DEVELOPMENT OF REPRODUCTIVE SYSTEM 797 



are associated with an ingrowth of cells from the ovarian septa into 

 the albuginean tunic. 



(2) The primitive cortex transforms into a thick secondary cortex, con- 

 taining many oocytes, some of which are surrounded by epithehal 

 cells. The complex of an oocyte enclosed by epithelial cells forms a 

 primitive egg follicle, which in mammals is called a primary Graafian 

 follicle. The complete development of the Graafian follicle, however, 

 does not occur until sexual maturity, although earlier stages may be 

 produced previous to this period. 



(3) A secondary medulla is formed containing a connective tissue net- 

 work, enclosing blood vessels. From these blood vessels branches extend 

 into the cortex. Some genitaloid cells may be found in the medulla. 



(4) The rete blastema remains as a compact mass of cells, sharply de- 

 limited from surrounding cells. It comes to lie in the area between 

 the ovary and the mesovarium, and forms the rete ovarii. 



The development of the human ovary differs somewhat from the account 

 given above in that active proliferation of cortical cords from the germinal 

 epithelium is problematical. The proliferation of cells in the developing human 

 ovary appears more gradual, and the egg cords of the primary cortex are 

 developed in a gradual manner from cells lying below the germinal epithelium 

 of the undifferentiated gonad (Felix, '12, p. 904). 



b. Chick 



The pattern of ovarian development in the chick follows that of the mammal, 

 and a cortex and a medulla are established. One clear distinction in the ovarian 

 development in the chick compared with that in the mammal occurs, however, 

 for the right sex-gland rudiment remains vestigial in the chick while the left 

 rudiment develops rapidly into the ovary. Thus it is, that sex differences can 

 be distinguished in developing chicks by macroscopic examination of the sex 

 glands during the latter part of the second week of incubation. The enlarged 

 appearance of the left ovary in the female chick becomes noticeable at 

 this time. 



c. Frog 



The developing ovary in the frog differs primarily from the developing 

 testis in two ways: 



( 1 ) The germ cells and accompanying epithelial cells remain peripherally 

 near the germinal epithelium, where they multiply and increase in 

 number; some of them enlarge during the formative stages of the 

 oocyte. 



(2) The mesonephric rete cords, which in the testis are much thickened, 

 appear slender in the developing ovary and fuse to form the lining 



