EXCRETORY AND REPRODUCTIVE SYSTEMS. 497 



ap. 



The segmental duct of each side divides into Wolffian 

 and Miillerian ducts. The Wolffian duct becomes in the 

 male the vas deferens, in the female it is an unimportant 

 Wolffian duct ; the Miillerian duct becomes in the female 

 the oviduct, in the male it is a mere rudiment. 



The muscles and other organs of Elasmobranchs retain 

 considerable quantities 

 of nitrogenous waste 

 products. 



There can be no doubt 

 that the body-cavity helps 

 in excretion, and gets rid 

 of waste through the two 

 abdominal pores. In some 

 Elasmobranchs these are re- 

 placed by openings (nephro- 

 stomes) into the kidney. 

 Occasionally there are both 

 nephrostomes and abdo- 

 minal pores. 



The male organs or 

 testes lie on each side 

 of the cardinal sinus, 

 moored by a fold of 

 peritoneum. Sperma- 

 tozoa pass from the 

 testis by vasa efferentia 

 into a tube surrounded 

 anteriorly by epididy- 

 mis. The tube of the 

 epididymis is continued 

 into the vas deferens, 

 which is dilated pos- 

 teriorly into a seminal 



vesicle and an adjacent sperm-sac. Finally, the two vasa 

 deferentia open into the urogenital sinus, whence the 

 spermatozoa pass into the cloaca. Thence, in copulation, 

 they pass into the complex " claspers " of the male, which 

 are said to be inserted into the cloaca of the female. 



The female organs or ovaries lie on each side of the car- 

 dinal sinus, moored by a fold of peritoneum. In young 

 skates they are like the young testes, but in the adults they 



32 



Fig. 



212. — Urogenital organs of female 

 skate. — In part after Monro. 



a-p., Aperture of united oviducts ; 1V.D., Wolffian 

 duct ; ov., ovary ; O.D.G., oviducal gland ; 

 .£., egg in mermaid's purse; Bl., bladder at 

 base of Wolffian ducts (arrow into cloaca) ; K. y 

 kidney ; arrow from base of oviduct into cloaca. 



