186 VERTEBRATE ZOOLOGY 



gill-clefts close, the skin changes its character, the tail-fin disappears, 

 and it emerges upon the land and lives a burrowing life. So exclu- 

 sively terrestrial does it become that it drowns if after metamorphosis 

 it is put in water for any length of time. Several other genera of 

 Apoda are viviparous, the embryos becoming several inches in length 

 before birth. 



The Apoda constitutes a very degenerate group. In some respects 

 they are more primitive than other living Amphibia, but Hfe in bur- 

 rows has caused a profoimd degeneration of structure. They are to 

 be included among the eel-hke type of senescent, degenerate forms. 



Order II. Urodela — (Tailed AMPmsiA) 



This order is represented by about 100 species of mud-puppies, 

 salamanders, newts, and efts. They range in habitat from forms Uv- 

 ing permanently in the water and breathing with external gills in ad- 

 dition to limgs, to forms that Uve after metamorphosis entirely on 

 land, favoring moist woods or other sheltered places. Some authors 

 group all forms with permanent external gills in a separate family, 

 Perennibranchiata; but this arrangement is beheved by the best author- 

 ities to be artificial in that the retention of the aquatic habit and lar- 

 val gills is probably due to arrested development and may have taken 

 place in more than one family. The classification given here is taken 

 from Gadow and is based on fimdamental anatomical characters. 



Family I. Amphiumidoe. — Without giUs in the definitive stage; 

 gill-clefts vestigial, consisting of one pair of small openings, or en- 

 tirely absent; maxillary bones present; teeth on both jaws; verte- 

 brae amphicoelous; both fore and hind Umbs present, but small; 

 small eyes without hds. 



The family is represented by two genera, Cryptobranchus and Am- 

 phiuma. Cryptobranchus allegheniensis (Fig. 109, A) occurs in the 

 mountain streams of our Eastern States. Another species, C. japon- 

 icus, is the giant salamander of Japan. There is only one species of 

 Amphiurm (Fig. 109, B), which is also an American species confined 

 to the southeastern States, from Carolina to Mississippi. 



Cryptobranchus allegheniensis, the "hellbender," is a comparatively 

 large salamander reaching a length of nearly two feet. Aii account 

 of the development of this species and certain excellent descriptions 

 of the larvae and the process of metamorphosis have been furnished 

 by B. G. Smith. The eggs are fertilized externally, males emitting 



