KIDNEYS or FISHES. 



535 



firmest at tlie fore-part of the gland ; visually of a reddisli-brown 

 colour; sometimes soaked, as it were, with dark pigment' It is 

 supplied by numerous small arteries from the abdominal aorta,^ 

 which form Malpighian corpuscles ; but these are fewer in 

 number and less complex than in the true kidneys of higher 

 Vertebrates. The primary branches of the tubuli uriniferi, gi^'cn 

 off from the long ureter, are extremely numerous ; their divisions 

 in the renal substance are comparatively few ; they are in most 

 fishes convoluted and of equal 

 diameter, extending through the 

 wliole renal substance, which 

 shows no distinction of cortical 

 and medullary jiarts, and has 

 neither ' pelvis ' nor ' mammil- 

 Ire : ' they are lined by a ciliated 

 epithelium. Sometimes a single 

 common ureter quits the coa- 

 lesced hinder ends of the kid- 

 neys, as in the Pike, and termi- 

 nates in a urinary bladder. More 

 frequently the essentially duplex 

 nature of the kidneys is mani- 

 fested by the emergence of two 

 ureters from the ventral surflice 

 of their posterior ends when these 

 have coalesced : in some fishes the 

 ureters unite together after quit- 

 ting the kidneys, and terminate by 

 a common gradually widening canal in the urinary bladder ; some- 

 times they enter the urinary bladder separately, as in the Wolf- 

 fish, where they both terminate on its left side, half an inch above 

 tlie cervix: rarely are any smaller accessory ureters seen, as e.g. 

 in the Stickleback, to terminate also, separately, in the bladder. 

 This, in aquatic animals apparently needless, receptacle of a fluid 

 excretion is, nevertheless, rarely absent in Osseous Fishes ; the 

 Pilchard, the Herring, and the Loach are among the few instances 

 where it is not developed. In the Loach a vei-y short, in the 

 Herring a long, common ureter terminates behind the anus. In 

 the Gymnotus the common ureter is so wide as to serve as a 

 receptacle, and it is directed forward to reach its termination 

 immediately behind the advanced vent. 



The urinary bladder is sometimes round, fig. 379, h, sometimes 

 ' As in Lepidosiren, xxxiii. p. 349. ^ Hunter, vii. vol. ii. p. 112. 



1. The anterior extremity of the kiiliiey, 

 /.");m. XXI. 2, Malpighian body and its 

 csscls, BdeUostviua. xxi. 



Bih-no- 

 bluud- 



