POSITION AND STRUCTURE OF HORSE 53 



in the wild asses of Africa, while the zebras and 

 quaggas of that country are marked by dark and 

 light stripes over the whole or a considerable 

 portion of the head, body, and limbs, it has been 

 considered probable that all the ancestral members 

 of the family were fully striped. Consequently 

 species like the Mongolian wild horse, the Asiatic 

 kiang, chigetai, and onager, and the North African 

 wild ass, which are more or less nearly self-coloured, 

 are presumed to have lost their stripes in accord- 

 ance with the special conditions of their natural 

 surroundings ; and also that the tendency in dun 

 horses, and it may be added mules, to the develop- 

 ment of stripes is an instance of atavistic reversion. 

 In addition to this tendency to develop stripes 

 on the limbs and shoulders in dun-coloured horses 

 and mules, there is a still stronger tendency among 

 domesticated horses of all colours except duns, but 

 more especially greys, to show dappled markings. 

 Attention was directed to this feature by Darwin,^ 

 who stated that it occasionally occurs among asses, 

 and who expressed the opinion that it was probably 

 connected in some way with the ancestral striping. 

 At a much later date Dr. E. Bonavia, a brigade- 

 surgeon in the Indian Medical Department, in a very 

 remarkable book entitled Studies in the Evolution 

 of Animals^ laid still greater stress on the frequent 



^ Animals and Plants under Domesiicaiioji, 2nd ed. vol. i. p. 58, 

 London, 1885. " London, 1895. 



