KIDNEYS OF FISHES. 



535 



firmest at the fore-part of the gland ; usually of a reddish-brown 

 colour ; sometimes soaked, as it were, with dark pigment. 1 It is 

 supplied by numerous small arteries from the abdominal aorta, 2 

 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, given 

 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 

 whole renal substance, which 

 shoAvs no distinction of cortical 

 and medullary parts, and has 

 neither ' pelvis ' nor ( mammil- 

 la} : ' 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 surface 

 of their posterior ends when these 

 have coalesced : in some fishes the 



in .1. The anterior extremity of the kidney, Bdcllo- 



ureters unite together alter quit- stoma. xxi. 2. Man-i^hum body ana its bioud- 



, . .. , . , vessels, Bdellostoma. XXI. 



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 

 the 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 5 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 very 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, b, sometimes 



1 As in Lepidosiren, xxxm. p. 349. 2 Hunter, vn. vol. ii. p. 112. 



