250 



THE CAT. 



[CHAP. VIIT. 



of a stratum of nucleated cells lying in close contact with 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 proligenis or cumulut, on the inner 

 surface of the membrana granulosa. This rounded body is the 

 ovum the special female sexual element. The larger Graafian 

 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. 



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

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

 external tough, elastic, and relatively thick tunic, the sona pellucida, 



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, 

 which is embedded in the cellular mass, 

 the cumulus, which connects the ovum 

 with the innermost coat (or membrana 

 granulosa) of the Graafian vesicle. Within 

 the zona pellucida is the yelk mass (as 

 some say enclosed within a distinct, but 

 extremely delicate, membrane) of protoplasm 

 and granular matter, with oil globules, 

 but having within it a nucleus termed the 

 germinal vesicle, about the -^^ of an inch 

 in diameter, and enclosing a minute opaque body or nuclcolus, known 

 as the germinal spot, which is from the -r^Vo to the -jrVo- f an 

 inch in diameter. 



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

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

 ovarium. This small body is analogous to the organ of Giraldes, 

 found in some male animals. Connected with the parovarium is 

 a delicate, cylindrical structure called Gaertner's duct, which 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 mouth of the Fallopian tube, is called a hydaiid in the 

 female, as are corresponding structures in the 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 



Fig. 120. THE OVUM, GREATLY 



MAGNIFIED. 



Its outer coat is the zona pellu- 

 cida, which shows a radiated 

 linear structure, Within this 

 is the yelk substance, with 

 granules and small oil glo- 

 bules ; towards one side is the 

 large germinal vesicle con- 

 taining the germinal spot. 



* Mr. Albari Doran lias ascertained tliese points by careful dissections. 



