26 Trans. A ((id. Sci. of St. Louis 



is physiological unrest. To escape the impleasantness 

 of this eiivironinent, the creature makes random move- 

 ments. There is no automatic adjusting the body so as 

 to have it symmetrically stimulated by the excitant. 

 Some internal stimulus causes forward movement until 

 some sensation factor induces it to change its course. If 

 physiological satisfaction is not obtained, it continues its 

 rambling until fatigue causes it to rest. 



For the purposes of this paper, several cases of what 

 appear to be typical tropisms have been selected and it 

 has been shown how experimental analyses demonstrate 

 that none of these are tropisms. It is thought that these 

 results constitute an unanswerable argument against the 

 careless manner in which the w^ord tropism is now used. 

 It is not contended that there are no such things as insect 

 tropisms. In the light of our present knowledge, that 

 would be claiming too much, for the scientific literature 

 contains records of a few cases of what appear to be real 

 tro])isms.° It may be that at certain critical periods in 

 the life of the insect, such as birth, emergence from hiber- 

 nation, just before pupation or hibernation, etc. — th'e 

 insect may be more or less under the control of tropisms, 

 but the behavior of normal insects under ordinary condi- 

 tions cannot be called tropisms. That is the message of 

 this paper. It insists that the term tropism be so defined 

 as to make it an easily recognized type of behavior, and 

 that nothing be called a tropism that does not stand the 

 test of critical experimental analysis. 



f* Loeb, Jacques; Studies in General Physiology, 1905, pp. 24-37. 



