The Gi-iietic Factors in the Development of the Housemouse, etc. igo 



either of the sort bred by me (bb) or of the ordinary kind ( li). 



These last, most commonly bred yellow mice have a colour which is 

 about that of No 6 and N" 24 of the coloured plate. His criticism of 

 our results with yellow mice is therefore not to the point, as our 

 material was not comparable. His "gelb-graue" mice are pink-eyed 

 agouti (ABCDeFGH), his "gelb-silbern" are lilac (ABCDeFgH), and such 

 mice, as can be seen from the coloured plate can only be called 

 yellow by courtesy. Miss Durham, who has seen skins of Plate's 

 mice confirms this. The yellow mice, commonly breed, such con- 

 taining li, may either have or lack the factor E. Such yellow mice 

 without E have the same colour as those having it, or sensibly so, 

 they differ only in the colour of the eye. I added together the 

 numbers of Ee and ee young produced in matings of heterozygous, 

 Ee, with ee mice. They were: 



133 black-eyed (Ee) and 154 pink-eyed (ee), the expected ratio 

 being 143.5 : 143.5. 



From the tables at the end of this paper can be seen the inde- 

 pendance of this factor E from the factors c, D, G and H. 



All the mice figured on the coloured plate have the factor E in 

 their formulae, with the exception of Nos 8 and 11. 



Factor F. 



This factor has, as far as I know, always been present in all the 

 mice studied by the different authors. It was so in all my first mice. 

 Mice without this factor were produced in my cultures as the result 

 of a loss of this factor from one gamete produced by an animal 

 homozygous for its presence (Mutation). 



a Animals do not differ from Ff ones or ff ones during the first 

 weeks of their existance, but when they moult, which may happen 

 at an age of nine weeks or a little earlier, the new coat is inter- 

 spersed with white hairs, which are sometimes distributed evenly over 

 the whole body, but which are sometimes limited to patches on the 

 back and sides. The same factor is acsent from silver rabbits and 

 a black mouse without f looks almost exactly like a medium silver 

 rabbit. Preliminary experiments with rabbits make it probable that 

 in this animal the medium silver is a black, or an agouti or a yellow- 

 agouti lacking F, but that in the dark silvers this silvering is due 

 to the presence of a second factor, absent from other rabits. Light 

 silver rabbits would than have both this last factor, and be without F. 



