306 Scientific Proceedings^ Uoijal Dublin Society. 



But then black and brown would differ from eacli other iu more than one 

 pair of factors, which is not in accordance with the facts. 



Thus, since each colour is the result of only one factor, it is impossible 

 for each to mate with more tlian one other at a time. Otherwise the zygote 

 would obtain three " half '' factors at once. This might be stated otherwise : 

 brown is dominant to botli black and chestnut, but it can mate with only one 

 at a time, for otherwise it would be impure for both at the same time. Thus 

 brown, black and chestnut are each the result of single factors which are 

 polygamous. 



If it were necessary this finding can be confirmed as follows. If brown, 

 black, and chestnut be polygamous and each the result of a single factor, then 

 in a horse population containing all three colours, there should be browns, 

 blacks, and chestnuts of the following constitutions : — 



Black Chestnut 



bCbT '^ 



Bl Ch Ch 



and sires of each of tliese different kinds of bays and blacks should be found 

 breeding in a definite manner when mated with a general population 

 containing all kinds of mares, thus: — 



It is impossible to predict the proportions iu which each colour should 

 occur from each mating, because that depends upon the persistence with which 

 each of the three colours has been bred from iu the past. The following table 

 gives the numbers and kinds of foals produced by 84 Shire horses when mated 

 with Shire mares of the three colours brown, black, and chestnut. It will be 

 noticed that, among those 84 sires, the five expected kinds occur. The few 

 exceptions in the progeny are again enclosed within brackets : — 



