220 Heredity and Eugenics 



in the amount of pigmentation, but represent the rapid 

 changes which are characteristic of Hpochrome pigments: 

 for example, in rubrivittata, in which the most striking 

 character is the bright red hypodermal color. This arises 

 suddenly as the result of experimental conditions and 

 reproduces itself when bred back to the parent species, 

 giving a color segregation into rubrivittata and hybrids, the 

 rubrivittata breeding true. The behavior of rubrivittata 

 is such as to suggest that in its main distinctive character 

 it is recessive to the parent species. 



In modifications of color we are dealing with superficial 

 chemical processes in the organism — the development of a 

 chromogen and the oxidation of that chromogen by one or 

 more oxidizing enzymes to a state of stability where simpler 

 compounds are produced which are productive of color. 

 In no experiments in the modification of color, especially 

 in colors such as the melanins, etc., has any modification 

 been produced which is not an accentuation or diminution 

 of the oxidative capacity of the organism. That is, in 

 the case of pallida, there is a decrease in the capacity of the 

 organism to produce either (i) the necessary oxidizing 

 agents, or (2) the requisite amount of chromogen, or (3) 

 the capacity of the organism to sustain the conditions 

 necessary for the oxidative processes a sufficiently long 

 time to enable a given amount of chromogen to be oxidized 

 to produce a stated amount of pigment. 



It has long been known that the series of color changes 

 may proceed from white, through yellowish, yellowish- 

 brown, reddish-brown, deeper browns, and finally to black, 

 then to a stUl further stage of oxidation — white, so that 

 with a given amount of chromogen and a given amount of 

 oxidizing enzyme, diverse results can be obtained from 



