OVULATIOX. 



291 



epithelium as to cause it to bulge macroscopically and then to rupture. 

 Through the opening thus made the liquor folliculi and the egg cell, sur- 

 rounded by more or less of its corona, are expelled into the peritonaeal 

 cavity. The discharge of the ovum from the follicle is known as ovula- 

 tion. Blood escapes from the tunica interna and forms a clot within the 

 empty follicle (Fig. 333). On all sides the clot is surrounded by prolifer- 

 ating cells which contain a yellow fatty pigment; thus they form a corpus 

 luteum. The lutein cells increase in size and number and the clot which 

 may show haematoidin crystals, is gradually absorbed. Between the 

 lutein cells there are strands of vascular connective tissue as shown in 

 Fig. 334. If pregnancy does not occur the corpus luteum attains its 

 maximum development in 12 days and degenerates within a few weeks. 



Connective tissue septa. 



Fibrous connective tissue. 



- Vacuoles. 



Lutein cells. 



A B 



FIG. 334. A, PORTION OF A CORPUS LUTEUM OF A RABBIT. B, PORTION OP A CORPUS 



LUTEUM OF A CAT. X 260. 

 In B the lutein cells have become fatty and contain large and small vacuoles. 



Connective tissue increases and the lutein cells disintegrate; the newly 

 formed vessels are obliterated and the mass becomes a nodule of dense 

 "scar tissue," the corpus albicans. If, however, ovulation is followed by 

 pregnancy the corpus luteum enlarges even to a diameter of from 1.5 to 

 3 cms., reaching the height of its development in five or six months. It 

 persists until the end of pregnancy. Thus the corpus luteum of preg- 

 nancy must be distinguished from the corpus luteum of ovulation. 



As to the origin of the granular, vacuolated lutein cells there is a 

 difference of opinion. Some consider that they arise from the stratum 

 granulosum, and others from the tunica interna. They have been com- 

 pared with the interstitial cells of the testis, and there is experimental 

 evidence that they produce an internal secretion without which an embryo 

 cannot develop within the uterus. 



