228 EVIDENCE THAT DAPHXIAS 



placing the yellow in another trough, as before, for 

 comparison. The preference for the yellow was as 

 marked as ever. In the experiments with the red and 

 yellow the numbers were re-<pectively 



Trough 1. Trough 2. 



Under the In the Under the In the 



yellow. uncovered half. red. uncovered half. 



670 330 498 502 



When, therefore, the red solution was sufficiently 



light, the Daphnia^ were indifferent to it. In the 

 experiments with light blue the numbers were — 



Trough 1. Trough 2. Trough 3. 



Under In the Under In the Under In the 



the uncovered the uncovered the porceleaa uncovered 



yellow. hall. blue. half. plate. half. 



687 313 286 714 336 664 



One other possilile objei'tion also suggrsted itself to 

 me. I thought it might be SHid that the Daphnias 

 went under the yellow and the green not on account of 

 any preference for yellow or green light, but on account 

 of the shelter afforded by the coveriDg. To test this, 

 I covered one half of a trough over with transparent 

 glass, leaving the other uncovered ; but after twenty 

 observations I found the number of Daphnias in each 

 half to be practically identical. The mtre fact of the 

 covering, therefore, made no diEference. In this way I 

 was able to test the preference of the Daphnias for 

 various colours, and the result made it abundantly clear 

 that Daphnias have the power of distinguishing between 

 liglit of diffrreut wave-lengths, and that they prefer 

 the light which we call yellow and greeu. A\'hether it 

 actually appears to them as it di es to us is, of course. 



