BIOPSYCHOLOGICAL 6ii 



there is no need, nor indeed much scope, for searching for food. 

 Unlike the crayfish, Daphnia shows no evidence of awareness of 

 other animals or bodies, except for an acceleration of the swimming 

 movements when disturbed." The water-mites of the genus Eyiais 

 feed on water-fleas, which they catch as they swim. They seem to 

 use no other sense than touch in discovering their prey. They rely 

 on chance collisions for coming in contact with it. Thus the differ- 

 ence in educability is not merely that the nervous systems of the 

 three types are at different levels — the brain of the crayfish easily 

 the highest. Agar's suggestion is that the difference should be 

 correlated "with the degree of psychological development required 

 for the normal life of the animals". 



(V) INSTINCTIVE BEHAVIOUR.— There can be no doubt that 

 this term, though definable, covers some variety. Thus the 

 behaviour of the female Yucca moth in pollinating the Yucca 

 flower and laying her eggs in the ovary, is a complex linkage of 

 instinctive acts, whereas the activity of the newly hatched Mound- 

 bird in struggling out of the great heap of fermenting vegetation is 

 more homogeneous, and more continuous. In the instinctive routine 

 of ants, bees, wasps, and termites, intelligence is usually conspicuous 

 by its absence ; but in the ways of birds intelligence seems often to 

 mingle with instinct. 



What are the characteristics of instinctive behaviour, such as is 

 familiar in the industry of ants and bees, in the spider's web-making, 

 in the bird's nest-building and brooding ? Physiologically considered, 

 instinctive behaviour is a concatenation of reflex actions; in other 

 words, there is an inborn predisposition of certain nerve-cells and 

 certain muscle-cells — part of the hereditary constitution, just as 

 much as are the neuro-muscular arrangements which regulate the 

 effective beating of the heart. And in what we have just said, it 

 is implied that the instinctive behaviour does not require to be 

 "learned" by the individual animal. The first web constructed by a 

 spider is usually true to type; a larger and stronger web may be 

 made later on, but the pattern of the first one is the pattern charac- 

 teristic of the species in question. Yet the characteristic "ready- 

 madeness" of instinctive behaviour must not be over-emphasised; 

 for the animal sometimes becomes more effective as it becomes more 

 experienced. Another feature involved in the innateness of instinc- 

 tive skill is its equality in all members of the species of the same sex. 

 There is little hint of the individual variability that is often so 

 marked in intelligent behaviour. 



From the frequent perfection of instinctive behaviour, it almost 

 follows that it must have remarkable limitations. The pre-estab- 

 lished neuro-muscular arrangements necessarily bind the animal to 

 a considerable routine. Instinctive behaviour is often extraordi- 



