THE URO-GENITAL SYSTEM 387 



Upon the inner side of each mesonephros appears a longitudi- 

 nal fold of its peritoneal investment, along the free edge of 

 which the cells become proliferated and form the germ gland ; 

 the remaining, or basal portion of this fold is later to form 

 the mesorchium or mesovarium, the suspensory ligament of 

 the mature testis or ovary respectively. The Wolffian (meso- 

 nephrotic) duct lies along the free edge of the mesonephros, 

 and not far from this is Muller's duct, suspended in a fold 

 which projects from the ventral surface of the mesonephros. 

 These two pairs of ducts are brought together at their distal 

 ends and form a common chamber, into which all four empty, 

 the uro-genital sinus. 



From this stage the conditions found in the female are 

 readily developed. [Plate III, c.] Its most important organs 

 are the germ gland, which becomes the ovary, and Muller's 

 duct, the upper part of which becomes the oviduct [uterine 

 (Fallopian) tube], and the lower part, the uterus. The en- 

 tire mesonephrotic system, since it is in no wise concerned in 

 the reproductive function and since the urinary function is 

 wholly assumed by the metanephrotic system, disappears ex- 

 cept for a few useless vestiges; its loss allows the mesone- 

 phrotic ligament to become continuous with that of Muller's 

 duct, and thus to extend as the broad ligament of oviduct and 

 uterus from the dorsal body wall to the latter organs. The 

 round ligament is formed from the posterior extension of this 

 latter, the ligamentum inguinale. 



Muller's duct gives rise to the oviduct, uterus and vagina, 

 which are thus seen to be nothing more than differentiations 

 of the various regions of a single tube. The ostium is much 

 nearer approximated to the ovary than in Sauropsida, and as 

 it opens and partly surrounds the latter during ovulation, the 

 entrance of the ova into the oviduct is practically assured. 

 In some mammals there is a special arrangement in the form 

 of a recess or pocket of peritoneum, the bursa ovarica, in which 

 the ovary lies, covered by the ostium, and in a few cases the 

 fusion of the edges of ostium and bursa convert the latter into 

 a capsule which may either open to the ccelom through a small 



