2 20 Heredity and Eugenics 



in ihe amount of pigmentation, but represent the rapid 

 clianges which arc characteristic of lipochrome i)igments: 

 for exam])le, in nthrivitlaUu in which the most striking 

 character is the bright red hjq^odermal 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 riibriviltata and hybrids, the 

 nihrivittala breeding true. The behavior of nibrivittata 

 is such as to suggest that in its main distinctive character 

 it is recessive to the parent species. 



In nKjdillcations 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 recjuisite amount of chromogen, or (3) 

 the capacity of the organism to sustain the conditions 

 necessary for the oxidative processes a sufficientlj' long 

 time to enable a given amount of chromogen to be oxidized 

 to [)roduce 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 iinally to black, 

 then to a still further stage of oxidation — white, S(j that 

 with a given amount of chromogen and a gi\'en amount of 

 oxidizing enzvme, di\'erse results can be obtained from 



