Experiments in Rhythmetic Periodicity 185 
dropped, and the light was admitted now from the opposite end. 
There were now 18 moths in the box. By 8:15, two were at the 
light, at 8:45, six and by 10 p. m., twelve were at the light end. 
During the night the others followed, so by day-break all were 
there. This of course was their normal period of flight. 
All of the 18 were left there, and the lighting was again re- 
versed by dropping the cover and raising it at the opposite end. 
This was done to see if they would travel to the light during the 
day. Up to 6 p. m., only three had moved to the light, but at 
that time the migration seemed to occur, for by 8 o’clock six 
more were there, and at 10:30, sixteen were there and the other 
two were dead, so the result may be considered 100 per cent. At 
11 p. m., the curtain was again dropped over the end where they 
were congregated and lifted at the opposite end. No detailed 
observations could be made during the night, but the next morn- 
ing at 6, all were again at the light end. 
Exp. 22. June 26, 1923. At 8 p. m.,, six eynthias which had 
emerged during the day were at rest on the south wall. Highteen 
males which had successfully made a flight to the roof two 
nights before were placed on the north wall. Then I shaded a 
60-watt lamp which hung in the middle of the room in such a 
way that the six moths were brilliantly lighted, and the wall 
with the 18 males was dimly lighted. This arrangement was 
left from 8 to 10 p. m., but it gave rise to no response in either 
direction, either toward the bright light or to the subdued light. 
Then I reversed the illumination, throwing the six in the dim 
and the eighteen in the strong light. During the next two hours 
there was no response from either group of moths. 
Before retiring, I placed whatever cynthia material I had on 
hand on the south wall, and left the room darkened excepting 
the light from the street which entered a small window with 
the shade half drawn near the north end. There were now 82 
moths, of which 54 were males and 28 females. At 3 a. m., ae 
of them had moved. I was not on hand at sunrise, but a little 
later I found great numbers of the moths at or near the window ; 
on the window and sash were 46 males and one female; on the 
walls near-by were 7 males and 7 females, making a total of 60. 
When a census was taken of those which had made no attempt 
to come to the light, there were 21 females and one male! 
Thus we see that practically all of the males moved to the 
