This
strong shell is, like that of the snail, a house for the tortoise to live
in; but this house is formed by arched bones, and is part of the creature
itself. The four feet of the tortoise or turtle, and a curious mouth rather
like the beak of a bird--without teeth, but with jaws hard enough to make
a bite from it very painful--and a little scaly tail; these are the only
parts of the animal not covered by the shields of its bony shells.
The Lizard has both limbs and teeth, but no shell. Lizards are wonderfully
active, darting away at the least alarm, so that it is not easy to catch
them.
We may think of the Crocodile of the African, and the Alligator of the
North American rivers, as enormous lizards; though they are now placed in a
class by themselves, on account of their horny covering, which is so strong
that it is almost impossible to pierce through it, and so smooth that a
bullet will glance off from it. Serpents have neither shell nor limbs.
Their vertebrae, as you will see, if you look at any skeleton of a snake in
the Museum, fit very beautifully one into the other; and owing to this they
are able to glide swiftly along the ground, to coil their shining length
round trees, and to dart their heads in every direction.
In one respect Tortoises, Lizards, and Serpents are alike--they all lay
eggs, only the shell is not made of lime and earth, but is soft like
leather. They are also cold-blooded animals, like fish.
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