354 ENTOMOLOGY 
near the ceiling. This upward flight in both cases is due to 
negative geotropism, not to phototropic activity. 
Il’. 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. IT’. antiopa does 
discriminate between light derived from a large luminous area 
and that from a small one, even when the hght 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. 
lV’. 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. 
