SECTION III 

 REPRODUCTION IN MAN 



THE DEVELOPMENT OF THE REPRODUCTIVE ORGANS 



THE most marked example of chemical correlation is found in the influence 

 exerted by the genital glands upon the other parts of the reproductive 

 apparatus and upon the body generally. Thus castration, i.e. removal of 

 the testes or ovaries, if carried out before the time of puberty, prevents the 

 development of the secondary sexual characters, which normally occurs 

 at this epoch in both sexes. Puberty denotes the period at which ripe 

 spermatozoa and ova are produced in the testis and ovary respectively. In 

 the human species this period is marked or preceded in the male by in- 

 creased growth of the skeleton, by growth of the larynx, leading to a lower- 

 ing in pitch of the voice, by the growth of hair on the face and pubes, and 

 by the development of sexual desire. In the female we find at puberty 

 enlargement of the breasts, attended by some growth of the mammary 

 glands and by a moulding of the whole form, making it more fit for the 

 bearing of children. The chief sign of puberty in the female consists in the 

 periodic changes in the uterus, which give rise to menstruation, i.e. a flow 

 of blood and mucus from the genital organs, lasting three to five days and 

 repeated every four weeks. Menstruation persists so long as the ovary is 

 functional, and is producing ripe ova. The activity of the ovary comes to 

 an end between the forty- fifth and fiftieth year (' the climacteric ' or ' change 

 of life '). With the cessation of its activity menstruation also stops, and 

 the uterus undergoes a process of atrophy. These secondary sexual charac- 

 ters must be ascribed to the influence of chemical substances produced in the 

 ovary and testis respectively. Castration after puberty, though not causing 

 any change in the skeleton, which has already assumed its permanent form, 

 brings about retrogressive changes in the other genital organs, analogous 

 to those occurring in the female at the climacteric. In animals the pheno- 

 mena of * coming on heat ' or ' rut ' seem to be analogous with menstrua- 

 tion in the human female, and like this depend on the normal activity of the 

 ovary. They are permanently abolished by extirpation of the ovaries, 

 but may be reinduced by implantation in the peritoneum of an ovary from 

 another animal of the same species. This fact shows that the changes in 

 the uterus responsible for rut, as well as for menstruation, are independent 

 of any nervous connections between the ovaries and the rest of the body, and 

 must therefore be brought about by the circulation in the blood of specific 



1217 39 



