45 2 THE OVUM. [SECT. 203. 



where the ovum is situated, the granular layer presents a papilliform 

 thickening, projecting inwards, around the ovum, for ^" in breadth, 

 and named the germinal eminence, or cumulus proligerus (fig. 184, e). 

 The roundish, polygonal cells of this epithelial layer are 0-003"' to 

 0-004'" in size, and are arranged in several layers; they are fur- 

 nished with rather large nuclei, and frequently contain some yel- 

 lowish fat-granules. These cells are extremely delicate, and become 

 indistinct soon after death, so that then the whole epithelium 

 appears only as a finely-granular memhrane, with numerous nuclei. 

 In the interior of the follicle there is a clear, slightly yellowish 

 fluid — liquor folliculi — of the nature of the blood-serum; this 

 almost always contains separate granules, nuclei, and cells, that 

 can scarcely be anything else than detached parts of the membrana 

 granulosa, and have not had their origin in the fluid itself. 



In the germinal eminence, near to the fibrous tissue of the fol- 

 licle, and, consequently, in the most projecting part of it, lies the 

 ovum, or ovulum, imbedded in the cells of which the eminence is 

 composed, and firmly fixed by them. When the follicle bursts, or 

 Fig. 185. if it be ruptured, the ovulum passes out, 



surrounded by the cells of the cumulus and 

 the neighbouring parts of the epithelium, 

 which embrace it after the manner of a ring 

 or disc (the discus proligerus, or germinal 

 disc, v. Baer). This so-called disc, however, 

 is not only placed so as to encircle the 

 Human ovuium, from a greatest breadth of the ovum, but completely 



middle sized follicle ; mas- - -, •. n • i mi 1 -j. ij? 



nitied 250 times, a. vitel- encloses it on ail sides. Hie ovulum ltsell 



line membrane (zona pellu- . i • 1  i j_i 



cida) ; b. outer limit of the is a spherical vesicle, measuring, in the 



yelk, and, at the same time, -,. . , ,,., , ,„ , . , , •, 



boundary of the vitelline mature COlKlltlOn, f to -f^ , which, thOUgll 

 membrane; c. germinal ve- , . . .,, , • , 



sicie, with the germinal peculiar in some respects, still has the nature 



and structure of a simple cell. The cell- 

 membrane, or vitelline membrane, is of the unusual thickness of 

 0-004'" to o'005'", and is seen by the microscope to surround the 

 contents, or yelk (vitellus), as a clear, transparent ring, whence it 

 is also called zona pellucida. It is structureless, very elastic and 

 firm, so that it can support a considerable distension without 

 tearing, and, in its chemical characters, it completely agrees w T ith 

 the membranes proprice (§ 14). The slightly yellowish yelk, which, 

 in fresh ovula, completely fills the vitelline membrane, consists of 

 a viscid fluid, with numerous fine pale granules interspersed in it. 

 In mature ovula, some fat-granules are also seen, and in these we 

 discover a beautiful vesicular nucleus, placed on one side of the 



