Beniiet Mills Allen 109 



nieinbrana propria by a cylindrical condensation of cytoplasm, fre- 

 quently so short that the nucleus appears to rest directly upon the 

 membrana propria. The axial portion of the tubule is occupied by a 

 loose network of protoplasm. At no time do these germinative cells 

 have definite boundaries. 



There are at this stage no transition forms between the germin- 

 ative cells and primitive sex cells. 



IS cm. Embryo. Female. — This stage shoAvs some interesting 

 points in the development of the intra-ovarian portion of the rete tis- 

 sue. Lying in the mesentery at the hilum, it extends but a short dis- 

 tance into the ovary, not reaching the inner ends of the adjoining 

 cords of Pfliiger. In this intra-ovarian portion of the rete, the oogonia 

 have in some cases developed so far as to be surrounded by well-de- 

 fmed follicles (Plate VI, Fig. 20). These young follicles have but a 

 single layer of granulosa cells and are exactly like the follicles formed 

 in the inner portions of the cortex, at this stage. With these rete 

 follicles are found sex cells in all stages of development, likewise re- 

 sembling corresponding sex cells in the cords of Pfliiger. The re- 

 semblance is made more complete by the fact that the sex cells of the 

 rete are undergoing the same process of degeneration as are corres- 

 ponding sex cells in the cords of Pfliiger. 



The portion of the rete lying in the mesonephros has become dis- 

 tinctly separated from the intra-ovarian portion just described. Most 

 noteworthy, however, is the fact that the few primitive sex cells found 

 in it have not developed beyond the original condition which they ex- 

 hibited in the early stages of development. 



Few of the open tubes of Pfliiger exist as such at this stage, most 

 of them having become transformed into solid cords of cells such as 

 characterize the cortex as a whole. 



20 cm. Emhryo. Female. — A careful study of the inner ends of 

 the cords of Pfliiger shows that many of the oocytes of the young 

 primitive follicle! have disappeared as a result of the process of de- 

 generation already described. The granulosa cells are apparently not 

 affected, but persist in solid elongated clumps, similar to the remains 

 of the medullary cords found scattered through the axial portion of the 

 ovary. 



All the primitive sex cells and oocytes of the rete tissue have disap- 

 peared, leaving only the granulosa cells and their homologues. 



25 cm. Emhryo. Female. — At this stage the surface of the ovary 

 is found to have become wrinkled and irregular. The cords of Pfliiger 

 form a thick, dense, cortical layer, within which is the medullary por- 



