452 



THE AMERICAN NATURALIST [Vol. XLVIII 



Yellow B y B by black bb. 



Jl Bb = gray. 



Gametes of 1\ vcllow" B v -b. 

 Gametes of pure black &-b. 



But if yellow and black and gray are not allelomorphic 

 the same matings should give the following results : 



On the second assumption yellow, gray and blaek 

 should appear in the back cross. The former and not the 

 latter view is therefore consistent with the actual results. 



It is, of course, a matter of secondary importance what 

 system of symbols is followed. The requirements are 

 simplicity, consistency and suggestiveness, but one can 

 not always arrange to have all three at the same time. 

 The simplest scheme, for a system of allelomorphs like 

 these, would be to have some common letter to indicate 

 their relation and an exponent to suggest the different 

 characters for which each stands. If we take the symbol 

 b (black) for the common letter, and use capitals for 

 dominance, the allelomorphs will be: 



If one preferred to take Y (yellow) as the common letter 

 the series would be y' h , y' s , y' w , Y' ; or, if one preferred 



Gametes of F, "yellow Y'b-Y'B-u'b-n'B. 

 Garu.'t. s ,if pure blaek t/'b-v'b. 



The Symbols Employ] 



B f - = gray gray belly. 



