*2i)S 



THE AMEBIC AN NATURALIST [Vol. XLTI 



to an understanding" of the animals' behavior in their 

 natural environment. The extension of these methods 

 into the study of such highly specialized and delicately 

 organized invertebrates as insects is fraught by many 

 dangers, and the failure to recognize certain inherent diffi- 

 culties must inevitably invalidate some of the general 

 conclusions which have been recently announced. 



Without reference to the psychological aspect of insect 

 behavior which I am in no way competent to consider, 

 there are a number of factors entering into the study of 

 reactions which I believe must be recognized if we are to 

 appreciate the fundamental difference between a natural 

 environment and an artificial reproduction of its single 

 features in the laboratory. 



Probably more experiments on insects have been re- 

 corded which bear upon the phenomena of phototropism 

 than upon any other single tropism, and we may there- 

 fore reasonably suppose that the results in this field rep- 

 resent actual conditions as well as, if not better than, 

 those on other tropisms. 



Turning to a recent paper by Frederick W. Carpenter 

 on the reactions of the pomace-fly, Brosophila ampelo- 

 phila, to various stimuli, 2 we see the statement : 



"Light has both a kinetic and directive effect. The insect moves 

 toward the source of light, | )0 j H o. positively phototropic. The directive 

 effect is apparent only when the kinetic stimulus is sufficient to induce 



This is merely a concise expression of the fact which 

 we have all observed many times of the fly buzzing on 

 the window. Under such conditions most Diptera are 

 positively phototropic and will go through long series of 

 alternating periods of activity and quiescence, the former 

 usually induced by some external stimulus; attempting 

 all the while to pass through the window toward the source 

 of illumination. With many species this may often con- 

 tinue until the death of the insect from exhaustion and 

 lack of food. 



