172 THE STUDY OF ANIMAL LIFE CHAP. 



number. In a case of this sort we are inclined to admit 

 intelligence, for the performance was rather subtle and 

 novel, and we know that the chimpanzee has a highly 

 developed brain. 



Difficulties increase when we pass to animals very 

 different from ourselves. Mile. Drzewina removed some 

 hermit-crabs from their borrowed shells and gave them 



O 



similar shells which had been plastered up. The hermit- 

 crabs spent a long time trying to get into these closed 

 shelters, but eventually gave it up as hopeless. When 

 some shells of the same sort, but empty, were put into 

 the aquarium, the hermit-crabs would not look at them. 

 The established association was too strong. Yet when 

 some other shells of a different shape were put in, the 

 hermit-crabs tried them at once. The question is whether 

 we have here to do with intelligent behaviour, or whether 

 it illustrates what we do not understand a profiting by 

 experience on a lower than an intellectual level, such as 

 probably forms the basis of the very effective agency of 

 the brainless starfish already referred to. 



Strongly suggestive of something like intelligence is 

 the behaviour of various kinds of animals, such as rats, 

 dogs, cats, and chicks, which learn in the course of time 

 to find their way out of labyrinths and puzzle-boxes. 

 After they have served an apprenticeship they are left 

 in peace for a few days and then replaced in the previous 

 difficult situation. It is often observed that they irake 

 fewer useless movements, that they sometimes make 

 none. The question is whether ideas are at work, whether 

 the creatures think. Have they remembered images of 

 their successful movements, or do they obey the prompt- 

 ings of an organismal registration in which ideas have 

 not been involved ? We must not be in a hurry in 

 answering this question. 



10. Registration and Habituation. The problem of 

 animal behaviour is complicated by the frequent occur- 

 rence of what may be called secondary simplicity. We 

 are familiar with this in the individual " habituation " of 

 exercises which originally required attentive selection 

 and detailed control. This is more or less readily effected 



