BY' F. P. SAXDES. 375 



Secondly : — The liquoi' foUiculi fills the follicle. In preserved 

 ovaries it is represented by coagulum, staining fairly well with 

 ordinary stains. 



Thirdly : — The membrana granulosa forms the epithelial part 

 of the follicular wall. It varies in thickness. At or about the 

 stigmatic area it is thinned, and is only four or five, or even two 

 or three layers of cells in thickness, whilst near the ovum it may 

 be seven to ten layers of cells in thickness. The cells are small 

 and compressed, with nuclei, some of which stain intensely with 

 iron-h?ematoxylin, whilst others stain faintly. Mitotic figures 

 are absent. Vacuoles are often present at the intercellular 

 angles. 



The membrana granulosa is bounded externally by the mem- 

 brana propria (see fig. 6), which forms a basal membrane on 

 which the cells of the membrana granulosa rest. This basal 

 membrane is homogeneous, clear and refractile on section, and on 

 its outer side lies the theca folliculi. It is present in most 

 animals, swine being an exception. Its nature and origin are 

 disputed ; probably it is an altered layer of the theca interna. 



Fourthly: — The theca follicidi is, from the point of view of this 

 paper, the most interesting of the structures surrounding the 

 ovum. In all animals whose ovaries have hitherto been studied, 

 the theca folliculi is described as being specialised into two layers, 

 an outer fibrous layer called the " theca externa," and an inner 

 " theca interna," whose cells are polygonal with rounded nuclei, 

 and contain in their cytoplasm granules of the so-called "lutein" 

 substance, and are separated from each other by a varying amount 

 of fibrous material. In Dasyurus, this specialisation of the theca 

 folliculi into theca externa and theca interna is extremely rudi- 

 mentary. Indications of it are seen in the theciie of primordial 

 follicles (see figs. 6 and 7), in which tliere can be made out an 

 outer theca externa of fibrous character, and an inner theca 

 interna, with irregular flattened connective tissue cells, having 

 oval nuclei with no karyokinetic figures, a granular cytoplasm, 

 but no definite lutein granules, and no obvious intercellular 

 substance. This layer contains the smallest blood vessels. As 



