The Genetic Factors in the Development of the Housemouse, etc. jq? 



simply because it was always present in all their animals. Without 

 any doubt the genetic factors in the development of a mouse, which 

 influence its colour arc exceedingly numerous, and the reason why 

 we only know about a dozen is that we can only study a genetic 

 factor if it be absent from at least one individual. In Ahis decumamis 

 there exist probably the same factors A, B, c, D. E, F, g. h, etc. as in 

 the mouse, only because all of them, excepting a and g and possibly 

 H are present in all the individuals, we can not study them. The 

 factor B thus, can only be studied in those animals where it is absent 

 from some individuals, the cavy, the rabbit and the mouse. (Recently 

 Mr. BONHOTE told me of the existance of a strain of Mus rattns, which 

 probably lacks this same factor.) All the animals lacking b are some 

 shade of yellow, the colour depending upon the presence or absence 

 of some of some of the other factors, notably c and G. The presence 

 or absence of this factor b gives generally a much greater difference 

 in colour than that of any of the others, not even excepting the 

 factors D and G. Thus is the difference between black (ABCDEFgH) 

 and tortoise (AbCDEFgH) in mice and rabbits, that between agouti 

 (ABCDEFGH) and yellow agouti (AbCDEFGH) in mice and rabbits and 

 cavies, between chocolate (ABcDEFgH) and orange (AbcDEFgH) due to 

 the presence or absence of b. 



It is because of the fact that the majority of my yellow mice 

 have been yellow because of an absence of B, and that therefore my 

 results with yellow mice were in complete accordance with those of 

 the authors who worked with rabbits and cavies, that I have formerly 

 accepted the records of yellow varieties, which it was impossible to 

 fix, with great caution. It is only recently that I have come to see 

 that the material used by most of the other authors on the inheritance 

 of yellow colour in mice, was in no way comparable with mine. 



The cooperation of the factor B with A, in the absence of c and G 

 (AHci)....gi produces a brown colour. It depends upon whether all 

 the factors D, E, f and H are present or whether any or all of these 

 are absent how intense this brown colour shall be. 



Thus is ABcDEFgH chocolate (N" 16) in mice as well as in rabbits. 

 The colour called chocolate in the cavy is not exactly the same one, 

 this is no doubt due to the fact that in the cavy factors exist which 

 complicate this colour, and which we do not yet know in the other 

 animals. I have seen rabbits of exactly the same colour as chocolate 

 cavies. In adding together those cases in which an animal, hetero- 



