CONCERNING THE RELATIVE PHOTOTROPISM OF 

 VESTIGIAL AND WILD TYPE DROSOPHILA. 



DR. ROBERT S. McEWEN, 

 DEPARTMENT OF ZOOLOGY, OBERLIN COLLEGE, OBERLIN, OHIO. 



In a previous investigation upon various phases of the light 

 and gravity reactions of Drosophila melanogaster, the present 

 writer concluded among other things, that the mutant race 

 known as vestigial is much less phototropic than is the wild fly. 1 

 Subsequent to this, however, W. H. Cole, using a somewhat 

 different technique from that of the author, arrived at quite 

 another conclusion. 2 He made his tests in a vertically placed 

 glass tube, with the source of light above it, and under these 

 conditions he found that vestigial flies when attempting to climb 

 the smooth walls of the tube constantly lost their footing, and 

 slipped back. Thus they made poorer records than did 

 winged insects, which, when they slipped, used their wings 

 to catch themselves. This circumstance, according to Cole, 

 entirely accounts for any apparent difference in the phototropic 

 response of these two types of Drosophila. The correctness of 

 this interpretation he seems to have proven by lining the glass 

 with thin rice paper which enabled the wingless animals to 

 obtain a secure footing, under which condition they made as 

 good records as did the flies with wings. 



It is to be noted that throughout these experiments only tests 

 with a vertically placed tube were made. This was done on the 

 assumption that the negative response to gravity which Droso- 

 phila gives would be constant, and that, therefore, any additional 

 response would be due solely to the light placed above the tube. 

 That this was apparently true Cole showed by testing the 

 insects when only a very dim red light was present, as well as 

 with lights of varying intensities. Nevertheless, in view of the 



1 McEwen, R. S., "The Reactions to Light and to Gravity in Drosophila and 

 its Mutants," Jour. Exp. Zoo/., 25: 49, February, 1918. 



2 Cole, W. H., "Note on the Relation Between the Photic Stimulus and the 

 Rate of Locomotion in Prosophila." Science, LV., No. 1434, June 23, 1922. 



354 



