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CHAPTER VII.

PROGRESS OF ANIMAL MORPHOLOGY.

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Sect. 1.-Rise of Comparative Anatomy.

HE most general and constant relations of the form of the organs, both in plants and animals, are the most natural grounds of classification. Hence the first scientific classifications of animals are the first steps in animal morphology. At first, a zoology was constructed by arranging animals, as plants were at first arranged, according to their external parts. But in the course of the researches of the anatomists of the seventeenth century, it was seen that the internal structure of animals offered resemblances and transitions of a far more coherent and philosophical kind, and the science of Comparative Anatomy rose into favour and importance. Among the main cultivators of this science at the period just mentioned, we find Francis Redi, of Arezzo; Guichard-Joseph Duvernay, who was for sixty years Professor of Anatomy at the Jardin du Roi at Paris, and during this lapse of time had for his pupils almost all the greatest anatomists of the greater part of the eighteenth century; Nehemiah Grew, secretary to the Royal Society of London, whose Anatomy of Plants we have already noticed.

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But Comparative Anatomy, which had been culti vated with ardour to the end of the seventeenth century, was, in some measure, neglected during the first two-thirds of the eighteenth. The progress of botany was, Cuvier sagaciously suggests, one cause of this; for that science had made its advances by confining itself to external characters, and rejecting anatomy; and though Linnæus acknowledged the dependence of zoology upon anatomy so far as to make

1 Cuv. Leçons sur l'Hist. des Sc. Nat. 414, 420.
2 Cuv. Hist. Sc. Nat. i. 301.
3 Ib.

the number of teeth his characters, even this was felt, in his method, as a bold step. But his influence was soon opposed by that of Buffon, Daubenton, and Pallas; who again brought into view the importance of comparative anatomy in Zoology; at the same time that Haller proved how much might be learnt from it in Physiology. John Hunter in England, the two Munros in Scotland, Camper in Holland, and Vicq d'Azyr in France, were the first to follow the path thus pointed out. Camper threw the glance of genius on a host of interesting objects, but almost all that he produced was a number of sketches; Vicq d'Azyr, more assiduous, was stopt in the midst of a most brilliant career by a premature death.

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Such is Cuvier's outline of the earlier history of comparative anatomy. We shall not go into detail upon this subject; but we may observe that such studies had fixed in the minds of naturalists the conviction of the possibility and the propriety of considering large divisions of the animal kingdom as modifications of one common type. Belon, as early as 1555, had placed the skeleton of a man and a bird side by side, and shown the correspondence of parts. So far as the case of vertebrated animals extends, this correspondence is generally allowed; although it required some ingenuity to detect its details in some cases; for instance, to see the analogy of parts between the head of a man and of a fish.

In tracing these less obvious correspondencies, some curious steps have been made in recent times. And here we must, I conceive, again ascribe no small merit to the same remarkable man who, as we have already had to point out, gave so great an impulse to vegetable morphology. Göthe, whose talent and disposition for speculating on all parts of nature were truly admirable, was excited to the study of anatomy by his propinquity to the Duke of Weimar's cabinet of natural history. In 1786, he published a little essay, the object of which was to show that in man, as well as in beasts, the upper jaw contains an intermaxillary bone, although

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the sutures are obliterated. After 1790, animated and impelled by the same passion for natural 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 Introduc tion 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 labours 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

4 Zur Morphologie, i. 2 34.

Spix, Cephalogenesis.

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5 Ib 250.

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French Academy in February 1824, entitled Composition de la Tête osseuse 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 that the skull of all vertebrate animals is pretty well reduced to a uniform structure, and the laws of its variations nearly determined.7

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 developement or addition of some parts which do not produce any essential change in the plan.

These four great branches of the animal world are 7 Cuv. Hist. Sc. Nat. iii. 442. 8 Regne Animal, p. 57,

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 back-bone 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 seaanimals.

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, 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

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