INSECT BEHAVIOR 2QI 



example, tonotropism, or the control of the direction of locomotion by 

 density, and eleclrotropism; not to mention any more. 



All these phenomena are responses of protoplasm to definite stimuli 

 and are almost as inevitable as the response of a needle to a magnet. 



The tropisms of the lower organisms have been experimented upon 

 by many skilled investigators, whose results furnish a broad basis for the 

 study of the subject in the higher animals a study which has scarcely 

 begun. Even in the simplest organisms, behavior is the resultant effect 

 of several or many stimuli acting at once, and the precise effect of each 

 stimulus can be ascertained only by the most guarded kind of experi- 

 mentation; while in the higher animals, with their complex organiza- 

 tion, including specialized sense organs, the study of behavior becomes 

 intricate and cannot be carried on intelligently without an extensive 

 knowledge of the behavior of unicellular organisms. The properties of 

 protoplasm are the key to the behavior of organisms, though compara- 

 tively little is known as yet in regard to these properties. Furthermore, 

 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 stim- 

 uli, arising from unknown conditions of the alimentary canal, reproduc- 

 tive organs, etc. 



A newly recognized property of protoplasm is that of adaptation, 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 adapt- 

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

 ing an explanation of the phenomena. 



As Loeb and Davenport have insisted, the mechanical reactions 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 rational, instead of purely 

 instinctive. 



