Cold-blooded Vertebrates (p. 19). The heart has the same structure as in
Mammals and Birds, but the left and right ventricles are usually only
incompletely divided from one another (p. 20). The body is invested with
horny scales or with bony plates covered by a horny layer. Reptiles are
very unlike Birds in appearance, but present many essential points of
resemblance to them in their skeleton; indeed, during earlier geological
times, there were transitional forms between the two classes. The
structure of the reptile egg, too, is very similar to that of the bird’s
egg; but the first has no lime-salts deposited in its shell. The egg is
not hatched out by the animal itself, but exposed to the heat of the sun
or to the warmth developed by decaying vegetable matter. Several
reptiles (adder, for example) keep their eggs in their bodies till the
young escape. Reptiles have either no limbs (snakes, a few lizards), or,
at any rate, the limbs are not well developed, and are so placed that
the body does not rest upon them, but is slung between them.
[Illustration:
FIG. 46.—Common Lizard (_Lacerta agilis_); 2, head of the same from
below; 3, tongue.
]
The Reptilia are divided into the Orders of =Crocodilia= (Crocodiles),
=Chelonia= (Turtles and Tortoises), =Lacertilia= (Lizards), =Ophidia=
(Snakes).
[Illustration:
FIG. 47.—The Adder (_Pelias berus_).
]
Our native reptiles have no agricultural importance. I will, however,
briefly mention the =Adder= (_Pelias berus_, Fig. 47), as it is
dangerous to man. Head broad; tail much smaller than the hinder end of
the body. Colour greenish grey or brownish. A black zigzag band runs
along the dorsal side of the body. Length about twenty inches. The two
hook-shaped poison-fangs are found in the front of the upper jaw;
opening the mouth widely causes them to be erected. They are traversed
by poison-canals through which the poison flows immediately into the two
bloodless wounds. The adder lives in woods and on mountain slopes, where
it devours mice. The poison has a decomposing action on the blood; it
causes fever, and swelling of the part bitten, as well as sometimes of
the neighbouring parts. The bite may be fatal. Alcohol is spoken of very
highly as a remedy.
[Illustration:
FIG. 48.—The Grass Snake (_Tropidonotus natrix_).
]
[Illustration:
FIG. 49.—Blindworm (_Anguis fragilis_).
]
The native =Ringed Snake= (_Tropidonotus natrix_, Fig. 48), three feet
long, is bluish with belly flecked with black and white; a yellow and a
black band on the neck. It is fond of going into the water, and eats
frogs, newts, and insects. The =Smooth Snake= (_Coronella lævis_), two
feet long, is brown, with black patches on the back, which, however, do
not form a continuous band. Head dark velvety black. Devours lizards and
blindworms. The =Blindworm= (_Anguis fragilis_) is indeed snake-like, or
rather worm-like (Fig. 49), but nevertheless belongs to the lizards,
with which its internal structure agrees.