REACTIONS TO LIGHT IN VANESSA ANTIOPA 417 



times the insect does not turn toward the source of hght until it 

 has gone a few centimeters beyond the edge of the beam. The 

 angle through which the butterflies turn before they proceed 

 toward the edge of the beam, varies in different individuals and 

 in the same individual under different conditions. Moreover this 

 angle bears no observable relation to the luminous intensity. It 

 was found to be the same in 200 mc. as in 2000 mc. 



4. In non-directive light, or before an open window, these 

 insects move in circles toward the functional eye, and continue to 

 do so, showing no apparent improvement. This is probably due 

 to the absence of changes of illumination on the surface of the 

 eye. Thus, the performance of circus movements is, in many 

 cases dependent upon the approximately equal illumination of 

 large areas of the functional eye in all the positions assumed by 

 the organism. 



5. Circus movements, however, throw no light on the nature 

 of the stimulus effective in orientation, for the slightest change in 

 position of the head may produce changes of intensity on certain 

 ommatidia in the functional eye. 



6. Vanessas with one eye blackened do not move in smaller 

 circles in strong light than they do in weak light, unless it is 

 extremely low. On the contrary, the evidence seems to indicate 

 that the stronger the light is the larger the circles are. These 

 results also are not in harmony with those demanded by the 

 'continuous action theory.' 



7. If, however, the intensity of non-directive light is made very 

 low, Vanessa with but one functional eye deflects neither to the 

 right nor to the left, and, if it is made still lower, it moves in 

 circles toward the blinded eye. 



8. These animals modify their behavior as the result of repeated 

 trials. This modification in reactions is shown in three respects: 

 (1) decrease in the number of circus movements made, (2) decrease 

 in the' angle of deflection and (3) increase in the promptness with 

 which they orient on reaching the edge of the beam. 



9. If the luminous intensity is suddenly changed when speci- 

 mens of Vanessa antiopa with one eye blackened have oriented in 

 a beam of light, and are moving toward the source of light at a 



