REACTIONS TO LIGHT AND GRAVITY IN DROSOPHILA 69 
hatching, they now averaged f. 1. 3.1. Thus, it does not ap- 
pear that the age at which the wings are cut off has anything to 
do with the effect. 
It should be added that the slight f. 1. excesses recorded in 
the above experiments are probably. not significant. From 
watching the actual behavior of the flies it did not appear to me 
that the operation did any more than to render them practi- 
cally indifferent to light. Indeed, I have never observed a 
clearly negative reaction in Drosophila. 
So far the apparent loss of phototropism might mean merely 
that the operation had made the insects inactive. However, 
since Drosophila is strongly negatively geotropic it was possible 
to use this reaction as a measure of general activity.’ ~For 
this purpose the system of testing several insects at a time, known 
as method II was used. The flies were introduced into the 
usual testing tube and given one trial for the reaction to light 
in the regular manner, except that no agitation was employed. 
- Following this the tube was fastened in a vertical position with 
the flies at the bottom, and at a distance of 41 cms. from a 100 
watt tungsten lamp hung so that its tip just touched the table. 
Three such tests were given, alternating with three light tests, 
and the indices for the two sets calculated as usual for the above 
method. The elimination of agitation in these tests was made 
necessary in order to make comparable the records of the flies 
with and without wings. When agitated the former move to- 
3 Regarding the relative strength of the two stimuli, ight and gravity, Cole 
decides in favor of the latter. He found that when flies were placed in a ver- 
tical cylinder illuminated from below the larger per cent went to the upper- 
most third. Carpenter, on the other hand, was able to attract the insects to 
the bottom of a similar cylinder without using as strong a light as did Cole. 
On account of the great variability of Drosophila, I suggest.that this discrep- 
ancy may be due to the small number of flies used, Cole employing only twenty- 
one and Carpenter only six. 
My own results are not strictly comparable with those of either of these 
authors, because I used a type of apparatus which did not directly oppose the 
two stimuli, but such evidence as I have agrees with that of Carpenter. Thus, 
a reference to any of the tables where the light and gravity indices of normal 
insects are recorded will show that the light index in any given case always ex- 
ceeds that for gravity. In any event, the matter of which stimulus is the stronger 
is not one of any great significance. 
