ENTOMOLOGY 



the study of tropic reactions is complicated by the fact that 

 they are due not only to external stimuli, but also to little- 

 understood internal stimuli, arising from unknown conditions 

 of the alimentary canal, reproductive organs, etc. 



A newly recognized property of protoplasm is that of adap- 

 tation, as manifested in the acclimatization of protoplasm to 

 untoward conditions of temperature, light, contact and other 

 stimuli ; and this adaptation to unusual conditions may take 

 place without the aid of natural selection. 



A tropic reaction occurs, whether it is to prove useful to the 

 organism or not. Thus a lady-bird beetle walks upward, on 

 a branch, on a fence, on one's finger. It walks upward as far 

 as possible and then flies into the air. If it happens to reach 

 the tip of a twig and finds aphids there, the beetle stops and 

 feeds upon them. This adaptive result is in a sense incidental. 

 Yet, upon the whole, tropic reactions are wonderfully adaptive 

 in their results. Here natural selection is of special value as 

 affording an explanation of the phenomena. 



As Loeb and Davenport have insisted, the mechanical reac- 

 tions to gravity, light, heat and other influences determine the 

 behavior of the organism. 



2. INSTINCT 



Insects are eminently instinctive; though their automatic 

 behavior is often so remarkably successful as to appear ra- 

 tional, instead of purely instinctive. 



Instinct, as distinguished from reason, attains adaptive ends 

 without prevision and without experience. For example, a 

 butterfly selects a particular species of plant upon which to lay 

 her eggs. Caterpillars of the same species construct the same 

 kind of nest, though so isolated from one another as to exclude 

 the possibility of imitation. Every caterpillar that pupates 

 accomplishes the intricate process after the manner of its kind, 

 without the aid of experience. 



Instinctive actions belong to the reflex type they consist 

 of co-ordinated reflex acts. A complex instinctive action is a 



