THE REPRODITCTIVE ORGANS OF AMPHIBIA. 189 



In the brain of tlie Amphibia tlie cerebellum is always 

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

 Jiemispberes are elongated, and contain ventricles. In 

 Proteus the mesencephalon is very indistinctly marked. 

 The optic nei-ves form a chiasma. 



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

 which runs along the sides of the body. 



The eyes are very small, and covered by the integument, 

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

 pereunibranchiate and derotreme Urodela have no eyelids ; 

 but most Batrachia have not only a well- developed upper 

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



Al\Amp>]iihia possess a fenestra ovalis with a cartilaginous, 

 or osseous, columeUlform stapes, the expanded proximal 

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

 many Batrachia, if not in aU, there is a fenestra rotunda, 

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

 certained. The Urodela, the GymnopMona, and the Peloba- 

 tidea, among the Batrachia, have no tympanic ca^dty, nor 

 membrane. In the other Batrachia there are tympanic 

 cavities communicating freely with the throat. Bach is 

 closed externally by a tympanic membrane, with which the 

 outer extremity of the stem of the stapes is connected. 

 In the Acjlossa, the two tympanic cavities communicate 

 with the mouth by a single Eustachian aj^erture ; 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 JSlasmo- 

 branchii,the proximal end of the oviduct is open, and commu- 

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

 unless a papillary elevation of the wall of the cloaca may 

 represent such an organ. The testes of the male Amphibia 

 are composed of tubules, and vasa efferentia convey the con- 

 tents 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- 



