CALLOSITIES OF EQUINE ANIMALS AND OTHERS 239 



of each species from the time it branched off from the common 

 stock. For all we know, ruminants may have had leg glands, 

 but some compensating condition may have rendered that feature 

 of little importance in some of them, and a cessation of selection 

 in that direction occurred, by which the leg glands were eventually 

 totally suppressed, while in others traces of them have been left 

 in the form of patches of hair of different colour and length from 

 the surrounding hair. 



As the Horse has them on all four legs we may assume that 

 Zebras 1 and Asses had them also on their hind-legs, although 

 now they have no traces of them there. It is not only callosities, 

 but other features may become often lost by suppression. It is 

 one of the factors in the origin of species. 



I have never found anything recorded by hunters of Zebras 

 on these leg glands. In these animals the callosities are very 

 large, and something, one would think, might be discovered about 

 their real nature and structure if proper investigation were made 

 when the Zebra was fresh after being shot. 



It would be very interesting also to ascertain whether in the 

 Horses which have become again semi-wild in South America 

 and Australia, these skin glands have ever re-acquired any of 

 their ancient activity. Not impossibly the ancestral possessors 

 of these leg glands may have been driven by their enemies from 

 regions of long grass to more open regions, and rocky places 

 with shorter grass ; or the long grass of certain regions may have 

 been devoured by the immense multitudes of these animals which 

 are recorded by hunters ; and so the leg glands may have become 

 less useful, and by degrees lost their selection value. Anyhow, 

 it seems more than probable that those singular tufts of hair 

 were in some ancestral form active skin-glands of some use to 



1 Grevy's Zebra seems to have lost them on both hind- and fore-legs. 



