Chap. II. THEIR COLOURS AND STRIPES. 61 



black. Zain is generally translated as dark without any white ; 

 but as Azara speaks of mules being " zain-clair," I suspect that 

 zain must have meant dun-coloured. In some parts of the world 

 feral horses show a strong tendency to become roans. 38 



In the following chapters on the Pigeon we shall see that in 

 pure breeds of various colours, when a blue bird is occasionally 

 produced, certain black marks invariably appear on the wings and 

 tail ; so again, when variously coloured breeds are crossed, blue 

 birds with the same black marks are frequently produced. We 

 shall further see that these facts are explained by, and afford 

 strong evidence in favour of, the view that all the breeds are 

 descended from the rock-pigeon, or Columba livia, which is thus 

 coloured and marked. But the appearance of the stripes on 

 the various breeds of the horse, when of a dun-colour, does not 

 afford nearly such good evidence of their descent from a single 

 primitive stock as in the case of the pigeon ; because no cer- 

 tainly wild horse is known as a standard of comparison ; because 

 the stripes when they do appear are variable in character ; 

 because there is far from sufficient evidence of the appearance 

 of the stripes from the crossing of distinct breeds ; and lastly, 

 because all the species of the genus Equus have the spinal stripe, 

 and several have shoulder and leg stripes. Nevertheless the 

 similarity in the most distinct breeds in their general range of 

 colour, in their dappling, and in the occasional appearance, 

 especially in duns, of leg-stripes ancf of double or triple shoulder- 

 stripes, taken together, indicate the probability of the descent 

 of all the existing races from a single, dun-coloured, more or 

 less striped, primitive stock, to which our horses still occasionally 

 revert. 



38 Azara, ' Quadrupedes du Para- describes two wild horses from Mexico 



guay,' torn. ii. p. 307 ; for the colour of as roan. In the Falkland Islands, where 



mules, see p. 350. In North America, the horse has been feral only between 60 



Catlin (vol. ii. p. 57) describes the wild and 70 years, I was told that roans and 



horses, believed to have descended from iron-greys were the prevalent colours, 



the Spanish horses of Mexico, as of all These several facts show that horses 



colours, black, grey, roan, and roan pied do not generally revert to any uniform 



with sorrel. F. Michaux (' Travels in colour. 

 North America,' Eng. translat., p. 235) 



