564 MATURATION AND DISCHARGE OF OVA. [CHAP. XXXIX. 



the menstrual periods in the human female as identical with those 

 of heat or rut in animals ; a view which has been especially ad- 

 vocated by Bischoff. 



The menstruation and escape of ova, then, in all animals, is a peri- 

 odical phenomenon, and even in the human subject, if not accqm- 

 panied with, is shortly followed by, increased sexual desire ; while, 

 Jn animals, sexual intercourse takes place at these times alone. 

 The rupture of the follicle is probably due to the increased local 

 determination of blood at these periods, by which the contents 

 of the Graafian follicle are forced towards the surface of the ovary. 

 Besides the escape of a certain quantity of blood into the follicle, 

 an exudation takes place from its lower part, so that the contents 

 of the follicle are gradually forced towards the surface, and at the 

 same time, the structures at this point gradually become thinner, 

 until at last the peritoneal coat, and the thin layer of the stroma, 

 give way, and the contents of the follicle escape through the 

 fissure. The opening soon closes, leaving a small cicatrix. 



After the ovum has arrived at the most superficial portion of the 

 follicle in the manner just described, and is about to escape, the 

 fimbria3 of the Fallopian tube grasp the ovary ; and the ovum, 

 after it has escaped from the ruptured follicle, ordinarily falls into 

 the funnel-shaped cavity at the base of the fimbrise, whence it is 

 transmitted into the Fallopian tube, along which it is gradually 

 propelled, chiefly, no doubt, by the vermicular contractions of the 

 walls, but in part, also, by the vibration of the cilia which line its 

 interior, into the uterus. In some distressing cases, happily very 

 rare, the ovum falls into the cavity of the peritoneum, instead 

 of entering the Fallopian tube, and the embryo becomes developed 

 in this situation. These cases usually terminate in death. Some- 

 times, however, the remains of the foetus escape by suppuration 

 through the abdominal walls, or into the intestine. 



Immediately after the escape of the ovum from the ovary, cer- 

 tain peculiar and characteristic changes ensue in the follicle which 

 contained it, and these are influenced by the occurrence of impreg- 

 nation. If impregnation has taken place, the lining membrane of 

 the uterus also becomes the seat of peculiar changes, which do not 

 occur under other circumstances. The changes which affect the 

 ovum itself, consequent upon impregnation, will be more conve- 

 niently considered when we have referred to the manner in which 

 corpora lutea are produced. The mode of formation of the mem- 

 brana decidua will be alluded to afterwards. 



Formation of Corpora Lutea. If the Graafian follicle of a mem- 



