MULTICELLULAR ANIMALS AND COLOR 339 



this animal is positive in ultra-violet indicate the same 

 thing. 



Lubbock's primary object in this work, however, was to 

 test the color vision of Daphnia. I can do no better than 

 to quote at length the experiments which bear on this 

 question: 



'' I placed (March 26) fifty Daphnias in a trough (i), 

 covering over one half of it w^th a pale green, and another 

 fifty in a trough (2) half of w^hich w^as covered with yellow 

 (aurine). On one side was a similar trough (3), one end 

 of which was shaded by a porcelain plate; and on the 

 other side a fourth trough (4), one end of which had a 

 little, though but little, extra light thrown on it by means 

 of a mirror. As before, I counted the Daphnias from 

 time to time, and turned the troughs round. All four 

 were in a light room, but not actually in direct sunshine. 

 Thus, then, in one trough I had half the water in some- 

 what green light; in the second trough, half the water in 

 yellow light; in the third, one half was exposed and the 

 other somewhat darkened; while the fourth, on the con- 

 trary, gave me a contrast with somewhat more vivid 

 light. If, then, the Daphnias w^ent 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, have avoided the 

 illuminated half. The results show that the third trough 

 was unnecessary, still I may as well give the figures; the 

 fourth proves that the Daphnias preferred a light some- 

 what brighter than the ordinary diffused light of the room. 

 Of course it does not follow that the effect of color is the 

 same as with us " (p. 226). 



The results of twenty trials are recorded, but since all 

 are essentially the same I shall quote only the following 

 five (p. 227) : 



