The word amphibian is generally interpreted as meaning “two-lives,” and as applied to the salamanders, toads, and frogs, we usually visualize these forms as living the first life in water, the second life on land. The first life is called the larval or tadpole stage and is ordinarily spent in the water. There the larva breathe mainly through gills; they are without legs in the first stages, and have a peculiarly flattened tail which propels them through the water. When these larva mature we expect them to lose their gills, grow some legs, and in the case of toads and frogs, to absorb their swimming tails.

These generalizations may be wholly acceptable, but when we study the amphibians more carefully we find that various forms have made short-cuts or have decided to shorten one or the other of their two lives, so as to enable them to survive in what would otherwise be an unfavorable environment..

The amphibians are divided into two groups, one possessing and retaining tails throughout their entire life (the tailed amphibians), and the second (the tailless amphibians) which are without this appendage in the adult stage. The salamanders belong to the former, the toads and frogs to the latter division.

Amphibians are usually distinguished from the reptiles by the fact that they have a moist skin which may be either slimy or warty, but in no case do they possess dry scales. For all general purposes this will serve to distinguish these two groups of vertebrates.

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