be called by the same name. In like manner, since the organization of the mollusks had become known, it could no longer be pretended that there were not between these animals many more differences than between the animals of a single class of vertebrata; and consequently again, since there was no parity between the beings comprised in these two divisions, there was no parity of division, and there ought, therefore, to be no parity of name.

But this was not all. By still comparing the structures, and taking them for a guide, it was not less evident that the crustaceans united to the insects, and these two groups to that of the worms with red blood, or annelids, formed by their importance, by the number of their species, by their structures so essentially diverse, a third division, similar either to that of the vertebrata or to that of the mollusks; and that all other animals, united thenceforth under the name of zoophytes, formed a fourth division similar to each of the three preceding. Considered under this new point of view the animal kingdom presents therefore four grand divisions or branches that of the vertebrata, that of the molluscas, that of the articulata, and that of the zoophyta.

Each of these divisions is formed on a particular and distinct plan; that is to say, one which cannot be reduced to that of the others; and they are all like one another in being of the same order; that is to say, that the beings they include present, in their structure, similar or equivalent resemblances or differences. Thus the vertebrata have their plan, the mollusks have theirs, the articulata, the zoophytes have theirs, and all these plans are alike circumscribed; that is to say, that no shading, no intermediary, no lien, can make them pass from one to the other without a rupture, without a saltus. A kind of circumvallation separates them. We can pass by modifications more or less graduated from man, considered in his organization to the other mammifers, from mammifers to birds, from birds to reptiles, from reptiles to fishes; but from fishes to mollusks, from mollusks to articulata, from articulata to zoophytes, there is no longer any gradation or natural transition. All at once the plan changes and a new form shows itself; but taken in itself this new form, this new type, is equally constant, prevalent, uniform; all the mollusks repeat as exactly their own type as the vertebrata, the articulata, the zoophytes, repeat theirs. Thus, in the immense chain of the animal kingdom there are four great forms, four grand types, and there are but four.

This capital fact is equally worthy of note whether we consider it as showing that, with the exception of a few secondary modifications, all animals enter exactly into one or the other of these great forms, or whether we consider it as showing that between each of these great forms there is no shading, no gradation, no intermediate form. The vertebrata alone have a spinal marrow, a long medullary cone, into the sides of which enter the nerves, and which is enlarged at its anterior extremity to form the encephalon; they alone have a double nervous system, that of the spinal marrow and that of the great sympathetic; they alone have a canal composed of bony or cartilaginous vertebrae. But all of them have this spinal marrow, this great sympathetic, these vertebræ; all have senses to the number of five, horizontal jaws to the number of two, red blood, a muscular heart, a system of chyliferons and absorbent vessels, a liver, a spleen, a pancreas, kidneys, &c. In a word, the more we examine their whole organization the more resemblances do we discover.

But the more differences do we also find as regards the other embranchments. The mollusks, for example, have also a brain, though infinitely reduced; but they have no spinal marrow, and consequently no vertebræ; they have no great sympathetic, and their single nervous system, instead of being placed above the digestive canal, as in the vertebrate animals, is always placed, with the exception of the single ganglion which represents the brain, below that canal, being consigned to the viscera; in fine, they have neither a true skeleton nor absorbent vessels, nor spleen, nor pancreas, nor vena-porta, nor kidneys; the organ of smell

is wanting in all; that of sight in many; a single family possesses that of hearing, &c., but they all have a complete and double system of circulation, circumscribed respiratory organs, a liver, &c. In a word, if, by the want of a spinal marrow, of vertebræ, of a skeleton, a great sympathetic, &c., they differ essentially from the vertebrates, they seem, by the richness of their vital organs, by their double circulation, their respiration, their liver, &c., to come immediately after them, and hence to deserve to form the second of the four branches of the animal kingdom. The third, or that of the articulata, differs not less from that of the mollusks than these differ from the vertebrata. The animals of this branch have a small brain like the mollusks, and this small brain is also situated upon the œsophagus ; but, what is wanting in the mollusks, they have a sort of spinal marrow composed of two cords which run along the belly and unite themselves with it from space to space by knots or ganglions from which issue the nerves; and yet this spinal marrow, which distinguishes them from the mollusks, does not associate them with the vertebrates, for, inversely as regards that of the vertebrates, always placed above the digestive canal, it is always placed below. By an opposite inversion the heart, which is below this canal in the vertebrata, is above in the articulata; and what I have just said of their spinal marrow may be said of their skeleton, when they have one; it is that this skeleton, while it divorces them from the mollusks, is not a feature which unites them with the vertebrates; for, inversely to that of the vertebrates, which is internal and covered by the muscles, it is external and covers the muscles. Again, in a word, the features which separate the articulata from the mollusks are essential and profound, and such as decide the nature of beings, and the features which seem to connect them with the vertebrates do so only in appearance.

The fourth branch presents characters not less circumscribed, not less determinate than the others. The first of these characters is that all the parts are disposed around a centre, like the radii of a circle; the second is the degradation, the successive simplification of their structure. From the first character is derived the name of radiata, or animals of which all the parts are radiate or stellate; and from the second that of zoophytes, or animal plants, animals which, in the simplicity of their organization, approach most nearly to plants. Thus the animal kingdom has four great types or forms, and a little consideration will disclose that each of these general forms of the body depends on the form itself of the dominant system of the animal economy; that is, on the nervous system. The vertebrate animals have a trunk on each side of which all their parts are symmetrically arranged; it is because their nervous system forms a central medullary cone, from each side of which proceed, in symmetrical order, the nerves of all those parts. The mollusks have a mass-like body; it is because their nervous system has but a confused arrangement. To the body of the articulata some degree of symmetry is restored, but it had been first impressed on their nervous system; the body is articulated externally, for the nervous system is articulated in the interior; in fine, even in the radiated animals, whenever the last vestiges of the nervous system are distinguishable it presents that star-like form which is affected by the whole body."

The form of the nervous system, then, determines the form of the animal; and the reason of this is simple: it is that, on the whole, the nervous system is virtually the animal, and all the other systems are present only for its service and sustentation. It is in nowise surprising, therefore, that, the form of this system remaining the same for each embranchment of the animal world, the general form of each should remain the same; nor that, this form changing from one embranchment to another, the form of each embranchment should change.

* * Having thus seen that the modifications of the nervous system give the first groups, the first divisions or embranchments, it follows from the principle of subordination of characters, which is but another expression for the subordination of the organs themselves, that the modifications of the organs of circula

tion and respiration, which come immediately after the nervous system in the order of their importance, will give the first subdivisions, or the classes. The vertebrate animals present either a simple and complete respiration, with a double circulation, which is the case with the mammifers; or a double respiration and double circulation, which is the case with birds; or a simple respiration, but complete one, since it is always aerial, and this combined with a simple circulation, being the case of reptiles; or a double circulation, combined with an incomplete, that is to say an aquatic, respiration, which is the case with fishes. Hence the vertebrate animals are distributed, according to their organs of circulation and respiration combined, into four classes-the mammifers, birds, reptiles, and fishes.

So it is, also, with the mollusks; some have three hearts, others two, others one of these hearts there are such as have but a single ventricle and a single auricle; others a single ventricle and two auricles; others, again, a single ventricle without an auricle, &c.; in fine, certain mollusks respire by a pulmonary cavity, others by branchiæ, &c.; and it will be readily conceived that the combination of all these variations of respiratory and circulatory organs will furnish classes of mollusks as it furnished the classes of vertebrata. The classes of mollusks, thus determined, are six in number-cephalopods, gasteropods, acephalates, pteropods, brachiopods, and cirrhopods.

The combination of the organs under consideration will give us, likewise, and in even a still more striking manner, the subdivision of the third branch into four classes: the annelids, whose blood is red like that of the vertebrata; the crustacea, whose blood is white like that of all other animals without vertebræ, and which, moreover, have a heart placed in the back, &c.; the arachnids, which have for heart only a simple dorsal vessel which sends forth arterial branches and receives venous ones; and insects, which have no vessels at all, neither arteries nor veins, which have only the vestige of a heart, and whose respiration is not effected by circumscribed organs, but by trachea, or elastic vessels distrib uted through the whole body. In this branch of the articulata we observe, therefore, the transition from animals which have a circulation to those which have none, and the corresponding transition from those which respire by means of circumscribed branchia to those in which tracheæ distribute the air to every part.

It is in the fourth branch, or that of zoophytes, or the radiata, that we observe the disappearance, the gradual and successive fusion of all the organs into the general mass. Thus, some of these animals have still closed vessels, distinct organs of respiration, &c.; others, which have neither such vessels for circulation nor such organs for respiration, have still visible intestines; it is only in the last of all that everything seems reduced to a homogeneous pulp; and it is on the different degrees of complication in their structure that is founded their subdivision into five classes: echinoderms, intestinal worms, acalephs, polyps, and infusoria.

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Thus the nervous system has furnished the branches; the organs of circulation and respiration combined, the classes; and it is easy to conceive that organs more and more subordinate would successively supply the orders, the families, the tribes, the genera, the sub-genera, in a word, the whole scaffolding of the method. Thus as regards the mammals, for instance, (for it would detain us too long to follow the unfolding of the method in all the classes,) the combined organs of touch and of manducation divide this class into nine orders: man, who has three sorts of teeth, (molar, canine, and incisive,) and who has the opposable thumb on the two anterior extremities alone; the quadrumana, which have also the three sorts of teeth, and, moreover, the opposable thumb on the four extremities; the carnivora, which again have the three sorts of teeth, but no opposable thumb and consequently no hands, which have only feet, but feet of which the digits or toes are movable, like those of the two above orders; the rodents, whose

toes differ little from those of the carnivora, but which have only two sorts of teeth, the molar and incisive; the edentata, in which order the toes have become less movable, and are almost confounded with large claws, and which have never any teeth but the molar and canine, sometimes only molar, and sometimes none at all; the marsupials, or animals with a pouch, a small series collateral to the three preceding orders, some of them corresponding to the carnivora, others to the rodentia, and others to the edentata; the ruminants, which form a strikingly distinct order in view of their cloven feet, their upper jaws without true incisors, their four stomachs; the pachydermata, which comprise all the other quadrupeds with hoofs; and the cetacea, which are wholly destitute of posterior extremities. The principal modifications of the combined organs of touch and manducation having given the orders, secondary modifications of these same organs will supply the families; and modifications more and more subordinated will give all the other groups, the tribes, the genera, the sub-genera, until we finally reach the species for which the whole scaffolding is constructed.

Thus, to confine ourselves again to a single order of the mammifers, that of the carnivora, for example, it has just been seen that one of the characters of that order is to have movable toes. Now, if we suppose these toes to have become very long, and to be united by membranes, so as to form an organ of flight, as in the bats, we shall have the family of cheiroptera; if we suppose that the animal, the toes remaining free, supports itself in walking on the entire sole of the foot, or, on the contrary, that it walks only on the ends of its toes, we shall have in the first case the tribe of the plantigrades, and in the second that of the digitigrades. And similarly as regards the organs of manducation, it has been seen that this order has three sorts of teeth, and it is this which constitutes its character as an order; but let us suppose that the molar teeth (which by their form always decide the diet of the animal) are feeble, and furnished with conic points, and we shall have the family of insectivora; or that these same teeth have become stronger, and, instead of simple conic points, are armed with parts more or less incisive, and we shall in that case have the family of carnivora ; and in this latter family, according as the molar teeth are entirely cutting or incisive, or more or less mingled with blunt tubercles, we shall have either the genus bear, of which almost all the teeth are tubercular; or that of dogs, which have only two tubercular; or that of cats, &c., which have none tubercular, and which consequently are exclusively carnivorous, while the dog is capable of receiving a certain amount of vegetable nourishment, and the bear may be entirely nourished on vegetable food. And herein lies one of the necessary relations between the organs which enables us to calculate with considerable certainty the proportions of the alimentary canal, from the extent of the tubercular surface of the teeth of animals, compared with the cutting or incisive surface.

What has been here said might be easily exemplified as regards all other families, tribes, and genera; and it will hence be seen that the simple placing of an animal in one of these groups, teaches us as exactly as the most detailed description, all that relates to the organization of that animal, or to the degree of organization which corresponds to the group in which it is placed. Let me be told, for instance, of some creature that its place is in the genus cat, and I shall at once conclude not only that its molar teeth are all sharp or incisive, as being a cat, but further, that it has three sorts of teeth, movable toes, &c., as being carnivorous; that it has a doble circulation and a complete respiration, as being a mammal; that it has, also, a spinal marrow, a canal composed of vertebræ, five senses, &c., as being one of the vertebrata. Thus I shall know the whole of its organization from its place alone, and what will remain for me to say of it will, of course, be reduced to a few words, for the indication of its proper or specific characters.

Now, as the number of known beings is immense, and, immense as it is, cannot fail to be much more augmented, we perceive the advantage of being able

thus to substitute a few words for a complete description; of having to say nothing of each species but what is proper to it; of being able to supply, by its place alone, all that it has in common with all the rest of the kingdom; but we also perceive that, for method to afford this advantage, it is necessary both that all its groups should be rigorously subordinated among one another, and that each of them should comprise only beings of the same structure.

Groups well constituted, alone admit of general propositions. Without general propositions there can be no method; without method no brevity; the highest merit of all science in which the number of facts is immense, as it is in every branch of the history of the beings of nature. A genus, a family, an order, illconstituted, stands in the way of every general proposition relating to that genus, family, or order. Thus, by placing the siren and the cel in the same genus, Gmelin rendered it impossible to say anything general upon that genus; by placing the cuttle-fish and the fresh-water polyp in the same order, he made it impossible to say anything general upon that order; and by placing the mollusks, the worms, and the zoophytes in the same class, Linnæus had rendered every general proposition relative to that class impossible, &c.

By means of well-constituted groups, then, we are enabled to say, at one time, for all the species they contain, what it would have been necessary, otherwise, to repeat as many times as there had been species remaining dispersed and detached. But, among all these groups, and under the point of view with which I am here concerned, the genera have an importance which is proper to themselves. It is, that being the first approximation of species, all the rest of the scaffolding is, so to say, founded upon them, and an ill-constructed genus would suffice to break the unity of a family, of an order, of an entire class. Besides, being nearer to the species, the more they shall combine only such species as are conformable with one another, the less there will remain to say for each of them; and it is herein that may be seen all the inconvenience of those large genera, into which, even of late, so many incongruous species have been thrust, and all the advantage of intersecting those genera by sub genera-a happy expedient which forestalls confusion, by approximating in a closer manner the species which present resemblances more particular or more intimate.

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But all this work of genera, sub-genera, &c., of which we have been speaking, supposes a work not less considerable, the positive establishment, namely, of species-a point in which the animal kingdom presented not less confusion than in all the others. It was not sufficient to have remodelled or created almost all the divisions of that kingdom; it was incumbent on M. Cuvier to revise all the species, to revise them one by one, and even their synonyms; for sometimes several were confounded under the same name, sometimes a single one passed, under different names, for several; and this criticism of so many names, imposed right or wrong, on such a number of species, was assuredly neither the part of the work which offered least difficulty to the author, nor that which has saved his successors least embarrassment. It suffices, in effect, to cast the eyes on the works upon natural history which have appeared since the first edition of the Règne animal, to see the happy fruits which have resulted from these labors upon synonyms of which I now speak, and that art of establishing divisions in the comprehensive genera of which I had been previously speaking.

I have said, with reference to branches, and again with reference to classes, that each of these groups is definitely circumscribed; as much may be said of all other groups in every degree. Linnæus had pronounced that "nature makes no leaps;" and Bonnet, that "the chain of beings is but one continuous line." The very reverse of these propositions would be much more exact. The truth is, that the different groups are separated from one another by intervals more or less marked and profound; and there is, in the very organization of the animals, an evident reason for all these intervals.

The organization of an animal is only, in effect, a certain combination of organs;