ON THE INTERPRETATION OF CERTAIN 

 TROPISMS OF INSECTS 1 



CHARLES THOMAS BRUES 

 Milwaukee Public Museum 



The great interest which has developed among zoolo- 

 gists during recent years regarding the behavior of 

 animals has resulted in such a large number of papers 

 on tropisms and related topics, that a short discussion 

 of the matter in regard to insects may seem rather un- 

 called for at present. 



The field of entomological research affords, however, 

 so many possibilities in this line that the activity which 

 was formerly confined to studies of lower invertebrates 

 is gradually showing a tendency to shift or to widen out 

 toward the insects in its search for fresh subjects, and 

 already the reactions of various species belonging to 

 several groups have been investigated by the commonly 

 accepted methods. The problem of studying the re- 

 sponses of insects to light, gravity, mechanical stimuli, 

 etc., involves so many factors which do not enter into any 

 consideration of simple organisms like protozoa or 

 planarians that its complexity is rarely appreciated by 

 those who give it their attention. The former animals 

 can be brought into the laboratory and placed where the 

 normal conditions of their natural environment are repro- 

 duced more or less faithfully. Under such circumstances 

 their reactions and behavior can be analyzed by means 

 of different mechanical contrivances which have been 

 devised to test the influence of certain stimuli to the ex- 

 clusion of others. To be brief, experience has shown that 

 conclusions derived from such experiments are fairly 

 trustworthy, and that a close approach can be thus made 



1 A paper read before the joint meeting of the Wisconsin Academy of 



