376 DWIGHT E. MINNICH 



in a rapid decrease of photic stimulation. As the loop is com- 

 pleted, the photoreceptor in turn experiences an increase in 

 stimulation. In non-directive illumination such as was employed 

 in the present experiments, however, these complications are 

 largely avoided. Photic stimulation here is maintained at a 

 fairly uniform and constant intensity over the entire surface of 

 the compound eye. 



Two slightly different types of experiment were performed. 

 The procedure in the first type was as follows. Bees were col- 

 lected from flowers in the morning between 8 and 10 o'clock, 

 brought into the laboratory and prepared for experimentation. 

 One and two hours later, respectively, they were given single 

 trials in the directive light area. On a basis of these records, 

 individuals of abnormal tendencies were discarded, and those evinc- 

 ing the greatest accuracy of orientation were selected. 



An hour or so later, the selected bees were tested in non- 

 directive light of 957 mc. Two sets of records, about one hour 

 apart, were made of each animal. Each set was composed of 

 one to several records, the aggregate duration of which, in gen- 

 eral, was between thirty and sixty seconds. An examination of 

 the records showed clearly whether the individual was normally 

 right-handed, left-handed, or variable in its deflection in non- 

 directive light. These results determined which eye should be 

 blackened. If, for example, a bee normally circled to the right, 

 the right eye was covered. Whatever influence was exerted by 

 photic stimulation, therefore, would tend to force the animal 

 toward the left. In this manner, responses which might other- 

 wise have been mistakenly attributed to photic stimulation were 

 to some extent eliminated. 



The operations of blackening the eye were carried out in the 

 late afternoon of the first day of experimentation, in accordance 

 with the technic previously described. On the following morn- 

 ing, before resuming experimentation, it was not infrequently 

 necessary to discard a few additional animals either because of 

 extreme weakness or occasionally death as a result of the operation. 



The majority of bees usually appeared quite normal, however, 

 and were subjected to several series of trials in non-directive 



