354 ZOOLOGICAL PHILOSOPHY 



It is only among the vertebrates, and particularly among the birds 

 and mammals, that we find the characteristics of a true skill ; for in 

 difficult situations their intelligence may assist them to vary their 

 actions notwithstanding their subjection to habit. These character- 

 istics however are not common and it is only in a few races that we 

 often witness them. 



Let us now enquire what constitutes the determining motive of action, 

 called will : and let us consider if it is actually, as has been supposed, 

 the motive of all the actions of animals. 



