REACTIONS TO LIGHT AND GRAVITY IN DROSOPHILA vi) 
being placed horizontally and the result designated as the hori- 
zontal index. The difference between these indices may thus be 
taken as the index of the animal’s reaction to gravity. After 
these tests the flies with the antennae removed were given fresh 
food and kept for 3 days. The light and gravity tests were 
then repeated. On the following day, for instance, 9 days 
after hatching, the. males of this group were given one more 
gravity test. At this point the alternating system for the ver- 
tical and horizontal positions of the tube was introduced, and 
used in all the subsequent tests of this experiment. 
In Set B three groups of flies were taken and from one group the 
antennae were removed. The other two were used as controls. 
Five days later one control group and the one from which the 
antennae had been cut were given the light and gravity tests as 
in Set A. The second control group was given only a gravity 
test. 
In Set C two groups of twenty insects were taken and from one 
group the antennae were removed as usual. At 5 days the 
animals which had been operated on were tested for light and for 
gravity. The control was tested for gravity only. Three days 
later the former group was again subjected to both light and 
gravity tests. 3 
Set D consisted of two groups of male flies only, each having 
been used previously in tests on the effect of wing removal. One 
group, which we will designate as a, had been used as a control 
and had not had the wings removed. In the other group, b, the 
wings had been cut off. This latter group was now etherized 
and the antennae as well as the wings were taken off. The con- 
trol group was etherized at the same time but no operation per- 
formed. Four hours later a gravity test was given to each 
group, and 3 days later these tests were repeated. 
From the results of this experiment it appears that there has 
possibly been a very slight reduction in phototropic response. 
However, it is certainly in no way comparable with the reduction 
which occurs regularly as the result of wing removal. Further- 
more, a study of the light responses of normal insects contained 
in other tables, shows such variation that it is extremely doubtful 
