342 LIGHT AND THE BEHAVIOR OF ORGANISMS 



the specimens collected in the red and yellow, whereas in 

 the sunlight spectrum most of them collected in the yel- 

 low, green and blue. In the former, then, they collected 

 nearer the red end than in the latter, and since the bright- 

 est part of the gas spectrum is somewhat nearer the red 

 end than it is in the sunlight spectrum, Yerkes concluded 

 that the reactions of Simocephalus are dependent upon 

 intensity rather than upon color. 



The results appear to me to demonstrate that intensity 

 is undoubtedly a factor in the reactions of Simocephalus, 

 but they do not appear to demonstrate that the reactions 

 are independent of the length of the waves of light. The 

 distribution in the spectrum of the power to stimulate 

 Simocephalus agrees roughly with that of brightness for 

 the human eye. If corrections are made for the difference 

 in width between yellow and blue in the sun spectrum, 

 then the 25 per cent for the blue, which is fully twice as 

 wide as the yellow, will be reduced to about twelve per 

 cent, and the percentage in the green will also be reduced 

 somewhat, showing that the yellow is the most active by 

 far. This however is not in opposition to the conclusions 

 reached from Lubbock's results, that the reactions depend 

 upon the length of the waves as well as upon the ampli- 

 tude. On the contrary, the fact that the distribution in 

 the spectrum of stimulating efficiency in these forms 

 does not correspond with the distribution of energy, indi- 

 cates that the reactions are dependent upon the wave 

 length, possibly in some such way as brightness is depend- 

 ent upon the wave length. This does not mean that the 

 chemical changes and the mechanism in general is the 

 same in these forms as that associated with brightness 

 sensations in man; and of course it does not demonstrate 

 the presence of brightness sensations in these Crustacea, 

 as the conclusions of Bert and Lubbock might lead one 

 to suspect. 



Considering the results of all the experiments on the 

 daphnias referred to above, it may be concluded: (i) that 



