Peet tay tet ly tes ‘ ns peat , itn ietathe th isan! riettiathe eaten attests Ne eat e atin etc! rons eter es Sarat leg Stn he . be ea ahaa tet best ni uiertmstssn Me Haatie xt Neti hohe a Pes taceu tase ae tagiatathty Payteat | ay ity Sa es ite a, tgs ty, Oa dig pares ot pear safieal ecg Sah: | x Bin hm Pan a tata ht Bal td Ce " pe ij toate baa Perens spar pig this th hatha s Hct Si me HS Serial ashe’ Pecan es eee Moh ih ftEg “y iy ii, ihe, fees Giiis tif ye ms res Coatathtee ae if f i tif Wits F if; ij fj & . Sia thig ETE a s needed t, . tas an Oa Kg tere ttntea big Wks * ‘ s. € : . bee : SOAR om Rint ‘ Ss ons aaah . “he, ‘ i : a tg Peas te es, ~~ ee ate tay tg he Me, . Ms im aejbang tag . a fey ~ % ty, r - PFs: Fifi ‘s3 thea: Premarin atte : . : sent : ‘ 2 ‘ Mu phe tn ett Sept reitine Nea? inetel teks Nish Ncontnatana teat heade ‘ Neate : . : Peters es ; nate i . , ie Yattntataeenusaiettlltags han ) iting tries it Sate tat eee Me, #2 fi, ashing a hysteria M iy. . . Sather: niteesertateete tet tert tyres SS Poiliathetacthstneeteas ya 4 si, nts Resta hy Pang ‘, Payahes, . ts "i reltes ae, - skh cts Ye tall tagien* * Mis hatter ct ee, wii YY 1, mts, hte? ty Pats " “antes! taede tatty vag ties eat attired ting tay tte, es Z, iti Jf ip arta tts INS SapPeactn as Ma 4 on . Beaten hh Jecteesitna sayy . ; : . Pees tiasaseaas HesSreiatenfetloai aes : . . ; : sets : Resin yhat mses tees Sta es ee, Ma he ) Letras L niaaaee a Lid@00Y WALYSA1 - > elm heen A teat Re tee amet NR CUR he ie the ete A A Se te ee eile am ~ PART Ic OF THE @iher VOLUME OF THE CONTRIBUTIONS TO THE NATURAL HISTORY OF THE UNITED STATES NORTH AMERICA, BY L.A Wee B68 ee gee (ae Le ESSAY ON CLASSIFICATION. it from On permanent depos the Botany School Cambridge University Library, | ESSAY ON CLASSIFICATION. CHAPITEG” Fest. THE FUNDAMENTAL RELATIONS OF ANIMALS TO ONE ANOTHER AND TO THE WORLD IN WHICH THEY LIVE, AS THE BASIS: OF THE NATURAL SYSTEM OF ANIMALS. Sie TLOs. 1. THE LEADING FEATURES OF A NATURAL ZOOLOGICAL SYSTEM ARE ALL FOUNDED IN NATURE. Mopern classifications of fan and plants are based upon the peculiarities of their_structure, and this is generally considered as the most important, if not the only safe guide in our attempts to determine the natural relations which exist between animals. This view of the subject seems to me, however, to circumscribe the foundation of a natural system of Zodlogy and Botany within too narrow limits, | to exclude from our consideration some of the most striking characteristics of the two organic kmgdoms of nature, and to leave it doubtful how far the arrangement thus obtained is founded in reality, and how far it is merely the expression of our estimate of these structural differences. It has therefore appeared to me appropriate to present here.a short exposition of the leading features of the animal kingdom as. an introduction to the embryology of the Chelonians, one of the most extraordinary types among Vertebrata, as it would afford a desirable opportunity of establishing a standard of comparison between the changes animals undergo during their growth, and the permanent characters of full grown individuals of other types, and, perhaps,. of showing also what other points beside structure might with advantage be consid- 4 ESSAY ON CLASSIFICATION. Part I. ered in ascertaining the manifold relations of animals to one another, and to the world in which they live, upon which the natural system may be founded. ~ In considering these various topics, I shall of necessity have to discuss many questions bearing upon the very origin of organized beings, and to touch upon many points. now under discussion among ‘scientific men. I shall, however, avoid contro- versy as much as possible, and only try to render the results of my own studies and meditations in as clear a manner as I possibly can in the short space I feel justified in devoting to this subject in this volume. : There is no question in Natural History on which more diversified opmions are entertained than respecting classification; not that naturalists disagree as to the necessity of some sort of arrangement in describing animals or plants, for since nature has become the object of special studies, it has been the universal aim of all naturalists to arrange the objects of their investigations in the most natural order possible, and even Buffon, who began the publication of his great Natural History by denying the existence in nature of any thing like a system, closed his work by grouping the birds according to certain general features exhibited m common by many ‘of them. It is true authors have differed in their estimation of the characters on which their different arrangements are founded; it is equally true that they have not viewed their arrangements in the same light, some having plainly acknowledged the artificial character of their systems, whilst others have urged theirs as the true expression of the natural relations which exist between the objects themselves. But whether systems were presented as artificial or natural, they have, to this day, been considered generally as the expression of man’s understanding of natural objects, and not as a system devised by the Supreme Intelligence, and manifested in these objects.? | There is only one “point in these innumerable systems on which all seem to meet, hamely, the existence in nature of distinct species, persisting with all their pecu- liarities, for a time at least, for even the immutability of species has been questioned.” Beyond species, however, this confidence in the existence of the divisions generally admitted in zodlogical systems diminishes greatly. With respect to genera, we find already the number of the naturalists who 1 The expressions constantly used with refer- own making, which ean, however, only be true in so ence to genera and species and the higher groups far as these groups are not true. to nature, if the in our systems as: Mr. A. has made such a species views I shall present below are at all correct. a genus; Mr. B. employs this or that species to form 2 Lamarck (J. B. pe) Philosophie zoologique, his genus; and in which most naturalists indulge Paris, 1809, 2 vols. 8vo.; 2de édit., 1830.—POWELL when spéaking of their species, their genera, their (Tue Rev. Baven) Essays on the Spirit of the In- families, therr systems, exhibit in an unquestiona- ductive Philosophy, etc., London, 1855, 1 vol. 8vo. ble light the conviction that such groups are of their Compare, also, Sect. 15, below. wna mista ei Cnar. L FUNDAMENTAL RELATIONS OF ANIMALS. 5 accept them as natural divisions much smaller, few of them having expressed a belief that genera have as distinct an existence in nature as species, and as to families, orders, classes, or any kind of higher divisions, they seem to be universally considered as convenient devices, framed with the view of facilitating the study of innumerable objects, and of grouping them in the most suitable manner. The indif. ference with which this part of our science is generally treated becomes unjustifiable, considering the progress which Zodlogy in general has made of. late. It is a matter of consequence, whether genera are circumscribed in our systematic works within these or those limits, whether families inclose a wider or more contracted range of genera, whether such or such orders are admitted in a class, and what are the natu- ral boundaries of classes, as well as how the classes themselves are related to one another, and whether all these groups are considered as resting upon the same foun- dation in nature or not. . Without venturing here upon an analysis of the various systems of Zoslogy, the prominent features of which are sufficiently exemplified for my purpose by the SYS- tems of Linnzus and Cuvier! which must be familiar to every student of natural history, it is certainly a seasonable question, to ask whether the animal kingdom exhibits only those few subdivisions into orders and genera, which the Linnean system indicates, or whether the classes differ among themselves to the extent which the system of Cuvier would lead us to suppose. Or is, after all, this complicated: structure of classification merely an ingenious human invention which every one may . shape as he pleases to suit himself? When we remember that all works on natural history admit-some system or other of this kind, it is certainly an inquiry worthy of a true naturalist to ascertain what is the real meaning of all these divisions. Embryology, moreover, forces the inquiry upon us at every step, as it is impos sible to establish precise comparisons between the different stages of growth of young animals of any higher group, and the permanent characters of full grown individuals of other types, without ascertaining first what is the value of the divisions, with which we may have to compare embryos. This is my reason for introducing here, in a work chiefly devoted to Embryology, a subject to which I have paid the most careful attention for many years past, and for the solution of which I have made special investigations. y Before, however, I proceed. any further, I would submit one case. to the consider- ation of my reader. Suppose that the imnumerable articulated animals, which are counted by tens of thousands, nay, perhaps by hundreds of thousands, had never made their appearance upon the surface of our globe, with one single exception, that, for instance, our lobster (Homarus americanus) were the only representative of 1 Compare Chap. III. 6 : ESSAY ON CLASSIFICATION. Parr I. that extraordinarily diversified type, how should we introduce that species of animals in our systems? Simply as a genus with one species, by the side of all the other classes with their orders, families, ete, or-as a family containing only one genus with one species, or as a class with one order and one genus, or as a class with one family and one genus? And should we acknowledge, by the side of Vertebrata, Mollusks, and Radiata, another type of Articulata, on account of the existence of that one lobster, or would it be natural to call him by a single name, simply as a species in contradistinction to all other animals? It was the consideration of this supposed case which led me to the investigations detailed below, which, I hope, may end in: the ultimate solution of this apparently inextricable question. Though what I have now to say about this supposed case cannot be fully appre- ciated before reading my remarks in the following chapter,’ respecting the character of the different kinds of groups adopted in our systems, it must be obvious that our lobster, to be what we see these animals are, must have its frame constructed upon that very same plan of structure which it exhibits now, and if I should succeed in showing that there is a difference between the conception of a plan and the manner in which it is executed, upon.which classes are founded in contradistinction to the types to which they belong, we might arrive at this distinction by a careful investi- gation of that single Articulate as well as by the study of all of them, and we might then recognize its type and ascertain its class characters as fully as if the type embraced several classes, and this class thousands of species. Then that animal has a form, which we could not fail to recognize, and if form can be shown to be char- acteristic of families, we could thus determine its family. Again, besides the general structure, showing the fundamental relations of all the systems of organs of the body to one another in their natural development, our investigation could be carried into the study of the details of that structure in every part, and thus lead to the recognition of what constitutes everywhere generic characters. Finally, as this animal has definite relations to the surrounding world, as the individuals living at the time bear definite relations to one another, as the parts of their body show definite proportions, and as the surface of the body exhibits a special ornamentation, the specific characters could be traced as fully as if a number of other species were at hand for comparison, and they might be drawn and described with sufficient accu- racy to distinguish it at any future time from any other set of species found atfter- wards, however closely these might be allied to it. In this case, then, we should have to acknowledge a separate branch in the animal kingdom, with a class, a family, and a genus, to introduce this one species in its proper place in the system of animals. But this class would have no order, if orders determine the rank as ascertained by 1 See Chap. IT. ee a =O x TPR LS LM NL TS TT a ee EEE a Cuar. I. FUNDAMENTAL RELATIONS OF ANIMALS. 7 the complication of structure; for where there is but one representative of a type, there is no room for the question of its superiority or inferiority in comparison to others within the limits of the class, orders being groups subordinate to the type of the class. Yet, even in this case, the question of the standing of Articulata as a type among the other great branches of the animal kingdom would be open to our investigations ; but it would assume another aspect from that it now presents, as the comparison of Articulata with the other types would then be limited to the lobster, and would lead to a very different result from that at which we may arrive now that this type includes such a large number of most extensively diversified represent- atives, belonging even to different classes. That such speculations are not idle must be apparent to any one who is aware that, during every period in the history of our globe, during the past geological ages! the general relations, the numeric proportions, and the relative importance of all the types of the animal kingdom have been ever changing until their present relations were established. Here, then, the individuals of one species, as. observed while livmg, simultaneously exhibit characters which, to be expressed satisfactorily and in conformity to what nature tells us, would require the establishment, not only of a distinct species, but also of a distinct genus, a distinct family, a distinct class, a distinct branch. Is this not in itself evidence enough that genera, families, orders, classes, and types have the same foundation in nature as species, and that the individuals living at the time have alone a material existence, they bemg the bearers not only of all these different categories of structure upon which the natural system of animals is founded, but also of all the relations which animals sustain to the surrounding world; thus showing that species do not exist in nature in a different way from the higher groups, as is so generally believed? _ The divisions of animals according to branch, class, order, family, genus, and species, by which we express the results of our investigations into the relations of the animal kingdom, and which constitute the first question respecting the scientific systems of Natural History which we have to consider, seem to me to deserve the consideration of all thoughtful minds. Are those divisions artificial or natura] ? Are 1 A series of classifications of animals and plants, of an accurate knowledge of the relative standing of all animals and plants, which can only be infer- red from the perusal even of those palzontological successive geological periods, considered singly and works, in which fossil remains exhibiting each a natural system of the types known to have existed. simultaneously during the several are illustrated accord- ing to their association in different geological forma- show in a strong light the different relations in tions, as in these w without reference to the types of other ages, would orks these remains are uni- formly referred to ‘a system established upon the study of all animals now known, thus lessening the impression of their peculiar combination for the trate in the most impressive manner the importance _ period under consideration which the classes, the orders, the families, and even the genera and species, have stood to one another during each epoch. Such classifications would illus- ——————— a nena 8 ESSAY ON CLASSIFICATION. Part I. they the devices of the human mind to classify and arrange our knowledge in such a manner as to bring it more readily within our grasp, and facilitate further investi- gations, or have they been instituted by the Divine Intelligence as the categories of his mode of thinking?! Have we, perhaps, thus far been only the unconscious interpreters of a Divine conception, in our attempts to expound nature, and when, in our pride of philosophy, we thought that we were inventing systems of science, and classifying creation by the force of our own reason, have we followed only, and reproduced in our imperfect expressions, the plan whose foundations were laid in the dawn of creation, and the development of which we are laboriously studying, thinking, as we put together and arrange our fragmentary knowledge, that we are anew intro- ducing order into chaos? Is this order the result of the exertions of human skill and ingenuity, or is it inherent in the objects themselves, so that the intelligent student of Natural History is led unconsciously by the study of the animal kingdom itself to these conclusions; the great divisions under which he arranges animals being indeed but the headings to the chapters of the great book which he is reading? To me it appears indisputable that this order and arrangement of our studies is based upon the natural, primitive relations of animal life; those systems, to which we have given the names of the great leaders of our science who first established them, being in truth but translations into human language of the thoughts of the Creator. And if this is indeed so, do we not find in this adaptability of the human intellect to the facts of creation, by which we become instinctively, and, as I have said, unconsciously, the translators of the thoughts of God, the most conclusive proof of our affinity with the Divine Mind, and is not this intellectual and spiritual connection with the Almighty worthy our deepest consideration? If there is any truth in the belief that man is made in the image of God, it is surely not amiss for the philosopher to endeavor by the study of his own mental operations to approximate the workings of the Divine Reason, learning from the nature of his own mind better to understand the Infinite Intellect from which it is derived. Such a suggestion may, at first sight, appear irrev- erent. But, which is the truly humble? He who, penetrating into the secrets of crea- | tion, arranges them under a formula, which he proudly calls his scientific system, or he who, in the same pursuit, recognizes his glorious affinity with the Creator, and, in deepest gratitude for so sublime a birthright, strives to be the faithful interpreter of that Divine Intellect with whom he is permitted, nay, with whom he is intended according to the laws of his being, to enter into communion. 1 Jt must not be overlooked here that a system . of a Creator, but merely as the expression of a may be natural, that is, may agree in every respect fact existing in nature, no matter how, which the -with the facts in nature, and yet not be considered -human mind may trace and reproduce in a system- by its author as the manifestation of the thoughts atic form of its own invention. Se OR Bark or a a aes eee 1 i pa re Cuap. I. FUNDAMENTAL RELATIONS OF ANIMALS. 9 I confess that this question as to the nature and foundation of our scientific classifications appears to me to have the deepest importance, an importance far greater indeed than is usually attached to it. If it can be proved that man has not invented, but only traced this systematic arrangement in nature, that these relations and proportions which exist throughout the animal and vegetable world have an intellectual, an ideal connection in the mind of the Creator, that this plan of crea- tion, which so commends itself to our highest wisdom, has not grown out of the necessary action of physical laws, but was the free conception of the Almighty Intellect, matured in his thought, before it was manifested in tangible external forms, —if, in short, we can prove premeditation prior to the act of creation, we have done, once and for ever, with the desolate theory which refers us to the laws of matter as accounting for all the wonders of the universe, and leaves us with no God but the monotonous, unvarying action of physical forces, binding all things to their imevitable destiny.. I thmk our science has now reached that degree of advancement, in which | we may venture upon such an investigation. The argument for the existence of an intelligent Creator is generally drawn from * T allude here only to the doctrines of material- for in whatever manner any state of things which ists; but I feel it necessary to add, that there are physicists, who might be shocked at the idea of being considered as materialists, who are yet prone to be- lieve that when they have recognized the laws which regulate the physical world, and acknowledged that these laws were established by the Deity, they have explained every thing, even when they have consid- ered only the phenomena of the inorganic world, as if the world contained no living beings and as if these living beings exhibited nothing that differed from the inorganic world. Mistaking for a causal relation the intellectual connection observable be- tween serial phenomena, they are unable to perceive any difference between disorder and the free, inde- pendent, and self-possessed action of a superior mind, and call mysticism, even a passing allusion to the existence of an immaterial principle in animals, which they acknowledge themselves in man. [Powett’s Essays, ete., p. 478, 385, and 466. ] I would further remark, that, when speaking of creation in contra- distinction with reproduction, I mean only to allude to the difference there is between the regular Course of phenomena in nature and the establishment of that order of things, without attempting to explain either ; 2 has prevailed for a time upon earth may have been introduced, it is self-evident that its establishment and its maintenance for a determined period are two very different things, however frequently they may be mistaken as identical. It is further of itself plain that the laws which may explain the phenomena of ; the material world, in contradistinction from the or- ganic, cannot be considered as accounting for’ the existence of living beings, even though these have a material body, unless it be actually shown that the action of these laws implies by their very nature the production of such beings. Thus far, Cross’s experi- ments are the only ones offered as proving such a result. I do not know what physicists may think about them now; but I know that there is scarcely a zodlogist who doubts that they only exhibited a mistake. Life in appropriating the physical world to itself with all its peculiar phenomena exhibits, how- ever, some of its own and of a higher order, which cannot be explained by physical agencies. The cir- cumstance that ‘life is so deeply rooted in the inor- ganic nature, affords, nevertheless, a strong tempta- tion to explain one by the other ; but we shall see presently how fallacious these attempts have been. ae ESSAY ON CLASSIFICATION. Paneth the adaptation of means to ends, upon which the Bridgewater treatises, for example, have been based! But this does not appear to me to cover the whole ground, for we can conceive that the natural action of objects upon each other should result in a final fitness of the universe, and thus produce an harmonious whole; nor does _— the argument derived from the connection of organs and functions seem to me more ' satisfactory, for, beyond certain limits, it is not even true. We find organs without functions, as, for mstance, the teeth of the whale, which never cut through the gum, the breast in all males of the class of mammalia; these and similar organs are pre- _ served in obedience to a certain uniformity of fundamental structure, true to the original formula of that division of animal life, even when not essential to its mode ’ of existence. The organ remains, not for the performance of a function, but with reference to a plan? and might almost remind us of what we often see in human s structures, when, for instance, in architecture, the same external combinations are : retained toe the sake of symmetry and harmony of proportion, even when they have ascertained by scientific investigations, and the discussions now carried on i the origin of organized beings. And though I know those who hold it to be very unscientific to believe that thinking is not something imherent in matter, and that there is an essential difference between inorganic and living and thinking beings, I shall not be prevented by any such pretensions of a false philosophy from expressing —— 1 The Bridgewater Treatises, on the Power, Wis- edit. 1837. — Kirpy, (Witt.,) The Power, Wisdom, | wry a ccaaiinniihiaiiedamniiieaibaaiiaabmele 7a cieraiiaien Dela dom, and Goodness of God, as Manifested in the Creation: Cuatmers, (Tuomas,) The Adaptation of External Nature to the Moral and Intellectual Consti- tution of Man, Glasgow, 1839, 2 vols. 8vo.— Kipp, (Joun,) On the Adaptation of External Nature to the Physical Condition of Man, London, 1833, 1 vol. 8vo. — WHEWELL, (WILL.,) Astronomy and General Physics considered with Reference to Natural Theol- ogy, London, 1839, 1 vol. 8vo. — Beit, (CHARLES,) The Hand, its Mechanism and Vital Endowments, as evincing Design, London, 1833, 1 vol. 8vo. — Roger, (Peter Mark,) Animal and Vegetable Physiology, considered with Reference to Natural Theology, Lon- don, 1834, 2 vols. 8vo.—BucKLanp, (WILL.,) Ge- ology and Mineralogy considered with Reference to Natural Theology, London, 1836, 2 vols. 8vo.; 2d and Goodness of God, as Manifested in the Creation of Animals, and in their History, Habits, and Instincts, London, 1835, 2 vols. 8vo.— Provt, (WILL.,) Chem- istry, Meteorology, and the Function of Digestion, considered with Reference to Natural Theology, Lon- don, 1834, 1 vol. 8vo. Compare also: STRAUSS- Durxuerm, (Herc.,) Théologie de la Nature, Paris, 1852, 3 vols. 8vo.— Mitier, (Hvexn,) Footprints of the Creator, Edinburgh, 1849, 1 vol. 12mo.— Bas- pace, (C.,) The Ninth Bridgewater Treatise, a Frag- ment, London, 1838, 1 vol. 8vo.; 2d edit. 2 The unity of structure of the limbs of club- footed or pinnated animals, in which the fingers are never moved, with those which enjoy the most per- fect articulations and freedom of motion, exhibits this reference most fully. mates Cuap. I. FUNDAMENTAL RELATIONS OF ANIMALS. 11 my conviction that as long as it cannot be shown that matter or physical forces do actually reason, I shall consider any manifestation of thought as evidence of the existence of a thinking being as the author of such thought, and shall look upon an intelligent and intelligible connection between the facts of nature as direct proof of the existence of a thinking God,! as certainly as man exhibits the power of thinking when he recognizes their natural relations. As I am not writing a didactic work, I will not enter here into a detailed illus tration of the facts relating to the various subjects submitted to the consideration of my reader, beyond what is absolutely necessary to follow the argument, nor dwell at any length upon the conclusions to which they lead, but simply recall the leading . features of the evidence, assuming in the argument a full acquaintance with the whole range of data upon which it is founded, whether derived from the affinities or the anatomical structure of animals, or from their habits and their geographical distri- bution, from their embryology, or from their succession in past geological ages, and the peculiarities they have exhibited during each? believing, as I do, that isolated and disconnected facts are of little consequence in the contemplation of the whole plan * IT am well aware that even the most eminent investigators consider the task of science at an end, as soon as the most general relations of natural phe- nomena have been ascertained. To many the in- quiry into the primitive cause of their existence seems either beyond the reach of man, or as be- longing rather to philosophy than to physics. To these the name of God appears out of | place in a scientific work, as if the knowledge of secondary agencies constituted alone a worthy subject for their investigations, and as if nature could teach nothing about its Author. Many, again, are no doubt pre- vented from expressing their conviction that the world was called into existence and is regulated by an intelligent God, either by the fear of being sup- posed to share clerical or sectarian prejudices; or because it may be dangerous for them to discuss freely such questions without acknowledging at the same time the obligation of taking the Old Testament as the standard by which the validity of their re- sults is to be measured. Science, however, can only prosper when confining itself within its legitimate sphere; and nothing can be more detrimental to its true dignity than discussions like those which took place at the last meeting of the German association of naturalists, in Géttingen, and which have since then been carried on in several pamphlets in which bigotry vies with personality and invective. * Many points little investigated thus far by most naturalists, but to which I have of late years paid particular attention, are here presented only in an aphoristic form, as results established by extensive investigations, though unpublished, most of which will be fully illustrated in my following volumes, or in a special work upon the plan of the creation. (See AGassiz, (L.,) On the Difference between Progres- sive, Embryonic, and Prophetic Types in the Succes- sion of Organized Beings, Proceed. 2d Meeting Amer. Assoc. for the Advancement of Science, held at Cam- bridge in 1849, Boston, 1850, 1 vol. 8v0., p. 432.) Meanwhile I refer in foot notes to such works as con- tain the materials already on hand for the discussion of these subjects, even when presented in a different light. I would only beg leave to add, that in these references I have by no means attempted to quote all the writers upon the various topics under consider- ation, but only the most prominent and most instruc- tive, and here and there some condensed accounts of the facts in more elementary works, by the side of the original papers. a pape ren oe a ee FS 12 ESSAY ON CLASSIFICATION. Part I. of creation, and that without a consideration of all the facts furnished by the study of the habits of animals, by their anatomy, their embryology, and the history of the past ages of our globe, we shall never arrive at the knowledge of the natural system of animals. Let us now consider some of these topics more specially. SECTION ITI. SIMULTANEOUS EXISTENCE OF THE MOST DIVERSIFIED TYPES UNDER IDENTICAL CIRCUMSTANCES. It is a fact which seems to be entirely overlooked by those who assume an exten- sive influence of physical causes upon the very existence of organized beings, that the most diversified types of animals and plants are everywhere found under iden- tical circumstances. The smallest sheet of fresh water, every point upon the sea- shore, every acre of dry land, teems with a variety of animals and plants. The narrower the boundaries are, which may be assigned as the primitive home of all these beings, the more uniform must be the conditions under which they are assumed to have originated; so uniform, indeed, that in the end the inference would be, that the same physical causes could produce the most diversified effects’ To concede, 1 Jn order fully to appreciate the difficulty al- luded to here, it is only necessary to remember how complicated, and at the same time how localized the conditions are under which animals multiply. The egg originates in a special organ, the ovary; it grows there to a certain size, until it requires fecundation, that is, the influence of another living being, or at least of the product of another organ, the spermary, to determine the further development of the germ, which, under the most diversified conditions, in dif- ferent species, passes successively through all those changes which lead to the formation of a new per- fect being. I then would ask, is it probable that the circumstances under which animals and plants originated for the first time can be much simpler, or even as simple, as the conditions necessary for their reproduction only, after they have once been created? Preliminary, then, to their first appearance, the conditions necessary for their growth must have been provided for, if, as I believe, they were crea- ted as eggs, which conditions must have been con- formable to those in which the living representatives of the types first produced, now reproduce them- selves. If it were assumed that they originated in a more advanced stage of life, the difficulties would be still ereater, as a moment’s consideration cannot fail to show, especially if it is remembered how com- plicated the structure of some of the animals was, which are known to have been among the first in- habitants of our globe. When investigating this sub- ject, it is of course necessary to consider the first appearance of animals and plants, upon the basis of probabilities only, or even simply upon that of pos- sibilities; as with reference to these first-born, at least, the transmutation theory furnishes no explana- tion of their existence. For every species belonging to the first fauna and the first flora which have existed upon earth, special - | | Z : 7 : , : Cuap. I. DIVERSIFIED TYPES FOUND EVERYWHERE. 18 on the contrary, that these organisms may have appeared in the beginning over a wide area, is to grant, at the same time, that the physical influences under which they existed at first were not so specific as to justify the assumption that these could be the cause of their appearance. In whatever connection, then, the first appear- ance of organized bemgs upon earth is viewed, whether it is assumed that they originated within the most limited areas, or over the widest range of their present natural geographical distribution, animals and plants beg everywhere diversified to the most extraordinary extent, it is plain that the physical influences under which they subsist cannot logically be considered as the cause of that diversity. In this, as in every other respect, when considering the relations of animals and plants to the conditions under which they live, or to one another, we are inevitably led to look beyond the material facts of the case for an explanation of their existence. Those who have taken another view of this subject, have mistaken the action and reaction which exist everywhere between organized beings, and the physical influences under which they live’ for a causal or genetic connection, and carried their mistake so far as to assert that these manifold influences could really extend to the production of these bemgs, not considering how inadequate such a cause would be, and that even the action of physical agents upon organized beings presupposes the very exist- ence of those begs.” The simple fact that there has been a period in the history relations, special contrivances must therefore have two questions, the influence of physical agents upon been provided. Now, what would be appropriate animals and plants already in existence, and the ori- for the one, would not suit the other, so that exclud- gin of these beings. Granting the influence of these ing one another in this way, they cannot have origi- agents upon organized beings to the fullest extent nated upon the same point; while within a wider to which it may be traced, (see Sect. 16,) there area, physical agents are too uniform in their mode remains still the question of their origin upon which of action to have laid the foundation for so many neither argument nor observation has yet thrown any such specific differences as existed between the first light. But according to some, they originated spon- inhabitants of our globe. taneously by the immediate agency of physical forces, 1 See, below, Sect. 16. and have become successively more and more diver- ? A critical examination of this’ point may dis- sified by changes produced gradually upon them, by pel much of the confusion which prevails in the dis- these same forces. Others believe that there exist cussions relating to the influence of physical causes laws in nature which were established by the Deity upon organized beings. That there exist definite in the beginning, to the action of which the origin relations between animals as well as plants and the of organized beings may be ascribed; while accord- mediums in which they live, no one at all familiar ing to others, they owe their existence to the im- with the phenomena of the organic world can doubt ; mediate intervention of an intelligent Creator. It that these mediums and all physical agents at work is the object of the following paragraphs to show in nature, have a certain influence upon organized that there are neither agents nor laws in nature bens is equally plain. But before any such action known to physicists under the influence and by the can take place and be felt, organized beings must action of which these. beings could have originated ; exist. The problem before us involves, therefore, that, on the contrary, the very nature of these be- ee ee 14 ESSAY ON CLASSIFICATION. Part I. of our earth, now well known to geologists! when none of these organized beings as yet existed, and when, nevertheless, the material constitution of our globe, and the physical forces acting upon it, were essentially the same as they are now,” shows that these influences are insufficient to call into existence any living being. Physicists know, indeed, these physical agents more accurately than the naturalists, who ascribe to them the origin of organized beings; let us then ask them, whether the nature of these agents is not specific, whether their mode of action is not spe- cific? They will all answer, that they are. Let us further inquire of them, what evidence there is, in the present state of our knowledge, that at any time these physical agents have produced any thing they no longer do produce, and what prob- ability there is that they may ever have produced any organized bemg? If I am not greatly mistaken, the masters in that department of science will, one and all, answer, none whatever. But the character of the connections between organized beings and the physical conditions under which they live is such as to display thought;® these connections are therefore to be considered as established, determined, and regulated by a thinking being. They must have been fixed for each species at its beginning, while the fact of their permanency through successive generations* is further evidence that with their natural relations to the surrounding world were also determined the relations of individuals to one another, their generic as well as their family relations, and every higher grade of affinity,’ showing, therefore, not only thought, in reference to the physical conditions of existence, but such comprehensive thoughts as would embrace simultaneously every characteristic of each species. Every fact relating to the geographical distribution of animals and plants might be alluded to in confirmation of this argument, but especially the character of every ings, and their relations to one another and to the to contain fossils at all, there is a variety of them world in which they live, exhibit thought, and can found together. (See Sect. 7.) Moreover, the simi- therefore be referred only to the immediate action larity in the character of the oldest fossils found in of a thinking being, even though the manner in different parts of the world, goes far, in my opin- which they were called into existence remains for ion, to prove that we actually do know the earliest the present a mystery. types of the animal kingdom which have inhabited 1 Few geologists only may now be inclined to our globe. This conclusion seems fully sustained by believe that the lowest strata known to contain fos- sils, are not the lowest deposits formed since the existence of organized beings upon earth. But even those who would assume that still lower fossiliferous beds may yet be discovered, or may have entirely disappeared by the influence of plutonic agencies, (Poweti’s Essays, ete., p. 424,) must acknowledge the fact that everywhere in the lowest rocks known the fact that we find everywhere below this oldest set of fossiliferous beds, other stratified rocks in which no trace of organized beings can be found. 2 See, below, Sect. 21. ? 8 See, below, Sect. 16. 4 See, below, Sect. 15. > See, below, Sect. 17. 6 See, below, Sect. 6. . Cuap. I. DIVERSIFIED TYPES FOUND EVERYWHERE. 16 . fauna and every flora upon the surface of the globe. How great the diversity of | animals and plants living together in the same region may be, can be ascertained by . the perusal of special works upon the Zodlogy and Botany of different countries, or | from special treatises upon the geographical distribution of animals and plants. I | need, therefore, not enter into further details upon this subject, especially since it is | discussed more fully below2 | It might, perhaps, be urged, that animals living together in exceptional conditions, | and exhibiting structural peculiarities apparently resulting from these conditions, such as the blind fish,» the blind crawfish, and the blind insects of the Mammoth Cave | m Kentucky, furnish uncontrovertible evidence of the immediate influence of those . exceptional conditions upon the organs of vision. If this, however, were the case, \ | how does it happen that that remarkable fish, the Amblyopsis speleus, has only such. ) ae remote affinities to other fishes? Or were, perhaps, the sum of influences at work to make that fish blind, capable also of devising such a combination of structural charac- ters as that fish has in common with all other fishes, with those peculiarities which at the same time distinguish it? Does not, rather, the existence of a rudimentary eye discovered by Dr. J. Wyman in the blind fish show, that these animals, like all others, were created with all their peculiarities by the fiat of the Almighty, and this rudiment of eyes left them as a remembrance of the general plan of structure of — the great type to which they belong? Or will, perhaps, some one of those natural- ists who know so much better than the physicists what physical forces may produce, and that they may produce, and have produced every living bemg known, explain also to us why subterraneous caves in America produce blind fishes, blind crustacea, and blind insects, while in Europe they produce nearly blind reptiles? If there is \ no thought in the case, why is it, then, that this very reptile, the Proteus angwinus, forms, with a number of other reptiles living in North America and in Japan, one of ee * Scumarpa, Die geographische Verbreitung der Thiere, 3 vols. 8vo. Wien, 1853. — Swaryson, (W.,) A Treatise on the Geography and Classification of Animals, London, 1835, 1 vol. 12mo.— ZimmEeRMANN, (E. A. G.,) Specimen Zoologiz geographic, Quadru- pedum domicilia et migrationes sistens, Lugduni-Ba- tav., 1777, 1 vol. 4to.— HumBoupr, Essai sur la géo- graphie des plantes, 4to., Paris, 1805; and Ansichten der Natur, 3d edit., 12mo., Stuttgardt and Tiibin- gen, 1849. — Ropert Brown, General Remarks on the Botany of Terra Australis, London, 1814.— Scuouw, Grundziige einer allgemeinen Pflanzengeo- graphie, 1 vol. 8vo., with atlas in fol., Berlin, 1823. —ALPH. DE CANDOLLE, Géographie botanique rai- sonnée, 2 vols. 8vo., Paris, 1855. References to special works may be found below, Sect. 9. | 2 See, below, Sect. 9. ° Wrman, (Jer.,) Description of a Blind Fish, from a Cave in Kentucky, Srnuiman’s Jour., 1848, vol. 45, p. 94, and 1854, vol. Lis po 2o8. — Ter KAMPF, (TH. G.,) Ueber den blinden Fisch der Mam- muthhéhle in Kentucky, in Miitier’s Archiv, 1844, p. 381. — TeLLKampr, (Tu. G.,) Beschreibung eini- ger neuer in der Mammuthhéhle aufgefundener Gat- tungen von Gliederthieren, Wrrqman’s Archiv, 1844, vol. L., p. 818. — Agassiz, (L.,) Observations on the Blind Fish of the Mammoth Cave,'S nal, 1851, vol. 11, p. 127, ILLIMAN’S Jour- cc “RS A RR CR NR ARRON ANANTRRNN Anna pian ih NB aie ieee mat eae a - - — a I AS te 16 ESSAY ON CLASSIFICATION. Part I. . | the most natural series known in the animal kingdom, every member of which | exhibits a distinct grade! in the scale? After we have freed ourselves from.the mistaken impression that there may be some genetic connection between physical forces and organized beings, there remains a vast field of investigation to ascertain the true relations between both, to their full extent, and within their natural limits? A mere reference to the mode of breathing of different types of animals, and to their organs of locomotion, which are more particularly concerned in these relations, will remind every naturalist of how great importance in classification is the structure of these parts, and how much better they might be understood in this point of view, were the different structures of these organs more extensively studied in their direct reference to the world in which ani- mals live. If this had been done, we should no longer call by the same common name of legs and wings organs so different as the locomotive appendages of the insects and those of the birds? We should no longer call lungs the breathing cavity of snails, as well as the air pipes of mammalia, birds, and reptiles? A great reform is indeed needed in this part of our science, and no study can prepare us better for it than the investigation of the mutual dependence of the structure of animals, and the conditions in which they live. en al men | | | | SECTION ELE. REPETITION OF IDENTICAL TYPES UNDER THE MOST DIVERSIFIED CIRCUMSTANCES. | As much as the diversity of animals and plants living under identical physical . conditions, shows the independence of organized beings from the medium in which | they dwell, so far as their origin is concerned, so independent do they appear again | from the same influences when we consider the fact that identical types occur every- | | where upon earth under the most diversified circumstances. If we sum up all these | various influences and conditions of existence under the common appellation of . cosmic influences, or of physical causes, or of climate in the widest sense of the i : word, and then look around us for the extreme differences in that respect upon the a whole surface of the globe, we find still the most similar, nay identical types (and I \ | allude here, under the expression of type, to the most diversified acceptations of the word) living normally under their action. _ There is no structural difference between the herrings of the Arctic, or those of the Temperate zone, or those of the Tropics, Ga SANE eSNG . 1 See, below, Sect. 12. 2 See, below, Sect. 16. PERL A I nn ee a ene ASSET came ma cm ‘Cuap. I. IDENTICAL TYPES FOUND EVERYWHERE. or those of the Antarctic regions; there are not any more between the foxes and wolves of the most distant parts of the globe.’ Moreover, if there were any, and the specific differences existing between them were insisted upon, could any relation between these differences and the cosmic influences under which they live be pointed out, which would at the same time account for the independence of their structure in general? Or, in other words, how could it be assumed that while these causes would produce specific differences, they would at the same time produce generic identity, family identity, ordinal identity, class identity, typical identity? Identity in every thing that is truly important, high, and complicated in the structure of ani- mals, produced by the most diversified influences, while at the same time these extreme physical differences, considered as the cause of the existence of these ani- mals, would produce diversity in secondary relations only! What logic! Does not all this show, on the contrary, that organized beings exhibit the most astonishing independence of the physical causes under which they live; an independ- ence so great that it can only be understood as the result of a power governing these physical causes as well as the existence of animals and plants, and bringing all into harmonious relations by adaptations which never can be considered as cause and effect ¢ When naturalists have investigated the influence of physical causes upon living beings, they have constantly overlooked the fact. that. the features which are thus modified are only of secondary importance in the life of animals and plants, and that neither the plan of their structure, nor the various complications of that struc- ture, are ever affected by such influences. What, indeed, are the parts of the body which are, in any way, affected by external influences? Chiefly those which are in immediate contact with the external world, such as the skin, and in the skin chiefly its outer layers, its color, the thickness of the fur, the color of the hair, the feathers, and the scales; then the size of the body and its weight, as far as it is dependent on , the quality and quantity of the food; the thickness of the shell of Mollusks, when | they live in waters or upon a soil containing more or less limestone, ete. The | rapidity or slowness of the growth is also influenced in a measure by the course of | the seasons, in different years; so is also the fecundity, the duration of life, etc. But all this has nothing to do with the essential characteristics of animals. A book has yet to be written upon the independence of organized beings of physical causes, as most of what is generally ascribed to the influence of physical agents upon organized beings ought to be considered as a connection established between them in the general plan of creation. 1 Innumerable other examples might be quoted, naturalists; those mentioned above may suffice for which will readily present themselves to professional my argument. 3 ES oy ee sa albdenetien taeieaenlaaein ieamemebemmanaiiieliae ESSAY ON CLASSIFICATION. SHEULLON LV. UNITY OF PLAN IN OTHERWISE HIGHLY DIVERSIFIED TYPES. Nothing is more striking throughout the animal and vegetable kingdoms than the unity of plan in the structure of the most diversified types. From pole to pole, in every longitude, mammalia, birds, reptiles, and fishes, exhibit one and the same plan of structure! involving abstract conceptions of the highest order, far transcending the broadest generalizations of man, for it is only after the most laborious mvestigations man has arrived at an imperfect understanding of this plan. Other plans, equally wonderful, may be traced in Articulata, in Mollusks, in Radiata,? and in the various types of plants? and yet this logical connection, these beautiful harmonies, this infi- nite diversity in unity are represented by some as the result of forces exhibiting no trace of intelligence, no power of thinking, no faculty of combination, no knowledge of time and space. If there is any thing which places man above all other beings in nature, it is precisely the circumstance that he possesses those noble attributes without which, in their most exalted excellence and perfection, not one of these 1 With reference to this point, consult: OKEN, (Lor.,) Ueber die Bedeutung der Schiidel-Knochen, Frankfort, 1807, 4to. (pamphlet.)—Srrx, (J. B.) Cephalogenesis, sive capitis ossei structura, formatio et significatio, Monachii, 1815, fol. — Grorrroy Sr. Hivaire, (Et.,) Philosophie anatomique, Paris, 1818-1823, 2 vols. 8vo., and several papers in the Annal. des se. nat., Annal. and Mém. du Muséum, etc. — Carus, (C. &) Von den Ur-Theilen des Knochen- und Schalengeriistes, Leipzig, 1828, fol.— Owen, (R.) On the Archetype and Homologies of the Vertebrate Skeleton, London, 1848, 8vo. 2 OxeN, (Lor.,) Lehrbuch der Naturphilosophie, Jena, 1809-11, 8 vols. 8vo.; Engl. Elements of Physio-philosophy, Ray Society, London, 1847, 8vo. — Cuvier, (G.,) Sur un nouveau rapprochement a établir entre les classes qui composent. le Regne Ani- mal, Annales du Muséum, vol. xix., 1812. — Savi- eny, (J. C.,) Mémoires sur les animaux sans verte- — bres, Paris, 1816, 8vo.—Bazr, (C. E. v.,) Ueber Entwickelungsgeschichte der Thiere, Konigsberg, 1828, 4to.—LevKARDT, (R.,) Ueber die Morphologie und die Verwandtschaftsverhiiltnisse der wirbellosen Thiere, Braunschweig, 1848, 8vo.— Acassiz, (L.,) Twelve Lectures on Comparative Embryology, Bos- ton, 1849, 8vo.—On Animal Morphology, Proc. Amer. Assoc. for the Adv. of Science, Boston, 1859, 8vo., p. 411. I would call particular attention to this paper, which has immediate reference to the subject of this chapter. — Carus, (V.,) System der thierischen Mor- phologie, Leipzig, 1853, 1 vol. 8vo. 8 Gorne, (J. W.,) Zur Naturwissenhaft tiber- haupt, besonders zur Morphologie, Stuttgardt, 1817- 24, 2 vols. 8vo.; French, Oeuvres d’histoire natu- relle, comprenant divers mémoires d’Anatomie com- parée, de Botanique et de Géologie, traduits et an- notés par Ch. Fr. Martins, Paris, 1837, 8vo. ; atlas in fol. DeCanponin, (Ay “P.) Organographie végétale, Paris, 1827, 2 vols. 8vo. — BRAUN, (At.,) Vergleichende Untersuchung iiber die Ordnung der Schuppen an den Tannenzapfen, als Einleitung zur Untersuchung der Blattstellung iiberhaupt, Act. Nov. Ac. Nat. Curios., vol. xv., 1829.— Das Individuum der Pflanze, Akad. d. Wiss., Berlin, 1853, 4to. Cuap. I. HOMOLOGIES IN DISCONNECTED ANIMALS. 19 general traits of relationship so characteristic of the great types of the animal and vegetable kingdoms, can be understood, or even perceived. How, then, could these relations have been devised without similar powers? If all these relations are almost beyond the reach of the mental powers of man, and if man himself is part and parcel of the whole system, how could this system have been called into existence if there does not exist One Supreme Intelligence, as the Author of all things? SCE Ou oY CORRESPONDENCE IN THE DETAILS OF STRUCTURE IN ANIMALS OTHERWISE ENTIRELY . DISCONNECTED. During the first decade of this century, naturalists began to study relations among animals which had escaped almost entirely the attention of earlier observers. Though Aristotle knew already that the scales of fishes correspond to the feathers of birds? it is but recently that anatomists have discovered the close correspondence which exists between all the parts of all animals belonging to the same type, however dif: ferent they may appear at first sight. Not only is the wing of the bird identical in its structure with the arm of man, or the fore leg of a quadruped, it agrees quite as closely with the fin of the whale, or the pectoral fin of the fish, and all these together correspond in the same manner with their hind extremities. Quite as strik- ing a coincidence is observed between the solid skull-box, the immovable bones of the face and the lower jaw of man and the other mammalia, and the structure of the bony frame of the head of birds, turtles, lizards, snakes, frogs, and fishes. But this correspondence is not limited to the skeleton; every other system of organs exhibits in these animals the same relations, the same identity in plan and structure, whatever be the differences in the form of the parts, in their number, and even in their functions. Such an agreement in the structure of animals is called their homology, and is more or less close in proportion as the animals in which it is traced are more or less nearly related. The same agreement exists between the different systems and their parts in Artic- ulata, in Mollusks, and in Radiata, only that their structure is built up upon respec- tively different plans, though in these three types the homologies have not yet been traced to the same extent as among Vertebrata. There is therefore still a wide 1 AristoTELss, Historia Animalium, Lib. I., Chap. Sect. 4, notes 1 and 2, and the many other works, 1, Sect. 4. 6 ydo év dort ategor, tovto év iyGvi pamphlets, and papers, quoted by them, which aré too éott demic. — Consult also the authors referred to in numerous to be mentioned here. a or 7 . . a ae Ra Ree ee ca though they perform the same functions. The alimentary canal is formed in a very 20 ESSAY ON CLASSIFICATION. Pane T field open for investigations in this most attractive branch of Zodlogy. ~ So much, however, is already plain from what has been done in this department of our science, that the identity of structure among animals does not extend to all the four branches of the animal kingdom; that, on the contrary, every great type 1s constructed upon a distinct plan, so peculiar, indeed, that homologies cannot be extended from one type to the other, but are strictly limited within each of them. The more remote resemblance which may be traced between representatives of different types, 1s founded upon analogy, and not upon affinity. While, for instance, the head of fishes exhibits the most striking homology with that of reptiles, birds, and mammalia, as a whole, as well as in all its parts, that of Articulata is only analogous to it and to its part. What is commonly called head in Insects is not a head like that of Vertebrata; it has not a distinct cavity for the brain, separated from that which communicates below the neck with the chest and abdomen; its solid envelope does not consist of parts of an internal skeleton, surrounded by flesh, but is formed of external rings, like those of the body, soldered together ; it contains but one cavity, which includes the cephalic ganglion, as well as the organs of the mouth, and all the muscles of the head. The same may be said of the chest, the legs and wings, the abdomen, and all the parts they contain. The cephalic ganglion is not homologous to the brain, nor are the organs of senses homologous to those of Vertebrata, even different way in the embryos of the two types, as are also their respiratory organs, and it is as unnatural to identify them, as it would be still to consider gills and lungs as homologous among Vertebrata now embryology has taught us that im differ- ent stages of growth these two kinds of respiratory organs exist in all Vertebrata in very different organic connections one from the other. What is true of the branch of Articulata when compared to that of Vertebrata, is equally true of the Mollusks and Radiata when compared with one another or with the two other types, as might easily be shown by a fuller illustration of the correspondence of their structure, within these limits. This inequality in the fun- damental character of the structure of the four branches of the animal kingdom points to the necessity of a radical reform in the nomenclature of comparative ; anatomy? Some naturalists, however, have already extended such comparisons respecting the structure of animals beyond the limits pointed out by nature, when they have attempted to show that all structures may be reduced to one norm, and 1 See Swanson, (W.,) On the Geography and = mologies of Radiated Animals, with Reference to j Classification of Animals, London, 1835, 12mo., p. the Systematic Position of the Hydroid Polypi, 129, where this point is ably discussed. Proc. of the Amer. Assoc. for the Adv. of Science 2 See Acassiz, (L.,) On the Structure and Ho- for 1849, Boston, 1850, 1 vol. 8vo. p. 389. Cuap. I. DEGREES AND KINDS OF RELATIONSHIP. 21 when they have maintained, for instance, that every bone existing in any Vertebrate must have its counterpart In every other species of that type. To assume such a uniformity among animals, would amount to denying to the Creator even as much freedom in expressing his thoughts as man enjoys. If it be true, as pointed out above, that all animals are constructed upon four different plans of structure, in such a manner that all the different kinds of animals are only different expressions of these fundamental formule, we may well compare the whole animal kingdom to a work illustrating four great ideas, between which there is no other connecting link than the unity exhibited in the eggs in which their most diversified manifestations are first embodied in an embryonic form, to undergo a series of transformations, and appear in the end in that wonderful variety of inde- pendent living beings which inhabit our globe, or have inhabited it from the earliest period of the existence of life upon its surface. The most surprising feature of the animal kingdom seems, however, to me to rest neither in its diversity, nor in the various degrees of complication of its struc- ture, nor in the close affinity of some of its representatives, while others are so different, nor in the manifold relations of all of them to one another and the sur- rounding world, but in the circumstance that beings endowed with such different and such unequal gifts should nevertheless constitute an harmonious whole, intelligibly connected in all its parts. Se Pen VI: VARIOUS DEGREES AND DIFFERENT KINDS OF RELATIONSHIP AMONG ANIMALS. The degrees of relationship existing between different animals are most diversified. They are not only akin as representatives of the same species, bearmg as such the closest resemblance to one another; different species may also be related as members of the same genus, the representatives of different genera may belong to the same family, and the same order may contain different families, the same class different orders, and the same type several classes. The existence of different degrees of affinity between animals and plants which have not the remotest genealogical connec- tion, which live in the most distant parts of the world, which have existed in periods long gone by in the history of our earth, is a fact beyond dispute, at least, within certain limits, no longer controverted by well informed observers. Upon what can this be founded? Is it that the retentive capacity of the memory of the physical forces at work upon this globe is such, that after bringing forth a type according to one pattern, in the infancy of this earth, that pattern was adhered to under conditions, 22 ESSAY ON CLASSIFICATION. Part I. no matter how diversified, to reproduce, at another period, something similar, and so on, through all ages, until at the period of the establishment of the present state of things, all the infinitude of new animals and new plants which now crowd its surface, should be cast in these four moulds, in such a manner as to exhibit, notwithstanding their complicated relations to the surrounding world, all those more deeply seated general relations, which establish among them the different degrees of affinity we may trace so readily in all the representatives of the same type? Does all this really look more like the working of blind forces than like the creation of a reflec- tive mind establishing deliberately all the categories of existence we recognize im nature, and combining them in that wonderful harmony which unites all things into such a perfect system, that even to read it, as it is established, or even with all the imperfections of a translation, should be considered as the highest achievement of the maturest genius ? Nothing seems to me to prove more directly and more fully the action of a reflective mind, to indicate more plainly a deliberate consideration of the subject, than the different categories upon which species, genera, families, orders, classes, and branches are founded in nature, and manifested in material reality in a succession of individuals, the life of which is limited in its duration to comparatively very short periods. The great wonder in these relations consists in the fugitive character of the bearers of this complicated harmony. For while species persist during long periods, the individuals which represent them are ever changing, one set dying after the other, in quick succession. Genera, it is true, may extend over longer periods; fami- lies, orders, and classes may even have existed during all periods during which animals have existed at all; but whatever may have been the duration of their existence, at all times these different divisions have stood in the same relation to one another and to their respective branches, and have always been represented upon our globe in the same manner, by a succession of ever renewed and short-lived individuals. As, however, the second chapter of this work is entirely devoted to the consider- ation of the different kinds and the different degrees of affinity existing among animals, I will not enter here into any details upon this subject, but simply recall the fact that, in the course of time, investigators have agreed more and more with one another in their estimates of these relations, and built up systems more and more conformable to one another. This result, which is fully exemplified by the history of our science is in itself sufficient to show that there is a system in nature 1 Sprx, (J.,) Geschichte und Beurtheilung aller naturelles, Paris, 1826, 4 vols. 8vo.— Histoire des Systeme in der Zoologie, Niirnberg, 1811, 1 vol. 8vo. sciences naturelles, etc., Paris, 1841, 5 vols. 8vo. — Cuvier, (G.,) Histoire des progrés des sciences — DrEBLAINVILLE, (H.,} Histoire des sciences de Cuap. I. RABIAEST TYPES -OF ANIMALS. 20 to which the different systems of authors are successive approximations, more and more closely agreeing with it, m proportion as the human mind has understood nature better. This growing coincidence between our systems and that of nature shows further the identity of the operations of the human and the Divine intellect ; especially when it is remembered to what an extraordinary degree many @ priori conceptions, relating to nature, have in the end proved to agree with the reality, in spite of every objection at first offered by empiric observers. SUCTION, (a Lt. SIMULTANEOUS EXISTENCE IN THE EARLIEST GEOLOGICAL PERIODS, OF ALL THE GREAT TYPES OF ANIMALS. It was formerly believed by geologists and paleontologists that the lowest animals first made their appearance upon this globe, and that they were followed by higher and higher types, until man crowned the series. senting at all the present state of our knowledge, may now furnish the evidence that this is not the case. On the contrary, representatives of numerous families of the animal kingdom, are well known to Every geological museum, repre- belonging to all the four great branches have existed simultaneously in the oldest geological formations.’ Nevertheless, I well remember when I used to hear the great geologists of the time assert, that the Corals were the first inhabitants of our globe, that Mollusks and Articulata followed in order, and that Vertebrates extraordinary change the last thirty years have brought about in our knowledge, and | the doctrines generally adopted respecting the existence of animals and plants in past may still differ in their views regarding the origin, ages! However much naturalists they now all know that neither Radiata, the gradation, and the affinities of animals, nor Mollusks, nor Articulata, sERLING, (Count ALEX. von,) The Geology of Russia in Europe, and the Ural Mountains, London, 1845, 2 vols. 4to.— Hatt, (Jamxs,) Paleontology of New York, Albany, 1847-52, 2 vols. 4to.— Bar- Vorganisation et de leurs progrés, Paris, 1847, 3 vols. 8vo. — Poucuet, (F. A.,) Histoire des sciences na- turelles au moyen Age, Paris, 1853, 1 vol. 8vo. Compare, also, Chap. II., below. 1 Murcurson, (R. IL.) The Silurian System, Lon- RANDE, (J.,) Systeme silurien du centre de la Bo- don, 1839, 1 vol. 4to.— Murcutson, (Str R. I.) heme, Prague and Paris, 1852, 2 vols. 4to.— Srpe- Siluria. The History of the Oldest Known Rocks wick, (A.,) and McKoy, (Fr.,) British Paleozoic containing Fossils, London, 1854, 1 vol. 8vo. — Mur- Rocks and Fossils, London, 1851, 4to. 2 fase.; not CHISON, (R. I.) pE VERNEUIL, (Ep.,) and Kat- yet complete. did not appear until long after these. What an } have any priority one over the other, as to the time — be «fe ~J \ 24 ESSAY ON CLASSIFICATION. Part I. of their first appearance upon earth; and though some still maintain that Vertebrata originated somewhat later, it is universally conceded that they were already in exist- ence toward the end of the first great epoch in the history of our globe. I think /it would not be difficult to show upon physiological grounds that their presence upon earth dates from as early a period as any of the three other great types of the animal kingdom, since fishes exist wherever Radiata, Mollusks, and Articulata are found together, and the plan of structure of these four great types constitutes a system intimately connected in its very essence. Moreover, for the last twenty years, every extensive investigation among the oldest fossiliferous rocks has carried the origin of Vertebrata step by step further back, so that whatever may be the final solution of this vexed question, so much is already established by innumerable facts, that the idea of a gradual succession of Radiata, Mollusks, Articulata, and Ver- tebrata, is for ever out of the question. It is proved beyond doubt, that Radiata, Mollusca, and Articulata are everywhere found together in the oldest geological for- mations, and that very early Vertebrata are associated with them, to continue together through all geological ages to the present time. This shows that even in those early days of the existence of our globe, when its surface did not yet present those diversified features which it has exhibited in later periods, and which it exhibits in still greater variety now, animals belonging to all the great types now represented upon earth, were simultaneously called into existence. It shows, further, that unless the physical elements then at work could have devised such plans, and impressed them upon the material world as the pattern upon which Nature was to build for ever afterwards, no such general relations as exist among all animals, of all geo- logical periods, as well as among those now living, could ever have existed. This is not all: every class among Radiata, Mollusks, and Articulata, is known to have been represented in those earliest days, with the exception of the Acalephs' and Insects only. It is, therefore, not only the plan of the four great types which must have been adopted’ then, the manner in which these plans were to be executed, the systems of form under which these structures were to be clothed, even the ulti- mate details of structure which in different genera pear definite relations to those of other genera; the mode of differentiation of species, and the nature of their rela- tions to the surrounding media, must likewise have been determined, as the character of the classes is as well defined as that of the four great branches of the animal kingdom, or that of the families, the genera, and the species. Again, the first rep- resentatives of each class stand in definite relations to their successors in later 1 Acalephs have been found in the Jurassic Lime- softness of their body. Insects are known as early stone of Solenhofen; their absence in other forma- as the Carboniferous Formation, and may have ex- tions may be owing simply to the extraordinary isted before. ae PP ce — ee ee Cuap. I. EARLIEST TYPES OF ANIMALS. 25 periods, and as their order of apparition corresponds to the various degrees of com- plication in their structure, and forms natural series closely linked together, this natural gradation must have been contemplated from the very beginning. There can be the less doubt upon this point, as man, who comes last, closes in his own cycle a series, the gradation of which points from the very beginning to him as its last term. I think it can be shown by anatomical evidence that man is not only the last and highest among the living beings, for the present period, but that he is the last term of a series beyond which there is no material progress possible upon the plan upon which the whole animal kingdom is constructed, and that the only | improvement we may look to upon earth, for the future, must consist in the develop- ment of man’s intellectual and moral faculties. The question has been raised of late how far the oldest fossils known may truly be the remains of the first inhabitants of our globe. No doubt extensive tracts of fossiliferous rocks have been intensely altered by plutonic agencies, and their organic contents so entirely destroyed, and the rocks themselves so deeply metamorphosed, that they resemble now more closely eruptive rocks even than stratified deposits. Such changes have taken place again and again up to comparatively recent periods, and upon a very large scale. Yet there are entire continents, North America, for instance, in which the palzeozoic rocks have undergone little, if any, alteration, and where the remains of the earliest representatives of the animal and vegetable king- doms are as well preserved as in later formations. In such deposits the evidence is satisfactory that a variety of animals belonging to different classes of the great branches of the animal kingdom have existed simultaneously from the beginning; so that the assumption of a successive introduction of these types upon earth is flatly contradicted by well established and well known facts.” Moreover, the remains found e everywhere closely allied to one another. In Russia, in m the oldest deposits, ar other parts of the world, where these oldest Sweden, in Bohemia, and in various formations have been altered upon a more 0 North America, where they have undergone little or no change, they present the that close correspondence in their structure and in the r less extensive scale, as well as in same general character, combination of their families, which shows them to have belonged to contempora- neous fauns. It would, therefore, seem that even where metamorphic rocks prevail, the traces of the earliest inhabitants of this globe have not been entirely obliterated. 1 AGASSIZ, (L.,) An Introduction to the Study Number of Animals in Geological Times, Amer. of Natural History, New York, 1847, 8vo. p- 57. Journ. of Science and Arts, 2d ser. vol. 17, 1854, 2 Agassiz, (L.,) The Primitive Diversity and p. 309. 4 wo atl ESSAY ON CLASSIFICATION. SECTION VIII. THE GRADATION OF STRUCTURE AMONG ANIMALS. There is not only variety among animals and plants; they differ also as to their standing, their rank, their superiority or inferiority when compared to one another. But this rank is difficult to determine; for while, in some respects, all animals are equally perfect, as they perform completely the part assigned to them in the general economy of nature; in other respects there are such striking differences between them, that their very agreement in certain features points at their superiority or inferiority im regard to others. This being the case, the question first arises, Do all animals form one unbroken series from the lowest to the highest? Before the animal kingdom had been studied so closely as it has been of late, many able writers really believed that all animals formed but one simple continuous series, the gradation of which Bonnet has been particularly industrious in trying to ascertain” At a later period, Lamarck’ has endeavored to show further, that in the complication of their structure, all the classes of the animal kingdom represent only successive degrees, and he is so thoroughly convinced that in his systematic arrangement classes constitute one grad- ual series, that he actually calls the classes “degrees of organization.” DeBlainville * has in the main followed in the steps of Lamarck, though he does not admit quite so simple a series, for he considers the Mollusks and Articulates as two diverging branches ascending from the Radiata, to converge again and unite in the Vertebrata. But since it is now known how the great branches of the animal kingdom may be circumscribed,» notwithstanding a few doubtful poimts; since it is now known how 1 EHRENBERG, (C. G.,) Das Naturreich des Men- - 4 BLaINvILye, (H. D. px,) De Organisation des schen, oder das Reich der willensfreien beseelten Na- Animaux, Paris, 1822, 1 vol. 8ve. turkérper, in 29 Classen iibersichtlich geordnet, Ber- 5 Biumensacn, (J. Fr.,) Handbuch der verglei- lin, 1835, folio, (1 sheet). chenden Anatomie, Géttingen, 1824, 1 vol. 8vo.; 2 Bonnet, (Cu.,) Considérations sur les corps Engl. by W. Lawrence, London, 1827, 1 vol. 8vo. organisés, Amsterdam, 1762, 2 vols. 8vo. — Contem- — Cuvier, (G.,) Lecons d’ Anatomie comparée, rec. plations de la Nature, Amsterdam, 1764-65, 2 vols. et publ. par MM. Duméril et Duvernoy, Paris, 8vo.— Palingénésie philosophique, Genéve, 1769, 2 1800-1805, 5 vols. 8vo.5 Qde édit., rev. par MM. vols. 8vo. : F. G. Cuvier et Laurillard, Paris, 1836-89, 10 vols. 3 Lamarck, (J. B. pE,) Philosophie zoologique, 8vo.— Cuvier, (G.,) Le Regne animal distribué Paris, 1809, 2 vols. 8vo. d@aprés son organisation, Paris, 1817, 4 vols. 8vo.3 ee Pe EY TP Cuap. I. GRADATION OF STRUCTURE AMONG ANIMALS. 27 most classes should be characterized, and what is their respective standing; since every day brings dissenting views, respecting the details of classification, nearer together, the supposition that all animals constitute one continuous gradated series, can be shown to be contrary to nature. Yet the greatest difficulty in this inquiry, is to weigh rightly the respective standing of the four great branches of the whole . animal kingdom; for, however plam the inferiority of the Radiata may seem, when | compared with the bulk of the Mollusks or Articulata, or still more evident when . contrasted with the Vertebrata, it must not be forgotten, that the structure of most Echinoderms is far more complicated than that of any Bryozoon or Ascidian of the . type of Mollusks, or that of any Helminth, of the type of Articulata, and, perhaps, . even superior to that of the Amphioxus among Vertebrata. These facts are so well ascertained, that an absolute superiority or inferiority of one type over the other must be unconditionally denied. As to a relative superiority or inferiority however, determined by the bulk of evidence, though it must be conceded that the Vertebrata rank above the three other types, the question of the relative standing of Mollusks ther to rest upon a difference in the tendency of their whole structure; concentration being the and Articulata seems ra organization, than upon a real gradation m their prominent trait of the structure of Mollusks, while the expression ‘outward display’ would more naturally ‘ndicate that of Articulata, and so it might seem as if Mollusks | 7 and Articulata were standing on nearly a level with one: another, and as much Leipzic, 1843-44, 1 vol. 8vo., 2d vol. by Frey and LeucKArDT ; Icones anatomice, Leipzig, 1841, fol. — Grant, (R. E.) Outlines of Comparative Anat- omy, London, 1835, 1 vol. fol. —Jonzs, (Rrmer,) A General Outline of the Animal Kingdom, London, 1838-39, 1 vol. 8vo. fig. ; 2d edit. 1854. — Topp, (R. B.,) Cyclopedia of Anatomy and Physiology, London, 1835-52, 4 vol. 8vo. fig—AGassiz, (L.,) and Goutn, (A. A.,) Principles of Zodlogy, Boston, 1 vol. 8vo., 2d edit. 1851. — Owen, (R.,) Lectures on the Inver- tebrate Animals, London, 18438, 1 vol. fig.; 2d edit. 1855.— Lectures on the Comparative Anatomy of the Vertebrate Animals, Fishes, London, 1846, 1 vol. . Qde édit. 1829-30, 5 vols. 8vo.; Be édit. illustrée 1836 et suiv; Engl. Trans. by Grirriru, London, ) 1824, 9 vols. 8vo.— Mxrcxet, (J. F.,) System der . . vergleichenden Anatomie, Halle, 1821-31, 6 vols. | 8vo.; French Transl., Paris, 1829-38, 10 vols. 8vo. . — Treviranus, (G. R.,) Biologie, oder Philosophie . der lebenden Natur, Gottingen, 1802-16, 6 vols. 8vo. 3 — Die Erscheinungen und Gesetze des organischen Lebens, Bremen, 1831-37, 5 vols. 8vo. — DELLE Cuiase, Istituzioni d’Anatomia e Fisiologia compa- rata, Napoli, 1832, 8vo.— Carus, (C. G.,) Lehrbuch der vergleichenden Anatomie, Leipzic, 1834,,2 vols.,. Ato., fig. 2d edit.; Grundsiitze der vergleichenden Ana- . tomie, Dresden, 1828, 8vo.; Engl. by R. J. GORE, 8vo.. fig. — SrEBOLD, (C. Tu. v..) und STANNIUS, Bath, 1827, 2 vols. 8vo. Atlas. — Carus, (C. G.,) and (Herm.,) Lehrbuch der vergleichenden Anatomie, Orro, (A. W.) Erliuterungstafeln zur vergleichen- Berlin, 1845-46, 2 vol. 8vo.; 2d edit. 1855; Engl. den Anatomie, Leipzic, 1826-40, fol. — WAGNER, Trans. by W. J. Burnertr, Boston, 1854. — Brerc- (R.,) Lehrbuch der vergleichenden Anatomie, Leipzic, MANN, (C.,) und LeucKkarpt, (R.,) Vergleichende 1834-35, 2 vol. 8vo.; Engl. by A. Tux, London, Anatomie und Physiologie, Stuttgardt, 1852, 1 vol. 1844, 1 vol. 8vo.; 2d edit. Lehrbuch der Zootomie, 8vo. fig. ill aad Tar: See e hiatal 28 acu & ON CLASSIFICATION. | Part I. above Radiata, as both stand below Vertebrata, but constructed upon plans expressing different tendencies. To appreciate more precisely these most general relations among the great types of the animal kingdom, will require deeper investigations into the character of their plan of structure than have been made thus far: Let, how- ever, the respective standing of these great divisions be what it may; let them differ only in tendency, or in plan of structure, or in the height to which they rise, admitting their base to be on one level or nearly so, so much is certain, that im each type there are representatives exhibiting a highly complicated structure and others which appear very simple. Now, the very fact that such extremes may be traced, within the natural boundaries of each type, shows that in whatever manner these great types are supposed to follow one another in a single series, the highest representative of the preceding type must join on to the lowest representative of | the following, thus bringing necessarily together the most heterogeneous forms? = It must be further evident, that in proportion as the internal arrangement of each great type will be more perfected, the greater is likely to appear the difference at the two ends of the series which are ultimately to be brought into connection with those of other series, in any attempt to establish a single series for all animals. I doubt whether there is a naturalist now living who could object to an arrange- ment in which, to determine the respective standing of Radiata, Polyps would be placed lowest, Acalephs next, and Echinoderms highest; a similar arrangement of Mollusks would bring Acephala lowest, Gasteropoda next, and Cephalopoda highest ; Articulata would appear in the following order: Worms, Crustacea, and Insects, and Vertebrata, with the Fishes lowest, next Reptiles and Birds, and Mammalia highest. I have here purposely avoided every allusion to controverted points. Now if Mol- lusks were to follow Radiata in a simple series, Acephala should join on to the Echinoderms; if Articulata, Worms would be the connecting link. We should then have either Cephalopods or Insects, as the highest term of a series beginning with Radiata, followed by Mollusks or by Articulates. In the first case, Cephalopods would be followed by Worms; in the second, Insects by Acephala. Again, the con- nection with Vertebrata would be made either by Cephalopods, if Articulata were considered as lower than Mollusks, or by Insects, if Mollusks were placed below Articulata. Who does not see, therefore, that in proportion as our knowledge of the true affinities of animals is improving, we accumulate more and more convincing evidence against the idea that the animal kingdom constitutes one simple series ? 1 [ regret to be unable to refer here to the con- ' between Progressive, Embryonic, and Prophetic tents of a course of lectures which I delivered upon Types, Proc. Am. Assoc. for 1849, p- 432. this subject, in the Smithsonian Institution, in 1852. 2 Ac assiz; (5) Animal Morphology, Proc. Am. Compare, meanwhile, my paper, On the Differences Assoc. for 1849, p. £15. Mt a ge Cuap. I. GRADATION OF STRUCTURE AMONG ANIMALS. 29 The next question would then be: Does the animal kingdom constitute several, — or any number of graduated series? In attempting to ascertain the value of the less when compared to one another, the difficulties seem to be comprehensive groups, It is already possible to mark out with tolerable precision, gradually less and less. the relative standing between the classes, though even here we do not yet perceive in all the types the same relations. Among Vertebrata, there can be little if any doubt, that the Fishes are lower than the Reptiles, these lower than Birds, and that Mammalia stand highest; it seems equally evident, that in the main, Insects and Crustacea are superior to Worms, Echinoderms to Acalephs and Polypi. of which over many Crustacea, would be difficult to prove; there are Worms which Cephalopods to Gasteropods and Acephala and But there are genuine Insects, the superiority in every respect appear superior to certain Crustacea; the structure of the highest Acephala seems more perfect than that of some Gasteropods, and that of the Halcyo- - noid Polyps more perfect than that of many aes es seem to be so limited in the range of their characters, as to justify in every type a complete serial arrangement among them. age et) hardly be doubted that the gradation of these natural divisions among themselves in | each class, constitutes the very essence of this kind of groups. As a special para- ! graph is devoted to the consideration of the character - orders in ny. next chapter, I need not dwell longer upon this point here! It will fs aide cge! for me to remark now, that the difficulties geologists have met with, m wee attempts to com- pare the rank of the different types of animals and plants with the order of their succession in different geological periods, they have expected to find a serial gradation, same type, where it is only incomplete, but even among the types themselves, between which such a gradation cannot be traced. Had they limited their compari- sons to the orders which are really founded upon gradation, the result would have been quite different; but to do thi yology and with Zodlogy proper, than can naturally be expected . of which are chiefly devoted to the investigation of the struct- Hydroids. Classes / do, therefore, not But when we come to the orders, it can | has chiefly arisen from the circumstance, that not only among the classes of the s requires more familiarity with Comparative Anatomy, with Embr of those, the studies ure of our globe. To appreciate fully the importance of this question of the gradation of animals, and to comprehend the whole extent of the difficulties involved in it, a superficial acquaintance with the perplexing question of the order of succession of animals in past geological ages, is by no means sufficient; a complete familiarity with the many attempts which have been made to establish a correspondence between the two, and with all the crudities which have been published upon this subject, might dispel 1 See Chap. II. j 30 . ESSAY ON CLASSIFICATION. Part I. every hope to arrive at any satisfactory result upon this subject, did it not appear now, that the inquiry must be circumscribed within different limits, to be conducted upon its true ground, The results to which I have already arrived, since I have perceived the mistake under which investigators have been laboring thus far, m this respect, satisfy me that the point of view under which I have presented the subject here is the true one, and that in the end, the characteristic gradation exhibited by the orders of each class, will present the most striking correspondence with the character of the succession of the same groups in past ages, and afford another startling proof of the admirable order and gradation which have been estab- lished from the very beginning, and maintained through all times in the degrees of ae NEN complication of the structure of animals. SHOCTION IX. RANGE OF GEOGRAPHICAL DISTRIBUTION OF ANIMALS. The surface of the earth being partly formed by water and partly by land, and the organization of all living beings standing in close relation to the one or the other | of these mediums, it is in the nature of things, that no single species, either of ani- mals or plants, should be uniformly distributed over the whole globe. Yet there are some types of the animal, as well as of the vegetable kingdom, which are equably distributed over the whole surface of the land, and others which are as widely scat- tered in the sea, while others are limited to some continent or some ocean, to some particular province, to some lake, nay, to some very limited spot of the earth’s surface.t As far as the primary divisions of animals are concerned, and the nature of the medium to which they are adapted does not interfere, representatives of the four great branches of the animal kingdom are everywhere found together. Radiata, Mollusks, Articulata, and Vertebrata occur together in every part of the ocean, in the Arctics, as well as under the equator, and near the southern pole as far as man has penetrated; every bay, every inlet, every shoal is haunted by them. So univer- 2 IER ERIE OR PAE RD IH f 1 The human race affords an example of the wide Ocean, how fishes may be circumscribed in the sea, | a distribution of a terrestrial type; the Herring and and that of the Goniodonts of South America in 1 | the Mackerel families have an equally wide distri-- the fresh waters. The Chaca of Lake Baikal is f 4" ; . bution in the sea. The Mammalia of New Hol- found nowhere else; this is ‘equally true of the : i if ' land show how some families may be limited to one Blindfish (Amblyopsis) of the Mammoth Cave, and \ | continent; the family of Labyrinthici of the Indian of the Proteus of the caverns of Carinthia. "| AE AEE Ae TIT eee sal is this association, / consider it as GEOGRAPHICAL RANGE OF ANIMALS. 3l Cuap.. I. not only at present but in all past geological ages, that I a sufficient reason to expect, that fishes will be found in those few fossiliferous beds of the Silurian System, in which thus far they have not yet been \ found! Upon land, we find equally everywhere Vertebrata, Articulata, and Mollusks, but no Radiata, this whole branch being limited to the waters; but as far as terres- trial animals extend, we find representatives of the other three branches associated, as we find them all four in the sea. Classes have already a more limited range of distribution. Among Radiata, all aquatic, they are all marine, inhabits fresh waters. marine and partly fluviatile, the Gasterop partly terrestrial, while all Cephalopoda are marine. partly terrestrial, while many are internal are partly marine, partly fluviatile, and 1 See, above, Sect. 7. 2 For the geographical distribution of Radiata, Dana, (J. D.,) Zoophytes. United States Exploring Expedition, under the’ command of Ch. Wilkes, U. S. N., Philadelphia, 1846, 1 vol. Ato. Atlas fol. —Minyz-Epwarps et Hare, (Jot) Recherches sur les Polypiers, Ann. Sc. Nat. 8e sér. vol. 9-18, Paris, 1848-52, 8vo. — ESCHSCHOLTZ, (Fr.,) System der Acalephen, Berlin, 1829, 4to. fi. — Lesson, (R. Pr.,) Histoire naturelle des Zoophy- tes, Acaléphes, Paris, 1843, 1 vol. 8vo. fig. Soni KER, (A.,) Die Schwimmpolypen und Siphonophoren von Messina, Leipzic, 1853, 1 vol. fol. fig. — Mut- Ler, (J.,) und Troscuet, (F. H.,) System der Asteriden, Braunschweig, 1842, 8vo. fig. — AGASSIZ, (L.,) Catalogue raisonné des familles, des genres et des espéces de la Classe des Echinodermes, Ann. des Se. Nat. 3e sér. vol. 6-8, Paris, 1847, 8vo. ® T need hardly say in this connection that the so-called fresh-water Polyps, Aleyonella, Plumatella, ete., are Bryozoa, and not true Polyps. * For the geographical distribution of Mollusks, consult: Lamarck, (J. B. DE,) Histoire naturelle des Animaux sans vertebres, Paris, 1815-22, 7 vols. 8vo.; 2de édit. augmentée de notes par MM. DusHayves and Mitne-Epwarps, Paris, 1835-48, 10 vols. 8vo.—Fervssac, (J. B. L. px,) Histoire naturelle des Mollusques terrestres et fluviatiles. Paris, 1819 et suiv, 4to. fig. fol., continuée par Des- consult: the Polypi, Acalephs, and Echinoderms’ are not only with a single exception, the genus Hydra, which Among Mollusks,* the Acephala are all aquatic, but partly oda partly marine, partly fluviatile and Among Articulata,’ the Worms Hayes.— Fervussao, (J. B. L. pzE,) et SANDER- Rane, (A.,) Histoire naturelle des Aplysiens, Paris, 1828, 4to. fig. fol.— Frrussac, (J. B. L. px,) et p’Orpieny, (A.,) Monographie des Céphalopodes eryptodibranches, Paris, 1834-48, fol. — Marrinq, (F. H. W.,) und Curmnirz, (J. H.) Neues syste- ‘matisches Conchylien-Kabinet, Niirnberg, 1769-95, 11 vols. 4to. fig; new edit. and continuation by Scuupert and A. WAGNER, completed by H. C. Kuster, Niirnberg, 11 vols. 4to. fig. — Kiener, (L. C.,) Spécies général et Icenographie des Coquilles vivantes, Paris, 1834, et suiv, 8vo. fig.— REEvE, (Lovell,) Conchologia Iconica; a Complete Repertory of Species of Shells, Pictorial and Descriptive, Lon- don, 1843, and foll., 4to. fig. — PFEIFFER, (L.,) Mon- egraphia Heliceorum viventium, Leipzig, 1847-48, 8vo. —Preirrer, (L.,) Monographia Pneumonopo- morum viventium, Cassel, 1852, 8vo., and all the special works on Conchology. 5 The mode of distribution of free or parasitic Worms, in different parts of the world and in differ- ent animals, may be ascertained from: Grusx, (A. Ep.,) Die Familien der Anneliden, Wiegman’s Ar- chiv, 1850. I mention this paper in preference to any other work, as it is the only complete list of An- nulata; and though the localities are not given, the references may supply the deficiency. — RupoLrut, (Kk. yials into ever new forms and new combinations. trace its existence, organized beings, on the contrary, transform these same mate- The carbonate of lime of all ages is the same carbonate of lime in form as well as composition, as long as it is under the action of physical agents only. Let life be introduced upon earth, 1 BaRRANDE’s Syst. Silur., q, a., p. 23. 2 Gr. G. v. Minster, Beitriige zur Petrefacten- kunde, q. a., p. 98. ® DesmareEsT, see Brongniart and Desmarest’s Hist. Nat. d. Tril. et Crust., q. a., p. 97. * See, above, p. 93. 5 Scuimper, (W. P.,) et Movexrot, (A.,) Mono- graphie des Plantes Fossiles du Grés-bigarré de la chaine des Vosges, Strasb. et Paris, 1840-43, 4to. fig. . 6 BucKLAND, (W.,) On the Cycadeoide, a Family of Plants found in the Oolite, ete., Trans. Geol. Soc. Lond. 2d ser. IL, p. 395. ” Uncer, (Fr.,) Chloris protogea, Beitrige zur Flora der Vorwelt, Leipzig, 1841, 4to. fig. — Herr, (O.,). Flora tertiaria Helvetie, Wintherthur, 1855, fol. fig. ‘8 Landscapes of the different geological periods are represented in Unenr, (FR.,) Die Vorwelt in ihren vershiedenen Bildungsperioden, Wien, fol. (no date.) These landscapes are ideal representations of the vegetation of past ages. Cuar. L SUCCESSION OF ANIMALS AND PLANTS. 101 and a Polyp builds its coral out of it, and each family, each genus, each species a different one, and different ones for all successive geological epochs. Phosphate of lime in paleozoic rocks is the same phosphate, as when prepared artificially by Man; but a Fish makes its spines out of it, and every Fish in its own way, a Turtle its shield, a Bird its wings, @ Quadruped its legs, and Man, like all. other Vertebrates, its whole skeleton, and during each successive period in the history of our globe, these structures are different for different species. What similarity is there between these facts! Do they not plainly idicate the working of different agencies excluding one another? Truly the noble frame of Man does not owe its origin to the same forces which combine to give a definite shape to the crystal. And what is true of the carbonate of lime, is equally true of all Inorganic sub- stances; they present the same characters Let us look upon the subject in still another light, and we shall see that the same is also true of the influence of all the only one to which, though erroneously, the The effects it may now in all ages past, as those they exhibit now. physical causes. Among these agents, the most powerful is certainly electricity ; formation of animals has ever been directly ascribed. produce, it has always produced, and produced them in the same manner. It has various earthy minerals and deposited them in crystalline reduced metallic ores and it has transported these and other form, in veins, during all geological ages; substances from one point to another, in times past, as we may do now in our Evaporation upon the surface of the earth has which after accumulating have been Rain drop marks in the carbonifer- laboratories, under its influence. always produced clouds in the atmosphere, condensed in rain showers in past ages aS NOW. ght to us this testimony of the identity of the to remind us that what these agents may the oldest geological times, and have ous and triassic rocks have brou operation of physical agents in past ages, do now, they already did in the same way, in Who could, in presence of such facts, assume any causal con- the one of which is ever obeying the successive period new relations, an done at all times. nection between two series of phenomena, same laws, while the other presents at every ever changing gradation of new combinations, dean Who does not see, on the contrary, that this identity of the totally disproves any influence on their part leading to a final climax with the appearance of Man? products of physical agents in all ages, : ‘in the production of these ever changing beings, which constitute the organic world, and which exhibit, as a whole, such striking evidence of connected thoughts! ESSAY ON CLASSIFICATION. SECTION XXII. LOCALIZATION OF TYPES IN PAST AGES. The study of the geographical distribution of the animals now living upon earth has taught us, that every species of animals and plants has a fixed home, and even that peculiar types may be circumscribed within definite limits, upon the surface of our globe. But it is only recently, since geological investigations have been carried on in remote parts of the world, that it has been ascertained that this special localization of types extends to past ages. Lund for the first time showed that the extinct Fauna of the Brazils during the latest period of a past age, consists of different representatives of the very same types now prevalent in that continent; Owen has observed similar relations between the extinct Fauna of Australia? and the types now living upon that continent. . If there is any naturalist left who believes that the Fauna of one continent may be derived from another portion of the globe, the study of these facts, in all their bearing, may undeceive him. It is well known how characteristic the Edentata are for the present Fauna of the Brazils, for there is the home of the Sloths, (Bradypus,) the Tatous, (Dasypus,) the Ant-eaters, (Myrmecophaga); there also have been found those extraordinary extinct genera, the Megatherium, the Mylodon, the Megalonyx, the Glyptodon, and the many other genera described by Dr. Lund and Professor Owen, all of which belong to this same order of Hdentata. Some of these extinct genera of Edentata had also representatives in North America, during the same geological period? thus showing that though limited within similar areas, the range of this type has been different in different epochs. Australia, at present almost exclusively the home of Marsupials, has yielded also a considerable number of equally remarkable species, and two extinct genera of that type, all described by Owen in a report to the British Association, in 1844, and in Michell’s Expeditions into the Interior of Australia. | 1 Lunp, (Dr.,) Blik paa Brasiliens Dyreverden of Extinct Mammalia, Ann. and Mag. Nat. Hist., 1846, for sidste Jordomveltning. K. Danske Vidensk. vol. 17, p. 197. - Selsk. Afhandl. VIII., Kidbenhavn, 1841, 4to. fig., p. ® Lerpy, (Jos.,) A Memoir on the Extinct Sloth 61, etc.; Engl. Abstract, Ann. and Mag: vol. 3, p. Tribe of North America, Smithson. Contrib. 1855, 4to. 422. fig. — Wyman, (J.,) Notice of Fossil Bones, ete., Am. 2 Owen, (R.,) On the Geographical Distribution Journ. Se. and A., 2d ser., 1850, vol. 10. Cuap. I. EARLY LOCALIZATION OF TYPES. 108 How far similar facts are likely to occur in other classes, remains to be ascer- tained. Our knowledge of the geographical distribution of the fossil remains is yet too fragmentary to furnish any further data upon this pomt. It is, however, worthy of remark, that though the types of the oldest geological periods had a much wider distribution than most recent families exhibit now, some families of fishes largely represented in the Devonian system of the Old World have not yet been noticed among the fossils the Cephalaspids, the Dipteri, and the Acanthodi. Again, of the many gigantic d Oolitic periods, none are known to occur elsewhere of that period in America, as, for instance, Reptiles of the Triasic an : it can hardly be simply owing to the less extensive dis- except in Europe, and of the world, since other fossils of tribution of these formations in other parts . the same formations are known from other continents. It is more likely that some of them, at least, are peculiar to limited areas of the surface of the globe, as, even in Europe, their distribution 1s not extensive. . Without, however, entering upon debatable ground, it remains evident, that before the establishment of the present state of things, peculiar types of animals, which ead formerly circumscribed within definite limits, have continued to occupy present period, even though no genetic. con- their representatives in these different forma- Such facts are in the most direct the same or similar grounds in the nection can be assumed between them, tions not even belonging to the same genera. contradiction with any assumption that physical agents could have any thing to do with their origin; for though their occurrence within might at first seem to favor such a view, it must be borne in mind gee these her types which have a much wider range, similar geographical areas so localized beings are associated with ot ore significant, they belong to different geological periods, have undoubtedly taken place. Thus the at the theory assumes; they prove a and, what is still m | between which great physical changes facts indicate precisely the reverse of wh organized beings during successive geological periods, not- continued similarity of ye sical conditions, which the withstanding the extensive changes, in the prevailing phy country they inhabited may have undergone, at different periods. In whatever direc- tion this theory of the origin of animals and plants, — stand a critical examiation. Only the delib- under the influence of physical agents, is approached, it can nowhere erate intervention of an Intellect, acti account for phenomena of this kind. ng consecutively, according to one plan, can ESSAY ON CLASSIFICATION. SHOT LO Beak seb LIMITATION OF SPECIES TO PARTICULAR GEOLOGICAL PERIODS. Without entering into a discussion respecting the precise limits within which this fact is true, there can no longer be any doubt, that not only species, but all other groups of animals and plants, have a definite range of duration, as well as individ- uals! The limits of this duration, as far as species are concerned, generally coin- cide with great changes in the physical conditions of the earth’s surface ;* though, strange to say, most of those investigators who would ascribe the origin of organ- ized beings to the influence of such causes, maintain also, that species may extend from one period to another, which implies that these are not affected by such changes.’ When considering, in general, the limitation of species to particular geological periods, we might very properly disregard the question of the simultaneity of the successive appearance and disappearance of Faune, as in no way affecting the result of the investigation, as long as it is universally conceded, that there is no species, known among the fossils, which extends through an indefinite series of geological formations. Moreover, the number of the species, still considered as identical in several successive periods, is growing smaller and smaller, in proportion as they are more closely compared. I have already shown, long ago, how widely many of the tertiary species, long considered as identical with living ones, differ from them} and also. how different the species of the same family may be, in successive subdivisions. of the same great geological formation.” Hall has come to ' the same result in his investigations of the fossils of the State of New York. Every monograph reduces: their number, in every formation. Thus Barrande, who has devoted so many years to the most minute investigation of the Trilobites of + Compare Sect. XTX. 2 Evie DE Beaumont, Recherches sur quelques- unes des Révolutions de la surface du Globe, Paris, 1830, 1 vol. 8vo. § For indications respecting the occurrence of all species of fossil organized beings now known, consult, Brown, (H. G.,) Index palxontologicus, Stuttgardt, 1848-49, 3 vols. 8vo. — Orpreny, (A. D’,) Prodrome de Paléontologie stratigraphique universelle etc., Paris, 1850, 2 vols. 12mo. — Morris, (J.,) Catalogue of the British Fossils, London, 1854, 1 vol. 8vo. * Acassiz, (L.,) Coquilles tertiaires reputées identiques avec les espéces vivantes, Neuchatel, 1845, Ato. fig. 5 Acassiz, (L.,) Etudes critiques sur les Mollus- ques fossiles, Neuchatel, 1840-45, 4to. fig. 6 Hart, (J.,) Paleontology of the State of New York, q.'a.,'p. 23, note 1. Cuap. I. LIMITATION OF SPECIES (IN TIME. | 105 Bohemia?! has come to the conclusion that their species do not extend from one formation to the other; D’Orbigny* dnd Pictet® have come to the same conclusion for: the fossil: remains ‘of all classes: “It. may well be, said that, as. fossil remaimse are studied more carefully, in a zoUlogical point of view, the supposed identity of species, in different geological formations, vanishes gradually more and more; so that the limitation of species in time, already ascertained in a general way, by the earlier investigations of their remains in successive geological formations, is circum- scribed, step by step, within narrower, more definite, and also more equable periods. Species are truly limited in time, as they are limited in space, upon the surface of. the globe. The facts do not exhibit a gradual disappearance of a limited number of species, and an equally gradual introduction of an equally limited number of new creation and the simultaneous destruc- ones; but, on the contrary, the simultaneous tion of entire faune, and a coincidence betwe and the great physical changes our earth has undergone. to attempt to determine the extent of the geographical range of these changes, and still more questionable to assert their synchronism upon the whole surface of the en these changes in the organic world Yet it would be premature globe, in the ocean and upon dry land. To form adequate ideas of the great physical changes the surface of our globe has undergone, and the frequency of these modifications of the character of the earth’s surface, and of their coincidence with the changes observed among the organ- ized beings, it is necessary to study attentively the works of Ele de Beaumont. He, for the first time, attempted to determine the relative age of the different sys- tems of mountains, and showed first, also, that the physical disturbances occasioned by their upheaval coincided with the successive disappearance of entire faune, and the reappearance of new ones. In his earlier papers he recognized seven, then twelve, afterwards fifteen such great convulsions of the globe, and now he has traced more or less fully and conclusively the evidence that the number of these disturbances has been at least sixty, perhaps one hundred. But while the genesis and genealogy of our mountain systems were thus illustrated, paleontologists, extend- ing their comparisons between the fossils of different formations more carefully to all the successive beds of each great era, have observed more and more marked differences between them, and satisfied themselves that faunz also have been more frequently renovated, than was formerly supposed; 80 that the general results of 1 BaRRANDE, Systeme silurien, etc., q. a.3; see, 4 Eire pe Beaumont, Notice sur les systemes de Montagnes, Paris, 1852, 3 vols. 12mo.; see, also, Bucu, (Lor. v.,) Ueber die geognotischen Systeme von Deutschland, Leonhard’s Taschenb., 1824, IL., p. also, my Monographies d’Echinodermes, q. a., p. 54. 2 D’Orzieny, Paléontologie Frangaise, q. a., p. 95. 8 Piotet, Traité de Paldéontologie, etc., q. a., p. 96, note 1. O01. 14 106 | ESSAY ON CLASSIFICATION. Part I. geology proper and of paleontology concur in the main to prove, that while the globe has been at repeated intervals, and indeed frequently, though after immensely long periods, altered and altered again, until it has assumed its present condition, so have also animals and plants, living upon its surface, been again and again extin- guished and replaced by others, until those now living were called into existence with man at their head. The investigation is not in every case sufficiently com- plete to show everywhere a coincidence between this renovation of animals and plants and the great physical revolutions which have altered the general aspect of the globe, but it is already extensive enough to exhibit a frequent synchronism and correlation, and to warrant the expectation that it will, im the end, lead to a com- plete demonstration of their mutual dependence, not as cause and effect, but as steps in the same progressive development of a plan which embraces the physical as well as the organic world. : In order not to misapprehend the facts, and perhaps to fall back upon the idea, that these changes may be the cause of the differences observed between the fossils of different periods, it must be well understood that, while organized beings exhibit through all geological formations a regular order of succession, the character of which will be more fully illustrated hereafter, this succession has been from time to time violently interrupted by physical disturbances, without any of these altering in any way the progressive character of that succession of organized beings. Truly this shows that the important, the leading feature of this whole drama is the development of life’ and that the material world affords only the elements for its realization. The simultaneous disappearance of entire faune, and the following simultaneous appearance of other faune, show further that, as all these faunz con: sist of the greatest variety of types, in all formations, combined everywhere into natural associations of animals and plants, between which there have been definite relations at all times, their origin can at no time be owing to the limited influence of monotonous physical causes, ever acting im the same way. Here, again, the intervention of a Creator is displayed in the most striking manner, in every stage of the history of the world. | 1 Dana, (J. D.,) Address, q. a., p. 94, note 1. ° Acassiz, (L.,) Geol. Times, q. a., p. 25. Cuap. I. SUCCESSION AND STANDING OF ANIMALS. SECTION: XLV. PARALLELISM BETWEEN THE GEOLOGICAL SUCCESSION OF ANIMALS AND PLANTS AND THEIR PRESENT RELATIVE STANDING. The total absence of the highest representatives of the animal kingdom in the oldest deposits forming part of the crust of our globe, has naturally led to the very general belief, that the animals of the history of our earth were inferior to those now living, nay, that there is d lowest animals to the highest now in exist- which have existed during the earliest period a natural gradation from the oldest an ence! To some extent this is true; form one simple series from the earliest times, of animals would have been represented, to the last period, when Man appeared at the head’ of the animal creation? Jt has already been shown (Sect. VII). that - representatives of all the great types of the animal kingdom have existed from the beginning of the creation of organized beings. Ie ESI a AOR EA Msi sive appearance of the great branches of the animal kingdom, that we may expect | succession in geological times and their relative pondence be observed between the but it is certainly not true that all animals during which only the lowest types to trace a parallelism between their standing at present. Nor can any such corres appearance of classes, at least not among Radiata, Mollusks, and Articulata, as their respective classes seem to have been introduced simultaneously upon our earth, with perhaps the sole exception of the Insects, which are not known to have existed mong Vertebrata, however, there appears already a before the Carboniferous period. A of the classes, between the time of their certain coincidence, even within the limits introduction, and the rank their representatives h But upon this point more hereafter. It is only within the limits of the different orders of each class, that the paral- lelism between the succession of their representatives in past ages and their respec- decidedly characteristic. But if this is true, it old, in comparison to one another. tive rank, in the present period, is must be at the same time obvious spondence may be influenced by the state of our and natural gradation of living animals, and that until our classifications have become the correct expression of these natural relations, with the succession of their representatives in past ages may be entirely overlooked. On that account it would be presumptuous on my part to pretend, that I could to what extent the recognition of this corre- knowledge of the true affinities even the most striking coincidence 1 See the paleontological works quoted in Sect. 21. 2 AcassizZ, (L.,) Twelve Lect., ete, p. 25 and 69. = ~ “ — ~~ Sree acl cc is Sans A nis. ODS ani. IAA thas" illic ME ain ati i ot atti Ss Sr OARS naar anOTNAAD DORR — a os Sean See = — : : . Sica eet aie Ls a deco a eee ll stile wt 2 a SS ——— = —- - 7 — " i oan a ie 108 ESSAY ON CLASSIFICATION. Part IL illustrate this proposition, through the whole animal kingdom, as such an attempt would involve the assertion that I know all. these relations, or that where there exists a discrepancy between the classification and the succession of animals, the classification must be incorrect, or the relationship of the fossils incorrectly appre- ciated. I shall therefore limit myself here to a general comparison, which may, however, be sufficient to show, that the improvements which have been introduced in our systems, upon purely zodlogical grounds, have nevertheless tended to render more apparent the coincidence between the relative standimg among living animals and the order of succession of their representatives in past ages. I have lately attempted to show, that the order of Halcyonoids, among Polyps, is superior to that of Actinoids;* that, in this class, compound communities constitute a higher degree of development, when contrasted with the characters and mode of existence of single Polyps, as exhibited by the Actinia; that top-budding is superior to lateral budding ; and that the type of Madrepores, with their top-animal, or at least with a defi- nite and limited number of tentacles, is superior to all other Actinoids.. If this be so, the prevalence of Actinoids in older geological formations, to the exclusion of Halcyonoids, the prevalence of Rugosa and Tabulata in the oldest deposits,” the later prevalence of Astreeoids, and the very late introduction of Madrepores, would already exhibit a correspondence between the rank of the living Polyps and the representatives of that class in past ages, though we may hardly expect a very close coincidence in this respect between animals the structure of which is so simple. The gradation among the orders of Echinoderms is perfectly plam. Lowest stand the Crinoids, next the Asterioids, next the Echinoids, and highest the Holo- thurioids. Ever since this class has been circumscribed within its natural limits, this succession has been considered as expressing their natural relative standing, and modern investigations respecting their anatomy and embryology, however extensive, have not led to any important change in their classification, as far as the estimation of their rank is concerned. This is also precisely the order in which the representa- tives of this class have successively been introduced upon earth in past geological ages. Among the oldest formations we find pedunculated Cinoids? only, and this order remains prominent for a long series of successive periods; next come free Crinoids and Asterioids; next Echinoids,’ the successive appearance of which since the triasic * For classification of Polypi, see DANA, q. 2, p- * See the works q. a. p.96; also: Mixier, (J.,) 31, note 2; also Minnn-Epwarps and Hare, q. a., and TroscHeL, (F. H.,) System der Asteriden, and Acassiz, (L.,) Classification of Polyps, Proc. Braunschweig, 1842, 4to. fig. — Mitiuer, (J.,) Ueber Am. Acad. Se. and Arts, 1856, p. 187. : den Bau der Echinodermen, Berlin, 1854, 4to. — T1n- * See Mitne-Epwarps and Ham, q. a., p. 31. DEMAN, (FR.,) Anatomie der Réhren-Holothurie, des ® Mitier, Crinoids, q. a. — D’ORBIGNY, q. a. — Seeigels, etc., Landshut, 1817, fol. fig. — VALENTIN, J. HA, q. a.— Austin, q. - p- 96. (G.,) Anat. du gerne Echinus, Neuchatel, 1842, 4to. Cuap. I. SUCCESSION AND STANDING OF ANIMALS. 109 period to the present day, coincides also with the gradation of their subdivisions, as determined by their structure ; and it was not until the present period, that the highest Echinoderms, the Holothurioids, have assumed a prominent position in their class. | Among Acephala there is not any more uncertainty respecting the relative rank of their living representatives, than among Echinoderms. Every zodlogist acknowl- edges the inferiority of the Bryozoa and the Brachiopods* when compared with the Lamellibranchiata, and among these the inferiority of the Monomyaria in compari- son with the Dimyaria would hardly be denied. Now if any fact is well established in Paleontology, it is the earlier appearance and prevalence of Bryozoa and_Bra- chiopods in the oldest geological formations, and their extraordinary development for a long succession of ages, until Lamellibranchiata assume the ascendency which they maintain to the fullest extent at present. : oht further show how close this correspondence is ‘s) A closer comparison of the differ- ent families of these orders m through all ages. ee Of Gasteropoda I have nothing special to say, as every paleontologist is aware have been investigated in comparison with what has how imperfectly their remains Yet the Pulmonata are known to be been done for the fossils of other classes. of more recent origin than the Branchifera, - than the Holostomata, and this exhibits already a general and among these the Siphonostomata to have appeared later coincidence between their succession in time and their respective rank. Our present knowledge of the anatomy of the Nautilus, for = science is indebted to the skill of Owen? may satisfy everybody that among Cephalopods the Tetrabranchiata are inferior to the Dibranchiata; and it is not too much to say, that one of the first points a collector of fossils may ascertain for oe is the exclusive prevalence of the representatives of the first of ibate types in the oldest formations, and the later appearance, about the middle ee sain of represent- atives of the other type, which at present 1s the most widely i eimns Of Worms, nothing can be said of importance with reference to our inquiry ; Sicilie, eorumque Historia et Anatomia, Parma, 1791-93, 2 vols. fol. fig., continued by Delle Chiaje. 2 OwEN, (R.,) Memoir on the Pearly Nautilus, London, 1832, 4to. fig. — VALENCIENNES, (A.,) Nou- velles Recherches anatomiques sur le Nautile. C. R., Paris, 1841, 4to.— Cuvier, (G.,) Mémoires pour servir 4 lHistoire et 4 ’ Anatomie des Mollusques, Paris, 1817, 4to. fig. — Epwarps, (H. M.,) QuaTRE- races, (AR. DE,) et Brancnarp, (Em.) Voyage en Sicile, Paris, 3 vols. 4to. fig. (without date.) 1 Orpreny, (A. d’,) Bryozoires, Ann. Se. Nat., 3e sér. 1851, vol. 16, p. 292. — Cuvier, (G.,) Mémoire sur l’animal de la Lingule, Ann. Mus. I. p. 69, fig. — Voer, (C.,) Anatomie der Lingula anatina, N. Mém. Soc. Helv. 1848, VIL, 4to. fig. — OWEN, (R.,) On the Anatomy of the Brachiopoda, Trans. Zool. Soe. I. Ato., p. 145, fig — On the Anatomy of the Terebratula, 1853, dto. fig. (Palwont. Soc.)—Bucu, (L. v.,) Ueber Terebrateln, q. a., p. 97.—Davipson, (TH.,) Monogr. ete. q. a, p. 97.— Port (Xav.,) Testacea utriusque ie ET a alt dae, A Potten 4 110 ESSAY ON CLASSIFICATION. Part I. but the Crustacea exhibit, again, the most striking coincidence. Without entering into details, it appears from the classification of Milne-Edwards that Decapods, Sto- mapods, Amphipods, and Isopods constitute the higher orders, while Branchiopods, Entomostraca, Trilobites, and the parasitic types, constitute, with Limulus, the lower orders of this class‘ In the classification of Dana,’ his first type embraces Deca- pods and Stomapods, the second Amphipods and Isopods, the third Entomostraca, including Branchiopods, the fourth Cirripedia, and the fifth Rotatoria. Both acknowl- edge in the main the same gradation; though they differ greatly in the combina- tion of the leading groups, and also the exclusion by Milne-Edwards of some types, as the Rotifera, which Burmeister first, then Dana and Leydig, unite justly, as I believe, with the Crustacea? This gradation now presents the most perfect coinci- dence with the order of succession of Crustacea in past geological ages, even down to their subdivisions into minor groups. Trilobites and Entomostraca are the only representatives of the class in paleozoic rocks; in the middle geological ages appear a variety of Shrimb, among which the Macrouran Decapods are prominent, and later only the Brachyoura, which are the most numerous in our days. The fragmentary knowledge we possess of the fossil Insects, does not justify us, yet, in expecting to ascertain with any degree of precision, the character of their succession through all geological formations, though much valuable information has already been obtained respecting the entomological faunse of several geological periods.* The order of succession of Vertebrata in past ages, exhibits features in many respects differing greatly from the Articulata, Mollusks, and Radiata. Among these we find their respective classes appearing simultaneously in the oldest periods of the history of our earth. Not so with the Vertebrata, for though Fishes may be as old as any of the lower classes, Reptiles, Birds, and Mammalia are introduced successively in the order of their relative rank in their type. Again, the earliest representatives of these classes do not always seem to be the lowest; on the con- trary, they are to a certain extent, and in a certain sense, the highest, in as far | as they embody characters, which, in later periods, appear separately in higher classes, (See Sect. 26,) to the exclusion of what henceforth constitutes the special character -of “the lower class. For instance, the oldest Fishes known partake of the characters, which, at a later time, are exclusively found in Reptiles, and no longer belong to the Fishes of the present day. It may be said, that the earliest Fishes are rather the oldest representatives of the type of Vertebrata than of. the 1 Mitng-Epwarps, Hist. Nat. des Crustacés, ° Lrypie, (FR.,) Raderthiere, etc., Zeitsch. f. Paris, 1834-40, 3 vols. 8vo. wiss. Zool. 1854, vol. 6, p. 1. 2 Dana, (J. D.,) Crustacea, q. a., p. 32. 4 HeER, q.a.; Bropix, q. a., p. 98. Guar. L SUCCESSION AND STANDING OF ANIMALS. Vi class of Fishes, and that this class assumes only its proper characters after the introduction of the class of Reptiles upon earth. Similar relations may be traced between the Reptiles and the classes of Birds and Mammalia, which they precede. I need only allude here to the resemblance of the Pterodactyli and the Birds, and to that of Ichthyosauri and certain Cetacea. Yet, through all these intricate rela- tions, there runs an evident tendency towards the production of higher and higher types, until at last, Man crowns the whole series. Seen as it were at a distance, so that the mind can take a general survey of the whole, and perceive the con- nection of the successive steps, without bemg bewildered by the details, such a series appears like the development of a great conception, expressed in such har- that every link appears necessary to the full comprehension monious proportions, to | dent and perfect in itself, that it might be of its meaning, and yet, so indepen mistaken for a complete whole, and again, ceding and following members of the series, , out of the other. What is universally acknowledged as characteristic of the highest . : , : ‘ s, a richness, a magnificen conceptions of genius, is here displayed im a fulness, ol ae aint aren a complication of relations, which baffle our so intimately connected with the pre- that one might be viewed as flowing an amplitude, a perfection of details, skill and our most persevering efforts t inciding to such an extent, and not read in them the 0 appreciate all its beauties. Who can look upon such series, co : ; : | successive manifestations of a thought, expressed at different -— im ever new forms, and yet tending to the same end, onwards to the SiGe ‘seedings senda in the first appearance of the earliest Fishes! advent is already prophesied ; | a somewhat different character from that The relative standing of plants presents of animals. Their great types are not built upon so strictly different plans of structure; they exhibit, therefore, a more uniform gradation from their lowest to their highest types, which are not personified in one highest plant, as the highest animals are in Man. ee ed respecting the limitation of the most compre- Again, Zodlogy is more advanc 3 while Botany is in advance respecting the hensive general divisions, than Botany, limitation and characteristics of families and genera. : s respecting the number, and the relative rank There is, on that account, more diversity of opinion among botanist of the vegetable kingdom, than among zovlogists respecting of the primary divisions While most writers+ agree in admitting the great branches of the animal kingdom. among plants, such primary groups as Acotyledones, Monocotyledones, and Dicotyle- co} dones, under these or other names, others would separate the Gymnosperms from the Dicotyledones? ee a It appears to me, that this pomt in the classification of the livmg plants cannot 2 1 GorreERT, etc, q. a, p- 93. Ap. BRONGNrAR?, ete, q. a, p. 93. At SOT eA A a cA. ~ a Bi eb seus em oe _— i " mace bee eas ce S 112 | ESSAY ON CLASSIFICATION. Part I. be fully understood without a thorough acquaintance with the fossils and their distribution in the successive geological formations, and that this case exhibits one of the most striking examples of the influence classification may have upon our appreciation of the gradation of organized beings in the course of time. As long as Gymnosperms stand among Dicotyledones, no relation can be traced between the relative standing of living plants and the order of succession of their repre- sentatives in past ages. On the contrary, let the true affinity of Gymnosperms with Ferns, Equisetacese, and especially with Lycopodiaceze be fully appreciated, and at once we see how the vegetable kingdom has been successively introduced upon earth, in an order which coincides with the relative position its primary divisions bear to one another, in respect to their rank, as determined by the complication of their structure. Truly, the Gymnosperms, with their imperfect flower, their open carpels, supporting their polyembryonic seeds in their axis, are more nearly allied to the anathic Acrophytes, with their innumerable spores, than to either the Mono- cotyledones or Dicotyledones; and, if the vegetable kingdom constitutes a graduated series beginning with Cryptoganes, followed by Gymnosperms, and ending with Monocotyledones and Dicotyledones, have we not in that series the most striking coincidence with the order of succession of Cryptogams in the oldest geological forma- tions, especially with the Ferns, Equisetacee, and Lycopodiacese of the Carboniferous period, followed by the Gymnosperms of the Trias and Jura and the Monocoty- ledones of the same formation and the late development of Dicotyledones? Here, as everywhere, there is but one order, one plan im nature. SECTION [es ¥. PARALLELISM BETWEEN THE GEOLOGICAL SUCCESSION OF ANIMALS AND THE EMBRYONIC . GROWTH OF THEIR LIVING REPRESENTATIVES. Several authors have already alluded to the resemblance which exists between the young of some of the animals now living, and the fossil representatives of the same families in earlier periods! But these comparisons have, thus far, been traced only in isolated cases, and have not yet led to a conviction, that the character of the succession of organized beings in past ages, is such, in general, as to show 1 Acassiz,(L.,) Poiss.. foss., q. a, p-54.—Em- ques _principes relatifs & la Classification naturelle bryonic Types, q. a., p. 11.— Twelve Lect., ete., p. 8. des animaux, An. Sc. Nat., 3e sér., 1844, 1 vol. — Epwarps, (H. Mizne,) Considérations sur quel- p- 69. ‘ Crap. TL. SUCCESSION AND DEVELOPMENT OF ANIMALS. 113 a remarkable agreement with the embryonic growth of animals; though the state of our knowledge in Embryology and Palzontology justifies now such a conclusion. The facts most important to a proper appreciation of this point, have already been considered in the preceding paragraph, as far as they relate to the order of suc- cession of animals, when compared with the relative rank of their living repre- sentatives. In examining now the agreement between this succession and the phases of the embryonic growth of living animals, we may, therefore, take for granted, that the order of succession of their fossil representatives is sufficiently present to the mind of the reader, to afford a satisfactory basis of comparison. Too few Corals have been studied embryologically, to afford extensive means of. com- parison; yet so much is known, that the young polyp, when hatched, is an inde- pendent, simple animal, that it is afterwards incased in a cup, secreted by the foot of the actinoid embryo, which may be compared to the external wall of the Rugosa, and that the polyp gradually widens until it has reached its maximum diameter, prior to budding or dividing, while in ancient corals this stage of enlargement seems to last during their whole life, as, for example, in the Cyathophylloids. None of the ancient Corals form those large communities, composed of myriads of united individ- uals, so characteristic of our coral reefs; the more isolated and more independent character of the individual polyps of past ages presents a striking resemblance to the isolation of young corals, in all the living types. In no class is there, however, so much to learn still, as in Polypi, before the correspondence of their embryonic erowth, and their succession in time, can be fully appreciated. In this connection I would also remark, that among the lower animals, it is rarely observed, that any one, even the highest type, represents in its metamorphoses all the stages of the lower types, neither in their development, nor in the order of their succession; and that frequently the knowledge of the embryology of several types of differ- ent standing, is required, to ascertain the connection of the whole series in both spheres. No class affords, as yet, a more complete and more beautiful evidence of the correspondence of their embryonic changes, with the successive appearance of their representatives in past ages, than the Echinoderms, thanks to the extensive and patient investigations of J. Miiller upon the metamorphoses of these animals? Prior to the publication of his papers, the metamorphosis of the European Comatula alone was known. (See Sect. XVIIL, p. 85.) This had already shown, that the early stages i myself seen further, that the successive stages of the embryonic growth of Comatula typify, as it were, the principal forms of Crinoids which characterize the successive 1 Mitne-Epwarps et Hamme, q. 4, p. 31. * Murxer, (J.,) Seven papers, q. a., p. 71. 15 \ of growth of this Echinoderm exemplify the peduncated Crinoids of past ages. I have r 7 . = : : — = ‘ A ar ae hin i. BOB ee ee ee ee MINI ' atu tts, tage, Soa om, Me, . pebesy .. + * SA hantnttg! Nerbeattes Suitec tiene Soe ta ; saiitatise tees tarhieetaeeton Das acehatacting inc etats Shae PRET S EERE a abe AS I RO eminem trstaan neem Ae EY A SENT NRA st Re A CAROLO DARWIN *FRANCISCVS DARWIN + larry Soane, 1882. ner PART I. OF THE FIRST VOLO 2 2277 ae CONTRIBUTIONS TO THE NATURAL HISTORY OF THE UNITED STATES OF NORTH AMERICA. Ne i Be Bo ae. | — Sais ade } 1) } I I 7} q | iB | i) | | i i! | 4 ' } i Hy iW fe RR ST a acer reeet ° ae tet BRANCHES OF THE ANIMAL KINGDOM, CHAT] EK." ae ON Ds LEADING GROUPS OF THE EXISTING SYSTEMS OF ANIMALS, SECTION 1. GREAT TYPES OR BRANCHES OF THE ANIMAL KINGDOM. Tur use of the terms types, classes, orders, families, genera, and species in the systems of Zovlogy and Botany is so universal, that it would be natural to suppose that their meaning and extent are well determined and generally understood; but this is so far from being the case, that it may, on the contrary, be said, there is no subject in Natural History respecting which there exists more uncertainty and Indeed, I have failed to find anywhere a definition a greater want of precision. of the character of most of the more comprehensive of these divisions, while the current views respecting genera and species are very conflicting. Under these cir- cumstances, it has appeared to me particularly desirable, to inquire into the founda- tion of these distinctions, and to ascertain, if possible, how far they have a real And while I hope the results of this inquiry may be welcome and— existence. satisfactory, I am free to confess that it has cost me years of labor to arrive at a clear conception of their true character. It is such a universal fact in every sphere of intellectual activity, that prac- tice anticipates theory, that no philosopher should be surprised to find zovlogists have adopted instinctively natural groups, in the animal and vegetable kingdoms, even before the question of the character and of the very existence of such groups in nature was raised. Did not nations speak, understand, and write Greek, Latin, German, and Sanscrit before it was even suspected that these languages and so many others were kindred? Did not painters produce wonders with colors before the nature of light was understood? Had not men been thinking about themselves and the world before logic and metaphysics were taught in schools? 18 | : | 4 : . = =: en = — = y. ene = ——— = -- - — : > <= ~ —= —e ree : mopman Soe 8 a en ST a ipiosnerens errr een — = M “- - z = a a mate — - ma - oe ee = a - . met (ae ; - eee oe = Se OE ee iene ete cesta ae — —— a a en _ _ wis nts naan tint alah i <= —_ » oe ; < a eae anne as ans | d — 2 —— Se eee = ———— ee = — : . 4 bee eS vee = RE ee 158 ESSAY ON CLASSIFICATION. — Part I. Why, then, should not observers of nature have appreciated rightly the relationship between animals or plants before getting a scientific clue to the classifications they were led to adopt as practical? ; Such considerations, above all others, have guided and encouraged me while I was seeking for the meaning of all these systems, so different one from the other in their details, and yet so similar in some of their general features. The history of our science shows how ‘early some of the principles, which obtain to this day, have been acknowledged by all reflecting naturalists. Aristotle, for instance, knew already the principal differences which distinguish Vertebrata from all other animals, and his distinction of Eneima and Aneima+ corresponds exactly to that of Vertebrata and Inwertebrata of Lamarck? or to that of Flesh- and Gut-Ammals of Oken? or to that of Myeloneura and Ganglionewra of Ehrenberg ; 4 and one who is at all familiar with the progress of science at different periods, can but smile at the claims to novelty or originality so frequently brought forward for views long before current among men. Here, for instance, is one and the same fact presented in different aspects; first, by Aristotle with reference to the character of the formative fluid, next by Lamarck with reference to the general frame, for I will do Lamarck the justice to believe, that he did not unite the Invertebrata simply because they have no skeleton, but because of that something, which even Professor Owen fails to express° and which yet exists, the one cavity of the body in Invertebrata con- taining all organs, whilst Vertebrata have one distinct cavity for the centres of the nervous system and another for the organs of the vegetative life. This acknowledg- ment is due to Lamarck as truly as it would be due to Aristotle not to accuse him of having denied the Invertebrata any fluid answering the office of the blood, though he calls them Aneima; for he knew nearly as well as we now know, that there moves a nutritive fluid in their body, though that information 1s generally denied him, because he had no correct knowledge of the circulation of the blood. - Again, when Oken speaks of Flesh-Animals he does not mean that Vertebrates consist of nothing but flesh, or that the Invertebrates have no muscular fibres; but he brings prominently before us the presence, in the former, of those masses, forming mainly the bulk of the body, which consist of flesh and bones, as well as blood and nerves, and constitute another of the leading features distinguishing Vertebrata and Invertebrata. Ehrenberg presents the same relations between the same beings as expressed by their nervous system. If we now take the expressions 1 Histor. Anim., Lib. I., Ch. 5 and 6. 4 Das Naturreich des Menschen; a diagram, upon 2 Anim. Vert., 2d édit., vol. 1,. p. 313. a large sheet, folio. 8 Naturphilosophie, 3d edit., p. 400. 5 Comparat. Anat. of Inv., 2d edit., p. 11. Cuap. II. BRANCHES OF THE ANIMAL KINGDOM. 139 of Aristotle, Lamarck, Oken, and Ehrenberg together, have we not, as characteristic of their systems, the very words by which every one distinguishes the most promi- nent features of the body of the higher animals, when speaking of blood relations, of blood and bones, or of having flesh and nerve? | Neither of these observers has probably been conscious of the identity of his classification with that of his predecessors; nor, indeed, should we consider either of them as superfluous, inasmuch as it makes prominent, features more or less differ- ent from those insisted upon by the others; nor ought any one to suppose that with all of them the field is exhausted, and that there is no more room for new systems upon that very first distinction among animals." As long as men inquire they will have opportunities to know more upon these topics than those who have gone before them, so inexhaustibly rich is nature in the innermost diversity of her treasures of beauty, order, and intelligence. So, instead of discarding all the systems which have thus far had little or no influence upon the progress of science, either because they are based upon _prin- ciples not generally acknowledged or considered worthy of confidence, I haye care- fully studied them with the view of ascertaining whatever there may be true in them, from the stand-point from which their authors have considered the animal kingdom; and IT own that I have often derived more information from such a careful consideration than I had at first expected. It was not indeed by a lucky hit, nor by one of those unexpected apparitions which, like a revelation, suddenly break upon us and render at once clear and comprehensible what had been dark and almost inaccessible before, that I came to understand the meaning of those divisions called types, classes, orders, families, gen- era, and species, so long admitted mm Natural History as the basis of every system, : generally considered as mere artificial devices to facilitate our studies. and yet so I had been laboring under the impression that they are founded in For years nature, before I succeeded in finding out upon what principle they were really based. I soon perceived, however, that the greatest obstacle in the way of ascertaining their true significance lay in the discrepancies among different authors in their use and application of these terms. Different naturalists.do not call by the same name groups of the same kind and the same extent: some call genera what others call subgenera; others call tribes, or even families, what are called genera by others; 1 By way of an example, I would mention the different from what is observed in any of the Inver- mode of reproduction. The formation of the egg in __ tebrata, that the animal kingdom, classified according Vertebrata; its origin, in all of them, in a more or to these facts, would again be divided into two great less complicated Graafian vesicle, in which it is groups, corresponding to the Vertebrata and Inverte- nursed ; the formation and development of the embryo brata of Lamarck, or the Flesh- and Gut- Animals of up to a certain period, etc., ete., are So completely Oken, or the Hneima and Aneima of Aristotle, ete. 140 ESSAY ON CLASSIFICATION. Part I. even the names of tribe and family have been applied by some to what others call sub-genera; some have called families what others have called orders; some consider as orders what others have considered as classes; and there are even genera of some authors which are considered as classes by others. Finally, in the number and limitation of these classes, as well as in the manner in which they are grouped together, under general heads, there is found the same diversity of opinion. It is, nevertheless, possible, that under these manifold names, so differently applied, groups may be designated which may be natural, even if their true relation to one another have thus far escaped our attention. It is already certain that most, if not all investigators agree in the limitation, of some groups at least, under whatever name they may call them, and however much they would blame one another for calling them so, or otherwise. I can there- fore no longer doubt that the controversy would be limited to definite ques- tions, if naturalists could only be led to an agreement respecting the real nature of each kind of groups. I am satisfied, indeed, that the most insuperable obstacle to any exact appreciation of this subject lies in the fact, that all naturalists, with- out exception, consider these divisions, under whatever name they may designate them, as strictly subordinate one to the other, in such a manner, that their differ- ence is only dependent upon their extent; the class being considered as the more comprehensive division, the order as the next extensive, the family as more limited, the genus as still more limited, and the species as the ultimate limitation in a natural arrangement of living beings, so that all these groups would differ only by the quantity of their characters, and not by the quality, as if the elements of structure in animals were all of the same kind; as if the form, for instance, was an organic element of the same kind as the complication of structure, and as if the degree of complication implied necessarily one plan of structure to the exclu- sion of another. I trust I shall presently be able to show that it is to a neglect of these considerations that we must ascribe the slow progress which has been made in the philosophy of classification. - Were it possible to show that all these eroups do not differ in quantity, and are not merely divisions of a wider or more limited range, but are based upon different categories of characters, genera would be called genera by all, whether they differ much or little one from the other, and so would families be called fam- ilies, orders be called orders, ete. Could, for instance, species be based upon absolute size, genera upon the structure of some external parts of the body, families upon the form of the body, orders upon the similarity of the internal structure, or the like, it is plain that there could not be two opinions respecting these groups in any class of the animal kingdom. But as the problem is not so simple in nature, it was not until after the most extensive investigations, that I seized the clue to Cuap. II. BRANCHES OF. THE ANIMAL KINGDOM, 141 guide me through this labyrinth. I knew, for instance, that though naturalists have been ‘disputing, and are still disputing, about species and genera, they all distin- guished the things themselves in pretty much the same manner. What A would call a species, B called only a variety or a race; but then B might call a sub- genus the very same aggregate of individuals which A called a species; or what A called a genus was considered by B as a family or an order. Now it was this something called no matter how, for which I tried to find out characters which would lead all to call it by the same name; thus limiting the practical difficulty in the application of the name to a question of accuracy in the observations, and no longer allowing it to be an eternal contest about mere nomenclature. At this stage of my investigation it struck me, that the character of the writ- ings of eminent naturalists might throw some light upon the subject itself, There are authors, and among them some of the most celebrated contributors to our knowledge in Natural History, who never busied themselves with classification, or paid only a passing notice to this subject, whilst they are, by universal consent, considered as the most successful biographers of species; such are Buffon, Reau- mur, Roesel, Trembley, Smeathman, the two Hubers, Bewick, Wilson, Audubon, Naumann, etc. Others have applied themselves almost exclusively to the study of genera. Latreille is the most prominent zodlogist of this stamp; whilst Linnezeus and Jussieu stand highest among botanists for their characteristics of genera, or at least for their early successful attempts at tracmg the natural limits of genera. Bota- nists have thus far been more successful than zodlogists in characterizing natural families, though Cuvier and Latreille have done a great deal in that same direction in Zodlogy, whilst Linnzeus was the first to introduce orders in the classification of animals. As to the higher groups, such as classes and types, and even the orders, we find again Cuvier leading the procession, in which have followed all the natu- ralists of this century. 7 Now let us inquire what these men have done in particular to distinguish them- selves especially, either as biographers of species, or as characterizers of genera, of families, of orders, of classes, and of types. And should it appear that in each case they have been considering their subject from some particular point of view, it strikes me that what has been acknowledged unconsciously as constituting the particular emi- nence or distinction of these men, might very properly be proclaimed, with grate- ful consciousness of their services, as the characteristic of that kind of groups which each of them has most successfully illustrated; and I hope every unprejudiced natu- ralist will agree with me in this respect. As to the highest divisions of the animal kingdom, first introduced by Cuvier under the name of embranchements, (and which we may well render by the good old English word éranch,) he tells us himself that they are founded upon distinct plans 142 ESSAY ON CLASSIFICATION. Part I. of structure, cast, as it were, into distinct moulds or forms. Now there can certainly be no reason why we should not all agree to designate as types or branches all such great divisions of the animal kingdom as are constituted upon a special plan? if we should find practically that such groups may be traced in nature. Those who may not see them may deny their existence; those who recognize them may vary in their estimation of their natural limits; but all can, for the greatest benefit of science, agree to call any group which seems to them to be founded upon a special plan of structure, a type or branch of the animal kingdom; and if there are still differences of opinion among naturalists respecting their limits, let the discussion upon this point be carried on with the understanding that types are to be characterized by different plans of structure, and not by special anatomical peculiarities. Let us avoid confounding the idea of plan with that of complication of structure, even though Cuvier himself has made this mistake here and there in his classification. The best evidence I can produce that the idea of distinct plans of structure is the true pivot upon which the’ natural limitation of the branches of the animal kingdom is ultimately to turn, lies in the fact that every great improvement, acknowledged by all as such, which these primary divisions have undergone, has consisted in the removal from among each, of such groups as had been placed with them from other considerations than those of a peculiar plan, or in conse- Let us Neither Infusoria nor Intestinal Worms are any longer arranged by competent naturalists among Radiata. Why they have been removed, may be considered elsewhere; but it was certainly not because they were ) supposed to agree in the plan of their structure with the quence of a want of information respecting their true plan of structure. examine this point within limits no longer controvertible. 1 It would lead me too far were I to consider here the characteristics of the different kingdoms of old expressions, in a somewhat modified sense, is found preferable to framing new ones. I trust the value of Nature. I may, however, refer to the work. of I. the following discussion will be appreciated by its Gerorrroy St. Hizarre, Histoire naturelle générale des régnes organiques, Paris, 18956, 8yvo., who has dis- cussed this subject recently, though I must object to the admission of a distinct kingdom for Man alone. 2 It is almost superfluous for me to mention here that the terms plan, ways and means, or manner in which a plan is carried out, complication of structure, form, details of structure, ultimate structure, relations of individuals, frequently used in the following pages, are taken in a somewhat different sense from their usual meaning, as is always necessary when new views are introduced in a science, and the adoption of intrinsic merit, tested with a willingness to understand what has been my aim, and not altogether by the rela- tive degree of precision and clearness with which I may have expressed myself, as it is almost impossible, in a first attempt of this kind, to seize at once upon I wish also to be understood as expressing my views more the form best adapted to carry conviction. immediately with reference to the animal kingdom, as I do not feel quite competent to extend the inquiry and the discussion to the vegetable kingdom, though I have occasionally alluded to it, as far as my in- formation would permit. Cuap. II. BRANCHES OF THE ANIMAL KINGDOM. 148 true Radiata, that Cuvier placed them in that division, but simply because he allowed himself to depart from his own principle, and to add another consideration, besides the plan of structure, as characteristic of Radiata, the supposed absence of a nervous system, and the great simplicity of structure of these animals; as if simplicity of execution had any necessary connection with the plan of structure. Another remarkable instance of the generally approved removal of a class from one of the types of Cuvier to another, was the transfer of the Cirripeds from among the Mollusks to the branch of Articulata. Imperfect knowledge of the plan of structure of these animals was here the cause of the mistake, which was cor- rected without any opposition, as soon-as they became better known. From a comparison of what is stated here respecting the different plans of structure, characteristic of the primary divisions of the animal kingdom, with what I have to say below about classes and orders, it will appear more fully, that it is important to make a distinction, between the plan of a structure and the man- ner in which that plan is carried out, or the degrees of its complication and _ its relative perfection or simplicity. But even after it is understood that the plan of structure should be the leading characteristic of these primary groups, it does not yet follow, without further examination, that the four great branches of the animal kingdom, first distinguished by Cuvier, are to be considered as the primary divisions which Nature points out as fundamental. It will still be necessary, by a. careful and thorough investigation of the subject, to ascertain what these primary groups are; but we shall have gained one poimt with reference to our systems, that what- ever these primary groups, founded upon different plans, which exist in nature, may be, when they are once defined, or whilst they are admitted as the temporary ex- pression of our present knowledge, they should be called the branches of the animal kingdom, whether they be the Vertebrata, Articulata, Mollusca, and Radiata of Cuvier, or the Artiozoaria, Actinozoaria, and Amorphozoaria of Blainville, or the Vertebrata and Invertebrata of Lamarck. The special inquiry into this pomt must be left for a special paper. I will only add, that I am daily more satisfied, that, in their general outlines, the primary divisions of Cuvier are true to nature, and that never did a naturalist exhibit a clearer and deeper insight into the most general relations of animals than Cuvier, when he perceived, not only that these primary groups are founded upon differences in the plan of their structure, but also how they are essentially related to one another. Though the term type is generally employed to designate the great fundamental divisions of the animal kingdom, I shall not use it in future, but prefer for it the term branch of the animal kingdom, because the term type is employed in too many different acceptations, and quite as commonly to designate any group of any kind, or any peculiar modification of structure stamped with a distinct and marked 144 | ESSAY ON CLASSIFICATION. Part I. character, as to designate the primary divisions of the animal kingdom. We speak, for instance, of specific types, generic types, family types, ordinal types, classic types, and also of a typical structure. The use of the word type in this sense is so frequent on almost every page of our systematic works, in Zodlogy and in treatises of comparative anatomy, that it seems to me desirable, in order to avoid every possible equivocation in the designation of the most important great primary divisions among animals, to call them branches of the animal kingdom, rather than types. ; That, however, our systems are more true to nature than they are often sup- posed to be, seems to me to be proved by the gradual approximation of scientific men to each other, in their results, and in the forms by which they express those results. The idea which lies at the foundation of the great primary divisions of the animal kingdom is, the most general conception possible in connection with the plan of a definite creation; these divisions are therefore the most comprehensive of all, and properly take the lead in a natural classification, as representing the first and broadest relations of the different natural groups of the animal kingdom, the general formula which they each obey. What we call branches expresses, in fact, a purely ideal connection between animals, the intellectual conception which unites them in the creative thought. It seems to me that the more we examine the true significance of this kind of groups, the more we shall be convinced that they are not founded upon material relations. The lesser divisions which succeed next are founded upon special qualifications of the plan, and differ one from the other by the character of these qualifications. Should it be found that the features in the animal kingdom which, next to the plan of structure, extend over the largest divisions, are those which determine their rank or respective standing, it would appear natural to consider the orders as the second most important category in the organization of animals. Experience, however, shows that this is not the case; that the manner in which the plan of structure is executed leads to the distinction of more extensive divisions (the classes) than those which are based upon the com- plication of structure (the orders). As a classification can be natural only as far it expresses real relations observed in nature, it follows, therefore, that classes take the second position in a system, immediately under the branches. We shall see below that orders follow next, as they constitute naturally groups that are more comprehensive than families, and that we are not at liberty to invert their respec- tive position, nor to transfer the name of one of these divisions to the other, at our own pleasure, as so many naturalists are constantly doing. Cuap. IL. . CLASSES OF ANIMALS. SROTITON Tf. CLASSES OF ANIMALS. Before Cuvier had shown that the whole animal kingdom is constructed upon four different plans of structure, classes were the highest groups acknowledged in the systems of Zodlogy, and naturalists very early understood upon what this kind of division should be founded, in order to be natural, even though in practice they did not always perceive the true value of the characters upon which. they established their standard of relationship. Linneeus, the first. expounder of the system of animals, already distinguishes, by anatomical characters, the classes he has adopted, though very imperfectly; and ever since, systematic writers have aimed at drawing a more and more complete picture of the classes of animals, based upon a more or less extensive investigation of their structure. | Structure, then, is the watchword for the recognition of classes, and an accurate knowledge of their anatomy the surest way to discover their natural limits. And yet, with this standard before them, naturalists have differed, and differ still greatly, in the limits they assign to classes, and in the number of them they adopt. It is really strange, that, applying apparently the same standard to the same objects, the results of their estimation should so greatly vary; and it was this fact. which led me to look more closely into the matter, and to inquire whether, after all, the seeming unity of standard was not more a fancied than a real one. Structure may be considered from many points of view: first, with reference to the plan adopted in framing it; secondly, with reference to the work to be done by it, and to the ways and means employed in building it up; thirdly, with reference to the degrees of perfection or complication it exhibits, which may differ greatly, even though the plan be the same, and the ways and means employed in carrying out such a plan should not differ in the least; fourthly, with reference to the form of the whole structure and its parts, which bears no necessary relation, at all events no very close relation, to the degree of perfection of the structure, nor to the manner in which its plan is executed, nor to the plan itself, as a comparison between Bats and Birds, between Whales and Fishes, or between Holothurians and Worms, may easily show; fifthly and lastly, with reference to its last finish, to the execution of the details in the individual parts. | It would not ‘be difficult to show, that the differences which exist among naturalists in their limitation of classes have arisen from an indiscriminate con- sideration of the structure of Sait in all these different points of view, and an oes t = . an : = a om es i =. See eg e eo : SE, Aan ae A a BE at RRA rch So erabe sn ae ¥e8 Pe * “ va 146 ESSAY ON CLASSIFICATION. Part I. equally indiscriminate application of the results obtained, to characterizing classes. Those who have not made a proper distinction between the plan of a structure and the manner in which that plan is actually executed, have either overlooked the importance of the great fundamental divisions of the animal kingdom, or they have unduly multiplied the number of these primary divisions, basing their dis- tinctions upon purely anatomical considerations, that is to say, not upon differences in the character of the general plan of structure, but upon the material develop- ment of that plan. Those, again, who have confounded the complication of the structure with the ways and means by which life is maintained through any given combination of systems of organs, have failed in establishing a proper difference between class and: ordinal characters, and have again and again raised orders to the rank of classes. For we shall see presently, that natural orders must be based upon the different degrees of complication of structure, exhibited within the limits of the classes, while the classes themselves are characterized by the manner in which the plan of the type is carried out, that is to say, by the various com- binations of the systems of organs constituting the body of the representatives of any of the great types of the animal kingdom ; or perhaps, still more distinctly, the classes are characterized by the different ways in which life is maintained, and the different means employed in establishing these ways. An example will suffice to show that this distinction implies a marked difference between class and ordinal characters. | Let us compare the Polyps and Acalephs as two classes, without allowing our- selves to be troubled by the different limits assigned to them by different authors. Both are constructed upon the same plan, and belong, on that account, to the type of Radiata. In establishing this fact, we do not consider the actual structure of these animals, whether they have a nervous system or not, whether they have organs of senses or not, whether their muscles are striated or smooth, whether they have a solid frame or an entirely soft body, whether their alimentary cavity has only one opening or two opposite openings, whether it has glandular annexes or not, whether the digested food is distributed m the body one way or another, whether the undigested materials are rejected through the mouth or not, whether the sexes are distinct or not, whether they reproduce themselves only by eggs, or by budding also, whether they are simple or not: all we need know, in order to refer them to the branch of Radiata, is whether the plan of their structure exhibits a general radiated arrangement or not. But, when we would distinguish Polypi, Acalephs, and Echinoderms as classes, or rather, when we would ascertain what are the classes among Radiata, and how many there are, we must inquire into the manner in which this. idea of radiation, which lies at the foundation of their plan. of structure, is actually expressed in all the animals exhibiting such a plan, and Cuap. II. | CLASSES OF ANIMALS. 147 we find easily, that while in some (the Polypi) the body exhibits a large cavity, divided by radiating partitions into a number of chambers, into which hangs a sac, (the digestive cavity,) open below, so as to pour freely the digested food into the main cavity, whence it is circulated to and fro in all the chambers, by the agency of vibrating cilia; in others, (the Acalephs,) the body is plain and full not to be compared to a hollow sac, traversed only in its thickness by radiating tubes, which arise from a central cavity, (the digestive cavity,) without a free com- munication with one another for their whole length, etc, etc. while in others still, (the Echinoderms,) there is a tough or rigid envelope to the body, inclosing a large cavity in which are contained a variety of distinct systems of organs, ete. Without giving here a full description of these classes, I only wish to show, that what truly characterizes them, is not the complication of their structure, (for Hydroid Meduse are hardly more complicated in their structure than Polyps,) but the manner in which the plan of Radiata is carried out, the ways in which life is maintained in these animals, the means applied to this end; in one word, the combinations of their structural elements. But the moment we would discern what are the orders of these classes, these considerations no longer suffice; their structure has to be viewed in a different light; it is now the complication of these apparatus which may guide us. Actinarians and Halcyonarians among Polypi, as orders, differ, the first by having a larger and usually indefinite number of simple tentacles, an equally large number of internal partitions, etc. while in Halcyonarians the eight tentacles are lobed and complicated, and all the parts are combined in pairs, in definite numbers, etc, differences which establish a dis- tinct standing between them in their class, assigning the latter a higher rank than the former. It follows, then, from the preceding remarks, that classes are to be distinguished by the manner in which the plan of thew type is executed, by the ways and means by which this is done, or, in other words, by the combinations of their structural elements, that is to say, by the combinations of the different systems of organs building up the body of their representatives. We need not consider here the various forms under which the structure is embodied, nor the ultimate details, nor the last finish which this structure may exhibit, as a moment’s reflection will convince any one that neither form nor structural details can ever be characteristic of classes. There is another pomt to which I would call attention, respecting the charac-. teristics of classes. These great divisions, so important in the study of the animal kingdom, that a knowledge of their essential features is rightly considered as the primary object of all investigations im comparative anatomy, are generally repre- sented as exhibiting each some essential modification of the type to which they 148 ESSAY ON CLASSIFICATION. Part I. belong. . This view, again, I consider to be a mistaken appreciation of the facts, to which Cuvier has already called attention, though his warning has remained unnoticed! There is in reality no difference in the plan of animals belonging to different classes of the same branch. The plan of structure of Polypi is no more a modification of that of Acalephe, than that of Acalephze or Echinoderms is a modification of the plan of Polyps; the plan is exactly the same in all three; it may be represented by one simple diagram, and may be expressed in one single word, radiation; it is the manifestation of one distinct, characteristic idea. But this idea is exhibited’ in nature under the most different forms, and expressed in different ways, by the most diversified combinations of structural modifications and in the most varied relations. In the innumerable representatives of each branch of the animal kingdom, it is not the plan that differs, but the manner in which this plan is executed. In the same manner as the variations played by a skilful artist upon the simplest tune are not modifications of the tune itself, but only different expressions of the same fundamental harmony, just so are neither the classes, nor the orders, nor the families, nor the genera, nor the species of any great type, modifications of its plan, but only. its different expressions, the different ways in which the fundamental thought embodied in it is manifested in a variety of living beings. ae In studying the characteristics of classes we have to deal with structural features, while in investigating their relations to the branches of the animal kingdom to which they belong, we have only to consider the general plan, the framework, as it were, of that structure, not the structure itself. This distinction leads to an important practical result. Since, in the beginning of this century, naturalists have begun, under the lead of the German physiophilosophers, to compare more closely the structure of the different classes of the animal kingdom, points of resemblance have been noticed between them which had entirely escaped the atten- tion of earlier investigators, structural modifications have been identified, which, at first, seemed to exhibit no similarity, so much so, that step by step these com- parisons have been extended over the whole animal kingdom, and it has been _ asserted, that, whatever may be the apparent differences in the organization of ani- mals, they should be considered as constructed of parts essentially identical. This assumed identity of structure has been called homology But the progress of — science is gradually restricting these comparisons within narrower limits, and it appears now, that the structure of animals is homologous only as far as they belong to the same branch, so much so, that the study of homologies is likely to afford one of the most trustworthy means of testing the natural limits of any of the 1 Cuvier, Regn. An., 2d edit., p. 48. 2 See Chap. I., Sect. 5. Cuap. II. CLASSES OF ANIMALS. | 149 great types of the animal kingdom. While, however, homologies show the close similarity of apparently different structures and the perfect identity of their plan, within the same branches of the animal kingdom, yet, they daily exhibit more: and more striking differences, both in plan and structure, between the branches themselves, leading to the suspicion that systems of organs which are generally. considered as identical in different types, will, in the end, prove essentially different, as, for instance, the so-called gills in Fishes, Crustacea, and Mollusks. It requires no great penetration to see already that the gills of Crustacea are homologous with the tracheze of Insects and the so- -called lungs of certain spiders, in the same manner as the gills of aquatic Mollusks are homologous with the so-called. lungs of our air-breathing snails and slugs. Now, until it can be shown that all these different respiratory organs are truly homologous, I hold it to be more natural to consider the system of respiratory organs in Mollusks, m Articulates, and in Verte- brates, as essentially different among themselves, though homologous within the limits of each type; and this remark I would extend to all their systems of organs, to their solid frame, to their nervous system, to their muscular system, to their digestive apparatus, to their circulation, and to their reproductive organs, etc. It would not be difficult to show now that the alimentary canal with its glandular appendages, in Vertebrata, is formed in an entirely different way from that of Articulates or Mollusks, and that it cannot be considered as homologous in all these types. And if this be true, we must expect soon an entire reform of our methods of illustrating comparative anatomy. Finally, it ought to be remembered, in connection with the study of classes as well as that of other groups, that the amount of difference existing between any two divisions is nowhere the same. Some features in nature seem to be insisted upon with more tenacity than others, to be repeated more frequently and more widely, and to be impressed upon a_ larger number of representatives. This unequal weight of different groups, so evident everywhere in the animal kingdom, ought to make us more cautious in estimating their natural limits, and prevent. us from assigning an undue value to the differences observed between living beings, never overrating apparently great discrepancies, nor underrating seemingly trifling variations. The right path, however, can only be ascertained ve extensive inves- tigations, made with special reference to this point. Everybody must know that the males and females of some species differ much more one from the other than many species do, and yet the amount of difference observed between species is constantly urged, even without a preliminary investi= gation, as an argument for distinguishing them. These differences, moreover, are not only quantitative, they are to a still greater extent also qualitative. In the state NAN 2 RN GO ATTA A i I Ra al aR AICI RR tena 150 ESSAY ON. CLASSIFICATION. Part I. same manner do genera differ more or less one from the other, even in the same family; and such inequality, and not an equable apportionment, is the norm through- out nature. In classes, it is not only exhibited in the variety of their forms, but also, to an extraordinary extent, in their numbers, as, for instance, in the class of Insects compared to that of Worms or Crustacea. The primary divisions of the ani- mal kingdom differ in the same manner one from the other. Articulata are by far the most numerous branch of the whole animal kingdom; their number exceeding greatly that of all other animals put together. Such facts are in themselves sufficient to show how artificial classifications must be which admit only the same number and the same kind of divisions for all the types of the animal kingdom. SECTION III. ORDERS AMONG ANIMALS. Great as is the discrepancy between naturalists respecting the number and limits of classes in the animal kingdom, their disagreement in regard to orders and families is yet far greater. These conflicting views, however, do not in the least shake my confidence in the existence of fixed relations between animals, determined by thoughtful considerations. I would as soon cease to believe in the existence of one God, because men worship Him in so many different ways, or because they even worship gods of their own making, as distrust the evidence of my own senses respecting the existence of a preéstablished and duly considered system in nature, the arrangement of which preceded the creation of all things that exist. From the manner in which orders are generally characterized and introduced into our systems, it would seem as if this kind of groups were interchangeable with families. Most botanists make no difference even between orders and families, and take almost universally the terms as mere synonyms. Zodlogists have more extensively admitted a difference between them, but while some consider the orders as superior, others place families higher; others admit orders without at the same time distinguishing families, and vice versé introduce families into their classification without admitting orders; others still admit tribes as intermediate groups between orders and families. A glance at any general work on Zodlogy or Botany may satisfy. the student how utterly arbitrary the systems are in this respect. The Régne animal of Cuvier exhibits even the unaccountable feature, that while orders Cuap. IL. ORDERS AMONG ANIMALS. 151 and families are introduced in some classes, only orders are noticed in others? ‘and even some exhibit only a succession of genera under the head of their class, : : Other classi- fications exhibit the most pedantic. uniformity of a regular succession in each class, of sub-classes, orders, sub-orders, families, sub-families, tribes, sub-tribes, genera, sub- without any further grouping among them into orders or families? genera, divisions, sections, and sub-divisions, sub-sections, etc. but bear upon. their face, that they are made to suit preconceived ideas of regularity and symmetry in the system, and that they are by no means studied from nature. To find out the natural characters of orders from that which really exists in nature, I have considered attentively the different systems of Zodlogy in which orders are admitted and apparently considered with more care than elsewhere, and in particular the Systema Nature of Linneus, who first introduced in Zodlogy that kind of groups, and the works of Cuvier, in which orders are frequently charac- terized with unusual precision, and it has appeared to me that the leading idea prevailing everywhere respecting orders, where these groups are not admitted at random, is that of a definite rank among them, the desire to determine the rela- tive standing of these divisions, to ascertain their relative superiority or inferiority, as the name order, adopted to designate them, already implies. The first order in the first class of the animal kingdom, according to the classification of Linnzeus, is called by him Primates, expressing, no doubt, his conviction that these beings, among which Man is included, rank uppermost in their class. Blainville uses here and there the expression of “ degrees of organization,” to designate orders. It is true Lamarck uses the same expression to designate classes. We find, therefore, here as everywhere, the same vagueness in the definition of the different kinds of groups adopted in our systems. But if we would give up any arbitrary use of these terms, and assion to them a definite scientific meaning, it seems to me’ most natural, and in accordance with the practice of the most successful investigators of the animal kingdom, to call orders such divisions as are characterized by differ- ent degrees of complication of their structure, within the limits of the classes. As such I would consider, for instance, the Actinoids and Halcyonoids in the class of Polypi, as circumscribed by Dana; the Hydroids, the Discophore, and the Cte- 1 In the classes Mammalia, Birds, Reptiles, and * The classes Echinoderms, Acalephs, and Infu- soria, are divided into orders, but without families * Such are his classes of Cephalopods, Pteropods 9 Brachiopods, and Cirripeds (Cirrhopods.) Of the Ce- Fishes, Cuvier distinguishes mostly families as well as orders. In the.class of Mammalia, some orders number no families, whilst others are divided into Tn the class of Gasteropods, phalopods, he says, however, they constitute but one order (Regn. An. vol. 3, p- 11), and, p- 22, he calls tribes instead of families. Annelids, Intestinal Worms, and Polyps, some of the orders only are divided into families, while the larger _ number are not. them a family, and yet he distinguishes them as a class, p. °8. . 152 ESSAY ON CLASSIFICATION. Part I. noids. among Acalephs; the Crinoids, Asterioids, Echinoids, and Holothurie among Echinoderms; the Bryozoa, Brachiopods, Tunicata, Lamellibranchiata among Acephala ; the Branchifera and Pulmonata among Gasteropods; the Ophidians, the Saurians, and the Chelonians among Reptiles; the Ichthyoids and the Anoura among Amphi- -bians, ete. | | Having shown in the preceding paragraph that classes rank next to branches, it would be proper I should show here that orders are natural groups which stand above families in their respective classes; but. for obvious reasons I have deferred this discussion to the following paragraph, which relates to families, as it will be easier for me to show what. is the respective relation of these two kinds of groups after their special character has been duly considered. From the preceding remarks respecting orders it might be inferred that I deny -all gradation among all other groups, or that I assume that orders constitute neces- sarily one simple series in each class. Far from asserting any such thing, I hold on the contrary, that neither is necessarily the case. But to explain fully my views upon this point, I must imtroduce here some other considerations. It will be obvious, from what has already been said, (and the further illustration of this subject will only go to show to what extent this is true,) that there exists an unquestionable hierarchy between. the different kinds of groups admitted in our systems, based upon the different kinds of relationship observed among animals, that branches are the most comprehensive divisions, including each several classes, that orders are subdivisions of the classes, families subdivisions of orders, genera subdivisions of families, and species subdivisions of the genera; but not in the sense that each type should necessarily include the same number of classes, nor even necessarily several classes, as this must depend upon the manner in which the type is carried out. A class, again, might contain no orders,’ if its represent- atives presented no different degrees characterized by the greater or less compli- cation of their. structure; or it may contain many, or few, as these gradations are more or less numerous and well marked; but as the representatives of any and every class have of necessity a definite form, each class must contain at least one family, or many families, indeed, as many as there are systems of forms under which its representatives may be combined, if form can be shown to be charac- teristic of families) The same is the case with genera and species; and nothing is more remote from the truth than the idea that a genus is better defined in proportion as it contains a greater number of species, or that it may be necessary to know .several species of a genus before its existence can be fully ascertained. A. genus may be more satisfactorily characterized, its peculiarity more fully ascer- 1-See Chap. I. Sect. 1. Cuap. IL ORDERS AMONG ANIMALS. 153 tained, its limits better defined, when we know all its representatives; but I am satisfied that any natural genus may be at least pointed out, however numerous its species may be, from the examination of any single one of them. Moreover, the number of genera, both in the animal and vegetable kingdom, which contain but a single species, is so great that it is a matter of ae in all these cases to ascertain their generic characteristics from that one species. Again, such species require to be characterized with as much precision, and their specific characters to be described with as much minuteness, as if a host of them, but not yet known, existed besides. It is a very objectionable practice among zodlogists and_ botanists, to remain satisfied in such cases with characterizing the genus, and perhaps to - believe, what some writers have actually stated distinctly, that in such cases generic and specific characters are identical. Such being the natural relations and the subordination of types, classes, orders, families, genera, and species, I believe, névertheless, that neither types, nor classes, (orders of course not at all,) nor families, nor genera, nor species have the same standing when compared among themselves. But this does not in the least inter- fere with the prominent features of orders, for the relative standing of types, or classes, or families, or genera, or species does not depend upon the degrees of complication of their structures as that of orders does, but upon other features, as I will now show. The four great types or branches of the animal kingdom, characterized as they are by four different plans of structure, will each stand higher or lower, as the plan itself bears a higher or lower character, and that this may be the case we need only compare Vertebrata and Radiata! The different classes of one type will stand higher or lower, as the ways in which and the means with which, the plan of the type to which they belong is carried out, are of a higher or lower nature. Orders in any or all classes are of course higher or lower according to the degree of perfection of their representatives, or according to the complication or simplicity of their structure. Families may stand higher or lower as the peculiarities of their form are determined by modifications of more or less important systems of organs. Genera may stand higher or lower as the structural peculiarities of the parts constituting the generic characteristics exhibit a higher or lower grade of development. Species, lastly, may stand one above the other, in the same genus, according to the character of their relations to the surrounding world, or that of their representatives to one another. These remarks must make it plain that the respective rank of groups of the same kind among . them- selves must be determined by the superior or inferior grade of those features upon 1 I must leave out the details of such comparisons, moreover, any text-book of comparative anatomy as a mere mention of the point suffices to suggest them ; may furnish the complete evidence to that effect. 20 ‘154 ESSAY ON CLASSIFICATION. Parr Lh which they are themselves founded; while orders alone are strictly ‘defined by the natural degrees of structural complications exhibited within the limits of the classes. | As to the question, whether orders constitute necessarily one simple series in their respective classes, I would say, that this must depend upon the character of the class itself, or the manner in which the plan of the type is carried out within the limits of the class. If the class is homogeneous, that is, if it is not primarily subdivided into sub-classes, the orders will, of course, form a single Series ; but if some of its organic systems are developed in a different way from the others, there may be one or several parallel series, each subdivided into gradated orders. This can, of course, only be determined by a much more minute study of the characteristics of classes than has been made thus far, and mere guesses at such an internal arrangement of the classes into series, as those proposed by Kaup or Fitzinger, can only be considered as the first attempts towards an estimation of the relative value of the intermediate divisions which may exist between the classes and their orders. | Oken and the physiophilosophers generally have taken a different view of orders. ‘Their idea is, that orders represent, in their respective classes, the characteristic features of the other types of the animal kingdom. As Oken’s Intestinal or Gelatin- ous animals are characterized by a single system of organs, the intestine, they contain no distinct orders, but each class has three tribes, corresponding to the three classes of this type, which are Infusoria, Polypi, and Acalephs. The tribes of the class of Infusoria, are Infusoria proper, Polypoid Infusoria, and Acalephoid Infu- soria; the tribes of the class of Polypi, are Infusorial Polypi, Polypi proper, and Acalephoid Polypi; the tribes of the class Acalephs, are Infusorial Acalephs, Polypoid ‘Acalephs, and Acalephs proper. But the classes of Mollusks which are said to be characterized by two systems of organs, the intestine and the vascular system, contain each two orders, one corresponding to the Intestinal animals, the other to the type of Mollusks, and so Acephala are divided into the order of Gelatinous Acephala and that of Molluscoid Acephala, and the Gasteropods and Cephalopods in the same manner into two orders each. The Articulata are considered as repre- senting three systems of organs, the intestinal, the vascular, and the respiratory systems; hence their classes are divided each into three orders. For instance, the Worms contain an order of Gelatinous Worms, one of Molluscoid Worms, one of Annulate Worms, and the same orders are adopted for Crustacea and Insects. Verte- prata are said to represent five systems, the three lower ones being the intestine, the vessels, and the respiratory organs, the two higher the flesh (that is, bones, muscles, and nerves) and the organs of senses; hence, five orders in each class of this type, as, for example, Gelatinous Fishes, Molluscoid Fishes, Entomoid Fishes, Carnal ch Cuap. IIL. FAMILIES. 155 Fishes, and Sensual Fishes, and so also in the classes of Reptiles, Birds, and Mammalia. 3 I have entered into so many details upon these vagaries of the distinguished German philosopher, because these views, however crude, have undoubtedly been suggested by a feature of the animal kingdom, which has thus far been too little studied: I mean the analogies which exist among animals, besides their true affinities, and which cross and blend, under modifications of strictly -homological structures, other characters which are only analogical. But it seems to me that the subject of analogies is too little known, the facts bearmg upon this kind of relationship being still too obscure, to be taken as the basis of such important groups in the animal kingdom as the orders are, and I would insist upon considering the complica- tion or gradation of structure as the feature which should regulate their limitation, if under order we are to understand natural groups expressing the rank, the relative standing, the superiority or inferiority of animals in their respective classes. Of course, groups thus characterized cannot be considered as mere modifications of the classes, being founded upon a special category of features. SHCOTION “TY. FAMILIES. Nothing is more indefinite than the idea of form, as applied by systematic writers, in characterizing animals. Here, it means a system of the most different figures having a common character, as, for instance, when it is said of Zoophytes that they have a radiated form; there, it indicates any outline which circumscribes the body of animals, when, for mstance, animal forms are alluded to in general, instead of designating them simply as animals; here, again, it means the special figure of some individual species. There is in fact no group of the animal king- dom, however extensive or however limited, from the branches down to the species, in which the form is not occasionally alluded to as characteristic. Speaking of Articu- lates, C. E. v. Baer characterizes them as the type with elongated forms; Mollusks are to him the type with massive forms; Radiates that with peripheric symmetry ; Vertebrates that with double symmetry, evidently taking their form in its widest sense as expressing the most general relations of the different dimensions of the 1 See further developments upon this subject in Naturgeschichte, vol. 4, p. 582. Compare also the Oxen’s Naturphilosophie, and.in his Allgemeine following chapter. 156 ESSAY ON CLASSIFICATION. Part I. body to one another. Cuvier speaks of form in general with reference to these four great types as a sort of mould, as it were, in which the different types would seem to have been cast. Again, form is alluded to in characterizing orders ; for instance, in the distinction between the Brachyourans and the Macrourans among Crustacea, or between the Saurians, the Ophidians, and the Chelonians. It is men- tioned as a distinguishing feature in many families, ex. gr. the Cetacea, the Bats, etc. Some genera are separated from others in the same family. on the ground of differences of form; and in almost every description of species, especially when they are considered isolatedly, the form is described at full length. Is there not, in this indiscriminate use of the term of form, a confusion of ideas, a want of precision in the estimation of what ought to be called form and what might be designated by another name? It seems to me to be the case. In the first place, when form is considered as characteristic of Radiata or Articulata, or any other of the great types of the animal kingdom, it is evident that it is not a definite outline and well-determined figure which is meant, but that here the word form is used as synonym for plan. Who, for instance, would describe the tubular body of | an Holothuria as characterized by a form similar to that of the Euryale, or that of an Echinus as identical with that of an Asterias? And who does not see that, as far as the form is concerned, Holothuria resemble Worms much more than they resemble any other Echinoderm, though, as far as the plan of their structure is concerned, they are genuine Radiates, and have nothing to do with the Articu- lates ? | | Again, a superficial glance at any and all the classes of the animal kingdom is sufficient to show that each contains animals of the most diversified forms. What can be more different than Bats and Whales, Herons and Parrots, Frogs and Sirens, Eels and Turbots, Butterflies and Bugs, Lobsters and Barnacles, Nautilus: and Cuttlefishes, Slugs and Conchs, Clams and compound Asidians, Pentacrinus and Spatangus, Beroe and Physalia, Actinia and Gorgonia? And yet they belong respec- tively to the same class, as they are coupled. here: Bats and Whales together, etc. It must be obvious, then, that form cannot be a characteristic element of classes, if we would understand any thing definite under that name. But form has a definite meaning understood everywhere, when applied to well- known animals. We speak, for instance, of the human form; an allusion to the form of a horse or that of a bull conveys at once a distinct idea; everybody would. acknowledge the similarity of form of the horse and ass, and knows how to distin- guish them by their form from dogs or cats, or from seals and porpoises. In this definite meaning, form corresponds also to what we call figure when speaking of men and women, and it is when taken in this sense, that I would now consider the value of forms as characteristic of different animals. We have seen that form Cuap. II. FAMILIES. - 157 cannot be considered as a character of branches, nor of classes; let us now examine, further, whether it is a character of species. A rapid review of some of the best known types. of the animal kingdom, embracing well-defined genera with many species, will at once show that this cannot be the case, for such species do not generally show the least difference in their forms. Neither the many species of Squirrels, nor the true Mice, nor the Weasels, nor the Bears, nor the Eagles, nor the Falcons, nor the Sparrows, nor the Warblers, nor the genuine Woodpeckers, ‘nor the true Lizards, nor the Frogs, nor the Toads, nor the Skates, nor the Sharks proper, nor the Turbots, nor the Soles, nor the Eels, nor the Mackerels, nor the Sculpins, nor the genuine Shrimps, nor the Crawfishes, nor the Hawkmoths, nor the Geometers, nor the Dorbugs, nor the Spring-Beetles, nor the Tapeworms, nor the Cuttlefishes, nor the Slugs, nor the true Asterias, nor the Sea-Anemones, could be distinguished among themselves, one from the other, by their form only. There may be differences in the proportions of some of their parts, but the pattern of every species belonging to well-defined natural genera is so completely identi- cal that it will never afford specific characters. There are genera in our system ‘hich as they now stand, might be alluded to as examples contrary to this state- ment ; but such genera are still based upon very questionable features, and’ are likely to be found in the end to consist of unnatural associations of heterogeneous species: at all events, all recent improvements in Zodlogy have gone to limit genera gradually more and more in such a manner, that the species belonging to each have shown successively less and less difference in form, until they have assumed, in that respect, the most homogeneous appearance. Are natural genera any more to be distinguished by their form one from the other? Is there any appreciable difference in the general form,—I say purposely general form, because a more or less prominent nose, larger or smaller ears, longer or shorter claws, ete. do not essentially modify the form,—is there any real difference in the general form between the genera of the most natural families? Do, for instance, the genera of Ursina, the Bears, the Badger, the Wolverines, the Raccoons, differ in form ? ‘Do the Phocoidx, the Delphinoide, the Falconine, the Turdine, the Fringilline, the Picine, the Scolopacinz, the Chelonioide, the Geckonina, the Colubrina, the Sparoide, the Elateride, the Pyralidoide, the Echinoide, etc., differ any more among themselves? Certainly not; though to some extent, there are differences in the form of the representatives of one genus when compared to those of another genus ; but when rightly considered, these differences appear only as modifications of the same type of forms. Just as there are more or less elongated ellipses, so do we find the figure of the Badgers somewhat more contracted than that of either the Bears, or the Raccoons, or the Wolverines, that of the Wolverimes somewhat more elongated than that of the Raccoons; but the form is here as completely ay 158 ESSAY ON CLASSIFICATION. Part I. as it is among the Viverrina, or among the Canina, or among the Bradypodide, or among the Delphinoide, etc., ete. We must, therefore, exclude form from the characteristics of natural genera, or at least introduce it only as a modification of the typical form of natural families. Of all the natural groups in the animal kingdom there remain then only families and orders, for the distinction of which form can apply as an essential criterion. But these two kinds of groups are just those upon which zodlogists are least agreed, so that it may not be easy to find a division which all naturalists would agree to take as an example of a natural order. Let us, however, do our best to settle the difficulty and suppose, for a moment, that what has been said above respecting the orders is well founded, that orders are natural groups charac- terized by the degree of complication of their structure, and expressing the respec- tive rank of these groups in their class, then we shall find less difficulty in pointing out some few groups which could be generally considered as orders. I suppose most naturalists would agree, for instance, that among Reptiles the Chelo- nians constitute a natural order; that among Fishes, Sharks and Skates constitute an order also; and if any one would urge the necessity of associating also the Cyclostomes with them, it would only the better serve my purposes. Ganoids, even circumscribed. within narrower limits than those I had assigned to them, and perhaps reduced to the extreme limits proposed for them by J. Miiller, I am equally prepared to take as an example, though I have in reality still some objec- tions to this limitation, which, however, do not interfere with my present object. Decapods, among Crustacea, I suppose everybody would also admit as an order, and I do not care here what other families are claimed besides Decapods to com- plete the highest order of Crustacea. Among Acephala, I trust Bryozoa, Tunicata, Brachiopods, and Lamellibranchiata would be also very generally considered to be natural orders. Among Echinoderms, I suppose Crinoids, Asterioids, Echinoids, and Holothurioids would be conceded also as such natural orders; among Acalephs the Beroids, and perhaps also Discophore and Hydroids; while among the Polypi, the Haleyonoids constitute a very natural order when compared with the Actinoids. Let us now consider these orders with reference to the characteristic forms they include. The forms of the genuine Testudo, of Trionyx, and of Chelonia are very different, one from the other, and yet few orders are so well circumscribed as that of Chelonians. The whole class of Fishes scarcely exhibits greater differences than those observed in the. forms of the common Sharks, the Sawfishes, the common Skates, and the Torpedo, not to speak of the Cyclostomes and Myxinoids, if these families were also considered as members of the order of Placoids. Ganoids cannot be circumscribed within narrower limits than those assigned to them by J. Miiller, and yet this order, thus limited, contains forms as heterogeneous as the Sturgeons, —Cuap. IL. FAMILIES. 159 the Lepidosteus, the Polypterus, the Amia, and a host of extinct genera and families, not to speak of those families I had associated with them and which Prof. Miiller would have removed, which, if included among Ganoids, would add_ still more heteromorphous elements to this order. Among Decapods, we need only remember the Lobsters and Crabs to be convinced that it is not similarity of form which holds them so closely together as a natural order. How heterogeneous Bryozoa, Brachiopods, and Tunicata are among themselves, as far as their form is concerned, everybody knows who has paid the least attention to these animals. - Unless, then, form be too vague an element to characterize any kind of natural groups in the animal kingdom, it must constitute a prominent feature of families. I have already remarked, that orders and families are the groups upon which zodlogists are least agreed, and to the study and characterizing of which they have paid least attention. Does this not arise simply from the fact, that, on the one hand, the difference between ordinal and class characters has not been understood, and only assumed to be a difference of degree; and, on the other hand, that the importance of the form, as the prominent character of families, has been entirely overlooked? For, though so few natural families of animals are well characterized, or characterized at all, we cannot open a modern treatise upon any class of animals without finding the genera more or less naturally grouped together, under the heading of a generic name with a termination in zde or me indicating family and sub-family distinctions ; and most of these groups, however unequal in absolute value, are really natural groups, though far from designating always natural families, being as often orders or sub-orders, as families or sub-families. Yet they indicate the facility there is, almost without study, to point out the intermediate natural groups between the classes and the genera. ‘This arises, in my opinion, from the fact, that family resemblance in the animal kingdom is most strikingly expressed in the general form, and that form is an element which falls most easily under our perception, even when the observation is made superficially. But, at the same time, form is most difficult to describe accurately, and hence the imperfection of most of our family characteristics, and the constant substitution for such characters of features which are not essential to the family. To prove the correctness of this view, I would only appeal to the experience of every naturalist. When we see new animals, does not the first glance, that is, the first impression made upon us by their form, give us at once a very correct idea of their nearest relation- ship? We perceive, before examining any structural character, whether a Beetle is a Carabicine, a Longicorn, an Elaterid, a Curculionid, a Chrysomeline ; whether ‘a Moth is a Noctuelite, a Geometrid, a Pyralid, etc.; whether a bird is a Dove, a Swallow, a Humming-bird, a Woodpecker, a Snipe, a Heron, ete, ete. But before we can ascertain its genus, we have to study the structure of some characteristic 160 ESSAY ON CLASSIFICATION. Parr I. parts; before we can combine families into natural groups, we have to make a thorough investigation of their whole structure, and compare it with that of other families. So form is characteristic of families; and I can add, from a careful investi- gation of the subject for several years past, during which I have reviewed the whole animal kingdom with reference to this and other topics connected with classifica- tion, that form is the essential characteristic of families’ I do not mean the mere outline, but form as determined by structure; that is to say, that families cannot be well defined, nor circumscribed within their natural limits, without a thorough investigation of all those features of the internal structure which combine to deter- mine the ‘form. : : | The characteristic of the North American Chelonians which follows, may serve as an example how this subject is to be treated. I will only add here, that how- ever easy it is at first, from the general impression made upon us by the form of animals, to obtain a glimpse of what may fairly be called families, few inves- tigations require more patient comparisons than those by which we ascertain the natural range of modifications of any typical form, and the structural features upon which it is based. Comparative anatomy has so completely discarded every thing that relates to Morphology; the investigations of anatomists lean so uniformly towards a general appreciation of the connections and homologies of the organic systems which go to build up the body of animals, that for the purpose of under- standing the value of forms and their true foundation, they hardly ever afford any information, unless it be here and there a consideration respecting teleological rela- tions. Taking for granted, that orders are natural groups characterized by the com- plication of their structure, and that the different orders of a class express the different degrees of that complication; taking now further for granted, that families are natural groups characterized by their form as determined by structural pecu- liarities, it follows that orders are the superior kind of division, as we have seen that the several natural divisions which are generally considered as orders, contain each several natural groups, characterized by different forms, that is to say, con- stituting as many distinct families. After this discussion it is hardly necessary to add, that families cannot by any means be considered as modifications of the orders to which they belong, if orders are to be characterized by the degrees of complication of their structure, and families * These investigations, which have led to most Dr. A. A. Gould, and which I would not allow to interesting results, have delayed thus far the publi- appear before I could revise the whole animal king- cation of the systematic part of the Principles of | dom in this new light, in order to introduce as much Zoology, undertaken in common with my friend, precision as possible in its classification. Cuap. IL. GENERA. , | 161 by their forms. I would also further remark, that there is one question relating to the form of animals, which I have not touched here, and which it is still more important to consider in the study of plants, namely, the mode of association of individuals into larger or smaller communities, as we observe them, particularly among Polyps and Acalephs. These aggregations have not, as far as their form is concerned, the same importance as the form of the individual animals of which they are composed, and therefore seldom afford trustworthy family characters. But this point may be more appropriately considered in connection with the special illustration of our Hydroids, to which my next volume is to be devoted. I have stated above, that botanists have defined the natural families of plants with greater precision than zodlogists those of animals; I have further’ remarked also, that most of them make no distinction between orders and families. This may be the result of the peculiar character of the vegetable kingdom, which is not built upon such entirely different plans of structure as are animals of different branches. On the contrary, it is possible to trace among plants a certain gradation between their higher and lower types more distinctly than among animals, even though they do not, any more than animals, constitute a simple series. It seems to me, nevertheless, that if Cryptogams, Gymnosperms, Monocotyledons, and Dico- tyledons can be considered as branches of the vegetable kingdom, analogous to Radiata, Mollusks, Articulata, and Vertebrata among animals, such divisions as Fungi, Algee, Lichens, Mosses, Hepatic, and Ferns in the widest sense, may be taken as classes. Diatomacex, Conferve, and Fuci may then be considered as orders; Mosses and Hepatice as orders; Equisetacee, Ferns proper, Hydropterids, and Lycopodiacese as orders also; as they exhibit different degrees of complication of structure, while their natural subdivisions, which are more closely allied m form or habitus, may be considered as families; natural families among plants having generally as distinct a port, as families among animals have a distinct form. We need only remember ‘the Palms, the Conifers, the Umbelliferse, the Composite, the Leguminose, the Lab- iatee, etc. as satisfactory examples of this kind. SOTO a vs GENERA. Linnzus already knew very well that genera exist in nature, though what he calls genera constitute frequently groups to which we give at present other names, as we consider many of them as families; but it stands proved by his writings 21 162 ESSAY ON CLASSIFICATION. | Pane”-f, that he had fully satisfied himself of the real existence of such groups, for he says distinctly in his Philosophia Botanica, sect. 169, “Scias characterem non con- stituere genus, sed genus characterem. Characterem fluere e genere, non genus e charactere. Characterem non esse, ut genus fiat, sed ut genus noscatur.” It is surprising that notwithstanding such clear statements, which might have kept naturalists awake respecting the natural foundation of genera, such loose ideas have become prevalent upon this subject, that at present the number of inves- tigators who exhibit much confidence in the real existence of their own generic distinctions is very limited. And as to what genera really are, the want of pre- cision of ideas appears still greater. Those who have considered the subject at all seem to have come to .the conclusion that genera are nothing but groups including a certain number of species agreeing in some more general features than those which distinguish species; thus recognizing no difference between generic and specific characters as such, as a single species may constitute a genus, when- ever its characters: do not agree with the characters of other species, and many species may constitute a genus, because their specific characters agree to a certain extent among themselves! Far from admitting such doctrines, I hope to be able to show that, however much or however little species may differ among themselves as species, yet they may constitute a natural genus, provided their respective generic characters are identical. I have stated before, that in order to ascertain upon what the different groups adopted in our systems are founded, I consulted the works of such writers as are celebrated in the annals of science for having characterized with particular felicity any one kind of these groups, and I have mentioned Latreille as prominent among zodlogists for the precision with which he has defined the genera of Crustacea and Insects, upon which he has written the most extensive work extant” An anecdote which I have often.heard repeated by entomologists who knew Latreille well, is very characteristic as to the meaning he connected with the idea of genera. At the time he was preparing the work just. mentioned, he lost no opportunity of obtaining specimens, the better to ascertain from nature the generic peculiarities _of these animals, and he used to apply to the entomologists for contributions to his collection. It was not show specimens he cared to obtain, any would do, for he used to say he wanted them only “to examine their parts.” Have we not here a hint, from a master, to teach us what genera are and how they should be characterized? Is it not the special structure of some part or other, which charac- 1 Spring, Ueber die naturhistorischen Begriffe 2 LaTREILLE, Genera Crustaceorum und Insect- von Gattung, Art und Abart, Leipzig, 1838, 1 vol. orum, Paris et Argent. 1806-1809, 4 vols. 8vo. 8vo. Cuap. II. SPECIES. | 163 terizes genera? Is it not the finish of the organization of the body, as worked out in the ultimate details of structure, which distinguishes one genus from another? Latreille, in expressing the want he felt with reference to the study of genera, has given us the key-note of their harmonious relations to one another. Genera are most closely allied groups of animals, differing neither in form, nor in com- plication of structure, but simply in the ultimate structural peculiarities of some of their parts; and this is, I believe, the best definition which can be given of genera. They are not characterized by modifications of the features of the fami- lies, for we have seen that the prominent trait of family difference is to be found in a typical form; and genera of the same family may not differ at all in form. Nor are genera merely a more comprehensive mould than the species, embracing a wide range of characteristics; for species in a natural genus” should not present any structural differences, but only such as express the most special relations of their representatives to the surrounding world and to each other. Genera, in one word, are natural groups of a peculiar kind, and their special distinction rests upon the ultimate details of their structure. SECTION VI. SPECIES. It is generally believed that nothing is easier than to determine species, and that of all the degrees of relationship which animals exhibit, that which consti- tutes specific identity is the most clearly defined. An unfailing criterion of specific identity is even supposed to exist in the sexual connection which so naturally brings together the individuals of the same species in the function of reproduc- tion. But I hold that this is a complete fallacy, or at least a petitio principii, not admissible in a philosophical discussion of what truly constitutes the characteristics’ of species. I am even satisfied that some of the most perplexing problems involved in the consideration of the natural limits of species would have been solved long ago, had it not been so generally urged that the ability and natural disposition of individuals to connect themselves in fertile sexual intercourse was of itself sufficient evidence of their specific identity. Without alluding to the fact that every new case of hybridity’ is an ever-returning protest against such an assertion, and 1 Wiecman, Gekronte Preisschrift iiber die Bas- ron, (S. G.,) Essay on Hybridity, Amer. Jour., tarderzeugung im Pflanzenreich, Braunschweig, 1828, 1847. — Additional Observations on Hybridity in 8vo.— Brawn, (A.,) Ueber die Erscheinung der Ver- Animals and on some collateral subjects, Charleston jiingung in der Natur, Freiburg, 1849, 4to.—Mor- — Med. Journ., 1850. pcsnanenennerenny 164 ESSAY ON CLASSIFICATION. ofp ae without entering here into a discussion respecting the possibility or practicability of setting aside this difficulty by introducing the consideration of the limited fer- tility of the progeny of individuals of different species, I will only remark, that as long as it is not proved that all the varieties of dogs, and of any others of our domesticated animals, and of our cultivated plants, are respectively derived from one unmixed species, and as long as doubts can be entertained respecting the common origin of all races of men from one common stock, it is not logical to admit that sexual connection resulting even in fertile offspring is a trustworthy evidence of specific identity. To justify this assertion, I would only ask, where is the unprejudiced naturalist who in our days would dare to maintain: Ist, that it is proved that all the domesticated varieties of sheep, of goats, of bulls, of Hamas, of horses, of dogs, of fowls, etc., are respectively derived from one common stock; 2d, that the supposition that these varieties have originated from the complete amalgamation of several primitively distinct species is out of the question; and 3d, that varieties imported from distant countries and not before brought together, such as the Shanghae fowl, for instance, do not completely mingle? Where is the physiologist who can conscientiously affirm that the limits of the fertility between distinct species are ascertained with sufficient accuracy to make it a test of specific identity ? And who can say that the distinctive characters of fertile hybrids and of unmixed breeds are sufficiently obvious to enable anybody to poimt ‘out the primitive feat- ures of all our domesticated animals, or of all our cultivated plants? As long as this cannot be done, as long as the common origin of all races of men, and of the different animals and plants mentioned above, is not proved, while their fertility with one another is a fact which has been daily demonstrated for thou- sands of years, as long as large numbers of animals are hermaphrodites, never requiring a connection with other individuals to multiply their species, as long as there are others which multiply in various ways without sexual intercourse, it is not justifiable to assume that those animals and plants are unmixed species, and that sexual fecundity is the criterion of specific identity. Moreover, this test can hardly ever have any practical value in most cases of the highest scientific inter- est. It is never resorted to, and, as far as 1 know, has never been applied with satisfactory results to settle any doubtful case. It has never assisted any anxious and conscientious naturalist in investigating the degree of relationship between closely allied animals or plants living in distant regions or in disconnected geo- graphical areas. It will never contribute to the solution of any of those difficult cases of seeming difference or identity between extinct animals and plants found in different geological formations. In all critical cases, requirmg the most minute accuracy and precision, it is discarded as unsafe, and of necessity questionable. Accurate science must do without it, and the sooner it is altogether discarded, the 5 a at in a —_ win a ase ee ee Cuap. II. SPECIES. 165 better. But, like many relics of past time, it is dragged in as a sort of theo- retical bugbear, and exhibited only now and then to make a false show in discus- ? sions upon the question of the unity of origm of mankind. — , il || rt There is another fallacy connected with the prevailing ideas about species to it which I would also allude: the fancy that species do not exist in the same way | | il in nature as genera, families, orders, classes, and types. It is actually maintained \ Si by some that species are founded in nature in a manner different from these groups; | that their existence is, as it were, more real, whilst that of the other groups is | considered as ideal, even when it is admitted that these groups have themselves a natural foundation. | Let us consider this point more closely, as it involves the whole question of individuality. I wish, however, not to be understood as undervaluing the impor- tance of sexual relations as indicative of the close ties which unite, or may unite, | Hy the individuals of the same species. I know as well as any one to what extent | | | they manifest themselves in nature, but I mean to insist upon the undeniable fact al that these relations are not so exclusive as those naturalists would represent them, who urge them as an unfailing criterion of specific identity. I would remind those who constantly forget it, that there are animals which, though specifically distinct kh do unite sexually, which do produce offspring, mostly sterile, it is true, in some species, but fertile to a limited extent in others, and in others even fertile to an extent which it has not yet been possible to determine. Sexual connection is the result, or rather one of the most striking expressions of the close relationship established in the beginning between individuals of the same species, and by no means the cause of their identity in successive generations. When first created, animals of the same species paired because they were made one for the other ; they did not take one another in order to build up their species, which had full existence before the first individual produced by sexual connection was born. This view of the subject acquires greater importance in proportion as it becomes more apparent that species did not originate in single pairs, but were created in large numbers, in those numeric proportions which constitute the natural harmonies between organized beings. It alone explains the possibility of the procreation of Hybrids, as: founded upon the natural relationship of individuals of closely allied species, which may become fertile with one another, the more readily as they differ less, structurally. To assume that sexual relations determine the species it should further be shown that absolute promiscuousness of sexes among individuals of the same species is the prevailing characteristic of the animal kingdom, while the fact is, that a large num- ber even of animals, not to speak of Man, select their mate for life and rarely have any intercourse with others. It is a fact known to every farmer, that differ- \ 166 ESSAY ON CLASSIFICATION. Part I. ent breeds of the same species are less inclined to mingle than individuals of the same breed. For my own part, I cannot conceive how moral philosophers, who urge the unity of origin of Man as one of the fundamental principles of their religion, can at the same time justify the necessity which it involves of a sexual intercourse between the nearest blood relations of that assumed first and unique human family, when such a connection is revolting even to the savage. Then again, there are innumerable species in which vast numbers of individuals are never developed sexually, others in which sexual individuals appear only now and then at remote intervals, while many intermediate generations are produced without any sexual connection, and others still which multiply more extensively by budding than by sexual generation. 1 need not again allude here to the phenomena of alternate generation, now so well known among ) Hi fact, that the Chelonara serpentina bites as soon as it up in its foetal envelopes, with a yolk larger than | is hatched. I have seen it snapping in the same itself hanging from its sternum, three months before fierce manner as it does when full-grown, at a time hatching. 176 ESSAY ON CLASSIFICATION. } Part I. durmg the embryonic growth, in the order of their subordination, there was no possibility of deriving from embryological monographs, that information upon this point, so much needed in Zodlogy, and so seldom alluded to by embryologists. Again, without knowing what constitutes truly the characters of the groups named above, there is no possibility of finding out the true characters of a genus of which only one species is known, of a family which contains only one genus, etc., and for the same reason no possibility of arriving at congruent results with refer- ence to the natural limitations of genera, families, orders, etc. without which we cannot even begin to build up a permanent classification of the animal kingdom; and still less, hope to establish a solid basis for a general comparison between the animals now living and those which have peopled the surface of our globe in past geological ages. ; 7 It is not accidentally I have been led to these investigations, but by necessity. As often as I tried to compare higher or more limited groups of animals of the present period with those of former ages, or early stages of growth of higher living animals. with full-grown ones of lower types, 1 was constantly stopped in my progress by doubts as to the equality of the standards I was applying, until I made the standards themselves the object of direct and very extensive investiga- tions, covering indeed a much wider ground than would appear from these remarks, for, upon these principles, I have already remodelled, for my own convenience, nearly the whole animal kingdom, and introduced in almost every class very unexpected changes in the classification. I have already expressed above’ my conviction that. the only true system is that which exists in nature, and as, therefore, no one should have the ambition of erecting a system of his own, I will not even .attempt now to present these results in the shape of a diagram, but remain satisfied to express my belief, that all we can really do is, at best, to offer imperfect translations in human language of the profound thoughts, the innumerable relations, the unfathomable meaning of the plan actually manifested in the natural objects themselves; and I should con- sider it as my highest reward should I find, after a number of years, that I had helped others on in the right path. : 1 See Chap. E., Sect. We, 09 7 Poon CONCLUSIONS. Cuap. II. SBHCTION IX. CONCLUSIONS. The importance of such an investigation as the preceding, must be obvious to every philosophical investigator. As soon as it is understood that all the different groups introduced into a natural system may have a definite meaning; as soon as it can be shown that each exhibits a definite relation among living beings, founded in nature, and no more subject to arbitrary modifications than any other law expressing natural phenomena; as soon as it is made plain that the natural limits of all these groups may be ascertained by careful investigations, the interest in the study of classification or the systematic relationship existing among all organized beings, which has almost ceased to engage the attention of the more careful original investigators, will be revived, and the manifold ties which link together all animals and plants, as the living expression of a gigantic conception, carried out in the course of time, like a soul-breathing epos, will be scrutinized anew, determined with greater precision, and expressed with increasing clearness and propriety. Fanciful and _ artificial classifications will gradually lose their hold upon a better informed community; scientific men themselves will be restrained from bringing forward immature and premature investigations; no characteristics of new species will have a claim upon the notice of the learned, which has not been fully investigated and compared with those most closely allied to it; no genus will be admitted, the structural peculiarities of which are not clearly and distinctly illustrated ; no family will be considered as well founded, which shall not exhibit a distinct system of forms mtimately combined and determined by structural rela- tions; no order will appear admissible, which shall not represent a well-marked degree of structural complication; no class will deserve that name, which ghall not appear as a distinct and independent expression of some general plan of struc- ture, carried out in a peculiar way and with peculiar means; no type will be recognized as one of the fundamental groups of the animal kingdom, which shall . not exhibit a plan of its own, not convertible into another. No naturalist will be justified in introducing any one of these groups into our systems without show- ing: Ist, that it is a natural group; 2d, that it is a group of this or that kind, to avoid, henceforth, calling families groups that may be genera, families groups that may be orders, classes or types groups that may be orders or classes; 38d, that the characters by which these groups may be recognized are in fact respectively specific, 23 Sn en A ERT A RPT A ne eee 178 ESSAY ON CLASSIFICATION. Part I. generic, family, ordinal, classic, or typical characters, so that our works shall no longer exhibit the annoying confusion, which is to be met almost everywhere, of generic characters in the diagnoses of species, or of family and ordinal characters in the characteristics of classes and types! _ It may perhaps be said, that all this will not render the study of Zodlogy more easy. ‘I do not expect that it will; but if an attentive consideration of what I have stated in the preceding pages respecting classification, should lead to a more accurate investigation of all the different relations existing among animals, and between them and the world in which they live, I shall consider myself as having fully succeeded in the object I have had in view from the beginning, in this inquiry. Moreover, it is high time that certain zodlogists, who would ‘call themselves investigators, should remember, that natural objects, to be fully under- stood, require more than a passing glance; they should imitate the example of astronomers, who have not become tired of looking into the relations of the few members of our solar system to determine, with increased precision, their motions, their size, their physical constitution, and keep in mind that every organized being, however simple in its structure, presents to our appreciation far more com- plicated phenomena, within our reach, than all the celestial bodies put together; they should remember, that as the great literary productions of past ages attract ever anew the attention of scholars, who can never feel that they have exhausted the inquiry into their depth and beauty, so the living works of God, which it is the proper sphere of Zodlogy to study, would never cease to present new attractions to them, should they proceed to the investigation with the right spirit. Their studies ought, indeed, inspire every one with due reverence and admiration for such wonderful productions. The subject of classification in particular, which seems to embrace apparently so limited a field in the science of animals, cannot be rightly and fully under- stood without a comprehensive knowledge of all the topics alluded to in the preceding pages. 1 As Ido not wish to be personal, I will refrain any characterization of genera, of families, of orders, from quoting examples to justify this assertion. I of classes, and of types, to satisfy themselves that would only request those who care to be accurate, to characters of the same kind are introduced almost examine critically almost any description of species, indiscriminately to distinguish all these. groups. ee Dae OH A PolEaties ida Hel). NOTICE OF THE PRINCIPAL SYSTEMS OF ZOOLOGY. SECTION I. GENERAL REMARKS UPON MODERN SYSTEMS. Wirnovr attempting to give an historical account of the leading features of all zodlogical systems, it is proper that I should here compare critically the practice of modern naturalists with the principles discussed above. With this view, it would hardly be necessary to go back beyond the publication of the “Animal Kingdom,” by Cuvier, were it not that Cuvier is still represented, by many naturalists, and especially by Ehrenberg, and some other German zoUlogists, as favoring the division of the whole animal kingdom into two great groups, one containing the Vertebrates, and the other all the remaining classes, under the name of Inverte- brates, while in reality it was he, who first, dismissing his own earlier views, introduced into the classification of the animal kingdom that fourfold division which has been the basis of all improvements in modern Zodlogy. He first showed that animals differ, not only by modifications of one and the same organic structure, but are constructed upon four different plans of structure, forming natural, distinct groups, which he called Radiata, Articulata, Mollusca, and Vertebrata. It 38 trac, that the further subdivisions of these leading groups have under- gone many changes since the publication of the “Reégne Animal.” Many smaller groups, even entire classes, have been removed from one of his “embranchments” to another; but it is equally true, that the characteristic idea which lies at the bottom of these great divisions was first recognized by him, the greatest zodlogist of all times. 1 Enrenserc, (€. G.,) Die Corallenthiere des rothen Meeres, Berlin, 1834, Ato., p. 30. lt at SA III a 180 Soe ESSAY ON CLASSIFICATION. Part I. The question which I would examine here in particular, is not whether the circumscription of these great groups was accurately defined by Cuvier, whether the minor groups referred to them truly belong there or elsewhere, nor how far these divisions may be improved within their respective limits, but whether there are four great fundamental groups in the animal kingdom, based upon -four differ- ent plans of structure, and neither more nor less than four. This question is very seasonable, since modern zodlogists, and especially Siebold, Leuckart, and Vogt have proposed combinations of the classes of the animal kingdom into higher groups, differing essentially from those of Cuvier. It is but justice to Leuckart to say that he has exhibited, in the discussion of this subject, an acquaintance with the whole range of Invertebrata,’ which demands a careful consideration of the changes he proposes, as they are based upon a critical discrimination of differences of great value, though I think he overrates their importance. The modifications intro- duced by Vogt, on the contrary, appear to me to be based upon entirely unphysio- logical principles, though seemingly borrewed from that all important guide, Em- bryology. The divisions adopted by Leuckart are: Protozoa, (though he does not enter upon an elaborate consideration of that group,) Coelenterata, Echinodermata, Vermes, Arthropoda, Mollusca, and Vertebrata. The classification adopted, many years before, by Siebold, in his text-book of comparative anatomy, 1s nearly the same, except that Mollusks follow the Worms, that Coelenterata and Echinoderms are united into one group, and that the Bryozoa are left among the Polyps. Here we have a real improvement upon the classification of Cuvier, imasmuch as the Worms are removed from among the Radiates, and brought nearer the Arthropods, an improvement however, which, so far as it is correct, has already been anticipated by many naturalists, since Blainville and other zodlogists long ago felt the impropriety of allowing them to remain among Radiates, and have been induced to associate them more or less closely with Articulates. But I believe the union of Bryozoa and Rotifera with the Worms, proposed by Leuckart, to be a great mistake; as to the separation of Coelenterata from Echinoderms, I consider it as an exaggeration of the difference which exists between Polyps and Acalephs on the one hand, and Echinoderms on the other. The fundamental groups adopted by Vogt,’ are: Protozoa, Radiata, Vermes, Mol- lusca, Cephalopoda, Articulata, and Vertebrata, an arrangement which is based solely upon the relations of the embryo to the yolk, or the absence of eggs. But, as * LevcKart, (R.,) Ueber die Morphologie und die 2-Voat, (CarL,) Zoologische Briefe. Naturge- Verwandtshaftsverhiltnisse der wirbellosen Thiere, schichte der lebenden und untergegangenen Thiere. Braunschweig, 1848, 1 vol., 8vo. | Frankfurt a. M., 1851; vol. 1, p. 70. 4 Cuap. III. MODERN SYSTEMS. 181 I have already stated, this is an entirely unphysiological principle, inasmuch as it assumes’ a contrast between the yolk and the embryo, within limits which do not exist in nature. ‘The Mammalia, for instance, which are placed, like all other Verte- brata, in the category of the animals in which there is an opposition between the embryo and the yolk, are as much formed of the whole yolk as the Echinoderms or Mollusks. The yolk undergoes a complete segmentation in Mammalia, as well as in Radiates or Worms, and most Mollusks; and the embryo when it makes its appearance no more stands out from the yolk, than the little Starfish stands out from its yolk. These simple facts, known since Sars and Bischoff published their first observations, twenty years ago, is in itself sufficient to show that the whole principle of classification of Vogt is radically wrong. Respecting the assertion, that neither Infusoria nor Rhizopoda produce any eggs, I shall have more to say presently. As to the arrangement of the leading groups, Vertebrata, Articulata, Cephalopoda, Mollusca, Vermes, Radiata, and Protozoa in Vogt’s system, it must be apparent to every zodlogist conversant with the natural affinities of animals, that a classification which interposes the whole series of Mollusks between the types of Articulata and Worms, cannot be correct. A. classification based, like this, solely upon the changes which the yolk undergoes, is not likely to be the natural expression of the manifold relations existing between all animals. Indeed, no system can be true to nature, which is based upon the consideration of a single part, or a single organ. After these general remarks, I have only to show more in detail, why I believe that there are only four great fundamental groups in the animal kingdom, neither more nor less. With reference to Protozoa, first, it must be acknowledged that, notwithstanding the extensive investigation of modern writers upon Infusoria and Rhizopoda, the true nature of these beings is still very little known. The Rhizopoda have been wandering from one end of the series of Invertebrata to the other, without finding a place generally acknowledged as expressing their true affinities. The attempt to separate them from all the classes with which they have been so long associated, and to place them with the Infusoria in one distinct branch, appears to me as mistaken as any of the former arrangements, for I do not even consider that their animal nature is yet proved beyond a doubt, though I have myself once sug- gested the possibility of a definite relation between them and the lowest Gaste- ropods. Since it has been satisfactorily ascertained that the Corallines are genuine Algz, which contain more or less lime in their structure, and since there is hardly any group among the lower animals and lower plants, which does not contain simple locomotive individuals, as well as compound communities, either free or adher- ing to the soil, [ do not see that the facts known at present preclude the possibility 182 ESSAY ON CLASSIFICATION. Part I. of an association of the Rhizopods with the Algx.! This would almost seem natural, when we consider that the vesicles of many Fuci contain a viscid, filamentous substance, so similar to that protruded from the body of the Rhizopods, that the most careful microscopic examination does not disclose the slightest difference in its structure from that which mainly forms the body of Rhizopods. The discovery by Schultze? of what he considers as the germinal granules of these beings, by no means settles this question, though we have similar ovoid masses in Algx, and though, among the latter, locomotive forms are also very numerous. With reference to the Infusoria, I have long since expressed my conviction that they are an unnatural combination of the most heterogeneous beings. A large number of them, the Desmidiee and Volvocine, are locomotive Algz. Indeed, recent investigations seem to have established beyond all question, the fact, that all the Infusoria Anentera of Ehrenberg are Algz. The Enterodela, however, are true animals, but belong to two very distinct types, for the Vorticellide differ entirely from all others. Indeed, they are, in my opinion, the only independent animals of that group, and so far from having any natural affinity with the other Enterodela, I do not doubt that their true place is by the side of Bryozoa, among Mollusks, as I shall attempt to show presently. Isolated observations which I have been able to make upon Paramecium, Opalina, and the like, seem to me sufficient to justify the assumption that they disclose the true nature of the bulk of this group. I have seen, for instance, a Planaria lay eggs out of which Paramecium were born, which underwent all the changes these animals are known to undergo up to the time of their contraction into a chrysalis state; while the Opalina is hatched from Distoma eggs. I shall publish the details of these observations on another occasion. But if it can be shown that two such types as Paramecium and Opalina are the progeny of Worms, it seems to me to follow, that all the Enterodela, with the exception of the Vorticellide, must be considered as the embryonic condition of that host of Worms, both parasitic and free, the meta- morphosis of which is still unstudied. In this connection, I might further remark, that the time is not long past when Cercaria was also considered as belonging to the class of Infusoria, though at present no one doubts that it belongs to the cycle of Distoma; and the only link in the metamorphosis of that genus which was not known is now supplied, since, as I have stated above, the embryo which is hatched from the egg laid by the perfect Distoma is found to be Opalina. All this leads to the conclusion, that a division of the animal kingdom to be called Protozoa, differing from all other animals in producing no eggs, does not exist in nature, and that the beings which have been referred to it have now 1 Comp. Chap. I., Sect. 18, p. 75. 2 Scnuttzz, (M. S.,) Polythalamien, q. a.; p. 24. 183 Cuap. III. MODERN SYSTEMS. to be divided, and scattered, partly among plants, in the class of Algs, and partly among animals, in the classes of Acephala, (Vorticelle,) of Worms, (Paramecium and Opalina,) and of Crustacea (Rotifera); Vorticelle being genuine Bryozoa and there- fore Acephalous Mollusks, while the beautiful investigations of Dana and Leydig have proved the Rotifera to be genuine Crustacea, and not Worms. _ The great type of Radiata, taking its leading features only, was first recognized by Cuvier, though he associated with it many animals which do not properly belong to it. This arose partly from the imperfect knowledge of those animals at the time, but partly also from the fact that he allowed himself, in this instance, to deviate from his own principle of classification, according to which types are founded upon special plans of structure. With reference to Radiata, he departed, indeed, from this view, so far as to admit, besides the consideration of their peculiar plan, the element of simplicity of their structure as an essential feature in the typical character of these animals, in consequence of which he introduced five classes among Radiata: the Echinoderms, Intestinal Worms, Acalephs, Polypi, and Infusoria. In opposition to this unnatural association, I need not repeat here, what I have already stated of the Infusoria, when considering the case of Protozoa; neither is it necessary to urge again the propriety of removing the Worms from among Radiata, and connecting them with Articulata. There would thus remain only three classes among Radiates, — Polypi, Acalephs, and Echinoderms, — which, in my opinion, con- stitute really three natural classes in this great division, inasmuch as: they exhibit the three different ways in which the characteristic plan of the type, radiation, is carried out, in distinct structures. Since it can be shown that Echinoderms are, in a general way, homologous in their structure with Acalephs and Polypi, it must be admitted that these classes belong to one and the same great type, and that they are the only representa- tives of the branch of Radiata, assuming of course that Bryozoa, Coralline, Sponges, and all other foreign admixtures have been removed from among Polyps. Now, it. is this Cuvierian type of Radiata, thus freed of all its heterogeneous elements, which Leuckart undertakes to divide into two branches, each of which he considers coequal with Worms, Articulates, Mollusks, and Vertebrates. He was undoubtedly led to this exaggeration of the difference existing between Echinoderms on one side and Acalephs and Polypi on the other, by the apparently greater resemblance of Medusz and Polypi,! and perhaps still more by the fact, that so many genuine Acalephs, such as the Hydroids, including Tubularia, Sertularia, Campanularia, etc, are still comprised by most zodlogists in the class of Polypi. 1 We see here clearly how the consideration of overridden the primary feature of branches, their anatomical differences which characterize classes has plan, to exalt a class to the rank of a branch. 184 ESSAY ON CLASSIFICATION. Part I. But since the admirable investigations of J. Miiller have made us familiar with the extraordinary metamorphosis of Echinoderms, and since the Ctenophere and the Siphonophoree have also been more carefully studied by Grube, Leuckart, Koélliker, Vogt, Gegenbaur, and myself, the distance which seemed to separate Echino- derms from Acalephs disappears entirely, for it is mo exaggeration to say, that were the Pluteus-like forms of Echinoderms not known to be an early stage in the transformation of Kchinoderms, they would find as natural a place among Ctenophore, as the larve of Insects among Worms. I therefore maintain, that Polypi, Acalephs, and Echinoderms constitute one indivisible primary group of the animal kingdom. The Polypoid character of young Meduse proves this as plainly as the Medusoid character of young Echinoderms. Further, nothing can be more unnatural than the transfer of Ctenophore to the type of Mollusks which Vogt has proposed, for Ctenophore exhibit the closest homology with the other Meduse, as I have shown in my paper on the Beroid Meduse of Massachusetts. The Ctenophoroid character of young Echinoderms establishes a second connection between Ctenophore and the other Radiata, of as great importance as the first. We have thus an anatomical link to connect the Ctenophoree with the genuine Meduse, = an embryological link to connect them with the Echinoderms. The classification of Radiata may, therefore, stand thus: — Ist Class: Polypi; including two orders, the Aetinoids and the Halcyc- noids, as limited by Dana. | 2d Class: Acalephae; with the following orders: Hydroids, (including Sipho- nophore,) Discophore, and Ctenophore. 3d Class: Echinoderms; with Crinoids, Asteroids, Eehinoids, and Holothu- rioids, as orders. The natural limits of the branch of Mollusks are easily determined. Since the Cirripeds have been removed to the branch of Articulata, naturalists have generally agreed to consider, with Cuvier, the Cephalopods, Pteropods, Gasteropods, and Acephala as forming the bulk of this type, and the discrepancies between modern investigators have mainly resulted from the views they have taken respecting the Bryozoa, which some consider still as Polyps, while others would unite them with the Worms, though their affinity with the Mollusks seems to me to have been clearly demonstrated by the investigations of Milne-Edwards. Vogt is the only naturalist who considers the Cephalopoda “as built upon a plan entirely peculiar ;1 though he does not show in what this peculiarity of plan consists, but only mentions the well-known anatomical differences which distinguish them from the other classes 1 Voat, (C.,) Zoologische Briefe, q. a.; vol. 1, p. 361. re Cnap. IIL. MODERN SYSTEMS. 185 of the branch of Mollusks. These differences, however, constitute only ‘class charac- ters and exhibit in no way a different plan. It is, indeed, by no means difficult to homologize all the systems of organs of the Cephalopods with those of the other Mollusks, and with this evidence, the proof is also furnished that the Cepha- lopods constitute only a class among the Mollusks. As to the differences in the development of the Cephalopods and the other Mollusks, the type of Vertebrata teaches us that partial and total segmentation of the yolk are not inconsistent with unity of type, as the eggs of Mammalia and Cyclostomata undergo a total segmentation, while the process of segmentation is more or less limited in the other classes. In Birds, Reptiles, and Selachians, the segmentation is only superficial ; in Batrachians, and most Fishes, it is much deeper; and yet no one would venture to separate the Vertebrata into several distinct branches on that account. With reference to Bryozoa, there can be no doubt, that their association with Polypi or with Worms is contrary to their natural affinities. The plan of their structure is in no way radiate; it is, on the con- trary, distinctly and essentially bilateral ; and as soon as their close affinities with the Brachiopods, alluded to above,’ are fully understood, no doubt will remain of their true relation to Mollusks. As it is not withm the limits of my plan to illustrate here the characters of all the classes of the animal kingdom, I will only state further, that the branch of Mollusks appears to me to contain only three classes, as follows :— . Ist Class: Acephala; with four orders, Bryozoa, including the Vorticellx, Bra- chiopods, Tunicata, and Lamellibranchiata. | 2d Class: Gasteropoda; with three orders, Pteropoda, Heteropoda, and Gas- teropoda proper. 3d Class: Cephalopoda; with two orders, Tetrabranchiata and Dibranchiata. The most objectionable modification introduced m the general classification of the animal kingdom, since the appearance of Cuvier’s Régne Animal, seems to me to be the establishment of a distinct branch, now very generally admitted under the name of. Vermes, including the Annulata, the Helminths, the Rotifera, and as Leuckardt would have it, the Bryozoa also. It was certainly an improve- ment upon Cuvier’s system, to remove the Helminths from the type of Radiates, but it was at the same time as truly a retrograde step to separate the Annelides from the branch of Articulata. The most minute comparison does not lead to the discovery of a distinct plan of structure, uniting all these animals into one natural primary group. What holds them together and keeps them at a distance? from other groups is not a common plan of structure, but a greater simplicity in their - * Chap. IL, Sect. 7, p. Lee Fae Wp) 1 Chap. I., Sect. 18, p. 72. 24 186 ESSAY ON CLASSIFICATION. Part I. organization." In bringing these animals together, naturalists make again the same mistake which Cuvier committed, when he associated the Helminths with the Radiates, only in another way and upon a greater scale? The Bryozoa are as it were depauperated Mollusks, as Aphanes and Alchemilla are depauperated Rosacee. Rotifera are in the same sense the lowest Crustacea; while Helminths and Annelides constitute together the lowest class of Articulata. This class is connected by the closest homology with the larval states of Insects; the plan of their structure is identical, and there exists between them only such structural differences as con- stitute classes. Moreover, the Helminths are linked to the Annelides in the same manner as the apodal larve of Insects are to the most highly organized cater- pillars. It may truly be said that the class of Worms represents, in perfect animals, the embryonic states of the higher Articulata. The two other classes of this branch are the Crustacea and the Insects, respecting the limits of which, as much has already been said above,* as is necessary to state here. The classification’ of the branch of Articulata may, therefore, stand thus:— Ist Class: Worms; with three orders, Trematods, (including Cestods, Planariz, and Leeches,) Nematoids, (including Acanthocephala and Gordiacei,) and Annelides. 2d Class: Crustacea; with four orders, Rotifera, Entomostraca, (including Cirripeds,) Tetradecapods, and Decapods. 3d Class: Insects; with three orders, Myriapods, Arachnids, and Insects proper. There is not a dissenting voice among anatomists respecting the natural limits of the Vertebrata, as a branch of the animal kingdom. Their character, however, does not so much consist in the structure of their backbone or the presence of a dorsal cord, as in the general plan of that structure, which exhibits a cavity above and a cavity below a solid axis. These two cavities are circumscribed by complicated arches, arising from the axis, which are made up of different systems of organs, the skeleton, the muscles, vessels, and nerves, and include, the upper one the centres of the nervous system, the lower one the different systems of organs by which assimilation and reproduction are carried on. The number and limits of the classes of this branch are not yet satisfactorily ascertained. At least, naturalists do not all agree about them. For my part, I believe that the Marsupialia cannot be separated from the Placental Mammalia, as a distinct class, since we observe, within the limits of another type of Verte- brata, the Selachians, which cannot be subdivided into classes, similar differences in the mode of development to those which exist between the Marsupials and the other 1 See above, Chap. I., Sect. 18, p. 74-78. # Compare Chapetl, Sock 9, pe 125! Y Pp Pp 7 Compare Chap. II, Sect. 1, p. 142. 4 Compare Chap. I., Sect. 18, p. 78-80. r¢ Cuap. III. EARLY ATTEMPTS. . 187 Mammalia. But I hold, at the same time, with other naturalists, that the Batrachia must be separated, as a class, from the true Reptiles, as the characters which distin- guish them are of the kind upon which classes are founded. I am also satisfied that the differences which exist between the Selachians, (the Skates, Sharks, and Chimerx,) are of the same kind. as those which distinguish the Amphibians from- the Reptiles proper, and justify, therefore, their separation, as a class, from. the Fishes proper. I consider also the Cyclostomes as a distinct class, for similar reasons; but I am still doubtful whether the Ganoids should be separated also from the ordinary Fishes. This, however, cannot be decided until their embryological development has been thoroughly investigated, though I have already collected data which favor this view of the case. Should this expectation be realized, the branch of Vertebrata would contain the following classes :— Ist Class: Myzontes; with two orders, Myxinoids and Cyclostomes. 2d Class: Fishes proper; with two orders, Ctenoids and Cycloids, 3d Class: Ganoids; with three orders, Coelacanths, Acipenseroids, and Sauroids ; and doubtful, the Siluroids, Plectognaths, and Lophobranches. Ath Class: Selachians; with three orders, Chimerx, Galeodes, and Batides. Sth Class: Amphibians; with three orders, Cecilie, Ichthyodi, and Anura. 6th Class: Reptiles; with four orders, Serpentes, Saurii, Rhizodontes, and Testudinata. 7th Class: Birds; with four orders, Natatores, Grallz, Rasores, and Insessores, (including Scansores and Accipitres.) 8th Class: Mammalia; with three orders, Marsupialia, Herbivora, and Car- nivora. I shall avail myself of an early opportunity to investigate more fully how far these groups of Vertebrata exhibit such characters as distinguish classes, and I submit. my present impressions upon this subject, rather as suggestions for further researches, than as matured results. SHOTION:. £1. EARLY ATTEMPTS TO CLASSIFY ANIMALS. So few American naturalists have paid special attention to the classification of the animal kingdom in general, that I deem it necessary to allude to the different principles which, at different times, have guided zodlogists in their attempts to group animals according to their natural affinities, This will appear the more 188 ESSAY ON CLASSIFICATION. Parr I. acceptable, I hope, since few of our libraries contain even the leading works of our science, and many zealous students are thus prevented from attempting to study what has thus far been done. Science has begun, in the introduction of names, to designate natural groups of different value with the same vagueness which still prevails im ordinary lan- guage in the use of class, order, genus, family, species; taking them either as synonyms or substituting one for the other at random. lLimneus was the first to urge upon naturalists precision in the use of four kinds of groups in natural history, which he calls classes, orders, genera, and species. Aristotle, and the ancient philosophers generally, distinguished only two kinds of groups among animals, yéo¢ and «dos, (genus and species.) But the term genus had a most unequal meaning, applying at times indiscriminately to any extensive group of species, and designating even what we now call classes as well as any other minor group. In the sense of class, it is taken in the following case: Aéyo 88 yévoc, lov ognda, xat (Oo, (Arist. Hist. Anim., Lib. I, Chap. I,) while eidos is generally used for species, as the following sentence shows: «ai éorw edn mleiw iydier zat ogvidor, though it has occasionally also a wider meaning. ‘The sixth chapter of the same book, is the most important in the whole work of Aristotle upon this subject, as it shows to how many different kinds of groups the term ys is applied. Here, he distinguishes between yéy péyore and yy peyeha and yevos shortly. Iéy 8: utnota tov Coov, sig & Suugeiver tédla Cou, cad soriv: & pev oovidor, &» SF iyOvor, GLO dz xjrove. Ado 88 yévog iati tO THY doTeAKodEQUOY” Tov d& owtav Coowv ovu got tH yin pEydha* ov yao mspueyes molad edn év eidoc,.... 1a 3 eye per, ad? cvodvrpe. ‘This is further insisted upon anew: zou 58 yévovg tay tetounddar Cooov nat Cowtoxwr edn per sic modda, cvroveua de Here eidog has evidently a wider meaning than our term species, and the accurate Scaliger translates it by genus medium, in contradistinction to ys, which he renders by genus summum. Eidos, however, is generally used in the same sense as now, and Aristotle already considers fecundity as a specific character, when he says, of the Hemionos, that it is called so from its likeness to the Ass, and not because it is of the same species, for he adds, they copulate and propagate among themselves: of xadovora juiovor Se ouoryra, ovt ovoa amhag to adrd eidog> nat yaQ oxevortos not yervovtee && addydov. In another passage it applies, however, to a group exactly identical with our modern genus Equus: éei éorw & w yévog nol ett tog *ovor yaitnr, opovoeoig xcadovugvog, olov ina xct Or nat dget nat yovm nor treo nat coig iv Sugig xahovpévoug udvors. Aristotle cannot be said to have proposed any regular classification. He speaks constantly of more or less extensive groups, under a common appellation, evidently considering them as natural divisions; but he nowhere expresses a conviction that these groups may be arranged methodically so as to exhibit the natural affinities of animals. Yet he frequently introduces his remarks respecting different animals aK Cuap. III. PERIOD OF LINNAUS. 189 in such an order and in such connections as clearly to indicate that he knew their relations. When speaking of Fishes, for instance, he never includes the Selachians. After Aristotle, the systematic classification of animals makes no progress for two thousand years, until Linneus introduces new distinctions and assigns a more precise meaning to the terms class, (genus summum,) order, (genus intermedium,) genus, (genus proximum,) and species, the two first of which are introduced by him for the first time as distinct groups, under these names, in the system of Zodlogy. SECTION III. PERIOD OF LINNAUS. When looking over the “Systema Naturs” of Linneeus, taking as the standard of our appreciation even the twelfth edition, which is the last he edited himself, it is hardly possible, in our day, to realize how great was the influence of that work upon the progress of Zodlogy.’ And yet it acted like magic upon the age, and stimulated to exertions far surpassing any thing that had been done in pre- ceding centuries. Such a result must be ascribed partly to the circumstance that he was the first man who ever conceived distinctly the idea of expressing in a definite form, what he considered to be a system of nature, and partly also to the great comprehensiveness, simplicity, and clearness of his method. Discarding in his system every thing that could not easily be ascertained, he for the first time divided the animal kingdom into distinct classes, characterized by definite features; he also for the first time introduced orders into the system of Zodlogy besides genera and species, which had been vaguely distinguished before? And though he did not even attempt to define the characteristics of these different kinds of groups, it is plain, from his numerous writings, that he considered them all as subdivisions of a successively more limited value, embracing a larger or smaller number of animals, agreeing in more or less comprehensive attributes. He expresses 1 To appreciate correctly the successive improve- reprints of the second; the seventh, eighth, and ninth ments of the classification of Linnzus, we need only are reprints of the sixth; the eleventh is a reprint of compare the first edition of the “Systema Nature,” the tenth; and the thirteenth, published after his published in 1735, with the second, published in 1740, death, by Gmelin, is a mere Sompilation, deserving the sixth published in 1748, the tenth published in little confidence. 1758, and the twelfth published in 1766, as they are * See above, Sect. 2, p. 188. The yen weywove. the only editions he revised himself. The third is of Aristotle correspond, however, to the classes of only a reprint of the first, the fourth and fifth are Linneus; the yey ueyade to his orders. 190 ESSAY ON CLASSIFICATION. Part I. his views of these relations between classes, orders, genera, species, and varieties, by comparisons, in the following manner:—? Classis. Ordo. Genus. - Species. Varietas. Genus summum. Genus intermedium. Genus proximum. Species. Individuum. Provincie. Territoria. Pareecie. Pagi. Domicilium. Legiones. Cohortes. Manipuli. Contubernia. Miles. His arrangement of the animal kingdom is presented in the following diagram, compiled from the twelfth edition, published in 1766. CLASSIFICATION OF LINNZAUS. - Mammalia. Ord. Primates, Bruta, Ferx, Glires, Pecora, Bellu, Cete. . Aves. Ord. Accipitres, Pice, Anseres, Gralle, Galline, Passeres. . Amphibia. Ord. Reptiles, Serpentes, Nantes. - Pisces.. Ord. Apodes, Jugulares, Thoracici, Abdominales. - Insecta. Ord. Coleoptera, Hemiptera, Lepidoptera, Neuroptera, Hymenoptera, Diptera, Aptera. - Vermes. Ord. Intestina, Mollusca, Testacea, Lithophyta, Zoophyta. In the earlier editions, up to the tenth, the class of Mammalia was called Quadrupedia, and did not contain the Cetaceans, which were still included among the Fishes. There seems never to have existed any discrepancy among naturalists respecting the natural limits of the class of: Birds, since it was first characterized by Linnzus, in a manner which excluded the Bats and referred them to the class of Mammalia. In the early editions of the “Systema Nature,” the class of Reptiles embraces the same animals as in the systems of the most recent investigators ; but since the tenth edition, it has been encumbered with the addition of the cartilaginous and semicartilaginous Fishes, a retrograde movement suggested by some inaccurate observations of Dr. Garden. The class of Fishes is very well limited in the early editions of the Systema, with the exception of the admission of the Cetaceans, (Plagiuri,) which were correctly referred to the class of Mammalia, in the tenth edition. In the later editions, however, the Cyclostoms, Plagiostoms, Chimerx, Sturgeons, Lophioids, Discoboli, Gymnodonts, Scleroderms, and Lopho- branches are excluded from it and referred to the class of Reptiles. The class of Insects” as limited by Linneus, embraces not only what are now considered as ? See Systema Nature, 12th edit., p. 18. He seems also to’ have understood correctly the ? Aristotle divides this group more correctly than natural limits of the classes of Mammalia and Rep- Linneus, as he admits already two classes, (yd tiles, for he distinguishes the Viviparous and Ovipa- wéyota) among them, the Malacostraca, (Crustacea,) rous Quadrupeds, and nowhere confounds Fishes with and the Entoma, (Insects.) Hist. Anim., Chap. VI. Reptiles. Ibid. See lien aac oe ee ES Cuap. III. PERIOD OF LINNAUS. 191 Insects proper, but also the Myriapods, the Arachnids, and the Crustacea; it }| corresponds more accurately to the division of Arthropoda of modern systematists. \ | The class of Worms, the most heterogeneous of all, includes besides all Radiata | i || f or Zoophytes and the Mollusks of modern writers, also the Worms, intestinal and free, the Cirripeds, and one Fish, (Myxine.) It was left for Cuvier! to introduce order in this chaos. : Such is, with its excellences and short-comings, the classification which has given Vil the most unexpected and unprecedented impulse to the study of Zodlogy. It is 1] useful to remember how lately even so imperfect a performance could have so | great an influence upon the progress of science, in order to understand why it is : | 1 still possible that so much remains to be done in systematic Zodlogy. Nothing, | | indeed, can be more instructive to the student of Natural History, than a careful | iil and minute comparison of the different editions of the “Systema Nature” of | Linneus, and of the works of Cuvier and other prominent zodlogists, in order to detect the methods by which real progress is made in our science. Since the publication of the “Systema Nature” up to the time when Cuvier published the results of his anatomical investigations, all the attempts at new classi- | i fications were, after all, only modifications of the principles introduced by Linnzeus 4 in the systematic arrangement of animals. Even his opponents labored under the influence of his master spirit, and a critical comparison of the various systems which were proposed for the arrangement of single classes or of the whole animal kingdom shows that they were framed according to the same principles, namely, Hy under the impression that animals were to be arranged together into classes, orders, | genera, and species, according to thew more or less close external resemblance. No sooner, however, had Cuvier presented to the scientific world his extensive researches into the internal structure of the whole animal kingdom, than naturalists vied with one another in their attempts to remodel the whole classification of animals, establishing new classes, new orders, new genera, describing new species, and introducing all manner of intermediate divisions and subdivisions under the name of families, tribes, sections, etc. Foremost in these attempts was Cuvier himself, and next to him Lamarck. It has, however, often happened that the divisions introduced by the latter under new names, were only translations into a more systematic form of the results Cuvier had himself obtained from his dis- A sections and pointed out in his “ Legons sur Yanatomie comparée,” as natural divisions, but without giving them distinct names. Cuvier himself beautifully expresses the 1 It would be injustice to Aristotle not to mention Speaking, for instance, of the great genera or classes, that he understood already the relations of the animals he separates correctly the Cephalopods from the united in one class by Linnzus, under the name of other Mollusks, under the name of Malakia. Wist. Worms, better than the great Swedish naturalist. Anim., Lib. I., Chap. VI. Bi. lc ne: 192 ESSAY ON CLASSIFICATION. Parr IL. influence which his anatomical investigations had upon Zovdlogy, and how the improvements in classification have contributed to advance comparative anatomy, when he says, in the preface to the “Régne Animal,” page vi.: “Je dus donc, et cette obligation me prit un temps considérable, je dus faire marcher de front Panatomie et la zoologie, les dissections et le classement; chercher dans mes pre- miéres remarques sur lorganisation, des distributions meilleures; m’en servir pour arriver & des remarques nouvelles; employer encore ces remarques 4 perfectionner les distributions; faire sortir enfin de cette fécondation mutuelle des deux sciences Pune par l'autre, un systéme zoologique propre & servir d’introducteur et de guide dans le champ de l’anatomie, et un corps de doctrine anatomique propre A servir de développement et d’explication au systéme zoologique.” Without entering into a detailed account of all that was done in this period towards improving the system of Zodlogy, it may suffice to say, that before the first decade of this century had passed, more than twice as many classes as Linneeus adopted had been characterized in this manner. These classes are: the Mollusks, Cirripeds, Crustacea, Arachnids, Annelids, Entozoa, (Intestinal Worms,) Zoophytes, Radiata, Polyps, and Infusoria. Cuvier’ admitted at first only eight classes, Duméril ? nine, Lamarck? eleven and afterwards fourteen. The Cephalopoda, Gasteropoda, and Acephala, first so named by Cuvier, are in the beginning considered by him as orders only in the class of Mollusks; the Echinoderms also, though for the first time circumscribed by him within their natural limits, constitute only an order of the class of Zoophytes, not to speak of the lowest animals, which, from want of knowledge of their internal structure, still remain in great confusion. In this rapid sketch of the farther subdivisions which the classes Insecta and Worms of Linnzus have undergone under the influence of Cuvier, I have not, of course, alluded to the important contributions made to our knowledge of isolated classes, by special writers, but limited my remarks to the works of those naturalists who have con- sidered the subject upon the most extensive scale. Thus far, no attempt had been made to combine the classes among themselves into more comprehensive divisions, under a higher point of view, beyond that of dividing the whole animal kingdom into Vertebrata and Invertebrata, a division which corresponds to that of Aristotle, into oa fame and toa évamea. All efforts were rather directed towards establishing a natural series, from the lowest Infusoria up to Man; which, with many, soon became a favorite tendency, and ended by being presented as a scientific doctrine by Blainville. * Cuvier, (G.,) Tableau élémentaire de Histoire ® Lamarck, (J. B. pe,) Systeme des Animaux naturelle des Animaux, Paris, 1798, 1 vol. 8vo. sans Vertebres ou Tableau général, etc., Paris, 1801, * Dumenrtr, (A. M. C.,) Zoologie analytique, etc., 1 vol. 8vo.— Histoire naturelle des Animaux sans Paris, 1806, 1 vol. 8vo. Vertebres, etc., Paris, 1815-1822, 7 vols. 8vo. Se a a aaa actin Cuap. III. PERIOD. OF CUVIER. 195 SECTION IV. PERIOD OF CUVIER, AND ANATOMICAL SYSTEMS. ? Pi The most important period in -the history of Zoblogy begins, however, with the year 1812, when Cuvier laid before the Academy of Sciences in Paris the results of his investigations upon the more intimate relations of certain classes of the animal kingdom to one another,’ which had satisfied him that all animals are con- I | structed upon four different plans, or, as it were, cast in four different moulds. A more suggestive view of the subject never was presented before to the appre- | ciation of investigators; and, though it has by no means as yet produced all the | results which certainly are to flow from its further consideration, it has already led | x to the most unquestionable improvements which classification in general has made since the days of Aristotle, and, if I am not greatly mistaken, it is only in as far as that fundamental principle has been adhered to that the changes proposed in our systems, by later writers, have proved a real progress, and not as many retro- grade steps. This great principle, introduced into our science by Cuvier, is expressed by him in these memorable words: “Si Yon considére le régne animal d’aprés les prin- cipes que nous venons de poser, en se débarrassant des préjugés établis sur les divisions anciennement admises, en n’ayant égard qu’a Yorganisation et 4 la nature ‘ ae des animaux, et non pas 4 leur grandeur, a leur utilité, au plus ou moins de autres circonstances accessoires, on connaissance que nous en avons, ni a toutes les trouvera qu’il existe quatre formes principales, quatre plans généraux, si l’on peut — s’ exprimer ainsi, d’aprés lesquels tous les animaux semblent avoir été modelés et | dont les divisions ultérieures, de quelque titre que les naturalistes les aient déco- rées, ne sont que des modifications assez légéres fondées sur le développement ou l’addition de quelques parties, qui ne changent rien 4 l’essence du plan.” It is therefore incredible to me how, in presence of such explicit expressions, Cuvier can be represented, as he is still occasionally, as favoring a division of | the animal kingdom into Vertebrata and Invertebrata.* Cuvier, moreover, was the first to recognize practically the inequality of all the divisions he adopts in his system; and this constitutes further a great and important step, even though he may not have found the correct measure for all his groups. For we must remem- ber that at the time he wrote, naturalists were bent upon establishing one con- | 1 Ann. du Muséum d’Histoire Naturelle, vol. xix., * EHRENBERG, (C. G.,) Die Corallenthiere des Paris, 1812. rothen Meeres, Berlin, 1834, 4to., p- 80, note. 25 a H | i 194 ESSAY ON CLASSIFICATION. : Part I. tinual uniform series to embrace all animals, between the links of which it was supposed there were no unequal intervals. The watchword of their school was: Natura non fact saltum. They called their system da chaine des étres. The views of Cuvier led him to the following arrangement of the animal kingdom : — CLASSIFICATION OF CUVIER. First Branch. ANnimMALIA VERTEBRATA. Cu.1. Mammalia. Orders: Bimana, Quadrumana, Carnivora, Marsupialia, Rodentia, Eden- tata, Pachydermata, Ruminantia, Cetacea. Ci.2. Birds. Ord. Accipitres, Passeres, Scansores, Gallinz, Gralle, Palmipedes. Cu. 3. Reptilia. Ord. Chelonia, Sauria, Ophidia, Batrachia. Cu. 4. Fishes. 1st Series: Fishes proper. Ord. Acanthopterygii;— Abdominales, Sub- brachii, Apodes;— Lophobranchii, Plectognathi; 2d Series: Chondropterygii. Ord. Sturiones, Selachii, Cyclostomi.? Second Branch. Animati1a Mo.iusca. Cu. 1. Cephalopoda. No subdivisions into orders or families. Ci. 2. Pteropoda. No subdivisions into orders or families. CL. 3. Gasteropoda. Ord. Pulmonata, Nudibranchia, Inferobranchia, Tectibranchia, Hetero- poda, Pectinibranchia, Tubulibranchia, Scutibranchia, Cyclobranchia. Ci. 4. Acephala. Ord. Testacea, Tunicata. Cu. 5. Brachiopoda. No subdivisions into orders or families. Ci. 6. Cirrhopoda. No subdivisions into orders or families. Third Branch. AnimaLiA ARTICULATA. Ci. 1. Annelides. Ord. Tubicole, Dorsibranchie, Abranchie. : Ci. 2. Crustacea. Ist Section: Malacostraca. Ord. Decapoda, Stomapoda, Amphipoda, Lamodipoda, Isopoda. - 2d Section: Entomostraca. Ord. Branchiopoda, Poecilopoda, Trilobite. Ci. 38. Arachnides. Ord. Pulmonarie, Trachearie. Ci. 4. Insects. Ord. Myriapoda, Thysanura, Parasita, Suctoria, Coleoptera, Orthoptera, Hemiptera, Neuroptera, Hymenoptera, Lepidoptera, Rhipiptera, Diptera. Fourth Branch. AnNimaLiA RapIATA. Cu. 1. Echinoderms. Ord. Pedicellata, Apoda. Cu. 2. Intestinal Worms. Ord. Nematoidea, (incl. Epizoa and Entozoa,) Parenchymatosa. Cui. 3. Acalephae. Ord. Simplices, Hydrostatic. Cr. 4. Polypi. (Including Anthozoa, Hydroids, Bryozoa, Coralline, and Spongie.) Ord. Carnosi, Gelatinosi, Polypiarii. Cu. 5. Infusoria. Ord. Rotifera and Homogenea, (including Polygastrica and some Algz.) 1 Le Régne animal distribué d’aprés son organisation, Paris, gone, compare his Tableau élémentaire, q. a., p. 192, his paper, 1829, 2de édit. 5 vols. 8vyo. The classes of Crustacea, Arach- q. a., p. 193, and the first edition of the Regne animal, published nids, and Insects have been elaborated by Latreille. For the in 1817, in 4 vols. 8vo. successive modifications the classification of Cuvier has under- * Comp. Regn. Anim., 2de édit., 2d vol., p. 128 and 383. ah ing one from the other, and of such genera he speaks as “ grands genres; Cuap. III. PERIOD OF CUVIER. When we consider the zodlogical systems of the past century, that of Lin- nus, for instance, and compare them with more recent ones, that of Cuvier, for example, we cannot overlook the fact, that even when discoveries have added little to our knowledge, the subject is treated in a different manner; not merely in consequence of the more extensive information respecting the internal structure of animals, but also respecting the gradation of the higher groups. Linneus had no divisions of a higher:order than classes. Cuvier introduced, for the first time, four great divisions, which he called “embranchemens” or branches, under which he arranged his classes, of which he admitted three times as many as Linnzeus had done. Again, Linneus divides his classes into orders; next, he introduces genera, and finally, species; and this he does systematically in the same gradation through all classes, so that each of his six classes is subdivided into orders, and these into genera with their species. Of families, as now understood, Linneus knows nothing. The classification of Cuvier presents no such regularity im its framework. In some classes he proceeds, immediately after presenting their characteristics, to the enumeration of the genera they contain, without grouping them either into orders or families. In other classes, he admits orders under the head of the class, and then proceeds to the characteristics of the genera, while in others still, he admits under the class not only orders and families, placing always the family in a sub- ordinate position to the order, but also a number of secondary divisions which he calls sections, divisions, tribes, etc., before he reaches the genera and _ species, With reference to the genera again, we find marked discrepancies in different classes. Sometimes a genus is to him an extensive group of species, widely differ- ” others are limited in their extent, and contain homogeneous species without farther sub- divisions, while still others are subdivided into what he calls sub-genera, and _ this is usually the case with his “great genera.” The gradation of divisions with Cuvier varies then with his classes, some classes containing only genera and species, and neither orders nor families nor any other subdivision. Others contain orders, families, and genera, and besides these, a variety | of subdivisions: of the most diversified extent and significance. This remarkable | inequality between all the divisions of Cuvier is, no doubt, partly owing to the state of Zodlogy and of zodlogical museums at the time he wrote, and to his determination to admit into his work only such representatives of the animal kingdom ‘as he could to a greater or less extent examine anatomically for him- self; but it is also partly to be ascribed to his conviction, often expressed, that there is no such uniformity or regular serial gradation among animals as many | naturalists attempted to introduce into their classifications, 195° ESSAY ON CLASSIFICATION. CLASSIFICATION OF LAMARCK. Histoire naturelle des Animaux sans vertebres, etc., Paris, 1815-1822, 7 vols. 8vo. — A second edition with notes has been pub- lished by Messrs. DesHayes and Milne-Edwards, Paris, 1835-1843, 10 vols. 8vo.— For the successive modifications this classi- fication has undergone, see also: Systeme des animaux sans vertebres, etc., Paris, 1801, 8vo. — Philosophie zoologique, etc., Paris, 1809, 2 vols. 8vo. — Extrait du Cours de Zoologie du Muséum d’Histoire naturelle, etc., Paris, 1812, 8vo. INVERTEBRATA. I. Apatuetic ANIMALS. Cu. 1. Infusoria. Ord. Nuda, Appendiculata. Ci. 2. Polypi. Ord. Ciliati (Rotifera), Denudati (Hydroids), stiles Do not feel, and move Vaginati (Anthozoa and Bryozoa), and Natantes (Crinoids, ; ly by thei ited irri- and some Halcyonoids.) Re eee Cu. 38. Radiaria. Ord. Mollia (Acalephe), Echinoderms, (includ- ing Holothurize and Actiniz.) Cu. 4. Tunicata. Ord. Bothryllaria (Compound Ascidians), Ascidia, (Simple Ascidians.) Ci. 5. Vermes. Ord. Molles and Rigiduli (Intestinal Worms and Gordius), Hispiduli (Nais), Epizoarize (Epizoa, Lerneans.) ; tability. No brain, nor elongated medullary mass ; no senses; forms varied ; rarely articulations. II. Sensitive ANIMALS. Ci. 6. Insects. (Hexapods.) Ord. Aptera, Diptera, Hemiptera, hse: ER es their sensations only per- Lepidoptera, Hymenoptera, Nevroptera, Orthoptera, Cole- Bes HAPS ares ais fhe ets ceptions of objects, a sort optera. ; . ; of simple ideas, which the .7. Arachnids. Ord. Antennato-tracheales (Thysanura and - ner : y are unable to combine to Myriapoda), Exantennato-tracheales and Exantennato-bran- : ‘ees ween obtain complex ones. No asa gieds 7 ; vertebral column; a brain .8. Crustacea. Ord. Heterobranchia (Branchipoda, Isopoda, : and mostly an elongated Amphipoda, Stomapoda) and Homobranchia (Decapoda.) .9. Annelids. Ord. Apoda, Antennata, Sedentaria. .10. Cirripeds. Ord. Sessilia and Pedunculata. .11. Conchifera. Ord. Dimyaria, Monomyaria. Cy. 12. Mollusks. Ord. Pteropoda, Gasteropoda, Trachelipoda, medullary mass; some dis- tinct senses; muscles at- tached under the skin; form symmetrical, the parts being in pairs. Cephalopoda, Heteropoda. J VERTEBRATA. : TI. Inrevyicenr ANIMALS. Feel; acquire preservable ideas; perform with them oper- CL. 1 3. Fishes. ations by which they obtain others; are intelligent in different Ci. 14. Reptiles. | Cu. 15. Birds. distinct senses; the muscles attached to the internal skeleton ; . Cu. 16. Mammalia. | form symmetrical, the parts being in pairs. degrees. A vertebral column; a brain and a spinal marrow ; It is not easy to appreciate correctly the system of Lamarck, as it combines abstract conceptions with structural considerations, and an artificial endeavor to arrange all animals in continuous series. The primary subdivision of the animal kingdom into Invertebrata and Vertebrata?! corresponds, as I have stated above, to * See, above, Chap. 2, Sect. 1, p. 138. : — Hanan raineteoniatetnsai oe atte aha ONAGARA e 4 9 ° e ‘4 Type I. IrreGuiar ANIMALS. 1st Subtype. Cu. 1. Infusoria. Type II. Reeurar ANIMALS. 2d Subtype. Cr. 2. Polypina. Ord. Bryozoa, Anthozoa. 3d Subtype. Cx. 8. Radiata. Ord. Acalephw, Echinodermata, Scytodermata. Type II. Symmerrricat ANIMALS. 4th Subtype. Cr. 4. Mollusca. Ord. Perigymna (Tunicata); Cormopoda (Acephala); Brachio- poda, Cephalophora (Pteropoda and Gasteropoda) ; Cephalopoda. 5th Subtype. Arthrozoa. Cu. 5. Vermes. Ord. Helminthes, Trematodes, and Annulati. Cu. 6. Crustacea. 1° Ostracoderma. Ord. Prothesmia (Cirripedia, Siphono- stoma, and Rotatoria); Aspidostraca (Entomostraca : Lophyropoda, Phyllopoda, Pecilopoda, Trilobite.) 2°. Malacostraca. Ord. Thoracostraca (Podoph- thalma); and Arthrostraca, (Edriophthalma.) Cu. 7. Arachnoda. Ord. Myriapoda, Arachnide. Cu. 8. Insecta. Ord. Rhynchota, Synistata, Antliata, Piezata, Glossata, Wiriksrata. ~ 6th Subtype. Osteozoa. (Vertebrata.) CE. 9. Pisees. " Cr. 10. A m'p hibia. Ci. ii: Aves: Ci. 12. Mammalia. The general arrangement of the classification of Burmeister recalls that of de Blainville; only that the order is inverted. His three types correspond to the three subkingdoms of de Blainville: the Irregular Animals to the Heterozoaria, the Regular Animals to the Actinozoaria, and the Symmetrical Animals to the Artiozo- aria; while his subtypes of the Symmetrical Animals correspond to the types de Blainville admits among his Artiozoaria, with this important improvement, however, that the Malentozoaria are suppressed. Burmeister reduces, unhappily, the whole branch of Mollusks to one single class) The Arthrozoa, on the contrary, in the investigation of which Burmeister has rendered eminent service to science, are pre- sented in their true light. In his special works,’ his classification of the Articulata is presented with more details. I have no doubt that the correct views he entertains 7 respecting the standing of the Worms in the branch of Articulata are owing to his inP extensive acquaintance with the Crustacea and Insects, and their metamorphoses. | 1 These works are: Beitriige zur Naturgeschichte 1836. — Die Organisation der Trilobiten, aus ihren | ; der Rankenfiisser, (Cirripedia,) Berlin, 1834, 1 vol. lebenden Verwandten entwickelt, Berlin, 1843, 1 vol. | | 4to.- Handbuch der Entomologie, Berlin, 1832-47, 4to.; Engl. by the Ray Society, London, 1847, | | 5. vols.. 8vo.; Engl. by W. E. Shuckard, London, 1 vol. fol. ESSAY ON CLASSIFICATION. CLASSIFICATION OF OWEN. The following diagram is compiled from R. Owen’s Lectures on the Comparative Anatomy and Physiology of the Invertebrate Animals, 2d edit., London, 1855, 1 vol. 8vo. Province. VERTEBRATA. Myelencephala. (Owen.) Mammalia. . A The classes Mammalia, Aves, and Reptilia are not yet included in the second volume Ves. : of the “Lectures,” the only one relating to Vertebrata thus far published. Reptilia. Pisces. Ord. Dermopteri, Malacopteri, Pharyngognathi, Anacanthini, Acanthopteri, Plectognathi, Lophobranchii, Ganoidei, Protopteri, Holocephali, Plagiostomi. Province. ArticuLaTa. Homogangliata. (Owen.) j Cu. Arachnida. Ord. Dermophysa, Trachearia, Pulmotrachearia, and Pulmonaria. Cyr. Insecta. Subclass: Myriapoda. Ord. Chilognatha and Chilopoda. Subclass: Hexapoda. Ord. Aptera, Diptera, Lepidoptera, Hymenoptera, Homoptera, Strepsiptera, Nevroptera, Orthop- _tera, and Coleoptera. Crustacea. Subclass: Entomostraca. Ord. Trilobites, Xiphosura, Phyllopoda, Cladocera, Ostracopoda, Copepoda. Subclass: Malacostraca. 1°. Edriophthalma. Ord. Lemodipoda, Isopoda, Amphipoda. 2°. Podophthalma. Ord. Stomapoda, Decapoda. Epizoa. Ord. Cephaluna,. Brachiuna, and Onchuna. Annellata. Ord. Suctoria, Terricola, Errantia, Tubicola. Cirripedia. Ord. Thoracica, Abdominalia, and Apoda. Province. Moriusca. Heterogangliata. (Owen.) Ct. Cephalopoda. Ord. Tetrabranchiata and Dibranchiata. Cr. Gasteropoda. A. Monecia: Ord. Apneusta (K6ll.), Nudibranchiata, Inferobranchiata, Tectibranchiata, Pulmonata. B. Diccia. Ord. Nucleobranchiata, Tubulibranchiata, Cyclo- branchiata, Scutibranchiata, and Pectinibranchiata. Pteropoda. Ord. Thecosomata and Gymnosomata. Lamellibranchiata. Ord. Monomyaria and Dimyaria. Brachiopoda. Only subdivided into families. Tunicata. Ord. Saccobranchiata and Tniobranchiata. Subprovince. Rapraria.} Echinodermata. Ord. Crinoidea, Asteroidea, Echinoidea, Holothurioidea, and Sipunculoidea. Bryozoa. Only subdivided into families. Anthozoa. Only subdivided into families. Acalephae. Ord. Pulmograda, Ciliograda, and Physograda. Hydrozoa. Only subdivided into families. Subprovince. Enrozoa. Cr. Celelmintha. Ord. Gordiacea, Nematoidea, and Onchophora. Ci. Sterelmintha. Ord. Tenioidea, Trematoda, Acanthocephala. — Turbellaria. Subprovince. Inrusortia. Ci. Rotifera. Only subdivided into families. Cyt. Polygastria. Ord. Astoma, Stomatoda, — Rhizopoda. 1 In the first edition of the work quoted above, published contradistinction of the subkingdoms, Mollusca, Articulata, in 1843, the three subprovinces, Radiaria, Entozoa, and Infu- and Vertebrata, and that subkingdom is subdivided into two soria are considered as one subkingdom called Radiata, in groups, Nematoneura and Acrita. em +s —— cite an a ne te nA ie lin a nS OS — eats : sats EE RUE NS Tt RS Te ee th a RE A TR ODOT LORE EEO COC wae OU git et is nial aati egy eantis mates Y ANATOMICAL SYSTEMS. —Cnap. III. 205 The classification with which Owen! introduces his “Lectures on Comparative ; Anatomy” is very instructive, as showing, more distinctly than other modern systems, | the unfortunate ascendency which the consideration of the complication of structure “4 has gained of late over the idea of plan. His provinces, it is true, correspond in the main to the branches of Cuvier, with this marked difference, however, that he does not recognize a distinct province of Radiata coequal with those of Mollusca, Articulata, and Vertebrata, but only admits Radiaria as a subprovince on a level with Entozoa and Infusoria. Here, the idea of simplicity of structure evidently | prevails over that of plan, as the subprovinces Radiaria, Entozoa, and Infusoria embrace, besides true Radiata, the lowest types of two other branches, Mollusks | . and Articulates. On the other hand, his three subprovinces correspond to the first three types of von Siebold; the Infusoria* of Owen embracing the same ~ animals as the Protozoa of Siebold, his Entozoa* the same as the Vermes, and his Radiaria the same as the Zoophyta, with the single exception that Owen refers the Annellata to the province of Articulata, whilst Siebold includes them among his Vermes.. Beyond this the types of Mollusca and Articulata (Arthropoda) of the two distinguished anatomists entirely agree. The position assigned by Owen to the provinces Articulata and Mollusca, not one above the other, but side by ce side with one another, is no doubt meant to express his conviction, that the com- plication of structure of these two types does not justify the idea that either of them stands higher or lower than the other; and this is perfectly correct. Several groups, established by previous writers as families or orders, are here es | admitted as classes. His class Epizoa, which is not to be confounded with that established by Nitzsch under the same name, corresponds exactly to the family | called Lernizs by Cuvier. His class Hyprozoa answers to the order Hyprowa of | Johnston, and is identical with the class called DimorpH#a by Ehrenberg. His class Ca@LetminrHa corresponds to the order of Inrestinavx Cavrrarres established + I have given precedence to the classification of Owen over those of von Siebold and Stannius, Milne-Edwards, Leuckart, ete., because the first edi- tion of the “Lectures on Comparative Anatomy” was published in 1843 ; but in estimating its features, as expressed in the preceding diagram, it should be borne in mind that, in the first edition, the classes alone are considered, and that the orders and families were only added to the second edition in 1855. I mention this simply to prevent the possibility of being understood as ascribing to Owen all those sub- divisions of the classes, which he admits, and which do not appear in the systems considered before his. 2 The Rhizopoda are considered as g group coequal to Rotifera and Polygastria, on p. 16 of ‘the “Lectures,” but on p. 59, they stand as a sub- order of Polygastria. an inde- pendent group, on p. 16, and referred as a suborder to the Trematoda, on p. 118. ® The Turbellaria are represented ag * From want of room, I have been compelled, in reproducing the classification of Owen in the preceding diagram, to place his provinces Articulata and Mollusca one below the other upon my page; according to his views, they should stand on a level, side by side with one another. 206 ESSAY ON CLASSIFICATION. Part I by Cuvier, with the addition of Gordius; while his class Sreretamra has the same circumscription as the order Inrystmvaux Parencuymateux of Cuvier. Generally speaking, it. should not be understood that the secondary divisions mentioned by the different authors, whose systems I have analyzed here, were established by them. They are frequently borrowed from the results obtained by special investigators of isolated classes. . But it would lead me too far, to enter here into a discussion of all these details. | This growing resemblance of the modern systems of Zodlogy is a very favorable sign of our times. It would, indeed, be a great mistake to assume, that it is solely owing to the influence of different authors upon one another; it is, on the con- trary, to a very great extent, the result of our better acquaintance with Nature. When investigators, at all conversant with the present state of our science, must possess nearly the same amount of knowledge, it is selfevident that their views can no longer differ so widely as they did when each was familiar only with a part of the subject. A deeper insight into the animal kingdom must, in the end, lead to the conviction that it is not the task of zodlogists to introduce order among animals, but that their highest aim should be simply to read the. natural affinities which exist among them, so that the more nearly our knowledge embraces the whole field of investigation, the more closely will our opinions coincide. As to the value of the classes adopted by Owen, I may further remark that recent investigations, of which he might have availed himself, have shown that the Cirripedia and his Epizoa are genuine Crustacea, and that the Entozoa can no longer be so widely separated from the Annellata as in his system. With reference to the other classes, I refer the reader to my criticism of older systems, and to the first. section of this Chapter. It is a great satisfaction for me to find that the views I have advocated in the preceding sections, respecting the natural relations of the leading groups of the animal kingdom, coincide so closely with the classification of that distinguished zoblogist, Milne-Edwards, lately presented by him as the expression of his present views of the natural affinities of animals. He is the only original investigator who has recently given his unqualified approbation to the primary divisions first proposed by Cuvier, admitting, of course, the rectifications among the group of secondary rank, rendered necessary by the progress of science, to which he has himself so largely contributed. As to the classes adopted by Milne-Edwards, I have little to add to what I have already stated before, with reference to other classifications. Though no longer overruling the idea of plan, that of complication of structure has still too. much influence with Milne-Edwards, inasmuch as it leads him to consider as classes, groups of animals which differ only in degree, and are therefore only orders. RSL ERRKE tad Saar eL ees EL —— 2 enema ca w= en a Sea NSA AER NE HO serene a ee ee Oe a i a SE ca Styne i enibangeaiateiaiilianatia tenant eatiemamanece eerenasiny sagunend acetal ue os Faint ~ hee gore = Cuap. IIL. _ ANATOMICAL SYSTEMS. 207 | Such are, no doubt, his classes of Molluscoids and those of Worms, besides the | Myriapods and Arachnids. Respecting the Fishes, I refer to my remarks in the first section (p. 187) of this Chapter. CLASSIFICATION OF MILNE-EDWARDS. | The following diagram is drawn from the author’s Cours élémentaire d’ Histoire naturelle, Paris, 1855 y 1 vol. 12mo., 7th edit., in which he has presented the results of his latest investigations upon the classifica- tion of the Vertebrata and Articulata; the minor subdivisions of the Worms, Mollusks, and Zoophytes, however, are not considered in this work.’ I. OstTEozoOARIA, or VERTEBRATA. Subbranch. Allantoidians. Subbranchh Anallantoidians. Cyr. Mammalia. 1°. Monodelphya. a. Propria. Ord. Bimana, Cr. Batrachians. Ord. Anura, Quadrumana, Cheiroptera, Insectivora, Rodentia, Edentata, Carni- Urodela, Perennibranchia, Czciliz. vora, Amphibia, Pachydermata, Ruminantia. 6. Pisciformia. Ord. Ci. Fishes. 1°. Ossei. Ord. Acan- Cetacea. 2°. Didelphya. Ord. Marsupialia, Monotremata. thopterygii, Abdominales, Subbrachii, | Cu. Birds. Ord. Rapaces, Passeres, Scansores, Galline, Apodes, Lophobranchii, and Plectog- . Gralle, and Palmipedes. ; nathi. 2°. Chondropterygii. Ord. Stu- TE Ci. Reptiles. Ord. Chelonia, Sauria, Ophidia. riones, Selachii, and Cyclostomi. | : Fe II. Enromozoa, or ANNELLATA. , Subbranch. Arthropoda. Subbranch. Vermes. Cu. Insecta. Ord. Coleoptera, Orthoptera, Nevroptera, Hymatioptcrss Cy. Annelids. Lepidoptera, Hemiptera, Diptera, Rhipiptera, Anoplura, and Thysanura. — Cit. Helminths. Cu. Myriapoda. Ord. Chilognatha and Chilopoda. CL. Turbellaria. Cu. Arachnids. Ord. Pulmonaria and Trachearia. CL. Cestoidea. Cr. Crustacea. 1°. Podophthalmia. Ord. Decapoda and Stomapoda. Ci. Rotatoria. 2°. Edriophthalma. Ord. Amphipoda, Lemodipoda, and Isopoda. 3°. Bran- | chiopoda. Ord. Ostrapoda, Phyllopoda, and Trilobite. 4°. Entomostraca. Ord. Copepoda, Cladocera, Siphonostoma, Lernzida, Cirripedia. 5°. Xiphosura. Il. Maxracozoaria, or MOLLusca. | Subbranch. Mollusks proper. Subbranch. Molluscoids. Cir. Cephalopods. Gr Tuhicatas CL. - Pteropods. Cu. Bryozoa. Cit. Gasteropods. Cir. Acephala. / IV. Zoopuyres. Subbranch. Radiaria, or Radiata. — Subbranch. Sarcodariéa. . Cit. Echinoderms. Cu. Infusoria. CL. Acalephs. Cu. Spongiaria. Cu. Corallaria, or Polypi. 1 Consult, for these, his recent papers upon Polyps, Mollusks, and Crustacea, in the Ann. des Se. Nat, ESSAY ON CLASSIFICATION. CLASSIFICATION OF VON SIEBOLD AND STANNIUS. This classification is adopted in the following work: Srmsoxp, (C. Tu. v.,) and Srannivs, (H.,) Lehrbuch der vergleichenden Anatomie, Berlin, 1845, 2 vols. 8vo. A second edition is now in press. EVERTEBRATA. I. Protozoa. Cu.1. Infusoria. Ord. Astoma and Stomatoda. Ci. 2. Rhizopoda. Ord. Monosomatia and Polysomatia. ZOOPHYTA. Cu. 3. Polypi. Ord. Anthozoa and Bryozoa. Ci. 4. Acalephae. Ord. Siphonophora, Discophora, Ctenophora. Ci. 5. Echinodermata. Ord. Crinoidea, Asteroidea, Echinoidea, Holothurioidea, and Sipunculoidea. : VERMES. Cx. 6. Helminthes. Ord. Cystici, Ces- Since the publication of the work quoted above, Sie- E bold has introduced most important improvements in the todes, Trematodes, Acanthocephali, ee . , ‘ classification of the Worms, and greatly increased our Gordiacei, Nematodes. knowledge of these animals. Ci. 7. Turbellarii. Ord. Rhabdoceli, Dendrocceli. Ci. 8. Rotatorii. Not subdivided into orders. Cu. 9. Annulati. Ord. Apodes and Chetopodes. Mo..usca. : Cxu.10. Acephala. Ord. Tunicata, Brachiopoda, Lamellibranchia. Cr. 11. Cephalophora, Meck., (Gasteropoda.) Ord. Pteropoda, Heteropoda, Gasteropoda, Sedo Ao phalop oda. Not subdivided into orders. ARTHROPODA. j Ci. 18. Crustacea. Ord. Cirripedia, Siphonostoma, Lophyropoda, Phyllopoda, Peecilopoda, | Lemodipoda, Isopoda, Amphipoda, Stomapoda, Decapoda, Myriapoda. Ci. 14. Arachnida. Orders without names. : | Cu. 15. Insecta. a. Ametabola. Ord. Aptera. 6 Hemimetabola; Ord. He-— miptera, Orthoptera. _ c. Holometabola. Ord. Diptera, Lepidoptera, Hymenop- tera, Strepsiptera, Nevroptera, and Coleoptera. VERTEBRATA. VI. VERTEBRATA. Cu. 16. Pisces. Subclasses: Ist. Leptocardii. 2d. Marsipobranchii. 34. Elasmobranchii; Ord. Holocephali, Plagiostomi. 4th. Ganoidei; Ord. Chrondrostei, Holostei. Sth. Teleostei; Ord. Acanthopteri, Anacanthini, Pharyn- , gognathi, Physostomi, Plectognathi, Lophobranchii. 6th. Dipnoi. Ci.17. Reptilia. Subclasses: 1st. Dipnoa; Ord. Urodela, Batrachia, Gymnophiona. 2d. Monopnoa: a. Streptostylica; Ord. Ophidia, Sauria. 6. Monimostylica; Ord. Chelonia, Crocodila. ) The subdivisions of the classes Pisces and Reptilia are taken from the sec- ond edition, published in 1854-1856, in which J. Miiller’s arrangement of the ~ Aves. Fishes is adopted; that of the Reptiles is partly Stannius’s own. The classes Aves and Mammalia, and the first volume of the second edition, are . Mammalia. not yet out. Cuar. IIL. ANATOMICAL SYSTEMS. . = Bee | The most original feature of the classification of von Siebold is the adoption of the types Protozoa and Vermes, in the sense in which they are limited here. The type of Worms has grown out of the investigations of the helminthologists, ’ who, too exclusively engaged with the parasitic Worms, have overlooked their rela- tions to the other Articulata. On the other hand, the isolation in which most ento- mologists have remained from the zodlogists in general, has no doubt had its share in preventing an earlier thorough comparison of the Worms and the larval conditions of Insects, without which the identity of type of the Worms, Crustacea, and Insects can hardly be correctly appreciated. Concerning the classes* adopted by von Sie- | bold and Stannius, I have nothing to remark that has not been said already. CLASSIFICATION OF R. LEUCKART. The classification of Leuckart is compiled from the following work: LevoKkarr, (R.,) Ueber die Mor- - phologie und die Verwandtschaftsverhiltnisse der wirbellosen Thiere, Braunschweig, 1848, 1 vol. 8vo. I. Cor venterata, Lkt. | Cu. 1. Polypi. Ord. Anthozoa and Cylicozoa (Lucernaria.) Ci. 2. Acale phae. Ord. Discophore and Ctenophore. | II. Ecurnopermata, Lkt. | Cu. 3. Pelmatozoa, Lkt. Ord. Cystidea and Crinoidea. | ¢ Cu. 4. Actinozoa, Latr. Ord. Echinida and Asterida. “fips Cu. 5. Scytodermata, Brmst. Ord. Holothurie and Sipunculida. Ill. Vermes. Cu. 6. Anenterati, Lkt. Ord. Cestodes and Acanthocephali. (Helminthes, Burm.) . Apodes, Lkt. Ord. Nemertini, Turbellarii, Trematodes, and Hirudinei. (Trematodes, Burm.) t Cy. 8. Ciliati, Lkt. Ord. Bryozoa and Rotiferi. 9. Annelides. Ord. Nematodes, Lumbricini, and Branchiati. (Annulati, Burm., excl. Ne- mertinis et Hirudineis.) IV. ARTHROPODA. Cr. 10. Crustacea. Ord. Entomostraca (Neusticopoda Car.) and Malacostraca. Cu. 11. Insecta. Ord. Myriapoda, Arachnida, (Acera, Latr.,) and Hexapoda. V. Mortusca, Cuv. (Palliata, Nitzsch.) : SS. Leuckart is somewhat inclined to consider the Tunicata a Cu. 12. | Tunicata. Ord. Ascidie (Tethyes not simply as a class, but even as another great type or branch, fy Sav.) and Salpe (Thalides Sav.) Cu. 18. Acephala. Ord. Lamellibranchiata (Cormopoda Nitzsch, Pelecypoda Car.) and Bra- intermediate between Echinoderms and Worms. chiopoda. Ci. 14. Gasteropoda. Ord. Heterobranchia, (Pteropoda, Inferobranchia, and Tectibranchia,) . 4 . Dermatobranchia, (Gymnobranchia and Phlebenterata,) Heteropoda, Ctenobranchia, Pulmo- nata, and Cyclobranchia. Ci. 15. Cephalopoda. VI. Verresrata. (Not considered.) 1 The names of the types, Protozoa and Vermes, are older ous ways for nearly half a century, while that of Worms was first than their limitation in the classification of Siebold. That of adopted by Linnaeus, as a great division of the animal king- Protozoa, first introduced by Goldfuss, has been used in vari- dom, but in a totally different sense. 27 210 ESSAY ON CLASSIFICATION. Part I. IT need not repeat here what I have already stated, in the first section, respecting the primary divisions adopted by Siebold and Leuckart. As to the classes, I may add that his three classes of Echinoderms exhibit only ordinal characters. Besides Birds and Cephalopods, there is not another class so well defined, and so little susceptible of being subdivided into minor divisions presenting any thing like class characters, as that of Echinoderms. Their systems of organs are so closely homo- logical, (compare p. 183,) that the attempt here made by Leuckart, of subdividing them into three classes, can readily be shown to rest only upon the admission, as classes, of groups which exhibit only ordinal characters, namely, different degrees of complication of structure. With reference to the classes of Worms, the same is equally true, as shown above. The arrangement of these animals proposed by Bur- meister is certainly more correct than those of von Siebold and of Leuckart, inas- much as he refers already correctly the Rotifera to the class of Crustacea, and does not, like Leuckart, associate the Bryozoa with the Worms. I agree, however, with Leuckart respecting the propriety of removing the Nemertini and Hirudinei from among the true Annelides. Again, Burmeister appreciates also more correctly the position of the whole type of Worms, in referring them, with de Blainville, to the branch of Articulata. 7 The common fault of all the anatomical classifications which have been proposed since Cuvier consists, first, in having given up, to a greater or less extent, the funda- mental idea of the plan of structure, so beautifully brought forward by Cuvier, and upon which he has insisted with increased confidence and more and more distinct con- sciousness, ever since 1812; and, second, in having allowed that of complication of structure frequently to take the precedence over the more general features of plan, which, to be correctly appreciated, require, it is true, a deeper insight into the struc- ture of the whole animal kingdom than is needed merely for the investigation of anatomical characters in single types. Yet, if we take a retrospective glance at these systems, and especially con- sider the most recent ones, it must be apparent to those who are conversant with the views now obtaining in our science, that, after a test of half a century, the idea of the existence of branches, characterized by different plans of structure, as expressing the true relations among animals, has prevailed over the idea of a gradated scale including all. animals in one. progressive series. When it is con- sidered that this has taken place amidst the most conflicting views respecting classi- fication, and even in the absence of any ruling principle, it must be acknowl- edged that this can be only owing to the internal truth of the views. first pro- pounded by Cuvier. We recognize in the classifications of Siebold, Leuckart, and others the triumph of the great conception of the French naturalist, even though their systems differ greatly from his, for the question whether there are four or ee a ta — Aen ated co nn tt i FRate B e nee ae a SE AM Eanes Sn SS ea eeene ee fn OE Cuap. III. PHYSIOPHILOSOPHICAL SYSTEMS. 211 more great plans, limited in this or any other way, is not a question of prin- ciple, but one involving only accuracy and penetration in the -investigation; and I maintain that the first sketch of Cuvier, with all its imperfections of details, pre- if sents a picture of the essential relations existing among animals truer to nature than the seemingly more correct classifications of recent writers. |. SECTION V. PHYSIOPHILOSOPHICAL SYSTEMS. About the time that Cuvier and the French naturalists were tracing the structure of the animal kingdom, and attempting to erect a natural system of Zovlogy upon this foundation, there arose in Germany a school of philosophy, under the lead of Schelling, which extended its powerful influence to all the departments of physical science. Oken, Kieser, Bojanus, Spix, Huschke, and Carus are the most eminent A naturalists who applied the new philosophy to the study of Zodlogy. But no | one identified his philosophical views so completely with his studies in natural < history as Oken. Now that the current is setting so strongly against every thing which recalls the German physiophilosophers and their doings, and it has become fashionable to speak ill of them, it is an imperative duty for the impartial reviewer of the history of science to show how great and how beneficial the influence of Oken has been upon the progress of science in general and of Zodlogy im particular. | It is moreover easier, while borrowing his ideas, to sneer at his style and_ his | ) nomenclature, than to discover the true meaning of what is left unexplained in | his mostly paradoxical, sententious, or aphoristical expressions; but the man who | | has changed the whole method of illustrating comparative Osteology,—who has carefully investigated the embryology of the higher animals, at a time when few | physiologists were paying any attention to the subject, who has classified the three | kingdoms of nature’ upon principles wholly his own, who has perceived thousands | of homologies and analogies among organized beings entirely overlooked before, who Hi has published an extensive treatise of natural history containing a condensed account 4 of all that was known at the time of its publication, who has conducted for twenty- | five years the most extensive and most complete periodical review of the natural i sciences ever published, in which every discovery made during a quarter of a ; century is faithfully recorded, the man who inspired every student with an ardent love for science, and with admiration for his teacher,—that man will never be forgotten, nor can the services he has rendered to science be overlooked, so long ; Wy as thinking is connected with investigation. " si in 9 Tn 2 ESSAY ON CLASSIFICATION. | CLASSIFICATION OF OKEN. The following diagram of Oken’s classification is compiled from his Allgemeine Naturgeschichte fiir alle Stiinde, Stuttgardt, 1833-1842, 14 vols. 8vo.; vol. 1, p. 5. The changes this system has undergone may be ascertained by comparing his Lehrbuch der Naturphilosophie, Iena, 1809-1811, 3 vols. 8vo.; 2d edit., Tena, 1831; 3d edit., Ziirich, 1848; Engl. Ray Society, London, 1847, 1 vol. 8vo.— Lehrbuch der Natur- geschichte, Leipzig, 1813; Weimar, 1815 and 1825, 8vo.— Handbuch der Naturgeschichte zum Gebrauch bei Vorlesungen, Niirnberg, 1816-1820, 8vo. — Naturgeschichte fiir Schulen, Leipzig, 1820, 1 vol. 8vo., and various papers in the Isis. lst Grade. Inrestinan AnrmALs; also called Body-animals and Touch-animals. Only one cavity; no head with a brain, only the lowest sense perfect, intestines and skin organs, but no flesh, that is no bones, muscles, or nervous marrow = Jnvertebrata. . Characterized by the development of the vegetative systems of organs, which are those of digestion, circula- tion, and respiration. Hence — Cycle I. Digestive Animals. = Radiata. Essential character: no development beyond an intestine. Ci. 1. Infusoria, (Stomach animals.) Mouth with cilia only, to vibrate. Cu. 2. Poly pi, (Intestine animals.) Mouth with lips and tentacles, to seize. Cx. 3. Acalephae, (Lacteal animals.) Body traversed by tubes similar to the lymphatic vessels. Cycle HI. Circulative Animals.= Mollusks. Essential character: intestine and vessels. Cu. 4. Acephala, (Biauriculate animals.) Membranous heart with two auricles. Ci. 5. Gasteropoda, (Uniauriculate animals.) Membranous heart with one auricle. Ci. 6. Cephalopoda, (Bicardial animals.) Two hearts. Cycle III. Respirative Animals. = Articulata. Essential character: intestine, vessels, and spiracles. Ci. 7. Worms, (Skin animals.) Respire with the skin itself, or part of it, no articulated feet. Cx. 8. Crustacea, (Branchial animals.) Gills or air tubes arising from the horny skin. Cx. 9. Insects, (Tracheal animals.) Trachez internally, gills externally as wings. 2d Grade. Fresu ANIMALS; also called Head-animals.—= Vertebrata. Two cavities of the body, surrounded by fleshy walls, (bones and muscles,) inclosing nervous marrow and intestines. Head with brain; higher senses developed. Characterized by the development of the animal systems, namely, the skeleton, the muscles, the nerves, and the senses. Cycle IV. Carnal Animals proper. Senses not perfected. Cui. 10. Fishes, (Bone-animals.) Skeleton predominating, very much broken up; muscles white, brain without gyri, tongue without bone, nose not perforated, ear concealed, eyes without lids. Cu. 11. Reptiles, (Muscle-animals.) Muscles red, brain without convolutions, nose perforated, ear without external orifice, eyes immovable with imperfect lids. Cu. 12. Birds, (Nerve-animals.) Brain with convolutions, ears open, eyes immovable, lids imperfect. \ Cycle V. Sensual Animals. All anatomical systems, and the senses perfected. Cit. 18. Mammalia, (Sense-animals.) Tongue and nose fleshy, ears open, mostly with a conch, eyes movable, with two distinct lids. = a pa ae mea TE AA TUNA ECNRNE A — as a a a a a I BR a A A AOR OEE LET NTE tas = atari: ~~ es — rn en Cnap. IIL. PHYSIOPHILOSOPHICAL SYSTEMS. 213 The principles laid down by Oken, of which this classification is the practical result for Zodlogy, may be summed up in the following manner: The grades or great. types of Animals are determined by their anatomical systems, such as the body and head; or the intestines, and the flesh and senses. Hence two grades in the animal kingdom. Animals are, as it were, the dismembered body of man made alive. The classes of animals are the special representation in living forms of the anatomical systems of the highest being in creation. Man is considered, in this system, not only as the key of the whole animal kingdom, but also as the standard measure of the organization of animals. There exists ‘nothing in the animal kingdom which is not represented in higher combina- tions in Man. The existence of several distinct plans of structure among animals is virtually denied. They are all built after the pattern of Man; the differences among them consist only in their exhibiting either one system only, or a larger or smaller number of systems of organs of higher or lower physiological impor- tance, developed either singly, or m connection with one another, in their body. The principles of classification of both Cuvier and Ehrenberg are here entirely negatived. The principle of Cuvier, who admits four different plans of structure in the animal kingdom, is, indeed, incompatible with the idea that all animals represent only the organs of Man. The principle of Ehrenberg, who considers all animals as equally perfect, is as completely irreconcilable with the assumption that all animals represent an unequal sum of organs; for, according to Oken, the body of animals is, as it were, the analyzed body of Man, the organs of which live singly, or in various combinations as independent animals. Each such com- bination constitutes a distinct class. The principle upon which the orders are founded has already been explained above, (Chap. IL, Sect. TIL, p. 154.) There is something very taking in the idea that Man is the standard of appre- ciation of all animal structure’. . But all the attempts which have thus far been made to apply it to the animal kingdom as it exists, must be considered as com- plete failures. In his different works, Oken has successively identified the systems of organs of Man with different groups of animals, and different authors, who have adopted the same principle of: classification, have identified them in still differ- ent ways. The impracticability of such a scheme must be obvious to any one who has satisfied himself practically of the existence of different plans of structure in the organization of animals. Yet, the unsoundness of the general principle of the classifications of the physiophilosophers should not render us blind to all that is valuable in their special writings. The works of Oken in particular teem with original suggestions respecting the natural affinities of animals; and his thorough acquaintance with every investigation of his predecessors and contemporaries shows him to have been one of the most learned zodlogists of this century. ms Re a ree ESSAY ON CLASSIFICATION. CLASSIFICATION OF FITZINGER. This diagram is extracted from Fitzinger’s Systema Reptilium, Vindobone, 1843, 1 vol. 8vo. I. Provincia. EverteBRaAta. Animalia systematum anatomicorum vegetativorum gradum evolutionis exhibentia. A. Gradus evolutionis systematum physiologicorum vegetativorum. I. Cireulus. GasTrozoa. Evolutio systematis nutritionis. a. Evolutio przvalens b. Evolutio prevalens c. Evolutio prevalens systematis digestionis. systematis circulationis. systematis respirationis. Cu. 1. Infusoria. CL. 2. Zoophyta. Ci. 3. Acalephae. If. Circulus. Puys10zoa. Evolutio systematis generationis. Cu. 4. Vermes. Cu. 5. Radiata. Ci. 6. Annulata. B. Gradus evolutionis systematum physiologicorum animalium. TIT. Circulus. DerMatozoa. Evolutio systematis sensibilitatis. Ci. 7. Acephala. Cu. 8. Cephalopoda. Cri. 9. Mollusca. IV. Circulus. ARFHROZOA. Evolutio systematis motus. Cui. 10. Crustacea. Ci. 11. Arachnoidea. Cr. 12. Insecta. If. Provincia. VERTEBRATA. Animalia systematum anatomicorum animalium gradum evolutionis exhibentia. A. Gradus evolutionis systematum physiologicorum vegetativorum. a. Evolutio systematis nutritionis, simulque ossium: . . Cr. 138. Pisces. b. Evolutio systematis generationis, simulque musculorum: CL. 14. Reptilia. B. Gradus evolutionis systematum physiologicorum animalium. ce. Evolutio systematis sensibilitatis, simulque nervorum: Cx. 15. Aves. d. Evolutio systematis motus, simulque sensuum:. . . Cx. 16. Mammalia. The fundamental idea of the classification of Fitzinger is the same as that upon which Oken has based his system. The higher divisions, called by him provinces, grades, and cycles, as well as the classes and orders, are considered as representing either some combination of different systems of organs, or some par- ticular system of organs, or some special organ. His two highest groups (provinces) are the Evertebrata and Vertebrata. The Evertebrata represent the systems of the vegetative organs, and the Vertebrata those of the animal organs, as the Gut- Cuap. III. PHYSIOPHILOSOPHICAL SYSTEMS. 215 animals and the Flesh-animals of Oken. Instead, however, of adopting, like Oken, anatomical names for his divisions, Fitzinger employs those most generally in use. His subdivisions or grades of these two primary groups are based upon a repetition of the same differences, within their respective limits. The Invertebrata, in which the vegetative organs prevail, are contrasted with those in which the animal organs prevail, and the same distinction is again drawn among the Vertebrata. Each of these embraces two circles founded upon the development of one particular system of organs, etc. It cannot be expected that the systems founded upon such principles should present a closer agreement with one another than those which are based upon anatomical differences; yet I would ask, what becomes of the principle itself, if its advocates cannot even agree upon what anatomical systems of organs their classes are founded? According to Oken, the Mollusks (Acephala, Gasteropoda, and Cephalopoda) represent the system of circulation, at least in the last edition of his system he views them in that light, whilst Fitzinger considers them as repre- senting the system of sensibility. Oken identifies the Articulata (Worms, Crustacea, and Insects) with the system of respiration, Fitzinger with that of motion, with the exception of the Worms, including Radiata, which he parallelizes with the system of reproduction, etc. Such discrepancies must shake all confidence m these systems, though they should not prevent us from noticing the happy com- parisons and suggestions, to which the various attempts to classify the animal king- dom in this way have led ‘their authors. it is almost superfluous to add, that, great as the disagreement is between- the systems of different physiophilosophers, we find quite as striking discrepancies between the different editions of the system of the same author. The principle of the subdivision of the classes among Invertebrata is here exemplified from the Radiata, (Echinodermata.) Each series contains three orders. [st Series. 2d Series. 8d_ Series. Evolutio prevalens Evolutio prevalens Evolutio przvalens systematis digestionis. systematis circulationis. systematis respirationis. Asteroidea. Echinodea. Scytodermata (Holothurioids.) 1. Encrinoidea. 2. Comatulina. 1. Aprocta. 2. Echinina. 1. Synaptoidea. 2. Holothurioidea. 3. Asterina. _ 8. Spatangoidea. 3. Pentactoidea. In Vertebrata, each class has five series and each series three orders; so in Mammalia, for example :— 1st Series. 2d Series. 38d_ Series. 4th Series. 5th Series. Evolutio prevalens Evolutio prevalens Evolutio prevalens Evolutio prevalens Evolutio prevalens sensus tactus. sensus gustus. sensus olfactus. sensus auditus. sensus visus. Cetacea. Pachydermata. Edentata. Unguiculata. Primates. 1. Balanodea. 1. Phocina. 1. Monotremata. 1. Glires. 1. Chiropteri. 2. Delphinodea. 2. Obesa. 2. Lipodonta. 2. Bruta. 2. Hemipitheci. _ 8. Sirenia. 3. Ruminantia. 3. Tardigrada. 3. Fer. 3. Anthropomorphi. nemeconan ad inant cm lla AGT tn te a A i ct el at i Di lag cll 216 ESSAY ON CLASSIFICATION. Part I. Instead of considering the orders as founded upon a repetition of the characters of higher groups, as Oken would have it, Fitzinger adopts series, as founded upon - that idea, and subdivides them further into orders, as above. These series, however, have still less reference to the systems of organs, which they are said to represent, than either the classes or the higher divisions of the animal kingdom. In these attempts to arrange minor groups of animals into natural series, no one can fail to perceive an effort to adapt the frames of our systems to the impression we receive from a careful examination of the natural relations of organized beings. Everywhere we notice such series; sometimes extending only over groups of species, at other times embracing many genera, entire families, nay, extending frequently to several families. Even the classes of the same branch may exhibit more or less distinctly such a serial gradation. But I have failed, thus far, to discover the principle to which such relations may be referred, as far as they do not rest upon complication of structure,' or upon the degree of superiority or inferiority of the features upon which the different kinds of groups are themselves founded. Analogy plays also into the series, but before the categories of analogy have been as carefully scrutinized as those of affinity, it 1s impossible to say within what limits this takes place. CLASSIFICATION OF McLEAY. The great merit of the system of McLeay, and in my opinion it has no other claim to our consideration, consists in having called prominently the attention of naturalists to the difference between two kinds of relationship, almost universally confounded before: affinity and analogy. Analogy is shown to consist in the repeti- tion of similar features in groups otherwise remote, as far as their anatomical characters are concerned, whilst affinity is based upon similarity in the structural relations. On account of the similarity of their locomotion, Bats, for instance, may be considered as analogous to Birds; Whales are analogous to Fishes on account of the similarity of their form and their aquatic mode of life; whilst both Bats and Whales are allied to one another and to other Mammalia on account of the identity of the most characteristic features of their structure. This important dis- tinction cannot fail to lead to interesting results. Thus far, however, it has only produced fanciful comparisons from those who first traced it out. It is assumed, for instance, by McLeay, that all animals of one group must be analogous to * Compare Chap. II., Sect. 8, p. 153. those of the German physiophilosophers, but on 2 I have introduced the classification of McLeay account of its general character, and because it is in this section, not because of any resemblance to . based upon an ideal view of the affinities of animals. mene OO — a LE A ig OE OLA EIR DE AAI TE Cuap. III. PHYSIOPHILOSOPHICAL SYSTEMS. 217 those of every other group, besides forming a circle in themselves; and in order to carry out this idea, all animals are arranged in circular groups, in such a manner as to bring out these analogies, whilst the most obvious affinities are set aside to favor a preconceived view. But that I may not appear to underrate the merits of this system, I will present it in the very words of its most zealous admirer and selfcomplacent expounder, the learned William Swainson? “The Hore Entomologice,* unluckily for students, can only be thoroughly understood by the adept, since the results and observations are explained in different parts; the style is somewhat desultory, and the groups, for the most part, are rather indicated than defined. The whole, in short, is what it professes to be, more a rough sketch of the leading peculiarities of the great divisions of animals, and the manner in which they are probably connected, than an accurate determination of the groups themselves, or a demonstration of their real affinities. More than this, perhaps, could not have been expected, considering the then state of science, and the herculean difficulties which the author had to surmount. The work in ques tion has now become exceedingly scarce, and this will be an additional reason with us for communicating occasional extracts from it to the reader. Mr. McLeay’s theory will be best understood by consulting his diagram; for he has not, as we have already remarked, defined any of the vertebrated groups. Condensing, how- ever, the result of his remarks, we shall state them as resolvable into the following propositions: 1. That the natural series of animals is continuous, forming, as it were, a circle, so that, upon commencing at any one given point, and thence tracing all the modifications of structure, we shall be imperceptibly led, after passing through numerous forms, again to the point from which we started ; 2. That no groups are natural which do not exhibit such a circular series; 3. That the primary divisions of every large group are ten, five of which are composed of comparatively large circles, and five of smaller: these latter being termed osculant, and being intermediate between the former, which they serve to connect; 4. That there is a tendency in such groups as are placed at the opposite points of a circle of affinity ‘to meet each other;’ 65. That one of the five larger groups into which every natural circle is divided, ‘bears a resemblance to all the rest, or, more strictly speaking, consists of types which represent those of each of the four other groups, together with a type peculiar to itself’? These are the chief and leading principles which Mr. McLeay considers as belonging to the natural system. We shall now copy his diagram, or table of the animal kingdom, and then endeavor, with this help, to explain the system more in detail.” 1 Swainson, (W.,) A Treatise of the Geography 2 McLray, (W. S.,) Hore Entomologice, or and Classification of Animals, London, 1835, 1 vol. Essays on the Annulose Animals, London, 1819-21, 12mo., p. 201-205. 2 vols. 8vo. 28 inane eamsemsasanvatnitan,- imndten wetettingmatactgmnanseenreshin ia ESSAY ON CLASSIFICATION. MOLLUSCA. Pteropoda. Acephala. Reptilia. P. Vaginati. Brachiopoda. Aves. ACRITA. VERTEBRATA. Di benis : gastria. Mammalia. P. Natantes. Amphibia. Intestina. Pisces. ‘WOPSULY 9[qGvJes59A OY} JO soulog poztuesio 4svorT Fistulida. Ametabola. Acalephide. Mandibulata. RADIATA. ANNULOSA. Echinide. || Crustacea. Meduside. Haustellata. Stelleride. Arachnide. < = ce a | os oo sae o “We must, in the first instance, look to the above tabular disposition of all animals, as forming themselves collectively into one great circle, which circle touches or blends into another, composed of plants, by means of the ‘least organized beings of the vegetable kingdom’ Next we are to look to the larger component. parts of this great circular assemblage. We find it, in accordance with the third proposi- tion, to exhibit five great circles, composed of the Moxvusca, or shellfish; Acriva, or polyps; Raprata, or star-fish; ANNULOsA, or insects; and Verreprata, or verte- brated animals; each passing or blending into each other, by means of five other groups of animals, much smaller, indeed, in their extent, but forming so many connecting or osculant circles.'| The number, therefore, as many erroneously suppose, is not five, but ten. This is quite obvious; and our opinion on this point is confirmed by the author himself, in the following passage, when alluding to his remarks upon the whole:—‘The foregoing observations, I am well aware, are far from accurate, but they are sufficient to prove that there are five great circular groups in the animal kingdom, each of which possesses a peculiar structure; and that 1 Tn the original diagram, as in that above, these but merely indicated by the names arranged like five smaller circles are not represented graphically, rays between the five large circles. ee ee cc nt ee Sse Same ~ Cuap. III. PHYSIOPHILOSOPHICAL SYSTEMS. 219 these, when connected by means of five smaller osculant groups, compose the whole province of Zodlogy. Now these smaller osculant groups are to be viewed as circles, for, as it is elsewhere stated, ‘every natural group is a circle, more or less complete’ This, in fact, is the third general principle of Mr. McLeay’s system, and he has exemplified his meaning of a natural group in the above diagram, where all animals are arranged under five large groups or circles, and five smaller ones. Let us take one of these groups, the Vertebrata: does that form a circle of itself? Yes; because it is intimated that the Reptiles (Reptilia) pass into the Birds, (Aves,) these again into the Quadrupeds, (Mammalia,) Quadrupeds unite with the Fishes, (Piésces,) these latter with the amphibious Reptiles, and the Frogs bring us back again to the Reptiles, the point from whence we started. Thus, the series of the vertebrated group is marked out and shown to be circular; therefore, it is a natural group. This is an instance where the circular series can be traced. We now turn to one where the series is imperfect, but where there is a decided tendency to a circle: this is the Mollusca. Upon this group our author says, ‘I have by no means determined the circular disposition to hold good among the Mollusca; still, as it is equally certain that this group of animals is as yet the least known, it may be improper, at present, to conclude that it forms any exception to the rule; it would even seem unquestionable that the Gasteropoda of Cuvier return into themselves, so as to form a circular group; but whether the Acephala form one or two such, is by no means accurately ascertained, though enough is known of the Mollusca to incline us to suspect that they are no less subjected, in general, to a circular disposition than the four other great groups. This, therefore, our author considers as one of those groups which, without actually forming a circle, yet evinces a disposition to do so; and it is therefore presumed to be a natural group. But, to illustrate this principle farther, let us return to the circle of Vertebrata. This, as we see by the diagram, contains five minor groups, or circles, each of which is again resolvable into five others, regu- lated precisely in the same way. The class Aves, for example, is first divided into rapacious birds, (Raptores,) perching birds, (Jusessores,) gallinaceous birds, ( asores,) wading birds, (Gradatores,) and swimming birds (Natatores); and the proof of this class being a natural group is, in all these divisions blending into each other at their confines, and forming a circle. In this manner we proceed, beginning with the higher groups, and descending to the lower, until at length we descend to genera, properly so called, and reach, at last, the species; every group, whether large or small, forming a circle of its own. Thus there are circles within circles, ‘wheels within wheels,—an infinite number of complicated relations; but all regulated by one simple and uniform principle,—that is, the circularity of every group.” tain. snescsachteataian. ies a lems Si a ill 220 ESSAY ON CLASSIFICATION. — Parr I. The writer who can see that the Quadrupeds unite with the Fishes, and the like, and yet says that Cuvier “was totally unacquainted. with the very first princi- ples of the natural system,” hardly deserves to be studied in our days. The attempt at representing graphically the complicated relations which exist among animals has, however, had one good result; it has checked, more and more, the confidence in the uniserial arrangement of animals, and led to the construction of many valuable maps exhibiting the multifarious relations which natural groups, — of any rank, bear to one another. SHeTION “we, EMBRYOLOGICAL SYSTEMS. Embryology, in the form it has assumed within the last fifty years, is as completely a German science as the “Naturphilosophie.” It awoke to this new activity contemporaneously with the development of the Philosophy of Nature. It would hardly be possible to recognize the leading spirit in this new development, from his published works; but the man whom Pander and K. E. von Baer acknowledge as their master must be considered as the soul of this movement, and this man is Ignatius Déllinger. It is with deep gratitude I remember, for my own part, the influence that learned and benevolent man had upon my studies and early scientific application, during the four years I spent in his house, in Munich, from 1827 to 1831; to him I am indebted for an acquaintance with what was then known of the development of animals, prior to the publication of the great work of Baer; and from his lectures I first learned to appreciate the im- portance of Embryology to Physiology and Zoédlogy. The investigations of Pander! upon the development of the chicken in the egg, which have opened the series of those truly original researches in Embryology of which Germany may justly be proud, were made under the direction and with the codperation of Dillinger, and were soon followed by the more extensive works of Rathke and Baer, whom the civilized world acknowledges as the founders of modern Embryology. The principles of classification propounded by K. E. von Baer seem never to have been noticed by systematic writers, and yet they not only deserve the most careful consideration, but it may fairly be said that no naturalist besides Cuvier has exhibited so deep an insight into the true character of a natural system, 1 PanveER, Beitriige zur Entwickelungsgeschichte des Hiihnchens im Eie, Wiirzburg, 1817, 1 vol. fol. Cuap.. III. EMBRYOLOGICAL SYSTEMS. 221 supported by such an extensive acquaintance with the subject, as this great embry- ologist has in his “Scholien und Corallarien zu der Entwickelungsgeschichte des Hiihnchens im Hie.”? These principles are presented in the form of general pro- portions, rather than in the shape of a diagram with definite systematic names, and this may explain the neglect which it has experienced on the part of those who are better satisfied with words than with thoughts. A few abstracts, however, | may show how richly the perusal of his work is likely to reward the reader. The results at which K. E. von Baer had arrived by his embryological inves- tigations, respecting the fundamental relations existing among animals, differed con- siderably from the ideas then prevailing. In order, therefore, to be correctly — understood, he begins, with his accustomed accuracy and clearness, to present a condensed account of those opinions with which he disagreed, in these words:— “Few views of the relations existing in the organic world have received so much approbation as this: that the higher animal forms, in the several stages of the development of the individual, from the beginning of its existence to its complete formation, correspond to the permanent forms in the animal series, and that the development of the several animals follows the same laws as those of the entire animal series; that consequently the more highly organized animal, in its individual development, passes in all that is essential through the stages that are permanent’ below it, so that the periodical differences of the individual may be reduced to the differences of the permanent animal forms.” Next, in order to have some standard of comparison with his embryological results, he discusses the relative position of the different permanent types of ani- mals, as follows :— “Tt is especially important that we should distinguish between the degree of perfection in the animal structure and the type of organization. The degree of perfection of the animal structure consists in the greater or less heteroge- neousness of the elementary parts, and the separate divisions of a complicated apparatus, —in one word, in the greater histological and morphological differen- tiation. The more uniform the whole mass of the body is, the lower the degree of perfection; it is a stage higher when nerve and muscle, blood and cellular tissue, are sharply distinguished. In proportion to the difference between _ these parts, is the development of the animal life in its different tendencies; or, to express it more accurately, the more the animal life is developed in its several tendencies, the more heterogeneous are. the elementary parts which this life brings into action, The same is true of the single parts of any apparatus. That organ- + Ueber Entwickelungsgeschichte der Thiere, Baer, Konigsberg, 1828, 4to.— See also Acta Nova Beobachtung und Reflexion von Dr. Karl Ernst von Acad. Leop. Cesar, vol. 18, and Meckel’s Arch., 1826. Ps ac sessilis nal ii i ca a, Part I. 2 ESSAY ON CLASSIFICATION. ization is higher in which the separate parts of an entire system differ more among themselves, and each part has greater individuality, than that in which the whole is more uniform. I call type, the relations of organic elements and organs, as far as their position is concerned. This relation of position is the expression of cer- tain fundamental connections in the tendency of the individual relations of. life ; as, for instance, of the receiving and discharging poles of the body. The type is altogether distinct from the degree of perfection, so that the same type may include many degrees of perfection, and, vice versd, the same degree of perfec- tion may be reached in several types. The degree of perfection, combined with the type, first determines those great animal groups which have been called classes. The confounding of the degree of perfection with the type of organization seems the cause of much mistaken classification, and in the evident distinction between these two relations we have sufficient proof that the different animal forms do not present one uniserial development, from the Monad up to Man.” The types he has recognized are :— I. The Peripheric Type. The essential contrasts in this type are between the centre and the periphery.» The organic functions of life are carried on in antag- onistic relations from the centre to the circumference. Corresponding to this, the whole organization radiates around a common centre. There exists besides only the contrast between above and below, but in a weaker degree; that between right and left, or before and behind, is not at all noticeable, and the motion is therefore undetermined in its direction. As the whole organization radiates from one focus, so are the centres of all the organic systems arranged, ring-like, around it, as, for instance, the stomach, the nerves and vessels, (if these parts are devel- oped,) and the branches extending from them into the rays. What we find in one ray is repeated in every other, the radiation being always from the centre outwards, and every ray bearing the same relation to it. | Il. The Longitudinal Type, as observed in the Vibrio, the Filaria, the Gordius, the Nais, and throughout the whole series of articulated animals. The contrast between the receiving and the discharging organs, which are placed at the two ends of the body, controls the whole organization. The mouth and the anus are 1 From this statement it is plain that Baer of structure as determining the relative rank of has a very definite idea of the plan of structure, and that he has reached it by a very different road from that of Cuvier. It is clear, also, that he understands “the distinction between a plan and its execution. But his ideas respecting the different features of structure are not quite so precise. He does not distinguish, for instance, between the complication the orders, and the different ways in which, and the different means with which the plans are executed, as characteristic of the classes. ? Without translating verbatim the descriptions Baer gives of his types, which are greatly abridged here, they are reproduced as nearly as possible in his own words. “:... EMBRYOLOGICAL Cuap. III. SYSTEMS. 223 always at opposite ends, and usually also the sexual organs, though their opening is sometimes farther forward; this occurs, however, more frequently in the females, in which these organs have a double function, than in the males. When both sexual organs are removed from the posterior extremity, the opening in the female usually lies farther forward than in the male. So is it in the Myriapods and the Crabs. The Leeches and Karthworms present a rare exception. The recep- tive pole being thus definitely fixed, the organs of senses, as instrumental to the receptivity of the nervous system, early reach an important degree of perfection. The intestinal canal, as well as the vascular stems and the nervous system, extend through the whole length of the body, and all organic motion in these animals has the same prevailing direction. Only subordinate branches of these organs arise laterally, and chiefly wherever the general contrast, manifested in the whole length is repeated in such a manner that, for each separate segment, the same contrast arises anew, in connection with the essential elements of the whole organ- ism. Hence the tendency in these animals to divide into many segments in the direction of the longitudmal axis of the body. In the true Insects, undergoing metamorphosis, these segments unite again into three principal regions, in the first of which the life of the nerves prevails; in the second, motion; in the third, digestion; though neither of the three regions is wholly deprived of any one of these functions. Besides the opposition between before and behind, a less marked contrast is observed in a higher stage of development between above and below. A difference between right and left forms a rare exception, and is gen- erally wanting. Sensibility and irritability are particularly developed in this series. Motion is active, and directed more decidedly forward, in proportion as the lon- gitudinal axis prevails. When the body is contracted as in spiders and crabs, its direction is less decided. The plastic organs are little developed; glands, espe- cially, are rare, and mostly replaced by simple tubes. Il. The Massive Type. We may thus call the type of Mollusks, for neither length nor surface prevails in them, but the whole body and its separate parts are formed rather in round masses which may be either hollow or solid. As the chief contrast of their structure is not between the opposite ends of the body, nor between the centre and periphery, there is almost throughout this type an absence of sym- metry. Generally the discharging pole is to the right of the receptive one. The discharging pole, however, is either near the receptive one, or removed from it, and approximated to the posterior extremity of the body. As the tract of the digestive apparatus is always determined by these two poles, it is more or less arched; in its simplest form it is only a single arch, as in Plumatella. When that canal is long, it is curled up in a spiral in the centre, and the spiral probably has its definite laws. For instance, the anterior part of the alimentary canal appears to be always placed under the posterior. The principal currents maseatasee each hai ia i AN ORT nn re a Yih alata. ia at, a emai et 224 ESSAY ON CLASSIFICATION. Part I. of blood are also in arches, which do not coincide with the medial line of the body. The nervous system consists of diffused ganglia, united by threads, the larger ones being around the cesophagus. The nervous system and the organs of sense appear late; the motions are slow and powerless. IV. The Vertebrate Type. This is, as it were, composed of the preceding types, as we distinguish an animal and a vegetative system of the body, which, though influencing one another in their development, have singly a peculiar typical organization. In the animal system, the articulation reminds us of the second type, and the discharging and receiving organs are also placed at opposite ends. There is, however, a marked difference between the Articulates and the Vertebrates, for the animal system of the Vertebrates is not only doubled along the two sides, but at the same time upwards and downwards, in such a way that the two lateral walls which unite below circumscribe the vegetative system, while the two tending upward surround a central organ of the animal life, the brain and spinal marrow, which is wanting in Invertebrates. The solid frame represents this type most com- pletely, as from its medial axis, the backbone, there arise upward arches which close in an upper crest, and downward arches which unite, more or less, in a lower crest. Corresponding to this we see four rows of nervous threads along the spinal marrow, which itself contains four strings, and a quadripartite grey mass. The muscles of the trunk form also four principal masses, which are particularly distinct in the Fishes. The animal system is therefore doubly symmetrical in its arrangement. It might easily be shown how the vegetative systems of the body correspond to the type of Mollusks, though influenced by the animal system. From the illustrations accompanying this discussion of the great types or branches of the animal kingdom, and still more from the paper published by K. E. von Baer in the Nova Acta,’ it is evident, that he perceived more. clearly and. earlier than any other naturalist, the true relations of the lowest animals to their respective branches. He includes neither Bryozoa nor Intestinal Worms among Radiata, as Cuvier, and after him so many modern writers, did, but correctly refers the former to the Mollusks and the latter to the Articulates. Comparing these four types with the embryonic development, von Baer shows that there is only a general similarity between the lower animals and the embryonic stages of the higher ones, arising mainly from the absence of differentiation in the body, and not from a typical resemblance. The embryo does not pass from one type to the other; on the contrary, the type of each animal is defined from the ? Beitriige zur Kenntniss der niedern Thiere, animals. These “ Beitriige,” and the papers in which Nova Acta Academie Naturz Curiosorum, vol. 13, | Cuvier characterized for the first time the four great Part 2, 1827, containing seven papers, upon Aspido- types of the animal kingdom, are among the most gaster, Distoma, and others, Cercaria, Nitzschia, Poly- important contributions to general Zodlogy ever stoma, Planaria, and the general affinities of all published. ee en ar sateen . Cuar. IIL EMBRYOLOGICAL SYSTEMS. 295 beginning and controls the whole development. The embryo of the Vertebrate is a Vertebrate from the beginning, and does not exhibit at any time a corre- spondence with the Invertebrates. The embryos of Vertebrates do not pass in their development through other permanent types of animals. The fundamental type is first developed, afterwards more and more subordinate characters appear. From a more general type, the more special is manifested, and the more two forms) of animals differ, the earlier must their development be traced back to discern— an agreement between them. It is barely possible that in their first beginning all animals are alike and present only hollow spheres, but the individual develop- ment of the higher animals certainly does not pass through the permanent forms — of lower ones. What is common in a_ higher group of animals is always sooner | developed in their embryos than what is special; out of that which is most general - arises that which is less general, until that which is most special appears. Each embryo of a given type of animals, instead of passing through other definite types, becomes on the contrary more and more unlike them. An embryo of a higher type is, therefore, never identical with another animal type, but only with an embryo. Thus far do the statements of von Baer extend It is evident from this, that he has clearly perceived the limitation of the different modes of embryonic develop- ment within the respective branches of the animal kingdom, but it is equally certain that his assertions are too general to furnish a key for the comparison of the successive changes which the different types undergo within their respective limits, and that he is still vaguely under the impression, that the development corresponds in its individualization to the degrees of complication of structure. * The account which Huxley gives of Baer’s views, (see Baden Powell’s Essays, Appendix 7, p- 495,) is incorrect. Baer did not “demonstrate that the classification of Cuvier was, in the main, simply the expression of the fact, that there are certain common plans of development in the animal kingdom,” ete., for Cuvier recognized these plans in the structure of the animals, before Baer traced “their development, and Baer himself protests against an identification of his views with those of Cuvier. (Baer’s Entwick., p. 7.) Nor has Baer demon- strated the “doctrine of the unity of organization of all animals,” and placed it “upon a footing as secure as the law of gravitation,” and arrived at “the grandest law,” that, up to a certain point, the develop- ment “followed a plan common to all animals.” On the contrary, Baer admits four distinct types of animals, and four modes of development. He only 29 adds:.“It is barely possible that in their first begin- ning all animals are alike.” Huxley must also have overlooked Cuvier’s introduction to the “ Regne Animal,” (2d edit. vol. 1, p. 48, quoted verbatim above, p. 193,) when he stated that Cuvier “did not attempt to discover upon what plans animals are con- structed, but to ascertain in what manner the facts of animal organizations could be thrown into the fewest possible propositions.” On the contrary, Cuvier’s special object, for many years, has been to point out these plans, and to show that they are characterized by peculiar structures, while Baer’s merit consists in having discovered four modes of development, which coincide with the branches of the animal kingdom, in which Cuvier recognized four different plans of structure. Huxley is equally mistaken when he says that Cuvier adopted the nervous system “as the Baise of his great divisions.” en ne ak it lit ot ihn HB. cents: Aar ct! 926 ESSAY ON CLASSIFICATION. ey. This could hardly be otherwise, as long as the different categories of the structure of animals had not been clearly distinguished! CLASSIFICATION OF K. E. VON BAER. In conformity with his embryological investigations, K. E. von Baer proposes the following classification. I. Peripheric Type. (Rap1ata.) Evolutio radiata. The development proceeds from a centre, producing identical parts in a radiating order. II. Massive Type. (Motiusca.) Evolutio contorta. The development produces identical parts curved around a conical or other space. III. Longitudinal Type. (Arricutata.) Evolutio gemina. The development produces identical parts arising on both sides of an axis and closing up along a line opposite the axis. IV. Doubly Symmetrical Type. (VreRTEBRATA.) Evolutio bigemina. The development produces identical parts arising on both sides of an axis, growing upwards and downwards, and shutting up along two lines, so that the inner layer of the germ is inclosed below and the upper layer above. The embryos of these animals have a dorsal cord, dorsal plates, and ventral plates, a nervous tube and branchial fissures. 1°. They acquire branchial fringes ; a. But no genuine lungs are developed. a. The skeleton is not ossified. Cartilagineous Fishes. 6. The skeleton is ossified.. Fishes proper. b. Lungs are formed. Amphibia. a. The branchial fringes remain. Sirens. 6. The branchial fringes disappear. Urodela and Anura. 2°. They acquire an allantois, but a. Have no umbilical cord; a. Nor wings and air sacs. Reptiles. 6. But wings and air sacs. Birds. 6. Have an umbilical cord. Mammalia. a. Which disappears early ; 1°. Without connection with the mother. Monotremata. 2°, After a short connection with the mother. Marsupialia. 6. Which is longer persistent ; 1°. The yolk sac continues to grow for a long time. The allantois grows little. Rodentia. The allantois grows moderately. Insectivora. The allantois grows much. Carnivora. 2°. The yolk sac increases slightly. The allantois grows little. Umbilical cord very long. Monkeys and Man. The allantois continues to grow for a long time. Placenta in simple masses. Ruminants. The allantois continues to grow for a long time. Placenta spreading. Pachyderms and Cetacea. 1 Compare Chap. II., Sect. 1 to 9. Cuap. III. EMBRYOLOGICAL SYSTEMS. 227 CLASSIFICATION OF VAN BENEDEN. Van Beneden has also proposed a classification based upon Embryology, which was first sketched in his paper upon the Embryology of Bryozoa: Recherches sur l’anatomie, la physiologie et 1’embryogénie des Bryozoaires, Bruxelles, 1845, 4to., and afterwards extended in his Comparative Anatomy: Anatomie comparée, Bruxelles, (without date, but probably from the year 1855,) 1 vol.. 12mo. I. HypocoryLepones or Hypovirrniians. (Vertebrata.) The vitellus enters the body from the ven- Cis CL. C1. BS Cre 4 (lee 3. tral side. Mammalia. (Primates, Cheiroptera, Insectivora, Rodentia, Carnivora, Edentata, Pro- boscidea, Ungulata, Sirenoidea, Cetacea.) Birds. (Psittacee, Rapaces, Passeres, Columba, Gallinz, Struthiones, Gralle, Palmipedes.) Reptiles. (Crocodili, Chelonii, Ophidii, Saurii, Pterodactyli, Simosauri, Plesiosauri, Ichthyosauri.) Batrachians. (Labyrinthodontes, Peromelia, Anura, Urodela, Lepidosirenia.) Fishes. (Plagiostomi, Ganoidei, Teleostei, Cyclostomi, Leptocardii.) II. Eprcorytepones or Epivireriians. (Articulata.) The vitellus enters the body from the dorsal Cn. side. Insects. (Coleoptera, Nevroptera, Strepsiptera, Hymenoptera, Lepidoptera, Diptera, Orthop- tera, Hemiptera, Thysanura, Parasita.) Myriapodes. (Diplopoda, Chilopoda.) Arachnides. (Scorpiones, Aranez, Acari, Tardigrada.) Crustacea. (Decapoda, Stomapoda, Amphipoda, Isopoda, Lemodipoda, Phyllopoda, Lophy- ropoda, Xiphosura, Siphonostoma, Myzostoma, and Cirripedia.) III. Axiocotyirepones or ALLOVITELLIANS. (Mollusco-Radiaria.) The vitellus enters the body neither Cr 10. CLs CL. Cin oie CL. 11. Le 13. 14. 15. from the ventral nor from the dorsal side. Mollusca. Including Cephalopoda, Gasteropoda, Pcecilopoda, and Brachiopoda. (Acephala, Tunicata, and Bryozoa.) Worms. (Malacopoda, Annelides, Siponculides, Nemertini, Nematodes, Acanthocephali, Scoleides, Hirudinei.) Echinoderms. (Holothuriw, Echinides, Stellerides, Crinoides, Trematodes, Cestodes, Rotiferi, Planarie.) Polyps. Including Tunicata, Bryozoa, Anthozoa, Alcyonaria, and Meduse, as orders. (Ctenophore, Siphonophore, Discophore, Hydroids, Anthophoride.) Rhizopods. Only the genera mentioned. Infusoria. Only genera and families mentioned. Van Beneden thinks the classification of Linnzeus truer to nature than either that of Cuvier or of de Blainville, as the class of Worms of the Swedish naturalist corresponds to his Allocotyledones, that of Insects to his Hypocotyledones, and the four classes of Pisces, Amphibia, Aves, and Mammalia to his Hypocotyledones. He compares his primary divisions to the Dicotyledones, Monocotyledones, and Acotyledones of the vegetable kingdom. But he overlooks that the Cephalopods pt a ea ae nn in da gd, let et: ea a = ne ea ESSAY ON CLASSIFICATION. } Part J. are not Allocotyledones, and that any eroup of animals which unites Mollusks, Worms, and Radiates in one ,great mass cannot be founded upon correct principles. As to his classes, I can only say that if there are natural classes among animals, there never was a combination of animals proposed since Linnzeus, less likely to answer to a philosophical idea of what a class may be, than that which unites Tunicata with Polyps and Acalephs. In his latest work, Van Beneden has introduced in this classification many important improvements and additions. Among the additions, the indication of the orders, which are introduced in brackets in the diagram above, deserve to be particularly noticed. These changes relate chiefly to the Mollusks and Polyps; the Tunicata and Bryozoa being removed from the | Polyps to the Mollusks. The Acalephs and Polypi, however, are still considered as forming together one single class. The comparison, instituted by Van Beneden between his classification of the animal kingdom and that of the plants most generally adopted now, leads me to call again attention to the necessity of carefully scrutinizing anew the vegetable kingdom, with the view of ascertainmg how far the results I have arrived at concerning the value of the different kinds of natural groups existing among animals," apply also to the plants. It would certainly be premature to assume, that because the branches of the animal kingdom are founded upon different plans of structure, the vegetable kingdom must necessarily be built also upon different plans. There are probably not so many different modes of development among plants as among animals; unless the reproduction by spores, by naked polyem- bryonic seeds, by angiospermous monocotyledonous seeds, and by angiospermous dicotylodonous seeds, connected with the structural differences exhibited by the Acotyledones, Gymnospermes, Monocotyledones, and Dicotyledones, be considered as amounting to an indication of different plans of structure. But even then these differences would not be so marked as those which distinguish the four branches of the animal kingdom. The limitation of classes and orders, which presents com- paratively little difficulty in the animal kingdom, is least advanced among plants, whilst botanists have thus far been much more accurate than zodlogists in charac- terizing families. This is, no doubt, chiefly owing to the peculiarities of the two organic kingdoms. a ta It must be further remarked, that in the classification of Wan Beneden the animals united under the name of Allocotyledones are built upon such entirely different plans of structure, that their combination should of itself satisfy any unprejudiced observer that any principle which unites them in that way cannot be true to nature. | 1 See Chap. IL, p. 187 to 178. Gum *iit. "~~ EMBRYOLOGICAL SYSTEMS. 229 DIAGRAM OF THE DEVELOPMENT OF ANIMALS BY KOLLIKER. Koiimer, (A.,) in his Entwickelungsgeschichte der Cephalopoden, Zurich, 1844, 1 vol. 4to., p. 175, has submitted the following diagram of the development of the animal kingdom. A. The embryo arises from a primitive part. (Evolutio ex una parte.) 1°. It grows in two directions, with bilateral symmetry. (Evolutio bigemina.) a. The dorsal plates close up. Vertebrata. b. The dorsal plates remain open and are transformed into limbs. Articulata. 2°. It grows uniformly in every direction. (Evolutio radiata.) And a. Incloses the embryonal vesicle entirely. a. This takes place very early. Gasteropoda and Acephala. 6. This takes place late. (Temporary vitelline sac.) Limax. b. Contracts above the embryonal vesicle. (Genuine vitelline sac.) Cephalopoda. A. The whole body of the embryo arises simultaneously. (Evolutio ex omnibus partibus.) 1°. It grows in the direction of its transverse axis, a. With its hind body. Radiata. (Echinoderms.) b. With the fore body, and a. The hind body does not grow. Acalephs. B. The hind body grows longitudinally. Polypi. 2°. It grows in the direction of its longitudinal axis. Worms. I have already shown how unnatural a zodlogical system must be which is based upon a distinction between total or partial segmentation of the yolk. No more can a diagram of the development of animals, which adopts this difference as fundamental, be true to nature, even though it is based upon real facts. We ought never to single out isolated features, by which animals may be united or sep- arated, as most anatomists do; our aim should rather be to ascertain their general relations, as Cuvier and K. E. von Baer have so beautifully shown. I think also, that the homology of the limbs of Articulata and the dorsal plates of Vertebrata is more than questionable. The distinction, introduced between Polyps and Acalephs and these and the other Radiates, is not any better founded. It seems also quite inappropriate to call the development of Mollusks, evolutio radiata, especially after Baer had designated, under that same name, the mode of formation of the branch of Radiates, for which it is far better adapted. a Chap. TEL, tects” 2, 17s gegenseitige Verwandtschaft der Thiere zu erlangen, 2 The principles of classification advocated by die verschiedenen Organisationstypen Baer are so clearly expressed by him, that I cannot von den verschiedenen Stufen der Aus- resist the temptation of quoting some passages from bildung stets unterscheiden. Dass man diesen the paper already mentioned above, p. 224, especially Unterschied gewohnlich nicht im Auge behalten hat, now, when I feel called upon to oppose the views of scheint uns zu den sonderbarsten Zusammenstel- one of his most distinguished colleagues. “Vor allen lungen gefiihrt zu haben.” Beitrage, etc., Acta Dingen muss man, um eine richtige Einsicht in die Nova, vol. 13, -p. 739. = Se ee seagate bi acs A i in Sa el oC A Ni waitin inant ore eee vere! Contrast between the Embryo and the Yolk. ve Transformation of the whole Yolk into the Embryo. No Ege. ESSAY ON CLASSIFICATION. CLASSIFICATION OF VOGT. I. Verteprata. Yolk ventral. Cu.1. Mammalia. 1°. Aplacentaria; Ord. Monotremata, Marsupialia. 2°. Placen- taria’: “Seri, Ord. Cetacea, Pachydermata, Solidungula, Ruminantia, and Edentata ; S. 2. Pinnipedia, Carnivora; 8.3. Insectivora, Volitantia, Glires, Quadrumana, Bimana. - Aves. Ser. 1. Insessores; Ord. Columb, Oscines, Clamatores, Scansores, Rapta- tores; Ser. 2. Autophagi; Ord. Natatores, Grallatores, Gallinacea, Cursores, - Reptilia. Ord. Ophidia, Sauria, Pterodactylia, Hydrosauria, and Chelonia. -4. Amphibia. Ord. Lepidota, Apoda, Caudata, Anura. -9. Pisces. Ord. Leptocardia, Cyclostomata, Selachia, Ganoidea, Teleostia. II. Arricutata. Yolk dorsal. Ci. 6. Insecta. Subcl.1. Ametabola; Ord. Aptera. Subcl.2. Hemimetabola; Ord. Hemiptera and Orthoptera. ‘Subcl. 8. Holometabola ; Ord. Diptera, Lep- idoptera, Strepsiptera, Nevroptera, Coleoptera, Hymenoptera. Ci. 7. Myriapoda. Only divided into families. Ci. 8 Arachnida. Series 1. Pycnogonida and Tardigrada; Ord.