AMOIfG SOME OF THE LOWER ANIMALS. 209 



The result was very mai^ked. The first two columns show the 

 usual preference for light. If the covered half had been quite 

 dark, no doubt the difference in numbers would have been 

 greater ; but a good deal of light found its way into the covered 

 half. Still the result clearly shows that the Daphnias preferred 

 the lighter half. The numbers were 2048 in the dark to 2952 

 in the light ; and it will be seen that the preference for the light 

 was shown, though in different degrees, in almost every series. 



The result in the blue gives, I think, no evidence as to color- 

 sense. The numbers were respectively 2046 against 2954, and 

 were therefore practically the same as in the preceding set. 

 Since, however, a certain quantity of light was transmitted 

 through the blue, the result may indicate a want of sensitiveness 

 to the blue rays. 



In the red the numbers were 1928 as against 3072 . 



As regards the yellow, the results were very different, the 

 numbers being, under the yellow 3096, in the uncovered part 

 1904. Here, therefore, we see a very distinct preference, all the 

 more remarkable because the amount of light was really less than 

 in the uncovered part. 



In the green the numbers were much more equal, namely, 2406 

 against 2594. I do not, however, wish for the moment to draw 

 any conclusion from these last figures, though I give them for 

 what they are worth. The colored medium was, I believe, some- 

 what too opaque. "With a more transparent green, as will be seen 

 subsequently, the result would have been very different. 



At any rate the above observations seemed to show a marked 

 preference for yellow. Still I thought it might be objected 

 that, though the Daphnias obviously preferred the uncovered to 

 the shaded half of the vessel, and the yellow to the uncovered 

 half of the vessel, perhaps in the former the uncovered water 

 was rather too bright, and in the latter the shaded part was rather 

 too dark, and that after all the yellow was chosen, not because 

 it was yellow, but because it hit off the happy medium of in- 

 tensity. The suggestion is very improbable, because the obser- 

 vations were made on several successive, and very different, days, 

 and at very different hours. I also thought that the green was 

 perhaps too dark ; I took therefore a lighter tint, and rearranged 

 my little apparatus as follows : — 



I placed (March 26) 50 Daphnias in a trough (1), covering- 

 over one half of it with a pale green, and another 50 in a 



16* 



