Experiments in Rhythmetic Periodicity 183 
ing a period of two weeks there was never a voluntary movement. 
I think this unusual lethargy may be attributed to the low 
temperature of that time. The minimum for the fourteen days 
varied from 38 to 64 F. When a female was handled or prodded, 
it slowly opened and closed the wings, and lapsed again into 
repose. 
One evening from 10:30 until midnight I permitted a very 
lively male to flutter about the room, and soon he turned his 
attention to the ten cages containing 18 females. The position 
of each of the moths was marked with paint on the outside of 
the cage. As his flutterings among them became more and more 
wild, I expected some sort of response, at least a movement of 
the wings, but not one of them stirred during the hour and a 
half, and the marks at the end of the time showed that no un- 
noticed movement had occurred. The temperature was 55. This 
temperature did not cool the ardor of the energetic male, but 
the females were indifferent in his presence when the tempera- 
ture was below optimum. On other similar occasions, when this 
factor was favorable, the females have displayed emotion. On 
May 18, when the temperature was 75, one female which had 
just concluded mating fluttered at intervals for six hours. 
Rythmic Periodicity in Platysamia cynthia. 
Cynthias are sluggish in cages and are seldom seen to move. 
They are good fliers, however, and in moving them from cage to 
cage one must be careful, for they are quick to escape, and oor 
out of the window they fly high, even when the sun is bright. 
But they do not like the sun, for they always come to rest in 
some shady spot. The females often remain motionless for days 
at a time, but if one is liberated in the open it flies high and 
more lightly and swiftly than cecropia. : 
We have seen in the cecropia that light of the optimum 
intensity at any time of day regulates the activity of the males 
and to a lesser degree that of the females. In nature, the normal 
time for the flight of cecropias is just before and during the 
hour of dawn; it seems that some of the males can perceive the 
approaching dawn and fly before dawn overtakes them. Under 
very exceptional circumstances, cecropias fly at other hours dur- 
ing the night, as noted in the early experiments on homing. The 
time of flight of cynthias is several hours before midnight. They 
present a distracting list of variations in their flight ; sometimes 
