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ANNALS NEW YORE ACADEMY OF SCIENCES 



It seems more reasonable, therefore, to assume that, if the three colors 

 are combined in a single carrier, it may have lost successively one after 

 another of its components as the black and chocolates arise. If we 

 assume that by the dropping out of the yellow and the ticking factor a 

 black mouse results, then gray would remain allelomorphic to black, 

 since the material body carries one or the other. This is so far consistent 

 with the results ; but on the same hypothesis, chocolate is due to loss of 

 black in the black mouse. If, then, gray is crossed to chocolate, not only 

 should grays result in the F x generation, but only grays and chocolates in 

 the second generation ; yet Miss Durham has shown that grays, blacks and 

 chocolates appear, which is inconsistent with the hypothesis. If, how- 

 ever, black and chocolate are stages in the development of the same sub- 

 stance, and the stage reached depends on another factor not present in 

 the common carrier, but in another one, then the situation is clearer. 

 Chocolate must be supposed to arise from black by the loss of this factor 

 M, and since the factor is present in gray, then when gray is crossed to 

 chocolate, the determiner for black is present as simplex, i. e., once only. 

 Its allelomorph is its absence. The formula for gray 6 would be (Y, Ch) 

 M, and that for chocolate Ch. The formula for the hybrid will be, there- 



Y Ch M 



fore, (YCh) M Ch. Tbre allelomorphs are ~, » — > and the gam- 

 etes (Y Ch) M, (Y Ch) 0, Ch M, Ch 0. Two such mice crossed will 

 give twelve grays (including three cinnamon agoutis), three blacks and 

 one chocolate, as the following table shows : 



•Omitting the ticking factor from (YCb). 



