BRADLEY M. PATTEN 



445 



This difference in response in the two cases is due to the difference in 

 the way the animals were brought into the field of light. When sub- 

 jected to balanced illumination, their initial direction of locomotion 

 was "in orientation" and it was only necessary to maintain it. The 

 symmetrically reduced photosensitive mechanism did this nearly as 

 effectively as the normal. Under lateral or anterior illumination the 



TABLE IV. 



Reactions to Balanced Illumination of Animals Previously Subjected to Symmetrical 

 Interference with Photoreceptive Mechanism. 



animal must change its direction of locomotion to come into orientation, 

 and this was accomplished less rapidly in animals with reduced photo- 

 sensitive areas than in normal individuals. Doubtless if the final 

 orientation were measured, it would vary but little from that of 

 normal animals. Since, however, the reactions are measured by 

 point of emergence from a standard circle, even slight variations in the 

 rate of coming into orientation became apparent, because the method 



