still more eminent degree of sagacity of observation transferred to all the parts of the animal-to its muscles, its vessels, its nerves, its organs of sense. Swammerdam, and Pallas,* who had embraced all the parts of the animal in their anatomizations, had confined these to certain species; in another genus Lyonnet had confined himself to a single one; in the case of Cuvier there was an entire class of animals, and of all animals the class least known, of which almost all the species were described and all the details, even the most delicate and obscure, of their structure were brought to light and developed.

The mollusks have all a heart, as already said; some, however, have but a single one, like the oyster and snail; others have two; others again, like the poulp and cuttle-fish, have as many as three distinct hearts. And yet it was with these animals whose organization is so rich, which have a brain, nerves, organs of sense and of secretion, that it had been the custom to confound others, which, like the zoophytes and polypes, for example, have for their whole organization only an almost homogeneous pulp.

The experiments of Trembley have rendered famous the polypus of fresh water, that animal which puts forth buds like a plant, and each part of which, separated from the others, forms a new and complete individual. The whole structure of this singular zoophyte reduces itself to a sac-that is to say, to a mouth and stomach. M. Cuvier has made known another zoophyte, whose structure presents something still more surprising, for it has not even a mouth; it is nourished by means of ramified suckers, like plants, and its internal cavity serves by turns as a stomach and sort of heart, for vessels enter it which conduct to it the nutritive juices, and other vessels issue from it which convey these juices to the members.

One of the most curious problems of the physiology of white-blooded animals which has been resolved by M. Cuvier is that of the nutrition of insects. Insects, as has been already said, have, in place of a heart, only a simple dorsal vessel; and, moreover, this dorsal vessel has no branch, no ramification, no particular vessel which either enters or issues from it. This was already known through the celebrated researches of Malpighi, Swammerdam, and Lyonnet. But M. Cuvier goes much further; he examines, one after the other, all the parts of the bodies of insects, and by this detailed examination he shows that no sanguineous vessel, or, what amounts to the same thing, no circulation, exists in these animals. How, then, is their nutrition effected?

M. Cuvier begins by remarking that the final object of the circulation is to conduct the blood to the air. Hence all animals which have a heart have a circumscribed respiratory organ, whether lungs or branchiæ, and the blood returned from the members to the heart is invariably constrained to traverse this organ, in order to be there subjected to the action of the air before returning to the members. But in insects the apparatus of respiration is wholly different. It is no longer a circumscribed organ which receives the air; it is an immense number of elastic vessels, called trachea, which convey it into all parts of the body, and which thus conduct it even to the nutritive fluid itself, which continually bathes those parts. In a word, while in other animals it is the nutritive fluid which by means of the circulation goes in search of the air, the phenomenon is reversed in insects, and it is the air, on the contrary, which goes to seek the nutritive fluid, and thereby renders all circulation useless.‡

Another discovery of M. Cuvier, not less important, is that of the circulatory apparatus of certain worms, such as the earth-worm and leech, which had until then been confounded with those zoophytes of a structure incomparably more

*Poli had also preceded him in the anatomy of several molluscs, but of multivalve and bivalve molluses only.

Namely, the blue rhizostome.

We are speaking here only of perfect insects. Since the researches of M. Cuvier which I have at present in view, M. Carus has discovered in certain larvæ a sort of circulation, or rather a movement of the blood, which movement, however, is not effected in vessels proper.

simple, which live only in the interior of other animals.* By a remarkable singularity the blood of these worms, with a circulatory apparatus,t is red: a new circumstance to show how inexact and vague was the denomination of animals with white blood, given till then, in a general manner, to animals without vertebræ.

By means of these admirable investigations M. Cuvier, it will be seen, had fixed the limits of the class of mollusks; he had determined that of the vermes with red blood, he had completely separated both from that of the zoophytes; finally, he had marked the true place of the zoophytes themselves, thenceforth consigned to the extreme limit of the animal kingdom. But a principle which he had employed in all these researches must needs lead him still further. This principle is that of the subordination of organs or of characters.

Method should not limit itself, in effect, to representing indistinctly the relations of structure; it ought to mark, besides, the particular order of these relations and the relative importance of each, and it is precisely to this end that the principle of the subordination of organs serves. Bernard and Laurent de Jussieu had already applied this principle, as fruitful as it is infallible, to botany, but the zoologists had not yet ventured to make the application of it to their own science, determined, no doubt, by the great number and complication of the organs which constitute the animal body, and which, for the most part, are wanting in vegetables.

The principle of subordination of organs could only be introduced into zoology when preceded by anatomy. The first step to be taken was to know the organs; the determination of their relative importance could be only the second. These two steps accomplished, there remained only to found the characters on the organs, and to subordinate these characters one to the other, as the organs are subordinated among themselves. Such was properly the object of the Animal Kingdom distributed according to its organization, (Règne Animal, &c.,) that great work in which the new zoological doctrine of the illustrious author is displayed as at length reproduced in all its entireness and co-ordinated in all its parts.

Dating from this work the art of methods has assumed a new face. Linnæus, as is well known, had seen in this art only a means of distinguishing species. M. Cuvier was the first who undertook to make method the very instrument of the generalization of facts. Method, viewed in itself, is for him only the subordination of propositions, of truths, of facts, one to another, according to the order of their generality. Applied to the animal world, it is the subordination of groups among themselves, according to the relative importance of the organs which constitute the distinctive characters of those groups. Now, the most important organs are also those which involve the most general resemblances. Whence it follows that in founding the inferior groups on the subordinate organs, and the superior groups on the dominating organs, the superior groups will always necessarily comprise the inferior, or, in other terms, it will always be practicable to pass from one to the other by progressive propositions, becoming more and more general in proportion as we ascend from the inferior groups towards the superior.

Method, therefore, properly considered, is but the generalized expression of science; it is science itself, but science reduced to its most simple expressions; it is still more: this linking together of facts according to their analogies, this linking together of analogies according to their degree of comprehensiveness, is not limited to the representation of known relations; it brings to light a multitudo of new relations, contained one in another; it disengages them from one another; it thus gives new forces to the understanding for perceiving and discovering; it creates for the mind new processes of logic.

* Namely the intestinal worms, that class of zoophytes which, for the most part, can only live and propagate in the interior of the bodies of other animals.

t Worms with red blood of Cuvier: annélides of Lamarck.

Hitherto M. Cuvier had seen, in each of these grand classes of invertebrate animals, mollusks, insects and zoophytes, only a group like each of the four classes of vertebrate animals, quadrupeds, birds, reptiles and fishes. It was because he had as yet considered only the organs of circulation.

In considering the nervous system, which is a much more important organ, he saw that each of the three great classes of animals without vertebræ corresponded or was equivalent not to such or such a class of vertebrate animals taken separately, but to all these vertebrate animals taken together. A first form of the nervous system unites all these vertebrate animals in a single group; a second form unites all the mollusks; a third unites the insects to the worms with red blood, and both to the crustacea, constituting the group of articulata; a fourth form, finally, unites all the zoophytes. There are thus four plans, four types in the animal kingdom, four embranchements, as M. Cuvier calls them; or, in plainer terms, and divested of everything vague, there are four general forms of the nervous system in animals.

This

In the sciences of observation and experiment the supreme art of genius is to transform questions from simple questions of reasoning into questions of fact. For more than a century the question had been debated whether, in animals, there was but one plan of organization, or whether there were several. question, couched till then in terms so vague, is transformed by M. Cuvier into this other question, positive and to the point, namely, how many distinct forms are there of the nervous system in animals? Now, as I have just said, there are four-one for the vertebrata, one for the mollusca, one for the articulata, one for the zoophyta; these four plans or types comprising the whole animal kingdom. Such is the light thrown upon the animal kingdom by the great work under consideration that, guided by this, the mind is enabled precisely to apprehend the different orders of relation which connect animals with one another; the relations of conformity (d'ensemble) which constitute the unity, the character of the kingdom; the relations more or less general which constitute the unity of the embranchements, of the classes; the more particular relations which constitute the unity of the orders, of the genera.

Nevertheless, this work of so vast a scope, of such immense detail, was not yet what M. Cuvier would have wished. It is the property of genius always to see something beyond and better than all that it has done. And, indeed, though all the species had been reviewed in this great work, the greater part of them had been scarcely more than indicated; it was, therefore, only an abridged, not a complete system of animals. Now, the idea of a complete system of animals, a system in which all the species should be not only indicated, distinguished, classified, but represented and described in their whole structure, was one of those with which M. Cuvier was most constantly occupied. Hence, scarcely was this great treatise on the animal kingdom terminated, when another was already commenced, and on a plan not less vast. I mean the "Natural History of Fishes," (Histoire naturelle des poissons,) the first volume of which appeared in 1828.

After having effected, in the earlier of these two works, the complete reform of the system of animals, what he had wished in the second was to show, by a detailed and thorough exposition of all the known species of a class, what could be done for all other species and all other classes. With this view he had chosen the class of fishes as being, among all those of the vertebrata, the most numerous, the least known, and that most enriched by the recent discoveries of travellers. The latest authors of note in ichthyology, Bloch and Lacépède, were scarcely acquainted with so many species of fish as 1,400; in the work of M. Cuvier the number of species would have amounted to more than 5,000; the entire work would have included not less than 20 volumes, all the materials were placed in order, and the nine volumes which made their appearance in less than six years fully attest the wonderful rapidity with which it was intended that this vast undertaking should proceed.

Pressed by want of time I must deny myself all details on this work, so astonishing for its extent, and yet still more astonishing for that profound art in the formation of genera and families, of which the author seems to have delighted to unveil the most hidden secrets, and for that science of characters which no one ever possessed in an equal degree; results of experience and fruits of a genins arrived at its full maturity."

Such is the assemblage of great labors by which M. Cuvier has renovated zoology; but a reform still more important, and of which that is in reality but the consequence, is what he had already effected, or was at the same time effecting in comparative anatomy. It is impossible to speak of the progress which this science owed to the researches of M. Cuvier without profound respect and even grateful acknowledgment; he himself regarded this branch of investigation, and with justice, as the regulator of all those which relate to organized beings, and death surprised him still meditating that great work which he had consecrated to it, and in which, collecting anew all its forces, his vast genius would have undoubtedly appeared in all its grandeur. But though this work remained unaccomplished, its principal elements subsist, as they are scattered in various memoirs, especially in his Leçons d'anatomie comparée and his Recherches sur les ossements fossiles, immortal labors which have communicated to comparative anatomy such an impulsion that, after having been so long the most neglected of the branches of natural history, it has suddenly outstripped and taken the lead of all of them.

The history of comparative anatomy counts three epochs clearly markedthe epoch of Aristotle, that of Claude Perrault, and that of Cuvier. Every one knows with how much genius the foundations of the science were laid by Aristotle among the ancients. But what is not as well known, though not less worthy of being so, is the force of intellect with which Claude Perrault, at the middle of the seventeenth century, undertook the reconstruction of the entire science from its very base-that is to say, from the consideration of particular facts. His descriptions are the first assured step taken by comparative anatomy in modern times. Daubenton advanced it still another, for he rendered those descriptions comparable. Vicq-d'Azyr went yet further. Rich through the labors of Daubenton, of Haller, of Hunter, of Monro, of Camper, of Pallas, Vicq-d'Azyr embraced comparative anatomy in its completeness; he brought to it that penetrating genius which sees in science the end to be attained, and that spirit of sequence which attains it; and by no one more than by him was that great reform promoted which M. Cuvier finally achieved for the science in question.

It was certainly fortunate for this science to have passed immediately from the hands of one of these two eminent men into the hands of the other. Vicq-d'Azyr had thrown on it the glance of the physiologist; M. Cuvier threw on it more particularly that of the zoologist, and we may concede that it had an equal need of being considered under both these points of view. It may well be thought that its reform would not have been so complete and its influence so general except that, having been by turns studied and adapted with a view both to zoology and physiology, it has become alike for both the guide and the lumi

nary.

However this may be, comparative anatomy was still but a collection of particular facts touching the structure of animals, when M. Cuvier transformed it into the science of the general laws of the animal organization. After having transformed, as we have seen, the zoological method from being a simple nomenclature into an instrument of generalization, he now proceeded to dispose the facts in comparative anatomy in such an order that, from their simple collocation, have proceeded so many admirable and progressively ascending laws; as, for example, that each kind of organ has its fixed and determined modifications; that a con

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See, respecting this work, the developments which I present in my Histoire des Travaux de M. Cuvier.

stant relation connects all modifications of the organism with one another; that certain organs exert on the collective animal economy a more marked and decisive influence, whence the law of their subordination; that certain facts of organization necessarily involve the presence of each other, while there are such, on the contrary, as are incompatible and exclusive, one of the other, whence the law of their correlation or coexistence; besides so many other laws, so many other general relations, which have, in the end, created and developed the philosophic part of the science.

Among so many discoveries, so many particular facts with which he has enriched that science, I must necessarily confine myself to a citation of the most prominent, and still the catalogue of even these will be far from complete. The researches of Hunter and of Tenon had already afforded valuable contributions to the theory of the development of the teeth; it was Cuvier who carried this theory to a perfection beyond which there can be little to desire. Those little bones which we call teeth appear at first glance to be very simple, and scarcely to merit the attention of the observer. These little bodies, however, are very complex; they possess secretory organs, as their germ, their proper membrane; secreted. substances, such as their enamel, their ivory; and each of these substances appears in its turn, each at a fixed epoch. They spring up, are developed, push forth their roots, die, fall, and are replaced by others with admirable order and regularity. Nor is it less admirable, though under another point of view, that all the circumstances of their organization and development are today rigorously demonstrated. It was chiefly through a study of the teeth of the elephant, where everything is seen on a large scale, that M. Cuvier succeeded in establishing the precise epoch at which each part of the tooth is formed, and by what mechanism it is formed; how each of these parts, having performed its function of productive organ, disappears; how the entire tooth disappears in its turn to give place to another, which will also have its development, both in the whole and in detail, its point of complete organization, and its decay and its fall.

Perrault, Hérissant, Vicq-d'Azyr, had, before Cuvier, distinguished some points in the structure of the vocal organs of birds; he has made that structure known in a general manner and by detailed comparisons. It was he also who first placed in a clear light the singular arrangement of the organ of hearing, and still more singular arrangement of the nasal fosse in the cetaceous tribes.

Every one knows the marvellous metamorphosis experienced by the frog in passing from the state of fœtus or tadpole to the adult state. It is known that after having respired, in the first case, by gills, like the fishes, it respires, in the second, by lungs, like the terrestrial animals. M. Cuvier has taught us the structure of the organs of respiration and of circulation in a species of reptiles, which presents something still more curious. The frog is by turns a fish in its first stage, and a reptile in its second. These new reptiles, still more singular, such as the proteus, the axolotl, the siren, are all their life reptiles and fish; have all the time both branchiæ or gills and lungs, and can hence breathe alternately in the air and in water.

M. Cuvier again was the first to give a connected comparison of the brain in the four classes of vertebrate animals; the first to point out the relations of the development of that organ with the development of intelligence, a branch of comparative anatomy which has since become so fruitful and extensive; the first, in fine, to deduce in a rigorous manner from the respective quantity of respiration of these animals, not only the degree of their natural heat, but that of all their other faculties, their force of movement, their subtility of perception, their rapidity of digestion.

But the most novel and brilliant application which he has made of comparative anatomy, is that which relates to fossil bones. Every one now knows that the globe which we inhabit presents, almost everywhere, irrefutable traces of stupendous revolutions. The productions of the actual creation, of living nature,