74 A MANUAL OF MENDELISM 



altogether, as they are exceedingly hable to misdescription 

 and are the progeny of browns, which are seldom de- 

 scribed as such but generally as blacks. The numbers of 

 each kind of progeny expected from black and yellow 

 cannot be given, as the pure black parents cannot be 

 distinguished from those containing red. Red and 

 yellow should give equal numbers of reds and yellows 

 and yellow and dun equal numbers of the four kinds 

 expected. The figures found are therefore in reasonable 

 agreement with expectation. 



But, if the data used to prove that cattle colours are 

 the result of single factors which are polygamous leave 

 something still to be desired, it is satisfactory to know 

 that the factors for the colours of horses are also single 

 and polygamous and that the available data are much 

 more reliable and less confusing. In their case no 

 intermediate hybrids are produced and, because all the 

 colours are related to each other as dominants and 

 recessives, the manner in which they group themselves 

 as a whole is of unusual interest. 



Among horses there are five colours : grey, dun, bay, 

 black, and chestnut — another impossible number. 

 Through all runs a series of shade factors which have 

 the effect of varying the chestnuts from bright gold at 

 the one extreme to dark liver at the other, the bays 

 from light bay to dark brown, and the duns from 

 cream to bluish dun, but have no identifiable effect 

 upon black and grey although undoubtedly present in 

 both. As yet little is known as to the inheritance 

 of these shade factors, and, in what follows, they are 

 entirely neglected. In addition to these, a pair of 

 factors is in operation whose effects are readily dis- 

 tinguishable in every colour but grey. The dominant 



