168 Trans. Acad. Sci. of St. Lowis 
not on the cages of the females, but on the windows facing the 
east where the first rays of light penetrated. These wild moths 
were placed in a wire cage, but when handled they became very 
active and beat their wings against the mesh so harshly that 
for their safety they were transferred to the big glass box. 
This box was darkened with several layers of blankets on three 
sides, top and bottom, but all of the moths continued their 
activity at the open end. After five minutes, I covered this 
end and opened the opposite end; within two minutes all seven 
of the males had fluttered to the newly lighted end. After three 
minutes, this end was darkened and the first end again uncov- 
ered ; almost immediately six of the seven flew back to the light 
end and continued their activity. While they were still active 
during a period of five minutes, I suddenly threw off the cover, 
permitting the light (the ordinary diffused light of a room on 
a clear day) to freely enter the box from four sides and top. 
I imagine their interpretation of this sudden flood of light was 
that daylight had come and it was time to rest, while the previ- 
ous condition, dim light from only one direction and elsewhere 
darkness, had seemed to them dawn, for almost immediately all 
of the moths quieted down and rested calmly. The actions of 
these cecropias under these experimental conditions look at first 
very much like a case of pure phototropism. This simple experi- 
ment shows that they are sensitive to differences in degree of 
light (differential sensitivity), but whether the creatures react to 
certain light waves in a fashion entirely mechanical, I think the 
work as a whole will disprove. 
But to resume the experiment, the moths were still exposed 
to the full light of the room, and all were quiet. So they re- 
mained for half an hour when two of them resumed activity, 
fluttering toward the light, despite the fact that there had been 
no disturbance or change in conditions that I could perceive. 
Then I covered the box entirely excepting a small peep-hole 
through which I could see that it took these two moths just two 
minutes to subside into quietude under these new conditions. 
After another half-hour the cage was again completely uncov- 
ered, but this change called forth no response. Whether this 
indifference was due to their fatigue, or whether strong light 
was as much an inducement to sleep as profound darkness, I 
cannot say. 
