Well does this extraordinary man enunciate the valuable truth, that since Natural History has taken Nature for the basis of its distri butions, its relationship with Anatomy has become more intimate. "One of these sciences," says he, "cannot take a single step without the other profiting by it. The approximations which the first establishes often indicate to the other the researches that ought to be made." And again, with equal truth he declares, that "the natural history of an animal is the knowledge of the whole animaL Its internal structure is to it as much as its external form, and perhaps more." That envier practised what he preached is evident from his own record of his mode of proceeding in constructing his system :— examined," says he, "one by one, all the species which I could procure ; I associated those which did not differ from each other, except in size, colour, or the number of some parts of little importance, and on these materials founded what I have called a sub-genus.
"Whenever I could, I dissected at least one species of each sub genus ; and if those to which the scalpel could not be applied be excepted, there exist in my book very few groups of this degree, of the organs of which I cannot produce at least some considerable portion." As in this work the various articles on the Animal Kingdom will 'be generally given subordinate to the great divisions indicated by Cuvier, we have added in the following page his arrangement in a tabular form.
The following are the distinguishing characters of the great divisions of this arrangement : Vertebrate Animals (Animalia vertebrata.)—They have all red blood, a muscular heart, a mouth furnished with two jaws placed one either before or above the other, distinct organs of sight, hearing, smell, and taste, situated in the cavities of the face ; never more than four limbs, the sexes always separated, and a very similar distribution of the medullary masses and of the principal branches of the nervous system. On examining each of the parts of this great series of animals more closely, there may always be detected some analogy even in those species' which are most remote front one another ; and the gradations of one single plan may be traced from man to the last of fishes.
In the second form there is no skeleton, the muscles are attache I only to the skin, which constitutes a soft contractile envelope, in which in many species are formed stony plates called shells, the pro duction and position of which are analogous to that of the mucous body ; the nervous system is contained within this general envelope together with the viscera, and is composed of several scattered masses, connected by nervous filaments, and of which the principal placed over the ccsophagus bears the name of brain. Of the four senses, the organs of those of taste and vision only can be distinguished, the latter of which are even frequently wanting. A single family alone presents organs of hearing. There is always, however, a complete
system of circulation, and particular organs for respiration. Those of digestion and of the secretions are little less complicated than in the vertebrated animals. We will distinguish the animals of this second form by the appellation of Molluscous Animals (Animalia Mollusca.)—Although the general plan of their organisation is not so uniform, as regards the external configuration of the parts as that of the vertebrates, there is always an equal degree of resemblance between them in the essential structure and the functions.
The third form is that observed in insects, worms, &c. Their nervous system consists of two long cords running longitudinally through tho abdomen, dilated at intervals into knots or ganglions. The first of these knots placed over the cesophagus, and called brain, is scarcely any larger than those which are along the abdomen, with which it communicates by filaments that encircle the oesophagus like a collar. The envelope of their trunk is divided by transverse folds into a certain number of rings, of which the teguments are sometimes hard, sometimes soft, but to the interior of which the muscles are always attached. The trunk often bears on its sides articulated limbs, but is frequently unfurnished with them. We will bestow on these animals the term Articulate Animals (Animalia Articulata.)—It is among these that the passage is observed from the circulation in closed vessels to nutri tion by imbibition, and the corresponding transition from respiration in circumscribed organs to that effected by tracheto or air-vessels dis tributed through the body. The organs of taste and vision are the most distinct in them, a single family alone presenting that of hearing. Their jaws, when they have any, are always lateral.
Lastly, the fourth form, which embraces all those animals known under the name of Zoophytes, may be designated Radiate Animals (Animalia Radiata.)—In all the preceding, the organs of sense and motion are arranged symmetrically on the two sides of an axis. There is a posterior and an anterior dissimilar face. In this last division, they are disposed as rays round a centre ; and this is the case even when they consist of but two series, for then the two faces are alike. They approximate to the homogeneity of plants, having no very distinct nervous system, nor organs of particular senses : there can scarcely be perceived in some of them the vestiges of a circula tion ; their respiratory organs are almost always on the surface of the body; the greater number have only a sac without issue for the whole intestine ; and the lowest families present only a sort of homogeneous pulp endowed with motion and sensi bility. Since the time of Cuvier con siderable advances have been made, especially in our knowledge of the lower forms of invertebrate animals, and many of his orders have been broken up and considerably modified.