180 Trans. Acad. Sci. of St. Louis 
not orient themselves to the cages on our roof. Of course it is 
possible that the faint light might have aroused them to action, 
and that they were flying aimlessly hither and thither, without 
any trail to follow, and we could not know this. Thus it is 
evident beyond doubt that moonlight is a potent factor in the 
activity of these creatures, arousing them to action in a consid- 
erable number of cases at all hours between 11 p. m. and the 
hour of dawn or 3:30. 
The species also vary in their response to moonlight. During 
these seven nights the wild cecropias came in at dawn in hordes, 
but only 7 responded to the moonlight at other hours, and none 
at all came in early without moonlight. The cecropias which 
had emerged from cocoons kept in the laboratory showed a far 
greater tendency to fly by night, not waiting for dawn as had 
the wild ones. Although the wild ones in the region far out- 
numbered the bred ones which we had liberated, yet 48 of the 
bred ones came in early as contrasted with only 7 of the wild 
ones. 
The polyphemus shows a much stronger tendency to fly at all 
hours of the night instead of confining their activity to the hour 
of dawn. Although they are not nearly so numerous as are 
the cecropias in this region, they came during the moonlight 
(table above) in equal numbers. The figures above indicate that 
polyphemus is more susceptible to moonlight. 
Thermotropism. 
On May 16 at 8 p. m., I had 20 male cecropias and 3 male 
polyphemus in the glass box. The temperature was low (54), 
and they did not respond readily to my light experiments, for 
only 4 moved. Therefore I placed an electric heater in the box 
and watched the thermometer go from 54 to 60. This brought 
an additional 6 to the light side. When the heater was turned 
off, they rested. An hour later the heat was again turned on 
and the thermometer reached 64. One by one the moths which 
were already at the light side of the box resumed their agita- 
tion, and were joined by ten others which had remained indif- 
ferent to all stimuli at a lower temperature, until soon all m 
the box were active. Now this temperature is not high for these 
species, for in Nature, during the period of their adult life the 
temperature is often above 80. The reaction is to be explained 
