterior end of st; cl, the valve between st and cl1; cl1, the cloaca or last division of the intestine ; an, the pos- terior opening of the intestine ; ac, the abdominal cavity; o, the nervous gan- glion ; r, r1, the retractor muscles of the head; r2, the retractor muscle of the stomach ; bd, a vcrv young bud ; in, the walls of the body partially doubled upon themselves, invaginated ; d, the posterior end of the individual.— Original. 200 THE ORGANIZATION perpendicular plane, and you will have the head (m) of the animal turned from you, its tail nearest to you, and its back upwards. Consequently, the flat valve is the right one and the hollow valve the left. ms ms1 sfl- pv an h h1 ao ao1 ov I in1 st m sh Fig. 121. Taking off, now, the right valve, and letting the other one lie over a little in your left hand, but in the same relative position Fig. 121. Ostrea Virginica. L. Natural size. The right mantle of the Oyster removed, and the internal organization displayed, sh, the anterior, and sh1 the posterior end of the shell; hn, the ligament which acts as a hinge to the shells; mn, the line along which the right mantle was cut away from the left; mn1, the edge of the left mantle ; m, the mouth; st, stomach ; st1, posterior end of st; st2, first bend of the intestine (in); in1, the intestine where it is buried in the liver (I, Zi) ; an, posterior end of the intestine; I, I1, the upper and lower sides of the liver; t, the right, and t1 the left halves of the outer, leaf-like appendage of the mouth; /2, the edge of the inner, leaf-like appendage ; gl, the anterior, and a/3, the posterior ends of the right and outer gill; gl1, gl*, the inner gill of the right side; oZ2, gl5, the inner gill of the left side; h, the auricle, and h1 the ventricle of the heart; ao, the posterior, and ao1, the anterior aortas, or dis- tributing branches of the circulatory system ; pv, the branchio-cardiac vessels returning the blood from the gills to the heart; v, v1, blood-vessels in the mantle; ov, the position of the reproductive organ, just behind the liver; ms, ms1, the two halves of the adductor muscle. — Original. OF THE OYSTER. 201 as before, lift up the thin, fringed, veil-like covering, (the mantle,) and you expose the gills, (gl to gl5,) which hang — as represented in this figure — from the lower side of the animal. They are four in number, and have the appearance of cross-ribbed bands which stretch from one end of the body to the other. It is in their inequality that the one-sidedness of the animal is most promi- nently set forth. The two (gl, gl3, and gl1, gl*) on the right side of the body are of unequal width, and both are narrower than the left pair (gl2, gl5) ; the latter extending much nearer to the edge of the mantle than the former. In front of the gills are four smooth, leaf-like bodies, (t, t1, t2,) which hang in pairs below and right and left of the mouth, (m,) and, being joined above, form a sort of hood over it. They are generally considered as organs of touch or prehension, and, like the gills, are of unequal width; the narrower (t) pendent on the right, and the larger (t1) and longer on the left. Near the posterior end of the gills, and above them, is the great double muscle (ms, ms1) which serves to keep the valves closed. In the shells its position may be recognized by the chestnut- colored, striped, agate-like spot, as big as one's thumb-nail. Immediately in front of the muscle is a hollow, which, in freshly opened specimens, seems to be the theatre of very active operations. On carefully removing the semi-transparent mantle with a pair of sharp scissors, the cause of this phenomenon becomes apparent. We find there a sort of double sac, (h, A1,) the two halves of which are constantly and alternately contract- ing and expanding, in moderately rapid succession. This sac is the heart. The anterior half, the ventricle, (A1,) by contraction forces the blood through the two vessels (ao, ao1) which go off from its narrower end into the body, and thence into the minute vessels (v, v1) which branch through the mantle (mn, mn1). From these, by means of other minute currents, the circulating fluid is brought back into the gills, (gl1 to gl5,) where aerification takes place, and then the blood is returned, through the so-called branchio-cardiac vessels, (pv,) to the posterior chamber, auricle, (h,) of the heart. From the latter the blood is injected into the 202 THE OYSTER. anterior chamber, (A1,) and the circulation again repeats the round from the ventricle (A1) into the body and mantle, thence to the gills, and finally back to the auricle. The digestive system consists of a tube, of varying thickness, which doubles upon itself twice in its course from mouth (m) to vent (an). From the mouth (m) the stomach (st, st1) broad- ens backwards, without the intervention of a throat, in the mass of brown liver (I, I1) which surrounds it, and then slightly nar- rowing, it passes in a direct line, below the heart and along the lower side of the muscle, (ms,) almost to the posterior end of the gills. There it abruptly narrows into an intestine, (in,) which, making a sudden bend, (st2,) passes pretty closely along the right side of the stomach, back to the liver, (I, I1,) into which it enters and passes along near its right side, (at in1,) and then across its forward end, nearly over the mouth, (m,) and down the left side, and then, making a long curve, rises again toward the upper side of the liver, and, passing out of it, bridges over the space in which the heart lies, and comes to a termination (aw) on the upper side of the adductor muscle, (ms,) and to the left of the line along which the stomach passes. The nervous system consists principally of two widely distant masses or groups of ganglions. One of them lies across the upper lip of the mouth, and the other below the great muscle near the first bend of the intestine; and the two are connected with each other by delicate nervous threads which pass along on each side of the body. The anterior mass is called the " cerebral ganglion," or brain, and the posterior one the "branchial gan- glion," on account of its supplying large nerves to the gills, as well as to other neighboring parts. The reproductive organ (ov) lies just behind the liver and under the stomach. It is an irregular mass, which, with the liver and certain other smaller bodies of an undetermined nature, form? a basis on which the stomach and intestine lie, or pass through. These organs, and the great double muscle, form the bulk of the body, upon which the right and left mantle is laid, and from which the four gills hang in long, parallel, unequal strips. Every- THE SNAIL. 203 thing is one-sided, and as if the body had been trodden upon and flattened out unequally, in such away as to force the whole right half up toward the back. In some kinds of oysters, e. g., Gryphaea, the left valve is so deep, and so much curved upon itself, in fact, partially rolled up spirally, as to leave but little of the body to be covered by the right valve. In this respect they approximate the form of the shell of the Snail, and the included body is likewise modified so as to conform to this configuration. In the Snail, (Helix,) the one-sided development of the body is carried to the highest pitch of asymmetry that is observable among Mollusca. It commences its career with a perfectly ac ao ng ma it og n o g c m Figr. 122. symmetrical body, but ere long the right side outgrows the other, and finally the whole organism has the spiral conformation represented here (figs. 122, 123). All that is usually seen of a Fig. 122. Helix albolabris. Say. Diagramic representation of the common Snail. 2 diam. ac, ac1, the abdominal cavity ; sh, the shell; I, the larger pair of feelers, with an eye (e) at the tip of each; t1, the smaller pair of feelers; m, mouth; st, stomach; in, intestine ; in1, posterior opening of in ; sg, the superior ganglion of the head; g, the inferior, or sub-oesophageal ganglion; c, the nervous collar ; n, ng, the foot nerves; og, the oesophageal, or gullet nerves ; h, the auricle, and A1 the ventricle of the heart; ao, the aorta, or main artery; pv, vein from the lung, or pulmonic vein ; ov, the ovary, or egg-bearing organ; ov1, the oviduct, or emptying conduit of ov ; o, exterior aperture of ov1; r, the fertilizing gland, or male element of the reproductive organs; ma, the matrix. — Original. 204 THE ORGANIZATION g1 ft ng Fie. 123. Snail is the forepart of its body, including its head, (t, t1,) the muscular disc, or foot (m to ac) upon which it creeps, and that portion which lies imme- diately above the latter and in- cludes the stomach, (st,) the bulk of the nervous system, (sg, c, g, n, ng,) and the emptying conduits of the reproductive or- gan (ov1, o). Within the shell are included the posterior half of the digestive system, the reproductive organ, (ov,) the heart, (A, A1,) and the lung (pv). That part of the body which is usually extended from the shell (sh) has an elongated spindle shape, and is flattened upon the lower side so as to form the creeping disc. At one end, which is the head, it is truncated, i. e., as if cut straight across. The head has four feelers, of which the upper pair (t) are the longer, and have each an eye-spot (e) at the end. The lower pair (t1) are mere tactile organs. The mouth (m) is situated on the lower side of the body, and just behind the truncate end. From it the stomach (st) extends directly backwards for about two thirds the length of the body, and then narrowirig into an intestine, with varying convolutions, passes within the spire of the shell, (sA,) and bending upward, forward, and considerably to the right, comes to a termination (in1) near the upper right edge of the aperture of the latter. The circulatory system consists of a heart (A, A1) with two cavities, one for receiving and the other for the distribution of Fig. 123. A foreshortened, diagramic view of fig. 122. lp, the lip at the anterior border of the mouth of the shell; st, the stomach; ac, the abdominal cavity; h, the auricle of the heart; h1, the ventricle of the heart; hv, the vein which brings the blood from behind to h ; pv, the pulmonic vein; ao, the aorta coming forward; ao1, the aorta which branches at ao^, in the region of the liver and reproductive organs; sg, the super-oesophageal nervous ganglions; g, the sub-oesophageal ganglions; g1, the inferior edge of the nervous collar; c, the lateral threads of the nervous collar; ng, the nerve which branches in the foot; n, transverse branch from nq; ov, the reproductive organ. — Original. OF HELIX. 205 blood,.and the vessels which carry the circulating fluid through the body. The heart lies obliquely across the mid-line of the body, considerably to the left of the forward bend of the intes- tine, and close to the surface of the back. From one cavity of the heart, i. e., the ventricle, (A1,) the blood is expelled into the arteries, (ao, ao\ao2,) which branch through all parts of the body. From the minute tips of the arteries the fluid then passes into return channels, the veins, one part of which unite in a vessel (hv) which goes direct to the auricle, (A,) and another set of them carries the blood to the net-work of vessels which branch through the lung. After being aerated, the blood passes from the smaller vessels into a single larger one, (pv,) which empties into the receiving chamber, the auricle, (A,) of the heart. By the con- tractions of the latter the blood is thrown into the ventricle, (A1,) and thence goes out, and circulates as I have just described. The nervous system is concentrated chiefly about the head, but sends off branches to various parts of the body. It consists of a double ganglion, (sg,) the brain so-called, which lies just above and across the throat, and of a still larger and broader double nervous mass (g, g]) which rests beneath the throat, and trans- verse to the axis of the body. The upper and lower pair are connected with each other by double or triple nervous threads, (c,) which form a collar as they pass from above downwards and backwards on each side of the throat. From the upper pair nerves pass forward to the feelers, (t, t1,) and backwards (og), on the right and left, over the stomach (st). The great nervous trunks (n, ng) originate one from each of the lower pair (g) of ganglions in the head, and pass backwards along the sides of the body, in nearly unbroken continuity, and with gradually diminishing diameter, until they vanish in the skin and muscles of the creeping disc. Where they branch there is more or less of a thickening, (ng,) but scarcely deserving the name of a ganglion. The reproductive system (figs. 122,123, ov, ov1, ma, o) lies princi- pally on the right side. Its essential part, (ov,) that in which the eggs are developed, is deep within the spiral portion of the shell, 206 THE ORGANIZATION and the oviduct, (ov1,) i. e., the canal through which the eggg pass to the outer world, extends in variously convoluted folds to a point near the right side of the head, where it opens (o) to give egress to its contents. Not far behind the outlet of the oviduct, a tubular blind-sac (ma) opens into the latter. It serves as a reservoir for the fertilizing fluid which is poured over the eggs as they pass along the oviduct (ov1) toward its aperture. If now we compare the relative position of these organs with that in the Oyster, (fig. 121,) we shall find that whereas in the latter the bulk of the organization is, as it were, pushed over to the left side, in the Helix it is reversed in this respect, and is enclosed entirely in a deep spiral shell, which corresponds to the right valve of the oyster. There is no left valve in the Helix, but in other Gasteropods it exists in the form of a horny, or shelly, flat, spirally marked shell, which is attached to the back of the creeping disc, near its posterior end. When the animal with- draws into its shell, this valve, the operculum, fits the aperture closely, and protects the body from all intruders. The most noteworthy features in Gasteropoda, as represented by Helix are the head-like configuration of the anterior end, and the great preponderance of the nervous ganglia in that region. These characteristics we find carried to a much higher degree in the Cephalopoda, the highest order of Mollusca. Fig. 124. Fig. 124. Loligopsis illecebrosa. Les. f of natural size. A profile view of the left side of a Squid, t, the eight shorter arms; fl, the pair of longer arms; hd, the head; fn, the fin; /, the funnel; I, the edge of the mantle"; mc, the cavity of the mantle; sh, the shell; sh1, the conical hollow of sh; m, the jaws ; th, th1, the throat; st, the first stomach or crop; in, the intestine; an, the pos- terior end of the intestine; Iv, the liver; h, the auricle of the heart; hl, the ventricle of the heart; ao, ao% the aorta which carries the blood forward; ao1, OF CEPHALOPODA. 207 ma ao Cephalopoda. As a representative of this order, I have taken the common Squid, (figs. 124, 125,) a species of Cuttle- fish that abounds along our ^j sea-shores during the warmer Pr\ months. It is represented here pA in a reversed position from that in which it swims, in order to /< bring the organs into the same pa\ relation, in regard to up and down, as those in the figures of the Snail and the Oyster have. El£-125- It usually swims with its back downwards, as I have already stated, (p. 121, note,) and most frequently backwards; although it moves with equal facility head foremost. In order to understand its mode of swimming you have to learn that its body is en- closed up to the neck in a loose muscular sac, (fig. 125, ma},) to the posterior aorta; a, a branch from ao1 going to the mantle; hv, the posterior, and hv1 the anterior veins, which unite in a common reservoir at v, from whence the blood enters the auricle (h) ; pa, the point of origin of the artery which passes along the lower side of the gill (gl) ; pv, the branchial vein; pv1, point of entrance of the blood from the gill, through pv, into the ventricle (hx) ; gl, the left gill; g"*, the super-oesophageal nervous mass ; g1, the sub-oesophageal ner- vous mass, or lower half of the nervous collar; op, the optic nerve, cut across; off, the superior, visceral nerve; n, the mantle nerve; e, the pupil of the eye; the outer, dotted circle indicates the outline of the eye; ov, the reproductive organ. — Original. Fig. 125. The same as fig. 124, representing a diagramic view, from the pos- terior end. ma1, the mantle ; /, the funnel; ma, inferior edge of the membra- nous, valvular prolongations (f1) from the funnel (/) ; mc, cavity of the mantle; sh, the shell; th, the throat; in, the mass which includes the posterior portion of the intestine, the oviduct, and the ink-bag; Iv, Iv1, the liver; A2, W, the right auricle ; h, the left auricle ; h1, the ventricle; ao, the anterior aorta ; pa, pa1, the artery going to the gills (gl); pv, pv1, pvz, the branchial vein, emptying at pv1 into the ventricle (h1) of the heart; gl, the gills, cut across; ff2, the super- oesophageal, and o1, the sub-oesophageal, nervous mass; op, the optic nerve; e1, the expansion of op at the back of the eye; og, the superior, visceral nerve; n, the mantle nerves; (og and n are dotted lines;) ov, the reproductive organ. — Original. 208 THE ORGANIZATION which it is attached along the lower side, (ma,) from head to tail. On the upper side of the neck there is a hollow, conical projection (/) called the funnel, from the base of which a flap (f1) passes down each side of the body to the point (ma) where the latter is joined to the sac (ma1). By the help of these two parts, then, the muscular sac, i.e., mantle, and the funnel, all the various motions of the body are accomplished. When the edge (fig. 124,1) of the mantle is open at the neck, water flows in until the space (mc) around the body is filled. If, now, the animal wishes to swim, it contracts the mantle, and the water consequently seeks an outlet; but as the flap (f1) of the funnel acts as a valve by pressing against the inner face of the mantle, the water is prevented from going out by the way it came in, and therefore is projected with great force through the funnel (/) toward the head, and the re- action of the outgoing current propels the body in the contrary direction, i. e., backwards. In order to reverse the direction the funnel is bent upon itself, as you would flex the finger, and then the water being forced out toward the tail, the reaction moves the body head foremost. If the creature wishes to turn round, the funnel is simply bent to one side, and the reaction of the excurrent water throws the head in the contrary direction. At the posterior end of the body there is a fin-like organ, (fn,) which is attached along its mid-line to the lower side of the tail. When the Squid is swimming, this fin is usually folded around the tail; but whilst turning or moving gently, it is used as a balancer, by spreading it out, and waving its edges up and down, as fishes do with the fins on each side of the neck. The head (hd) is set off from the rest of the body by a slight constriction, or neck. Around the mouth, (m,) which is at the end of the head, there are arranged, right and left, ten arms, (t, t1,) five on one side and five on the other, set so closely together as to form a complete circle above, at the sides, and below. Of these ten, eight (t) are in one circle, and the other two (t1), much larger than the rest, are attached one on each side immediately within the circle of eight, and in the interval between the first and second upper arms of the right and left sides. The whole OF CEPHALOPODA. 209 inner face of each of the eight shorter arms is covered from base to tapering tip with a double row of suckers, by which the animal adheres with great tenacity to its prey, and in fact to the hand that makes it captive. The longer pair of arms (t1) have a uni- form thickness from the base to near the tip, where they expand moderately into a sort of spindle-shaped disc, covered by numer- ous suckers like those on the shorter arms. With these arms, and a pair of large, staring eyes, (e,) the Squid may be truly said to have a formidable aspect. And such it proves itself to be to one who may incautiously take hold of it; quick as a cat it throws its head around to the hand which seizes it, fastens its slimy arms to the skin, and buries its sharp, hooked jaws (m) in the flesh. Fortunately, our native species is but just large enough to draw blood from the hand. Rarely does the body exceed ten inches in length. The foreign species, some of which have arms as thick as a man's thigh, and jaws as large as those of a snapping-turtle, are much more formi- dable. Most of the internal organization is included under the cover of the mantle, the organs of the head alone being excepted. The mouth is a highly distensible aperture which lies at the bottom of a sort of cup which is formed by the circle of arms and a membrane which extends between the bases of the latter. Immediately within the mouth is a pair of horny jaws, (m,) placed one above and the other below, in such a way that the upper slides over the lower one so as to cut like a pair of shears. From this point the throat, forming a narrow tube, (th,) passes obliquely through the neck to the lower side of the body, where it extends (th1) along the middle line, with a moderate increase in thickness, to a point just behind the first half of the body, and immediately under the heart (A). At this place it expands sideways, to the left, into the first stomach, (st,) or crop; a highly muscular, oval organ, which tapers away posteriorly and ends about half-way to the end of the tail. After giving off this blind sac, it becomes the intestine, which proceeds but a short distance, and then opens into the true stomach. This is a large 14 210 THE ORGANIZATION sac which lies on the right side of the inferior mid-line, and just behind the heart. From this the intestine bends forward and upward, and, passing under the right limb of the heart, rises (at in) to the upper surface of the liver (Iv, Iv1), and terminates (an) not far behind the neck, slightly to the left of the middle dorsal line, and near the base of the funnel (/). The liver (Iv, Iv1) is an immense, elongate oval, brown mass, which extends from the neck to the heart, and occupies nearly the whole space between the upper and lower, and right and left sides of the visceral mass in this half of the body. The circulatory system consists of a triple chambered heart, and arteries and veins. The heart (A, A1, A2, A3) lies at the pos- terior end of the liver, (Iv,) and exactly in the middle line of the body. The main chamber, the ventricle, (A1,) is more elevated than the two auricles, (A, A2, A3,) on its right and left. In the pro- cess of circulation, the blood issues from the ventricle and passes into the great anterior (ao2, ao) and posterior (ao1) arteries, the first running along the lower side of the body close to the left of the throat and into the head, and the second extending along the upper face of the posterior visceral mass, and thence, after dividing into numerous large and small branches, to the various organs. From the tips of the various arterial branches the blood escapes into return channels, and these coalescing into larger vessels, the anterior (Ay1) and posterior (Ay) veins, the cir- culating fluid is emptied into the right (A2, A3) and left (A) auri- cles. From these the blood is injected into the right and left gills (gl) through a vessel (pa, pa1) which runs along the lower edge of each, and branches within them in regular, parallel, trans- verse channels. The blood, being thus aerated, is taken up by the return currents in equally minute, parallel channels, and poured into a larger vessel, (pv, pv1, pv2,) which, passing along the upper side of each gill, empties its contents into the right and left (atpv1) sides of the ventricle; and thus the circuit is finally completed. The gills, (gl,) which perform so important a part in this sys- tem, are two elongate, leaf-shaped bodies, placed symmetrically, OF CEPHALOPODA. 211 one on the right and one on the left of the body, half-way be- tween the upper and lower sides, and extend from the heart nearly to the anterior end of the liver. They are free from the latter, but are attached along one edge to the mantle ; and thus, during the contractions and expansions of the latter, the water is brought in large quantities against the surface of these respira- tory organs, and the commingled air is taken up and absorbed by the blood within their numerous capillary vessels. This pro- cess is called the aerification of the blood, and corresponds to the breathing of air in the lungs of warm-blooded animals. The nervous system preponderates largely in the head; and we find here, as in all of the higher groups of animals, that the tendency toward the head, cephalization, is a marked feature in the organism. The great centre of this system may be likened to a thick, broad, heavy ring, (fig. 125, g1, g2, op,) lying immedi- ately behind the jaws, and through which the throat, (th.) or gullet, passes. It is situated pretty close to the lower side of the head. Its principal regions are four in number, namely, 1, the so- called optic lobe, (g1,) which is a prominent bulging on the lower middle line of the main mass ; 2, a pair of small lobes, one on each side of, but slightly posterior to,the third; 3, another prominent swelling (g2) on the upper median line; and 4, the optic gan- glions, (e1,) two swellings, or rather expansions, one on each side and between the first and third masses, and so wide in their extent that they cannot be said to lie either above or below, but rather on the equatorial line. It is equally clear, too, that the optic nerve (fig. 125, op) for either eye springs from a point (fig. 124, op) exactly opposite the side of the throat (th). From the foregoing it would seem to be pretty evident that the upper (g2) and lower (g1) median lobes must share equally in the duty of forming by their junction the ganglions which supply the organs of vision, and that the so-called optic lobes, the first, are not ex- clusively devoted to the eyes. The principal nerves which originate from this centre are few, but easily demonstrable. In the fore part of the head there are two sets : one above, known as the throat, or (esophageal nerve and ganglion, and one below 212 THE ORGANIZATION the gullet, called the buccal nerves and ganglion, because they supply the parts about the mouth. From behind the brain (g2) three great nerves originate, namely, a single median and two lateral. The single median one (og) arises from the upper median lobe, and passes along the upper side of the liver, (Iv,) and branches to supply the various organs of the viscera. On this account it is called the visceral nerve. The two lateral nerves (n) originate from the pair of small lobes which lie on each side of the great upper one, (g2,) and belong to a system which has such complicated relations as to puzzle comparative anatomists in regard to what they correspond with in the group to which the Snail belongs. They are termed the mantle nerves; but as they are also continued, on each side, to the extreme posterior end of the body, and there supply the highly muscular fin, (fn,) in all probability they correspond to the great foot-nerves of the Snail (fig. 122, n, ng) ; and consequently the two small lobes from which they arise, notwithstanding they are situated rather above the level of the throat, homologize with the widely separated pair of ganglions, sub- cesohageal, (figs. 122, 123, g,) which lie at the lower borders of the gullet of the Snail. The reproductive organ (figs. 124, 125, ov) is an oval or sphe- roidal body, varying in size according to the season of the year, which lies to the right of the first stomach (st). Its outlet, oviduct, is a narrow canal which passes upward and forward, and opens near the posterior end (an) of the intestine. The ink-bag lies close to the side of the posterior end of the intestine, (at hv1,) and opens near the aperture of the latter. When alarmed, the animal beclouds the water about it by ex- pelling the dark brown contents of this bag. The rudiment of a shell (sh, sh1) is imbedded in the thickness of the mantle along the whole length of its lower middle line. It consists of a semi-transparent, amber-colored, delicate, horn- like substance, and has the shape of a straight sword-blade, gradually widening toward the point; and at its posterior end is fashioned into a hollow cone (sh1) with the concavity facing for- wards and obliquely upwards. In position it corresponds with OF CEPHALOPODA. 213 that of Spirula, another ten-armed cephalopod, which has a highly organized, cross-partitioned, spiral shell, very much like that of the common Nautilus, but placed in exactly the reverse position from the latter. The shell of the Nautilus occupies the same relative position as that of the Snail, whilst the shell of the Cuttle-fish, Squid, Spirula, &c, is placed upon the opposite side, i. e., the lower side of the body.* * Looking at Nautilus from this point of view, the highly muscular " hood " falls very naturally into the place of a creeping disc, or foot; and in this respect it agrees in position with what the old HoUandish naturalist Rumphius ascribes to it when the animal is creeping with the shell above the body, like that of a Snail. 214 THE RELATIVE RANK OF CHAPTER XIL ARTICULATA. There is one feature in the organization of Articulata, and indeed the most prominent one, which would appear to be strongly demonstrative that this grand division ought to be classed in a lower rank than that of Mollusca. I refer to the repetition of similar parts in Articulata, as contrasted with the total absence of this character in Mollusca. Were it confined to the exterior, we might ascribe to it a merely functional char- acter, a jointing of the shelly or parchmenty covering in order to produce a complete flexibility of the body; but, as we find it equally conspicuous among the internal organs, the intestines, heart, lungs or gills, nervous system, and the reproductive sys- tem, one cannot avoid the conclusion that it is typical of the whole organization. As it has already been shown (pp. 82, 84) that in many cases this repetition of parts is merely the multiplication of a kind of obscure individuality, it may be said, in a not very far-fetched sense, that the group of Articulata is composed of compound individuals, whereas the group of Mollusca, hardly excepting the Bryozoa, Tunicata, and Salpae, consists of single individuals, which possess the utmost uniformity of organization. It is true that the Articulata progress far in that direction; but yet the highest of them, the Insects, do not attain to that singleness of character which exists even in the lower middle ranks of Mol- lusca. But as this is not the only available character by which we may judge of the point in question, and as there is a more universal and elevated quality, which, under the form of instinct, is so much more highly developed among the immense numbers of the superior ranks, the Insects and Spiders, we can hardly refrain, from a psychical point of view, from classing the Ar- ARTICULATA AND MOLLUSCA. 215 ticulata as a whole, if not above, at least fully on a par with the Mollusca. There is a remarkable correspondence to each other in the respectively repeated parts; for example, the nerve ganglions or knots correspond to the joints of the body ; so do the successive chambers of the heart, and the breathing apertures, stigmata, or gills, which open along the sides of the joints. This is especially noticeable in the lower kinds of Articulata ; but as we ascend to- ward the more elevated groups, these repetitions are subjected to the same systematic reduction as we have seen operating among Zoophytes. Of all the Articulata, perhaps none are so lowly organized, and yet at the same time exemplify the typical idea of this di- vision so fully, as the Tape-worms. These I have already given an account of, (p. 83,) and I need, therefore, merely to recur to them here for the sake of bringing their characters into place at the lowest point in the successively rising scale of rank. The much more highly organized Myrianida, which I have also described, (p. 80,) will serve as an example of the extent to which the marine worms carry out the idea of serial repetitions, and through a much greater range than Taenia, in fact to the high- est degree that is known among Articulata. It might seem to you that on this account Myrianida should rank below Taenia; but the latter is far inferior to the former simply because it almost totally lacks some of the organs which are so highly developed in the marine worm, and therefore the diversity and degree of specialization being also less than in the Myrianida, it of course stands lower in the scale. Bonellia. The most decided step toward that uniformity of organization which culminates in the highest orders of Insects is taken by a group of worms which, curiously enough, until of late years has been classed by almost all naturalists among the Tre- pangs, — one of the classes of the grand division of Zoophytes. To this group belongs the worm whose organization I have illus- trated by these diagrams (figs. 126, 127). There is scarcely a trace, only a mere rudiment, of the external locomotive append- 216 THE ORGANIZATION oi)i ov't g Fig. 127. ov* Us gl ov1 Fig. 126. ages and gills so numerously repeated along the sides of the body of Myrianida, (fig. 43,) and the interior, with the exception of the string of numer- ous nervous ganglions, (fig. 126, g1,) pre- sents a uniformity of organization scarcely inferior to that of Insects. When in its native habitat, a cavity in a rock on the sea-shore, it extends its narrower anterior end (hd) to an enormous length, as much as eight times as long as the body, and expands the tip side- ways, so as to give the whole proboscis the form of a very high T with its right and left arms curled more or less back- wards. The mouth (m) is not, as one would be apt to suppose, at the Fig. 126. Bonellia viridis. Rol. One half natural size. A diagramic view of a marine worm, in a contracted state, hd, the proboscis ; m, the mouth; st, the stomach; i, the intestine; a, the posterior end of i; brl, the respiratory organs; br, the point at which br1 communicates with the intestine; h, the heart; h1, the median dorsal vessel; h2, the same in the proboscis; A4, point of junction of A2 with the lateral vessels (h3, h5); hi, point of union of h5, A3, under the stomach; A8, the vascular ring about ov3; A6, A9, a small posterior vessel; g, g1, o3, the ven- tral nervous cord ; o2, the nervous collar which follows the path of the lateral blood-vessels in the proboscis; ov, the reproductive organ ; ov1, the matrix; ov2, the outlet of ov1; ov3, the trumpet-shaped entrance to ov1. — Compiled from the illustrations of Lacaze Dulhiers. Fig. 127. A diagramic end-view of fig. 126, from behind, i, the intestine; br1, the respiratory organs; br, point of junction of or1 withi; h, the heart; A3, lateral blood-vessels; A7, inferior blood-vessel; g, the ventral nervous cord; ff2, the upper commissure of the lateral branches (ff*) of the nervous collar; ov1, the matrix; ov2, outlet of ov1; g1, lateral branches of g. OF WORMS. 217 end of the proboscis, but at its base, and exactly in the inferior middle line of the body. Starting from the mouth with consid- erable breadth (st), the digestive canal thins rapidly to a small calibre, and winds in several overarching folds (i) alternately from one side to the other, until it comes to a termination (a) at the posterior end of the body. The respiratory organs, if such they may be called, are a pair (figs. 126, 127, br1) of spindle-shaped sacs, which are at- tached on each side of the intestine, and open (at br) into it just before its posterior termination (a). The whole surface of these sacs is covered by branching tubes, which form so many pro- longations from the main cavity upon which they are based. The circulatory system, owing to the enormous extensibility of the proboscis, has a more complicated appearance than really exists. That part of it which most probably corresponds to the heart (A) lies in the posterior half of the body, above the intes- tine, and is to be distinguished from the rest of the system by a considerable thickening at that point, and a puckering of its wall. From the heart the blood is impelled into a vessel (A1) which passes along the middle line of the body and proboscis to the tip of the latter; at this point (A4) it divides right and left, and follows the borders of the T-shaped part along the front and then the back edge, and then courses on each side (A3, A5) of the main stem to the body. Passing on each side of and below the gullet, close to the mouth, the vessels make a junction (A7) behind the latter, but immediately separate to form a ring (A8) about the trumpet-shaped entrance (ov3) of the emptying con- duit, matrix, (ov1,) of the reproductive organ, and then unite again into a larger single vessel, which carries the blood along the lower side of the body to the double posterior cavity of the heart. From thence the blood passes upward and forward into the main chamber (A) from which it started. If, now, we take a foreshortened view (fig. 127) of this system, we shall see that it is a mere ring about the intestine, with the heart, (A,) and its anterior prolongation, above ; the two branches along the limbs and stem of the T-shaped proboscis forming the two lateral 218 THE ORGANIZATION OF halves (A3) of the ring ; and the main recurrent vessel, (A7,) along the lower middle line of the body, standing at the junction of the vessels which come from the proboscis. The nervous system has the same apparently complicated dis- tribution as the circulatory system, but it is even more simple than the latter. The main portion of it is a thick string (g) which rests on the lower middle line of the body, below all the other organs, and extends, with scarcely a diminution in its thickness, from the mouth to the posterior end of the intestine, (from g to g3). At numerous points along its whole length it gives off at right angles, on each side, parallel twigs (g*) which taper into slender threads and bury themselves in the thickness of the highly muscular skin. According to Lacaze Duthiers, from whose figures the diagrams are constructed, there are no ganglionic swellings where these twigs are given off; but yet, inasmuch as we find, in most of the Articulata, such swellings where branches diverge, I think I shall not err if I assume that we have what are essentially the same in Bonellia. Beside these lateral twigs, there are others which branch over the various or- gans. That part of the system which corresponds to the so-called brain and nervous collar of the higher groups, is most singularly disguised in this animal, and is used, it would seem, merely for the purpose of touch. The part in question arises from the anterior end (g) of the main ventral cord, and passes, on each side of the throat, into the proboscis. There the two branches (g2, g*) follow its margin, just within, and below the level of, the line of vessels (A3, A4, A5) which run there, and meet along the front of the trans- verse projections. The latter are said to be extremely sensitive to touch, and apparently in accordance with this, the nervous cord sends off innumerable minute threads which penetrate the skin in the same way that they do in the tactile organs of other ani- mals. Throughout the whole length and breadth of the probos- cis the nervous collar preserves a uniform thickness, which is less than one half of that of the main ventral cord (g); and there is no part of it which might be called the brain, properly speak- ing; unless we judge that to be it, from its position, which lies at WORMS AND CRUSTACEA. 219 and about the junction of the lateral halves of the collar, and which exhibits such a high degree of sensitiveness. The reproductive system consists of an egg-bearing portion (ov) and the emptying conduit, (ov1, ov2, ov*,) or matrix, as it is called. The former is an elongate narrow mass, with an irregular surface, which stretches along the lower median line of the body, from its posterior end to its middle, and just above the main nervous cord. The matrix (ov1) is a hollow, spindle-shaped body which opens (ov2) exteriorly not far behind the mouth, and close to the main nervous cord, (g,) either just to the right or the left of it. Not far from this outlet a trumpet-shaped body (ov3) projects from the upper side of the matrix. The trumpet is hollow, and forms a means of communication between the cav- ity of the body and the interior of the matrix, and thence with the exterior. When, therefore, the eggs are dropped from the ovary (ov) they float freely in the body cavity, and in process of time are taken up by the trumpet and passed into the matrix, and by that are cast out, through its inferior opening, (ov2,) into the surrounding element. The various transitions of form from the lower to the higher groups are so clearly exhibited to the eye among the Articulata, that I would be glad to find time to illustrate all the details of the series of changes which the organs pass through in order to arrive at the most elevated ranks of organization; but I must content myself with a mere indication of some of the great steps, regarding only the more superficial parts of the body. The Crustacea, such as shrimps, lobsters, and crabs, stand next in rank above the Worms. In this group, or class, as it is called, we find, as we pass from the simpler to the more highly organized, i. e. from the shrimps to the lobsters and thence to the crabs, that the tendency is to mass or concentrate the body in front, and thin it out behind. Those Crustaceans which stand lowest in this class exhibit this tendency by a lengthen- ing of the anterior rings of the body, — as is shown in this fig- ure, (fig. 128,) — forming wrhat is called a head-chest, or cephalo- thorax (cr). Eventually, as we ascend the scale, we find this 220 THE LAWS OF CENTRALIZATION cephalothorax becoming a prominent feature and the tail a less conspicuous one; the former gradually extending backwards so as to overlap several of the rings behind it, whilst the latter be- comes by degrees bent under the fore- part. In this condition you will find the lobster; and in the crab, by the still further carrying out of this law,— as the most eminent and profound of American naturalists* has shown it to be, —the tail is almost entirely obscured, and the cephalothorax covers the entire length and breadth of the body. In the next higher class, the Arach- nida, or Scorpions and Spiders, the law of centralization and cephalization (ten- dency toward a head) is carried out in a different form from what appears among Crustacea. Among scorpions the body is divided into two principal regions, a chest, so called, and a tail, but both are elongated and distinctly ringed. In the Spider-group, at least among the highest of them, both the chest (fig. 129, cr) and tail, or abdomen (t) more prop- erly speaking, are concentrated, and the joints are entirely obliterated. We have thus a dis- tinct specialization of two parts of the animal, a division of the body which foreshadows the more eminent Insects; and in still further con- firmation of the tendencies of this group, we find among the highest of them, the Garden Spiders and the like, an initiatory step to sep- Fig. 128. Fig. 129. * See J. 1). Dana, in Silliman's American Journal of Science, 1856, vol. xxn. Fig. 128. Cyclops quadricornis. Mull. 50 diam. A fresh-water, shrimp- like Crustacean, seen from the back, cr, the cephalothorax ; t, the tail; /, the AND CEPHALIZATION. 221 arate that part of the head-chest which embraces the mouth and eyes from the region behind it. The full realization of this process we find in the free and movable head of Insects. They, of all the great division of Articulata, attain to the highest degree of cephalization. Fig. 130. This figure (fig. 130) of the common Carrion-Beetle will serve larger and f1, the smaller pairs of feelers; 1, 2, 3, the ends of the natatory pad- dles ; m, the throat; st, the stomach; i, the intestine; a, posterior end of i; e, the single median eye; A, a heart-like cavity, but not pulsating ; es, the exterior egg-sacs, partially empty; es1, the funiculus which joins es to the body; eg, the egg; p, the germinal vesicle of eg. — Original. Fig. 129. Epeira trifolium. Hentz. Natural size. A " garden spider," seen from above, cr, the cephalothorax; t, the abdomen; pi, the feelers, or palpi; /, I1, I2, P, the four pairs of legs. — From Hentz. Fig. 130. Necrophorus Americanus. Oliv. Slightly magnified. A common Carrion-Beetle, seen from above, e, the antennae or feelers of the head; i, upper jaws; II, feelers of lower jaws; in, iv, upper lip; v, top of the head; 222 THE ORGANIZATION to illustrate the degree of centralization and cephalization of the lower orders of Insects, and this other one, (fig. 131,) a profile, internal view of a gigantic moth, may typify the perfection of the law. In the carrion-beetle, (fig. 130,) the head (v) is perfectly distinct from the chest, (vni,) but yet it has a broad neck, (vi,) M h qi th b cr iii i ov whereas that of the moths, flies, and bees,—insects of the three highest orders, — is a narrow pivot. The chest (thorax) of the bee- c g gl l st g- g* n y* d o a v ' Fig. 131. tie remains as yet in two quite distinct divisions, (vm and ix, x,) whilst in the moth, (fig. 131,) &c, it is an almost or quite solid piece of concentration. As regards the abdomen (fig. 130, xi/ to xi") of beetles, and the nearly related lower orders, the rings are quite distinct, and among the higher orders they are as a general thing much more consolidated, and in fact so closely united in certain moths, butterflies, bees, hornets, and flies, as to appear to be altogether massed into one. The common House-fly is an example of the highest degree to which the law we are speaking of rises, and I am inclined to look upon the order Diptera, to which it belongs, as the most eminent vi, the neck; vn, the compound eyes; vm, the prothorax, or first joint of the chest; ix, the scutellum of the mesothorax; x, the third or last joint of the chest; xi' to xi", the joints of the abdomen; m, the left anterior wing ; the right one is cut off; n, n1, the posterior pair of wings ; the vein-like ridges (ve) are omitted in n1; q, the thigh ; t, the tibia; w, the tarsi, or foot-like part of the leg, terminated by double claws; s to s\ the apertures (spiracles) of the breath- ing organs. — From Leconte. Fig. 131. Sphinx Ligustri. Lin. The Privet Hawk-Moth. Natural size. A longitudinal, sectional view, an, antennae, or feelers; hd, the head, or first joint of the body; th, the thorax, consisting of the 2d, 3d, and 4th rings; b to b1, the eight rings of the abdomen; I, the base of the legs; p, the tubular proboscis; gl, the gullet; st, stomach ; cr, crop; t, intestine; a, posterior end of i; h, A1, A2, heart; sg, superior nerve ganglions of head; g, g1, ganglions of the thorax; c, nervous collar ; n, main abdominal nerve; g2, g3, g*, ganglions of n; ov, ovary; d, oviduct; o, exterior aperture of d. — Slightly altered from Newport. OF INSECTS. 223 of all in the class of Insects. We have, in the peculiar mouth apparatus of the fly, the large, extremely versatile head, the com- pact thorax, the single pair of wings, and the concentrated abdo- men, a series of specializations, reductions to uniformity, and, in fine, the very acme of cephalization, such as are to be found in no other order of Insects. As an illustration of the internal organ- ization of Insects, I have selected one of the moths, (figs. 131, 132,) known as the hawk-moth, or Sphinx. I have already Fig. 132. indicated its division into the three distinct regions, head (hd), thorax (th), and abdomen (b to b1). The head carries a pair of feelers, antennce, (an,) and a tubular proboscis, (p,) with which it sucks up the fluid nectar of flowers and various other juices. A pair of compound eyes project from the right and left sides of the head, like those of the carrion-beetle (fig. 130, vn). The thorax (th) has two pair of wings attached at the sides, and three pair of legs (/). The abdomen consists of eight incon- spicuous rings (b to bl). The entrance to the mouth is between the two slender, furrowed pieces which together form the proboscis (p). The gullet (gl) passes from the mouth in a straight line through the thorax, to the abdomen, and there joins the stomach (st). The latter is a broad, puckered sac which tapers behind into a considerably con- voluted intestine (i). Near the junction with the gullet is an oval sac which performs the office of a crop (cr). The intestine (i) terminates by an opening (a) at the extreme posterior end of the abdomen. The circulatory system possesses such an extreme simplicity as to induce some naturalists to place the Spiders, which seem Fig. 132. An ideal end-view of fig. 131. 6, the periphery of the body; /, the base of the legs; st, the intestine; A, the heart; sg, the super-oesophageal ganglions, or brain ; ff, the sub-oesophageal ganglions; c, the nervous collar ; ov, the pair of reproductive organs; d, the oviducts; o, aperture oft/; br1, the respiratory tubes, trachea;; br, external aperture, spiracle, of br1. — Original. 224 THE ORGANIZATION to have a more complicated system, above Insects. But the truth is, the blood circulation in Spiders is not so intricate nor so highly specialized, when compared with that of Insects, as has been asserted. In Insects the only definitely circumscribed canal of the system is the so-called dorsal vessel, or heart (A, A1, A2). It is a mere tube which lies close to the back, in the mid- dle line, and extends from the head to the posterior end of the abdomen. It is open at both ends, (A, A2,) and at the successive ' points where it is narrowed are a pair of apertures, one on each side, which are guarded by a valve on the inside. There is also a pair of internal valves at the posterior opening. The process of circulation is a very simple one : the blood enters the poste- rior and lateral apertures of the heart as it expands; then upon its contraction all the valves are closed and the blood is forced toward the head, and, passing out at the anterior opening, flows, in numerous currents, and, at first appearances, in undetermined channels, among the various organs, and into the legs and wings. A careful examination of some of the more transparent insects, such as the May-fly, (Ephemera,) Gall-fly, (Cynips,) Plant-louse, (Aphis,) Lace-winged fly, (Chrysopa,) Dragon-fly, (JEshna, Agrion, Libellula,) and the grub or worm of many more, has convinced me, that, notwithstanding the apparent lack of walls to the channels of circulation, the course of the blood is none the less definite; always passing in one set of channels going from the heart, and returning toward it in another set. This is particularly noticeable in the head, legs, and wings. The breathing organs consist of numerous branching tubes, trachea, (fig. 132, br1,) which spread out from certain fixed points along the right and left sides of the body. The air enters the body through minute apertures, spiracles, (br,) of which there are two in each ring, one on each side, as in this beetle (fig. 130, s to s1). At each spiracle (fig. 132, br) a tube (br1) arises and branches into innumerable twigs, which spread themselves over the various internal organs. The walls of the tracheas being very thin, the contained air finds a ready absorbent in the circu- lating fluid. OF INSECTS. 225 The nervous system consists of a series of swellings, ganglions, united by threads, which extend from the head to the posterior end of the body, along its lower median line. In the head is a double ganglion, (sg,) the so-called brain, which lies across the upper side of the throat (gl) just behind the mouth. From the " brain " a thread passes around on each side of the throat to the lower side, and unites with the first ganglion (g) of the tho- rax. This constitutes the nervous collar, (c,) and serves to unite that part of the system above the intestinal tract to that below it. The anterior (fig. 131, g) of the thorax-ganglions is scarcely separate from the succeeding one, and the latter (g1) is the result of the intimate fusion of the second and third. Their consoli- dation corresponds to the degree of concentration that the rings of the thorax attain to; there being in the latter an imperfect separation between the first and second joints. The abdominal ganglionic chain (n) is single, and passes backwards in a direct line from the posterior double thoracic ganglion, with a ganglion (g-2, g3, g*) at nearly every joint. From these ganglions minute nerves pass off, right and left, above them and on each side to the various organs; and likewise similar nerves, arising from the " brain," supply the feelers, expand in the eyes, and branch over the upper side of the throat and stomach. The reproductive system lies in the posterior part of the abdo- men. It consists of a pair of bunches (ov) of wavy tubes, which converge into one channel, oviduct, (d,) on each side. The two oviducts pass down each side of the intestine to a point just in front of its termination, where they unite in one com- mon outlet (o) on the middle, inferior line of the body. The eggs are generated in the bunches of tubules, ovaries, (ov); and when ripe they pass into the oviducts, and thence through the common channel (o) to the place of deposit. 15 226 THE ORGANIZATION CHAPTER XIII. VERTEBRATA. As I have already and at considerable length (p. 124) dis- cussed the characteristic features of Vertebrata, I need not enter into any further details in regard to their relation to the typical form, but simply ask you to make the comparison for yourselves between the ideal figures (figs. 63, 64) of this type and the diagrams of the actual organization which I am about to describe. I hardly need to say that you will not find an identity in the details, but a perfect accordance in the relative position of the four systems of organs, namely, the nervous, ver- tebral, digestive, and circulatory. Among the lower groups of Vertebrata these systems are more clearly demonstrable in a diagram than among the higher ranks, as you may see by a comparison of this diagramic illustration of a Fish (fig. 133) Fig. 133. Fig. 133. Amphioxus lanceolatus. A diagramic figure of the Lancelet. Nat- ural size. /, the head ; v, v1, the notochord, or vertebral column ; vs, the sheath of v, v1; be, the buccal cirrhi; j, the buccal ring at the entrance to the mouth ; I, II, oval bodies projecting freely into the buccal cavity; bo, the lateral bran- chial openings ; ff1, entrance to the throat or branchial cavity ; g, posterior end of the latter, and entrance to the intestine proper (i) ; i1, posterior end of i; Iv, Iv1, appendage to i, opening into it at Iv1; A, the heart; A1, A2, the anterior blood- vessels ; A3, recurrent branches of those, from A4, which supply I, II; A'1, A6, the OF FISHES. 227 with the ideal Vertebrate, (fig. 63,) when both are contrasted with the more complicated, warm-blooded quadruped (fig. 134). Amphioxus. The most lowly organized of all known Ver- tebrates is a fish which is commonly called the Lancelet, and sometimes the Sand-Eel, on account of its habit of burrowing in the sand of the sea-shore. It is so remarkably transparent that its whole internal organization can be seen with a good microscope. It has no external appendages excepting a circle of feelers (fig. 133, be) about the mouth, (/,) and therefore, for the lack of fins, the whole duty of locomotion devolves upon the highly muscular, lance-like tail. The head (f) is peculiarly adapted, by its sharp, thin front, for the purpose of penetrating the compact sand-beach. The mouth (/) is an elongate open- ing situated on the under side of the head, at a considerable dis- tance behind its front. The feelers (be) which surround it are largely supplied with nerves, and therefore in all probability are highly sensitive organs of touch, and serve as efficient means for obtaining food. Between the mouth and the entrance (g1) to the throat, there is considerable space, the buccal cavity, within which certain oval bodies (I, II) project from above like a pair of palates. The latter are covered by constantly vibrating threads, cilia, which keep up a current of water from the mouth toward the gills, (b to b1,) and at the same time furnish the means of floating fine particles of food into the throat. The entrance to the latter is a moderate aperture, (g1,) but the throat itself is a very large cavity, which performs at the same time the office of a breathing apparatus, or gill-chamber. Its sides are perforated by several parallel slits, (bo,) which extend from its upper (b) to its lower (b1) margins, through which the water pours, as between the dorsal artery; A5, the abdominal vessel; b, the upper, and b1, the lower point of junction of the branchial vessels (br) with the dorsal (A4, ffi) and ventral (A1, h5) vessels ; ac, abdominal cavity; ap, abdominal pore; nr1, the anterior, and nr, the posterior end of the main nerve or spinal marrow ; ns, sheath of nr, nr1; o, the eye; n, the olfactory nerve; nv, the facial nerves; ov, the reproductive organ. — From Owen. 228 THE ORGANIZATION gills of ordinary fishes, into the general cavity (ac) of the body, and thence passes out of the abdominal pore, (ap,) to the exterior world. The true intestine (i) commences with a moderate aper- ture (g) at the posterior end of the branchial gullet, and pro- ceeds to its termination (i1) in a nearly direct line. Near its beginning a saccular organ (Iv, Iv1) which is thought to perform the office of a liver, opens into it. The circulatory system can hardly be said to possess a heart. The oval enlargement (A) in the diagram is an exaggeration, merely to render conspicuous the position in which the heart belongs. The whole system of vessels is said, by those who have examined the animal in a living state, to contract from one end to the other. According to this diagram the blood courses from the central cavity, heart, (A,) in a backward direction, in a single vessel (A5) along the lower side of the body to the tip of the tail, and then, doubling upon itself, it passes along the upper median line (A6 to A4) of the general cavity of the body, and directly over the gill-chamber (b to b1) into the head. At the fore part of the gill-chamber it forks (at A4) and sends a branch into each of the ciliated palate-like bodies (I, II) of the buccal cavity; and after penetrating to the tips of these, the two branches double upon themselves, and, returning, (A3,) unite again into one vessel (A2). This continues its course along the dorsal median line (A2) further into the head to a point over the anterior edge of the mouth, and there, by two vessels, joins the return current, (A1,) which passes along the lower middle line of the gill-chamber to the heart. The circulation is further com- plicated by intermediate currents which pass from the upper median vessel (A4) directly downwards in smaller channels (br) which lie between the slits (bo) of the gills, and empty into the lower median vessel (A1) where it joins the stream coming from the head. In full-grown specimens of the Lancelet there are as many as fifty of these transverse branchial vessels. The more recent investigations of Quatrefages differ* in their * Quatrefages, Voyage en Sicile, vol. n. p. 12, and Annales des Sciences Naturelles, 1845, vol. iv. OF FISHES. • 229 results from what is given by Owen, inasmuch as the former represents the currents as passing from the heart (A) partly for- ward into the head, and in part through the branchial ves.sels (b, b1, br) upward to join the dorsal vessel (A4, A6) bearing the cur- rent from the head toward the tail, and from the latter re- turning to the heart in the lower median vessel, (A5,) which passes along the inferior side of the intestine. The vertebral column or spine is represented by a mere cord (v, v1) of jelly-like matter, which extends along the middle of the back, from the front (/) to the posterior end of the tail. It is enclosed in a membranous sheath, (vs,) within which it lies so loosely that it can be taken out entire by simply opening a gash along the back. It usually goes by the name of the notochord, and corresponds with the first rudiment of the spinal column of the embryo of higher animals.* The nervous system consists of a main cord (nr, nr1) and numerous branching prolongations which project right and left from its sides. At its anterior end (nr1) there is no sensible dilatation which corresponds to the brain. The nerves of the eye (o) and nose (n) arise from near its rounded end in the same simple way as the other less specialized nerves (nv) which spring up near them and branch in the head. The reproductive system is a mere elongated oval mass (ov) attached to the upper median line of the general cavity, just behind the branchial chamber. The eggs reach the outer world by dropping from the ovary into the visceral cavity and thence passing out through the abdominal pore, (ap,) an aperture which lies in the lower side just behind the heart. If now I have given you a clear understanding of the relation and nature of the organs of the Lancelet, there will be no dif- ficulty in comprehending, by the help of a few words of explana- tion, the organization of one of the highest of the Vertebrates. With the preliminary knowledge of the simpler structure of the one, the apparently puzzling complication of the other may be * See the embryology of the Turtle, in chap, xvn., where this body is called the chorda dorsulis. 230 THE ORGANIZATION resolved at a glance. In the Lancelet, and in all fishes, and even in the lower grades of reptiles or reptilian fishes, (Lepi- dosiren, chap, xvi.,) the head is not distinctly separated from the body; but, as we ascend the scale, through the groups of the higher reptiles, (Lizards, Turtles, &c.,) birds, and finally the warm-blooded vertebrates, Mammals, (figs. 26, 134,) the process of cephalization becomes more and more clearly marked by an external configuration, and within the head by a concentration of the regions of the brain, and the growing preponderance of the divisions devoted to the more delicate sensations of sight and reasoning. Fig. 134. Mammalia. — The body of the higher Vertebrates is divided into head, chest, and abdomen; the first contains the brain (fig. Fi«-. 134. A diagramic longitudinal section of a Mammal, sk, skull; v, ver- tebrae ; a, dorsal arches of the vertebrae; va, the upper and lower portions of the vertebral arch; j, lower jaw ; b, bone of the leg; m, muscle; d, teeth; t, tongue; a, gullet; *, thyroid gland; st, stomach ; i, intestine; i1, end of i; Iv, liver; p, pancreas; s, spleen; k, kidneys; k1, appendages to k, known as the suprarenal capsules; ur, outlet of k; bl, bladder; e, epiglottis, or entrance to the wind- pipe (f); I, lung; A, heart; ao, abdominal aorta; ao1, carotid artery going to the head; vc, vena cava inferior, or abdominal vein; la, pulmonic artery; dp, diaphragm ; o, the eye; en, cerebrum; cr, cerebellum ; n, olfactory nerve ; au, the outer ear; nr, spinal marrow, or main nervous cord; ov, the ovary, or egg- bearing portion of the reproductive organ ; fl, the trumpet-shaped Fallopian tube through which the eggs pass into the uterus (ut) ; vg, the vagina, or outlet of ut; mm, the mammae, or milk-bag. — From Oioen. Slightly altered. fl\ OF MAMMALIA. 231 134, en, cr) and the organs of sensation (o, n, t); the second encloses the heart (A) and lungs (1), and the third, which is sep- arated from the second by a transverse membranous, muscular partition, the d diaphragm, (dp,) is occupied by the stomach, (st,) intestines, (i,) liver, (Iv,) kidneys, (k,) spleen, (s,) bladder, (bl,) and the organs of reproduction, (ov,fi, Ut, vg). The first, the head, is in great part an expansion of the spinal column, / \ ii • n -,-, e ut vg h gn (v, va,) under the guise of the skull, Fig. 135. (sk,) and has appended to it the jaws, (j,) between which and the skull is the mouth, the enclosed tongue, (t,) and the entrance to the throat (g) and windpipe (e, f). The spinal column (v, va, a) consists of a longitudinal series of bones which, as it were, overarch the organs of the chest and abdomen and continue into the tail. Each bone of the series consist of a central portion, the centrum, (v,) and a hollow arch (a) above the latter. Within this arch the great nervous cord (en, cr, nr) runs from the skull, which is the first arch, to the tip of the tail. The ribs and bones of the limbs (b) are lateral ap- pendages of the vertebral column, to which they are attached by ligaments, and upon which they are moved backward and forward by muscles (m) which surround them. We have by this arrangement what appears to be a separation of the body into two distinct superposed cavities, the one containing the centre of the nervous system, and the other the visceral organs; but if now we turn back to the Lancelet, (fig. 133,) I do not think we shall revive any impression of such a state of things existing there. In the latter case we have a mere gelatinous cord (fig. 133, v, v1) underlying the nervous cord (nr, nr1); the Fi«r. 135. An ideal foreshortened view of 134, as if seen from behind. In ad- dition to the letters in fig. 134, there are dr, the skin; ac1, the periphery of the abdominal cavity (ac) ; g1, the posterior pair of sensory nerves; g2, the anterior pair of motory nerves; c, the glosso-pharyngeal nerve, forming in part the nerve of taste, which is concentrated (at gn) under the tongue. — Original. 232 THE ORGANIZATION former evidently having no sort of relation to the latter, as regards its connection with the other organs, in a functional sense, but purely one of position. Not only is this true of the Lancelet, but also of many other nearly related fishes, such as Lamprey- Eels, Myxine, and certain Sharks; and it is not until, by follow- ing up the series, we arrive among the considerably more elevated forms, that we find the arch completely encircling the nervous cord ; and not even in the whole class of fishes are the successive arches so close together as to lead any one but an over-eager advocate of such a view to conceive that the series of perfora- tions which they enclose are functionally a closed cavity. The open spaces between the successive arches are much wider than the spaces which they enclose, and it is only in the highest an- imals that this proportion is reversed. Yet even in the latter case, the interspaces are by no means closed ones, but are open to a greater or lesser extent to allow the passage of the great lateral nerves (fig. 135, g1, g2) which diverge right and left from the main cord (nr) and branch through the various organs.* The digestive system comprises the mouth, teeth, (d,) a slender gullet (g) leading through the diaphragm (dp) to an oval expan- sion, the paunch or stomach, (st,) then contracting in a long, con- voluted intestine (i) which terminates (i1) at the posterior end of the body. Appended to the fore part of the intestine, just behind the stomach, is the large concavo-convex liver, (Iv,) and close to it the spleen (s). Near the back are the kidneys, (k,) which filter off the waste fluid of the body, and through slender tubes (ur) pour it into the bladder (bl). * Should any one urge that the vertebral arches embrace what is to all intents and purposes a closed cavity, as contradistinguished from the visceral chamber, and that in the lower Vertebrates the mere rudiments of the arches are sufficient indications of the universal presence of such a cavity, I am willing to admit the truth of the assertion, provided that I may claim at the same time that the car- tilaginous box of the head of Cephalopoda, and the more or less complete arches which border the main nervous cord of Insects, form what is essentially a similar segregated cavity. The basis of difference between the Vertebrata and the other grand divisions lies in the notochord, and not in the presence of an imagi- nary upper and lower cavity. OF MAMMALIA. 233 The circulatory system has its starting-point in a highly mus- cular, fourfold sac, the heart, (A,) which lies about in the median line of the chest, below the gullet (g) and close to the breast- bone. The principal vessels connected with it are the arteries which carry the blood to the head, lungs, and posterior regions of the body, and the veins in which the return currents bring back that fluid to the heart. The course of the blood in com- pleting its circuit is rather complicated, if we follow it in all its details, but the essential lines of travel are quite simple in their connections. Starting from one of the chambers of the heart, which is called the left ventricle, the blood passes, through the great artery, (ao,) a short distance forward, and then, as it turns upward, a smaller current diverges toward the head in what is called the carotid artery, (ao1,) whilst the main current (ao) con- tinues up to the lower face of the spine and follows its line backwards in what is known at this part of its course as the abdominal artery. From the latter numerous vessels are given off to the various visceral organs, and from the carotid (ao1) the organs in the neck and head are supplied with branches. The return currents start in the minute, branching, capillary vessels which are continuous with the equally minute, branching ter- minations of the arteries. The capillary return vessels, veins, gradually unite in fewer and larger vessels, which finally coalesce in one large vein in front, coming from the head, and in another great vein behind, (vc,) coming from the abdomen. Each vein, the vena cava superior, and the vena cava inferior (vc), empties its contents separately into the right auricle of the heart, and thus one branch of the circuit is completed. The other branch of the circulation is devoted purely to the aeration of the blood. The venous blood passes from the chamber in which it was received, i. e. the right auricle, into the riglifventricle, and from thence it is thrown through the pulmonic artery (la) into the minute branch- ing vessels of the lungs (I). After being aerated there, the blood flows through the capillary veinlets into the great recu>rent vessels, the pulmonary veins, from each lung, and thence enters the left auricle, and finally completes its tour by passing into 234 THE ORGANIZATION the left ventricle, the same from which it went out in its first circuit. The organs of respiration are a windpipe and a pair of lungs. The windpipe (f) opens (at e) at the root of the tongue, and after passing backward a considerable distance, and in front of the gullet, (g,) it forks into two branches, of which one goes to the right and the other to the left lung. The lungs (I) are great sacs divided into numerous, irregular compartments, like the in- terstices of a sponge, in the thickness of whose meshes the mi- nute arteries and veins pass and repass, to carry the blood from and to the heart, during the process of aerification. The nervous system I have already stated to lie in a partially overarched furrow upon the back of the spinal column. The anterior part of it, the main organ, (en, cr,) is enclosed within the cranium, (sk,) and consists of two great double masses, whose halves lie symmetrically right and left of the median line of the head. The anterior mass, the cerebrum, (en,) is by far the greater of the two, and from it proceed the nerves of the two most deli- cate senses, namely, sight (o) and smell (n). The posterior mass, the cerebellum, (cr,) is completely overlapped by the cerebrum in man, but projects beyond it in the monkeys and the groups below them. The nerves of hearing and of taste (fig. 135, gn, c) arise from the medulla oblongata, that part of the brain which underlies the cerebellum (cr) and forms the immediate transition to the main cord, (nr,) or spinal marrow, which joins it at the base of the skull. The nerves which control the motions of the body, the motory nerves, (fig. 135, g2,) and the nerves of sensa- tion, (g1,) originate in pairs from the right and left sides of the spinal marrow, (nr,) along its whole length. The reproductive organs lie symmetrically right and left of the axis of the body, and consist of a pair of small, oval, egg-bearing organs, the ovaries, (ov,) and two outgoing conduits (fl) which unite in one common receptacle, the uterus (ut). When the eggs are ripe, they drop from the ovary (ov) into the trnmpet- shaped mouth (fl) of the conduit, Fallopian tube, and thence are conducted to the uterus (ut). There they undergo a change. OF MAMMALIA. 235 and, taking on the form of the parent, remain until they have attained to a certain degree of development, and then make their exit through the vaginal outlet (vg). For the nourishment of their young the warm-blooded Vertebrates possess an organ for the secretion of milk, which is called the mammary gland, (mm,) and which, in such animals as the cow, sheep, and goat, is known as the milk-bag, and either hangs, as in most of the quadrupeds, between the hind legs, or extends to a greater or less distance along the belly. Among the higher groups the mam- mae lie between the fore limbs. 236 THE REAL AND THE IDEAL CHAPTER XIV. THE DISTINCTNESS OF THE FIVE GRAND DIVISIONS. I think I have said enough already to convince you that I do not advocate the possibility of a transition from one grand divis- ion to another; and it is here that I shall probably disappoint many who believe that there are no distinct types of form in the animal kingdom. Even Lamarck advocated the distinctness of certain types, and moreover he expressed a belief in the possi- bility of discovering others. That there are certain ideal transi- tions or relations between the five grand divisions, you must have learned from the description of these diagrams of the ideal types (figs. 55 to 64). Life is the first ideal relation among them that impresses us ; then there is bilaterality, then bipolarity, i. e., the opposition of above and below, and in more or less in- timate relation with this is the tendency of the nervous system to condense toward the side opposite the heart, and at the same time to preponderate in the regions next the head. All these are ideal, and are the expressions of a gradational prog- ress from a lower to a higher type; from an idea of low, un- determined, diffuse organization, as in Protozoa, to the highest degree of specialization and concentration, such as is to be seen in the Vertebrates as a whole, and in Man; in whom the crown- ing effort was centered on the brain, the throne of thought, before which all the other faculties stand in inferior ranks. Now if these which I have called " ideal relations between the great types " were not so, but rather real relations, i. e., rela- tions of consanguinity, we ought to be able to trace the organi- zation of an animal of one type into that of another; and in order now to show that this cannot be done, I shall proceed to make comparisons between the types of the grand divisions, as RELATIONS OF ANIMALS. 237 if I were trying to prove their identity; and in this way I shall be able to make the closest comparison possible. For the sake of conformity to my previous method of procedure, I begin with the lowest types, and from them rise to the higher forms. Protozoa and Zoophyta. The first on my list is the alleged transition from the Protozoa to Zoophyta. Among Protozoa the Vorticellce (Epistylis, p. 161, fig. 95) are those which have the closest resemblance to Zoophyta; and among Zoophyta, Hydra (p. 55, fig. 27) most resembles Vorticell®. Let us place these two forms side by side and try to find what are their points of relationship, if they have any. This can be most easily ac- complished by recurring to the descriptions which I have already given of their internal structure. The Epistylis, or " Bell-ani- malcule," as I have shown, (p. 161, fig. 95,) possesses an oblique mouth, (m,) a spiral gullet, (g, g1,) a one-sided digestive cavity, (m to s,) a peculiar pulsating sac, or contractile vesicle, (cv,) and an internal organ of reproduction (n). On the other hand, I have described (p. 55, fig. 27) Hydra as a simple sac or tube whose mouth opens directly into a wide digestive cavity, (s,) which occupies the whole length and breadth of the body, to the exclusion of any other organ whatever. The Epistylis has a type of organization which unmistakably allies it with such animals as Zoothamnium, (p. 175, fig. 104,) Stentor, (p. 62, fig. 30,) Paramecium, (p. 163, fig. 96,) Pleuronema, (p. 170, fig. 99,) Dysteria, (p. 171, fig. 100,) &c, all of which are connected in a common type by their spiral contour, oblique mouth, one-sided digestive cavity, contractile vesicle, and a pe- culiar, internal, reproductive organ. There are certain of the Protozoa which would appear to be an exception to the typical oblique form ; such an one is represented in this figure (Podoph- rya, p. 51, fig. 25). It is an irregular, four-sided, inverted pyra- mid, whose apex rests upon a stalk, and whose four corners are occupied by a group of feelers (/) ; and within are the charac- teristic contractile vesicle (cv) and reproductive organ (n). This is its conformation in its adult stage, when, as is frequently the case with many other animals, it assumes a disguised shape, and 238 A COMPARISON OF belies the relationship which its internal organization reveals. In its younger stages (fig. 25, A, B) its exterior form possesses the characteristic obliquity of the type to which it unquestion- ably belongs. In the Hydra, on the contrary, we find altogether different ten- dencies. What are the peculiarities of the type to which it be- longs I have already (p. 177) described, when speaking of the organization of Zoophytes; but I wish at this point to say a few words in explanation of those nearly related Hydroids which form the connecting link between it and the more complicated forms. The first one that I shall take up is interesting because it not only illustrates this transition, but also displays a bilateral character in a most unquestionable light. It is a Hydroid by the name of Tubularia, (fig. hid 136,) and is common on the whole North At- lantic coast, both in Europe and America. The cylindrical stem (s to s1) supports a distinct head, (hd,) which at the base bears a wreath of twenty to twenty-five tentacles, (t,) and pro- jects into a broad, cy- lindrical proboscis, (p,) whose end is pierced by the mouth and covered by several rows of short tentacles (t1, t2). Upon cutting across the stem, we find that it does not embrace a single cavity like that of the Fig. 136. Hydra, but that its centre (fig. 137, c) is a A ch Fig. 137. Fig. 136. Tubularia indivisa. Lin. Natural size. Marine. From Boston Harbor, s to s1, the stem; hd, the head; t, the posterior tentacles, or corona ; t1, t2, the tentacles of the proboscis (p). — Original. Fig. 137. An actual transverse section of the upper part of the stem of fig. HYDROIDA WITH PROTOZOA. 239 solid mass of cells, and its periphery is occupied by several lon- gitudinally arranged tubes (ch, ch1). One (ch) of these tubes is much larger than the others; and if we trace it toward the pos- terior end of the stem, it appears as the original one from which the others have arisen right and left. It is, therefore, the domi- nant feature of the stem, and constitutes the basis upon which to estimate the relations of the regions about it. A line drawn through it to the opposite side (through A, B) divides the stem into symmetrical right and left parts; that is to say, the stem is bilateral, and its periphery is occupied by several laterally re- peated tubes. The crown of tentacles (fig. 136, t) at the base of the head is not, as it appears to be, a single row, but is composed of at least three circles placed one before the other relatively; but yet as the feelers of each circle alternate with those in the others, all three circles are enabled to overlap each other so closely as to produce the appearance of a single one. If, however, their development is watched during the earlier stages of growth, their separate origin can be easily verified.* The manner in which the tentacles of the proboscis comport themselves now and then illustrates, in a very apt way, their 136. 12 diam. a, the parchmenty sheath ; b, the outer wall; d, the inner wall; c, the solid core ; ch, ch1, the channels at the periphery of c. — Original. * This diagram (fig. 138) will serve to illustrate the manner in which the ten- tacles of the crown originate and change their position during the process of de- velopment of the young. Tubularia is usually born with eight tentacles in the co- rona. These may be represented by those in the centre (i, I, A, D) of the figure. Next, eight more (n, n, B, E) begin to develop farther back than those of the first group, but as they grow they gradually press forward and fill the intervals be- tween the latter (i. e. as if 6 were to follow the direction indicated by the arrow). Meanwhile a third group (in, in, F, C) of sixteen springs up still farther back than the second, each tentacle (in) alternating with those of the first (i) and second (n) groups, and in process of time they too push forward and occupy the intervals between the members of the first and second groups (i. e. as if a and c were to follow the directions indicated by the arrows). This is the way in which the tentacles (fig. 136, t) of the corona of an adult head happen to appear to be in a single circle. Upon close examination, however, even of a very old head, one may detect a difference in the relative level of these tentacles. 240 THE BILATERALITY OF arrangement in the crown. Usually the proboscidal tentacles stand in three or four transverse circles, the older ones (t1) near- est the end, and the youngest (t2) the farthest from it; but occa- sionally the mouth of the proboscis expands very widely, like the end of a trumpet, and at the same time decreases its length, by which the alternating tentacles of the three circles are reduced to one level, so as to lie in a single unbroken circle. The change of place which they undergo in order to arrive at this position is precisely that to which the feelers of the corona, at the base of the head, are subjected as they successively develop in their re- spective circles. This diagram (fig. 138) presents an end-view of three circles of tentacles, and is intended to illustrate their rel- ative position at the end of the proboscis. The inner circle rep- resents the larger ones (i) nearest the mouth; those of the next outer circle (n) alternate with the first; and in the third or out- ermost circle they (in) alternate with those of both inner circles. They appear, therefore, to be arranged in spirals, which, as the dotted lines indicate, may wind either to the right or to the left; but a study of their process of development discloses the fact that their arrangement is simply one of alternation, and not that of a true spiral. In order to bring the three alternating groups into one, the tentacles of the two outer circles (n, in) have but to move in direct lines toward the centre, as the arrows indicate ; or, what is more frequently the case, reversing the direction of the arrows, the two inner (i, n) must move outwardly. Fig. 138. Diagramic representation of the relative position of the tentacles of the proboscis of Tubularia, (fig. 136, p,) and serving to illustrate the mode of development of the tentacles of the corona (fig. 136, t). A, B, C, D E F the same as i, n, m, for which see the body of the work. — Original. Fig. 139. The Scyphostoma of A urelia flavidula. Per and Les. Magnified 8 diameters. The ends of the tentacles (t) are left out of view (see p. 67 6*. D E F Fig. 138. HYDROIDA. 241 The tentacles (fig. 139, t) of the Scyphostoma of Aurelia (p. 70, fig. 37) seem to be in a single circle, whereas < they have the same arrangement as those of the corona of Tubularia. The internal organization of the Scyphostoma, as well as the mode of de- velopment of its tentacles, has an unquestion- able relation to right and left. At a very early period the interior is subdivided into four longi- tudinal, partially separated compartments, by the projection of four equidistant, thick semi-parti- tions. In full-grown individuals (fig. 139) these semi-partitions (fig. 140, a,) extend from the base of the tentacles (i, tl) half- way to the bottom of the general cavity (gc). On account of their transparen- cy, they have been mistaken for tubes, and the fold (b, b1) opposite each one of them, in the muscular layer, has also been erroneously described* as a chan- nel in which the fluids circulate; but each of the first (a) is a solid, jelly-like mass standing out like a pilaster, and the second (b) is so doubled upon itself longitudinally as to present a quadruple contour, like the two outer and two inner profiles of a tube. The thickness of the walls at the base (d) of the circle of tentacles has also the appearance of a circular tube into which the four supposed lon- 34). a, the base; m, the partially extended proboscis, encompassed by the ten- tacles (t) ; d, the incipient formation of the discs of the Ephyra, foreshadowed by transverse rings. — Original. Fig. 140. An end-view of the head of fig. 139. 20 diam. t, t1, the tenta- cles ; p, p1, the margin of the four-sided proboscis; gc, the cavity of the body ; ac, the bottom of gc, where the cavity (s) of the stem opens; d, the periphery of gc, at the base of the tentacles; a, the semi-partitions, or pilasters; c, the depression immediately over the anterior end of each pilaster, which appears like an aperture; b, b1, the longitudinal fold. — Original. * See Frantzius on the Scyphostoma of Cephea borbonica, in Zeitsch. fur wissenschaft. Zoblogie, June, 1852. Also Gegenbaur upon the same, in his Generationswecbsel, 1854, Taf. n. fig. 34. 16 242 THE RELATIONS OF PROTOZOA TO HYDROZOA. Fig. 140a. gitudinal tubes seem to empty. Such is one of the curious fal- lacies into which naturalists have fallen in their desire to homol- ogize in a special manner the organization of the Scyphostoma with that of the full-grown Aurelia. Now when we trace the development of the tentacles, we find that they arise at points which have definite relations with the position of the four equidistant pilasters (a). In the first stage of growth, after the egg-phase, the embryo has a cylindrical m form, like this, (fig. 140a,) and at one end a simple ■ aperture (m) for a mouth, which leads to an elongate cavity (d) within. After swimming about for awhile d by means of its vibratile cilia, it settles down on the end opposite to the mouth, and becomes fastened to whatever it rests upon. Soon after this, the four pi- lasters, which I just spoke of, make their appearance within the elongate cavity of the cylinder, and about the same time, the tentacles begin to develop. At first, either two, as in this figure, (fig. 1406, t,) or at most four tentacles, spring up at as many alternate points with the pilasters ; then four others, either consentaneously or alternately, originate opposite the pilasters; and the succeeding ones, in successively overlap- ping circles, and alternating with those which have preceded them, develop in the same way, and eventually are merged into an apparently single circle, as I have described in Tubularia. There are, however, certain Hydroids, whose tentacles are un- questionably arranged in a spiral; for instance, those of Rhizo- geton (p. 73, fig. 38) and Coryne (p. 78, fig. 42). But the spiral in this case has a different relation to the organization from Fig. 1406. Fig. 140a. The planula stage of Aurelia flavidula. Per and Les. 100 diam. m, the mouth; d, the cavity of the body. The body is covered by vibratile cilia. — Original. Fig. 1406. The primary, or bitentaculate stage of the Scyphostoma oi Aure- lia flavidula. Per and Les. 100 diam. s, the stem; m, the mouth; d, the di- gestive cavity ; t, the tentacles. — Original. THE RELATIONS OF PROTOZOA TO MOLLUSCA. 243 what obtains in Protozoa; in the latter the plane of the axis is rolled in a spiral, whereas in the Zoophytes the plane is fixed and the spiral winds around it. Among all the other forms of Zoophytes there are none, neither among Polyps nor Starfishes, of which it could be urged, with the faintest show of reason, that they are related to Protozoa. Hydra, and its congeners, although the best and most favorable instances of relationship to Protozoa, failing to hold what is claimed for them, the rest of the Zoophytes are of course out of the question. Protozoa and Mollusca. We will pass now to the considera- tion of the alleged relations of the Vorticellrae (one of the several groups among Protozoa) to Mollusca. As long ago as 1846, Van der Hoeven, a HoUandish naturalist, suggested the rela- tionship of the Vorticellae to Mollusca, saying that " probably one day they will be ranked among Bryozoa." The latter is one of the lowest groups of Mollusca. Since that time others have repeated his suggestion. It is my task now to ascertain what amount of truth there may be in the HoUandish naturalist's prophecy. As I have already described and recapitulated (p. 160-176) the structure of the Protozoa, I need only refer to that group whilst I proceed to take in hand the Bryozoans. The remarkable symmetry of the various constituents of their organization, which I have spoken of on a former occasion, (p. 195,) will be recalled to your minds by reference to these figures, (figs. 118,119,120, Pectinatella and Fredericella); and therefore I need not enter into any details in regard to that point.* What is most likely to attract your attention, in the comparison of the two groups, is the distinctness of the stomach (st) and intestine (cl to an) of the Bryozoa from the rest of the body, and the equally free play allowed to the muscles, (r, r1,) to say but a word in regard to the distinctness and especially assigned posi- tion of the nervous ganglion (g). When, therefore, we analyze the impression which we receive from the contemplation of these two groups, e. g., Vorticellee (fig. 95) and Bryozoa (figs. 118, * The symmetry of the young Bryozoan, and the peculiarity of the type to 244 THE RELATIONS OF PROTOZOA 119, 120), it turns out that nothing but a certain general, exter- nal resemblance in form is the basis upon which their relation- ship has been claimed.* Protozoa and Articulata. The fallacy of certain alleged tran- which it belnn"-o. Wnme evident at an early period. This may be as well illustrated by its growth in the bud as by that in the egg. The bud commences as <-•& a mere internal, globular projection, (fig. \ca 120, bd, and fig. 140c, a,) formed by the two walls (fig. 140c, w, w1) of the general cavity. The first indication of a cavity appears in the form of a hol- lowing (ca) in the core of the bud. In process of time the bud elongates and doubles upon itself, (fig. 140c, t to st1,) and, one end becoming broadened, a cir- cle of feelers, (t,) fourteen in number in Fredericella, becomes apparent, at first as a scalloped edge, whilst the internal wall is differentiated into a general muscular layer (w2, to3) and a group of distinct mus- cles (r, r1, r2,) like those of the adult. When the organs have developed to a certain degree, the walls of the stem opposite the two ends (at t and an) of the body of the embryo are perforated by a process of resorption, and the young Bryozoan is at liberty to protrude its head, and commence its first meal. * In all probability Van der Heaven was led to suggest the relationship of Vorticellae to Bryozoa by the assertion of Ehrenberg that the former possesses a distinct intestine which doubles Opon itself, somewhat in the way that it does in the latter. Subsequent naturalists, being led to disbelieve the truth of Ehren- berg's observations, have had far less reason than the HoUandish observer to claim such a position for the Vorticellae. Fig. 140c. The end of a branch of Fredericella regina, Leidy, MS., with two young budding. 100 diam. ek, the parchmenty sheath ; w, the outer, and to1, to2, to3, the inner walls, the latter having a semi-muscular nature ; a, b, the two walls of the incipient bud; ca, the first trace of a digestive cavity; /, the incipient tentacles of a far-advanced bud; st1, the stomach; an, the posterior end of the intestine ; r, r1, the right and left retractor muscles of the head; r2, the retractor muscle of the intestine, projecting over st1 like an outer wall at r3, and forming a continuous layer over the head (at r4) in connection with to2. — Original. TO ARTICULATA. 245 sitions between Protozoa and Articulata is the more difficult to detect because the examples brought forward from the latter group are so simple in their organization as to present a meagre basis of comparison. When you call to mind what has already been said in regard to the marked resemblance between all animals at a very early period of life, you can readily imagine how slight must be the means of distinguishing two diverse kinds which have just begun to lose their general resemblance, and to assume the peculiarities proper to the type to which each respectively belongs. This, in all probability, is the condition of the instance which I shall now lay before you. At first sight this creature, Opalina, (fig. 141,) strikes one as being most decidedly Infusorian. This arises from the m fact that it is slightly one-sided, and covered with vibratile cilia. A closer inspection, however, does h not reveal the presence of a mouth where one would expect to find it, that is, near the inward curvature °* at the narrower end, nor at any point. As for the vibratile cilia, they occur in a large number of animals beside the Protozoa, so that their presence alone cannot have any weight. The so-called contractile vesicle (A) of Opalina is described by the discoverer of this species to " have this pecu- liarity, that, at times, instead of undergoing a total contraction, it constricts itself from point to point in such a way as to trans- form itself into a series of rounded vesicles, disposed, one after the other, like the beads of a rosary." This is a characteristic of the pulsating vessels of a certain class of worms ; and what renders the relationship the more certain is that those worms, which moreover are mostly parasitic and intestinal, have neither mouth nor intestine.* There are other species of Opalina, closely allied to this, * See the description of Taenia, and the general remarks upon intestinal worms, on pages 79 to 84. Fig. 141. Opalina recurva. Clap. 150 diam. A ciliated, infusorian-like worm, m, the hook-shaped body; h, the pulsating vessel; ov, the reproductive organ. — From Clapare'de. 246 THE RELATIONS OF ZOOPHYTA which form a series of transitions of a most unmistakable character, finally leading from the one before us to those which have a decidedly articulate body. It is to be noted that the latter as well as the former, and the species before us, have a so-called " nucleus," i. e., a reproductive organ, (ov,) and moreover the peculiar hook-shaped body which is so prominent in some of the jointed forms is also present (m) in the one which I have illus- trated. In conclusion, therefore, it may be said that everything tends to show that the Opalinas are members of the group of Articulata, whilst, on the other hand, their relationship to Pro- tozoa is based upon far-fetched resemblances. Zoophyta and Articulata. I have already spoken of the con- tested position of certain worm-like animals, which had been classed among the Zoophytes by the earlier naturalists, and as I gave such a full description of two of these forms, e. g., Cau- dina (figs. 114, 115, 116) and Bonellia (figs. 126, 127), which most closely approximate each other, from each side of the di- viding line between Zoophyta and Articulata, I shall only recur to them again simply to mention the most characteristic features which separate the one from the other. In the Caudina, (fig. 114,) it is the strict conformation to the Zoophytic type, the sys- tematic lateral repetitions of the organs, such as the aquiferous circulatory tubes, (aq to aq1,) the nervous cords, (fig. 116, n,) and the muscular bands (fig. 115, ms) along the sides of the body, which distinguish it from all Articulata; and, on the other hand, in Bonellia, (fig. 126,) it is not only the single ventral nervous cord (g, g1, g3) and its peculiar loop (g2) about the throat, but also its series of numerous, successively repeated, longitudinally arranged ganglionic enlargements, (g1,) and the therefrom arising transverse nervous threads, which give it an unquestionable claim to be ranged in the type of Articulata; whilst a total absence of anything like a lateral repetition of the organs offers no chance whatever for a comparison in this respect with the Zoophyta; not even with the singularly worm-like Caudina. Bryozoa and Zoophyta. It is contended by eminent author- ity, even at the present day, that the Bryozoans belong to the TO ARTICULATA. 247 group of Zoophyta rather than to Mollusca; but there are others, whose opinion is equally as worthy of attention, who claim for them a place among the latter. As frequently happens, the only basis for the assertion of their zoophytic affinities is that of gen- eral resemblance, no more than you may see in these two figures, one of a Polyp (Metridium, fig. 106) and the other of a Bry- ozoan (Fredericella, fig. 120). If, now, we cover the head of each, the circle of feelers is concealed, and all trace of resem- blance between the two vanishes. It is true that in both there is a free digestive cavity (st) or stomach, properly speaking, but in the Polyp it (fig. 106, st) terminates (at jt?) within the great body chamber, so that the food is left to the final assimilation by the general internal surface; whereas in the Bryozoan there is a complete intestinal canal, (fig. 120, ae, st, cl1,) within which the di- gestion is carried on exclusively. But what forms a most decided separation is the difference in the relations of the surrounding parts. In the Polyp the organs are repeated like parallel lines along the sides of the body, and have a direct reference to the dis- position of the feelers. This I need not describe in detail, as it has already been done (pp. 57 to 60, and in chap, x.) in former lectures. In the Bryozoan, (fig. 120,) on the contrary, there are no such lateral duplications of similar organs, but everything is de- voted to a unity of purpose; there is the single retractor muscle (r2) of the intestine, the single pair of right and left muscles (r, r1) for withdrawing the head within the sheath, (ek,) and the unique nervous ganglion (g) placed exactly on the middle line of the head, all of which find no parallel in the Polyp. 248 THE PREDOMINANCE CHAPTER XV. THE MIMETIC FORMS OP DIVERSE TYPES OP ANIMALS. My principal aim in the last lecture was to show, by compar- ison, the distinct lines of separation which exist between the five grand divisions, which I had stated were characterized, in the several groups, by certain relations, through means of which they might be recognized, and distinguished, the one from the other. Thus the Protozoa are characterized by the relation of their or- ganization to a spiral (p. 175). The Zoophyta repeat their organization in parallel lines, along the length of the body (p. 177). The Mollusca are based upon a uniformity of organiza- tion ; they are monomerous (p. 195). The Articulata repeat their parts from point to point along the body, so that it appears jointed from one end to the other (p. 214). And the Vertebrata have an upper and a lower region, separated from each other by the vertebral axis (pp. 126, 231). I then referred to the so-called transitions from one division to another, and showed that they could not hold out, that they were illusory. Now the reason why it has been, and is, even at the present day, so difficult, in some instances, to discover the proper posi- tion of certain animals, is twofold. In the first place, it often happens that a newly discovered creature is not in its adult state, and in consequence of a lack of development its characteristics have not been marked out. You will recollect that I have said that all animals in their earliest stages of growth possess certain characters in common. This is the condition in which animals, belonging to one grand division, may oftentimes be mistaken for those of another division. How much, for instance, this figure (fig. 145) of a young Starfish, or this of a young Molluscan (fig. 149), resembles OF BILATERALITY. 249 a worm. Place them side by side with this embryo (fig. 148) of a genuine worm, and no one could say positively, if they were new to him, which is not a worm. Until it passes beyond this embryonic condition, it is oftentimes extremely difficult to deter- mine in which of the five grand divisions an animal belongs. This difficulty arises from the fact that the predominant idea in all animals is bilaterality; and for the reason that during the early stages of growth this idea is expressed with a degree of exclusion which obscures the subordinate idea, which finally is superimposed upon the predominant one. Let us follow out the development of this idea among the examples we have here, and see how it addresses itself to our eyes. In these two figures (figs. 142, 143) of young Trepangs, you Will notice that the arrangement of the visible parts of the organization is in reference to a line which may be drawn lengthwise through the middle of the body; that is, the organs are either immediately upon the axial line, as in this figure, (fig. 142,) or situated symmetrically right and left of it, as represented here (fig. 143). This feature is the most prominent one; and notwithstand- ing there is the beginning of a lat- eral repetition of parts in one of the figures, (fig. 143,) it is not so decided, nor so far developed, as to Fig. 144. Fig. 142. Holothuria tremula. Gunn. Natural size about -fe of an inch long. A view of the back of a very young Trepang. m, the future mouth; t, feelers beginning to develop; ov, the madreporic body, lying beneath the skin. — From Koren and Danielssen. Fig. 143. The same as fig. 142, but a little older. A view of the lower or ventral side, m, the mouth developing; t, t1, the incipient feelers; s, the first pair of sucker-like feet. — From Koren and Danielssen. Fig. 111. Holothuria tremula. Gunn. The same as figs. 142, 143, at a far 250 THE PREDOMINANCE enable one to determine whether the embryo, per se, is one of the Zoophytic types, or is one of those worms (Tape-worms, &c.) which bear a crown of hooks or suckers about the mouth, or is a member of that group of TrepangJike worms to which Bonellia (p. 216, fig. 126) belongs, and of which some possess a circle of feelers at the end of the head. In fact, I have already stated that some good naturalists persist to this day in classing this latter group, the Sipunculacea, with the Holothuria (Tre- pangs). If, however, we trace the development of these embryos, as did the Norwegian naturalists from whose work these figures are copied, we shall find that eventually, as the other parts of the or- ganization become prominent, as they appear in this figure, (fig. 144,) they demonstrate by their arrangement a decided length- wise lateral repetition (see the description of the figure at the bottom of the page). In these other two figures, (figs. 145, 146,) which represent the two opposite sides of the same individual, (an embryo Starfish,) one of them (fig. 145) has all the characters of a jointed worm, with its joints, as it were, strung on a longitudinal axis; nor does the other (fig. 146) present a much less artic- Fig. 145. ulate form than the former; but yet for those who are familiar with the Fig. 146. more advanced period of development. Considerably magnified. (See chap. xvn. § Zoophyta, in the section on Holothuria.) A view of the lower side. t, t1, the feelers; m, the mouth; /, the buccal ring; aq, one of the sack-form ap- pendages, Polian vesicle, of the circular aquiferous canal around the mouth; mc, the madreporic canal; aq*, aq?, the median longitudinal aquiferous canal; aq2, aq2, the right and left inferior aquiferous canals; s, s3, «•*, s5, the di.sciform ends of the sucker-like feet (s2) which arise from the lower median line of the body; s1, the aquiferous tube by which the feet are distended with fluid from the median vessel (aq*); bd, the transverse muscular bands; the five longitudinal muscular bands occupy the same place as the longitudinal aquiferous canals, (aq2, aq*,) each one OF BILATERALITY. 251 young of this group, there is sufficient of the starfish physiog- nomy about its anterior end, to enable them to refer it to its proper place among the Zoophytes. Here, again, in these two figures (figs. 147, 148) of a young worm, the younger one (fig. 147) shows scarcely the trace of articulation, whilst its bilaterality is prominently set forth by the pair of eyes, and the two 6 right and left groups of vibratile Fig. 147. cilia (a). In the older one (fig. 148) * it is clear that the jointed structure of the body is Fig. 148. superimposed upon a bilateral basis; for it is still quite as evi- dent as in the younger one, that not only the eyes, but also the groups of vibratile cilia (a) are arranged in reference to a right and a left, notwithstanding the partial obscuration of this feature by the prominency of the articulation. Finally I will recall to your minds the young worm-like Mol- luscan, (fig. 149,) simply to show how little it resembles its adult state, as represented in this figure, (fig. 150,) and yet how strictly it conforms to the bilateral type. If, now, we turn to the lowest forms of each grand division, we shall find this idea carried out in another guise. This will of the latter lying in a furrow along the middle of one of the former; gs, the cloaca, a saccular enlargement at the posterior end of the intestinal canal. — From Koren and Danielssen. Fig. 145. A view of the back of a worm-like embryonic stage of a Starfish. Magnified about 40 diameters. — From J. Miiller. Fig. 146. A view of the front side of the same as in fig. 145. s, the sucker- like feet in an incipient stage of growth; a, the end of one of the five short, blunt, rounded arms, from which s arise ; b, c, the joint-like divisions of the body. — From J. Miiller. fFi". 147. Protula elegans. M. Edw. Highly magnified. A view of the back of a young marine worm, in its earliest stage, at the moment of its birth. a, the groups of vibratile cilia at the anterior end; b, the posterior end; the eyes are two dots just in front of a. — From M. Edioards. Y\°. 148. The same as fig. 147, in a more advanced stage of growth, a, b, as in fie 14 7. — From M. Edwards. 252 THE PERMANENTLY Fig. 150. explain the second branch of the difficulty. You A will recollect that I have said (page 158) that the higher animals of a group pass through certain forms in their de- velopment which correspond to the per- manent adult condition of the lower animals of that same group; e. g., the Rabbit passes from that degree of or- ganic simplicity which corresponds to that of a fish, to a higher state which resembles that of a reptile, and then onward to that phase which is typical of the organization of a bird, and finally it assumes its adult condition. A Butterfly, one of the highest of the group of Articulata, in its youngest stages is a grub or worm, so-called, whose numerously jointed body and frequently re- peated internal organs recall the many-jointed, true worms, such as the earth-worm, and marine worms, (p. 80, fig. 43,) but more strictly correspond to those of the earwigs, and the thousand-legs, or ringed worms, so common under sticks and stones on the ground. This idea was first put forth by Von Baer, thirty-six years ago, in 1828, (Uber Entwickelungsgeschichte, &c, Theile i. p. 230,) and, taking the cue from him, other observers have traced its prevalence throughout the animal kingdom, not only among the living, but also through the numerous groups of extinct fossil animals of past ages. From this you may judge that all the members of a group do not come to the same degree of perfection, but that some remain in what corresponds to the embryonic stages of the higher ani- mals of that group. Now from this you may also infer that we would have the same difficulty with these permanently embry- Fig. 149. Pneumodermon violaceum. D. Orb. Natural size, 0.1b>», i. e., $fc of a line long. A worm-like stage of development. A, the head; B, the tail. The body is encircled by three groups of vibratile cilia. — From Gegenbaur. Fig. 150. Pneumodermon violaceum. D. Orb. 3 diam. An adult Pteropo- dous Molluscan which swims in the open sea. h, the head; b, the main part of the body; c, the tail; /, the pair of feelers; f1, the suckers of f; w, the fins which are used like wings. — From Woodward. EMBRYONIC FORMS. 253 onic forms in determining their position, as we noticed in regard to the young trepang, starfish, worm, or molluscan ; for example, one of the lowest fossil forms of the group to which the Zoo- phytic Trepang belongs, a Hemicosmites (p. 128, fig. 66) has been mistaken for one of the Mollusca, a Chelyosoma, whose body is covered by similar, many-sided, pavement-like scales. Again, certain of the group of Articulata, for instance, some of the Planarians, (like fig. 47, p. 92,) e. g., Eolidiceros, have a re- markable resemblance in form to certain of the so-called naked Mollusca, namely, Janus, and also exhibit the same habits, in the manner of walking, and also in crawling back-downwards along the surface of the water. It is not a little curious, too, that Eoli- diceros and Janus should resemble each other in regard to their nervous system.* Among Mollusca, the Bryozoa, especially those which have a simple circle of tentacles around the mouth, have been mistaken for Polyps. This point I have already discussed, when compar- ing the Bryozoa with Polyps, in a previous lecture (p. 247). Even among Vertebrates, there are those, for instance, certain kinds of Lamprey-eels, (Myxine,) which might at first sight be mistaken for worms; and in fact they have been described as such by Linnaeus; and others, such as the Lancelet, (Amphi- oxus,) (fig. 133, p. 226,) have been wrongly classified with sea- slugs, a group of naked Mollusca. This was owing to the un- developed state of the vertebral axis of the Lancelet, and the otherwise singular resemblance of this fish to certain Mollusca (Firolidce and the like) which swim rapidly in the open sea. * We owe to Blanchard (Voyage en Sicile, vol. in.) the first decided and conclusive proof that the Planarians are true Articulates, by his demonstration of the successive ganglionic repetitions along the nervous threads, at the right and left sides of the mid-line of the body of a large Planarian (Polycladus Gayi. Blanch.). 254 THE RELATIONS OF THE MINOR GROUPS. CHAPTER XVI. THE TRANSITIONS AMONG THE SUBORDINATE TYPES OF THE FIVE GRAND DIVISIONS. Since, therefore, there are no transitions from one grand divis- ion to another, it is very natural to infer that it is among the groups of each particular division that we shall find the passages from one form to another. This inference corresponds, too, with the strongest tendencies of belief among the majority of natural- ists in regard to the relations of animals; for although there are many who more or less incline to see transitions from one grand division to another, yet it is very seldom that any one makes a positive assertion to this effect; whereas, in regard to the tran- sitions from one class to another, e. g., from Fishes (through Lep- idosiren, fig. 169) to Reptiles, or from Reptiles (through Ptero- dactylus, fig. 186) to Birds, (through Archeopteryx,) we have the strongest expressions and most positive assertions that the one has no definite boundary which separates it from the other. If I now place before you certain pictures of animals, one from each class of the five grand divisions of the animal king- dom, such as the advocates of the fixity of the subordinate types would select, you will no doubt be inclined to say, " How very clear the proof is; these must be distinct types." I have arranged in this table the names of the classes of each grand division in groups of relationship, so that you may inform your- selves as to the alliance of one class with another, according to their degree of proximity. THE CLASSIFICATION OF ANIMALS. 255 Vertebb ATA. Mammals (fig. 151.) Birds (fig. 152). Reptiles (fig. 153). Fishes (fig. 154). Mollusca. Cephalopoda (fig. 155). Gasteropoda (fig. 156). Acephala (fig. 157). Bryozoa (fig. 158). Articulata. Insecta (fig. 159). Arachnida (fig. 160). Crustacea (fig. 161). Vermes (fig. 162). Zoophyta. Echinodermata (fig. 163). Acalephce (fig. 164). Po%i (fig. 165). Protozoa. Ciliata (fig. 166). Suctoria (fig. 167). Rhizopoda (fig. 168). 256 THE CLASSIFICATION Description of figs. 151 to 168, on pages 257 to 261: Vertebrata. Fig. 151. See p. 118, fig. 51, for the description of the lettering. Fig. 152. Dendroica virens. Baird. Black-throated green warbler. £ nat- ural size. — From Audubon. Fig. 153. Scleroporus consobrinus. B. and G. Natural size. A lizard, from our southwestern territory. — From Baird Sr Girard. Fig. 154. Argyreus atronasus. Heck. Natural size. The common brook minnow. — From Storer. Moll use a. Fig. 155. Loligopsis illecebrosa. -§ natural size. The common squid of this coast. For the description see p. 206, fig. 124. Fig. 156. Helix albolabris. The common snail. 2 diam. For the descrip- tion see p. 203, fig. 122. Fig. 157. Ostrea Virginica. L. The common oyster. For the description see p. 200, fig. 121. Fig. 158. Fredericella regina. Leidj', MSS. One of the fresh-water Bryozoa. For the description see p. 198, fig. 120. Articulata. Fig. 159. Sphinx Ligustri. L. Natural size. The haiok privet-moth. For the description of the lettering see p. 119, fig. 53. Fig. 160. Epeira trifolium. Hentz. Natural size. A common garden spider. For description of lettering see p. 220, fig. 129. Fig. 161. Cyclops quadricornis. 50 diam. A minute, shrimp-like Crustacean. For description see p. 220, fig. 128. Fig. 162. Myrianida fasciata. M. Edw. 2 diam. A marine worm. For the description of the lettering see p. 80, fig. 43. Zoophyta. Fig. 163. Psolus phantapus. Strfldt. ^ natural size. A trepang from this coast. For description of lettering see p. 192, fig. 117. Fig. 164. Tubularia indivisa. L. Natural size. A Hydroid Acaleph from Boston harbor. For description see p. 238, fig. 136. Fig. 165. Metridium marginatum. M. Edw. \ natural size. A Polyp from Boston harbor. For description see p. 57, fig. 28. Protozoa. Fig. 166. Epistylis flavicans. Ehr. 250 diam. One of the highest of the group of Ciliata. For description see p. 161, fig. 95. Fig. 167. Podophrya Cyclopum. Clap. 300-350 diam. A pedicellate in- fusorian belonging to the group Suctoria. For description see p. 51, fig. 25. Fig. 168. Amozha diffluens.. Ehr. 100 diam. An Amoeba or Protean ani- malcule, belonging to the group of Rhizopoda. For description see p. 9, fig. 1. OF ANIMALS. 257 vg vt ov fl w k k] p va dp a ao nr v g sk cr au en o mm bl i s it Iv I vc h la ao* Fig. 151. Fig. 153. Fig. 154. 17 258 THE CLASSIFICATION Fig. 155. Fiir. 156. Fig. 157. Fir?. 153. OF ANIMALS. hd k glth b cr h1 i ov C g g1 I st gl g& n g*d o a Fig. 159. 259 p' cr [1 P 13 Fig. 160. h 1 "2 3eg p es t Fig. 161. 6 5 4 Fig. 162. 260 THE CLASSIFICATION a w v Fig. 165. OF ANIMALS. l-ig. 166. Fig. 167. 262 TRANSITIONS AMONG THE CLASSES Now it would be impossible for me to show all the details of transition among these various groups, from one into another, because, in the first place, time would not allow it, and secondly, it could not be done except by the actual inspection of speci- mens ; and even then the demonstration would have to be illus- trated in a superficial manner. These transitions, in the majority of cases, are such as are addressed to the eye and thought of the well-studied observer of nature; and when they can be illus- trated, they afford a view of only the more general relations. It is on this account that, in a course of lectures like these, many things are to be taken for granted upon the assertion of the lecturer, whilst occasionally he is able to bring forward more or less of his proofs in detail. In the latter case, the presentation of facts involves a form of special pleading which can hardly be addressed to an audience which is not directly and practically interested in the subject. The dryness of the details are beyond the patience of those who, at most, look forward to the final exhibition of the more general results. It would be extremely onerous, for instance, to attempt to show in what points certain Fishes and certain Reptiles cannot be distinguished from one another, and in what points they essentially or manifestly differ. We can only say, for instance, that certain kinds of Catfish or Horned-pouts have an organi- zation so much like that of certain Salamanders and frog-like Reptiles, that naturalists class the two together in one group; and that not only are they related in this most general way, but there are among them certain forms which cannot be definitely and unequivocally proved to be either Fish or Reptile; and on this account naturalists are all the more inclined to look upon two groups which have no definite boundary line as merging into one another. Here is an instance in illustration of this relation. This creature (fig. 169) has a fish-like form, but so have the tadpoles of Salamanders, and certain adult Salamanders. Its body is covered with scales, whose structure, however, is not like that of the scales of ordinary fishes, but rather of the Lizards (fig. 153). It has internal gills like those of a fish, but a part OF A GRAND DIVISION. 263 of them do not perform the functions of such organs, and are the remains of gills of a younger state; just such a structure as we may see in the remains of gill-like bodies on the gill-arches in certain salamanders, e. g., Siren. In its younger stages of growth it has tufts of external gills on each side of the head, like those of the tadpole of frogs and toads, and the permanent ones of certain adult salamanders, such as Siren, Axolotl, and Menobranchus; but on the other hand they equally resemble those of the embryos of some of the sharks and skates. The heart is not a double cavity as in the bony fishes, but the posterior half is divided into two; yet as the partition in this case is a mere net-work, the division is not a complete one, but of that sort which obtains among the so-called Reptilian fishes; and so I might go on to enumerate every character which this singular genus exhibits, without giving one which does not find its counterpart either in fishes or reptiles. There is one character, however, which has determined some naturalists to class the Lepidosiren among fishes, and that is, it has no nostrils, and on this account Owen decided that it is rather a fish than a reptile; but in specimens which Bischoff examined, the nostrils are present; and therefore the preponderance passes over to the side of reptiles, if Bischoff's opinion is alone to be taken into account. Between the two authorities, however, the ditference is so slight as to amount, I suspect, to an individual disparity; Fig. 169. Lepidosiren annectens. Owen, ^natural size. From the River Gambia, Africa, go, the gill-opening; g, the remains of the external tuft of "ills of the vounn-est stase of growth; /, the anterior, and f1 the posterior, flat- tened lash-like limbs; df, the dorsal fin-like crest; vf the ventral fin-like keel; / the row of scales in the trend of the so-called lateral lymphatic canal; except- ing on the head, the rest of the scales are omitted.— Original, from a specimen kindly lent to me by Prof. Jeffries Wyman. 264 THE RELATIONS OF BIPOLARITY AND BILATERALITY an amount of which no definite estimate could be made that would be sufficient to separate the animal in question either from fishes on the one hand or from reptiles on the other. Now this is the way in which naturalists proceed, step by step, balancing, through all the intimate details of an organization, the several features which are opened to their eyes by the help of the dissecting knife and the microscope. Of course you must see, even from this slight sketch, that it would be a work of weeks, and even months, if I were to undertake to go through even the prin- cipal groups of the animal kingdom, to say nothing of the lesser communities of relations, such as exist among specific characters. The case of the Lepidosiren is one among many that are just as remarkable and indeterminable, if one wishes to make defi- nite, sharp boundary lines, like checker-board work, between all the various groups of animals. But the relations of Nature are not of this kind; the square, rule, and compass and the checker- board formulae are but the expressions of the limitations of human comprehension among the untutored; but as we advance in the knowledge of our own minds, and by degrees take in the immense breadth of intellect with which man is endowed, we gradually come to a better understanding of the workings of that greater mind which originally conceived, and gave us birth. We have already had some glimpses of the order of things which reigns among the animal groups; we have seen that the principle of life is the expression of a grand idea which shines forth in all Organic Nature; we have seen that from and upon this idea is erected the idea of form in a twofold relation, that of the animal physiognomy on the one hand, and that of the plant on the other; but yet related in such a way that a concep- tion of their difference would seem to be beyond the power of the finite human mind, and we fain would come to the conclu- sion that the difference is but one of degree. For the animal kingdom we have traced an idea of progres- sion which is expressed in several ways; and these ways are seen to refer more or less to each other, as if they were but the collat- eral branches of one main line. At the outset the principle of life takes on an outward form in the bipolarity oi the egg. This TO THE FIVE GREAT TYPES. 265 principle is, as it were, set against itself; the opposing poles are antagonistic only in one sense, though ; they cannot exist the one without the other, any more than can the positive and negative poles of the electrical sphere which wraps this globe in an invis- ible shell. The idea of a balance between these upper and lower poles seems, as a natural consequence, to necessitate the consideration of lateral relations ; and these we find progressively elaborated and set forth in the idea of bilaterality. Everywhere we see the idea of progression, from a lower to a higher, man- ifested in various relations. The ideal relation of progress is that which is the most general. And now when we come to the consideration of the charac- teristics of the five grand divisions, we seem to have lighted upon certain ideas which have no relation whatever to the fun- damental idea of the typical animal; it seems at first glance as , if five new seals were impressed upon the original stamp, and obscured or blotted out its distinguishing features; but I am inclined to look upon the matter in another light. You will recollect what I told you some time ago (p. 85) in regard to the tendency of the egg, especially of the lower animals, to divide into two or more, and that in this way the so-called monstrosi- ties among higher animals were formed. You will call to mind, too, that I pointed out the prevalence of the self-dividing process of reproduction among the lower forms (chap. in. and p. 110). Among the Protozoa (Infusoria) this process takes place in such a way as to not only divide the animal transversely, but also lengthwise ; that is, the creature not only repeats itself by cross- wise division, but also by lengthwise or longitudinal repetition. Now how do we see this idea carried out in the groups above Protozoa ? In the Zoophyte division we have taken note (p. 61) of the longitudinal splitting of the Polyps, especially of the com- pound forms, the branching corals. Among the single Polyps this splitting totally divides the individual into two; but in the branch- ing corals the splitting only divides the head and stomach, and thus a many-headed creature is formed. The tendency would seem to be to separate the laterally repeated parts, as so many individuals, from each other. 266 THE RELATIONS OF BIPOLARITY AND BILATERALITY We may observe everywhere in the animal kingdom that a manifold repetition of parts, whether longitudinally as in Polyps, or transversely as in Worms, is attended with an indeterminate relation of individuals: in some cases individuality is distinctly marked, whereas in other instances, and under various forms, the individual is more or less merged into the repeated parts. Now in tha Articulate animal group, where the repetition of parts is from point to point, along a line, the body is divided into joints, and, as if to exemplify the individual character of these joints, among the lowest intestinal worms, each joint at the period of transverse division is separated from its fellows, and plays, for a time, an independent part (p. 84). Among the aquatic worms I have already shown how a number of joints divide off together and form an individual (p. 80). Nowhere do we find in this grand group a longitudinal self-division, but always, in conformity with the type, a transverse one. The Mollusca fully exemplify their type, as one which has a unity of conformation, with neither lateral nor longitudinal repetition of parts; for they do not possess the faculty of self- dividing. I mean, of course, that they do not, as a rule, take this method to reproduce themselves. It is true that some of the lower groups are compound; but they become so by a pro- cess which is purely a matter of budding, (p. 243, note,) and not of self-division, properly speaking. The instances of self- division or of fissigemmation, which I have pointed out as occur- ring, not only in Mollusca and Articulata, but even in Verte- brates, when discussing the matter of monstrosities, (p. 85,) were then given merely to show how universal an idea may be in its relations, although its practical and normal effects are confined to a more or less circumscribed circle. Even the idea of bilaterality is involved with that of reproduc- tion, and the manner in which this relation manifests itself, shows that the idea of a right and a left may possibly be the expression of two individuals united side by side, instead of the duplication of the organs of one individual. I have already referred (p. 85) to the remarkable investigations of Lereboullet upon the embry- ology of the Fish. Without stopping now to go into the details TO THE FIVE GREAT TYPES. 267 of the subject, I will merely state some of the general results of these investigations, as far as they have a direct bearing upon the point which we are now discussing. Lereboullet discovered that not only will an egg divide into two distinct individuals at the outset, but also, in some cases, the two individuals are formed so closely side by side that the right side of one and the left side of the other become more or less united, and form, at the point of junction, a single trunk. Sometimes this occurred at the tail, sometimes at the middle, or at the head; and the manner in which the united parts are joined to each other shows clearly and unmistakably that the right side of an animal is not neces- sarily a different part of the body from, and in direct opposition to the left side; for we see that the one may take the place of the other; and we might say without exaggeration that they are mutually interchangeable. This could not possibly happen, if the two halves were not positively identical with each other. In this sense, then, the body consists of two individuals acting as one; it is a duality. From this point of view, then, I think we may see that there is a certain form of connection between the ideal relations of bipolarity, bilaterality, and the type of division, on the one hand, and, on the other hand, the reproductive process, which is the basis of relation by consanguinity. It is, then, through this pro- cess, that, from the apparently purely ideal relations of all animals to each other, the transition is made to those relations or ties of consanguinity which bind certain groups, as it were, in one family. We cannot say where the ideal relation meets or interlocks with the relation by blood; the point of junction seems to vary in the different groups. Among the lower forms of animals the ideal relations of bipolarity and bilaterality are the most prom- inent, and the division type is but faintly shadowed forth; but, as we rise in the scale, the latter becomes more decided, and sometimes so strongly presents itself as to nearly obscure bilat- erality. This is most notable among Starfishes and Jelly-fishes; and it has misled some into the belief that radiation is the pre- dominant feature to which all other characters are subordinate in these animals. 268 THE INTERCHANGEABLE RELATIONS OF But I have demonstrated (p. 177) that this so-called radiation is merely a lateral repetition of parts, and I have also shown, that, among the highest forms of these Zoophytes, this repetition is less and less frequent, and that bilaterality is consequently more clear to the view. Now, as we see the two ideas, represented by bilaterality on the one hand, and the type of a grand division on the other, mutually and alternately intensified, and bearing such a variety of degrees of the prominence of the one or the other; so may we also detect a similar relation between these two ideas and the characteristic features which blood relationship transmits from family to family. Will any one undertake to show how bilaterality is propagated from parent to offspring, if it is not an inheritance by blood; but if it is an inheritance by blood, at what point, then, does it cease to be altogether ideal in relation, and begin to be hereditary ? I think it would be just as difficult to answer this question, as it would be to show where the ideal relation of the Lepidosiren to the Fish or the Reptile begins, and where the relation by consanguinity terminates. I think I can illustrate the complicated interchanges of these ideas to the fullest extent by explaining the nature of the rela- tions of the animals which are arranged here. It is a group of Articulate animals. Judging from their forms alone, you might conclude that there are several family types represented ; — for instance, the worms seem to be illustrated in one place (Lingua- tula, fig. 170 (A); Dendroccelum, fig. 182 (M)), and the spiders (fig. 176 (G)) in another. Others you might take for caterpillars (Tardigrada, fig. 178 (I)), and some for shrimps (Squamella, fig. 184 (O), and Cyclops, fig. 185 (P)). Now I could not say posi- tively whether you would be right or wrong in some instances ; for the very reason that several of these animals are related in intermediate ways to more than one family, and in a very com- plicated form of relation. On this account I will undertake to point out but a few of the features which characterize them ; and in order that I may do this in the simplest, systematic man- ner, I have jotted down a tabulated arrangement of characters, which I will endeavor to illustrate by these figures. ( (A) Lingiuttida. ( \ Worm-form \ ( Spider-mite. ( (B) Linguatula (young). Spider-mite. (C) Anchorella. ( (D) Nymph on. ( (E) Phytoptus Nerve concentrated. Hooked feet. Branching stomach. (II) Myzostoma. f Proboscis. Branching stomach. Hermaphrodite. Suckers. I (K) Prosfomvm. Stylet tail like Itotifera. lion. ( A Crustacean of < Spider-like s the Lernean group. ( Crustacean. ( •ftoptus. ( Four-legged \ Tardigrade. *| ( (F) Demodej\ ((J) Spider. Spider-mite. Like the Spider-mite (F). Hooked feet. Branching stomach. Hermaphrodite. Tardigrades. Planarian- r \ (J) Tardigrada. Nerve a chain of ganglions. Mouth suctorial. Hermaphrodite. Worm-like. (J) Lydella. Eight-jointed legs. • Tardigrades. Mite-likc Rotifera. Worm-like Crustaceans, or Crustacea-like Worms. • Worms. (L) Albert in. Parasite, like Intestinal worms, in Snails and Earth-worms. UN) Conochiliis. Jointed feelers like Crustaceans. (0) Sipiamclla. Winter eggs. Shield-like covering. Male and female unlike, as in Barnacles. j (V) Cyclops. I A Crustacea] Crustacean characters. (M) Dendrocirlum.. A Planarian... .Worm-like. Aquiferous canals. *) (filiate mouth. f Rotiferan Vermiform vounc. [character O W w > O c CO C > w H >—i O d r > > Bodv contractile. 270 THE INTERCHANGEABLE RELATIONS OF m b Fig. 170 (A) to ant Fig. 180 (K) Fig. 182 (M). Fig. 181 11. CERTAIN GROUPS OF ARTICULATA. 271 h an aril arfi cl h Fig. 174 (E). Fig. 173 (D). Fig. 175 (F). Fig-176(G). J Fig. 183 (N). Fig. 185 (P). 272 THE INTERCHANGEABLE RELATIONS OF This worm-shaped figure, (A) Linguatula, represents an an- imal which was at one time classed among the intestinal worms, Fig. 170 (A). Linguatula proboscidea. Rud. About half natural size. At the broad end, which is the head, are a few recurved hooks. — From Quatre- fages. Fig. 171 (B). The young of fig. 170, just hatched. Highly magnified, m, the mouth-; b, the bristles which are protruded from the mouth, and are used to pierce the tissues of animals; cl, the two pairs of hooked feet. — From Van Beneden. Fig. 172 (C). Anchorella uncinata. Mull. Natural size about fa of an inch long. The male, m, the mouth; an, an1, the two pairs of feelers; cl, the two pairs of hooked feet. — From Nordman. Fig. 173 (D). Nymphon grossipes. Magnified considerably. A very young individual, seen in profile, h, the head; an, the pincer-like claws; an1, the hooks of an; an% one of the feelers; cl, the hooked feet. — From Kroyer. Fig. 174 (E). Phytoptus, sp. ? Dujardin. 150 diam. One of the Tardi- grada with only two pairs of legs (cl) ; A, the head; cl, the legs; eg, the eggs. — From Dujardin. Fig. 175 (F). Demodex folliculorum. 150 diam. A view of the lower side of a worm-like Spider-mite, which lives as a parasite, buried in the skin at the roots of the hairs of animals, and thereby forming a pustule; m, the mouth; cl, the four pairs of feet; ab, the abdomen. — Originally from Simon. Fig. 176 (G). Epeira trifolium. Hentz. Natural size. For description of lettering see fig. 129, p. 220. Fig. 177(H). Myzostoma cirrhiferum. Leuck. Natural size about fa of an inch long. An external parasite on a kind of starfish (Comatula). A view from below. m, the mouth; m1, the proboscis protruded from m ; m2, the aperture of m1; ph, the throat; ph to an, the whole length of the intestine; v, v1, u8, the branching prolongations from the intestine; n, the concentrated nervous mass, which gives off branches toward the head and tail, and to the five pairs of hooked feet (cl); ov% ov*, ov*, the right and left V-shaped male reproductive organs; ov, ov1, the apertures of the last; pe, pe'2, the right and left oviducts through which the eggs (w, w) pass when laid; joe', the common aperture of pe, pe*; cl, the five pairs of short, jointed, hook-tipped legs; sk, sk1, sk2, the four pairs of suckers, or sucker-like organs of adhesion.' Fig. 178(1). Tardigrada,sp.? Duj. 160 diam. A profile view of a Tar- digrade which has four pairs of short, clawed legs (cl); m, the mouth; th, the throat; j, the gizzard or internal jaws; st, the intestine ; an, posterior end of st.— From Dujardin. Fig. 179 (J). Lydella, sp.? Duj. 600 diam. A Tardigrade which has four pairs of long and distinctly jointed legs (cl); th, the throat; ;, the gizzard-like internal jaws. — From Dujardin. CERTAIN GROUPS OF ARTICULATA. 273 not only on account of its shape, but also because it fives in the intestines of a serpent, the Boa - constrictor ; but, by the re- searches of Van Beneden, it was ascertained that in the youngest stage of growth, just at the period of hatching from the egg, it has the form represented here (B). This at once convinced its discoverer that the Linguatula is not a worm ; but yet it does not appear to have proved the relationship of the animal to any particular group; for although Van Beneden says that the young have a close affinity with those of Anchorella, an animal well known to be a Shrimp, he is not positive as to this relation- ship ; and, on the other hand, there are naturalists who think that the young Linguatula exhibits fully as much the characters Fig. 180 (K). Prostomum lineare. (Est. For the lettering and description see p. 36, fig. 19. Fig. 181 (L). Albertia vermiculus. Duj. 100 diam. A view from below. m, the mouth; j, the internal jaws; c, glands attached to the sides of the throat, probably for the purpose of applying saliva; p, the throat; g, lateral pouches of the stomach; cv, the vessels of the aquiferous circulatory system; e, el, the eggs; in e1 the young is far advanced in development; t, the tail. — From Du- jardin. Fig. 182 (M). Dendroccelum lacteum. (Est.? 3 diam. For the description of the lettering see p. 92, fig. 47. Fig. 183 (N). Conochilus volvox. Ehr. From fresh water. Natural size 0.260 millimetre long. A worm-shaped Rotifer, lb, the cilia-bearing lobes of the head; an, the feelers; t, t1, the tail; m, the mouth; m\, cavity of the mouth; j, the jaws; st, st1, sfi, the three apartments or subdivisions of the stomach; o, the pair of eyes; eg, an egg; ms, longitudinal muscles used to retract the body into the gelatinous sheath in which the animal lives. — From Cohn. Fig. 184 (O). Squamella oblonga. Ehr. 200 diam. From fresh water. A view from below of a Rotifer which has a distinct shell or carapace (s, s1, s2). s, the anterior transverse edge of the carapace; s1, the anterior, and s9, the pos- terior corners of the carapace; s3, the border of the oval, flat area which occu- pies the lower face of the carapace; lb, the cilia-bearing lobes of the head; t, the fork of the tail (t1) ; m, the mouth; j, the jaws; j1, muscles which move j, st, the stomach; cv, the contractile vesicle, or heart of the aquiferous circulatory system- cd', cr2, the right, and cv'3, cv1, the left aquiferous circulatory vessels; eg, eg1, and ev,# y OF ARTICULATA. 299 The first distinct trace of organization is to be found at the sur- face, where a well-marked layer of large cells (fig. 198, c) encom- passes nearly the whole circuit of the body. At the point where this layer is deficient (ac1 to ac2) the yolk granules (y) extend to the surface, whilst that part of the body over which the layer of cells is spread appears lighter and less opaque (d). This layer (c) might be compared to a ball-cover split open on one side, and then we should have the split trending across the back of the embryo, and one half of the cover representing the head, and the other half the posterior region of the body. You may see from this that the embryo is, as it were, doubled upon itself, and, I will add, in anticipation of what will appear presently, in such a way that its back lies next the centre of the ball, i. e., it is doubled upon itself backwards. Which end is the head does not become apparent until the next phase. At the latter period (fig. 199) we find the layer of large cells, the ger- k minal layer, and the region which it covers, seemingly narrowed, or con- tracted upon itself (ab) along about two y1 thirds of its length, but at one end (k) rather more widely extended than in the previous phase, so that, on the whole, when seen in front, it resembles a clumsy sort of Y. We have now, at the broader end of this figure, the first indication of the position of the head, (k,) but as yet no intimation anywhere as to whether the embryo is an Articulate or Molluscan, or any one of the five types of animals. In the next stage, (fig. 200,) however, the true character of the animal, as far as its general typical relations are concerned, begins to develop, under the form of a series of indentations (i, i1) which divide the anterior half of the body from point to point along the front or abdominal side, into successive joints Fi". 199. The same as fig. 198, at a more advanced stage. 220 diam. k, the head in profile; k1, the right side of k in the distance; k% the left side of k, next the observer; ab. the abdominal region; tl, the posterior end of ab; y, y1, the yolk. — From Zaddach. . --■ w*-\cr \ab 300 THE DEVELOPMENT i . "3< - ' ,f c q, o j A) y Fig:. 200. (a1, c1, c2, c3, c4, c5). A peculiarity of this phase, not before noticeable, and which is the forerunner of a remarkable change in the relative position of front and back, is evinced by the backward curvature of the head (k) so as to sink it inward toward the centre of the yolk mass, (y,) and allow the tail (tl) to overlap it. Not yet, though, are we permitted to pronounce upon the special relations of this creature, since the most that its jointed body teaches us is that it is an Articulate animal; and, for all we can see, it may be a worm instead of an insect. But in regard to the latter category, we do not remain long in doubt; for in a short time three pairs of legs (fig. 201, e, f, g) begin to develop from the last three of the joints just mentioned, and in front of them arise ,j, four pairs of jointed appendages which appertain to the head, and perform the office of feelers, (a,) and upper (b) and lower (c, d) jaws. The presence of legs Fig. 201. determines the character of the embryo as that of an Articulate which is higher in grade than the, worms, and their number, namely, three pairs, distinguishes it Fig. 200. The same as figs. 198, 199, in the third stage. 220 diam. k, the head ; ab, the abdomen ; tl, the tail, overlapping k; a1, the first joint of the body after the head; c1, the second, and c2, the third joint of the same; c3, the first, c4, the second, and c3, the third joint of the thorax, from which the first, sec- ond, and third pair of legs develop; i, i1, the transverse furrows between the segments; y, y1, the j oik. — From Zaddach. Fig. 201. The same as figs. 198 to 200, in a further advanced stage. 220 diam. A profile view, k, the head; d\ the first, d$, the fifth, and d®, the tenth joint of the abdomen; tl, the bend of the tail; B, the forehead; a, the feelers; b, the upper jaws; c, d, the under jaws; C2, the joint of the body from which d arises; e,f g, the first, second, and third pair of legs; y, the remains of the yolk. — From Zaddach. OF ARTICULATA. 301 from the spiders, which possess four pairs of legs. In addition to these there are two other characters which, taken in connec- tion with those just mentioned, would, did we not know its origin, vindicate the claim of this embryo to be classed with the Insects proper as contradistinguished from the Spiders. I mean the isolation of the head (k) from the rest of the joints, and the distinct, tenfold jointed division of that part of the body which lies behind the legs, and corresponds to the abdomen (dv to d10). It is here that we see for the first time the beginning of the change in the relative position of front and back which I hinted at just now. This is indicated at two points, and in two sepa- rate ways, namely, by the elevation of the head (k) from the retroverted position in which it laid at the last stage, (fig. 200,) and by a backward folding of the end (fig. 201, d10) of the tail so as to bring it down upon the preceding joints. The meaning of these movements on the part of the head and tail are fully explained in the next phase, (fig. 202,) where we find the tail (tl) completely doubled under the body, the head (k) standing out as a distinct division, and the back (y) projecting above the rest of the body and occupying the region for- merly filled by the upturned abdomen; that is to say, the body has completely reversed its relations to the shell in which it is enclosed, by changing from its former retroflexed condition to a conduplicate position. In addition to the increased elongation of the legs (e,f, g-).and the jaws (b, c) and feelers, the complete formation of the rings of the abdomen, (d1, tl,) and the appearance of a group of eye- rie. 202. The same as fijrs. 198 to 201, but more advanced in development. 220 diam. The position is reversed by doubling the tail (tl) under the body, k, k1, the rifht and left halves of the head; o, the eye; tl, the tail; d1, the first joint of the abdomen; b, the upper, and c, the lower jaws; e,f, g, the legs; y, the remnant of the yolk, on the back; h, h1, a furrow in y where the heart de- velops.— From Zaddach. 302 THE DEVELOPMENT OF ARTICULATA. spots, (o,) there is a beginning of the formation of the heart, by a hollowing of a longitudinal furrow (h, h1) along the middle of the back, and in the midst of the remains of the yolk mass (y). By one more step we come upon that condition of things in which the proportions of the embryo are nearly the same as those which it has when hatched, and commencing the first of its three phases of self-sustaining life, i. e., its worm state. Al- though the body has completed its unrolling, the throat (th) be- come a distinctly marked channel, and the furrow (h) in which the heart forms is nearly or completely covered over, nothing has been added which renders the embryo any more insect-like than in the last stage ; but one or two characters have become developed by which its relations to the Caddice-worms may be inferred. e f 9 The principal of these is exemplified in the forked tail, (fig. 203, d10,) upon h the prongs of which are eventually developed a hook or claw by means y of which the larva clings to the inside of its tubular, aquatic tenement. The other feature is set forth in the very weak, unjaw-like jaws, (6, c,) which, Fig. 203. even in the adult state of the Caddice- fiy are scarcely more than feeble organs of prehension, and are called by that name because they occupy the same position as the genuine masticatory organs of other insects, rather than on account of the office which they perform. When hatched — which happens in the water — the larva construots about itself a cylindrical tube of bits of sticks, which it glues together with a sort of glairy substance similar to that which silk-worms produce to construct their cocoons. After re- siding for a time in their portable domiciles, and becoming fullv Fig. 203. The same as figs. 198 to 202, just before the period of hatching. 220 diam. k, the head; o, the eye; a, the feeler; b, the upper jaw; c, the lower jaw; gn, the lower lip; e,f, g, the legs; r/10, the last joint of the abdomen; th, the throat; y, the remnant of the yolk; h, the furrow in which the heart is de- veloped. — From Zaddach. THE DEVELOPMENT OF VERTEBRATA. 303 developed as larvte, they close up the aperture of the tube, and, changing to a chrysalis, lie dormant until the time for their ap- pearance in a perfect state, when the chrysalis-shell is burst open and the perfect caddice-fly takes to its wings. § Vertebrata. Next to those of the common fowl, none of the eggs of Ver- tebrata are so accessible, and to be had in such large num- bers, as those of Turtles and Tortoises; and, insomuch as they do not require, for hatching, more than the natural heat of the ground in which they are buried when laid, they are, of all eggs, by far the most easily preserved in a healthy state during the time of incubation. All that is required to obtain them is to collect a number of turtles in early spring, before May, and keep them enclosed in some shady spot where they can have easy access to water and soft earth, and feed them well with fresh herbage, such as plantain-leaves, lettuce, beet-leaves, &c, &c, and in the course of time, usually in May and June, they may be caught, at early dawn, digging holes in the earth with their hind legs, and depositing therein their brood of eggs, and then covering them up. As the eggs are required for study they should be taken out one at a time, — carefully, so as not to disturb the others in the least, — and, whilst held in the same position as when in the nest, the shell removed at the upper side so far down as to expose the whole yolk. The eggs of turtles and tortoises have an en- velope of albumen, the so-called white, very much like that of birds; and in order to keep it, as well as the yolk, in shape, and moist, during prolonged observation, it is necessary to sink the egg in some kind of fluid. For a short period water will suffice; but, as it eventually produces an injurious effect, some denser material, such as thin syrup, which does not react so rapidly, had better be used. The fluid which is left after beef-blood has coagulated is perhaps as good as anything that can be had. The first trace of an organization presents itself in the form of a round, light-colored disc which lies close to the surface of 304 THE DEVELOPMENT Fig. 204. the yolk. Upon close examination it will be found that this disc gfl ^ al ali s[l is but the thicker portion (fig. 204, gl) of a layer (gl1) of cells which has been formed all over the periphery of the yolk (y). This layer is called the germinal layer, and the thicker, disc-shaped portion of it the embryonic disc. Owing to the influx of a portion of the liquified albumen, the re- gion (at1) immediately beneath the disc is very transparent at this time; and, by throwing a strong ray of light through it, we may get such a profile view of the various parts as are repre- sented in this figure (fig. 204). One of the chief elements in the formation of the organs of the young turtle is the development of what I have called the subsidiary layer* This is a stratum (si1) of loose yolk granules which originates at the surface of the yolk, and extends all around it. I have called it the subsidiary layer, because it is a sort of intermediary between the unappropriated yolk and the definitely fixed parts of the growing organization ; in fact, as I Fig. 204. Chelydra serpentina. Schweig. 2 diam. A diagramic, profile representation of the incipient germinal disc of the common snapping turtle, as it lies within the egg. al, the white of the egg; y, the yolk ; y1, the surface of the yolk; vs, the periphery of the yolk ; al1, the clear, albuminous region beneath the disc; gl, the disc; gl1, the germinal layer; si, si1, the subsidiary layer. — Original. * See my observations to this effect in Agassiz's " Contributions to the Nat- ural History of the United States," vol. n. p. 536. I would add, in reference to the " European naturalists " mentioned in the " Note on Scientific Property," p. 38, see Kblliker, " Entwickelungsgeschichte, fyc, Akademie Vortrage," 1861, p. 20 ; Gegenbaur, " Bau Sr Entwickl. Wirbelthiereier," Archie, fur Anat. und Phy- siol., 1861, p. 497 ; and also Leuckart, " Berichte " in Wiegman's (TroscheVs) Ar- chie, filr Naturgeschichte, 1864-5. From American scientific men I have re- ceived abundant recognition of my claim, both by correspondence and in public lectures; to say nothing of their free and outspoken sympathy in personal in- tercourse. OF VERTEBRATA. 305 shall show presently step by step, every organ takes its origin from it by a separation of a portion of the thickness of its upper side. I might say, therefore, in the strictest sense, that the ger- minal layer (gl, gl1) is the first to split off from the subsidiary layer. We have, then, in this phase, the following features, namely, the yolk sac (vs) partially occupied by liquified albumen (al1) which has infiltrated through its tissue; the whole raa^ of the yolk (the egg proper) removed from the centre of The white (al) and buoyed up near its upper side, taking the place of the absorbed albumen; the germinal disc (gl) and its peripheric extension, the germinal layer (gl1); and finally, the subsidiary layer (si, si1) from which the germinal layer (gl, gl1) split off. As yet there is no indication of right and left, nor of head and tail, in the germinal disc. These two features develop almost simultaneously. The latter, however, is the first to ap- pear, and may be recognized as a am tl thickening (fig. 205, hd) of one edge of the disc, and a sinking of the germinal layer at that point 9J\ and also at the opposite edge, (am,) so that two shallow furrows are formed. The former becomes ev- ident before the latter has com- pletely developed itself, and may be recognized as a faint, straight, *J&- 205, shallow furrow which passes through the middle anl at the upper surface of the germinal disc (gl). This is called the prim- itive stripe, and corresponds to the axis of the body. In the next phase (figs. 206, 207) the characteristic feature of Vertebrata makes its first appearance; the primary element — the so-called chorda dorsalis — of the vertebral column is formed. Fig. 205. The same as fig. 204, with the shell and white taken off, but further developed. 2 diam. y, the yolk; y1, surface of y; alx, clear, albuminous spate ; gl, the germinal disc; gl1, gt2, the extension of gl beyond the body; hd, the head; tl, the tail; si, si1, sP, the subsidiary layer; am, the furrow around gl; am1, the peripheric fold of am. — Original. 20 306 THE DEVELOPMENT sll Kiifi th1 glps1 si ch ps lid am1 Fig. 206. In this profile figure (fig. 206) it is the thin strip (ch, ch1) which is split away from the subsidiary layer, (si,) except at its anterior (ch) and posterior (ch1) ends, and in the transverse section (fig. 207) it appears as the small circle (ch) which immediately under- lies the primitive stripe, (ps,) and is flanked right and left by a thick layer, (v,) — likewise split off from the subsidiary layer,— which thins out to a sharp edge (v1, v2) near the margin of the disc. With these additions and the further development of the parts already begun we have the following characters, namely, the infiltrating albumen (al1) occupying the -whole upper half of the egg; the germinal layer, not only depressed so as to form a furrow all around the germinal disc, but its fold bent inward (at am1, am?) and elevated so as to partially overlap the slightly in- curved and sunken head (hd) and tail and sides, as it were, enclosing the embryo in a sort of socket, — the beginning of a development of the amniotic sac; the head (hd) considerably increased in thickness, or depth; the primitive stripe (ps, ps1) Fig. 206. The same as figs. 204, 205, still more advanced. 2 diam. y, the yolk; y1, surface of y; al1, the clear, albuminous space ; gl, the germinal disc ; hd, the head; ps,psi, the primitive stripe; ch, ch1, the chorda dorsalis; am1, am3, the peripheric fold of the amniotic sac; am!2, the space beneath am1, and closed below by sP ; si, sll, si2, the subsidiary layer.— Original. Fig. 207. A transverse section of the body, and the layers immediately about it, of fig. 206. al1, the clear, albuminous space; ps, the primitive stripe; gl, the germinal layer of the disc; ch, the chorda dorsalis ; v, the vertebral layer; v1, v2, the edges of v; am}, the peripheric fold of the amniotic sac ; am2, the space beneath the fold of am1; si, si, si2, the subsidiary layer. — Original. OF VERTEBRATA. 307 furrowed deeper into the head and thinning out, i. e., growing shallower toward the mid-length of the body; the chorda dor- salis (ch, ch1) lying between the right and left halves of the body, and just beneath the primitive stripe (ps); the vertebral layer, (v,) upon which the back-bone is eventually developed, com- pletely split off from the upper surface of the subsidiary layer (si) and lying in equal parts right and left of the chorda dorsalis (ch); the subsidiary layer (si) lying close to the under face of the disc, and slightly depressed by the downward curvature of the head and tail, but separated from the rising fold of the ger- minal layer, and extending directly (at sl\ si2) to the periphery of the yolk. In the next phase (fig. 208) it is clear that the embryo has ad- vanced considerably both in regard to the development of those organs already initiated, and by am^hiamii 'i the institution of new features. n The body is nearly enveloped by the uprising and contracting edge (am1, am2) of the amniotic sac. tl The head (hd) and tail (tl) are deeply sunken toward the centre yi of the yolk mass, (y,) and so strongly incurved toward each other as to form a cavity between Fig. 208. them, which opens on the lower side into the great area occupied by the albumen, (al1,) and on the upper is bounded by the inferior surface of that portion of the subsidiary layer (si) which lies between the two ends of the body. The furrow of the primitive stripe extends more than two thirds of the length of the body, and Fig. 208. The same as figs. 204 to 207, but further advanced. A profile view. 2 diam. y, the yolk; yl, the surface of y; al1, the clear, albuminous space; gl, the original germinal disc, now, more properly speaking, the body; hd the head; tl, the tail; ch, the anterior, and ch1, the posterior end of the chorda dorsalis; v, the primitive vertebrae ; am1, am3, the edges of the fold of the amniotic sac; am'2, am'2, the space beneath am1, am3; il, the intestinal layer; h, the heart, a channel in the intestinal layer (il) ; si, the subsidiary layer; si1, st2, that part of the subsidiary layer in which the vascular area is formed. —Original. 308 THE DEVELOPMENT forms a nearly closed tube by the folding together of its edges. In the head this tube is wide and deep, (at hd,) and there con- stitutes the anterior end of the nervous cord, i. e., the brain. Consentaneously with the formation of the hollow nervous cord, the juxtaposed edges of the halves of the vertebral layer become elevated and form a sheath about it. Consequently, we find this layer here, as seen in profile, at the same level with the upper edge of the nervous cord, and extending below to the horizon of the lower face of the chorda dorsalis (ch, ch1). The extent of this layer is rendered conspicuous, in this profile view, by the presence of a few of the preliminary vertebrae, (v,) which have developed from it by a transverse division of its whole thickness into successive squares. The principal additional feature is ob- servable in the inception of the intestinal layer (il). This is formed by the separation of a stratum of cells from the upper face of the subsidiary layer; first at its central portion (si) along the lower face of the body, and then extending centrifugally, not only as far as the head, tail, and sides, but eventually beyond these points, as we shall see presently. We may also see at this period the manner in which the blood-system begins to form, which is by a mere hollowing of channels in the upper surface of the subsidiary layer. The first distinctly bounded cavity of this system is that of the heart, (h,) which, almost from the be- ginning of the formation of the blood-vessels, indicates its char- acter by feeble pulsations. It is a simple, broad, and short tube which lies lengthwise exactly in the lower mid-line of the body, and a short distance behind the head. At the present period the blood merely surges backward and forward in the channels, under the influence of the contraction and expansion of the heart. I shall next lay before you the illustration of a phase of devel- opment which is considerably in advance of the last one, but in Fig. 209. The same as figs. 204 to 208, in a more advanced state of develop- ment than the last. 2 diam. A bird's-eye view of the embryo, vs, the periphery of the yolk ; y, the yolk ; y1, the edge of the upper surface of y; hd, the head ; tl, the tail; n, the region of the nervous cord; ch, the anterior, and ch1, the poste- rior end of the chorda dorsalis (cA3) ; h, the heart; vn, the median blood-vessel; OF VERTEBRATA. 309 which no new organs are intro- p1 rs «'«4 ™ af duced whose origin cannot be easily understood without going through all the intermediate stages. , In regard to the body proper, two things will be noticed at once: the one is that it has fallen on its ,, side, and the other that it is en- tirely enclosed by the amniotic sac (fig. 209, am*, am5). Another prominent general feature lies in the large area oi blood-vessels (ef, cv, cv1, af1). These vessels are but an extension of those whose initiatory formation was pointed out in the last stage. The principal chamber of this system, the heart, (h,) has become transformed into a one-sided, nearly double cavity, by folding upon itself and narrowing the space between its two halves. The blood-vessels are hollowed in the subsidiary layer in two sets, which are respectively named the efferent and afferent ves- sels, i. e., those which carry the blood away from the heart and those which bring it to it again. In the former phase these ves- sels were so undetermined in their course, and so intermingled, that the blood, as I stated, merely surged backward and forward in the same channels ; but since that period they have extended more widely and far beyond the body, and are separated into two groups, which are arranged in this wise: taking the heart (h) as a starting-point, the efferent vessels commence with a single current (vn) which passes from the heart backward and along the mid-line of the lower face of the body to its end. From this single one the vessels of the great net-work (vascular area) arise right and left, and pass, with a few forkings (ef) and inosculations, to a considerable distance beyond the body, where they unite in an irregular circular channel, the vena terminalis, (cv, cv1,) which carries the blood forward beyond the head and ef, the efferent vessels of the vascular area; cv, cv1, the circular vessel (vena terminalis) of the vascular area; af, af1, the afferent vessel; am\ am5, the amniotic sac. — Original. 310 THE DEVELOPMENT empties it into a large single vessel, the afferent vessel, (af, af1,) by which it is transported directly to the posterior chamber (auricle) of the heart. By the increased incurvation of the head (hd) and tail (tl), and the infolding of the sides of the body, the space which lies be- tween these parts is pretty nearly isolated and shaped into a body- cavity. At its anterior region this is entirely closed over, from the head to the point, just behind the heart, where the afferent vessel (af, af1) enters. The preliminary vertebrae are devel- oped along nearly the whole length of the body in a backward direction, and, as a natural consequence, the tubular nervous cord, (n,) or spinal marrow, has likewise closed over to an equal extent. In front, the vertebrae have extended only a short dis- tance, in fact, as far as they will ever appear as distinct bodies. At this period the eyes and ears are so far advanced in develop- ment as to be clearly recognizable in their respective positions. But one stage further we find the relations of the organs and their state of development very much in the condition of those of some of the more lowly organized fishes, and, in certain respects, like those of the Lancelet, (p. 226, fig. 133,) which I described in a previous lecture. This resemblance is especially noticeable ys tj * ejl aj >■ cr ey ao1 ch Fig. 210. Fig. 210. The same as figs. 204 to 209, but more highly developed. 6 diam. A profile view of the body proper and a part of the vascular area. The amni- otic sac has been removed, ey, the eye; e, the ear; cr, the anterior end of the OF VERTEBRATA. 311 in the series of transverse fissures (fig. 210, bf) on each side of the neck, and the blood-vessels (ba) which pass between them, when respectively compared with those of the Lancelet (fig. 133, br, bo). On account of this resemblance — in fact by some assumed as an identity both in form and function — the fissures have been called by embryologists the branchial fissures, and the vessels the branchial aortce, the former corresponding with the pas- sages between the gills of fishes, and the latter with the vessels which supply the gills with blood. In respect to the whole blood- system, there are several additions to, as well as modifications of it, beyond what obtained in the last phase. These will be most easily understood by a description of the courses of the vessels as they now exist. The blood passes from the anterior chamber (h) of the heart in a forward direction, and immediately separates into the four branchial aortae, (ba,) which carry it to the main aorta, (ao, ao,2 aos,) that runs along the upper mid-line of the general cavity of the body. Within the latter the blood passes in two directions. One part of it goes forward into the head in what is called the cephalic aorta, (ao,) which, after branching there, unites (at ao1) its scattered currents into two parallel, recurrent vessels (vn) which run on each side of the aorta to a point (at vn1) near the posterior cavity (h1) of the heart, and there join that organ at the same place with the vessels which come from behind. The other part runs in the main aorta (ao2, aos) to the waist of the body, and there again divides into two sets of currents. One of these continues direct to the end of the tail in the main aorta (aoz), and brain; cr1, the middle region of the brain ; n, the posterior end of the brain; v, v1, the primitive vertebrae, or vertebrae, dorsales ; ch, the anterior end, and ch1, the posterior end of the chorda dorsalis ; ch2, the chorda dorsalis as seen through the vertebra; dorsales; h, the anterior, (ventricle,) and h1, the posterior (auricle) chamber of the heart; ba, the branchial arteries; ao, the cephalic aorta; ao1, the end of ao ; ad2, ao3, the main aorta; ao*, the end of ao2, ao3, where it joins the afferent vessels (vn3) ; ef, ef1, the main efferent vessel; ef2, the net-work of efferent vessels; af, af1, the afferent vessel, or return current, of the vascular area; vn, vn1, the cephalic vein; vn2, vn1, the abdominal vein, or afferent vessel of the right side of the body; bf, the branchial fissures; fl, the right edge of the abdominal aperture; ys, neck of the nutrient organ. — Original. 312 THE DEVELOPMENT there branching and reuniting, — as in the head,—passes forward in a single current (vn2, vns) along each side of the mid-line of the body to the posterior end of the auricle (h1) of the heart. The currents of the other set arise at several points, right and left, along the abdominal aorta, (ao3,) and pass out of the body in numerous channels, (ef, ef1, ef2,) of varying calibre, into the great net-work of vessels of the vascular area, and thence into the as yet devel- oping, half-formed vessels in the depths of the yolk mass. From these the blood is gathered into return currents, which finally unite in the great afferent vessel, (af, of1,) thai passes into the abdominal cavity just behind the heart, and empties its contents into the auricle (h1) at the same point with the termination of other afferent vessels (vn1, vn2). The approximating sides (fi) of the body have not only narrowed the lateral extent of the general cavity, but have closed over a considerable space just in front of the tail. In consequence of this, the membrane or layer over which the vessels of the vascular area are spread is nar- rowed to a sort of neck (ys). In view of this we might say that the yolk is contained in a great saccular prolongation of the sides of the abdominal region; and in consideration that the blood-vessels plunge through it in every direction, and divide it into a sponge-like mass, the name nutrient organ would not be inappropriate for it; at least, it will serve to indicate its nature and peculiar function at this period of life. There is no conspicuous change in the development of that part of the nervous cord which lies behind the head, but that portion which lies in front of the ear, (e,) and corresponds to the brain, has commenced the division of its cavity into two cham- bers, by slight constrictions. The first division extends from the end (cr) of the head backwards to a point nearly opposite the end (ch) of the chorda dorsalis, and corresponds to the cerebral region of the adult (see p. 230, fig. 134); the second division reaches from the termination of the last to the ear, (e,) and an- swers to two parts of the brain ; namely, in front, to the posterior lobes of the cerebrum, and behind, (n,) in the neighborhood of the ear, to the cerebellum, or posterior region of the brain (see OF VERTEBRATA. 313 p. 230, fig. 134, cr). The latter (n) is not as yet closed over so as to form a perfect tube; in fact, even in the adult its opposite edges are united by a thin membrane which is rather the sheath of, than a part of, the tube itself. The eye (ey) is very large in comparison to the size of the head, and, as its position indicates, originates in connection with the anterior part of the brain, whereas the ear (e) is developed from a totally different region, i. e., the cerebellum. Both the eye and ear are saccular prolon- gations or projections from the regions whence they originate ; the one being formed into a cup-shaped body into whose mouth the rays of light pour from every direction, and the other taking the guise of a drum, against whose sides the reverberations of the air pulsate with varying intensity. Beyond this stage the process of development has more especial reference to the formation of a particular kind of reptile, i. e., a turtle, than to the construction of a Vertebrate in general; and I shall therefore merely indicate the further growth of the embryo in as brief terms as possible. The stomach and intes- tine are formed by a folding together of the right and left halves of the membrane in which the blood-vessels run, in such a way as to leave a hollow channel extending from one end of the body to the other, except at that part of it where the yolk sac is at- tached, and there it lies in open communication with the latter. The lungs arise as hollow, saccular prolongations of the sides of the throat. The liver is a thickening of the same membrane from wrhich the stomach was formed, and is perforated in every direction by a dense net-work of blood-vessels. The reproduc- tive organs arise in intimate connection with the posterior end of the intestine. The legs develop as direct outgrowths from the right and left sides; first as mere rounded protuberances, and finally expanding into flattened pads or paws. The shield is formed by a lateral expansion of the regions of the back and front, with anterior and posterior apertures into which the head and legs can be withdrawn. During the progress of the above- mentioned developments, and the increasing size of the body proper, the nutrient organ becomes gradually lessened, and 314 CONCLUSION. finally, just after the hatching of the young, is completely drawn into the body, and resorbed by the intestine. § Conclusion. Thus it appears that there is a plainly visible, intelligent, con- trolling power, which is manifested, with unvarying regularity of character, in each of the five groups of animals. Shall we now undertake to say how far, how minutely, that power operates; and shall we assume that we can tell at what point in time or place this power ceases to act undisturbed in the regularity of its proceedings, and allows itself to be swerved from its course by the apparently disturbing influence of circumstances? Who shall say that these circumstances have not been pro- vided for, or even regulated in the succession of events so as to become a part of the plan ? We all know that the physical agents, light, heat, electricity, magnetism, &c, have a law according to which they evince their operations, — as the science of meteorology teaches; and if, now, these so-called secondary causes have a method among themselves, we should expect to find them likewise affecting the processes of organic nature in the same orderly manner that they affect each other interchangeably ; and consequently evincing the presence of the same directing hand in the one case as the other. We cannot arbitrarily assume that these forces are included in the plan, in one case,— for instance, heat and air in hatching the bird's egg, — and reject them in another, or class them as accidental. How far time and the progress of science may lead us on to a better understanding of the mode of operation of these forces, it is impossible to foresee; but we may, I think, venture the conjecture, that, since in all the thus-far-known phenomena of Nature we have learned to recognize a more or less intimate and direct relation to each other, either in the condition of influ- encing or of being influenced, we shall presently discover that many of the so-called variable influences and accidents have a CONCLUSION. 315 true periodicity of intensification and relaxation, which hitherto has seemed to be irregular, simply because of the individual character of the organism upon which they operate. Every day reveals to us new channels in the courses of nature; but as we trace them back to their source, we find them all to be the branches of one great current, which forces everything before it onward and straightforward into the universal ocean, — the end of all things and the beginning of the new; that great reservoir from which the elements of all beings are derived, and to which they all return, in one' eternal circle of changes, from the elab- orate composition of the body of the growing man to his going down again into the disintegrating, fluttering atoms, and then- final diffusion into the primitive vapors. ADDENDUM. On page 162, line 20, at "vibrating lash," add as a note the following: — I have ascertained by observation, while these pages were going through the press, that this so-called lash is an optical illusion, and that it is really a row of closely set, vibrating cilia seen edgewise, or foreshortened; just as the teeth of a comb would appear if their points projected toward the eye. This has been confirmed by investigations of other species of Vorticellidae, e. g. Epistylis galea, Ehr?, E. grandis, Ehr?, Vorticella nebulifera, Ehr., Carchesium polypinum, Ehr., and Trichodina pediculus, Ehr.; and I conclude, therefore, that the so- called " bristle of Lachman," described and figured as long ago as 1856, (Lachman in " Miill. Archiv. 1856,") does not exist in nature. See, for further details, my forthcoming memoir on the " Anatomy and Physiology of Trichodina," in the "Memoirs of the Boston Society of Natural History." Cambridge, Mass., November 16, 1865. INDEX. A. Abdominal pore, 228. Acanthometrae, 50. Actinophrys, 44, 156. Adults, the primordial state of animals, 106. Aerification, 211.- Affinity, chemical, 7. inorganic, 7. organic, 7. vital, 7. Agassiz on the systematic position of Infusoria, 174. the parasites of Hydra, 174. Vorticellidae and Bryozoa, 174. Albertia, 274. Albumen and yolk of eggs, diverse origin of, 35. of the egg, 33. Alcohol, composition of, 8. Algae, 134, 155. Alternate generation, 67. Aninioeoetes, 125. Ammonia, composition of, 8. Amniotic sac, 306, 309. Amoeba, 9. organic functions of, 11. Amphioxus, 126, 226. Anchorella, 272, 274. Animal-egg, the, 88. Animal-flower, 57. Animals, the lowest forms known, 15. allied by progressive relations, 5. false ideas of development of, 6. and plants, distinction, 131, 151. Animate being, the universe ruled by an, 5. Aquiferous circulatory system of Echi- noderms, 186, 190. Arachnida, 220. Archeopteryx, 277. Area, vascular, 309. Arrangement, spiral, in corals, 60. Articulata, 119, 214. and Protozoa, relations of, 244. compound nature of, 214. and Zoophyta, 246. development of, 298. Artificial division, experiments on Pla- naria, 92. of Amoeba, 95. of Sea-anemones, 89. reproduction after, 89. Ascaris, 36. Asteracanthion, 181. Aurelia, 67, 70. motions in decomposing cells, 98. Axial plane, of Mollusca, 197. Axolotl, 263. B. Bacterium, 18, 23,102. Balbiani on eggs of Infusoria, 31. Beetle, 221. Beings, all living, chemical composition of, 6, 8. Bell-animalcules, 101. Bilaterality, 128, 267. the predominant feature in animals, 249. early appearance of, in ani- mals, 251. relation of, to reproduction, 266. of Zoophyta, 179. Bipolarity, 267. Birds' eggs, 37. Bisymmetry and bilaterality, 185. Blanchard on Planarians, 253. Blood circulation of Echinoderms, 186, 191. Bonellia, 215, 246. Brain, experiments on removal of, 127. duplicity of, 127. relative position of, among animals, 125. Branchial aortae of the embryo, 311. fissures of the embryo, 311. ganglion, 202. Bryopsis, 139. Bryozoa, 195. and Zoophyta, 246. Buccal plates, 190. Budding, individuals arising by, 54. of Bryozoa, 244. Fredericella, 244. Sea-anemone, 60. 318 INDEX. C. Caddice-fly, development of, 298. Carrion-beetle, 221. Caudina, 187, 246. Cells, the egg the type of all, 33. Cellular structure of sponges, 42. Centimetre, 17. Centrum, 231. Cephalization, 211, 220, 230. Dana on, 220. etc., note on, 193. Cephalopoda, 207. position of shell of, 212. Cephalothorax, 219. Ceratium, 147, 156. Cerebral ganglion, 202. Cereus, 58, 179. Chelydra serpentina, 304. Chelyosoma, 253. Chemical affinity, natural, 7. Chilodon, 167. Chipping sparrows, 277. Chlamidomonas, 133, 145, 156. Chorda, 143, 155. Chorda dorsalis, 229, 305. Ciliata, 286. Ciliated infusoria, 148. Circulation in Insects, 224. plants, 166. Cladophora, 140. Claparede on Opalina, 245. Classes of animals, transitions among, 254. Classification of Cuvier, 117. Lamarck, 117. of the principal groups, 255. Clava, 75. Cobbold, on the development of a Sea- anemone, 289. Collar, nervous, 125, 225. Compound individuals, 54. Confervae, spores of, 134. Consanguinity, relations of, 236. Contractile vesicle, 151, 163, 168. of Actinophrys, 47- Contractility in animals, 144. Cornuspira, 13. Coryne. 75, 77, 242. Creation, primary and continued, 30. Creator, primary interposition of, 4. Crustacea, 219. cephalization in, Dana on, 220. Currents of circulation in sponges, 43. Cuttle-fish, 207. Cuvier, classification of, 117. Cyclops, 220, 268, 274. Cytoblastema, 45. D. Dana, J. D., on cephalization, 220. Danielssen and Koren on Siphonactinia, 180. Decomposition, experiments on, 95, 97. Degrees, phenomena of nature differ by, 113. Demodex, 274. Dendroccelum, 92, 268. Design, thoughtful, evidence of, 5. Development of animals, 283. Articulata, 298. Caddice-fly, 298. Mollusca, 294. Mystacides, 298. Protozoa, 285. Sea-anemone, 178, 289. Vertebrata, 303. Zoophyta, 289. old theory of, 158. progressive, 160. phases of, common to all animals, 158. theory, old, 3. new, 3. Difflugia, 11. Digestion in Rhizopoda, 14. mode of, among tape-worms, etc., 100. Digestive system of Infusoria, 167. Diptera, 222. Disc, germinal, 305. Duality of individuals, 267. Duck-billed quadruped, 53. Duck-mole, 279. young of, 53. Dulse, 143. Dysteria, 171. E. Echinodermata, development of, 290. Echinoderms, 181. Egg, mulberry state of, 285. of Infusoria, 31. Laomedea, 33. Rabbit, 32. Sow, 32. place of origin of, variable, 52. segmentation of, 284. structure of, 31, 33, 36. the, and the animal identical, 52. is the first phase of the ani- mal, 52. Eggs, bipolar bodies, 40. floating in the air, 29. Ehrenberg on Infusoria, 167. Embryo, degree of dependence upos the parent, 53. relation of, to external causes, 53. to the parent, 53. Embryonic disc, 304. eggs, 40. forms, Von Baer on, 252, state of animals, 40, 252, INDEX. 319 Encrinite, fossil, 128. Eolidiceros, 253. Epeira, 221. Ephyra of Aurelia, 68. Pelagia, 75. Epistylis, 161, 237. Euglena, 134, 144, 156. Eye-animalcule, 144. Eye-spot of animalculae, 144. false, in Zoospores, 140, 144. F. Fallopian tube, 234. False circulation in Actinophrys, 47. Family traits, 276. Feathered reptile-like bird, 277. Ferment cells, 20. Firolidaj, 253. Fissigemmation explained, 81. Flat-worm, 92. Fly, 222. Flying lizard, 278. Fowl's egg, structure of, 37. Fredericella, 198, 243, 247. budding, 244. Funnel of Cuttle-fish, 208. G. H. Hartshorn, composition of, 8. Hawk-moth, privet, 223. Head-chest, 219. Helix, 20*i. Hemicosmites, 128, 253. bilaterality in, 128. Hereditary transmission, 279. influence, 279. Heteromastix, 134, 146, 156. Heteromita, 134. Holothuria, development of, 291. bilaterality of young, 249. Hood of Nautilus, 213. House-fly, 222. Hydra, 55, 84, 89, 177, 237. artificial division of, 89. budding, 56. experiments on, 89. fresh-water, 55. reproduction of lost parts, 89. Hydro-medusae, 73. individuality of, 73. I. Ideal eggs, 34. relations of the five types, 236. transitions, 236. types, 122, 126. Individual, the true, 54. Individuality, 54, 75, 91. Infusoria, ciliated, 148. development of, Agassiz on, 174. development of, in boiled solu- tions, 15, 101. resistance to heat, 26. Inorganic affinity, 7. bodies, 8. Inosculating groups, 276. Insects, 221. formation of eggs in, 35. Intelligence of Infusoria, 170. Interchangeable relations of animals, 268 Interlocked groups, 276. Intestinal layer, 308. J. Janus, 253. Jaw-like bodies of Infusoria, 173. Jelly-fish, 177. K. Kolpoda, 18, 102. L. Lamarck, classification of, 117. Laminaria, 143, 155. Lancelet, 126, 226. Laomedea, egg of, 33. egg-sesmentation of, 284. Larva of Caddice-fly, 302. Mystacides, 302. Laver, 143. Law of cephalization, 220. reproduction by buddiug, 109. Layer, germinal, 304. intestinal, 308. subsidiary, 304. Lepidosiren, 263. Leivboullet on monstrosities, 85, 267. Garden spider. 220. Generation, spontaneous, 15, 110. Geology in past times, 104. Germigenous organ, 36. Germinal disc, 305. dot, 35. layer, 304. vesicle, 32, 35. character of, 33. layer of Articulate embryo, 299. Globe-animalcule, 153. Glosso-pharyngeal nerve, 231. Gonium, 155. Grand divisions of the animal kingdom, 160. Green Dulse, 143. Groups of the animal kingdom, 121, 160. Growth, parallelisms of, 159. Gryphaea, 203. 320 INDEX. Lereboullet on development of Lymneus, 294. Mollusca, 294. Lerneans, 274. Life, limits of manifestation of, 95. lowest condition of, in the egg, 28, 31. origin of, 3. organic, 8. principle of, 7. Linguatula, 268, 272. Lithocampe, 49, 156. Loligopsis, 206. Longitudinal axis of Sea-anemone, 179. Starfishes, 183. repetition of parts in Artic- ulata, 215. Lowest kinds of animals, 9. Lydella, 274. Lymneus, development of, 294. native, young of, 297. M. Madreporic canal, 185, 191. in young Holothurian, 293. Madreporiform body, 185, 191. Mammalia, 230. Mammary gland, 235. Mantle of Mollusca, 201, 208. Medulla oblongata, 234. Medusa of Coryne, 77. Medusae developed directly from the egg, 75. Meduso-genitalia, 75. Menobranchus, 263. Method in the operations of the Creator, 103. Metridium, 57, 84, 178, 247. Milne Edwards on self-division of worms, 81. Mimetic forms, 248. Mites, 274. Mollusca, 118, 195. development of, 294. and Protozoa, relations of, 243. Monads, 18. Monomerous, the type, 195. Monostroma, 155. Monstrosities, 86. Motile decomposing cells, 98. Motory nerves, 234. Mould, blue, 21. white, 21. Mulberry state of the egg, 285. Miiller on self-division of worms, 81. Multiple self-division, 80. Muscle, decomposition of, 95. Myrianida, 80, 215. Mystacides, development of, 298. Myxine, 125, 253. Myzostoma, 275. N. " Natural Theology " of Paley, 104. Nautilus, 213. position of shell of, 212. Necrophorus, 221. Nervous collar, 125, 225. system, correspondence of, in the grand divisions, 125. system of Stentor, 64. Note on scientific property, 37, 304. Notochord, 229. Nucleolus, 32. Nucleus, 20. Nutrient organ of the Vertebrate embryo, 312. O. Oblique or spiral type, 160. Omne vivwn ex ovo, 85. One-celled animals, 99. Opalina, 174, 245. Order of things, 264. Organic affinity, 7. and inorganic bodies, difference between, 48. life, 8. Ornithorhynchus, 53, 279. Oscillatoria, 25. Ostrea, 200. Ovary, 225. Oviduct, 225. Owen on Amphioxus, 229. Archeopteryx, 278. secondary causes, 102. Oyster, 199. P. " Paley's Philosophy," 5 Paramecium, 163. development of, 286. Parasites of Hydra, Agassiz on, 174. Parentage, common, of species, 277. Pectinatella, 196, 243. Pelagia, 75. Pentatremites, 183. Physical agency in the development of animals, 53. forces, 3. force, relation of the egg to, 100, 102. laws, 3. Physicists, older, laws of, 5. Phytozoa, 156. Planaria, artificial division of, 92. Planariae, 275. Planarians, articulate character of, 263. Plane of the axis of Zoophyta, 243. Protozoa, 243. Plan of creation, original, 106. Plant-animals, 156. Planula of Aurelia, 242. Pleuronema, 148, 156, 170. INDEX. 321 Pneumodermon, 252. Podophrya, 51, 157, 174, 237. development of, 286. Polarity in animals, 127. Poles of the egg, 33, 35. Polyeystinae, 49. Polymerous, dorso - ventrally, the Zo- ophyta, 195. uro-cephally, the Articulata, 195. Polypi, development of, 289. anatomy of, 57, 177. Pore, abdominal, 228. Primarily created animals, condition of, 105. Primitive stripe, 305. Primordial state of the first created ani- mals, 105. Privet Hawk-Moth, 222. Progressive steps, animals related by, 265. Property, scientific, note on, 37, 304. Prostomum, 35. Protean animalcule, 9. Protococcus, 133, 136. Protozoa, 160. and Articulata, relations of, 244. Zoophyta, relations of, 237. Mollusca, relations of, 243. bilaterality of, 175. development of, 285. progressive development of, 40. self-division of, 61. Protula, 251. Pseudopodia, 12, 44. rapid movement of, 13. Psolus, 192. Pterodactylus, 278. Purkinjean vesicle, 32. Q. Quatrefages on Amphioxus, 228. R. Radiata, bilaterality in, 128. Rank, relative, of Articulata, 124, 214. Mollusca, 124, 214. Red-snow plant, 135. Reduction of repeated parts in Articulata, 215. Zoophyta, 187, 192. Relation of organs in typical forms, 126, 159. Reproduction by budding, law of, 109. of lost parts in animals, 94. relation of, to form, 265. bilaterality, 266. Reptilian fishes, 263. Respiratory branches, 190. Rhizogeton, 73, 242. Rhizopoda, 14. Right and left in animals, 127. Rotalia, 14. Rotifera, 275. Round-worm, formation of egg in, 36. S. Sagitta, 96. Saltatory cilia of Infusoria, 150. Sand-eel, 227. Saprolegna, 133, 141. Sarcode, 11. Scientific property, note on, 37, 304. Scorpions, 220. Scyphostoma of Aurelia, 67. tentacles of, 242. organization of, 241. Sea-anemone, 57, 177. young of, 177. development of, 289. Secondary causes, Owen on, 102. relation of embryo to, 111. prevalence of, a matter of degree, 112. Seeds floating in the air, 29. Segmentation of the egg, 284. Self-division among Corals, 61. Protozoa, 61. Vertebrates, 85. in Tape-worms, 82. of Myrianida, 80. worms, 80. Sea-anemone, 61. Shell, relative position of, in Cephalopoda, 212. Shrimps, 274. Siamese twins, 86. Similarity of all animals at earliest pe- riod of growth, 111. Siphonactinia, 180. Siphydora, 41. Sipunculacea, 250. Siren, 263. Snail, 203. development of, 294. Snapping turtle, 304. Song-sparrows, 277. Species, affinities among, 276. Sphinx, 223. Spiders, 220. Spinal column, rudiment of, 229. nature of, 231. Spinal cord, double, 127. Spiracles, "224. Spiral type of animals, 160, 175. Spirillum, 2*3. Spirostomum, egg of, 31. Sponge, 40, 156. Spontaneous generation, 15. origin of theory, 28. probability of, 106. 322 INDEX. Spores, 136. of plants, resistance to heat, 23. Squamella, 268. Squid, 206. Starfish, 177, 181. reproduction of lost parts, 91. Stentor, 62, 84, 160, 163. budding of, 65. development of, 288. egg of, 31. nervous svstem of, 64. young of," 148, 288. Sting-blubber, 70. Stomachs of Infusoria, 167. Stripe, primitive, 305. Subordination of types to bilaterality, 128. Subsidiary layer, 304. Suctoria, 285, 286. Sunfish, 67. Symbolical form of animals, 122, 158. T. Taenia, 83. Tape-worms, 82, 215. Tardigrada, 268, 274. Tentacles, 57, 177. Tetraspora, 155. Thorax of Insects, 222. Thuret on spores of aquatic plants, 133. sea-weeds, 133. Torula, 20. Tracheae, 224. Transitions among classes, 254. minor groups, 262. species, 276. ideal, 236. Trembley's experiments on Hydra, 89. Trepang, 120, 177, 187. Trumpet-animalcule, 62. Tubularia, 75, 79, 238. bilaterality of, 239. arrangement of tentacles of, 239. development of tentacles, 239. Turtle, snapping, 304. development of, 304. Turtles and Tortoises, development of, 303. Turtles' eggs, 37. Twins, 86. Type of division, 160. Types of animals, 117, 122. the five great, 122, 160, 248. Typical animal, 265. bird, 277. egg, 32. forms, relation of organs in, 126. U. Ulva, 143, 155. Uniformity of the organization of Mol- lusca, 195. Up and down, relations of animals to, 121. V. Van Beneden on Linguatula, 273. Lerneans, &c, 274. Van der Hoeven, on Vorticellae, 243. Vascular area, 309. Vaucher on spores of plants, 132. Vena terminalis, 309. Vertebral dorsales, 311. Vertebras, preliminary, of embryo, 310 Vertebral arches, 232. column, elements of, 125. layer, 307. Vertebrata, 118, 226. development of, 303. Vibrio, 96. baccillus, 25. rugula, 18, 102. resistance to heat, 23, 26. Vibrios, false, 97. Vital affinity, 7. Vitality, degrees of, in eggs, &c, 99. Vitelligenous organ, 36. Volvox, 153, 156. Von Baer on embrvonic types, 252. Vorticella;, 161, 237. Vorticellidae, Agassiz on, and Bryozoa, 174. W. Wagnerian vesicle, 32, 35. Water, composition of, 8. What is an animal, 132. Winged mammals, 278. quadrupeds, 278. Winter-eggs, 275. Worm-shaped embryo of Starfish, 248, 250. Molluscan, 248. Wright, Dr. Strethill, on Zooteira, 50. Wyman, Prof. J., experiments of, 15. Y. Yeast-plant, 20. development of, 20. Yolk and albumen of eggs, diverse ori- gin of, 35. of the egg, 33. Z. Zoogloea, 19. Zoophyta, 120, 177. development of, 289. and Articulata, 246. Bryozoa, 246. Protozoa, relations of, 237. Zoospores, 140. Zooteira, 50, 156. Zoothamnium, 163, 175. I J T Mm WiP hb8*p! m :Vl'-