212 



THE FEMALE REPRODUCTIVE SYSTEM 



break from their surrounding follicle and through the saccular 

 covering of the o\ary into the body cavity from which they pass 

 into the oviducts. After the mature eggs of the breeding season 

 have been discharged, the ovary collapses to a small body having 

 the appearance of a bit of folded whitish membrane. Within this 

 membrane are the small undeveloped oogenic cells that will give 

 rise to ova of the succeeding breeding seasons. (Fig. 132.) The 

 gelatinous mass that surrounds the discharged eggs of amphibians 

 is added by the oviducts as the eggs pass outward. 



Fig. 132.— Photograph of a section of an ovary of the frog. The ovarian tissue 

 is composed of several sacs, each containing a number of immature ova supported 

 in a delicate connective tissue. 



Reptiles.— The ovary of a reptile during breeding season is com- 

 posed of a number of eggs of various sizes. In the lizard, for example, 

 the o\-aries are not sacculated, as in the case of the frog, and the 

 germinal center is quite compact and more easily disco\'ered. 

 (Fig. 133.) In it are developing oocytes and a series of develop- 

 mental stages continuing into an adjacent string of ova of increasing 

 size. At first each ovum is surrounded by a single layer of nurse 

 cells, but these cells become more numerous and stratified as the 

 egg increases in size. The increase in egg size is due to the increas- 

 ing amount of yolk supphed to the ovum by the surrounding nurse 

 cells. The size of the eggs, therefore, indicates the relati\e age, the 

 largest being the most mature, the smallest the least mature. A 

 theca of vascular coimective tissue surrounds the follicle cells. 

 When the elaboration of yolk is com])letcd, n rupture occurs in 



