220 DAPHNIAS SUPPOSED TO PERCEIVE 



con£rre"ate wherevor the liirbt is stvoiii^ost. Their eye-i 

 nre, however, so delicate thut one would naturally ex])Oct, 

 a 2^riori, that there would be a limit to this; and, in 

 fart, direct suushino is somewhat too ftrong for their 

 ooinfort. 



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

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

 })nt 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 

 u ere as follows : — 



At 10 40 a.m 



„ i^-'-o „ 



„ 1.10 „ 



„ i:!"' „ 



„ 1-50 „ 



., 2 5 , 



,, -2 10 „ 



„ 3.0 „ 



„ 40 „ 



„ 4o0 , 



r.a -1 17 



This seems eh-arly to show that they avoid the full 

 sunlight. 



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

 ments the yellow light \N'as too brilliant for them ; and 

 the following experiments seem to show that, when 

 sufficiently difl'iisod, they prelV'r yellow to white light. 

 M. Merejkousky. however, denies to the Crustacea 

 any sense of color whatever. His experiments were 

 made ^^ith Luva> of Balioiiis and \\ith a ujarine cope- 

 pod, Dias loiKjirt'iuis. 'J'hese, if I understand him 

 correctly, havt' given iileutical I'esults. \\v considers 



