OOGENESIS IN THE WHITE MOUSE 271 



study of the origin and development of the rete ovarii in the 

 mouse, reserving it for a possible future work. The suggestion 

 is ventured that it apparently arises by ingrowths from the 

 mesonephros. The rete is found as a constant structure in the 

 adult ovary. 



An interesting feature of the ovary of the mouse is the marked 

 development of a peritoneal fold, forming a more or less complete 

 covering or capsule for the organ (figs. 8, 9, 10, 12, 13). Huber 

 ('15) mentions, but does not describe, a similar 'periovarian 

 capsule' or 'bursa ovarica' in the rat. Van Beneden ('80) 

 described in the bat a periovarian capsule which he said was 

 closed, with no communication with the peritoneal cavity. 

 Sobotta ('95) found in the mouse a connective tissue capsule 

 which completely surrounds the ovary. He states that the 

 space between capsule and ovary is filled with a clear ser- 

 ous liquor and that during heat the capsule becomes enlarged. 

 Similar structures have been described for other mammals 

 (Schmaltz, '11). 



My material shows that this membrane arises as a fold of the 

 peritoneum which grows over and encloses the ovary. The 

 oviduct is in the fold as it develops, so that when the capsule is 

 completely formed (embryo of 23 mm. length) the fimbriated 

 end is inside, opening toward the ovary. This capsule is a 

 delicate membrane made up of two layers of peritoneal epithe- 

 lium between which is a small amount of connective tissue in 

 which a few small blood vessels run. This was found to be 

 apparently a complete capsule in rather more than half the cases 

 examined ; in the others there was an opening into the peritoneal 

 cavity close to the hilum of the ovary, near where the oviduct 

 penetrates the capsule. 



OOGENESIS 



As has been described above, there are in the ovary of the 

 mouse, two proliferations of cells from the germinal epithelium, 

 one during embryonic and foetal life, and the second extending 

 from birth, or a day or so after, nearly to sexual maturity. The 

 second proliferation constitutes oogenesis proper; but it is 



