REP ROD UCTION. 



893 



epithelium immediately surrounding the ovum is the discus proligerus. Within 

 the discus the ovum grows and becomes surrounded by the zona pellucida. In 

 the process of growth the Graafian follicle approaches the surface of the ovary. 



FIG. 309. Diagram of the female reproductive organs (modified from Henle and Symington) : o, ovary ; 

 O.f, Graafian follicle containing an ovum ; c.l, corpus luteum ; p, parovarium ; /, fimbriated end of F. t t 

 Fallopian tube ; u, body, and c, cervix of uterus ; o.e, os uteri externum ; vg, vagina ; h, hymen ; u, open- 

 ing of urethra ; v, vulval cleft ; n, labia minora, or nymphse ; l.m, labia majora. 



and finally comes to form a minute rounded vesicular projection covered only 

 by the ovarian epithelium. When fully ready for discharge, the wall of the 

 follicle becomes ruptured, probably by the increasing pressure of the contained 

 liquid, and the ovum with its zona pellucida and a portion or all of the discus 

 proliyerus, now called the corona radiata, is cast out upon the surface of the 

 ovary to be taken up by the Fallopian tube. The empty follicle undergoes 

 changes and becomes the corpus luteum (c.l). Usually the corpus luteum de- 

 generates within a few days and ultimately disappears. If, however, pregnancy 

 follows ovulation, it grows very large, perhaps because of the congested state 

 of the reproductive organs, and remains for months before the retrograde 

 metamorphosis sets in. Not all Graafian follicles reach maturity and burst, 

 for many, after developing to a considerable size, undergo degenerative 

 changes, characterized by liquefaction and disappearance of their contents. 



The discharge of the ovum is known technically as ovulation. In most 

 animals ovulation is a periodic phenomenon accompanying certain seasons, and 

 is marked by general sexual activity. In woman and many domesticated ani- 

 mals the relation to the seasons no longer exists, but too little is known of the 

 causes and time-relations of the phenomenon and its general bearings upon 

 other physiological processes, notably upon menstruation in woman. A large 



