LIMITS OF VISION OF DAPHNIAS. 215 



red end of the spectrum, I used the same arrangement 

 as before, placing the trough so that the extreme 

 division was in the ultra-red, and the second in the red. 

 I then placed sixty Daphnias in the ultra-red. After 

 five minutes' exposure, I counted them. There were in 

 the— 



Red. Ultra-red, 



Exp. 1 54 ... 5 



„ 2 56 ... 4 



I now gave them four divisions to select from — dark, 

 red, ultra-red, and dark again. The numbers were — 



I then left them access to a division on the other side 

 of the red, which, however, I darkened by interposing a 

 piece of wood. This euabled me better to compare the 

 ultra-red rays with a really dark space : — 



Dark. Red. Ultra-red. 



Exp. 1 4 43 3 



„ 2 3 45 2 



These observations appear to indicate that their 

 limits of vision at the red end of the spectrum coincide 

 approximately with ours. 



I then proceeded to examine their behaviour with 

 reference to the other end of the spectrum. 



In the first place, I shut them off from all the rays 



