88 ROBERT STANLEY McEWEN 
INHERITANCE OF PHOTOTROPISM IN DROSOPHILA 
In the Biological Bulletin, 1911, Dr. Fernandus Payne gives 
the results of some phototropic tests made upon Drosophila 
which had been bred for 69 generations in the dark. In the 
course of the work he discovered, as I have done, that there 
was great variation among individuals and he therefore made an 
attempt to test the inheritance of the reaction. He was unable, 
however, to obtain any significant results and this, so far as I 
know, is the only effort to study the inheritance of this reaction 
in Drosophila that has ever been made. 
It was with great interest, therefore, that I discovered that a 
certain stock of flies in this laboratory Showed very little re- 
sponse to light. This stock was a combination of three separate 
mutants which were being carried along together for the sake of 
convenience. It is known as eosin, tan, vermillion. Eosin and 
vermillion are eye colors while tan refers to a slightly tan tinge 
to the body and a clear tan in the antennae. The antennae of 
the wild flies are gray. At first thought, of course, it appeared 
likely that the peculiar reaction to light was due to the light 
eye color. Stock in which these eye colors occurred without the 
tan were therefore secured and tested. Neither of these eye 
colors, however, were any less phototropic than normal. It is 
unnecessary to give the figures for the tests here, since experi- 
ments performed later in connection with colored lights amply 
demonstrate the phototropism of these breeds. The fact still 
remained that the peculiar reaction of eosin and vermillion might 
be due to a combination in one fly of the factors producing these 
characters. As tan had arisen as a mutation in eosin vermil- 
lion stock, the only way to test this was to get the tan separated 
from the two eye colors. By a suitable series of crosses this was 
ultimately accomplished. It was then possible to test tan by 
itself. The test immediately showed that either the factor for 
tan itself or some other factor very closely linked with tan, was 
responsible for the peculiar light reaction. Whenever an insect 
was homozygous for tan it failed to react to ight. It may be 
stated at this point that tan is a recessive sex linked character. 
That is, the daughters inherit the factor for the character from 
