HELIOTROPISM OF ANIMALS 55 
in their existence. In the experiments of Lubbock the 
workers contained in the nest not only collected under red 
glass, but also carried their larve there. The animals are 
therefore negatively heliotropic.* 
All these facts, however, do not yet exhaust the connec- 
tion between sexuality and heliotropic irritability. The 
heliotropism of the male and female ants is also different, 
inasmuch as it requires more intense light to cause helio- 
tropic movements in females than in males. In isolating 
the males and females of the same swarm I noticed that the 
females had ceased to execute heliotropic movements before 
it seemed as if twilight had really begun. The males how- 
ever still collected on the window side of the tube long after 
sunset. Experiments with colored glasses succeeded in males 
when the light was so faint that I had difficulty in dis- 
tinguishing the color of the glasses. On dark, cloudy days 
females showed no heliotropic reactions toward the window, 
while the males did. It harmonizes with this observation 
that on cloudy afternoons I saw occasionally winged males 
leave the nest, but no females. 
As soon as the intensity of the light had become so small 
that heliotropic phenomena were no longer produced, another 
form of irritability appeared in the winged ants, especially 
in the females, namely, stereotropism. The animals then 
crowded into all crevices. I placed the animals in a dark 
box, and laid a small, folded piece of velvet into one corner 
of it. After a few moments they had crept into the folds of 
the velvet. With the males it took a much longer time than 
with the females. This irritability, however, did not appear 
as long as the light was sufficiently intense to call forth 
heliotropic phenomena. When exposed to light, the animals 
crept neither under the piece of velvet nor into crevices. It 
is very probable that a similar difference in heliotropic irri- 
1 The observations recorded in Lubbock’s paper admit another possibility. [1903] 
Digitized by Microsoft® 
