98 SEXUAL DIMORPHISM 



antlers are the following : Firstly, they are permanent, not 

 annually shed and reproduced ; secondly, they are encased in 

 cornified skin ; thirdly, the bone itself is hollow, not merely 

 spongy in the interior like the antler; fourthly, they are 

 simple and not branched. It seems to me that all these 

 peculiarities are chiefly, if not entirely, due to the fact that 

 horns have been developed by impacts and blows applied less 

 violently and with less regular periodicity, which have there- 

 fore produced a slow and permanent growth. In sheath- 

 horned ruminants there is no such brief and well-marked 

 rutting season as in deer, while most of them agree with the 

 Reindeer and differ from the other species in being per- 

 manently gregarious. The significance of these facts is far 

 greater than that of proportions between the numbers of the 

 sexes or any process of selection. The less intense friction, 

 I would suggest, is the reason why the skin over the bony 

 outgrowth has been hardened into horn instead of being torn 

 away and shed as in the antler, and also why the bony 

 outgrowth itself has not branched out at various points. 

 The extension of the frontal sinuses into the horns offers no 

 special difficulty, but is merely a consequence of the mode of 

 growth of the bone. 



.The antelopes form in some respects a transition from 

 deer to cattle in their habits and form of body. Antilope 

 saiga, which lives in eastern Europe and Asia, is stated by 

 Darwin, on the authority of Pallas, to be the most inordinate 

 polygamist in the world, a single male being found with about 

 a hundred females and kids. It is in accordance with this 

 that the females should be without horns, for all the fighting 

 is done by the male. The graceful spiral horns of the kudu 

 of South Africa are also confined to the males. In the eland, 

 Ant. oreas, on the other hand, and in several other species 

 the horns are developed in both sexes. 



In Antilocapra americana the horns are rudimentary in 



