406 DWIGHT E. MINNICH 



The resultant effect of these impulses on the opposite side of 

 the body is most probably an increase in the tonus of the extensor 

 muscles. I have no direct evidence on this point in the case of 

 the honey-bee. However, Holmes ('05) and Holmes and 

 McGraw ('13), in experiments dealing with unilateral stimulation 

 of photopositive insects, frequently observed that -the legs on 

 the side away from the stimulated eye were strongly extended, 

 while those on the same side exhibited a pronounced flexion. 

 Recently, Garrey ('17) has published an account of numerous 

 experiments in which the same phenomenon was observed. In 

 such animals it is clear that orientation is effected through a 

 difference in the posture and not through a difference in the speed 

 of the legs on the two sides of the body. This conclusion is 

 further substantiated by the results obtained by Dolley ('17) on 

 Vanessa. Careful measurement of the velocity of these butter- 

 flies showed that they did not creep faster in a very intense 

 illumination than they did in a fairly weak one. From the above 

 observations, therefore, it is clear that in many insects orienta- 

 tion is effected through changes of tension in the leg muscles. As 

 previously stated, I have not been able to observe any constant 

 and pronounced difference in the muscular tension on the two 

 sides of the body in the honey-bee, although I have made only 

 casual observations in this direction. I do believe that orienta- 

 tion is produced in this manner, however, and that the failure 

 to detect it was due to the slight degree of the tensions together 

 with the extreme rapidity of their execution. 



This attempt to analyze the process of orientation in the honey- 

 bee is, of course, far from complete. Certain features of it, how- 

 ever, may be defined with reasonable certainty. Thus, it is 

 clear that the stimulus regulating photic orientation is continu- 

 ous and not intermittent. Furthermore, it appears to be essen- 

 tial that at least some of the impulses arising in the eye be 

 transmitted to the opposite side of the body, where they probably 

 regulate the tonus of the extensor muscles. As far as it is known, 

 therefore, the process of orientation in the honey-bee is in strict 

 conformity with the 'continuous action theory.' 



