In the further course of development of the graafian follicles at this period, the most advanced now reapproach the surface of the ovary, so that a fully-matured follicle comes to occupy almost the entire thickness of the cortical substance, and may even give rise to a localized bulging of the surface of the organ. In such a mature follicle, which has attained nearly the size of a pea, we recognize an outermost connective-tissue investment (_theca folliculi_), consisting of condensed ovarian stroma, in which two layers are distinguished, sometimes called simply _outer tunic_ and _inner tunic_, sometimes known by the names of _tunica fibrosa_ (outer) and _tunica propria_ (inner), respectively; within this is the cellular layer known as the _membrana granulosa_ (or _stratum granulosum_), the portion of which, now greatly enlarged, immediately surrounding the ovum is known as the _discus proligerus_ (or _cumulus oöphorus_); the interspace between the _discus proligerus_ and the membrana granulosa is filled with a clear fluid, the _liquor folliculi_. In consequence of the continued increase in its fluid contents, the graafian follicle ultimately bursts along the most prominent portion of the superficial wall, and the ovum passes out through the rupture, finding its way under normal conditions into the Fallopian tube and through this into the uterus. The follicle itself then undergoes a regressive metamorphosis, forming the _corpus luteum_, the rent in the envelope of which, after the absorption of the yellowish semi-fluid contents, undergoes cicatrization. Contemporaneously with this development at puberty of the process of ovulation, menstruation also for the first time makes its appearance, recurring thenceforward at four-weekly intervals as the regular catamenial discharge.