310 ENTOMOLOGY 



No light reactions are obtained from the butterfly when shadows are 

 thrown upon any part of the body except the head. When one eye is 

 painted black the butterfly creeps or flies in circles ("circus move- 

 ments") with the unaffected eye always toward the center. When both 

 eyes are painted black all phototropic responses cease and the insect flies 

 upward. Butterflies with normal eyes liberated in a perfectly dark room 

 come to rest near the ceiling. This upward flight in both cases is due 

 to negative geotropism, not to phototropic activity. 



V. antiopa does not discriminate between lights of greater or less 

 intensity provided they are all of at least moderate intensity and of 

 approximately equal size. V. antiopa does discriminate between light 

 derived from a large luminous area and that from a small one, even when 

 the light from these two sources is of equal intensity as it falls on the 

 animal. These butterflies usually fly toward the larger areas of light. 

 This species remains in flight near the ground because it reacts positively 

 to large patches of bright sunlight rather than to small ones, even 

 though the latter, as in the case of the sun, may be much more 

 intense. 



V. antiopa retreats at night and emerges in the morning, not 

 so much because of light differences, as because of temperature 

 changes. On warm days it will, however, become quiet or active, 

 without retreating, depending upon a sudden decrease or increase of light. 



The maggots of the muscid Phormia regina are, as the author has 

 observed, negatively phototropic until full grown, when they become 

 positively phototropic for an hour or less, leave the decaying matter in 

 which they have developed and wriggle 'along the ground toward the 

 sun; or if the sunlight is diffused by clouds, wander about aimlessly, 

 but at length bury themselves in the ground to pupate. Here the 

 positive phototropism just before pupation is adaptive. 



The swarming of the honey bee is likewise a case of periodic positive 

 phototropism, as Kellogg has observed. 



Winged ants of both sexes are strongly positively phototropic when 

 they swarm from the ground for the nuptial flight. After mating, 

 however, the female becomes negatively phototropic and positively 

 thigmotropic ; enters the ground, sheds her wings, and enters upon a 

 subterranean existence, during which she is intensely positively thigmo- 

 tropic. In connection with this subject, it is a significant fact that the 

 pomace fly, Drosophila, loses its phototropism when its wings are 

 removed artificially. 



In autumn, gravid females of the mosquito, Culex pipiens, become 



