382 WILLIAM L. DOLLEY, JR. 



It shows, moreover, that in 16 of the 27 individuals tested on 

 more than one day orientation occurred in more trials of the last 

 day than in those of the first, and that in 18 of the 27 individuals 

 orientation at the edge of the beam occurred more promptly 

 during the trials on the last day than it did during those on the 

 first. This is well illustrated by the reactions of butterfly 

 10/25-a, described in table 1 and in figures 2, 3, and 4. 



It shows, furthermore, that in 20 of the 27 individuals circus 

 movements decreased in number, and that in 20 the average 

 angle of deflection was less in the trials of the last day than it 

 was in those of the first. Although not shown in table 1, 10 indi- 

 viduals performed fewer circus movements in the last trials of 

 the first day of the tests than in the first trials on this day. 



This seems to indicate clearly that with practice there is in 

 Vanessa with but one functional eye improvement in the accuracy 

 of orientation in three respects, as previously stated : (a) increase 

 in promptness of orientation, (b) decrease in the number of circus 

 movements performed, and (c) decrease in the angle of deflection. 



If this is true, then it is evident that orientation is not depend- 

 ent upon the stimulation of both retinas by equal amounts of light 

 energy. This conclusion is strongly supported by the fact that 

 in 171 out of 3077 trials the organism with but one functional eye 

 did not turn either to the right or the left, but moved fairly 

 directly toward the source of light. It is moreover supported 

 by the results obtained in observations on: the relation between 

 the degree of curvature in circus movements and the luminous 

 intensity, relation between the angle of deflection and the lumin- 

 ous intensity, and reorientation after changing the direction of 

 the beam of light. These are discussed in the following para- 

 graphs. 



2. Relation between the degree of curvature in circus movements 

 and the luminous intensity 



According to the 'continuous action theory' smaller curves 

 should be made in the strong light in the beam than are made in 

 the weak light outside the beam, for the adherents of this theory, 

 as stated above, hold that the tension of the muscles of the legs 



