492 



ALFRED O. GROSS 



The flies were then tested with balanced hghts of the same 

 colors to determine to what extent the percentages of the responses 

 can be depended on to express the relative potencies of the lights 

 used. The results of tliis test are shown in table 6. 



The extreme amount of deviation in the percentages in table 

 6, which is only 4 units less than the expected theoretical ratio 



of 50 % 



50 % is found in the red. 



TABLE 6 

 Reactions of Drosophila to pairs of monochromatic lights of the same quality atir) 



of equal intensity 



In the following experiments on the responses of Drosophila 

 to balanced lights of different colors not less than 300 and some- 

 times as many as 500 individuals were used in each combination 

 of colors. The large numbers used tend to reduce the size of 

 the error of the results and to give a more correct representation 

 of the relative efficiencies of the four colored lights. Table 7 

 is a summary of the reactions of the pomace flies to balanced 

 pairs of monochromatic lights of different spectral qualities. 



A number of tests were made in which the flies were caught 

 in the retaining cylinder and run through a second series of 

 trials. This was done to determine whether or not flies exhibit- 

 ing a negative reaction to the individual colors or to the more 

 refrangible color of any pair of lights are permanently negative 

 or indifferent. The factor of mechanical stimulation of the flies 

 was eliminated in these experiments by allowing the flies to rest 

 and to become dark-adapted before using them in a second test. 

 The results of five such tests are shown in table 8. 



The results shown in tables 5, 6 and 7 are combined and 

 condensed into the simple table 9. 



