28 THE PHYSIOLOGY OF REPRODUCTION 



known to drop his antlers as soon after the rutting season as 

 December, while, on the other hand, some immature animals 

 in the Lake District are said to carry them until May. After 

 the shedding of the antlers new ones begin to grow from the 

 pedicles, the growth taking place chiefly in July and August. 

 When the new antlers have reached their full development 

 the " velvet " is shed (about the beginning of September). The 

 size of the antlers, and the number of branches or " points," go 

 on increasing every year throughout the reproductive period of 

 the stag's hfe and until he begins to dechne with old age.^ 



In the American prongbuck (Antilocapra americana), which 

 is unique among hollow-horned ruminants in shedding the horns 

 every year, the shedding follows the rutting season more closely 

 than in the stag. The rutting in this species begins in September, 

 and lasts about six weeks. In old bucks the horns are shed in 

 October, while the new growth is not completed until July or 

 August in the following year.^ 



A secondary sexual character of a comparable kind occurs in 

 the male salmon, in which the tip of the lower jaw, during the 

 breeding season, is turned up and enlarged, as if to protect the 

 fish in fighting when charged by another male.* 



In Polypterus, during the breeding season, the oval fin of the 

 male becomes greatly enlarged and thickened, and has its 

 surface thrown into folds between the fin-rays. The object of 

 this modification is not known.* 



The papillae on- the hind Hmbs of the breeding male 

 Lepidosiren are structures which seem to possess a special 

 significance, since Kerr ^ has shown that they probably serve as 

 accessory organs of respiration. During the greater part of 

 the year they are relatively inconspicuous ; but as soon as the 

 animal is set free at the beginning of the wet season, they begin 

 to grow with remarkable rapidity, forming slender filaments 

 two or three inches in length and blood-red in colour from their 

 intense vascularity. After the breeding season is over the 

 filaments commence to atrophy, and eventually shrink to their 



1 Cunningham (J. T.), Sexual Dimorphism, London, 1900. 

 ' Cunningham (J. T.), loc. cit. 



" Darwin, Descent of Mem, Popular Edition, London, 1901. 

 * Budgett, loc. cit. ^ Kerr, loc. cit. 



