MELANIN COLOR FORMATION. 333 



Cuenot's concluding statement : " In regard to albinos all is 

 explained if we admit that the germ-plasma contains only 

 mnemons of the enzymes, that of the chromogen being totally 

 absent. With these conditions, colored hair cannot be formed 

 in albinos, since one of the substances indispensable to the reac- 

 tion is absent, but one easily understands that the albino will 

 transmit to its progeny either the mnemons for the two enzymes, 

 or one mnemon only if it possesses but one." To this statement 

 must be opposed first the opinion of Durham that the skins of 

 the albino mammals studied by her contained no tyrosin-oxidizing 

 enzymes ; a second much more weighty and conclusive objection 

 is that the absence of melanin chromogens in albinos is practically 

 inconceivable. It is now certain that tyrosin and its many related 

 compounds are such chromogens, and that these compounds 

 have a distribution in the universe almost or quite co-extensive 

 with protoplasm itself. The postulation of the formation of chro- 

 mogen-containing, and non-chromogen-containing gametes is there- 

 fore reduced to an absurdity. It is moreover quite certain that the 

 food of tJie albino mouse must daily bring it quantities of chro- 

 mogens, even if such could have been excluded from the germ cells. 

 There is no doubt and no middle ground here. Cuenot's concep- 

 tion fails completely. 



Space does not permit a discussion of the facts and interpreta- 

 tions of the inheritance of coat colors of mice since the work of 

 Cuenot ; a subject which has been investigated or discussed by 

 many workers, notably by Bateson, Allen, Cuenot, Morgan, 

 Wilson, Castle and Durham. A detailed consideration of these 

 results is omitted also because the facts are well known and do 

 not belong here. The behavior of the color yellow first reported 

 by Cuenot ('05) is, however, of such unusual interest as to de- 

 serve special mention. It was found that yellow is " dominant " 

 in mice, whereas elsewhere in animals it is usually " recessive " 

 to black ; this is an unexpected result from the Mendelian stand- 

 point, and the difficulties which it presents have called forth 

 several highly complex, supplementary Mendelian hypotheses. 

 It seems not to have occurred to anyone that yellow may be a 

 blend formed from the union of other colors, e. g., between 

 albino and black. A glance at our scale of colors (p. 326) sug- 



