74 ROBERT STANLEY McEWEN 
b. Gluing the wings 
Several attempts were made to glue the wings in such a way 
that though uninjured, the insect could not use them. These at- 
tempts were made fruitless, however, by the fact that a fly whose 
wings are stuck thoroughly enough so that they can not be freed, 
will spend all its time in an effort to do so, and will scarcely re- 
spond to any other stimulus during the process. This experiment, 
therefore, had to be given up. 
There remained two other possibilities. First, the effect of 
operations as such could be determined, by operating on other 
parts of the insect. Secondly, the existence in this laboratory 
of mutations of all degrees of winglessness made it possible to 
discover the effect of the absence, or partial absence, of wings in 
Drosophila upon which no operation had been performed. The 
effects of other operations will be considered first. 
c. Cutting off legs 
For this purpose eleven males and ten females, newly hatched, 
were selected and kept in vials until five days old, this being the 
usual procedure when records comparable with those made by 
other groups were desired. Before placing in the vials each in- 
sect was operated on, and the tarsus and tibia of the middle 
pair of legs cut off. It was thought that removal of the middle 
pair in this manner would interfere least with the animal’s 
balance and ability to crawl. On the fifth day these flies were 
tested with a resulting index of 53.1 for the males and of 86.3 
for the females. Under similar conditions it will be recalled that 
a normal index would be approximately 95 and 97, though I 
have cages where it was considerably lower. ‘Thus, though there 
may be a slight effect from this operation, it is obviously not 
very great. Furthermore, it must be remembered that however 
quickly and accurately these flies might orient, they were neces- 
sarily handicapped in their speed of movement except when they 
took to wing. Since this experiment was performed under agi- 
tation this was frequently the case. As a matter of fact, orien- 
tation and movement toward the light was perfectly constant 
