THE VERTEBRAL COLUMN OF FISHES. 185 



or consideration, in the very manner in which 

 they were intended to be appUed. They act, 

 not because they reflect that they are structurally 

 fitted for this or that plan of operation, but 

 because instinct impels them, and instinct never 

 impels to any action which the animal has not 

 the means of accomplishing. No animal hesi- 

 tates in what manner to attack its prey, or in 

 what manner to avoid its pursuer. No animal 

 hesitates as to the mode of life it shall lead, or 

 the labours it shall perform. No animal 

 emulates the habits of another, unless it is, 

 in hke manner, organized for them. This 

 organization for definite modes of fife, of ac- 

 quiring food, of avoiding enemies, is palpable in 

 the structure of the limbs and spine ; the modi- 

 fications of which are as varied as are the 

 instincts and habits of the numerous tribes of 

 earth, air, and water ; nor are these modifica- 

 tions limited to those parts — they are carried 

 out, more or less strongly, through all the 

 details of the animal body, every part, so to 

 speak, being dove-tailed into lyiison with the 



rest. 



When we speak of the instincts of animals in 

 accordance with their structure, we naturally 

 revert to man, and the question suggests itself, 



