496 THE HORSE'S POSITION IN THE ANIMAL WORLD 



Size. — One liorse differs from iinother not only in the characteristics 

 described, but even to a much greater extent in size. Comparing the 

 smallest pit pony of thirty-six inches with the carriage or the cart horse 

 of eighteen or nineteen hands, it is often difficult to realize that both 

 belong to the same species. Nevertheless the apparently widely different 

 animals are in all essential features, excepting in size, the same. The 

 vast diff"erence in bulk is largely due to the efforts of the breeder in 

 applying the principle of artificial selection. Pit ponies are required 

 to w^ork in mines where the seams are only a few feet high; laroe 

 horses are wanted for special work or for appearance. Both require- 

 ments must be met, and the skill of the breeder, aided by climate and 

 by food, is equal to the demand. 



The Ass. — Next to the horse (Equus cdballus) comes the ass 

 {Equus asinus) with its varieties, which include the zebras. Naturalists 

 affirm that really wild horses are rare, i.e. horses which have descended 

 directly from parents which have never been domesticated. AVild asses, 

 on the contrary, are common in many parts of the world — in Africa, in 

 Syria, in Persia, in Tartary, in Tibet, up to the frontier of China. 



Though asses have a general resemblance to each other, they still 

 diff"er so far in size, in form, and in shade of colour or of markings as to 

 justify their division into three varieties. 



The domestic ass presents some features which require notice. Its 

 size varies in different countries, as also does its colour. The tail is bare 

 of long hairs, excepting the tuft at the end. The ears are longer in 

 comparison with its head than those of the horse, and there are no cal- 

 losities below the hock joint as there are in the horse. There is commonly 

 a dark stripe running vertically from the top of the shoulder, and another 

 darker in colour extending along the middle of the back, and occasionally 

 there are transverse markings on the legs. 



Zebras (Equus zehra) belong to the group of striped asses. There 

 are several varieties, which are distinguished by the length of the ears, 

 by the fulness of the tail and the mane, by the colour and the arrangement 

 of the stripes, by the absence of the callosities on the hind-leg, and by 

 the existence of a modified form on the fore-legs. Quaggas [Equus 

 quagga) are really modified zebras, from which they are chieffy dis- 

 tinguished by the concentration of the stripes on the head and the neck, 

 the markings beina; less and less distinct from the shoulders back to the 

 haunches, which are perfectly free from stripes. All the varieties of the 

 ass agree in having the horny callosities in a modified form only on the 

 fore-legs. With regard to these bodies, which have attracted so much 

 attention and led to so much diversity of opinion as to their nature and 



