134 HEREDITY AND SEX 



dropped, and are replaced, if at all, by imperfect ant- 

 lers, and these are never renewed. 



These facts make it clear that there is an intimate 

 relation between the orderly sequence of development 

 of the horns in the deer and the presence of the male 

 sexual glands. 



In the case of sheep, the evidence is more explicit. 

 Here we have carefully planned experiments in which 

 both sexes have been studied ; and there are breeding 



FIG. 68. Dorset; male (horned) and female (horned). 



experiments also, in which the heredity of horns has 

 been examined. 



In some breeds of sheep, as in the Merinos and 

 Herdwicks, horns are present in the males, absent in 

 the females (Fig. 67). In other breeds of sheep, as 

 in Dorsets, both males and females have horns (Fig. 

 68). In still other breeds both sexes lack horns, as 

 in some of the fat-tailed sheep of Africa and Asia 

 (Fig. 69). 



Marshall has made experiments with Herdwicks - 

 a race of sheep in which the rams have large, coiled 

 horns and the ewes are hornless. Three young rams 

 (3, 4, and 5 months old) were castrated. The horns 

 had begun to grow (3, 4^, and 6 inches long) at the 

 time of operating. They ceased to grow after the 

 operation. 



