observation and for general views, which had produced his Metamorphosis of Plants, he pursued his speculations on these subjects eagerly and successfully. And in 1795, he published a Sketch of a Universal Introduction into Comparative Anatomy, beginning with Osteology ; in which he attempts to establish an "osteological type," to which skeletons of all animals may be referred. I do not pretend that Göthe's anatomical works have had any influence on the progress of the science comparable with that which has been exercised by the labors of professional anatomists; but the ingenuity and value of the views which they contained was acknowledged by the best authorities; and the clearer introduction and application of the principle of developed and metamorphosed symmetry may be dated from about this time. Göthe declares that, at an early period of these speculations, he was convinced that the bony head of beasts is to be derived from six vertebræ. In 1807, Oken published a "Program" On the Signification of the Bones of the Skull, in which he maintained that these bones are equivalent to four vertebræ; and Meckel, in his Comparative Anatomy, in 1811, also resolved the skull into vertebræ. But Spix, in his elaborate work Cephalogenesis, in 1815, reduced the vertebræ of the head to three. "Oken," he says," "published opinions merely theoretical, and consequently contrary to those maintained in this work, which are drawn from observation." This resolution of the head into vertebræ is assented to by many of the best physiologists, as explaining the distribution of the nerves, and other phenomena. Spix further extended the application of the vertebral theory to the heads of all classes of vertebrate animals; and Bojanus published a Memoir expressly on the vertebral structure of the skulls of fishes in Oken's Isis for 1818. Geoffroy Saint-Hilaire presented a lithographic plate to the French Academy in February 1824, entitled Composition de la Tête osseuze chez l'Homme et les Animaux, and developed his views of the vertebral composition of the skull in two Memoirs published in the Annales des Sciences Naturelles for 1824. We cannot fail to recognize here the attempt to apply to the skeleton of animals the principle which leads botanists to consider all the parts of a flower as transformations of the same organs. How far the application of the principle, as here proposed, is just, I must leave philosophical physiologists to decide. By these and similar researches, it is held by the best physiologists 5 Zur Morphologie, 250. 6 • Spix, Cephalogenesis. that the skull of all vertebrate animals is pretty well reduced to a uniform structure, and the laws of its variations nearly determined.' The vertebrate animals being thus reduced to a single type, the question arises how far this can be done with regard to other animals, and how many such types there are. And here we come to one of the important services which Cuvier rendered to natural history. Sect. 2.-Distinction of the General Types of the Forms of Animals. -Cuvier. ANIMALS were divided by Lamarck into vertebrate and invertebrate; and the general analogies of all vertebrate animals are easily made manifest. But with regard to other animals, the point is far from clear. Cuvier was the first to give a really philosophical view of the animal world in reference to the plan on which each animal is constructed. There are, he says, four such plans;-four forms on which animals appear to have been modelled; and of which the ulterior divisions, with whatever titles naturalists have decorated them, are only very slight modifications, founded on the development or addition of some parts which do not produce any essential change in the plan. 8 These four great branches of the animal world are the vertebrata, mollusca, articulata, radiata; and the differences of these are so important that a slight explanation of them may be permitted. The vertebrata are those animals which (as man and other sucklers, birds, fishes, lizards, frogs, serpents) have a backbone and a skull with lateral appendages, within which the viscera are included, and to which the muscles are attached. The mollusca, or soft animals, have no bony skeleton; the muscles are attached to the skin, which often includes stony plates called shells; such molluscs are shell-fish; others are cuttle-fish, and many pulpy sea-animals. The articulata consist of crustacea (lobsters, &c.), insects, spiders, and annulose worms, which consist of a head and a number of successive annular portions of the body jointed together (to the interior of which the muscles are attached), whence the name. Finally, the radiata include the animals known under the name of zoophytes. In the preceding three branches the organs of motion and of sense were distributed symmetrically on the two sides of an axis, "Cuv. Hist. Sc. Nat. iii. 442. 8 Règne Animal, p. 57. so that the animal has a right and a left side. In the radiata the similar members radiate from the axis in a circular manner, like the petals of a regular flower. The whole value of such a classification cannot be understood without explaining its use in enabling us to give general descriptions, and general laws of the animal functions of the classes which it includes; but in the present part of our work our business is to exhibit it as an exemplification of the reduction of animals to laws of Symmetry. The bipartite Symmetry of the form of vertebrate and articulate animals is obvious; and the reduction of the various forms of such animals to a common type has been effected, by attention to their anatomy, in a manner which has satisfied those who have best studied the subject. The molluscs, especially those in which the head disappears, as oysters, or those which are rolled into a spiral, as snails, have a less obvious Symmetry, but here also we can apply certain general types. And the Symmetry of the radiated zoophytes is of a nature quite different from all the rest, and approaching, as we have suggested, to the kind of Symmetry found in plants. Some naturalists have doubted whether these zoophytes are not referrible to two types (acrita or polypes, and true radiata,) rather than to one. 9 This fourfold division was introduced by Cuvier.10 Before him, naturalists followed Linnæus, and divided non-vertebrate animals into two classes, insects and worms. "I began," says Cuvier, "to attack this view of the subject, and offered another division, in a Memoir read at the Society of Natural History of Paris, the 21st of Floreal, in the year III. of the Republic (May 10, 1795,) printed in the Decade Philosophique in this, I mark the characters and the limits of molluscs, insects, worms, echinoderms, and zoophytes. I distinguish the redblooded worms or annelides, in a Memoir read to the Institute, the 11th Nivose, year X. (December 31, 1801.) I afterwards distributed these different classes into three branches, each co-ordinate to the branch formed by the vertebrate animals, in a Memoir read to the Institute in July, 1812, printed in the Annales du Muséum d'Histoire Naturelle, tom. xix." His great systematic work, the Règne Animal, founded on this distribution, was published in 1817; and since that time the division has been commonly accepted among naturalists. [2nd Ed.] [The question of the Classification of Animals is discussed in the first of Prof. Owen's Lectures on the Invertebrate Ani 9 Brit. Assoc. Rep. iv. 227. 1 Règne A, 61. mals (1843). Mr. Owen observes that the arrangement of animals into Vertebrate and Invertebrate which prevailed before Cuvier, was necessarily bad, inasmuch as no negative character in Zoology gives true natural groups. Hence the establishment of the sub-kingdoms, Mollusca, Articulata, Radiata, as co-ordinate with Vertebrata, according to the arrangement of the nervous system, was a most important advance. But Mr. Owen has seen reason to separate the Radiata of Cuvier into two divisions; the Nematoneura, in which the nervous system can be traced in a filamentary form (including Echinoderma, Ciliobrachiata, Cælelmintha, Rotifera,) and the Acrita or lowest division of the animal kingdom, including Acalepha, Nudibrachiata, Sterelmintha, Polygastria. Sect. 3.-Attempts to establish the Identity of the Types of Animal Forms. SUPPOSING this great step in Zoology, of which we have given an account, the reduction of all animals to four types or plans,-to be quite secure, we are then led to ask whether any further advance is possible;—whether several of these types can be referred to one comon form by any wider effort of generalization. On this question there has been a considerable difference of opinion. Geoffroy Saint-Hilaire," who had previously endeavored to show that all vertebrate animals were constructed so exactly upon the same plan as to preserve the strictest analogy of parts in respect to their osteology, thought to extend this unity of plan by demonstrating, that the hard parts of crustaceans and insects are still only modifications of the skeleton of higher animals, and that therefore the type of vertebrata must be made to include them also:-the segments of the articulata are held to be strictly analogous to the vertebræ of the higher animals, and thus the former live within their vertebral column in the same manner as the latter live without it. Attempts have even been made to reduce molluscous and vertebrate animals to a community of type, as we shall see shortly. Another application of the principle, according to which creatures the most different are developments of the same original type, may be discerned12 in the doctrine, that the embryo of the higher forms of animal life passes by gradations through those forms which are perma 11 Mr. Jenyns, Brit. Assoc. Rep. iv. 150. 12 Dr. Clark, Report, Ib. iv. 113. nent in inferior animals. Thus, according to this view, the human fœtus assumes successively the plan of the zoophyte, the worm, the fish, the turtle, the bird, the beast. But it has been well observed, that "in these analogies we look in vain for the precision which can alone support the inference that has been deduced;" and that at each step, the higher embryo and the lower animal which it is supposed to resemble, differ in having each different organs suited to their respective destinations. པ་*ཡ་་ Cuvier1* never assented to this view, nor to the attempts to refer the different divisions of his system to a common type. "He could not admit," says his biographer, "that the lungs or gills of the vertebrates are in the same connexion as the branchia of molluscs and crustaceans, which in the one are situated at the base of the feet, or fixed on the feet themselves, and in the other often on the back or about the arms. He did not admit the analogy between the skeleton of the vertebrates and the skin of the articulates; he could not believe that the tænia and the sepia were constructed on the same plan; that there was a similarity of composition between the bird and the echinus, the whale and the snail; in spite of the skill with which some persons sought gradually to efface their discrepancies." Whether it may be possible to establish, among the four great divisions of the "Animal Kingdom," some analogies of a higher order than those which prevail within each division, I do not pretend to conjecture. If this can be done, it is clear that it must be by comparing the types of these divisions under their most general forms: and thus Cuvier's arrangement, so far as it is itself rightly founded on the unity of composition of each branch, is the surest step to the discovery of a unity pervading and uniting these branches. But those who generalize surely, and those who generalize rapidly, may travel in the same direction, they soon separate so widely, that they appear to move from each other. The partisans of a universal "unity of composition of animals, accused Cuvier of being too inert in following the progress of physiological and zoological science. Borrowing their illustration from the political parties of the times, they asserted that he belonged to the science of resistance, not to the science of the movement. Such a charge was highly honorable to him; for no one acquainted with the history of zoology can doubt that he had a great share in the impulse by which the "movement" was occasioned; or that he him 18 Dr. Clark, p. 114. 14 Laurillard, Elog. de Cuvier, p. 66. |