382 PROCEEDINGS OF THE AMERICAN ACADEMY. 



the larger light. Since such results appeared to be due to chance 

 orientation at the beginning of the trial, or after the insect had lost 

 its orientation by fluttering, the records of the direction of its response 

 were not made until it had crossed a line, on either side, at a dis- 

 tance of about 25 cm. from the normal axis. In the later trials no 

 attempt was made to place the insects in normal orientations at the 

 beginning of the trials, but they were dropped at random as nearly 

 as possible at the central position on the table. About the same 

 proportion between negative and positive responses was obtained as 

 when the attempt had been made to orient the animals. 



In all 1G4 trials were made in this way upon 7 different individuals 

 of Vanessa, with the following results : 



Toward large light. Indifferent. Toward small light. Total. 



143 1 20 = 164 



Thus it will be seen that 87.2 per cent of the responses were toward 

 the large light; 12.2 per cent were toward the small light; while 

 only a single one, or O.G per cent could be called indifferent. The ex- 

 cess of responses toward the large light .over those toward the small 

 was 123, or just 75 per cent of the whole. This result therefore con- 

 firms Parker's conclusion that Vanessa antiopa discriminates between 

 lights of different area falling with equal intensity upon the animal. 

 That so many as 12 per cent of the responses were toward the smaller 

 light is probably to be accounted for largely upon the chance orienta- 

 tion and the condition of making the record as soon as the insect had 

 crossed a given line at a certain distance from the starting place. One 

 or two instances were observed in which the butterfly actually turned 

 and went back toward the large light after having passed this limit in 

 the direction of the smaller one. 



7. Water Scorpion {Ranatra fusca Pal. B.). 



The interesting work by Holmes (: 05*) on the reactions of the 

 water bug Ranatra to light suggested this form as a favorable one 

 for use in the study of image-formation. Except under certain con- 

 ditions, Ranatra is very strongly positive to light, apparently of any 

 intensity, and reacts to it with great uniformity and persistence. 

 Holmes says (p. 315): " Light seems to dominate entirely this creature's 

 behavior when the phototactic reactions are once started. It does not 

 manifest any fear or awareness of any object in its environment save 

 the light which it so strenuously seeks. Its excitement increases the 

 longer it is operated with, and after a time it may be picked up 

 without feigning death, or with only a momentary feint." 



