1 6 PSYCHE [February 



sition is here an instinctive act, not performed until it is evoked by some sort of 

 stimulus — perhaps an olfactory one — from a particular kind of plant. 



Some determinate sensory stimulus is, indeed, the necessary incentive to any 

 reflex act. The first movements of a larva within the egg-shell are doubtless due 

 to a sensation, 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 voraciously devouring leaves, can the caterpillar be supposed to know that 

 it is storing up a reserve supply of food for the distant period of pupation and the 

 svibsequent imaginal stage. I'he ends of these reflex actions are proximate and not 

 ultimate, except from the standpoint of higher intelligence. 



An action can be regarded as purely instinctive in its initial performance only, 

 because every subsequent performance may have been modified by experience; in 

 other words, habits may have been forming and fixing, so that the results of instinct 

 become blended with those of experience. Thus the first flight of a dragon-fly is 

 instinctive and erratic, but , later eftorts, aided by experience, are well under control. 



When once shaped by experience, reflex or instinctive actions 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 consumes the 

 remainder of the shell, — a reflex act, started by a stimulus of contact against the 

 jaws and continued until the cessation of the stimulus, unless some stronger stimu- 

 lus should intervene. It has been said that the larva eats the remains of the shell 

 because they might betray its presence to its enemies. Whether this is true or not, 

 to assume conscious foresight of such a result on the part of an inexperienced 

 caterpillar is worse than unnecessary. 



With insects, as with other animals, many instincts are transitory ; even when 

 partially fixed by habit, they are replaceable by stronger instincts. Thus the 

 gregarious habit of larvae is finally overpowered by a propensity to wander, which 

 does not mature, however, until the approach of the transformation period. The 

 reproductive instinct is another of those impulses that do not ripen until a certain 

 age in the individual. 



Broadly speaking, instinctive actions lack individuality, — are performed in the 

 same way by every individual of the species. The solitary wasps of the same spe- 

 cies are remarkably consistent in architecture, in the selection of a special kind of 

 prey, the way in which they sting it, carry it to the nest and dispose of it ; all these 



