QUANTITATIVE DETERMINATION OF LIGHT REACTIONS 227 



r 



a 



r 



Fig. 2 Three examples of test trails which pass the standard orientation test. 

 Each pair of trails was made by a different larva. Though there is some differ- 

 ence in the sharpness of orientation, each trail comes to lie parallel to the new 

 direction of light. 



Fig. 3 Three examples of test trails which do not pass the standard orientation 

 test. Each pair of trails was made by a different larva. Though there is a re- 

 sponse to the new direction of light in all cases, the larva fails in one or both of 

 its trails to come to complete orientation. 



