THE EARLY DEVELOPMENT OF THE MAMMAL 375 



to four cells deep, spaces begin to appear within the follicle, 

 usually toward one side. On the side opposite these spaces the 

 follicular cells multiply more rapidly and form a definite accu- 



FIG. 145. Section through part of the ovary of a dog. After Waldeyer. a. 

 "Germinal epithelium"; b, egg tubes; c, small ovarian follicles; d, older ovarian 

 follicles; e, ovum surrounded by discus proligerus; /, second ovum in follicle 

 with e. (Only rarely are two ova thus found in a single follicle.) g. Outer cap- 

 sule of the follicle; h, inner capsule of the follicle; i, membrana granulosa; 

 k, collapsed, degenerating follicle; I, blood-vesesls; m, sections through tubes 

 of the parovarium; y, involuted portion of superficial epithelium; z, transi- 

 tion to peritoneal epithelium. 



mulation known as the discus proligerus, in the midst of which 

 the ovum is buried (Fig. 145). The follicle cells immediately 

 surrounding the ovum become markedly elongated forming the 



