584 MENSTKUATION AND PREGNANCY. 



concealed in the ovarian tissue. "We have distinguished them so 

 late as nine and a half months after delivery. They finally disap- 

 pear entirely, together with the external cicatrix which previously 

 marked their situation. 



During the existence of gestation, the process of menstruation 

 being suspended, no new follicles are ruptured, and no new corpora 

 lutea are produced ; and as the old ones, formed before the period of 

 conception, gradually fade and disappear, the corpus luteum which 

 marks the occurrence of pregnancy after a short time exists alone 

 in the ovary, and is not accompanied by any others of older date. 

 In twin pregnancies, we of course find two corpora lutea in the 

 ovaries ; but these are precisely similar to each other, and, being 

 evidently of the same date, will not give rise to any confusion. 

 Where there is but a single foetus in the uterus, and the ovaries 

 contain two corpora lutea of similar appearance, one of them 

 belongs to an embryo which has been blighted by some accident 

 in the early part of pregnancy. The remains of the blighted em- 

 bryo may often be discovered, in such cases, in some part of the 

 Fallopian tubes, where it has been arrested in its descent toward 

 the uterus. 



After the process of lactation comes to an end, the ovaries again 

 resume their ordinary function. The Graafian follicles mature and 

 rupture in succession, as before, and new corpora lutea follow each 

 other in alternate development and disappearance. 



We find, then, that the corpus luteum of menstruation differs from 

 that of pregnancy in the extent of its development and the dura- 

 tion of its existence. While the former passes through all the im- 

 portant phases of its growth and decline in the period of two 

 months, the latter lasts from nine to ten months, and presents, 

 during a great portion of the time, a larger size and a more solid 

 organization. It will be observed that, even with the corpus 

 luteum of pregnancy, the bright yellow color, which is so import- 

 ant a characteristic, is only temporary in its duration ; not making 

 its appearance till about the end of the fourth week, and again 

 disappearing after the sixth month. 



The following table contains, in a brief form, the characters of 

 the corpus luteum, as belonging to the two different conditions of 

 menstruation and pregnancy, corresponding with different periods 

 of its development. 



