406 



WILLIAM L. DOLLEY, JR. 



Butterfly 10/3-a (right eye blackened) was placed in non- 

 directive light of very low intensity, and this intensity was then 

 still further decreased. It was found that circus movements 

 toward the functional eye continued to be performed until the 

 intensity reached 0.24 mc. When it was, however, still further 

 decreased, the courses became more and more direct, until at 0.09 

 mc. the animal moved in a fairly straight line. When the in- 

 tensity was lowered still further the butterfly deflected toward 

 the hlackened eye, and when it had reached 0.0265 mc. the insect 

 moved in 'circles,' turning toward this eye. 



Fig. 18 Reproduction of trails made in non-directive light of low intensity, 

 2 mc, by butterfly 10/13-a (left eye blackened). Note that the animal moves in 

 small 'circles' continuously toward the functional eye. 



The reactions described above are typical of those exhibited 

 by the twenty-one butterflies exposed to non-directive light of 

 different intensities, as is shown in tables 7 and 8. 



From table 7 it can be seen that out of sixteen animals tested 

 in non-directive illumination of two intensities, one 230 times 

 greater than the other, in not a single case did an animal move 

 in smaller 'circles' in the higher than in the lower intensity. On 

 the contrary, four butterflies actually made much smaller 'circles' 

 in the weak light than they did in the strong light, and three 

 animals made shghtly smaller 'circles' in the weaker light. More- 

 over, one insect which made circus movements in the weaker 

 light did not make any at all in the stronger, but rather went in 



