158 TROPISMS 



These manifestations oi' a highly developed stereo- 

 tropism in the segments of the reproductive organs are 

 probably widespread in the animal kingdom. The late 

 Professor Whitman told the writer that male pigeons 

 when kept in isolation will try to go through the motions 

 of mating with any solid object in their held of vision, 

 e.g., glass bottles, and even with objects which give only 

 the optical impression of a solid, namely, their own 

 shadow on the ground. 



In ants, the winged males and females become intensely 

 positively heliotropic at the time of mating. Copulation 

 occurs in the air, in the so-called nuptial flight. At a cer- 

 tain time — in the writer's observation toward sunset, 

 when the sky is illuminated at the horizon only — the whole 

 swarm of males and females leave the nest and fly in the 

 direction of the glow. The wedding flight is a heliotropic 

 phenomenon 287 presumably due to substances produced 

 in the body during this period. After copulation the 

 female loses its wings and also its positive heliotropism. a 

 It becomes now intensely stereotropic. When kept in a 

 dark box with pieces of cloth in folds the wingless female 

 will now be found in the folds where its body is as closely 

 as possible in contact with the solids. This positive 

 stereotropism leads the queen to begin a subterranean 

 existence which marks the founding of a new nest. Helio- 

 tropism and stereotropism are, therefore, the controlling 

 factors in mating and the starting of a new nest in these 

 ants. 287 



V. L. Kellogg 265 has made observations which show 

 that the nuptial flight in bees is also due to an outburst 

 of positive heliotropism as in the ant. 



a It has already been mentioned that artificial removal of the wings of 

 the fruit fly will also abolish its heliotropism. 



