WAVE LENGTH 111 



if we take cognizance of the analogy between heliotropism 

 and the other tropisms we realize that the heliotropism of 

 the bees and their reactions to blue are separate and 

 independent phenomena, which need not be mutually ex- 

 clusive and which in all probability depend upon different 

 parts of the brain. When in certain cases the relative 

 heliotropic efficiency of the various parts of the spectrum 

 is identical with the curve for its apparent relative bright- 

 ness to a totally color blind person, we may conclude 

 that the photosensitive substances responsible for the two 

 groups of phenomena behave similarly or may even be 

 identical, but not that the sensations of brightness of the 

 color blind and the heliotropic reactions of insects are 

 identical or analogous phenomena. 



Many mutants of Drosophila differ in regard to the 

 pigments of the eye. It was natural to raise the question 

 whether or not such hereditary variations of pigmentation 

 of the eye influence the reaction of the flies to monochro- 

 matic light. McEwen investigated this possibility with 

 the following result : * ' Colored lights which may be con- 

 veniently described as violet, green and red, are effective 

 in the order named upon the insects whose eye color is 

 lighter than the red eye of the wild fly. In the case of 

 wild flies, and flies whose eyes are of a still darker 

 shade called sepia, red is more effective than green" 

 (McEwen 549 ). 



