137).
The _Amphibians_ of the Permian period belong principally to the
order of the _Labyrinthodonts_, which commenced to be represented
in the Carboniferous, and has a large development in the Trias.
Under the name, however, of _Paloeosiren Beinerti_, Professor
Geinitz has described an Amphibian from the Lower Permian of
Germany, which he believes to be most nearly allied to the existing
"Mud-eel" (_Siren lacertina_) of North America, and therefore
to be related to the Newts and Salamanders (_Urodela_).
[Illustration: Fig. 138.--_Protorosaurus Speneri_, Middle Permian,
Thuringia, reduced in size. (After Von Meyer.) [Copied from Dana.]]
Finally, we meet in the Permian deposits with the first undoubted
remains of true _Reptiles_. These are distinguished, as a class,
from the _Amphibians_, by the fact that they are air-breathers
throughout the whole of their life, and therefore are at no time
provided with gills; whilst they are exempt from that metamorphosis
which all the _Amphibia_ undergo in early life, consequent upon
their transition from an aquatic to a more or less purely aerial
mode of respiration. Their skeleton is well ossified; they usually
have horny or bony plates, singly or in combination, developed
in the skin; and their limbs (when present) are never either
in the form of _fins_ or _wings_, though sometimes capable of
acting in either of these capacities, and liable to great
modifications of form and structure.
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