Warm and temperate regions with abundant moisture are the localities favourable to all the Batrachians. Extreme cold, as well as dry heat, and all sudden changes are alike unfavourable to them. In temperate climates, where the winters are severe, they bury themselves under the earth, or in the mud at the bottom of pools and ponds, and there pass the season without air or food, till returning spring calls them forth. The species of this family are very numerous. MM. Duméril and Bibron state that the Frogs, _Rana_, number fifty-one species; the Tree Frogs, _Hyla_, sixty-four; and the Toads, _Bufo_, thirty-five. They are found in all parts of the world, the smallest portion being found in Europe, and the largest in America. Oceania is chiefly supplied with the Tree Frogs. There are several curious forms in Australia, and one species only is known to inhabit New Zealand. The enormous fossil _Labyrinthodon_, of a remote geological era, is believed to have been nearly related to these comparatively very diminutive Batrachians.[10] [10] In Dr. Günther's Catalogue of the _Batrachia Salientia_ (as Dr. Gray terms them) in the collection of the British Museum, published in 1858, and which includes all the ascertained species up to the time of publication, as many as 282 are enumerated, which are arranged under twenty-five groups holding the rank of families.--ED. TAILED BATRACHIANS, Sometimes called Urodeles, from +oura+, "tail," +dêlos+, "manifest." The constant external character which distinguishes these Amphibians in a general manner is the presence of a tail during the whole stage of their existence. Nevertheless they are subject to the metamorphoses to which all the Amphibians submit. "The division, therefore, of reptiles," says Professor Rymer Jones, "into such as undergo metamorphoses and such as do not, is by no means philosophical although convenient to the zoologist, for all reptiles undergo a metamorphosis although not to the same extent. In the one the change from the aquatic to the air-breathing animal is never fully accomplished; in the tailed Amphibian the change is accomplished after the embryo has escaped from the ovum."