136 GENETICS AND EUGENICS 



and later coats. For the colts are born with colored coats, 

 but at the first shedding of the hair, white hairs begin to 

 come in mingled with the colored ones. (See Fig. 84.) Later 

 white hair may almost completely replace the colored ones. 

 The eyes of gray horses are always colored. The term gray 

 as applied to horses has the same significance as when applied 

 to human beings. It means the occurrence of white hairs 

 among colored ones, more or less completely replacing them. 

 Wlien among horses the original coat partially replaced by 

 white was a black one, an ordinary or " iron " gray coat 

 results; but when the original coat was bay or sorrel, then a 

 roan coat is produced. 



White spotting is of frequent occurrence among horses, 

 though it is usually less extensive than among cattle. In this 

 variation the loss of pigment from the body area affected is 

 complete and is present from birth on, so that its nature is 

 evidently very different from the gray variation already 

 described. (Figs. 81-85.) It corresponds physiologically 

 with white spotting in cattle and in rodents. The com- 

 monest form of white spotting is the occurrence of a white 

 spot in the forehead sometimes extendmg down over the nose, 

 or the possession of one or more white feet, or both. These 

 are regular features of the coloration of Clydesdale and Shire 

 horses. More extensive spotting takes the form of irregular 

 white areas extending across the neck or body. (Fig. 81a.) 

 It is less common than the former and unlike it behaves as a 

 dominant character in crosses. Often seen in children's 

 ponies, it is probably genetically distinct from the spotting 

 of horses with white stockings and blaze. The pacing gait in 

 American race horses is a character recessive to the trotting 

 gait, according to Bateson. In pacing the two legs of the 

 same side of the body move in unison or nearly so, while in 

 trotting the foreleg of one side moves almost simultaneously 

 with the hind leg of the other side. Some trotters may be 

 made to acquire the pacing gait and these, of course, may 

 produce trotters, but natural pacers produce only natural 

 pacing colts when bred with each other, whereas in crosses 

 trotting dominates. 



