8 Cunningham, Unisexual Inheritance. 



The reasons then for regarding secondary sexual characters as 

 due to blastogenic variations are by no means conclusive, and such a 

 view affords no explanation of the remarkable correspondence between 

 the development of such characters and the life and habits of the 

 animal possessing them. On the other hand such characters have a 

 much greater resemblance to acquired characters, and when so re- 

 garded their peculiarities are seen to be due to antecedent conditions, 

 instead of arising by a kind of spontaneous generation in the germ 

 plasm. 



The growth of the antlers of a stag resembles physiologically the 

 formation of a knob of bone or exostosis which occurs when the 

 periosteum or membrane covering the bone is mechanically irritated. 

 Stags fight with their antlers, and if they fought originally with their 

 foreheads before antlers existed, we could understand the origin of 

 these structures. The females do not butt with their heads, and these 

 have no antlers. When the antler is developed the external skin and 

 periosteum are removed in the process known as the peeling of the 

 velvet. Now bone denuded of its periosteum by injury or disease sooner 

 or later dies and dead bone is absorbed or thrown out of the body. 

 The antler likewise when the velvet is shed becomes a mass of dead 

 bone, although the circulation of blood and the life of the bone may 

 continue for some time in the centre. Absorption then takes place at 

 the base of the dead structure and the antler is shed, to be followed 

 by a larger successor. The phases in the history of the antler 

 correspond to the phases in the activity of the reproductive organs. 

 The growth of the antler takes place in summer, when the testes 

 are quiescent but maturing. The velvet is shed in August after which 

 the stag begins to fight and the testes are active. The fighting and 

 pairing season lasts from September to December, and the antlers are 

 shed usually in the following April. 



All these facts become intelligible if we regard them as the here- 

 ditary repetition of processes of growth and absorption originally pro- 

 duced directly by the mechanical irritations caused by fighting. Stags 

 are in the habit of rubbing the velvet from the fully developed antlers 

 purposely, but probably the shedding of the velvet and all the other 

 processes in the history of an antler would take place in a stag at 

 the present day by heredity alone. It is consistent with physiological 

 science however to suppose that originally the antler began to grow 

 in consequence of the blows received in fighting, that the velvet was 

 torn from the same cause and that the shedding of the antler followed 

 in consequence. After the old antler was shed the same results would 

 be produced at the next rutting season. The unisexual inheritance 

 and the remarkable effects of castration are explained by the hypo- 

 thesis that the new processes of growth and absorption are necessarily 



