638 REPRODUCTIVE ORGANS. 



radiata extend. These processes are to be regarded as inter- 

 cellular bridges (Retzius) ; and, according to Palladino, they occur 

 not only between the ovum and the corona radiata, but also 

 between the follicular cells themselves. In the ripe human ovum 

 the pores are apparently absent (Nagel), and it is very probable 

 that they have to do with the passage of nourishment to the grow- 

 ing egg. Retzius believes that the zona pellucida is derived from 

 the processes of the cells composing the corona radiata, which at 

 first interlace and form a network around the ovum. Later, the 

 matrix of the membrane is deposited in the meshes of the net- 

 work, very probably by the egg itself." 



Ovum. The human ovum has a diameter of from 0.22 to 0.32 

 mm. The external envelope is the zona pellucida, the origin of 

 which, as has been stated, is uncertain. Within this is the vitellus 

 with its nucleus, the germinal vesicle, whose diameter is from 30 p. 

 to 40 p.. The vitellus consists of a protoplasmic network, in the 



FIG. 425. Portion of broad ligament stretched to show the parovarium (p) lying 

 between the folds and consisting of the head-tube and cross-tubules (Gegenbaur). 



meshes of which are embedded highly refractive oval bodies, the 

 yolk-globules. 



The germinal vesicle has a distinct enveloping membrane, and 

 within it is a scanty framework with a small amount of chromatin, 

 and one or two false nucleoli, germinal spots, due to the thickening 

 of the chromatin. These structures have a diameter of from 7 // 

 to 10 //. 



Parovarium (Fig. 425). This structure is known also as the 

 epoophoron and the organ of Rosenmuller. It lies within the 

 broad ligament, between the Fallopian tube and the ovary, and 

 represents what remains of the Wolffian body of the' fetus. The 

 tubules of that organ being the short canals of the parovarium, 

 and the upper part of the Wolffian duct being represented by the 

 head-tube. This latter sometimes persists as a patent canal, con- 

 stituting Gartner's duct, which is the homologue of the vas 

 deferens. The paroophoron is a structure sometimes observed 



