18 BIOLOGY AND SOCIAL PROBLEMS 



mals midway in the zoological scale, such as 

 the insects, for instance, are not without in- 

 terest. A fly in the neighborhood of food 

 moves, now this way, now that, partakes of 

 a little moisture, and, if disturbed by the ap- 

 proach of a person, rises in the air, circles 

 once or twice, and settles near the food to be- 

 gin again its irregular foraging. Evidently in 

 these responses smell, touch, and sight are 

 in continual play exciting various reflexes, no 

 one class of which predominates over another. 

 There is a condition of approximate balance 

 with momentary fluctuations, now this way, 

 now that. Catch such a fly in the hand and, 

 after a moment, liberate it ; it speeds with the 

 utmost rapidity to the nearest window. To the 

 casual observer the movements of the fly in 

 foraging were of the same mixed nature as 

 those which we exhibit in many of our daily 

 occupations, and the rush to the window seems 

 to be an effort to escape. But the same rush 

 is made to a closed as to an open window, and, 

 if the room in which the trial is made is dark- 

 ened by having the blinds drawn and is illu- 

 minated by a single artificial light, the rush is 

 made not at the window or even at the open 

 door, if it leads to darkness, but at the source 



