250 THE CAT. [chap. yiii. 



of a stratum of nucleated cells lying in close contact witli the inner 

 surface of the ovisac. Enclosed within these layers is a clear and 

 colourless albuminous fluid, and a small, rounded body, embedded 

 in a cellular mass, the discus proJifjenis or cumulus, on the inner 

 surface of the membrana granulosa. This rounded body is the 

 crum — the special female sexual element. The larger Grnafian 

 vesicles are found at, or near, the surface of the ovary, and it has 

 been found that they approach the surface as they develop. They 

 are indeed primitively formed at the periphery, but they subse- 

 quently sink inwards, and afterwards return once more to the 

 surface. At first the Graafian vesicle is but the envelope of the 

 minute ovum it contains. It subsequently increases, so as to exceed 

 in size the contained ovum to a greater and greater, and ultimately 

 to a very great, degree. 



§ 26. The OVUM is a minute spheroidal mass of protein substance, 

 about the y-i-^ to -p^-^ of an inch in diameter. It consists of an 

 external tough, elastic, and relatively thick tunic, the zona pelluckla, 



which is quite transparent and struc- 

 tureless, though apparently perforated by 

 many excessively minute pores. Exter- 

 nally the zona pellucida is invested by a 

 layer of epithelial cells, the tunica granulosa, 

 Avhich is embedded in the cellular mass, 

 the cumulus, which connects the ovum 

 Fig. 120. -The Ovum, gue.uly witli the innermost coat (or membrana 

 MAGNIFIED.' grauulosa) of the Graafian vesicle. Within 



'''''^,^.^:::T^^a the zona pellucida is the yelk mass (as 

 linear .structure, witiiin tiii.s some sav eucloscd witliiu a distiuct, but 



1.S tlic vulk suli.stitiice, witli , tit; i ^ i> j_ i 



jp-auuios ami .suiaii dii gi„- oxtrcmely aelicate,mcmbrane)oiprotopla.sm 

 lalS^J;^™;"!:!"":^!;;'^^^- and grmmlar matter, with oil globules, 

 taining ti.e germinal .spct. ]r,^^t having mtliiu it a nuclcus termed the 



germinal vesicle, about the ^^-^ ^f an inch 

 in diameter, and cnclo.sing a minute opaque body or nucleolus, known 

 as the germinal spot, which is from the -5-3V0- to the -stVo of an 

 inch in diameter. 



Beside the ovary, within the folds of broad ligament, are certain 

 small tubules, Avhicli together constitute what is called the par- 

 ovarium. Tbis small body is analogous to tlie organ of Giraldes, 

 found in some male animals. Connected with the parovarium is 

 a delicate, cylindrical structure called Gaertncr's duct, wliich runs 

 from the parovarium down the side of the body of the uterus, when 

 it ends blindly.* 



A small pedunculated body in the vicinity of the parovarium, or 

 of the moutli of the Ealloi)ian tube, is called a Jnjdaiid in the 

 female, as are corresponding structures in tlie male. 



The function of the ovary is of course mainly to secrete ova, but 

 the formation of the Graafian vesicles, in which the ova arc 



* Viv. Alban Doran lias "hscertainctl these points by careful dissections. 



