728 THE AMEBIC AN NATURALIST [Vol. XLIX 



who has worked with the same types as Durham, feels 

 uncertain as to the real significance of black-eyed whites 

 and as to the occurrence of a distinct factor for dominant 

 spotting. This uncertainty I also felt and have tried to 

 show further reasons for not considering Miss Durham's 

 work as establishing the existence of a dominant spotting 

 factor. 



Castle (1905) has found that in guinea-pigs black-eyed 

 whites behave in inheritance in much the same way that 

 the same type of mouse behaves, namely that black-eyed 

 whites do not breed true but give, when crossed inter se, 

 a whole range of spotted forms in addition to some like 

 themselves. 



One can by selection progress in either direction through 

 a series of spotted forms, decreasing or increasing the 

 number and extent of pigment patches. Great difficulty, 

 however, was encountered in trying to fix the color pat- 

 tern at any particular stage in the series. Up to the 

 present time this has not been proved possible. 



Experimental 

 In the early winter of 1913 Dr. Castle obtained from a 

 fancier in England two pairs of black-eyed white mice. 

 These he kindly handed over to me for investigation. 

 From the outset the progeny of these mice proved to be 

 extremely healthy and vigorous. 



1. Black-eyed White Crossed Inter Se 

 This cross gave two distinct classes of young, black- 

 eyed white and 4 'piebald." The distinction between the 

 two classes can best be shown by the tabulation of their 

 progeny on the basis of the amount of dorsal pigmenta- 

 tion they possess. I have for some time estimated the 

 per cent, of the dorsal surface pigmented in the case of 

 all spotted animals recorded. This gives a basis for clas- 

 sification which, though it may at first glance seem to 

 inexact, nevertheless has been shown by comparing the 



