TROPISMS IN INSECT BEHAVIOR 



By C. H. TUKNER 



Dr. Jacques Loeb's experiments demonstrating that 

 certain invertebrates exhibit a form of activity identical 

 with what students of plant life call tropisms gave a new 

 impetus to the study of animal behavior and stimulated 

 numerous investigators to add a large amount of mate- 

 rial to our scientific literature. Unfortunately some of 

 this material will not stand critical analysis. So elated 

 were some of these men over the discovery of what 

 seemed a simple mechanical interpretation of animal be- 

 havior, so certain were they of its universal application, 

 that almost any simple kind of behavior was called a 

 tropism. No wonder Claperade exclaimed: ''A physiolo- 

 gist of another world, knowing nothing of our language, 

 coming here might well, on noticing the numerous points 

 of attraction which, in the shape of taverns, draw the 

 human crowd, invent ethylotropism, which would cer- 

 tainly be one of the most universal after heliotropism. He 

 might ascribe, also, a negative heliotropism among bak- 

 ers, actresses and other persons who turn day into night, 

 a nostropism for physicians, a necrotropism for under- 

 takers, a phytotropism for gardeners, a geotropism for 

 field laborers." This is humorous and, at first blush, 

 may sound ridiculous; but, is it not warranted by the 

 loose manner in which the word tropism is used? 



So varied are the ways in which the term is used that 

 the standard dictionary defines a tropism as "The inher- 

 ent tendency of living matter to respond definitely to an 

 external stimulus." Any reflex action is a definite 

 response to an external stimulus and is an inherent tend- 

 ency of living matter. If a tropism is not something 

 different from reflex action, differential sensibility, trial 



