134 GENETICS AND EUGENICS 



Horses. The original color of wild horses is probably seen 

 in a wild horse still existing on the plains of central Asia 

 (Mongolia) and known as Prevalski's ^ horse. (See Fig. 81.) 

 It has somewhat the appearance of an ordinary bay horse, 

 except that the yellow pigment is paler and the black pig- 

 ment more diffuse dorsally. The mane, tail and legs are black, 

 the back reddish or yellowish brown shading off into pale 

 sooty yellow below. In tame horses of the bay color variety 

 as compared with this, the yellow pigmentation is of a 



TABLE 14 



brighter and more intense sort, called red, and more free 

 from black dorsally, while the black markings of mane, tail, 

 and feet are probably more distinct, changes that seem to 

 have come in with caref id selective breeding. For in mongrel 

 horses of no particular breeding the fine points of the bay are 

 often wanting, the yellow being of a dull shade and mixed 

 dorsally with black and approaching a " dun " in general 

 appearance. Unit-character variations are less in evidence 

 in domestic horses than in cattle. The bay appears to be an 

 improved type of wild-horse coloration not produced by 

 abrupt changes in any particular characters but by gradual 

 changes in several characters. Black is a color variety reces- 

 sive to bay in crosses. It seems to f^ave arisen in the same 

 way that black varieties of rodents usually arise, by loss of a 

 pattern factor. In rodents it is the agouti factor which 

 having disappeared produces a black (non-agouti) variety. 



^ The common spelling of this name is Prejvalski, but as this makes in English 

 an impronounceable combination, I take the liberty of dropping the j in the interest 

 of my readers, without intentional disrespect to Mr. Prejvalski or his horse. 



