376 THE CORPUS LUTEUM OF DASYURUS, 



the follicle ripens, this differentiation becomes practicall}' indis- 

 tinguishable, the theca interna being represented by an indistinct 

 layer of flattened nucleated cells, next the membrana propria, 

 and resembling very closely the theca externa. 



When the follicle is ripe, the stroma of the ovary generally is 

 scanty; it is seen between adjacent ripe follicles as a thin layer 

 of fibrous tissue, showing occasional nuclei, and contains larger 

 blood vessels for the supply of the follicles. The stroma of the 

 ovary is also very thin in the neighbourhood of the stigmatic 

 urea, where rupture will take place (see fig. 5). In Dasj^urus, 

 therefore, the theca folliculi has a rudimentary theca interna, 

 which in the ripe follicle is reduced to a minimum, and never 

 approaches the condition described in other animals. 



The Rupture of the Follicle and its Closure. 



AVhen the follicle has become rijDe it bursts, diminishes in size, 

 iind the position of its rupture can be seen on the surface of the 

 ovary. The surface epithelium has broken awa}', and the fibrous 

 wall opens to allow the extrusion of the ovum with discus proli- 

 gerus and most of the liquor folliculi. The blood vessels of the 

 thinned ovarian stroma throw out blood which in Das3^urus is 

 found constantly upon the surface of the ovary. Intra-follicular 

 haemorrhage is very exceptional in this animal, and if it occurs 

 is very slight, never more than a dozen i-ed corpuscles being 

 found in a ruptured follicle. The ova were found in the oviduct, 

 some unsegmented, some giving off the polar body, some in the 

 one- and two-celled stages. With the release of intra-follicular 

 pressure the walls of the follicle tend to become approximated, 

 corrugated and thickened, whilst at the site of rupture the two 

 opposed surfaces of the meml)rana granuloma come together and 

 adhere, so that there is foi-med a plug of epithelial cells (Bouchon 

 epithelial), which closes the follicle (see figs, 8-9). This closure 

 is an early event in Dasyurus, and takes place within the first 

 few hours, before there is any attempt at formation of the corpus 

 luteum. 



