354 ENTOMOLOGY 



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 posi- 

 tively 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, as it is in the 

 case of sexually mature ants, which make a nuptial flight into 

 the sunlight when they have acquired wings. The swarming 

 of the honey bee is likewise a case of periodic positive photo- 

 tropism, as Kellogg has observed. 



Though adaptive in their results, these phototropic reac- 

 tions can scarcely be said to be performed on account of 

 their usefulness. They are performed anyway, and may re- 

 sult harmfully, as when they lead a moth into a flame or, to 

 take a more natural example, when they expose an insect to 

 its enemies. 



