494: HISTOKY OF PHYSIOLOGY. 



catch its necessary victims." 81 By such considerations lie has been 

 able to reconstruct the whole of many animals of which parts only were 

 given ; a positive result, which shows both the reality and the value 

 of the truth on which he wrought. 



Another great example, equally showing the immense importance 

 of this principle in Cuvier's hands, is the reform which, by means of 

 it, he introduced into the classification of animals. Here again we 

 may quote the view he himself has given 32 of the character of his own 

 improvements. In studying the physiology of the natural classes of 

 vertebrate animals, he found, he says, " in the respective quantity of 

 their respiration, the reason of the quantity of their motion, and con- 

 sequently of the kind of locomotion. This, again, furnishes the rea- 

 son for the forms of their skeletons and muscles; and the energy of 

 their senses, and the force of their digestion, are in a necessary pro- 

 portion to the same quantity. Thus a division which had till then 

 been established, like that of vegetables, 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 sensation ; 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 principle of the Condi- 

 tions of Existence, as applied by its great assertor. 



It is clear, indeed, that such a principle could acquire its practical 

 value only in the hands of a person intimately acquainted with anatomi- 

 cal details, with the functions of the organs, and with their variety in 

 different animals. It is only by means of such nutriment that the 

 embryo truth could be developed into a vast tree of science. But it 

 is not the less clear, that Cuvier's immense knowledge and great pow- 

 ers of thought led to their results, only by being employed under the 

 guidance of this master-principle : and, therefore, we may justly consi- 

 der it as the distinctive feature of his speculations, and follow it with 

 a gratified eye, as the thread of gold which runs through, connects, 

 and enriches his zoological researches : gives them a deeper interest 

 and a higher value than can belong to any view of the organical 

 sciences, in which the very essence of organization is kept out of 

 Bi<rht. 



91 Theory of the Earth, p. 90. M Hist. Se. Nat. i. 293. 



