204 Trans. Acad. Sci. of St. Louis 
them back, and would have come oftener if I could have kept up 
with their speed. The number of trips made by the 17 males 
were as follows: 
Trips. No. of Males. 
i te S$ 7 
10 to 19 6 
20 to 29 1 
30 to 39 1 
40 to 42 2 
The high or low number of reactions did not occur on any one 
day, so one cannot say that conditions of environment caused 
them. 
The polyphemus females showed surprising promptness in 
flying to the light, but the experiment was set at 9 p. m., the hour 
at which the moths become busy. In fact, 7 of the 12 females 
had responded within the first 45 minutes, in spite of the fact 
that the only light was that which came in at the third floor 
window from the street lights below. They did not continue 
their activity, however; one of them remained absolutely indif- 
ferent during the three days of experimentation, 9 responded 
only once or twice, and the other three made 7, 10 and 18 flights 
respectively. The very fact that some females should respond 
so many times would lead one to suspect that learning or the 
innate possibilities to reaction is much more pronounced in some 
than in others. These simple experiments reveal that there is 
abundant variation in their reactions to light stimuli. Photo- 
tropism, at least, does not victimize the entire population at the 
same time and in the same way. 
The Light of Dawn. 
The time of flight of the majority of wild cecropias was the 
hour of dawn, about 3:30 to 4:30. This hour was divided into 
thirds, and records kept for eight days of the number of moths 
that came in during the darkest 20 minutes, the medium and the 
lightest 20 minutes, which was the full morning light just be- 
fore sunrise. 
