86 



LIFE IN THE SEA 



[CH. Ill 



and behaviour. We must assume the quality of 

 memory on the part of the animal it may be some 

 kind of unconscious memory. Then it follows that 

 an animal will react not entirely in response to the 

 stimulus which reaches it from without, but also in 

 response to all the stimuli which have affected it in 

 the past ; that is to say its behaviour at any time is 

 modified by its experience. Now if one attentively 

 studies the facts of migration it seems that this way 

 of looking at them is more in accord with what one 

 sees than simply to suppose that the behaviour is 

 a series of inevitable responses to changes in the 

 environment 



The quantitative plankton net. 



