358 ENTOMOLOGY 



probably one of temperature. Simple contact with the egg- 

 shell is probably sufficient to stimulate the jaws to work, and 

 the caterpillar eats its way out; yet it cannot foresee that its 

 biting is to result in its liberation. Nor, later on, when vora- 

 ciously devouring leaves, can the caterpillar be supposed to 

 know that it is storing up a reserve supply of food for the dis- 

 tant period of pupation and the subsequent imaginal stage. 

 The ends of these reflex actions are proximate and not ulti- 

 mate, except from the standpoint of higher intelligence. 



Just as simple reflexes link together to form an instinctive 

 action, so may instincts themselves combine. The complex 

 behavior of a solitary wasp is a chain of instincts, as the Peck- 

 hams have show r n. All the operations of making the nest, 

 stinging the prey, carrying it to the nest, etc., are performed 

 as a rule in a definite, predicable sequence, and even a slight 

 interference with the normal sequence disconcerts the insect. 

 Just as the performance of one reflex act may serve as the 

 stimulus for the next reflex in order, so the completion of one 

 instinctive action may be in part the stimulus for the next one. 



Modification of Instincts. An action can be regarded as 

 purely instinctive in its initial performance only, because every 

 subsequent performance may have been modified by experi- 

 ence; in other words, habits may have been forming and fix- 

 ing, so that the results of instinct become blended with those 

 of experience. Thus the first flight of a dragon fly is instinc- 

 tive and erratic, but later efforts, aided by experience, are well 

 under control. 



When once shaped by experience, reflex or instinctive ac- 

 tions tend to become intense habits. Thus, certain caterpillars, 

 having eaten all the available leaves of a special kind, will 

 almost invariably die rather than adopt a new food plant, 

 whereas larvae of the same species will eat a strange plant if 

 it is offered to them at birth. An act is strengthened in each 

 repetition by the influence of habit, to the increasing exclusion 

 of other possible modes of action. Many a caterpillar, having 

 eaten its way out of the egg-shell, does not stop eating, but 



