AMONG SOME OF THE LOWEE ANIMALS. 127 



Under the film of Under the 



chromate of potash. water. 



Exp. 1 8 52 



„ 2 4 56 



„ 3 10 50 



„ 4 7 53 



Evidently even a film of chromate of potash exercises a 

 very considerable influence ; and indeed I doubt not that, if a 

 longer time had been allowed, the difference v7ould have been 

 even greater. 



It seems clear, therefore, that a film of a 5-per-cent. solution of 

 chromate of potash only -i- inch in thickness, which cuts off the 

 ultra-violet rays, though absolutely transparent to our eyes, is by no 

 means so to the Daphnias. 



I then again returned to the sulphate of quinine ; but instead 

 of placing it close to the water, I suspended it at a height of 

 3 feet, so that the Daphnias were far less directly illuminated by 

 the scattered light. 



As in the preceding case, 1 placed by the side of it a similar 

 cell containing water, and suspended them side by side over the 

 water containing the Daphnias, and reversed the position after 

 each experiment. The numbers were as follows : — 



Under the Under the 



sulphate of qiiinine. water. 



Exp. 1 13 47 



„ 2 17 43 



„ 3 12 48 



„ 4 11 49 



„ 5 20 40 



„ 6 18 42 



„ 7 20 40 



„ 8 15 45 



Although the contrast in this latter series is not so great, stiU 

 it is unmistakable. It seems to me, therefore, though I differ 

 with great reluctance from so eminent an authority as M. Paul 

 Bert, that the limits of vision of Daphnias do not, at the violet 

 end of the spectrum, coincide with ours, but that the Dap hnia, 

 like the ant, is affected by the ultra-violet rays. 



