174 BATRACHIA. 



CLASS F. BATRACHIA. (THE BATRACHIANS.) 



Cold-blooded vertebrates, intermediate between the fishes and the 

 reptiles. They differ from the fishes chiefly in the absence of rayed 

 fins, the limbs being usually developed and functional with the 

 skeletal elements of the limbs of reptiles, and in the reduction or 

 absence of the various bones of the branchial, opercular and sus- 

 pensory systems. 



The Batrachians undergo a more or less complete metamorphosis ; 

 the young (" tadpoles ") being fish-like and more or less aquatic, 

 breathing by means of external gills. These differ from the gills 

 of fishes in standing on fleshy processes of the branchial bones and 

 not on the bones themselves. In the tadpole, the tail is provided 

 with a more or less distinct fin-like membrane, which usually dis- 

 appears with age. Later in life, lungs are developed, and in most 

 cases the gills disappear. Skin mostly naked and moist, used to 

 some extent as an organ of respiration. Heart with two auricles 

 and a single ventricle. 



Reproduction by means of eggs which are of comparatively 

 small size, without hard shell. These are deposited in water or in 

 damp places. In one salamander the young are born alive. Pro- 

 fessor Cope recognizes nine orders of Batrachians, four of these 

 being extinct. (ftaTpaxos, frog.) 



Orders of Batrachia. 



a. Body lengthened, with a distinct tail throughout life; hind limbs, if present, 



not especially enlarged. 



b. External gills and gill-clefts persistent throughout life, the gills 3 on 

 each side; no eyelids; vertebrae amphicoelian ; maxillary small or 

 wanting. 



c. Body eel-shaped, without hind legs; teeth on vomer; floor of mouth 

 rough; jaws with horny sheath. . . . TKACHYSTOMATA, XXIV. 

 cc. Body salamander-shaped, the hind limbs present; jaws with teeth. 



PROTEIDA, XXV. 



bb. External gills normally disappearing in adult life ; limbs 4 (or want- 

 ing, present in all our species); jaws with teeth; maxillaries and 



palatines present UKODELA, XXVI. 



aa. Body short, depressed; tail disappearing with age; limbs 4, the posterior 

 much enlarged SALIENTIA, XXVII. 



