TIIK OVMUES 



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C()\eriii<i' the einhryoiiic ()\-ary jjrolifcratcs cords of cells, called 

 Pfliiger's egg cords, which extend in toward the enihryonic connec- 

 tive tissue and earlier formed germinal cells. At first there is no 

 clear differentiation possible between the cells that will become the 

 ova and those that will form the follicle cells. Later on, regions 

 of the cord segment and a large central cell, the oocyte, is surrounded 

 by several of the smaller follicle cells. The early ovum surrounded 

 by the several flattened follicle cells is known as a primary follicle. 



Fig. 135. — Photograph through the cortex of the ovary of a new-born dog. Along 

 the outer margin is a region with many primary follicles. A few developing follicles 

 occur in the deeper region toward the medulla. 



(Fig. i;')").) Just before birth in man, and shortly after birth in some 

 of the other mammals, the up-growing mesenchyme develops the 

 tunica albuginea subjacent to the germinal epithelium. The for- 

 mation of this layer of connective tissue prevents further develop- 

 ment of cords of cells from the germinal epithelium. During this 

 l)eri()d the primordial sex cells and indifferent cells in the deepest 

 regions of the ovary have degenerated, and this region becomes 

 the medulla. The cortex now contains all the remaining primary 

 follicles, and some of these begin a progressive de\el()i)ment pre- 

 liminary to sexual maturity and the beginning of a reproductive 



