No. 582] SHORTER ARTICLES AND DISCUSSION 3*1 



potentially a heterozygous gray (agouti) with a yellow carrying black 

 but no agouti and albinism. . . . Cuenot recognized that the ratio ex- 



If one turns to Cuenot 's experiment 5 he finds that Cuenot 

 crossed an albino carrying black ( AX i to an albino carrying gray 

 (AC) in order to obtain a ''dozen" white mice with the formula 

 AGAN, and similarly he crossed a black mouse (OX) to a white 

 mouse carrying yellow (AJ) in order to obtain another "dozen" 

 mice with the formula CXAJ. We are not told whether each 

 dozen came from the same parents, or from several similar com- 

 binations. It will be observed that the yellow (J) and black X 

 were brought together to make one I\, and that gray and black 

 were brought together to make the other F 1? hence since gray was 

 in one F x and yellow in the other F 1 it is not possible to tell 

 whether they behave as allelomorphs to each other. There is no 

 reason, then, for making gray and yellow both allelomorphic to the 

 same factor (N), black; for, in the first cross the gametes (omitting 

 A and C) might have been Gj (gray > and gj (black) and in the 

 other cross gj (yellow) and gj (black). The numerical results 

 would then be those obtained by Cuenot. which would prove noth- 

 ing in regard to the allelomorphism of gray, yellow and black. 

 In other words, the letter N stands in this cross simply as a sym- 

 bol for anything in the black mouse that could be treated as 

 allelomorphic to G in the one case, and to J in the other ; just as 

 at first when rose comb in fowls was found to give a 3 to 1 ratio 

 with single comb it was treated as an allelomorph to single; and 

 likewise when pea was found to give 3 to 1 with single it too was 

 regarded as allelomorphic to single. Later it was found that S 

 (single) stood for two factors (•'absences'*), small r and small p. 



3. Little thinks that both Cuenot and I have fallen into the 

 same error in regard to black: but he fails to see that from our 

 points of view in regard to the other colors it was inevitable that 

 we should come independently to the same conclusion. Little 

 says that the "true" series of allelomorphs is yellow, white- 

 bellied gray, gray-bellied gray, and non-agouti (not "black"). 

 The factor that Little prefers to call non-agouti, I call the black 

 factor. He regards a non-factor as a member of an allelomorphic 

 series, while I regard the black mouse as the result of the action 

 black. By the same criterion as that by which 



