498 



THE AMEBIC 



NATURALIST 



[Vol. XLII1 



(dilue) D. The presence of F changes chocolate to black, the 

 presence of D (in the absence of F) changes black to chocolate, 

 and chocolate to dilute chocolate (or silver fawn). 



In certain races of colored mice, the eyes are pink (absence of 

 pigment) as in albinos. The presence of the factor that pro- 

 duces this condition has an effect on the coat color, according 

 to Cuenot, hence he introduces a further set of factors that affect 

 the color. By means of these several factors the inheritance in 

 complex cases was explained. 



It has been pointed out that in all gray rodents the color gray 

 is due to a banded or barred condition of each hair. Each hair, 

 in fact, contains bands of yellow, black and chocolate, arranged 

 in definite sequence and in definite regions of limited extent. 

 Hence gray is not a color in the sense that yellow or black or 

 chocolate are colors, but is made up of all three. It is their ar- 

 rangement that is the chief agent in producing gray animals. 

 For this reason Castle has introduced a further factor, a barring 

 or ticking factor instead of a gray factor. Hence gray is no 

 longer allelomorphic to the other colors, but these colors are 

 characterized by the absence of the barring factor and by the 

 presence of one (or more) of the other colors. 



Finally the hairs of black mice are known to contain chocolate 

 pigment, so that black is not strictly allelomorphic to chocolate, 

 although crossed with chocolate the Mendelian ratio for black 

 and chocolate appears. 



These and other discoveries show that the first representation 

 of the pairs of characters will no longer suffice to account for 

 the conditions that exist, although they give the Mendelian 

 expectation for the cases first studied. We may next proceed 

 to examine in more detail the hypotheses advanced to meet the 

 more complex situation. 



Bateson and his co-workers have discovered certain cases of 

 inheritance which have led them to assume that in crosses the 

 allelomorph of a given character is the absence of that char- 

 acter. For miee the following symbols are used : 



. Gray or agouti 

 . Black 



.Cinnamon agouti 

 . Chocolate 



CgB 



CGg 

 Cgb 



