186." Trans. Acad. Sci. of St. Louis 
light, and about one-fourth of the females also. In all prob- 
ability these cynthias did respond to the light of early dawn, 
because in the homing experiments many of them did come in 
with the cecropias at about 4 a.m. In this case, as in the other 
species, it is surprising that the moths did not respond to the 
glare of the automobile headlights flashing intermittently in the 
windows before the hour of 3 when I examined them. 
In the first part of the experiment there was no reaction to 
the intense light, because physiologically they were not attuned 
to become active in those conditions, but later experiments will 
show that even when the hour recurs for their activity, they 
will not react if the stimulus of correct light is lacking. It is 
interesting to note that, when once they are in the light, there 
they remain quietly at rest throughout the day, regardless of 
the fact that the hot sun is curtailing their lives*; they have 
never been observed to make the slightest move to seek a more 
sheltered place. When once in the light they seem to be trapped. 
During these periods they cling tenaceously to their support; 
unless one has the task of pulling them off, one little suspects 
that their feeble-looking tarsi possess so much power. With the 
return of night, they fly wildly about the window pane. 
In this experiment where all of the males and 25 per cent of 
the females went to the light, one would expect all of the females 
to have mated; on the contrary, only one pair mated, even in 
this close proximity. In this species as in the cecropia, the pur- 
pose of the action is to fly to the females, and the stimulus is 
light rays of a certain intensity, but in the excitement of the 
reaction or for some unkown cause, they pass by the females 
even when in close proximity and the vital purpose is defeated. 
Someone may stretch a point to say that the passing by of the 
males when too near to the females may be an adaptation to in- 
sure cross fertilization, since probably all the adults of a limited 
area are from the eggs of one mother. But who, pray tell me, 
would be so bold as to make a case of this speculation? It is 
much more likely that there was no mating at the window be- 
cause there was no motion of the air. 
Exp. 23. June 27, 11:50 p. m. Room dark; only three-quar- 
ters of one window in the northeast corner uncovered ; no wind 
*In the case of an insect that takes no food, the duration of life 
See Rau, Trans. 
is shortened by warmth and lengthened by coolness. 
Acad. Sci., St. Louis, 23:1-78, in 1914. 
