UROGENITAL ORGANS 373 



When the Wolffian body degenerates the fold becomes the broad 

 ligament while another fold continues down the Miillerian duct as the 

 ligament of the ovary. In some mammals the ovaries have, in addi- 

 tion, a special fold of the peritoneum, which in the rats and mice 

 encloses the ovary, the ostium tubae connected with its opening. 



The testes are relatively small and are shaped much Uke the 

 ovaries and at first they are at about the same level. The outer 

 surface is smooth, a fibrous envelope, the tunica albuginea, having 

 developed around them, which sends trabeculae inward, dividing the 

 seminiferous tubules into lobules. Except in the monotremes (fig. 

 396) the testes descend farther into the pelvic cavity, remaining per- 

 manently in the pelvis in many insectivores, some edentates, ele- 

 phants, whales and Hyrax. In other groups they pass outside the 

 pelvic cavity to be enclosed in a special sac, the scrotum. The testes 



Fig. 397. — Schematic representation of the descent of the testis, after O. Hertwig. 

 c, abdominal coelom; m, transverse abdominal muscle, p, peritoneum; s, scrotum; sc, 

 ccelom of scrotum; ;, testis; v, vas deferens. 



are supported by a cord, the gubemaculum, the homologue of both 

 ligaments of the ovary. 



The change in position of ovary and testis is accomplished in part by 

 the unequal growth of body wall and the supporting ligaments. In the case 

 of the male this descent of the testis is complicated. In outline it is as follows; 

 By the unequal growth of gubernaculum and body wall the testes are drawn 

 down into the scrotum which is a protruding part of the body wall into which a 

 part of the ccelom extends (fig. 397). This wall is formed in part from the 

 genital folds (see copulatory organs, below) which surround the genital eminence. 

 It lies in front of the penis in the marsupials, behind it in all placental mammals. 

 When the canal connecting the cavity of the scrotum (bursa inguinalis) remains 

 open (fig. 397, B) as it does in marsupials, bats, rodents, insectivores, etc., the 

 descent is temporary, the testes being withdrawn into the peritoneal cavity 

 at the dose of the breeding season by the cremaster muscle, developed from the 

 transverse abdominal muscle. In other mammals the descent is permanent, 

 though sometimes it does not occur until the time of sexual maturity. 



Two regions are differentiated in the MUllerian ducts of the female 



