52 STUDIES IN GENERAL PHYSIOLOGY 
soon ceased. Under the influence of light, the animals also 
moved from a region having a temperature of 12° to one 
having a temperature of 24°. 
VIII. THE CONNECTION BETWEEN HELIOTROPISM AND SEXU- 
ALITY IN ANTS 
At the time of sexual maturity the male and female ants 
fly from the nest on a warm day to pair in the air. This 
“nuptial flight’ is, as shown by the following observations, 
determined by a very pronounced positive heliotropism, 
which appears especially at the period of sexual maturity. 
I discovered a nest of brown garden ants in the wall of a 
house which was struck late in the afternoon by direct sun- 
light. In August, 1888, I observed that on warm days in 
the afternoon, as soon as the sun struck the wall, at about 5 
o'clock, the winged ants came out in swarms and then flew 
away in the direction of the rays of sunlight. I procured a 
large number of winged ants from such a swarm and studied 
their behavior toward light. These animals were energeti- 
cally positively heliotropic, and behaved in all respects like 
the caterpillars of Porthesia chrysorrheea. 
When I put the winged ants into a test-tube and placed 
this with the longitudinal axis perpendicular to the plane of 
the window, the animals moved to the window side as often 
as the tube was turned around. The velocity of the helio- 
tropic movements was greater in these animals than in any 
others that I have studied. When the tube was not disturbed 
the animals remained on the window side nearest the win- 
dow. When the longitudinal axis of the test-tube lay par- 
allel to the plane of the window, the animals distributed 
themselves evenly over the whole length of the tube. When 
one-half of the tube was in direct sunlight, while the other 
half was in diffuse daylight, but nearer the window, the ani- 
mals collected in the window side of the tube, they went from 
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