METAMORPHOSIS OF BATRACHIANS. 477 
size. The next important change is the growth of the front 
Jegs and the partial disappearance of the tail ((’), while very 
small toads (D and #), 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 (7ri- 
ton) the gills are in three pairs, larger and 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. 
Fig. 484.—Metamorphosis of the Toad.—After Owen ; from Tenney’s Zoology. 
In certain Batrachians as the Alpine salamander, the Su- 
rinam toad (Pipa) and the Hylodes 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 larve 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 
Amblystoma mavortium breeds at an altitude of about 8000 
feet in the Rocky Mountains. Rana septentrionalis Baird 
extends to Okak, Northern Labrador, where the climate is as 
extreme as that of Southern Greenland ; frogs have also been 
