COUPLING 91 



production of equal numbers of males and females. 

 But which is the hybrid ? Let us assume, in the mean- 

 time, that it is the female. If the assumption be wrong, 

 it can be revised. 



But will this hypothesis fit in with the phenomenon 

 that certain definite characters accompany either one 

 sex or the other ? There is a well-known American 

 breed of fowl called the Barred Plymouth Rock on 

 whose feathers the distribution of the black colour is 

 not continuous but interrupted by cross bars of a lighter 

 shade. This breed is now half a century old and is 

 known to have originated in a cross in which one parent 

 was an earlier barred breed called the Dominique, a 

 native of the West Indies. In the Barred Rock breed, 

 an occasional black chicken is thrown, though both 

 parents are barred. Thus barring is dominant to non- 

 barring. There are strains in which, through the 

 persistent elimination of offending parents, black 

 chickens have not been thrown for many years, but, 

 in the breed as a whole, these unwelcome black chickens 

 appear not very infrequently ; and the extraordinary 

 thing about them is that, both parents being barred, 

 they are always liens. How is this to be accounted 

 for? 



Non-barring beilig recessive, these black hens must 

 be pure for non-barring and must have received a 

 non-barring factor from each of their parents. Both 

 parents therefore must have been of the constitution, 

 putting B for barring and b for non-barring : 



Males Females 



B B 



b b 



