THE GERM CELLS 



v.t. X 



Fig. 3. — Diagrammatic longitudinal section of an un- 

 incubated hen's egg (Allen Thomson in Heisler) : b.l, germ- 

 inal disc; w.y, white yolk, which consists of a central fiask- 

 shaped mass, and a number of concentric layers surrounding 

 the yellow yolk iy.y.); v.t, vitelline membrane; x, a some- 

 what fluid albuminous layer which immediately envelops 

 the yolk; w, albumen, composed of alternating layers of 

 more and less fluid portions; ch.l, chalazae; a.ch, air chamber 

 at the blunt end of the egg — simply a space between the 

 two layers of the shell membrane; i.s.m, inner, s.m, outer 

 layer of the shell membrane; s, shell. 



Fig. 4. — Section of human ovary, 

 including cortex: a, germinal epithe- 

 lium of free surface; b, tunica albu- 

 ginea; c, peripheral stroma contain- 

 ing immature Graafian follicles [d) ; e, 

 weU-advanced follicle from whose wall 

 membrana granulosa has partially 

 separated; /, cavity of liquor follic- 

 uli; g, ovum surrounded by cell mass 

 constituting cumulus oophorus (Pier- 

 sol). 



Fig. S. — Section of well-developed Graafian follicle 

 from human embryo (von HerfE); the enclosed ovum 

 contains two nuclei. 



Fig. 6. — Uterine tube and ovary with 

 mature Graafian follicle about ready to burst 

 (Ribemont-Dessaignes) . 



the Graafian follicle, within which the ovum is eccentrically located (Figs. 4 and 

 230) . The cells of the Graafian follicle immediately surrounding the ovum form 

 the corona radiata (Fig. 1) when the ovum is set free. 



