CALLOSITIES OF EQUINE ANIMALS AND OTHERS 237 



of once glandular surfaces of the skin, which have ceased to be of 

 any use to the animals that possessed them, and have now ceased 

 to have selection value. In 

 some, as in the equine family, 

 they have dwindled into mere 

 callosities with thickened 

 epidermis, while in others 

 they have become covered 

 with hair of a different tint 

 and length from the surround- 

 ing hair. In the Camels of 

 South America, with possibly 

 certain exceptions, they ap- 

 pear to be in the same condi- 

 tion as those of the Zebra 

 and Wild Ass, only much 

 reduced in size. 



It would seem safe to look 

 upon all these callous surfaces 

 as vestiges of skin glands, similar to those in front of the eye of 

 certain Deer, like that shown in Fig. 87. 



Sheep have glands between the hoofs of all four legs ; and 

 goats have them only between the hoofs of their fore-legs, and 

 sometimes not even there.^ 



Now we come to another and more obscure point of our 

 research. What could have been the use of skin glands on the 

 legs of the common ancestors of all these different mammals — 

 Horses, Asses, Zebras, Deer, and Camels ? 



Well, in the ancestral history of these animals, skin glands on 

 the legs, which secrete an odoriferous substance, may have been of 

 ^ Royal Natural History, vol. ii. p. 234. 



Fig. 87. — Gland in front of the eye of Peruvian 

 Roebuclc ( Coriacus (Furci/er) antisiensis). 



