THROWING BACK 75 



exact than in the case of the albinos. In the first 

 place the colour may be grey or black ; in the second 

 place there may be patches, of greater or less extent, 

 of white fur, as well as the grey or black in the coat ; 

 various degrees of piebaldness being thus produced. 

 There may therefore be, roughly, four kinds of mice 

 in Group B : mice which have a completely grey coat ; 

 (No. 7) — self-coloured greys as they are called ; self- 

 coloured blacks (No. 8) ; piebald greys (No. 9) ; and 

 piebald blacks which are not figured. Amongst the 

 piebalds there may be every gradation between a 

 mouse which, but for the possession of a few white 

 hairs (on the forehead usually), would be a self- 

 coloured mouse, to one which has no more than 

 a small patch of grey or black, which is usually 

 near the ears. The extreme form of piebald in 

 this direction is a white mouse with black eyes ; but 

 this type has never occurred in my experiments. 

 There are also differences in the intensities of the 

 grey and black, so that the number of possible 

 different types of coloration in the second hybrid 

 generation is very great indeed. All the members of 

 Group B, however, possess the following characters 

 in common : (a) black eyes ; and (b) a greater or 

 less amount of a dark colour, either black or grey, 

 in the coat. 



Mice included in Group C correspond to the 

 fawn-and-white (waltzing) pink-eyed mice. But here, 

 again, the correspondence is not exact. For just as 

 in Group B, which corresponds roughly to the first 

 hybrid generation, there were blacks as well as greys, 



