Vertehrata. 



349 



(Selachians), and in the Amphibia, branches arise from the urinary 

 tubules and run to the surface of the kidney to open there by 

 ciliated funnels (nephrostomes), so that they communicate 

 directly with the body-cavity. The urine escapes through the 

 ureters, which open either into the cloaca, or else by a single 

 orifice near the anus. For the urinary bladder see the 

 different groups. 



In Fish* and Amphibia, each kidney is connected with the 

 testis of the same side by fine transverse canals, so that the 

 spermatozoa can escape through the urinary tubules and ureters. 

 Usually the testis is only thus connected with the anterior and 

 often narrow end. At an early stage of development a pair of 

 embryonic kidneys is developed in Reptilia, Aves, and 

 Mammalia, and these for some time act as the excretory organs. 

 Later, however, they are replaced by another pair, quite independent 

 of the first, the adult kidneys, which are functional throughout 



Fig. 288. 



Fig. 289. 



Fig. 288. Testis, Kid- 

 ney, etc., of an Amphi- 

 bian, diagrammatic. c 

 cloaca, t testis, u anterior, 

 tt' posterior portion of 

 kidney, ug ureter, ug' ducts 

 of posterior portion of 

 kidney which open into the 

 hindmost portion of the 

 ureter. — Orig. 



Fig. 289. Testis, em- 

 bryonic kidney, etc. 

 of the embryo of a higher 

 Vertebrate ; diagrammatic, 

 c cloaca, t testis, u anterior 

 portion of embryonic kidney 

 (which forms the epididy- 

 mis), u' posterior portion 

 which atrophies, 'ug duct of 

 embryonic kidney (seminal 

 duct). — Orig. 



life. The embryonic kidneys and their ducts (Wolffian ducts) which 

 open into the cloaca, are lost in th^ female, whilst in the male the 

 testis becomes connected by fine tubules with the anterior portion of 

 the embryonic kidney, and this part persists throughout life as the 



* The aberrant conditions of the Teleostei are diaregarclecl here. See Pisces. 



