REACTIONS TO LIGHT AND GRAVITY IN DROSOPHILA 87 
If the wings of Drosophila are removed, the insect’s response to 
light is greatly reduced. Furthermore, if they are partially re- 
moved, the reduction in response is roughly proportional to the 
amount taken off. That such a reduction is really due to a loss 
of phototropism and not to a general decrease in activity’ is 
proven by the fact that the insect’s response to the stimulus of 
eravity is reduced, very slightly, if at all. It now remained to 
show that the effect was directly due to the loss of the wings 
and not to the operation in itself. This has been accomplished 
first by performing other than wing operations and noting their 
effect and, secondly, by using breeds of insects which are hatched 
with imperfect wings. The operations performed involved the 
removal of legs and antennae. However, except in so far as 
general speed of locomotion was affected by the former operation, 
it could not be concluded that such injuries specifically affected 
the response to light. One incidental suggestion arising from 
these operations, however, is to the effect that removal of the an- 
tennae may materially affect the reaction to gravity. There is 
no obvious explanation for this, since Cole* has shown that the 
stimulus of gravity is probably received through the leg muscles. 
The second method, namely, the use of vestigial, strap and curled 
wing flies gave results which still further bear out the hypothesis 
that it is the condition of the insect’s wing as such that in some 
way directly affects the response to light. The possibility that 
sense organs on the wings were responsible for this peculiar re- 
sult was tested by injuring the wing so as to break the nerve con- 
nection with some of these sense organs. It was found, however, 
that these organs had nothing to do with the response to light. 
That the stimulus for this response is received chiefly through 
the compound eyes was proved by testing eyeless stock contain- 
ing individuals with and without these organs. Finally, the 
notion that the effect may be due to a variation in the weight 
of the wing is made very improbable by the fact that the wings 
of curled insects, though deformed, are apparently just as large 
as those of normals. 
*W. H. Cole, The reactions of Drosophila ampelophela Loew to gravity and 
air currents. Jour. Animal Behavior, Jan., Feb. 1917. 
