THE DOCTRINE OF FINAL CAUSES. 501 



being considered as having the function for its end. 

 We must say a few words on each of these views. '4 

 It had been pointed out by Cuvier, as we have 

 seen in the last chapter, that the animal kingdom 

 may be divided into four great branches ; in each of 

 which the plan of the animal is different, namely, 

 vertebrata, articulata, mollusca, radiata. Now the 

 question naturally occurs, is there really no resem- 

 blance of construction in these different classes,? 

 It was maintained by some, that there is such a 

 resemblance. In. 1820 1 , M. Audouin, a young 

 naturalist of Paris, endeavoured to fill up the chasm 

 which separates insects from other animals ; and by 

 examining carefully the portions which compose the 

 solid frame-work of insects, and following them 

 through their various transformations in different 

 classes, he conceived that he found relations of posi- 

 tion and function, and often of number and form, 

 which might be compared with the relations of the 

 parts of the skeleton in vertebrate animals. He 

 thought that the first segment of an insect, the head 3 , 

 represents one of the three vertebrae which, accord- 

 ing to Spix and others, compose the vertebrate head : 

 the second segment of the insects, (the prothorax of 

 Audouin,) is, according to M. Geoffroy, the second 

 vertebra of the head of the vertebrata, and so on. 

 Upon this speculation Cuvier 3 does not give any 

 decided opinion ; observing only, that even if false, 

 it leads to active thought and useful research. 

 1 Cuv. Hist. Sc. Nat. iii. 422. * Ib. 437. 3 Ib. 441. 



