MAMMALS 



103 



lower its sexual activity in winter, and the activity 

 would revive again, as in deer, after the plentiful food of 

 summer. 



Antelopes generally belong to the warmer temperate 

 regions if not specially to the tropical, and the ancestor of 

 the prong-buck probably entered America from Asia. The 

 species, however, is not necessarily derived from a form which 

 had fully-developed permanent sheaths like other antelopes. 

 If this were the case it is doubtful whether the horn when 

 the old sheath was cast would be covered with hairy skin at 

 its lower portion. It is thus more probable that the shedding 

 of the horn-sheath began at a stage when the conversion of 

 the epidermis into horn had only recently taken place and 

 the roots of the hairs had not degenerated. In this case 

 when the sheath was separated the deeper parts of the hairs 

 would, of course, be left alive in the uncornified part of the 

 epidermis. I presume that when the horn-sheath of an ox or 

 cow is shed from injury there are no hairs in the living 

 epidermis left beneath. It is even possible that the shedding 

 of the horn-sheath in the prong-buck commenced at a stage 

 when only the apex of the horn was cornified, and that the 

 extent of the cornified region extended gradually downwards 

 after the periodical shedding had become established. The 

 cornification might extend a little lower down after each 

 shedding, and in each generation. In this case the reproduc- 

 tion of the new horn-sheath after shedding would follow the 

 course by which it had been evolved. 



The existence of the second or anterior point of the horn- 

 sheath is to be attributed to more intense irritation at this 

 point. The bony core is as simple* as in other antelopes, so 

 that the periosteum is not affected. 



Strong support to the above arguments is afforded by the 

 statement of Caton, that the older the animal the earlier the 

 horn matures and the sooner it is cast, though, of course, 



