The Genetic Factors in the Development of the Housemouse, etc. joi 



factors, two of which seem not hitherto to have been studied in mice. 

 With the exception of one factor, described by Miss Durham, I got 

 to know all the genetic factors studied by the diverse authors on 

 the subject. 



The genetic factors. 



I have hesitated some time bef(Ht: deciding what symbols to use 

 to indicate the different factors. From one point of view, it would 

 have been wisest to use the symbols that have been made use of by 

 the principal authors on the subject, CuEnot and Miss Durham. 

 CuENOT, however, uses for each separate genetic factor two symbols, 

 one to denote the presence of each factor and another to denote its 

 absence, which unnecessarily complicates the formulae. It would 

 therefore remain for me to use the symbols of Miss Durhaji, which 

 I probably would have done, were it not for the fact that recently 

 Plate, publishing the result of some crossing experiments with mice, 

 has used some of Miss Durham's symbols wrongly, that is to say 

 for quite different genetic factors, thus creating a serious confusion. 

 It happens that I know one of these factors, which Miss Durham 

 could not study because it was always present in all her mice. If, 

 therefore, I should for my factors want to use those symbols, which 

 are "the only correct ones by right of priority" (as Plate, in a criticism 

 ot Prof. Baur's recent book, wants me to do), I would have the 

 choice of either using the symbols in the sense in which they were 

 used by Miss Durham, in which case I would have to invent a new 

 symbol for the factor discovered by Plate, or else of calling this 

 factor by the name which Pl.ate uses for it, and taking an other 

 symbol for the factor studied by Miss Durham under this name. 



To obviate this and similar difficulties I have taken the advise 

 of Baur, and have simply used the first letters of the alphabet to 

 denote the genetic factors studied in my experiments. Plate, in his 

 already cited critism, seems to think that this practice must lead 

 to confusion, but I think that anything is better than the now existing 

 confusion in the use of the different symbols for the genetic factors 

 which influence the coatcolour of the domestic rodents. One need 

 only look at the comparati\e list of svmbols used, to be convinced 

 of tlie truth of my assertion. 



Several authors are of the opinion that the symbols used to 

 denote the factors must in some way recall to our mind the characters 

 resulting from these factors. This, I fully agree with Baur, is a \try 



