AMONG SOME OP THE LOWER ANIMALS. 207 



spectrum, a little, however, if anything, towards the green end. 

 After scattering the Daphuias equably, I left them for five 

 minutes, and then put a piece of blackened cardboard over the 

 brightest part. After five minutes more, there were: — 



At the green end. In the dark. At the red end. 



Obs. 1. ...... 78 2 20 



2 72 3 25 



3 89 2 9 



4 82 4 14 



5 89 3 8 



410 14 76 



Here the two ends of the trough were equally illuminated ; but 

 the preference for the green over the red side was very marked. 



I then took five porcelain vessels, 7^- inches long, 2| broad, and 

 1 deep, and in each I put water containing 50 Daphuias. One 

 half of the water I left uncovered ; the other half I covered re- 

 spectively with an opaque porcelain plate, a solution of aurine 

 (bright yellow), of chlorate of copper (bright green), a piece of 

 x'ed glass, and a piece of blue glass. Every half-hour I counted 

 the Daphuias in each half of every vessel, and then transposed the 

 coverings, so that the half which had been covered was left exposed, 

 and vice versa. I also changed the Daphnias from time to time. 



Here, then, in each case the Daphnias had a choice between 

 two kinds of light. It seemed to me that this would be a crucial 

 test, because in every case the colored media act by cutting off 

 certain rays. Thus the aurine owes its yellow color to the fact 

 that it cuts ofi" the violet and blue rays. The light beneath it 

 contains no more yellow rays than elsewhere ; but those rays pro- 

 duce the impression of yellow, because the yellow is not neu- 

 tralized by the violet and blue. In each case, therefore, there 

 was less light in the covered than in the uncovered part. 



After every five experiments I added up the numbers of the 

 Daphnias; and the following Table gives 20 such totals, each con- 

 taining the result of 5 observations, making in all 100. 



My reason for adding one vessel in which one half had an 

 opaque cover was to meet the objection that possibly the light 

 might have been too strong for the Daphnias ; so that when they 

 went under the sheltered part they did so, not for color, but for 

 shade. I was not very sanguine as to the result of this arrange- 

 ment, because I had expected that the preference of the Daphnias 

 for light would have overcome their attachment to yellow. 



The numbers wer-e as follows : — 



LINN. JOTIKN. — ZOOLOGY, VOL. XYII. 16 



