164 WILLIAM L. DOLLEY, JR. 



the ratio between the duration of the light and dark periods is 

 1/3 are of higher stimulating efficiency than the lights of corre- 

 sponding flash-frequency but in which the ratio between the 

 light and dark periods is 1/1 and 3/1. Similarly, those lights 

 of flash-frequencies of 5 and 2 per second in which the ratio 

 between light and dark periods is 1/3 are of lower stimulating 

 efficiency than those lights of corresponding flash-frequency but 

 in which the ratio between light and dark periods is 1/1 and 3/1. 

 This indicates that the stimulating efficiency of intermittent 

 light depends on the ratio between the duration of the light 

 and dark periods and that the ratio at which it is most efficient 

 at higher flash-frequencies is different from that at which it is 

 most efficient at lower flash-frequencies. This conclusion is 

 confirmed by the results obtained in all of the experiments made 

 which are presented in tables 5 and 6. The significance of the 

 results presented in table 5 is not evident, however, until the 

 data are analyzed, as is done in table 6. 



The data hi table 6 may be made clearer by a brief explanation 

 of those given for one of the lights, e.g., intermittent light of a 

 flash-frequency of 15 per second produced by a disk with one- 

 half removed. This is given the serial number "2" because 

 66.66 per cent, or 4 out of the 6 butterflies tested in this light 

 and in the light of a flash-frequency of 15 per second produced 

 by a disk with three-fourths removed deflected more toward 

 the source of intermittent light in the former than in the latter. 

 In the same way a greater proportion of butterflies deflected 

 more in the same direction in the lights listed under serial order 

 number "1" than in those under "2." 



It is to be noted that the relative stimulating efficiency of 

 many of the lights is determined by comparatively small per- 

 centages. For example, the light of a flash-frequency of 15 

 produced by a disk with one-fourth removed is assigned a higher 

 stimulating efficiency than the light of a flash-frequency of 2 per 

 second produced by a disk with three-fourths removed because 

 only 60 per cent of the animals tested in both of these lights 

 deflected more toward the source of intermittent light than 

 toward the other source in the former than in the latter light. 



