The Problem of Orientation 85 



tively moving animal. In one set of experiments 

 the insect was placed in a jar lined below and at 

 the sides with white paper. "This was covered by 

 a cone of the same material in the apex of which 

 was placed an electric light. A small peep hole 

 permitted the observation of the insects in the jar. 

 In several experiments the insect was placed in a 

 small circular glass dish in the center of the en- 

 closure. Whether the insect turned to the right 

 or to the left in this apparatus the amount of light 

 entering the eyes was approximately the same. In- 

 sects with one eye blackened over were placed in 

 the jar and stimulated to activity whenever they 

 came to rest by tapping on the jar, or when this 

 failed by poking them with a wire. The very slight 

 variations in the light entering the eye in the dif- 

 ferent positions of the insect would have different 

 effects, according to the theory of differential sen- 

 sibility, depending on the position of the insect, and 

 would not tend to produce a constant deviation of 

 the path in any particular direction. The same may 

 be said of variations caused by movements out of 

 the horizontal plane. Since the slight effects of dif- 

 ferential sensibility would tend to neutralize one an- 

 other, any uniformly directed movements may be at- 

 tributed, with considerable probability, to the con- 

 stant stimulating effect of the light." 



Several negatively phototactic beetles placed in 

 the apparatus showed a general tendency to turn 

 toward the blackened eye. A Jerusalem cricket, 



