REACTIONS TO LIGHT. 



91 



to react positively or negatively, they were put into a rectangular aquarium im- 

 pervious to light, except at the ends, and divided by a median partition. The ends 

 were covered with translucent celluloid film, care being taken, of course, to have 

 each end equally light. Random observations taken through 20 days show: 

 A, once in the blue compartment and 34 times in the red ; b, 6 times in blue and 39 

 times in red; c, 27 times in blue and 18 times in red; a total of 34 times in the 

 blue and 91 times in the red. 



If only A and b had been used, we would have been justified in concluding that 

 Amblyopsis is positively tropic toward the red end of the spectrum as against the 

 blue. If only c had been used, we would have been justified to draw the opposite 

 conclusion. The fishes in the red compartment had become nervous and were 

 swimming near the red window, that is, on the side opposite the opening between 

 the compartments. Their proneness to remain in the same compartment may 

 have been partly due to this nervousness, the cause for which was not apparent. 



Four specimens of Chologaster were placed in the apparatus having 6 different 

 colored compartments. Between January 26 and February 4 rather irregular 

 observations were made. 



The number of specimens for each compartment on a purely chance distribu- 

 tion would have been 12.6, leaving out of consideration the element that the end 



