62 MENDELISM chap. 



by X, and as far as it is concerned the Himalayan is con- 

 stitutionally XX. The Himalayan contains the intensi- 

 fying factor, for such pigment as it possesses in the points 

 is full coloured. At the same time it is black, i.e. lacking 

 in the factor G. With regard to these three factors, there- 

 fore, the constitution of the Himalayan is ggllxx. The 

 last character which we have to consider in this cross is 

 the Dutch character. This was found by Hurst to be- 

 have as a recessive to self-colour (5), and for our present 

 purpose we will regard it as differing from a self-coloured 

 rabbit in the lack of this factor.' The Himalayan is really 

 a self-coloured animal, which, however, is unable to show 

 itself as a full black owing to its not possessing the fac- 

 tor X. The results of breeding experiments then sug- 

 gest that we may denote the Himalayan by the formula 

 ggllxxSS and the yellow Dutch by GGiiXXss. Each 

 lacks two of the factors upon the full complement of 

 which the agouti colour depends. By crossing them the 

 complete series GIXS is brought into the same zygote, and 

 the result is a reversion to the colour of the wild rabbit. 

 Most of the instances of reversion yet worked out are 

 those in which colour characters are concerned. The 

 sweet pea, however, supplies us with a good example of 

 reversion in structural characters. A dwarf variety 

 known as the "Cupid" has been extensively grown for 



1 Hurst's original cross was between a Belgian hare and an albina 

 Angora, which turned to out be a masked Dutch. 



