378 



WILLIAM L. DOLLEY, JR. 



In all but the fourth and fifth trials the organism turned toward 

 the functional eye, crossed the beam at a definite angle which 

 was smaller than on the preceding days, and, on reaching the 

 edge of the beam, turned at once to the left and walked along 

 this edge toward the glower. In the fourth trial it responded 

 very much like a normal specimen, walking down the center of 

 the beam in a fairly straight line. In the fifth it deflected toward 

 the blackened eye. No circus movements were made in any of 

 the trials on this day. 



ij b\ i" V !' " M lnT4 ^'.,7 b\ 



Fig. 4 Reproduction of 23 successive trails made by butterfly 10/25-a (left 

 eye blackened) on the third day of the tests, a and b, limits of horizontal beam 

 of light; 1-23, trails made in successive trials; small arrows, direction of movement 

 of animal; large arrows, direction of rays of light; illumination at x, 906 mc; at 

 y, 266 mc. Compare figures 2, 3 and 4 and note that the insect on the third day 

 made no circus movements, while on the two preceding days, it made numerous 

 ones. Note also that the angle at which it deflected with the rays of light 

 decreased. 



* By comparing all of the reactions observed during the three 

 days it will be seen that modification occurred in three different 

 respects, as follows: (1) On the first two days there were numer- 

 ous circus movements; on the third day there were none what- 

 ever; (2) On the first two days the butterfly usually passed into 

 the shaded region a considerable distance before it turned and 

 went toward the glower ; on the third day it turned toward the 

 glower promptly on reaching the edge of the beam; (3) The 

 angle of deflection was greatest on the first day and least on the 

 third, the average angle at the edge of the beam for the three 

 days being respectively 100, 89.5, and 41.5 degrees. The reac- 



