PHOTIC REACTIONS OF TADPOLES 



255 



The sensitivity of animals was tested under the two conditions: 

 1) skin alone and, 2) eye and skin. Such experiments furnished 

 further data for a test of the validity of the Bunsen-Roscoe law 

 as applying to the photosensitivity of this animal. 



In table 4 are given the reaction-times of tadpoles to lights of 

 different intensities when eye and skin are exposed to light (A) 

 and after the eyes had been removed (B), the light in both 

 instances being applied from the side. The reaction-times of 



@« 



Fig. 3 Diagram of apparatus for testing the sensitivity of the eye as compared 

 with the skin, m, rectangular glass aquarium; n, light. 



animals with eye and skin were so similar to those obtained 

 from corresponding intensities with blind tadpoles either when 

 the source of stimulus w^as from the side or from above, that 

 it was not found necessary to carry the work beyond five inten- 

 sities, only four of which were effective. This is apparent by 

 comparing the results in table 4 with those in tables 1 and 3. 

 That with the gradual increase in the intensity of illumination 

 the stimulus becomes more and more effective for bringing about 

 a prompt form of response is again demonstrated here by the 

 gradual decrease in the standard deviation and probable error 



