214 EXPERIMENTS. 



Of course, it must be remembered that the yellow band 

 is much narrower than the green. I reckoned as yellow 

 a width of three-quarters of an inch, and the width of 

 the green two inches. 



M. Paul Bert observes Qoc. cit.) that in his experiments 

 the Daphnias followed exactly the brilliance of the 

 light. It will be observed, however, that in my expe- 

 riments this was not the case, as there were more 

 Daphnias in proportion, as well as absolutely, in the 

 green, although the yellow is the brightest portion of 

 the spectrum. In fact, they follow the light up to a 

 certain brightness ; but, as will be seen presently, they 

 do not like direct sunshine. 



I then arranged the trough so that the yellow fell in 

 the middle of one of the divisions. The result was — 



Number of Daphnias. 



25 113 12 



May 18. — In order to test the limits of vision at the 



