Experiments in Rhythmetic Periodicity 167 
The following experiments will show that odors are not al- 
ways necessary to induce reaction to light; that under certain 
conditions of light the moths will react to it. 
The tests were made to see to what degree the recurring 
rhythmic periods can be changed. In Samia cecropia, the period 
has become fixed (with certain exceptions) at the hour of dawn, 
or between 3:30 and 4:30 at this time of year. In so far as 
light conditions are concerned, this period covers all the degrees 
from blackest night just preceding dawn to the light of day 
just before sunrise. The idea in this work was to create at 
various hours during the twenty-four a condition of diffused 
light in as close imitation as possible to that which caused their 
reaction at dawn. For a long time preceding these imitation 
dawns, of course, the moths were kept in darkness, to make more 
realistic these make-believe dawns at various times of day. 
The statement is made by Reamur** that ‘‘most of the night- 
flying moths which are at liberty in the country fly only at 
night or on the approach of night. Some, moreover, of the 
same class when kept enclosed in boxes or cages show the time 
when their inclination leads them to flight. During the day 
they are quiet in their prisons, passing hours, often days, with- 
out Moving, in the same place. But when night had come, even 
before the sun is ready to set, they move their wings and are 
ready to fly as much as their box will permit.”’ 
Without having access to Reaumur’s original publication, 
one does not know to what species he refers; however, my wor 
thus far indicates that night-flying moths, at least those herein 
referred to, do not fly at all hours of the night, but the state- 
ment that when they are enclosed in dark boxes they “‘show 
the time when their inclination leads them to flight,’’ and ‘‘even 
before the sun is ready to set they move their wings and “ec 
ready to fly’’ cannot be accepted without further observation. 
The following experiments will show whether in a really dark 
compartment the moths become active with the recurring period 
of their normal activity. They will also show if these periods 
of activity can be changed by artificial conditions. 
During the early morning period of activity, seven male 
cecropias had flown into the laboratory. As very often hap- 
Pened when they flew in from the west, we found them at rest, 
cas 
**Bouvier, Psychic Life of Insects. 
