Note: The Amphibia are distinguished by having usually no
scales, by having eggs and embryos similar to those of
fishes, and by undergoing a complete metamorphosis, the
young having gills. There are three living orders: (1)
The tailless, as the frogs ({Anura}); (2) The tailed
({Urodela}), as the salamanders, and the siren group
({Sirenoidea}), which retain the gills of the young
state (hence called {Perennibranchiata}) through the
adult state, among which are the siren, proteus, etc.;
(3) The C[oe]cilians, or serpentlike Amphibia
({Ophiomorpha} or {Gymnophiona}), with minute scales
and without limbs. The extinct Labyrinthodonts also
belonged to this class. The term is sometimes loosely
applied to both reptiles and amphibians collectively.