966 THE PHYSIOLOGY OF REPRODUCTION. 



surface it forms a vesicle projecting to the exterior. This projecting 

 portion is nearly bloodless and thinner than the rest of the wall of 

 the follicle. It is designated as the stigma. When fully mature the 

 follicle ruptures at the stigma and the egg, together with the sur- 

 rounding follicular cells of the discus proligerus and a portion of the 

 membrana granulosa, is extruded, the egg being received into the 

 open end of the Fallopian tube. According to Clark,* the rupture of 

 the follicle is brought about by an increasing vascular congestion 

 of the ovary. The tension within the ovary is thereby increased, 

 the follicle is forced to the surface, and the circulation at the most 

 projecting portion is interfered with to such an extent as to cause 

 necrotic changes at the stigma, at which rupture finally occurs. After 

 the bursting of the follicle its walls collapse, and the central cavity 

 receives also some blood from the ruptured vessels of the theca. 

 Later on the vesicle becomes filled with cells containing a yellow 

 pigment. These cells increase rapidly and form a festooned border 

 of increasing thickness around the central blood clot. The vesicle 

 at this stage, on account of the yellow color of the new cells, is 

 known as a corpus luteum. The structure thus formed increases 

 in size for a period and then undergoes retrogressive changes and 

 is finally completely absorbed. The duration of the period of growth 

 and retrogression varies according as the egg liberated becomes 

 fertilized or not. If fertilization does not occur, as is the case in 

 the usual monthly periods, the corpus luteum reaches its maximum 

 size within two to three weeks and then begins to be absorbed. 

 It is frequently designated under these circumstances as the false 

 corpus luteum (corpus luteum spurium) or corpus luteum of men- 

 struation. In case the egg is fertilized and the woman becomes 

 pregnant the life history of the corpus luteum is much prolonged. 

 Instead of undergoing absorption after the third week it continues 

 to increase in size by multiplication of the lutein cells during the 

 first few months of pregnancy, and does not show retrogressive 

 changes until the sixth month or later. The total size of the corpus 

 in such cases is much larger than in menstruation, and it was des- 

 ignated, therefore, by the older writers as the true corpus luteum 

 (corpus luteum verum) or corpus luteum of pregnancy. Later 

 observers agree that there is no essential difference in structure 

 between the true and the false corpus luteum, although the former 

 has a longer history and attains a greater size. The point of 

 greatest structural interest in the corpus luteum is the origin of the 

 yellow (lutein) cells. Histologists have been and still are divided 

 upon this point ; some believe that they arise from the cells of the 

 membrana granulosa, others that they come from the connective 

 tissue cells in the internal capsule (theca interna) of the follicle. 

 * Clark, "Johns Hopkins Hospital Reports,'' 7, 181, 1898. 



