44 THE COMMON FROG. [chap. 



and the same is the case with AmpJiiitma. Thus in 

 these animals the metamorphosis is less complete. 



In the subterranean caverns of Southern Austria 

 (Carniola and Istria) is found the Proteus. This is an 

 elongated Urodele, with slender limbs, and but two 

 toes to each hind foot. Passing its whole life in 

 perpetual darkness, it is blind and colourless, except 

 the external gills, which are red. This animal retains 

 during the whole of life not only the gill-aperture on 

 each side, but also the external plumose gills which are 

 transitory in the Anoura and in all the Urodela 

 hitherto mentioned. Here then we first meet with an 

 animal which may be said to be a permanent and 

 persistent Tadpole, yet rather like an Eft-tadpole than 

 like that of the Frog (fig. i8). 



A North American Urodele, misnamed (for it is 

 silent enough) Siren, also presents us with permanent 

 external gills, and it offers another interesting resem- 

 blance to the tadpole of the Frog, in that it is furnished 

 throughout life with a horny beak. It has also 

 another remarkable character in which it stands alone 

 in its class. Hitherto every relative of the Frog has 

 had, like it, four limbs in the adult condition. In the 

 Siren, however, we for the first time make acquaintance 

 with a creature belonging to the class (though not to 

 the order) of Frogs and Toads, which is devoid alto- 

 gether of hinder (or pelvic) limbs, being in this respect 

 like the whales and porpoises amongst beasts, and 

 like the little lizard, Chirores^ amongst reptiles. 



Another North American Urodele, MeiiobrancJms, 

 possesses throughout the whole of life both gill- 

 openings and external gills. But it is furnished with 



