The Genetic Factors in the Development of the Ilousemouse, etc. nß 



heredity", which he probably overlooked. Plate uses the name "blue" 

 for hh mice under manifest protest, as of course fade black ABCDEFgh 

 (N" 21) mice are by no means blue. 



The ordinary lighter colours in cavies can, as Miss SollaS has 

 shown, be due to the absence of several factors, which each by their 

 presence would make the colour somewhat darker. It is very probably 

 that in mice some of these factors have been permanently lost in all 

 individuals. (All cavycolours are somewhat more pronounced than 

 the corresponding colours in mice). Still, in mice there exist several 

 of those factors, but for simplicity's sake I will limit myself to the 

 description of only one. 



Cases like this, where we are dealing with several factors, which 

 all by their cooperation to the development influence it in the same 

 direction, have been studied by Nilsson-Ehle in the colours of 

 wheat and oats, and by CuEnot in partial albinism of mice. 



I believe that, whenever such a series of factors presents itself, 

 we should not, as some authors tend to do, denote them by one 

 common letter, as xi, x^, x», x* etc. These factors only therefore 

 seem identical or in some way analogous to us, because we can not 

 easily disentangle the action of each of them on the development. 

 Ne\'crtheless we have every reason to believe that these factors are 

 absolutely independant one from the other, and that they are segre- 

 gated independantly in gametogenesis. 



I believe it would be wiser in such cases to give a separate name 

 to each one of these factors, if only to avoid giving rise to the 

 manifestly false idea that, because these factors all have a somewhat 

 identical influence on the development, they must be, physiologically 

 speaking, identical or at least analogous. 



We have seen that the factors D, E, F, and h in the rodents all 

 have superficially about the same influence on the ultimate colour 

 of the animal. But on a narrower inspection, it will be seen, that 

 the lightening of the coat-colour resulting from an absence of e. g. D, 

 is due, physiologically, to a different cause from that which results 

 from an absence of E, or H or F. I feel sure it will ultimately be 

 possible to know each of such a set of factors separately, though in 

 such cases the analysis is exceedingly difficult. 



One of the difficulties continually met by those people who bned 

 mice or rabbits for shows, is the production of hh young by their 

 stock. It is evident that no amount of selection of h animals will 



Induktive Abstammungs- und Vcierbungslchre. V[. S 



