REACTIONS OF AMBLYOPSIS TO LIGHT. 319 



fishes in the end of greater intensity could not have been due to 

 a preference for that end. 



With the light in the same position and with half of the 

 aquarium darkened by means of a light screen, counts were again 

 taken as before. First one half of the aquarium and then the 

 other was made dark. Sometimes these counts showed more 

 fishes in the dark ; at others more in the light. Under natural 

 conditions the fishes swim very slowly. During these observations 

 their movements were much faster, thus indicating that they are 

 photodynamic. All subsequent observations, whether the light 

 was of a low or high intensity, brought out this fact very 

 distinctly. 



On account of the shape of the lamp, it could not be brought 

 closer than 32 inches and still illuminate the whole aquarium. 

 I therefore made a small aquarium, 7 inches long, 5 inches high 

 and 4 inches wide, and suspended it within the larger. In this 

 case the heat screen was removed as there was always three or 

 four inches of water between the fishes and the lamp. With the 

 lamp only nine inches from the end of the small aquarium and 

 with half of the aquarium darkened in various ways, I took a 

 large number of counts. These observations were made on three 

 series of fishes. The results were again conflicting. In the 

 majority of cases a larger, sometimes a much larger number of 

 fishes were seen in the dark, but sometimes a larger number were 

 observed in the light. The fishes seem to be disturbed more 

 with the light at this distance than when it is 32 inches from the 

 end of the aquarium. 



At the university an 800 candle power arc lamp was used. 

 The heat and light screens were again placed in position and dur- 

 ing the observations the^ entire aquarium, except the end where 

 the light entered, was covered with heavy black cloth. The 

 fishes were transferred from the cave to the aquarium in a closed 

 vessel and hence were not exposed to the light. They were left 

 in the aquarium, at least twenty-four hours before observations 

 were made, so they could become accustomed to the new condi- 

 tions. Also after taking one series of counts they were left sev- 

 eral hours before making other observations. With the lamp 16 

 inches from the end of the aquarium, counts were taken every 



