Experiments in Rhythmetic Periodicity 199 
as they had flown to the lighted area each was immediately re- 
placed on the blanket. 
The experiments A and B, recorded in Tables 7 and 8 for 
male cecropia moths show that males do not react similarly or 
simultaneously or an equal number of times, although condi- 
tions and handlings were maintained as nearly uniform as pos- 
sible. The column of totals reveals that the number of flights 
varied from 1 to 12, but there was no relation between the age 
of the individuals and the number of flights accomplished; 
moths young and old made both few and many flights. It is 
especially interesting, however, that all of the 33 males gave at 
least one reaction. 
During the daylight series of experiments (A), begun at 
6:30 a. m., some individuals reacted to the light within a half- 
hour, others were indifferent for varying lengths of time up 
to 13 hours. During the second series (B), begun in the eve- 
ning, the first ones responded within a few minutes, while 
others were motionless for 3, 6, 12 or even 45 and 53 hours, be- 
fore finally they were aroused and flew to the light. Not only 
was there great variation in the delay before their first flight, 
but even after the moths had once been aroused to action there 
was equally marked variation in the interval between their 
flights. 
It seems that if the definition of tropism actually is ‘‘a form 
of externally induced behavior in which the organism automa- 
tically so adjusts itself as to have morphologically symmetrical 
portions equally stimulated,’’ then why does not this external 
inducement treat all of the organisms that come under its in- 
fluence alike, when age and conditions are alike? 
The foregoing data were for the cecropia males. Tables 9 and 
10 give the results of similar tests of the females, at the same 
time and conditions. 
In the group of males, every individual in the lot responded 
to the call of the light (Tables 8 and 9). Among the females, 
there were five individuals which made absolutely no response 
during the entire period of experimentation. It happens that 
all of these were among the first lot, which were tested while 
the temperature was 64 to 68 F. Among those which were 
tested while the temperature was 70 to 80, every one of the 
females responded. Moreover, the latter averaged 444 flights 
