38 Scientific Reviews. 



which occurs among the vertebrated animals, if we represented a 

 cephalopodous molluscum to ourselves as a vertebral animal, whose 

 trunk had been bent back upon itself to the height of the umbili- 

 cus, so that the pelvis should come in opposition with the neck. 

 •' One of our learned brethren/' said M. Cuvier, " seizing with en- 

 thusiasm this new view, announced that it completely refuted every- 

 thing I had said upon the distance which separates the moUusca 

 from the vertebrated animals. Going even much farther than the 

 authors of the memoir, he concluded from it that zoology has, to the 

 present day, had no solid basis, — that it has been an edifice con- 

 structed only on sand, — and that its only indestructible base will 

 be a principle which he calls the ' unity of composition.' 



M. Cuvier, determined to discuss the reality of this principle, 

 began by examining the question in its particular relation with the 

 mollusca. 



" But before every thing," said he, " it is necessary to define the 

 terms clearly, and to determine what we understand by the expres- 

 sions ' unity of composition,' ' unity of plan.' If we took the words 

 in their most rigorous acceptation, we could only say that there is 

 unity of composition in two kinds of animals, when they are com- 

 posed of the same organs ; and to prove that there is unity of plan 

 in their organization, it would be required to show that these iden- 

 tical organs are disposed in the same order in both of the animals. 



" Now, it is impossible to suppose that the naturalists who speak 

 of unity of composition and of unity of plan, in the whole animal 

 kingdom, have thus understood things, or that they wished to as- 

 sert that all animals are composed of the same organs, arranged in 

 the same manner. 



" The terms thus defined, the principal of unity, restrained as 

 it ought to be, appears an incontestable truth, but is far from 

 being new. It forms, on the contrary, one of the bases upon which 

 zoology has reposed from its origin, — one of the principles upon 

 which Aristotle, its creator, founded it, — a basis upon which all 

 zoologists, worthy of that name, have sought to enlarge, and to the 

 establishment of which all the efforts of anatomy have been di- 

 rected. 



" Thus every day we can discover in an animal a part with 

 which we were not acquainted, and which allows us to seize upon 

 some further analogy between that animal, and those of the different 

 genera and classes. It may be the same with respect to connexions 

 of the relations newly perceived. Labours undertaken in this di- 

 rection are eminently useful, and those of Mr. Geoffroy St. Hilaire, 

 in particular, are worthy of the esteem of all naturalists. When, 

 for example, he discovered that in comparing the head of a foetus 

 of a quadruped with that of a reptile or an oviparous animal, rela- 

 tions may be remarked in the number and the arrangement of 

 pieces, which could not be perceived in adult heads, — when he 

 proved that the os qtiadratiim in birds, is analogous to the tympa- 

 num in the foetus of mammiferae, he made real and important dis- 



