INSTINCT AND REASON 253 
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 secn. 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. 
fle 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 
