THE CORPUS LUTEUM 357 



of pregnancy, when it attains a diameter of about half an 

 inch. This size is maintained — at any rate in the rabbit — 

 mitil a late period of gestation or even into lactation. 

 It then undergoes degeneration and becomes transformed 

 into interstitial tissue. The persistence of the corpus luteum 

 is dependent upon the presence of the foetus in the uterus 

 in all those animals such as Man which do not experience 

 pseudo-pregnancy. 



In animals which do experience pseudo-pregnancy (p. 351) 

 the corpus luteum persists for a period as long, or almost 

 as long, as in true pregnancy. 



Internal Secretion of the Ovary 



WTicn both ovaries are excised in early hfe the changes 

 characteristic of puberty do not occur. There are no 

 oestrous cycles, the uterus remaining in an infantile con- 

 dition. Secondary sexual characteristics fail to appear, 

 there being in some animals an approach to the male 

 physical form. 



On removal of the ovaries after puberty, menstruation 

 ceases, while the uterus, and sometimes the breast, undergo 

 atrophic changes. 



In some animals the ovaries have been removed and 

 other ovaries grafted. Under these conditions folUcle- 

 formation occurs in the graft and the oestrous cycle is 

 resumed. 



Any reflex connection between the ovarian and uterine 

 changes is out of the question. This is proved not only 

 by the transplantation experiments mentioned above, but 

 also by the fact that the changes in the uterus occur when 

 all nervous connection with the ovary is destroyed by 

 removal of the lumbo-sacral part of the cord. 



The ovary therefore produces a hormone which is neces- 

 sary for the nutrition of the uterus. As the ovary under- 

 goes its cycle of changes it is probable that the secretion 

 varies in amomit, and that this variation determines the 

 parallel cycle of changes in the uterus. 



