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THE AMERICAN NATURALIST [Vol. XLTI 



from the light during the day, yet the proximity of an 

 unnaturally brilliant light quickly upsets their normal 

 instincts, and they are irresistibly attracted, although 

 the appearance of the moon or the dawn affects them in 

 no such manner. 



Another tropism which is easily investigated by ex- 

 perimental observation is geotropism, and the agreement 

 reached by a number of workers is that many insects 

 when confined in an unnatural environment are negatively 

 geotropic. To quote again from the same paper on 

 Drosophila : 



"Gravity has a directive effect upon the active insect which is 

 negatively geotropic, that is, the insect moves away from the center 

 of the earth." 



Such is indeed the action of almost any insect, par- 

 ticularly an active species or a flying one when placed in 

 any sort of a receptacle where it is deprived of food, or 

 where it can not enjoy the freedom to which it is accus- 

 tomed. It immediately flies or crawls upward, and usu- 

 ally will repeat the process almost indefinitely if for any 

 reason it finds itself again at the bottom. Since it always 

 goes to the top of the jar if not attracted in another direc- 

 tion by other stimuli, negative geotropism is taken to be 

 one of its normal attributes. 



This negative geotropism, however, becomes an ab- 

 surdity as soon as we attempt to apply it in a general 

 way to insects in their natural environment. Crawling 

 insects do not congregate at the tops of objects in their 

 environment, and neither do flying insects approach high 

 altitudes, far from the surface of the earth. After their 

 first escape from unnatural restraint, their negative geo- 

 tropism vanishes as quickly as did their positive photo- 

 tropism. The effect of any sudden and unnatural dis- 

 turbance on the action of a flying insect is very easy of 

 observation and is experimentally tested many hundreds 

 of times during a season by any active collector of in- 

 sects. Take, for example, a common bumblebee, which on 

 account of its large size can be easilv followed by the eye 



