Page:Natural History, Reptiles.djvu/271

Rh

In this Order the body is lengthened, slender, and lizard-like, with four well-formed limbs, furnished with toes, and a long tail, which remains through life. The ribs are very short, the vertebræ or joints of the spine numerous and moveable. The tympanum, or membrane of the ear, is concealed beneath the skin. Respiration in the earlier stages of existence is aquatic, the necessary oxygen being separated from the water by external gills, as in the tadpoles of the Anoura; in the adult or perfect condition it is aërial, and performed by means of cellular lungs. Both jaws are furnished with minute teeth, and there are two longitudinal rows of equal teeth on the palate, attached to the bone. The head is much flattened.

The Urodela undergo a metamorphosis similar to that of the Anoura; the young animal is a tadpole of similar form, inhabiting the water; and this is the case no less with those species that are terrestrial in their perfect state, than with those that are permanently aquatic. In the metamorphosis, the fore limbs are first developed, an order contrary to that which prevails in the Frogs.

The power of reproducing certain parts of the body which have been injured or removed