90 ROBERT STANLEY McEWEN 
TABLE 21 
LIGHT GRAVITY (VERTICAL) 
Male Female Male Female 
Temperature 24° 
GroupeAss:20 sara oes Sepa 16.6 7.5 03.3 41.6 
Temperature 23° 
Group saat wre te ee Sh Rene tee 7.5 5.8 78.3 44.1 
Groupe @uce. ee Sears Sere xe oe see 18.3 20.8 81.6 70.8 
Motels eae eek ace eer ere eee 42.4 34.1 213.2 | 156.5 
AVERT AD ESE esas eat ey emer reore ere 14.1 11.3 71.0 62.1 
further borne out by observation of the insects. They are fully 
as active as are those from normal stock. 
Finally, a number of normal, white and vermillion eyed and 
tan flies have been sectioned and examined, both with and with- 
out staining. So far, no histological abnormality has been dis- 
covered in the eyes of the tan insects, to account for their peculiar 
lack of response to light. 
EFFECT OF COLORED LIGHTS ON NORMAL AND MUTANT 
EYE COLORS 
A very considerable amount of work has been done by various 
investigators upon the effects of different wave lengths on or- 
ganisms which respond either positively or negatively to light. 
Though it has generally been found that animals as well as plants 
respond more readily to the more refrangible rays of the spec- 
trum, such is by no means invariably the case. In Daphnia, 
for instance, Lubbock (Journ. of the Linnean Society, 1881) and 
others have found that the green and yellow rays are more effec- 
tive than any of the others, including the blue and violet. Also 
in the case of simpler organisms, it has been shown by Engel- 
mann (Mast’s account, Mast ‘‘Light and the Behavior of the 
Lower Organisms’’) that Bacterium photometricium tends to 
form aggregations in the infra red. 
The general apparatus used in this work has already been de- 
scribed. The composition of the liquids used, together with the 
