100 



SEXUAL DIMORPHISM 



accurately, the process of shedding and regeneration of the 

 horn-sheath in Antilocapra. The growth of the new horn 

 begins before the old is shed, and is simply the normal 

 process of horn-formation intensified, so as to be acute at a 

 certain season instead of chronic as in ordinary cases. The 

 horn is produced, like normal horn, by proliferation of the 

 cells of the epidermis and the hardening of the outer layers 

 of cells. There are, however, important peculiarities in the 

 mode of development. The growth proceeds from above 

 downwards. When the old sheath has been just cast off 

 there is a new horn extending several inches from the top of 

 the core. The top of this for nearly half an inch is already 

 hardened into perfect horn. Below this it is softer, and a 

 little way down it has lost the horny texture, then it passes 

 by gradual transition into thick massive skin of a high 



temperature and with much blood. 

 Still lower down the core is 

 covered with thinner, ordinary 

 skin bearing coarse hairs. 



As the development of the 

 horn proceeds the outer part of 

 the epidermis is converted into 

 horn from above downwards, and 

 when the lower part is mature 

 the hairs are embedded in the 

 horn. From Caton's description 

 it appears that the progress of 

 the horn downwards is caused 

 by the conversion of the epidermis 

 between the hairs into horn, not 

 by the displacement of the skin by the horn coming down 

 from above. This suggests that the horn was originally 

 produced by the hardening of hairy skin, the hairs, having 

 deep roots, being involved in the process and embedded in 



Fig. 9. Horn-sheath of Antilocapra as 

 it appears when shed. From a 

 specimen in the British Museum of 

 Natural History. 



