ORDER I. _Urodela._ Amphibia having usually poorly developed
appendages. Tail persistent through life. Examples: mud puppy, newt,
salamander.
ORDER II. _Anura._ Tailless Amphibia, which undergo a metamorphosis,
breathing by gills in larval state, by lungs in adult state.
Examples: toad and frog.
Characteristics of Reptilia.--These animals are characterized by having
scales developed from the skin. In the turtle they have become bony and are
connected with the internal skeleton. Reptiles always breathe by means of
lungs, differing in this respect from the amphibians. They show their
distant relationship to birds in that their large eggs are incased in a
leathery, limy shell.
[Illustration: Box tortoise, a land reptile. (From photograph loaned by the
American Museum of Natural History.) About one fourth natural size.]
[Illustration: The gila monster, a poisonous lizard. About one twelfth
natural size.]