THE DEVELOPMENT OF VERTEBRATA. 291 



dition. It may be true in certain cases that the characters 

 are coupled with the sex character, but it is difficult to 

 believe that mutations could ever occur, and occur so fre- 

 quently, which consisted of structures which not only were 

 adapted to a particular function, e.g. the excrescences of 

 the frog's fore-foot for holding the female, but actually 

 developed in the breeding season when the function was 

 required and disappeared afterwards. Such a close corre- 

 spondence between the structure, and the season of its 

 development, and its function seems to point very strongly 

 to the conclusion that the function itself, which is confined 

 to the male, must be the cause of the structure. 



16. Growth and Shedding of Antlers. The antlers 

 of stags are in many respects the most remarkable of 

 secondary sexual characters : there is no other case in 

 which so large a mass of bony tissue is annually produced 

 and annually shed. The growth begins in spring soon 

 after the old antlers have dropped off. The new bone is 

 covered with skin and hair, the skin being very vascular 

 and the hair short, whence the covering is called the 

 velvet. The growth of the great branched structures is 

 complete by the end of August or beginning of September, 

 and then the animal voluntarily scrapes off the velvet by 

 rubbing the antlers against the trunks of trees or palings. 

 The velvet at this time is not actually dead, but full of 

 blood, yet the process seems to give the animal no pain. 

 At the base of the antler, where the skin joins the bare 

 bone, is produced a projecting ring of bone called the 

 " burr." With the bare antlers the stags fight with one 

 another during the breeding season, which lasts from 

 September to Christmas. Then at some time in the 

 beginning of the following year the bone below the burr 

 is absorbed, the antler drops off, and the whole process is 

 repeated. The most important fact about this history of 

 the antler is that the processes which take place in the 

 stag by heredity are essentially the same as those which 

 occur occasionally in mammals in general in consequence 

 of injury or disease. It is a well-known fact that bone can- 

 iiot live after the death of the periosteum tha.t surrounds 



