INTERPRETATION OF REVERSION 121 



[Parents] Fa\^^l and white x White 



with pink eyes | with pink eyes 



[First Hybrid Gen.] Grey with black eyes 



[Second Hybrid Gen.] 1 Fawn or lilac, with pink eyes 



2 Grey or black, with black eyes 

 1 White with pink eyes 



The attempt to fit this last case into the scheme 

 brings out another point — the similarity of the pro- 

 portion 1:2:1 to that of 3:9:4. This similarity 

 should, however, be merely accidental, because the 

 3:9:4 (or 9:3:4) is supposed to follow from 

 the 9:3:3:1 ratio, and its connection with the 

 1:2:1 ratio is thus very remote and devious. 

 For my own part, I am inclined to think that 

 the resemblance is not accidental. I find it 

 difiicult, for instance, to regard the fact that in 

 both the 3:9:4 and the 1:2:1 the colourless forms 

 occur in the proportion of 25 per cent, of the genera- 

 tion as a mere fluke, and entirely without significance. 

 But I do not think that it is profitable to discuss 

 this matter until more cases of second hybrid genera- 

 tions, in which these ratios are said to occur, have 

 been bred on a scale large enough to satisfy statisticians 

 that they really do occur. 



For instance, in the case of the mice, it is possible 

 that the ratio in that case is 3 : 9 : 4 and not 1 : 2 : 1. 

 And the question which of the two it is has still to 

 be decided. 



Moreover, in this chapter I have been merely 

 concerned to point out that certain cases of reversion 



