METHOD OF ORIENTATION TO LIGHT 369 



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 different positions of the insect 

 would have different effects, according to the theory of differen- 

 tial sensibility, 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 the varia- 

 tions caused by movements out of the horizontal plane. Since 

 the slight effects of differential sensibility would tend to neu- 

 tralize one another, any uniformly directed movements may be 

 attributed, with considerable probability, to the constant stim- 

 ulating effect of the light. 



Several experiments with different species of insects gave 

 very indefinite results. Some insects would not move, or simply 

 went to one side of the enclosure and crept around in contact 

 with the wall ; in other cases the movements were apparently 

 at haphazard. In general where the movements were indefinite 

 inside the enclosure they were equally so outside of it. Several 

 beetles belonging to three different species showed a tendency 

 to turn toward the blackened eye. Previous tests showed the 

 beetles to be negatively phototactic and their turning to the 

 blackened eye is what one might expect if they behaved within 

 the enclosure as most negative forms do under ordinary condi- 

 tions of unilateral stimulation. There was a considerable amount 

 of irregular spasmodic movement, as there generally is in the 

 phototactic activities of beetles, but their tendency to turn 

 toward the blackened eye was sufficiently pronounced to be 

 unmistakable. 



A Jerusalem cricket, Stenopelmatus, which is negative to 

 light was placed in the enclosure after having its left eye black- 

 ened over. When crossing from one side to the other it invari- 

 ably turned to the left, and when it came in contact with the 

 edge it continued to go around in that direction. When headed 

 in the other direction it would go but a short distance toward 

 the lighted side and then turn around again. 



Experiments with butterflies gave results that were variable 

 and in some respects puzzling. In one experiment a Euvanessa 

 antiopa with the right eye blackened over circled toward the 

 left directly eight out of eleven times. In the other three trials 

 it went ahead a short distance and then to the left. In seven 



