AMONG SOME OF THE LOWER ANIMALS. 



125 



I afterwards gave them only the option of ultra-violet, violet, 

 and darkness : — 



CJltra-violet. 



Exp. 1 8 



„ 2 6 



„ 3 12 



,, 4 15 



„ 5 4 



45 



Violet, 

 48 

 48 

 47 

 42 

 53 



238 



Dark. 

 4 

 6 

 1 

 3 

 3 



17 



I then tried ultra-violet and dark. The width of the violet was 

 2 inches ; and I divided the ultra-violet portion again into divi- 

 sions each of 2 inches, which we may call ultra-violet, further 

 ultra-violet, and still further ultra-violet. The results were : — ■ 



Number of Daphuias. 



Still further Further 



ultra-vioret. ultra-violet. Ultra-violet. 



Exp. 1 6 52 



„ 2 5 52 



„ 3 6 50 



„ 4 4 53 



„ 5 4 54 



286 



Dark. 

 2 

 3 

 4 

 3 

 2 



14 



May 18. — I again tried them with the ultra-violet rays, using 

 three divisions — namely further ultra-violet, ultra-violet, and 

 dark. The numbers were as follows, viz. under the 



Exp. 1. 



To my eye there was no perceptible difference between the 

 further ultra-violet and the ultra-violet portion ; but slightly un- 

 diffused light reached the two extreme divisions. It may be 

 asked why the still further ultra-violet division should have been 

 entirely deserted, while in each case two or three Daphnias were 

 in the darkened one. This, I doubt not, was due to the fact that 

 the darkened division being next to the ultra-violet, one or two 

 in each case straggled into it. 



