chap, vii.] URETERS AND BLADDERS. 263 



female, and undergoes more or less degeneration in 

 the male), and the Wolffiaii duct, which remains 

 connected with the mesonephros, and carries away its 

 products and those of the testes in the male. The 

 ureter, like the collecting ducts of the inetanephros, 

 becomes developed from part of the Wolffian duct, 

 which, when this ureter is 'present, only carries away 

 the secretion of the testes. 



In the Cyclostomata, the ducts that have the 

 functions of ureters open to the exterior by a papilla 

 (the urinogenital papilla), which is placed .behind the 

 anus ; they first, however, open into a cloaca, into 

 which also the generative products make their way by 

 the abdominal pores. Among the Ichthyopsida 

 the renal and generative products ordinarily pass into 

 a cloaca, which is common to them and to the rectal 

 orifice of the intestine ; but in the Teleostei the 

 genito-urmary is distinct from and posterior to the 

 rectal, and the urinary pore is, as a rule, separate 

 from and behind the genital. The terminal portion 

 of the ureteric ducts of fishes is often enlarged, to 

 form a so-called bladder ; this, however, must not be 

 regarded as the homologue of that of Amphibians, 

 or of the Amniota, where the bladder is an out- 

 growth of the ventral wall of the cloaca. In the 

 Amphibia and in some Reptilia this bladder retains 

 its primitive position, or, in other words, does not 

 become part of the direct line of passage between the 

 kidneys and the exterior ; in the Ophidia, Crocodilia, 

 and Aves, the bladder is atrophied. 



It is in the Mammalia only that the bladder is 

 found on the direct line of passage between the ure- 

 ters and the exterior, and is not so found in the lowest 

 division or Prototheria, where rather it occupies 

 the same position as in the frog ; in the Metatheria 

 the ureteric ducts open into the base of the bladder ; 

 in the Eiitheria they open at various points along its 



