526 



PISCES FISHES. 



Excretory and reproductive systems. - - The dark red 

 kidneys lie far back on each side of the vertebral column. 

 They are developed from the hind part of the mesonephros. 

 Several tubes from each kidney combine to form a ureter. 

 The two ureters of the male open into the urogenital 

 sinus, whence the waste products pass out by the cloaca ; 

 in the female they open into little bladders, the dilated 



ends of the Wolffian 

 ducts, and thence by 

 a common aperture 

 into the cloaca. 



The segmental duct 

 of each side divides 

 into Wolffian and Miil- 

 lerian ducts. The 

 Wolffian duct becomes 

 in the male the vas 

 deferens, in the female 

 it is an unimportant 

 Wolffian duct ; the 

 Miillerian duct be- 

 comes in the female 

 the oviduct, in the 

 male it is a mere rudi- 

 ment. 



The muscles and 

 other organs of Elas- 

 mobranchs retain con- 

 siderable quantities of 

 nitrogenous waste pro- 

 ducts. 



-OV. 



FIG. 254. Urogenital organs of female 

 skate. In part after Monro. 



., Aperture of united oviducts ; W.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. t 

 kidney ; arrow from base of oviduct into cloaca. 



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 replaced by openings (nephrostomes) into the kidney, 

 sionally there are both nephrostomes and abdominal pores. 



Occa- 



The male organs or testes lie on each side of the cardinal 

 sinus, moored by a fold of peritoneum. Spermatozoa pass 

 from the testis by vasa efferentia into a tube surrounded 

 anteriorly by epididymis. The tube of the epididymis is 



