REACTIONS TO LIGHT AND GRAVITY IN DROSOPHILA 63 
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Age in hours Age in days 
Graph 3 
to flies of different ages, as well as on the problem of time of 
maximum activity. 
The first of these experiments was designed to show the effect 
of testing flies aged 18 to 24 hours three times with an interval 
of 2 hours between the tests. Seven groups of insects were 
thus tested, each group save three containing sixteen flies, eight 
male and eight female. Groups A and B only contained six 
flies of each sex, and Group E only five. The usual three trials 
constituted a test for each group, the sexes as always being 
tested separately. The average of the three trials is given as the 
index for the test in question.2. The following summary of the 
results was obtained by averaging the indices of the seven groups 
(table 4). 
Along with this series of tests there was run a parallel series 
similar in every respect except that the insects were 9 days 
old instead of 18 hours. Only six groups were used in this case, 
but there were eight flies in every group. A separate single 
2 It is to be noted that in this experiment as well as in the one on fatigue, 
the testing tube was only divided into four sections instead of five. The sec- 
tions were then valued as follows: 100, 75, 25 and 0. 
With this variation calcula- 
tions were made as described under method II. 
