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In the adult or perfect condition, the form of these animals differs much from that common to the Amphibia, the body being short, broad, and flattened horizontally, and destitute of every vestige of a tail. There are four limbs, well developed, and furnished with toes, five on each foot, but the thumb of the fore foot is a mere tubercle; the posterior limbs are longer than the others, and are formed for leaping. The ribs are totally wanting; the vertebræ or joints of the spine are few and soldered together. The tympanum or drum of the ear is exposed.

In the tadpole condition, the form is fish-like, the body being lengthened, compressed, and terminating in a long thin tail; there are no limbs, these being developed in the process of metamorphosis; the water is the medium which the animal in this its infancy inhabits, in which it swims with ease, by the lateral undulation of its oar-like tail. Respiration is performed by gills or branchiæ alone, which project on each side of the neck in the form of little tufts. As the period of the change approaches, these are gradually withdrawn into the chest, and the animal becomes an air-breathing Frog or Toad, more or less terrestrial in its habits.

The eggs are enveloped in a clear and tenacious jelly, and are laid either in long strings, or in