THE RESPIRATORY ORGANS OF AMPHIBIA. 163 



which opens into the cloaca, and does not receive the ureters. 

 The kidneys of the Amphibia appear, like those of fishes, to 

 be persistent Wolffian bodies. 



In the brain of the Amphibia the cerebellum is always 

 very small, and represented by a mere band; the cerebral 

 hemispheres are elongated, and contain ventricles. In Proteus 

 the mesencephalon is very indistinctly marked. The optic 

 nerves form a chiasma. 



As in fishes, the pneumogastric gives off a lateral nerve, 

 which runs along the sides of the body. 



The eyes are verj' small, and covered by the integument, 

 in Proteus, the Gymnophiona, and the genus Pipa. The . 

 perennibranchiate and derotreme Urodela have no eyelids ; 

 but most Satrachia have not only a well-developed upper 

 eyelid, but a nictitating membrane, moved by special muscles. 



All Amphibia possess a fenestra ovalis with a cartilagi- 

 nous, or osseous, columelliform stapes, the expanded proximal 

 end of which is fixed to the membrane of the fenestra. In 

 many Patrachia, if not in all, there is a fenestra rotunda, 

 though the presence of a distinct cochlea has not been ascer- 

 tained. The Zfrodela, the Oym,nophiona, and the Pelobatidea, 

 among the Batraohia, have no tympanic cavity, nor mem- 

 brane. In the other Batrachia there are tympanic cavities 

 communicating freely with the throat. Each is closed exter- 

 nally by a tympanic membrane, with which the outer extremity 

 of the stem of the stapes is connected. In the Afflossa, the 

 two tympanic cavities communicate with the mouth by a single 

 Eustachian aperture ; and the outer end of the stapes expands 

 into a great cartilaginous plate coextensive with the tympanic 

 membrane. 



The ducts of the reproductive organs of the Amphibia, 

 like those of the Ganoidei, always communicate directly with 

 the urinary ducts : and, as in most Ganoidei and all Elasmo- 

 hranchii, the proximal end of the oviduct is open, and com- 

 municates with the peritoneal cavity. The male has no penis, 

 unless a papillary elevation of the wall of the cloaca may rep- 

 resent such an organ. The testes of the male Amphibia are 

 composed of tubules, and vasa efferentia convey the contents 

 of these away. In the Urodela, the vasa efferentia of each 

 testis enter the inner side of the corresponding kidney, and 

 traverse it, leaving its outer side to enter a genito-urinary 

 duet, which lies on the outer side of the kidney, ends blindly 

 in front, and opens behind into the cloaca. The uriniferous 

 tubuli also pass directly from the outer margin of the kidneys 



