THE VERTEBRAL COLUMN OF FISHES. 183 



diversities of structure, their instincts precisely 

 correspond; nor does instinct ever vrge to any 

 act or the performance of any operation for 

 which organs are not expressly provided. Is 

 an animal urged by instinct to chase its prey 

 through the air, then it will have wings : the 

 anterior limbs, the spine, and the whole frame- 

 work, will be modified accordingly. Is an 

 animal taught by instinct to live underground 

 and there procure its food, then it will be pro-, 

 vided with scrapers, and every part, even to its 

 fur and the development of the eyes, will accord 

 to fit it for its destined mode of life. Is an 

 animal led by instinct to hang to the branches 

 of trees and there gather its leafy diet, then will 

 it be provided with the means — look at the 

 arboreal sloth. Are races destined for aquatic 

 existence, expressly for such a life will be their 

 organization, — among mammalia, the whab; 

 among birds, the penguin ; among reptiles, lira 

 marine tortoises may be cited ; while one great 

 class, that of the fishes, is par excellence 

 aquatic. 



It has been said that animals are induced by 

 their organization to certain modes of life, tliat 

 their structure influences their instinct — but 

 this we cannot agree vnth. It is very true that 



