188 Trans. Acad. Sci. of St. Louis 
supposes that the sounds must be emitted by the female, if the 
male is equipped for hearing such sounds. Here in two cages 
were 90 females of attractive ages at one end of the room, and 
if they had emitted a sound which the males could hear, surely 
at least one out of the 48 which were at liberty in the same 
room should have responded. 
After the moon had reappeared and the moths had resumed 
their fluttering against the pane, I turned on the 50-watt lamp 
in the middle of the room to find if, while they were in this 
state of excitement, their attention could be directed from the 
moonlit window to the bright light near by. It will be remem- 
bered that in Exp. 22, when the moths were quiet, there was 
no reaction to this type of test. After 30 minutes, 23 of these, 
or about half the number, were flying vigorously about the room. 
At 10 p. m. the room was darkened and all of the males, now 
47 in number, and 10 females were placed on the south wall. 
At 3:25 I awoke, early enough I thought to observe the migra- 
tion, but I was mistaken, for already 43 males were resting on 
the window sash at the northeast corner of the room. Whether 
they had responded to the lure of the moonlight during the 
night, or whether they had been guided by an impulse to move 
at the accustomed hour, I do not know, but at that time the 
moon was low in the west, while the window faced the east. 
At 9 a. m., there was no change in their. positions, so all were 
replaced on the south wall, to see if they would react to the 
lighted window in the same way during the day. They were 
watched at frequent intervals, but not one moved to the window 
during daylight hours. Between 8 and 9 p. m., however, there 
was a general exodus, 40 males and 3 females making their way 
to the window at that time. The moon could not have caused 
the exodus, for it did not rise until 9:30. I have wondered what 
part the flashing headlights of automobiles, as they came out 
the park gate opposite, might have had to do with their action 
after dark. 
At 11:05 the old and decrepit males were eliminated, thus re- 
dueing the number to 27. These were again placed on the dark 
south wall. The next morning, all but 3 were again at the win- 
dow. It had been my intention to take a nap until two o’clock 
and then watch them constantly until dawn, to get the actual 
time of their movement, but the weakness of flesh prevailed, and 
