254 



VASIL OBRESHKOVE 



front of the aquarium sufficient to bring about the desired inten- 

 sity of illumination was placed the electric bulb (n) properly 

 connected with a switch within easy reach. The arrangement of 

 the remainder of the apparatus was the same as when the light 

 came from above. 



TABLE 3 



Reaction-times in seconds of eyeless tadpoles of Rana clamitans to lights of differ- 

 ent intensities. Temperature, 19°C. Source of light above 



Usually two individuals at a time were placed in the aquarium. 

 These were kept far enough apart to avoid any shadow effect. 

 After the application of the stimulus the time of reaction of the 

 individual to move first was recorded. With an apparatus thus 

 arranged the eye as well as the side of the animal was illuminated. 



