- 102 ROBERT STANLEY McEWEN 
to light. It appears fairly certain on the other hand that the 
chief light receiving organs are the compound eyes as shown by 
experiments with eyeless stock. 
3. Operations on the antennae may produce a weakening of 
the response to gravity, though they have little effect on the 
reaction to light. 
4. In a mutant stock of flies known as tan, there 1s clear-cut 
evidence for the sex linked inheritance of a character which may 
be described as indifference to light. It is apparently not due 
to any structural defect in the eye. 
5. Colored lights which may be conveniently described as vio- 
let, green and red, are effective in the order named upon insects 
whose eye color is lighter than the red eye of the wild fly. In 
the case of wild flies, and flies whose eyes are of a still darker 
shade called sepia, red is more effective than green. 
GENERAL DISCUSSION 
In most of the earlier work on various organisms, both animals 
and plants, the conclusion generally reached was that the blue 
and violet rays possessed much more stimulating value than 
aid those which are less refrangible, particularly the red and 
orange. Thus Payer (42) using both the solar spectrum and col- 
ored media found that seedlings turned toward blue and violet 
light but not toward red, yellow, orange or green. Sachs in 
1864 obtained similar results, using colored solutions and glass. 
Also in the case of animals Engelmann (’82) found that Euglena 
viridis collected in the blue of a solar and gas spectrum, while 
KE. B. Wilson (91) working on Hydra viridis with colored glasses 
again found the maximum effect in blue. Finally, Loeb’s ear- 
lier work (90-93) led him to conclude that as between red and 
blue, the latter color was the more effective for fly larvae, plant 
lice, caterpillars of Porthesia chrysorrhoea, moths of Sphinx 
euphorbia, Geometra piniaria, various copepeds, the meal worm 
Tenebrio molitor, the larvae of Polygordius, Limulus polyphemus, 
and the June bug Melolontha vulgaris. 
Even some of the early investigators, however, found cases in 
