PHOTIC REACTIONS OP HONEY-BEE 375 



taken by the animals under these conditions assumed no specific 

 direction. They either continued to circle in a fairly limited 

 area or proceeded in a looping fashion in any direction whatever. 

 The variability of this response, moreover, was much greater 

 than in the case of the response to directive light. Thus, a num- 

 ber of animals circled almost continuously toward the covered 

 eye in non-directive light, while still others varied, circling some- 

 times toward the covered eye, sometimes toward the functional 

 eye. This was doubtless true for much the same reasons that 

 normal bees also exhibited a greater variability of response in 

 non-directive light. 



Circus movements attendant upon the elimination of one pho- 

 toreceptor undoubtedly represent the orienting process of an 

 asymmetric animal. The specific photic stimulus, therefore, 

 which produces these reactions must be identical with that which 

 effects orientation in the normal animal. Whatever the nature 

 of this stimulus be, moreover, it is afforded by both directive 

 and non-directive light, since circus movements occur in either 

 situation. What is the nature of this orienting stimulus? Per- 

 haps the best method of demonstrating the dependence of a par- 

 ticular response upon a certain stimulus is to show that the in- 

 tensity of the response varies with the intensity of the stimulus in 

 question. It seemed possible to attack this problem, therefore, 

 through a study of the relationship existent between the amount 

 of turning displayed by an animal with one eye blackened and 

 the intensity of the illumination to which it was subjected. 



Non-directive illumination was chosen in preference to direc- 

 tive illumination because of the simpler experimental conditions 

 which the former affords. In directive light, every movement 

 of the entire animal is accompanied by more or less complicated 

 changes not only in the intensity of the stimulation received, but 

 also in the area of the eye stimulated. As an animal with one 

 eye covered moves toward a light source, the stimulation of the 

 functional eye steadily increases. As it loops toward this eye, 

 however, this steadily increasing stimulus is subjected to rapid 

 and transitory fluctuations. When the animal begins to loop, 

 the functional eye is first turned away from the light, resulting 



