{ Viviparous I. MAMMALIA.
{ Hot blood { Oviparous II. BIRDS.
{ With vertebræ { Cold red blood { With lungs III. AMPHIBIA.
Body { { With gills IV. FISHES.
{ { Have antennæ. V. INSECTS.
{ Without vertebræ. Cold white blood { Have tentacula. VI. WORMS.
3. The first class, or MAMMALIA, consists of such animals as produce living
offspring, and nourish their young ones with milk supplied from their own
bodies; and it comprises both the quadrupeds and whales.
4. This class has been distributed into seven ORDERS; of _primates_,
_bruta_, _feræ_, _glires_, _pecora_, _belluæ_, and _cete_, or whales. The
characteristics of these are founded, for the most part, on the number and
arrangement of the teeth; and on the form and construction of the feet, or
of those parts in the seals, manati, and whales, which supply the place of
feet.
_ORDERS OF MAMMALIA._
I. PRIMATES Have the upper _front teeth_ generally four in number,
wedge-shaped, and parallel; and two _teats_ situated on the breast, as
the _apes_ and _monkeys_.
II. BRUTA Have no _front teeth_ in either jaw; and the _feet_ armed with
strong hoof-like nails, as the _elephant_.
III. FERÆ Have in general six _front teeth_ in each jaw; a single _canine
tooth_ on each side in both jaws; and the grinders with conic
projections, as the _dogs_ and _cats_.
IV. GLIRES Have in each jaw two long projecting _front teeth_, which
stand close together; and no _canine teeth_ in either jaw, as the _rats_
and _mice_.
V. PECORA Have no _front teeth_ in the upper jaw; six or eight in the
lower jaw, situated at a considerable distance from the grinders; and the
_feet_ with hoofs, as the _cattle_ and _sheep_.
VI. BELLUÆ Have blunt wedge-shaped _front teeth_ in both jaws; and the
feet with hoofs, as the _horses_.
VII. CETE Have _spiracles_, or breaking holes on the head; _fins_ instead
of fore-feet; and a _tail_ flattened horizontally, instead of hind feet.
This order consists of the _narwals_, _whales_, _cachalots_, and
_dolphins_.
5. The second class, or BIRDS, comprises all such animals as have their
bodies clad with _feathers_. Their _jaws_ are elongated, and covered
externally with a horny substance called a bill or beak, which is divided
into two parts called mandibles. Their _eyes_ are furnished with a thin,
whitish, and somewhat transparent membrane, that can at pleasure be drawn
over the whole external surface like a curtain. Birds _respire_ by
air-vessels, which are extended through their body, and which, in the
abdominal cavity, adhere to the under surface of the bones. Their organs of
motion are two _wings_ and two _legs_; and they are destitute of external
ears, lips, and many other parts which are important to quadrupeds.