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 shown. 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 larve of the same species will eat a strange plant 1f 
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 
