220 DAPHNIAS SUPPOSED TO PERCEIVE 



congregate wherever the light is strongest. Their eyes 

 are, however, so delicate that one would naturally expect, 

 a priori, that there would be a limit to this ; and, in 

 fact, direct sunshine is somewhat too strong for their 

 comfort. 



For instance, I took a porcelain trough, seven and a 

 half inches long, two and a half broad, and one deep, and 

 put in it some water containing fifty Daphnias. One 

 half I exposed to direct sunlight, and the other I shaded, 

 counting the Daphnias from time to time, and trans- 

 posing the exposed and shaded halves. The numbers 

 were as follows: — 



53 447 



This seems clearly to show that they avoid the full 

 sunlight. 



I believe, then, that in some of my previous experi- 

 ments the yellow light was too brilliant for them ; and 

 the following experiments seem to show that, when 

 sufficiently diffused, they prefer yellow to white light. 



M. Merejkowsky, however, denies to the Crustacea 

 any sense of color whatever. His experiments were 

 made with larvse of Balanus and with a marine cope- 

 pod. Bias longiremis. These, if I understand him 

 correctly, have given identical results. He considers 



