SECTION III 

 REPRODUCTION IN MAN 



THE DEVELOPMENT OF THE REPRODUCTIVE ORGANS 



THE most marked example of chemical correlation is found by 

 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 increased growth of 

 the skeleton, by growth of the larynx, leading to a lowering 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 con- 

 sists in the periodic changes in the uterus, which give rise to menstrua- 

 tion, i.e. a flow of blood and mucus from the genital organs, lasting 

 three to five days and repeated every four weeks. Menstruation per- 

 sists so long as the ovary is functional, i.e. 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 characters 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 phenomena of ' coming on heat ' or ' rut ' seem to be 

 analogous with menstruation 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 



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