152 ANIMAL INSTINCTS. 



rendered useless by captivity ? From what structure 

 can come that prevision of the future implied in the 

 simple building of a bird's nest? or what subtleties of 

 the external senses can explain those selective instincts 

 as to food common to every creature of the animal 

 world ? 



Instances of this kind might be endlessly multi- 

 plied, as significant as curious. They go far to sanc- 

 tion that phrase of Cuvier's where he describes the 

 instinct of animals as ' un reve qui les poursuit 

 toujours.' But if so, what puts into motion these 

 wonderful dreams of instinctive life? Anatomy, even 

 the most searching, gives no answer to this question, 

 and all reasoning and speculation are equally mute. 

 It is that ultimate mystery to which allusion has 

 already been made. 



While thus separating the great mass of instincts 

 from anything we can see or conceive of mere struc- 

 ture, it is needful to recognise the many instances 

 where the domestication of animals, or other less ob- 

 vious, external causes, have altered both the bodily 

 conformation and habits of the species, impressing the 

 character of instincts, in fixity and force, on the habits 

 so transmitted from one generation to another. Such 

 changes belong chiefly, if not exclusively, to what I 

 have termed the border-land, where intelligence is 

 closely blended with instinct ; and they are most strik- 

 ing where domestication by man has worked upon the 

 highest degree of natural intelligence. Our social re- 

 lations with the higher apes are happily not such as to 

 furnish much illustration. But the dog, as concerns 



