POLYGAMOUS FACTORS 77 



The first of these results, drawn from a breed which 

 also contains greys and possibly a few blacks, confirms 

 the first inference from Dr. Crampe's observations that 

 these other colours are doriiinant to chestnut while the 

 second and third are definite that bay is dominant to 

 and differs from chestnut in one pair of characters only ; 

 for, if it differed in more, the mating of hybrid bay with 

 chestnut would produce more than equal numbers of 

 bays and chestnuts. 



Thus there are now two colours, black and bay, both 

 of which are simple dominants to chestnut. So far 

 the case is parallel to that of the fowls' combs at the 

 stage when both rose and pea were found dominant to 

 single comb ; but the parallelism goes no farther, for, 

 when black and bay are mated, no new colour is pro- 

 duced, but blacks and bays only and chestnuts, their 

 common recessive. Two sets of figures are available : 

 one from Dr. Walther's volume and the other from the 

 Stud Book of the English Shire Horse Society : 



Bays Blacks Chestnuts 

 With black German mares, 



68 bay sires get . . 281 124 20 



With black Shire mares, 28 



bay sires get . . 409 225 35 



No inference can be drawn from the relative numbers of 

 each colour because it is impossible to tell how many of 

 the black and bay sires were hybrid and how many pure. 

 How is this phenomenon to be explained ? It might 

 be suggested that there are two pairs of factors and 

 two inseparable bay groups according to the scheme : 

 X X X X 



Y y Y y 



Bav Black Chestnut 



