THE DOCTRINE OF FINAL CAUSES. 519 



Another great example, equally showing the 

 immense importance of this principle in Cuvier's 

 hands, is the reform which, by means of it, he in- 

 troduced into the classification of animals. Here 

 again we may quote the view he himself has given 23 

 of the character of his own improvements. In 

 studying the physiology of the natural classes of 

 vertebrate animals, he found, he says, "in the re- 

 spective quantity of their respiration, the reason 

 of the quantity of their motion, and consequently 

 of the kind of locomotion. This, again, furnishes 

 the reason for the forms of their skeletons and 

 muscles ; and the energy of their senses, and the 

 force of their digestion, are in a necessary propor- 

 tion to the same quantity. Thus a division which 

 had till then been established, like that of vegeta- 

 bles, only upon observation, was found to rest upon 

 causes appreciable, and applicable to other cases." 

 Accordingly, he applied this view to invertebrates ; 

 examined the modifications which take place in 

 their organs of circulation, respiration, and sensa- 

 tion; and having calculated the necessary results 

 of these modifications, he deduced from it a new 

 division of those animals, in which they are arranged 

 according to their true relations. 



Such have been some of the results of the prin- 

 ciple of the conditions of existence, as applied by 

 its great assertor. 



It is clear, indeed, that such a principle could 

 23 Hist. Sc. Nat. i. 293. 



