vi REVERSION 57 



acter which we have to consider in this cross is the 

 Dutch character. This was found by Hurst to 

 behave as a recessive to self-colour (S), and for our 

 present purpose we will regard it as differing from 

 a self-coloured rabbit in the lack of this factor. 1 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 factor X. The results 

 of breeding experiments then suggest 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 com- 

 plete 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 exten- 

 sively grown for some years. In these little plants 

 the internodes are very short and the stems are 

 few in number, and attain to a length of only 9-10 

 inches. In course of growth they diverge from one 

 another, and come to lie prostrate on the ground (PL 

 II., 2). Curiously enough, although the whole plant 

 is dwarfed in other respects, this does not seem to 

 affect the size of the flower, which is that of a normal 

 sweet-pea. Another though less-known variety is 

 the " Bush " sweet-pea. Its name is derived from 



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

 Angora which turned out to be a masked Dutch. 



