186 THE BREEDING OF ANIMALS 



in the transmission of all characters. Sexual vigor is 

 associated with the development of the secondary sexual 

 characters, and sexual vigor is a desirable character in 

 the domestic animals. The general efficiency of the 

 reproductive process is undoubtedly correlated with the 

 secondary sexual characters. The breeder, therefore, 

 is making no mistake in emphasizing the importance of 

 evidences of strong sexuality as indicated by the develop- 

 ment of the secondary sexual characters. 



174. Effects of castration and ovariotomy on the 

 secondary sexual characters. There is ample evidence 

 of the close correlation existing between the essential 

 organs of sexual reproduction and the secondary sexual 

 characters. The full development of the secondary 

 sexual characters is closely connected with sexual maturity. 

 In the Merino breed of sheep, the males are always horned 

 while the females are hornless. If the male is castrated 

 before the horns begin to develop, the horns fail to grow 

 and the wether remains hornless. If the males are 

 castrated after the horns have started to develop, the 

 horns cease to grow. Marshall, in experiments with 

 Herdwick sheep, a breed in which the males are supplied 

 with large coiled horns and the females are hornless, found 

 that castration at varying ages invariably caused a 

 cessation in the growth of the horns of the male. When 

 the ovaries of the female were removed, there was no 

 apparent tendency toward the growth of horns, although 

 small scurs appeared in one spayed ewe that was kept for 

 seventeen months after removal of the ovaries. Marshall 

 concludes, " The development of horns in the males of 

 a breed of sheep in which well-marked secondary sexual 

 differentiation occurs (as manifested especially by presence 

 or absence of horns) depends upon a stimulus arising in 



