VANESSA ANTIOPA LINN. 463 



was resting in the shadow of a cloud, a movement of the hand might be made much 

 more extensive and much nearer the insect than that used in the shadow experiment, 

 without causing any disturbance. Hence I believe the reaction to be due to the 

 shadow. When the shadow was made to pass on or off the butterfly with great quick- 

 ness, the animal usually made some sudden movement, as, for example, a momentary 

 closing of the wings, but these responses would be repeated only once or twice, after 

 which quick shadow movements had no apparent effect. These slight reactions were 

 observed not only when artificially produced shadows were used, but also when natural 

 shadows, like those of a well-defined cloud, passed on or off the butterfly. In fact on 

 several occasions I have observed resting butterflies thrown into flight by the sudden 

 coming or going of a well-defined cloud-shadow. 



By means of the finger or, better, by a lead-pencil, in very clear sunlight, a 

 shadow of sufficient sharpness could be thrown to allow one to test the sensitiveness 

 of different parts of the butterfly's body. When a butterfly was resting in full sun- 

 light and a shadow was thrown on its wings, no reactions were ever observed with 

 certainty. The same was true when the shadow was thrown on the abdomen or the 

 thorax. When the shadow covered the head, however, the butterfly reacted much as 

 it did to shadows covering its whole body. Thus a butterfly, with its abdomen and 

 thorax in shadow, but with the rest of its body in full sunlight, remained quiet for 120 

 seconds; but when the shadow was transferred to the head the animal showed signs 

 of uneasiness at the end of 18 seconds. On repeating this experiment the periods 

 intervening between the moment when the shadow was applied and when the first 

 sign of uneasiness was observed were found to be respectively 14, 17, 15, and 16 

 seconds. Although these are longer intervals than those obtained when the whole 

 animal was in shadow, I do not think that they indicate that the general surface 

 of the body is sensitive to light, but that the shadow of the hand is deeper and hence 

 more effective than that of the pencil. Conclusive evidence on this point will be 

 given farther on. 



Since the head is the portion stimulated by light, it is natural to suspect that 

 the eyes are the particular parts concerned. Loeb ('97) has pointed out that the 

 orientation of an organism in fight is dependent upon the equal stimulation of 

 symmetrical points on its body. Should the eyes be the parts stimulated, any inter- 

 ference with one of these ought to result in a disturbance of the direction of the butter- 

 fly's locomotion. Thus, if the cornea of one eye were blackened, the insect in loco- 

 motion, being positively phototropic, ought to move as though that eye were in shade, 

 namely, in a circle, with the unaffected eye toward the centre. Specimens prepared 

 by blackening the cornea of one eye showed the expected response. When the right 



