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 chrysorrhoea. 



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 



