VERTEBRATA, r) “SS 
most important of the latter section being the tribes of Sharks, Rays 
(Skates, &c.), Sturgeons, and Lampreys. 
Amphibians.—The class Amphibvans* receives its name from the fact 
that many of the species belonging to it are capable of living 
either on dry land or in water. Many naturalists regard it merely 
as an order of the class of Reptiles, to which the name of Batra- 
chian* Reptiles is given, the frog being taken as the type of the whole. 
The most essential differences between Amphibians and Reptiles are, 
that young Amphibians undergo metamorphoses, and that Amphibians 
breathe by gills alone in the earlier part of their life, whilst in 
their adult state most of them breathe by lungs alone, although some 
have both lungs and gills. Most of the Amphibians, in an adult state, 
have four limbs, although in some these are altogether wanting, 
and others have only one pair; but in the early stages of their life 
none of them have limbs at all, and their form is fish-like, of which 
we have a familiar example in the tadpole, the young of the frog, 

Fig. 71.—Successive stages of the Frog: 
In the order of the numbers—from the egg almost to the perfect form. 
Frogs, toads, newts, and salamanders are the best known Amphibians ; 
but some of those of other countries greatly exceed oe of Britain 
in size. 
Reptiles.—Reptiles? agree with Amphibians and Fishes in being cold- 
blooded. They differ from Amphibians in breathing by lungs throughout 
the whole period of their existence. Three orders of reptiles are generally 
1 From Greek amphibios, having a double life, 3 From Latin repo, to creep. 
2 From Greek batrachos, a frog. 
* 
