356 



growth and 3. Period of Constancy followed by gradual disappearance 

 and these three stages will be dealt with in order. It will be necessary 

 however, first, to refer briefly to the mature follicle in order to call 

 attention to some interesting differences between it and the similar 

 structure in the Eutheria. 



The ovum, whose structure has been fully treated by Hn.L (8), 

 is surrounded by a discus proligerus and situated peripherally in the 

 follicle. The cells of the discus are similar to those of the membrana 

 granulosa to which they are connected by a retinacula and they begin 

 to break apart in the ripe follicle just before the expulsion of the 

 ovum. The membrana granulosa forms the lining of the follicle, and 

 varies in thickness from eight to nine cells near the discus to two 

 or three cells at the stigmatic area. It is limited externally by the 

 membrana propria, a homogenous basal membrane (see fig. 1). 



The theca folliculi with its contained small blood vessels is 

 situated outside the membrana propria. It is worthy of notice because 

 in the ripe or nearly ripe follicles it is practically impossible to 

 distinguish it in layers corresponding to the theca interna and theca 

 externa of the higher mammals, the whole resembling the theca 

 externa. It is only in the primordial follicle, as Sandes has pointed 

 out, that there are indications of this differentiation, but in course of 

 time the theca interna becomes more and more rudimentary. 



Period of Formation. 



The ripening of the follicle is followed by its bursting and the 

 extrusion of the ovum together with some of the liquor folliculi. 

 The remainder of the liquor folliculi with some of the ruptured 

 follicular cells and a few blood corpuscles form the coagulum always 

 to be seen in the early stages of the corpus luteum (fig. 2). Only 

 a very little of the blood spilled by the rupture finds its way into 

 the follicle, the larger part is to be found on the outside of the ovary. 

 The point of rupture is closed by the coming together of the two 

 edges of the membrana granulosa. As the follicle decreases considerably 

 in size after bursting the membrana propria becomes folded and the 

 folds are occupied by the dilated blood vessels of the theca. Following 

 the closure of the follicle comes the period of the formation of the 

 corpus luteum. 



The first noticeable change is the irruption of the theca folliculi, 

 in the form of connective tissue ingrowths at a number of different 



