Experiments in Rhythmetic Periodicity 151 
may be more rich and exciting and noisy than the daylight 
fauna. Tropical day and night are always twelve hours long 
throughout the year, while the night in southern England or 
northern United States is only eight hours long in midsummer. 
Very little is known on the day and night rhythms of moths 
and butterflies. | With Lepidoptera collectors almost outnum- 
bering the Lepidoptera, it does seem strange that all we know 
about these activities is that moths fly at night and butterflies 
in the daytime. But this information is not sufficient. A day- 
flying moth is not in flight during all of the daylight hours, and 
neither is a nocturnal moth thus active throughout the night; 
each creature has its hours of activity; what are these hours 
for each species, and why are these certain hours chosen above 
all others? In behavior work this is an important point. For 
instance, Turner’s careful work on behavior in the hearing of 
Saturniid moths with its excellent conclusions probably would 
have given him even better results if he had considered for each 
Species its natural period of activity. It is logical to expect that 
the reactions of the moths would have been different during their 
hours of intense alertness and activity than during their period 
for slumber. 
Regarding the material now in hand, we have stated in the 
previous pages that the cecropias become active during the hour 
of 3:30 and 4:30 a.m. The polyphemus are abroad from 3:20 
to 4:30 a. m. and from 11 p. m. until midnight. The prometheas, 
for no reason which we have yet fathomed, choose to fare forth 
at 3:40 to 6:40 in the bright daylight, while the cynthias are 
active from 3 a. m. until dawn, and from 9 p. m. until mid- 
night. Other observers have found the period of activity for 
allied moths to be as follows: Mayer, too, finds the prometheas 
active between 2 p. m. and sunset. According to Fabre, the 
reat peacock moth requires the dusk of the early part of the 
hight, 9 to 10:30 p. m., while the lesser peacock requires the 
brilliant light of the middle of the day. The banded monk or 
oak-egger flies between 3 and 6 in the afternoon. C. M. Weed 
Says that cynthia moths occasionally fly on cloudy days. 
Before we can determine that rhythmic periodicity per se ie 
Controlling factor in these moths, we must first eliminate t : 
reactions that are purely sensory. There is nothing we can eal 
