320 FERNANDUS PAYNE. 



minute for thirty minutes and with ten fishes in the aquarium. 

 First the right half was darkened. These counts gave me 84 

 fishes in the light to 216 in the dark. I then lighted the whole 

 aquarium to see whether they would seek the end away from the 

 light, i. <?., the end of less intensity. These counts gave me 85 

 fishes in the end of greater and 215 in the end of less intensity. 

 Here is a difference of 130, while with the one hundred candle 

 power lamp 32 inches from the end of the aquarium, there was 

 a difference of only 26. 



With the aquarium just sufficiently light for me to see the 

 fishes, I took counts to see whether they remained at the surface 

 or near the bottom. These counts showed 10 1 fishes in the 

 upper half and 199 in the lower. This indicates that they are 

 positively geotropic. To determine whether their positive geo- 

 tropism would be overcome by their negative heliotropism, I 

 darkened first the lower and then the upper half of the aquarium. 

 With the lower half dark, the counts showed 56 fishes in the 

 light to 244 in the dark and with the upper half dark 1 2 1 in the 

 light to 1 79 in the dark. While their geotropic reaction is partly 

 overcome by their negative heliotropism, it is not wholly so. 



To determine whether the direction of the rays of light 

 plays any part in the movements of the fishes, the light was 

 placed 14 inches above the surface of the water. As no conve- 

 nient heat screen was at hand, a clear glass which fitted snugly 

 against all sides of the aquarium, was lowered 2^/ 2 inches beneath 

 the surface. Thus there was always 2^ inches of water between 

 the fishes and the light. With the lamp in this position, I dark- 

 ened first one end and then the other and took counts as before. 

 Thirty counts with the left end dark showed 68 fishes in the light 

 and 232 in the dark, and with the right end dark 64 in the light 

 and 236 in the dark. At the end of each count, I shifted the 

 light screen to the opposite end, and each time the fishes within 

 two or three minutes changed to the dark end again. This im- 

 mediate change, with the shifting of the light, proves conclusively 

 that the light is the only factor which caused them to seek the 

 dark. These counts confirm the conclusion of Eigenmann that 

 they seek the dark regardless of the direction of the rays. 



With the light coming from above, we get a larger percentage 



