54 STUDIES IN GENERAL PHYSIOLOGY 



late in the afternoon escaped through the window on the next 

 day at any time that I freed them. The scent of the females 

 therefore does not determine the nuptial flight of the males, 

 and vice versa; after sunset the ants no longer flew away 

 when liberated. 



I have already shown that direct sunlight or intense dif- 

 fuse daylight calls forth flight movements in plant lice and 

 day Lepidoptera. This also occurs in winged ants. In dif- 

 fuse daylight the male and female ants move toward the 

 source of light only by using their legs; in direct sunlight, 

 however, they fly. 



Sunlight, therefore, causes flight movements in ants at the 

 time of sexual maturity, and this fact determines the nuptial 

 flight. Immediately after copulation another form of irrita- 

 bility becomes more prominent 1 which compels the ants to 

 to crowd into crevices (to "found a new nest"). 



The connection between sexuality and heliotropism in ants 

 is shown still further by the fact that at the time of the nup- 

 tial flight no heliotropism can be demonstrated in the workers. 

 Workers taken from the same nest as the other ants when 

 placed in a test-tube moved about irregularly in it, and finally 

 came to rest on the stopper, no matter in what position I 

 placed the tube with reference to the window. I then placed 

 several winged ants which reacted energetically toward light 

 in the same tube with the workers. The workers apparently 

 became now also positively heliotropic, that is to say, they 

 moved with the winged ants to the window side of the tube 

 whenever it was reversed. This lasted, however, only some 

 ten minutes, when the workers settled again permanently on 

 the stopper and were no longer affected by the light while 

 the winged ants reacted to the light just as before. 



The observations of Lubbock seem to indicate that helio- 

 tropism may be present also in the workers at certain periods 



i Stereotropism. [1903] 



