76 BREEDING 



so in Group C, which corresponds roughly to the fawn- 

 and-white mice (No. 2), there are " lilacs " as well as 

 fawns. The parallel, indeed, between the two cases 

 is very close, for the fawn colour may be regarded as 

 a dilute grey ; and the lilacs as a dilute black. 

 " Lilac " was the name I first gave to these mice, 

 and I have adhered to it, but " pale lavender " more 

 accurately conveys the exact colour. Then, again, 

 as in Group B, there may be " selfs " as well as 

 piebalds. But whilst in Group B the piebald was the 

 new appearance, in Group C the " self " is. In 

 other words, in the case of the dark colours (grey and 

 black) the ** self " appears first in the first hybrid 

 generation, and the piebald does not appear till the 

 second ; but in the case of the paler colours (fawn 

 and lilac) the fawn exists first in a piebald form in 

 one of the parents of the cross, and does not appear 

 as a " self " until the second hybrid generation. • 



There may, therefore, be — as in Group B — four 

 kinds of mice in Group C : self-coloured fawns (No. 11), 

 self-coloured lilacs (not figured), piebald fawns (No. 12), 

 and piebald lilacs (No. 13, which has a white face). 



The second hybrid generation is made up of the 

 representatives of the three Groups, A, B and C, in 

 the ratio of about 25 per cent. A, 50 per cent. B, 

 and 25 per cent. C, or, roughly, one of A, two of B, 

 and one of C in every four, on the average. These 

 ratios obviously do not obtain in every litter, even 

 if only because the number of young in a litter is 

 not necessarily a multiple of four ; in fact, in none 

 of the twenty litters, selected at random and shown 



