476 THE AMERICAN NATURALIST [Vol. LIV 



mice were genetically Type "A" (WwSs) and their dis- 

 tribution is shown graphically in Fig. 3, broken line. 

 This distribution resembles that of the Type "A"s pro- 

 duced by crossing black-eyed white with self, except that 

 the former are somewhat less variable, due to the ab- 



sence of classes lighter than 25 per cent, white, and their 

 mean is somewhat lower for the same reason. These 

 differences^are probably due to the selection of dark Type 

 "C"s as parents and it will be seen later that the darker 



