408 



WILLIAM L. DOLLEY, JR. 



fairly straight courses with a decided curve toward the uncovered 

 eye. In the case of seven individuals the trials made in the two 

 conditions of illumination were indistinguishable. 



In table 8 are given the results obtained when non-directive 

 light of a very low intensity was used. 



TABLE 8 



Amount of decrease in intensity of non-directive light necessary to force the butter- 

 flies to cease making circus movements toward the functional eye and to make 

 circus movements in the opposite direction 



This table shows, in general, that the animals placed in non- 

 directive light of low intensity, half a meter-candle or less, make 

 circus movements toward the functional eye ; that if the inten- 

 sity of the light is then decreased, the insects deflect less and 

 less until their courses become relatively straight; and that if 

 the intensity is then still further decreased, they move in 'circles' 

 toward the blackened eye. 



It must be concluded from these reactions that it is probably 

 true that in light below certain limits, the effect of the light 

 and that of the covering of the eye, may become equal. But, if 

 this is true, it does not necessarily mean that the nature of the 

 stimulus produced by the contact of the covering with the eye 

 and that caused by light in the opposite eye is the same. It is 

 possible that while the covering probably stimulates through its 

 continuous action, light may stimulate by virtue of change of 

 intensity. This may well be so, and yet the effect of the two 



