AMPHIBIA. 



227 



FIG. HI- o> SipJionops annulatus, one of tho Caecilians, much reduced ; & Head of the 

 same ; c Mouth, showing the tongue, teeth, and internal openings of the nostrils ; d 

 Tail of the same. (After Dumeril and Bibron.) 



ORDER II. URODELA or ICHTHYOMORPHA (Gr. ichthus, a 

 fish, and morphe, shape). In this order are a number of fish- 

 like Amphibians, of which the Newts and Land-salamanders 

 are the most familiar examples. In all the members of this 

 section, the skin is naked, and never develops any hard struct- 

 ures, and in all there is a well-developed, fish-like tail, which 

 is retained throughout life. The vertebras are sometimes hol- 

 low at both ends (amphiccelous), sometimes hollow behind 

 and convex or rounded in front (opisthocoelous). The ribs are 

 rudimentary and the bones of the forearm (radius and ulna\ 

 and of the shank (tibia and^frw/a), are separate, and are not 

 combined so as to form single bones. 



The Ichthyomorpha are not unfrequently spoken of as the 

 "Tailed" Amphibians (Urodeld), and they fall into two natu- 

 ral sections, according as the gills are permanently retained 

 throughout life, or are cast off before maturity is attained. 

 The animals belonging to the first section are often called 

 " perennibranchiate," while those belonging to the second are 

 said to be " caducibranchiate." 



Among the Perennibranchiate forms, in which the gills are 

 permanently retained after the lungs make their appearance, 

 the best-known examples are Axolotl (Fig. 112), the curious 

 Proteus anguinus, and the Mud-eel (Siren). The Axolotls 



