XIIT 



PHYLUM CHOPvDATA 



215 



Urinogenital Organs. — The lidncys (Fig. 865, hd., and Fig. 

 8GiJ, Ji) are of great size, extending the wliole length of tlic dorsal 

 wall of the abdomen, above the air-bladder, and partly fused 

 together in the middle line. They arc derived from the meso- 

 nephros of the embryo. Their anterior ends (Fig. 865, led, Fig. 

 869, li) are much dilated ;nid consist in the adult of lymphatic 

 tissue, thus ceasing to discharge a renal function. The ureters 

 (mesonephric ducts, nr.) unite into a single tube, which is dilated 

 to form a urinary Uaddcr (Fig, 865, 

 u. LI., Fig. 869, v.), and discharges into 

 the urinogenital sinus. 



The gonads arc of great size in the 

 sexually mature fish. The testes (Fig. 



p.s.c 



ot.1 



Fio. S6S.— Salmo fario 



from the inner side 

 separately below. a. 



The right aiiditory organ, 

 the otolith? arc shown 

 .5. c. anterior semicircular 

 canal ; and. nv. aaditor3- nerve ; h. s. c. horizontal 

 canal ; ot. 1 — 3, otoliths ; p. s. c. ijosterior canal ; 

 sac. sacculus ; \i,t. utriciihis. 



Fio. 809.— Salmo fario. The kidneys 

 and; adjacent parts. il, ijrecaval 

 vein; if (to the right) kidney; R{to 

 the left), degenerate anterior portion 

 of kidney ; rr, efferent renal vein ; 

 .V. subclavian vein ; v,, ur, ureter ; v, 

 bladder. (From Gegenbaur's Coni- 

 parative Anatomy.) 



865, ts.) are long, smooth, pinkish, paired organs, extending the 

 whole length of the abdominal cavity ; each is continued pos- 

 teriorly into a duct (r. df.) which opens into the urinogenital 

 sinus, and the homology of wdiich with the ducts of the primitive 

 nepliridial system is still uncertain. The ovaries are also of 

 the full length of the abdominal cavity and are much wider 

 than the testes : they are covered with peritoneum on their 

 inner or mesial faces only, and the numerous ova, which are about 

 4 mm. in diameter, are discharged when ripe from their outer 

 faces into the coelome. There are no oviducts, but the anterior 

 wall of the urinogenital sinus is pierced by a pair of genital pores 



o 2 



