HORMONES AND REPRODUCTION 55 



testosterone stimulates the growth of the ducts which 

 carry the sperm from the testis; the seminal vesicles in 

 which the sperm are stored; the various glands which 

 supply nourishment and fluid for the sperm to swim in; 

 and the penis (if this is present) for the transmission of 

 the sperm to the female. It also induces the growth of 

 those adornnients which a male commonly possesses 

 for the excitement and stimulation of the female. 



Most of these changes are the result of true growtn, 

 that is of cell multiplication by mitosis. It has recently 

 been suggested that this is a fundamental function of 

 both androgenic and oestrogenic hormones, so that the 

 term mitogenic hormone has been proposed to cover 

 them alL^"^ It is now also evident that these substances 

 not only stimulate growth by mitosis in tissues and 

 organs related to sex function, but that they may also do 

 this in other tissues as well. So the accessory and secon- 

 dary sexual tissues and organs, which respond so strongly 

 to the stimulating presence of male hormone, may merely 

 have developed an unusual sensitivit}'^ to this substance. 

 It also follows that all tissues and organs have the 

 potentiality of enlargement in relation to sexual processes 

 should a special need arise. In this way there must have 

 originated the comb and wattles on the head of a cock; 

 the thumb pads by which the male frog maintains a grip 

 on the female; and the modified posterior end of the 

 kidney from which, during the breeding season, a male 

 stickleback secretes the sticky substance used in the 

 manufacture of the nest. 



If the male hormone is primarily a mitosis stimulator, 

 it remains to be determined whether it also exerts this 

 influence in the testis itself. It has been generally believed 

 that the testis, like the ovary, depends for its develop- 

 ment and function only on the hormones of the anterior 

 pituitary. Recently, however, this view has been chal- 

 lenged by Gaarenstroom and de Jongh®^ and by 

 BuUough.^' It appears that in the complete absence of 

 the pituitary hormones, testosterone is able to maintain 



