330 



ZOOLOGY. 



(tetards), and are formed for an aquatic life: at birth they have 

 a tail, but no feet; gills projecting externally (b b, Fig. 293), 

 and their skeleton is cartilaginous. 



Fig. 292,-Crapaud (the Toad). 



These projecting gills or branchiae in some continue through- 

 out life, as in the proteus, axolotl (Fig. 294), and siren. 



Fig. 294. Axolotl. 



But in most batrachia these branchiae 

 soon wither away and disappear, al- 

 though the aquatic life ontinucs. tor 

 the tadpole has internal branchiit . like 

 tishrs, as well as external (Fig. 'J'.'")): 

 these fixed or internal branchiae in the 



Fi g .293.-Tad P oleoftheFrog. Jadpok- ar, attached under th, neck 

 to cartilaginous arches belonging to 

 the hyoid bones, and are protected by the skin ; the water 



