396 DWIGHT E. MINNICH 



d. Effect of contact stimulus. The effect of the contact stimu- 

 lus afforded by the blackening material on the eye and the adja- 

 cent parts of the head must also be recognized as a considerable 

 factor in modification of photic behavior. The influence of this 

 stimulus has been clearly demonstrated by DoUey ('16, pp. 394- 

 397) on Vanessa antiopa. With one eye blackened, this butter- 

 fly, when creeping in total darkness, turned, with few exceptions, 

 continuously toward the blinded eye. The tendency to circle 

 was often quite pronounced, and showed little or no modification 

 from day to day. The effect of contact stimulus on the covered 

 eye was, therefore, antagonistic to that produced by light on the 

 opposite, functional eye. 



I tried experiments with the honey-bee similar to those car- 

 ried out by Dolley on Vanessa. Bees with one eye blackened 

 were allowed to creep on smoked paper in total darkness. Un- 

 fortunately, the trials were of such duration that the bee recrossed 

 its course many times. This made it quite impossible to decipher 

 the records, and I have not since had an opportunity to repeat the 

 experiments. It is not unlikely, however, that the effect of con- 

 tact stimulus on the eye of the bee is similar to that demonstrated 

 for Vanessa. If such be the case, it probably accounts for much 

 of the circling toward the covered eye, which was evinced by 

 numerous individuals particularly in non-directive light. 



e. Asymmetry of the animal. As was previously pointed out, 

 normal bees frequently exhibited a marked tendency to turn more 

 or less constantly toward the right or left when creeping in non- 

 directive light. Such tendencies are doubtless due to a lack of 

 perfect symmetry on the part of the animal. The asymmetry 

 may be physiological; it may be anatomical. It may consist of 

 a differential sensitivity of the photoreceptors on the two sides 

 of the body, as Patten ('14, p. 259) has suggested, or it may be due 

 to an inequality of any two symmetrically located elements of 

 the neuromuscular mechanism. Under the influence of directive 

 light, these idiosyncracies are, as a rule, continually corrected. 

 In non-directive illumination or total darkness, however, they at 

 once assert themselves. Since the eye to be blackened was always 

 chosen so that the effect of photic stimulation would be opposite 



