ORDERS OF AMPHIBIA. 385 



and they have short ribs attached to the transverse processes. 

 The bones of the fore-arm (radius and ulna) on the one hand, 

 and those of the shank (tibia and fibula) on the other, are not 

 anchylosed to form single bones. 



In one section of the order formerly called Amphipneusta 

 the gills are retained throughout life, and the animal is there- 

 fore " perennibranchiate." In this section are the Proteus, 

 Siren, and Menobranchus. In the remaining members of the 

 order the gills disappear at maturity, and the animal is there- 

 fore " caducibranchiate." In this section are the land and 

 water salamanders. One form, however the Axolotl of 

 Mexico appears to be sometimes caducibranchiate, though 

 generally perennibranchiate. The genera Amphiuma and Meno- 

 poma, also, exhibit a partially intermediate state of parts, for 

 though they lose their branchiae when adult, they nevertheless 

 retain the branchial apertures behind the head. 



Fig. 147. Head and fore-part of the body of Proteus anguinus, showing the 

 external branchiae and tridactylous fore-limb. 



Of the perennibranchiate Urodela, one of the best known is 

 the singular Proteus (Hypochthori) anguinus (fig. 147), which 

 is only found inhabiting pools in certain caves in Illyria and 

 Dalmatia. It is of a pale flesh-colour, or nearly white, with 

 three pairs of scarlet branchiae on each side of the neck. It 

 attains a length of nearly a foot, and has two pairs of weak 

 limbs, of which the anterior have three toes, and the posterior 

 only two. From its habitat, the power of vision must be quite 

 unnecessary, and, as a matter of fact, the eyes are altogether 

 rudimentary. Several varieties of Proteus are known, and the 

 one figured above has been described as a distinct species (P. 

 zanthostictus). 



Of the Sirenidce, the most familiar are the Siren itself and the 

 Axolotl. The Siren, or Mud-eel, is found abundantly in the 

 rice-swamps of South Carolina, and attains a length of three 

 feet. The branchiae are persistent, and the hinder pair of legs 

 wholly wanting. Two other species are known, but they are 

 likewise confined to North America. 



The Axolotl (Siredon pisciforme, fig. 148) is a native of the 



VOL. II. 2 B 



