154 Trans. Acad. Sci. of St. Lowis 
are less sensitive, and hence harder to arouse than others, The 
fact that some males were aroused almost simultaneously with 
her first wing movements, and at the end 8 were still indifferent 
in the same environment suggests a wide range of individual dif- 
ferences in a very essential character in the life of the species. 
These males were native moths which had flown into the 
laboratory at dawn that morning; in the next experiment we 
shall study a similar phenomenon with males bred from cocoons 
in the laboratory which have had no outside experience; hence 
any possibility of the interference of fatigue will be eliminated. 
Exp. 2. May 29, 11 p. m. In the glass box I placed 41 
male ceeropias which had emerged in the room; 14 were 4 to 4 
day old, and 27 were from 1 to 1% day old when they were 
placed in the box at 11 p.m. Since the males in the last experi- 
ment had shown such positive reaction to the light after having 
been awakened by sex excitement, it was decided to test these 
for their reactions to the light alone before introducing the 
females into the game, to see if after spending a period in 
absolute darkness they would react to light rays when no female 
odor was present. The whole box was darkened by covering 
with several layers of blankets and roping these about the table 
legs so not even a pencil ray of light eould penetrate from below. 
At 10:10 the next morning, I found 32 males precisely where I 
had left them, and 9 had wandered about a bit. This little 
incident shows of course that if they become active each night 
at stated hours because they are instinctively attuned to do so 
(rhythmic periodicity), then all or the majority of them would 
have changed their positions, especially since during this period 
of confinement in the box (from 11 p. m. to 10:10 a. m.) they 
passed through this time when they are usually active. Hence 
in the absence of light or sex stimulus, their rhythmic perio- 
dicity failed in this case. 
When the blankets were folded back from one end of the box, 
at 10:10 a. m., one male immediately became active, and after 
ten minutes ae more were wildly fluttering the wings; these 
three moved to the light end, while two more at the rear (dark) 
end slowly moved their wings up and down. This is the sum 
total of the activity of 41 males for a period of 30 minutes after 
