x URINOGENITAL ORGANS 467 



aperture into the cloaca ; while in the male, four of 

 them on either side unite to form a wide main ureter 

 before communicating with a similar median sinus, 

 which, as it receives the products both of the spermaries 

 and kidneys, is called the urinogenital sinus (A, ug. s). 



The spermaries are a pair of soft, elongated organs, 

 suspended to the dorsal body-wall by delicate peritoneal 

 folds and invested by lymphoid tissue (see pp. 507 and 

 515) which unites them together posteriorly. From 

 the anterior end of each the delicate efferent ducts 

 referred to above pass to the epididymis to become 

 connected with the convoluted spermiduct. The latter 

 dilates posteriorly, where it underlies the functional 

 kidney, forming an elongated, spindle-shaped seminal 

 vesicle (s.v.), which opens (s.v') into the base of a thin- 

 walled, blind reservoir of about the same length, the 

 sperm-sac (sp. s) ; just to the inner side of its aperture 

 are the openings of the ureters (ur r ). The sperm-sac 

 is continuous posteriorly with the urinogenital sinus, the 

 opening of which into the cloaca is situated on a papilla. 



The female Scyllium has a single ovary (B, ov) sus- 

 pended by a fold of peritoneum, its fellow having become 

 aborted. In the adult it is studded all over with rounded 

 ova in different stages of development, varying in 

 diameter from 12-14 mm. downwards : in other Verte- 

 brates which produce large eggs, a similar reduction of 

 one ovary may take place (e.g., Birds). The paired 

 oviducts (ovd) are not coiled as in the frog ; they extend 

 along the whole length of the dorsal wall of the ccelome, 

 'below the kidneys, and anteriorly unite with one another 

 below the gullet and just in front of the liver, where 

 they communicate with the ccelome by a common 

 aperture (ovd') ; posteriorly they open together by a 

 single aperture (ovd") into the cloaca, behind the 

 rectum (r). About the anterior third of each oviduct is 



