OVIPONT IN MAMMALIA. 



711 



Graafian vesicle and ovum, Rabbit ; 

 magn. cix. 



granulosa,' those which surround the ovum itself form the ( pro- 



ligerous disc,' ib. e, and the mass of cells thereto adhering is the 



' cumulus.' The ( hyalinion,' or proper tunic of the ovum, thickens 



into the clear substance called ' zona 



pellucida,'/. 1 The cells immediately 



around the ovum, as it ripens, elongate 



and become pyriform, with the pointed 



end attached to the ( zona ' : those of 



the cu mulus diverge irregularly into the 



fluid intervening between them and the 



' membrana granulosa ' of the ovisac : 



but the four groups, defined by Barry 2 



as f retinacula,' ib. d, and fig. 559, g 



2, may be an exceptional disposition. 



The ripe ovarian ovum, freed from 

 its cellular precipitate, fig. 557, is inclosed in the thick trans- 

 parent structureless ( hyalinion,' a : its vitelline contents are 

 opaque through the abundance of granular yolk-substance, b : 

 in this is the ' germinal vesi- 

 cle,' with its nucleus or ( ma- 

 cula,' ib. c : it is more readily 

 seen when the yolk is dis- 

 charged from the ruptured 

 ovum under pressure, as at b. 



§ 396. Ovipont. — The ma- 

 turation of ova occasions the 

 ( rut ' or ' heat ' : in many 

 brutes it is annual ; in the 

 Ferret twice a year ; in the 

 domestic Rabbit, Cat, Hog, 

 Bitch, it may recur three 

 times a year or oftener : in the Human female it is menstrual. The 

 number of ovisacs and ova which ripen at each rut varies accord- 

 ing to the multiparity or uniparity 

 of the species : in the Sow, e.g. fig. 

 558, there may be from four to six or 

 more in each ovary ; in the Orni- 

 thorhynchus, fig. 5C&, there are two 

 only, and these limited to the left 

 ovarium ; in the Human female 

 there is rarely more than one. The 

 rut involves a determination of 



1 As here shown it looks like a ' zone ;' but is a lui 





Mammalian ovarian ovum ; magn. cccvur. 



008 



Ovary, Sow, witli ripe follicles burst; 



nat. size. ccnn". 

 g, not a belt. " cix. 



