400 ANIMAL STUDIES 



through the fence. When the eagle came down on the 

 other side, he moved across to the first. And this was con- 

 tinued until the eagle gave up the chase. It is instinct 

 that leads the eagle to swoop on the rabbit. It is instinct 

 again for the rabbit to run away. But to run along the line 

 of a barbed wire fence demands some degree of reason. If 

 the need to repeat it arose often in the lifetime of a single 

 rabbit it would become a habit. 



The difference between intellect and instinct in lower 

 animals may be illustrated by the conduct of certain mon- 

 keys brought into relation with new experiences. At one 

 time we had two adult monkeys, " Bob " and " Jocko," be- 

 longing to the genus Macacus. Neither of these possessed 

 the egg-eating instinct. At the same time we had a baby 

 monkey, " Mono," of the genus Cercopithecus. Mono had 

 never seen an egg, but his inherited impulses bore a direct 

 relation to feeding on eggs, just as the heredity of Macacus 

 taught the others how to crack nuts or to peel fruit. 



To each of these monkeys we gave an egg, the first that 

 any of them had ever seen. The baby monkey, Mono, 

 being of an egg-eating race, devoured his egg by the opera- 

 tion of instinct or inherited habit. On being given the 

 egg for the first time, he cracked it against his upper teeth, 

 making a hole in it, and sucked out all the substance. 

 Then holding the egg-shell up to the light and seeing that 

 there was no longer anything in it, he threw it away. All 

 this he did mechanically, automatically, and it was just as 

 well done with the first egg he ever saw as with any other 

 he ate. All eggs since offered him he has treated in the 

 same way. 



The monkey Bob took the egg for some kind of nut. 

 He broke it against his upper teeth and tried to pull off 

 the shell, when the inside ran out and fell on the ground. 

 He looked at it for a moment in bewilderment, took both 

 hands and scooped up the yolk and the sand with which it 

 was mixed and swallowed the whole. Then he stuffed the 



