74 



WILLIAM H. COLE 



single lamp was used either at the top or the bottom. When 

 the top lamp was lighted 98.5 per cent of the flies went to the 

 top after one minute, the others reaching the middle section. 

 Twenty trials with 12 different animals were made. 



With illumination from below 70 trials on 21 flies resulted 

 in 61 per cent going to the uppermost third and 22.5 per cent 

 remaining in the lowest third. Thus when light acts contrary 

 to gravity a smaller number of flies are found at the top. It 

 is interesting to note that the light stimulus, contrary to expec- 

 tation, did not predominate over gravity. An increase of the 

 light intensity from 16 candle power to 40 made no difference 

 in the results. 



A set of records from an experiment in which the light was 



below the cylinder and therefore acted contrary to gravity is 



given in Table III. 



TABLE III 



Showing the position of 5 flies in 14 trials after having been in the light box with 

 a single lamp (15-watt Mazda) below the cylinder; 55.7 per cent crept to the upper- 

 most third. 



Number of Flies in the Different Sections of Cylinder 



These results corroborate previous work on this subject in 

 so far as a negative response to gravity is concerned. But in 

 this, as well as in all previous work, mechanical or light stimuli 

 have been operating. The former cannot be eliminated in such 

 experiments since it is impossible to invert the cylinder without 

 moving it. Consequently I next tried a series of centrifuging 

 experiments in which these two kinds of stimuli could be neg- 

 lected. So far as I am aware the effect of centrifugal force on 

 Drosophila has never before been studied. 



