Chapter I: Introduction

ZOOLOGY is that branch of Natural History which treats of animals, and embraces not only their structure and functions, their habits, instincts, and utility, but their names and systematic arrangement.

Various systems have been proposed by different naturalists for the scientific arrangement of the animal kingdom, but that of Cuvier, with some modifications, is now thought the best, and a sketch of it will be found under the head of the Modern System in this Introduction. As, however, the System of Linnæus was formerly in general use, and is still often referred to, it has been thought advisable to give a sketch of it first; that the reader may be aware of the difference between the old system and the new one.

_LINNÆAN SYSTEM._

According to the system of Linnæus, the objects comprehended within the animal kingdom were divided into six classes: Mammalia or Mammiferous Animals, Birds, Amphibia or Amphibious Animals, Fishes, Insects, and Worms, which were thus distinguished:

CLASSES.

{ With vertebræ { Hot Blood { Viviparous I. MAMMALIA.
{ { { Oviparous II. BIRDS.
Body { { Cold red Blood { With lungs III. AMPHIBIA.
{ { With gills IV. FISHES.
{ Without vertebræ Cold white Blood { Having antennæ V. INSECTS.
{ Having tentacula VI. WORMS.

ORDERS OF MAMMALIA.

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 the cetacea.

This class was divided by Linnæus into seven Orders: viz. _primates_, _bruta_, _feræ_, _glires_, _pecora_, _belluæ_, and _cetacea_ (this order was called Cete by Linnæus) or whales. The characteristics of these were 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 cetacea, which supply the place of feet:

I. PRIMATES.--Having 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.--Having no front teeth in either jaw; and the feet armed
with strong hoof-like nails, as the elephant.

III. FERÆ.--Having 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.--Having 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.--Having 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 cattle and sheep.

VI. BELLUÆ.--Having blunt wedge-shaped front teeth in both jaws;
and the feet with hoofs, as horses.

VII. CETACEA.--Having spiracles or breathing-holes on the head;
fins instead of fore feet; and a tail flattened horizontally,
instead of hind feet. This order consists of the narvals, whales,
cachalots, and dolphins.

ORDERS OF BIRDS.

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. 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. That part of Zoology which treats of Birds is called Ornithology.

Linnæus divided this class into six Orders:

1. _Land Birds._

I. RAPACIOUS BIRDS (_Accipitres_).--Having the upper mandible
hooked, and an angular projection on each side near the point, as
the eagles, hawks, and owls.

II. PIES (_Picæ_).--Having their bills sharp at the edge, somewhat
compressed at the sides, and convex on the top, as the crow.

III. PASSERINE BIRDS (_Passeres_).--Having the bill conical and
pointed, and the nostrils oval, open, and naked, as the sparrow and
linnet.

IV. GALLINACEOUS BIRDS (_Gallinæ_).--Having the upper mandible
arched, and covering the lower one at the edge, and the nostrils
arched over with a cartilaginous membrane, as the common poultry.

2. _Water Birds._

V. WADERS (_Grallæ_).--Having a roundish bill, a fleshy tongue, and
the legs naked above the knees, as the herons, plovers, and snipes.

VI. SWIMMERS (_Anseres_).--Having their bills broad at the top, and
covered with a soft skin, and the feet webbed, as ducks and geese.

ORDERS OF AMPHIBIA.

Under the third class, or Amphibia, Linnæus arranged such animals as have a cold, and, generally, naked body, a lurid colour, and nauseous smell. They respire chiefly by lungs, but they have the power of suspending respiration for a long time. They are extremely tenacious of life, and can repair certain parts of their bodies which have been lost. They are also able to endure hunger, sometimes even for months, without injury.

The bodies of some of them, as the turtles and tortoises, are protected by a hard and horny shield or covering; those of others are clad with scales, as the serpents, and some of the lizards; whilst others, as the frogs, toads, and most of the water-lizards, are entirely naked, or have their skin covered with warts. Many of the species shed their skins at certain times of the year. Several of them are furnished with a poison, which they eject into wounds that are made by their teeth. They chiefly live in retired, watery, and marshy places; and, for the most part, feed on other animals, though some of them eat water-plants, and many feed on garbage and filth. None of these species chew their food; they swallow it whole, and digest it very slowly.

The offspring of all these animals are produced from eggs, which, after they have been deposited by the parent animals in a proper place, are hatched by the heat of the sun. The eggs of some of the species are covered with a shell; those of others have a soft and tough skin or covering, not much unlike wet parchment; and the eggs of several are perfectly gelatinous. In those few that produce their offspring alive, as the vipers and some other serpents, the eggs are regularly formed, but are hatched within the bodies of the females.

This class Linnæus divided into three Orders:

I. REPTILES.--Having four legs, and walking with a crawling pace,
as the tortoises, toads, and lizards.

II. SERPENTS.--Having no legs, but crawling on the body.

III. NANTES.--Living in the water, furnished with fins, and
breathing by means of gills. These are true Fishes, principally of
the group termed _Chondropterygii_, or Cartilaginous Fishes, by
Cuvier.

ORDERS OF FISHES.

Fishes constituted Linnæus’s fourth class of animals. They are all inhabitants of the water, in which they move by certain organs called fins. Those situated on the back are called dorsal fins; those on the sides, behind the gills, pectoral fins; those below the body, near the head, are ventral; those behind the vent are anal; and that which forms the tail is called the caudal fin. Fishes breathe by gills, which, in most species, are situated at the sides of the head. Fishes rise and sink in the water, generally by a kind of bladder in the interior of the body, called an air-bladder. Some of them do not possess this organ, and consequently are seldom found but at the bottom of the sea, from which they can only rise by an effort. The bodies of these animals are usually covered with scales, which keep them from injury by the contact of the water.

The fishes were divided by Linnæus into four Orders:

I. APODAL.--Having no ventral fins, as the eel.

II. JUGULAR.--Having the ventral fins situated in front of the
pectoral fins, as the cod, haddock, and whiting.

III. THORACIC.--Having the ventral fins situated directly under the
pectoral fins, as the perch and mackerel.

IV. ABDOMINAL.--Having the ventral fins on the lower part of the
body below the pectoral fins, as the salmon, herring, and carp.

ORDERS OF INSECTS.

The fifth class of Linnæus comprised the Insects; and the branch of Zoology which treats of them is called Entomology. Nearly all insects go through certain great changes at different periods of their existence. From the egg is hatched the larva, which is a grub or caterpillar, and destitute of wings; this afterwards changes to a pupa, or chrysalis, wholly covered with a hard shell, or strong skin, from which the perfect or winged insect bursts forth. Spiders and their allies, which were included by Linnæus in the insects, issue from the egg in nearly a perfect state.

Linnæus divided his class of insects into seven Orders:

I. COLEOPTEROUS.--Having elytra, or crustaceous cases covering the
wings; and which, when closed, meet in a straight line along the
middle of the back, as the cockchafer.

II. HEMIPTEROUS.--Having four wings, the upper ones partly
crustaceous, and partly membranous; not divided straight down the
middle of the back, but crossed, or incumbent on each other, as the
cockroach.

III. LEPIDOPTEROUS.--Having four wings covered with fine scales
almost like powder, as the butterflies and moths.

IV. NEUROPTEROUS.--Having four membranous and semi-transparent
wings, veined like network; and the tail without a sting, as the
dragon-fly and ephemera.
V. HYMENOPTEROUS.--Having four membranous and semi-transparent
wings, veined like network; and the tail armed with a sting, as the
wasp and bee.

VI. DIPTEROUS.--Having only two wings, as the common house-flies.

VII. APTEROUS.--Having no wings, as the spiders.

ORDERS OF VERMES, OR WORMS.

The sixth and last Linnæan class consisted of Worms, or Vermes. These are slow of motion, and have soft and fleshy bodies. Some of them have hard internal parts, and others have crustaceous coverings. In some of the species, eyes and ears are very perceptible, whilst others appear to enjoy only the senses of taste and touch. Many have no distinct head, and most of them are destitute of feet. They are, in general, so tenacious of life, that parts which have been destroyed will be reproduced. These animals are principally distinguished from those of the other classes by having tentacula, or feelers, and are divided by Linnæus into five Orders:

I. INTESTINA.--Are simple and naked, without limbs; some of them
live within other animals, as the ascarides and tape-worms; others
in water, as the leeches; and a few in the earth, as the
earth-worm.

II. MOLLUSCA.--Are simple animals, without shells, and furnished
with limbs, as the cuttle-fish, medusa, star-fish, and sea-urchin.

III. TESTACEA.--Are animals similar to the last, but covered with
shells, as oysters, cockles, snails, and limpets.

IV. LITHOPHYTA.--Are composite Polyps, dwelling in cells in a
calcareous base which they produce, as corals and madrepores.

V. ZOOPHYTA.--Are usually composite animals, but do not reside in
stony cells. The coral, sponge, and polyps are instances of this
order, which also includes the Infusorial Animalcules.

_MODERN SYSTEM._

It will be found by reading the following sketch of the Modern System that the greatest change has taken place in the latter two classes. The others remain nearly the same in effect, though their distinctions are different, and the classes are not arranged in the same order.

According to Cuvier, all animals are arranged in four great divisions, which are subdivided into classes and orders, as follows:--

Divisions Classes No. of Orders
I. VERTEBRATA. } 1. Mammalia Nine.
Four Classes. Twenty-seven Orders. } 2. Aves Six.
} 3. Reptilia Four.
} 4. Pisces Eight.
II. MOLLUSCA. } 1. Cephalopoda One.
} 2. Pteropoda One.
Six Classes. Fifteen Orders. } 3. Gasteropoda Nine.
} 4. Acephala Two.
} 5. Brachiopoda One.
} 6. Cirrhopoda One.

III. ARTICULATA. } 1. Annelides Three.
} 2. Crustacea Seven.
Four Classes. Twenty-four Orders. } 3. Arachnida Two.
} 4. Insecta Twelve.

IV. RADIATA. } 1. Echinodermata Two.
} 2. Entozoa Two.
Five Classes. Eleven Orders. } 3. Acalephæ Two.
} 4. Polypi Three.
} 5. Infusoria Two.

THE VERTEBRATED ANIMALS

Have a backbone divided into vertebræ or joints, whence they take their name. They have also separate senses for hearing, seeing, tasting, smelling, and feeling; a distinct head, with a mouth opening by two horizontal jaws; a muscular heart, and red blood. The four classes of Vertebrata and their orders are as follow:--

I. THE MAMMALIA are all furnished with mammæ, or teats, through
which they give milk to their young, which they bring forth alive.
They have warm blood, which all circulates from the heart through
the lungs, and returns to the heart before it passes through the
body. Their skins are naked, or covered with wool or hair, and
their mouths are generally furnished with teeth. There are eleven
orders, which are thus distinguished:--