PREFERENCE FOR YELLOWISH GREEN. 



213 



Daphnias in a shallow wooden trough fourteen inches 

 by four inches, and divided by cross partitions of glass 

 into divisions, so that I could isolate the parts illumi- 

 nated by the different coloured rays. The two ends of 

 the trough extended somewhat beyond the visible 

 spectrum. I then placed fifty specimens of Daphnia 

 pulex in the trough, removing the glass partitions so 

 tliat they could circulate freely from one end of the 

 trough to the other. Then, after scattering them 

 equally through the water, I exposed them to the 

 light for ten minutes, after which I inserted the glass 

 partitions, and then coanted the Daphnias in each 

 division. The results were as follows : — 



101 



138 



12 



I may add that the blue and violet divisions were 

 naturally longer than the red and green. 



May 25. — Tried again the same arrangement, but 

 separating the yellow, and giving the Daphnias the 

 choice between red, yellow, green, blue, violet, and 

 dark : — 



18 



170 



36 



23 



