154, HISTORY OF THE WOEKS OF CUVIER. 



of tlie human T)0(ly and that of quadvupcds, birds, and fislies, and shows how, by 

 gradual changes from a horizontal to a vertical attitude, it is possible "to trans- 

 form a cow into a bird, a quadruped into a man, &c." Finally this striking idea 

 is seen pervading the writings of Vicq-d'Azyr, who says that " nature seems always 

 to work after a primitive and general pattern, from which she deviates only with 

 reluctance ; that we observe every where those two characters which seem impressed 

 on all beings, that of constancy in the type and variety in the modifications."* 



Nevertheless, this opinion of a constant unifonniti/ of design, oi an astonishing 

 analogy, of a primitive and general pattern, rested as 3'et only on a perception 

 vague and more or less confused. And it is in our own times alone that this 

 complicated question of the analogy of structure has been disentangled and 

 divided ; that it has adopted as a field of discussion determinate and precise 

 facts ; that, become a positive question, it is capable of being discussed in a 

 rio-orous and detailed manner. 



This question has been termed the question of unity of organization; it might 

 quite as well have been termed the question oi variety of organization ; all depends 

 in effect on the point of view under which it is considered ; for since there are 

 different species of animals, unity here supposes necessarily a certain variety ; 

 and since, on the other hand, these different species all resemble one another, 

 at least on that common ground which consigns them to the same kingdom, it is 

 evident that this variety necessarily supposes also a certain unity or conformity. 

 Tlie true title of the question, or rather its true object, was therefore the deter- 

 mination of the limits where stop, by turns, the resemblances and differences in 

 the orii'anization of animals; an organization at once so similar and so varied. 

 Once divided, as I have just said, the question has taken quite another aspect. 

 The general resemblance of animals has been no longer concluded from son.e 

 particular resemblances, nor limited to certain hranchcs, to certain classes. Ai? 

 regards the osseous system, for example, it had been presently perceived that, 

 onlv pertaining to vertebrate animals, this system can only yield results limited 

 to that embranchment, to that type. The resemblances of the osseous system 

 which testify so strongly to a common ground-jilan, to a unity of structure, testify 

 to them, therefore, only in reference to the sole type which possesses an osseous 

 system," the type of vertebrates. 



Considered collectively, the osseous sj'stem forms the skeleton, which is 

 divided into several parts : the apparatus of the vertebnc, that of the cranium, 

 those of the face, of the ear, of the hyoide, of the opercnla, of the ribs, of the 

 sternum, of the shoulder, of the pelvis, of the limbs. Now, there is not a mem- 

 ber of this diversified apparatus which does not, in the different classes, vary in 

 the form, the numbef, the complication of the pieces which constitute it. For 

 the most part, and saving the variations just spoken of, they are reproduced in 

 all. There are, however, some which are wantiug in such and such a class ; 

 there are some which are the exclusive attribute of a single one. The question 

 is to see what is the particular character of each a])paratus in each class ; that is 

 to say, of what pieces it is there composed, what there is the form and the com- 

 bination of those pieces. Now, such an examination shows that, among all these 

 parts of which the skeleton is composed, some are essential, and hence more con- 

 stant ; others accessory, and hence more variable ; that the vertebrae, the cra- 

 niiun, which lodge the spinal marrow, the encephalon, may readily var\' from one 

 class to another in the number and form of their bones, but are found in all ; 

 that, on the contrary, the ossicles of the ea-r, the opercnla, the limbs, &c., all 

 accessory and subordinate parts, may be wanting, and are so in effect, when the 

 conditions of audition, of respiration, of locomotion, are no longer the same. 

 These are analogies, then, graduated like the importance of the parts which })re- 

 sent theur ; each part has its proper limits, both of variety and analogy ; each 

 should be studied apart ; and it might hence be said that there is a particular 



* See especially his memoir " Sur Ic varallcle des extremites. Sfc." 



