78 ROBERT STANLEY McEWEN 
if the slight falling-off of some of the antennaeless groups in 
table 13 is of any significance at all. From this result, therefore, 
as well as that obtained by the removal of legs we are led to con- 
clude that any operation as such is not sufficient to cause a loss 
of phototropism. Incidentally, however, a rather interesting re- 
sult does appear here as to the specific effect of the removal of 
the antennae and reaction to gravity. From the small amount 
of data on hand, it appears that the loss of these organs greatly 
reduces a fly’s negative geotropism. It also seems to produce a 
slight reduction in general activity. There are not, however, 
sufficient data collected on these particular points to do more 
than suggest a line for further investigation. 
EXPERIMENTS ON MUTANT WING-CHARACTERS 
We are now in a position to attempt the second method of 
analyzing our problem by testing the various sorts of wing mu- 
tants which have arisen in this laboratory. These mutants vary 
all the way from vestigial, in which the wings are mere stubs to 
curled, in which the wings though of normal length are turned 
upward at the end and are not very effective in flying. There 
are many other variants between these two, one of which is desig- 
nated as strap. Strap has wings almost as long as normal, but 
they are narrow, often cleft at the end, held off from the body 
at a peculiar angle and are useless for flight. These three mu- 
tants therefore were selected as bearing the closest approximation 
to insects with one-fourth, one-half and three fourths of the wing 
removed. The flies in question are represented in figure 2. A 
normal insect is also included for the sake of comparison. 
The tests on the above mutants have all been made ac- 
cording to the plan already outlined in one of the experiments 
for testing the effect of the removal of wings on light and gravity 
(p. 69). In brief, three tests were made for light, alternating 
with three tests for gravity, with the tube in the vertical posi- 
tion only. No agitation was used during any of these tests. 
Only one new point needs to be mentioned and that is in regard 
to an improvement in the apparatus. Under the former system 
of testing for geotropism the lamp whose rays struck the tube at 
