REPRODUCTION IN MAN 1219 



growth of the glands, which occurs at puberty, can certainly not be ascribed 

 to the presence of a foetus in the uterus, and must be connected with the 

 growth of ripe ova, or, as suggested by the two French authors, with the 

 growth of the tissue of the corpus luteum, resulting from the discharge 

 of ova. 



There seem also to be obscure relationships between the activity of the 

 sexual organs and that of certain so-called ductless glands. Thus castra- 

 tion at an early age leads to persistence of the thymus gland, whereas 

 normally this gland atrophies just before the sexual organs commence their 

 functional activity. The existence of a connection between the thyroid 

 and the ovaries has been a popular belief for 2000 years. In many individuals 

 the thyroid is perceptibly enlarged at each menstrual period. On the other 

 hand, extirpation of the thyroid before puberty brings about, among the 

 other signs of cretinism, failure of development of the ovaries, so that 

 puberty is delayed partially or completely. 



We must thus regard the germ- cells not only as representing the cells 

 from which the individuals of the new generation may be developed, but 

 also as concerned in the formation of chemical substances which, dis- 

 charged into their hosts, affect many or all of the functions of the latter, 

 with the object of finally subordinating the activities of the individual 

 to the preservation and perpetuation of the species. 



THE MALE REPRODUCTIVE ORGANS 



In all the higher animals we may divide the reproductive organs into 

 the essential organs, which form the germ-cells, the spermatozoa and ova 

 respectively, and the accessory organs, which have as their office the facilita- 

 tion of the access of the spermatozoa to the ova (fertilisation), and in the 

 female the nutrition of the product of fertilisation during the early period 

 of its development. 



The essential sexual organ of the male is represented by the testis. 

 This is made up of a collection of convoluted tubules, the seminal tubules, 

 which are contained in a number of compartments separated by fibrous 

 septa. The tubules present few or no branches, each one being about 

 500 mm. long. The testis is formed in the first instance in the peritoneal 

 cavity from the germinal epithelium, but early in life leaves the abdominal 

 cavity by the abdominal ring to lie in a pouch of skin the scrotum. Several 

 tubules unite to form a straight tubule, which leads by a series of 



duced by artificial rupture of a ripe follicle. Whenever this occurs there is a develop- 

 ment of the mammary glands. If no impregnation has taken place (e.g. if the buck has 

 been sterilised by ligature of the vas deferens), the glands develop for fourteen days 

 and then begin to atrophy. This period corresponds to the period of active growth 

 of the corpus luteum. The continued growth during the latter half of pregnancy these 

 authors ascribe to the production of another hormone by a special glandular tissue 

 (' myometrial gland ') which makes its appearance about the fourteenth day in the wall 

 of the uterus, at the site of implantation of the placenta, and lasts until the end of 

 pregnancy. 



