33 2 REPRODUCTION 



is the corona radiata already mentioned. The zona pel- 

 lucida is just underneath the corona. 



Usually a Graaiian follicle contains only one ovum. The 

 follicles and their contained ova begin to be formed early in 

 fetal life. Probably none are newly formed after the child 

 is two years old, but they are undeveloped before puberty. 

 It is estimated that some 72,000 follicles and ova exist in 

 the two ovaries of the average woman; but of these not 

 more than 400 reach full development, the others undergoing 

 retrograde changes and disappearing. 



Up to puberty the follicles and ova are small, but at that 

 time some of them begin to enlarge, and at more or less 

 regular intervals one of these follicles bursts and allows the 

 escape of its contained ovum into the fimbriated extremity of 

 the Fallopian tube a process known at ovulation. Previ- 

 ous to its rupture the Graafian follicle has been enlarging. 

 It is always located in the cortical part of the ovary, but it 

 may now not only form a distinct protrusion above the sur- 

 face of the organ, but may by its size encroach upon the me- 

 dullary portion. It may at this time have a diameter of half 

 an inch. Meantime the more superficial part of the tunica 

 vasculosa has been undergoing fatty degeneration, has lost 

 its blood supply and become very thin. Hlere rupture oc- 

 curs, and the mature ovum, ready for impregnation, escapes 

 upon the surface of the ovary. 



Corpus Luteum. When the ovum has been extruded hem- 

 orrhage occurs, filling the empty follicle with blood. By 

 contraction of the extra-vesicular adjacent tissue the walls 

 of the Graafian follicle become folded into the cavity. Soon 

 proliferation of the cells of the follicular wall takes place 

 into the blood clot, vascular loops are formed, and the tunica 

 vasculosa itself becomes greatly hypertrophied. The clot 

 .later disappears and the mass then has a yellowish color and 

 is known as the corpus luteum. 



Whether or not the ovum that escaped from the follicle 

 which was the antecedent of any given corpus luteum was 



