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* 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 
1Stereotropism. [1903] 
Digitized by Microsoft® 
