686 



ZOOLOGY 



SECT. 



Development. — The ova of Mammals (Fig. 1213), like those 

 of Vertebrates in general, are developed from certain cells of 

 the germinal epithelium, the primitive ova (pr. ov.). Each of 



^r.e/, 



pr.ov 



H.V 



r/cli 



Fig. 1213. — Part of a sagittal section of an Ovary of a new-born child, hi. v. blood-vessels ; foil. 

 strings and groups of cells derived from the germinal epithelium becoming developed into 

 follicles ; g. ep. germinal epithelium ; in. ingrowing cord of cells from the gei'minal epithelium ; 

 yr. ov. primitive ova. (BYom Hertwig, after Waldeyer.) 



these, surrounded by smaller unmodified cells of the epithelium, 

 sinks into the stroma of the ovary^ in which it becomes embedded, 

 the small cells forming a Graafian follich {foil.) which encloses it. 



memh 



yrterrtif 



Fig. 1^14.— Two stages in the development of the Graafian follicle. A, with the follicular 

 fluid beginning to appear ; B, after the space has largely increased, cain. capsule ; di&c. 

 cumulus proligerus ; inemh. membraua granulosa ; ov. ovum ; sj>. space containing fluid. 

 (After Hertwig.) 



Spaces filled with fluid soon appear among the follicle cells (Fig. 

 1214, Asp.), aad these eventually coalesce to form a single cavity. 

 This cavity, which in some Mammals is crossed by strings of 



