REPRODUCTION. 235 



Menstruation is a periodic discharge of blood from the mucous membrane 

 of the uterus, due to a fatty degeneration of the small blood-vessels. Under 

 the pressure of an increased amount of blood in the reproductive organs, 

 attending the process of ovulation, the blood-vessels rupture, and a hemor- 

 rhage takes place into the uterine cavity; thence it passes into the vagina. 

 Menstruation lasts from five to six days, and the amount of blood discharged 

 averages about five ounces. 



Corpus Luteum. For some time previous to the rupture of a Graafian 

 vesicle it increases in size and becomes vascular; its walls become thickened 

 from the deposition of a reddish-yellow, glutinous substance, a product of 

 cell growth from the proper coat of the follicle and the membrana granulosa. 

 After the ovum escapes there is usually a small effusion of blood into the 

 cavity of the follicle, which soon coagulates, loses its coloring-matter, and 

 acquires the characteristics of fibrin, but it takes no part in the formation of 

 the corpus luteum. The walls of the follicle become convoluted and vascular 

 and undergo hypertrophy, until they occupy the whole of the follicular 

 cavity. At its period of fullest development the corpus luteum measures 

 of an inch in length and \ of an inch in depth. In a few weeks the mass 

 loses its red color and becomes yellow, constituting the corpus luteum, or 

 yellow body. It then begins to retract and becomes pale; and at the end of 

 two months nothing remains but a small cicatrix upon the surface of the 

 ovary. Such are the changes in the follicle if the ovum has not been 

 impregnated. 



The corpus luteum, after impregnation has taken place, undergoes a much 

 slower development, becomes larger, and continues during the entire period 

 of gestation. The difference between the corpus luteum of the unimpreg- 

 nated and pregnant condition is expressed in the following table by Dalton: 



Corpus Luteum of Menstruation. Corpus Luteum of Pregnancy. 



At the end of three Three quarters of an inch in diameter; central clot 



weeks. | reddish; convoluted wall pale. 



One month I Smaller; convoluted] Larger; convoluted wall 



wall bright yellow; ! bright yellow; clot still reddish. 



clot still reddish. 



Two months Reduced to the con- 



I dition of an insignifi- 

 i cant cicatrix. 



Seven eigths of an inch in 

 diameter; convoluted wall 

 bright yellow; clot perfectly 

 decolorized. 



