METAMORPHOSIS OF BATRACHIANS. 



477 



vSize. The next important change is the growth of the front 

 legs and the partial disappearance of the tail (0), while very 

 small toads (D and E), during midsummer, may be found on 

 the edges of the pools in which some of the nearly tailless tad- 

 poles may be seen swimming about. It is three years before 

 the Amphibia are capable of breeding. In the newts (Tri- 

 ton) the gills are in three pairs, larger ard more complex 

 than in the frog ; the fore limbs are the first to grow out, 

 and the gills persist long after the hind limbs are developed. 

 In the newts we have the larval state of the toads and frogs 

 persistent ; thus the successive steps in the development of 

 the individual frog is an epitome of the evolution of the 

 typical forms of the class to which it belongs. 



Pig. 434. Metamorphosis of the Toad. After Owen ; from Tenney's Zoology. 



In certain Batrachians as the Alpine salamander, the Su- 

 rinam toad (Pipa) and' the Hy lodes of Guadaloupe in the 

 West Indies, the metamorphosis is suppressed, development 

 being direct ; though the young have gills, they do not lead 

 an aquatic life. In the axolotl there is a premature devel- 

 opment of the reproductive organs, the larvae as well as the 

 adults laying fertile eggs. 



The Batrachians are inhabitants of the warmer and tem- 

 perate zones. Frogs extend into the arctic circle. The 

 AmUystoma mavortium breeds at an altitude of about 8000 

 feet in the Eocky Mountains. Rana septentrionalis Baird 

 extends to Okak, Northern Labrador, where the climate is as 

 extreme as that of Southern Greenland ; frogs have also been 



