AMONG SOME OP THE LOWER ANIMALS. 211 



went under the green and yellow glass, not on account of the 

 color, but for the sake of shade, then in trough 3 a majority of 

 them would have gone under the porcelain plate. On the other 

 hand, if the porcelain plate darkened the water too much, and 

 yet the open water was rather too light for the Daphnias, then 

 in the fourth trough they would of course avoid the illuminated 

 half. The results show that the third trough was unnecessary ; 

 still I will give the figures, as the fourth proves that the Daphnias 

 preferred a light somewhat brighter than the ordinary diffused 

 light of the room. 



It may be said that perhaps in the previous experiments (p. 208) 

 the red and blue were too dark. I therefore took a very pale 

 solution, and counted the number 20 times for the red and 10 for 

 the blue, placing the yellow in another trough, as before, for 

 comparison. The preference for the j'^ellow was as marked as 

 ever. In the experiments with the red and yellow the numbers 

 were respectively 



Trough 1. Trough 2. 



When therefore the red solution was sufficiently light the 

 Daphnias were indifferent to it. In the experiments with light 

 blue the numbers were : — 



Trough 1. Trough 2. Trough 3. 



One other possible objection alsc suggested itself to me. I 

 thought it might be said 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 

 covering. To test this, I covered one half of a trough over with 

 transparent glass, leaving the other uncovered ; but after 20 

 observations I found the number of Daphnias in each half was 

 practically identical. The mere fact of the covering therefore made 

 no difference. On the whole, then, it seems to me that the 

 Daphnias have the power of distinguishing between light of dif- 

 ferent wave-lengths, and that they prefer the light which we call 



