ACTION OF THE FEMALE. 591 



of zona pellucida. The several parts of the Ovum now described are shown 

 in Fig. 5, Plate I. 



740. From the researches of Dr. Barry on the early development of the 

 Ovum, it appears that the Germinal Vesicle is the part which can first be dis- 

 tinctly traced. In Fig. 1 (Plate I.) is seen a representation of one of its inci- 

 pient stages in the Rabbit ; there is nothing here visible, but a collection of 

 very transparent vesicles, surrounded by a mass of dark granules. In the 

 succeeding stage, represented in Fig. 2, some of the vesicles have enlarged, 

 and the granules immediately surrounding them have become developed into 

 cells. A more advanced condition is represented (on a smaller scale) in Fig. 

 3 ; in which a distinct spot (b) is seen on the central vesicle (a\ marking it as 

 the Germinal Vesicle ; whilst many of the granules surrounaing it have be- 

 come cells, and have taken on a very regular arrangement. After a time, a 

 membrane forms around each cluster of granules, separating it from the stroma 

 of the ovarium ; this is the Ovisac. At a later period, a separation takes place 

 between the inner and outer portions of the mass of granular matter, included 

 between the ovisac and the germinal vesicle ; and the separation is completed 

 by the development of a membrane, which envelops the inner stratum. This 

 stratum becomes the Yolk, and includes most of the oil-particles which pre- 

 viously existed within the ovisac ; whilst the portion of the granular mass, 

 exterior to this, gives origin in Mammalia to certain structures of a very pecu- 

 liar character, which seem to be concerned in the liberation of the ovum from 

 the Graafian follicle or Ovisac. The appearance of the Human Ovisac and its 

 contents is seen in Fig. 4. The granules immediately surrounding the Ovum 

 assume the appearance of cells ; and these unite to form a sort of membrane, 

 to which the name of tunica granulosa has been given. This is seen at tg 

 (Fig. 7). The granules lining the Ovisac also combine themselves into a 

 membranous structure ; to which Dr. Barry has given the designation of 

 membrana granulosa (gg, Fig. 6). These are connected by four band-like 

 extensions of the same cellulo-membranous structure, which seem to suspend 

 the ovum in its place ; and these ar,e called retinacula (rr, Figs. 6 and 7). 

 The space between the Tunica Granulosa and the Membrana Granulosa, which 

 is not occupied by the Retinacula, is filled with fluid, in which few or no cells 

 can be seen. The uses of this structure, so far as they are apparent, will be 

 described, when the processes by which the Ovum escapes from the Ovary are 

 detailed. The Ovisac does not form the entire structure which has been de- 

 scribed as the Graafian follicle ; for this consists of two layers, of which the 

 inner one is the true Ovisac, whilst the outer results from a thickening and 

 condensation of the surrounding layer of the Stroma of the Ovarium. It is the 

 outer layer only which is vascular ; the inner presents no trace of structure ; 

 and the increase of the ovum must take place by simple imbibition, through 

 it, of the supply of nutritive matter brought into contact with its exterior. The 

 Ovarium may be seen, even in the foetal animal, to contain immature Ova; in 

 which the several parts can be clearly distinguished. At a later period, how- 

 ever, the number of Ova greatly increases ; and the development of some ad- 

 vances, whilst others degenerate. According to the recent valuable inquiries 

 of Dr. Ritchie,* it appears that, even during the period of childhood, there is 

 a continual rupture of Ovisacs, and discharge of Ova, at the surface of the 

 Ovarium. The Ovaria are studded with numerous minute copper-coloured 

 maculee ; and their surface presents delicate vesicular elevations, which are 

 occasioned by the most matured ovisacs : the dehiscence of these takes place 

 by minute punctiform openings in the peritoneal coat ; and no cicatrix is left. 

 At the period of puberty, the stroma of the ovarium is crowded with Ovisacs; 



* London Medical Gazette, 1844. 



