PHOTIC REACTIONS OF HONEY-BEE 391 



VII. VARIABILITY OF PHOTIC RESPONSE 



The honey-bee is remarkably constant in the strong positive 

 phototropism which it evinces. The course of individuals creep- 

 ing in directive light is a straight path toward the source. Yet, 

 as has been shown, occasional departures from this behavior do 

 occur. In non-directive light, moreover, the responses of normal 

 bees are frequently extremely variable. The animal may turn 

 markedly toward a given side in one trial, and in the next, turn 

 quite as markedly toward the opposite side. Again, the direc- 

 tion of turning may be completely changed several times in the 

 course of a single trial. 



It is not surprising, therefore, that bees with one eye blackened 

 also exhibit considerable variability of response in both directive 

 and non-directive illumination. In non-directive light particu- 

 larly, there were a number of cases in which animals turned little 

 or not at all toward the functional eye, while there were still 

 others in which they circled chiefly toward the covered eye. In 

 fact, over 25 per cent of the first four pairs of determinations on 

 the fifty-two bees, when averaged, gave negative values. These 

 departures from the more usual tendency, to turn toward the 

 functional eye, sometimes characterized the entire behavior of 

 an individual ; again, they appeared only spasmodically. 



Thinking that some of the results above mentioned might be 

 attributed to a loss of phototropism, either permanent or extend- 

 ing over a considerable interval of time, I frequently subjected the 

 animals exhibiting them to one or more immediate trials in direc- 

 tive light. This, however, failed to show anything which might 

 be construed as a loss of phototropism. The variations of 

 response noted, therefore, must be referred to external and internal 

 factors which are capable of modifying, in a more or less profound 

 way, the dominating effect of unilateral photic stimulation. 

 Such factors are of two sorts, those which are continuously effec- 

 tive and those which are not continuously effective, but fluctuate 

 from time to time. Both types played so considerable a role in 

 the experiments previously described, that I have felt they mer- 

 ited the somewhat extended analysis presented in the following, 

 pages. 



