152 MAMMALIAN SEXUAL CHARACTERS 



the scrotum is confined to the males, the ' descent ' 

 or dislocation takes place in the foetus, and not at 

 the period of puberty. This is in accordance with 

 the fact that the mechanical conditions to which the 

 change is attributed are not related to sexual habits, 

 but to the general habits of life which begin soon 

 after birth. The development, therefore, may be 

 considered to be related to the presence of a hormone 

 derived from the normal testis, but not to a special 

 quantity or quality of hormone associated with 

 maturity or the functional activity of the organ. In 

 Rodents, however, there is a difference in the organs, 

 not only at maturity, but in every rutting season, 

 at any rate in Muridae such as rats and others. In 

 the rutting season the testes become much larger and 

 descend into the scrota! sacs, at other times of the 

 year being apparently more or less abdominal. In 

 rabbits and hares, which have a much more im- 

 pulsive progression, the organs seem to be always in 

 the scrotal sacs. 



It might be thought that in this case, although the 

 hormone theory of heredity might be applied, there 

 was no reason to suppose that a hormone derived 

 from the testis in the individual development was 

 necessary in order that the hereditary change 

 should take place. If the individual was male and 

 therefore had a testis, this organ would by heredity 

 go through the process of dislocation. But there is 

 the curious fact that when the descent is not normal 

 and complete, in what is called cryptorchidism, the 

 organs are always sterile. The retention of the 

 testes within the abdomen may be regarded as a 

 case of arrested development, like many other 

 abnormalities, but this does not explain why the 



