100 INFLUENCE OF HORMONES 



bodies and of other parts of the mammaHan ovary. 

 The mature foUicle containing the ovum differs from 

 that of other Vertebrates in the fact that it is not 

 completely filled by the ovum and the follicular cells 

 surrounding it, but there is a cell-free space of large 

 size into which the ovum covered by follicular cells 

 projects. In the wall of the follicle two layers are 

 distinguished, the theca externa, which is more 

 fibrous, and the theca interna, which is more cellular. 

 In the connective tissue stroma of the ovary between 

 the follicles are scattered, or in some cases aggregated, 

 epithelioid cells known as the interstitial cells, and 

 it is stated that the cells of the theca interna are 

 exactly similar to the interstitial cells. According 

 to Limon ^ and Wallart ^ the interstitial cells are 

 actually derived from those of the theca interna of 

 the follicles. Numbers of ova die without reaching 

 maturity, the follicular cells degenerate, and the 

 follicle becomes filled with the cells of the theca 

 interna, which have a resemblance to those of the 

 true corpus luteum. These degenerate follicles have 

 been termed spurious corpora lutea, or atretic 

 vesicles. The interstitial cells are the remains of 

 these atretic vesicles. The true corpora lutea arise 

 from follicles in which the ova have become mature 

 and from which they have escaped through the sur- 

 face of the ovary. As a result of the escape of the 

 ovum and the contents of the cell-free space, the 

 follicle contracts and the follicular (so-called granu- 

 losa) cells secrete a yellow substance, lutein, and 

 enlarge. Buds from the theca interna invade the 

 follicle and form the connective tissue of the corpus 

 luteum. 



* Arch. d'Anai. micr., v., 1902. 2 ^rch. /. Gynoek, vi. 271. 



