THE UNIMPEEGNATED OYUM. 719 



mucous follicles are scattered beneath the mucous mem- 

 brane composing these parts of the external organs of 

 generation ; and at the side of the fore part of the vagina, 

 are two larger lobulated glands, named vulvo-vaginal, or 

 Duverney's glands, which are analogous to Cowper's glands 

 in the male. 



Having given this general outline of the several parts 

 which, in the female, contribute to the reproduction of the 

 species, it will now be necessary to examine successively 

 the formation, discharge, impregnation, and development 

 of the ovum, to which these several parts are subservient. 



Uhimpregnated Ovum. 



If the structure and formation of the human ovary be 

 examined at any period between early infancy and advanced 

 age, but especially during that period of life in which the 

 power of conception exists, it will be found to contain, on 

 an average, from fifteen to twenty small vesicles or mem- 

 branous sacs of various sizes ; these have been already 

 alluded to as the follicles or vesicles of De Graaf, the 

 anatomist who first accurately described them ; they are 

 also sometimes called ovisacs. At their first formation, the 

 Graafian vesicles, according to Schron, are near the surface 

 of the stroma of the ovary, but subsequently become more 

 deeply placed ; and again, as they increase in size, make 

 their way towards the surface. When mature, they form 

 little prominences on the exterior of the ovary, covered 

 only by the peritoneum. Each follicle has an external 

 membranous envelope, composed of fine fibro-cellular 

 tissue, and connected with the surrounding stroma of the 

 ovary by networks of blood-vessels (fig. 201). This enve- 

 lope or tunic is lined with a layer of nucleated cells, forming 

 a kind of epithelium or internal tunic, and named membrana 

 granulosa. The cavity of the follicle is filled with an albu- 

 minous fluid in which microscopic granules float ; and it 

 contains also the ovum or ovule. 



