Chapter III: Section III: Aquatic Mammalia, having no Hind Limbs, and the Fore

Limbs converted into Fins._

XI. _Cetacea_, or sea mammalia, the principal of which are the
whale family, the dolphin family, the manati, the porpoise family,
and the narwhal, or sea-unicorn.

THE AVES, OR BIRDS,

Lay eggs from which their young are hatched by what is called incubation. Their skins are covered with feathers; and their jaws are horny, without teeth. Their blood is warm, and circulates like that of the mammalia. The six orders of Aves are as follow:--

1. _Raptores_, or birds of prey. These birds are distinguished by a
very strong and sharp bill more or less curved, but always hooked
at the extremity of the upper mandible, which is covered at the
base with a kind of skin called the cere. The nostrils are usually
open. The legs are very strong, the feet are large, and the toes,
which are four in number, are armed with very strong, sharp, curved
claws. The principal raptorial birds are the vultures, including
the condor; the falcon family, including the eagles, hawks, kites,
and buzzards; and the owls.

2. _Insessores_, or perching birds. These birds have all feet
formed for perching, the hind toe springing from the same place as
the other toes, which gives them great power of grasping. Their
legs are of moderate length, and their claws not sharply curved.
This order includes the thrushes, nightingales, and all the finest
songsters of our groves, with the robin-redbreast, the sparrow, and
other birds seen about dwellings, the swallows, the larks, the crow
family, the kingfishers, the birds of paradise, and the humming
birds.
3. _Scansores_, or climbers. These birds have two toes before and
two behind. This construction gives them such great power of
climbing, that they can ascend the perpendicular trunk of a tree.
The principal birds in this order are the parrots, the cuckoos, and
the woodpeckers.

4. _Rasores_, or gallinaceous birds. These birds have the head
small in proportion to the body. The bill is generally short, with
the upper mandible somewhat curved. The nostrils have usually a
protecting fleshy membrane. The tarsus, or lower part of the leg,
is long and bare, and there are four toes, those in front being
united by a slight membrane, while that behind is generally higher
up the leg, and smaller than the others. This order comprises most
of the birds used as food, and includes the peacock, the turkey,
the common cock and hen, the partridge, the pheasant, and the
pigeon family.

5. _Grallatores_, or Waders. These birds are characterised by their
long and slender legs, and by the thighs being more or less bare.
There are three anterior toes, more or less united at the base by a
membrane, or rudimentary web. The hind toe is wanting in some
members of the order. This order contains the ostrich family, the
bustards and plovers; the cranes, herons, and storks; and the
snipes and woodcocks.

6. _Palmipedes_, or web-footed birds. These birds have the legs and
feet short, and placed behind, with their fore toes united by a
thick and strong membrane. The neck is much longer than the legs,
and their bodies are covered with a dense layer of down beneath the
outer plumage, which is close, and imbued with an oily fluid that
repels the water. The principal birds in this order are the grebes,
the auks and penguins, the petrels, the pelican and cormorant and
the swans, ducks, and geese.

By many ornithologists the pigeons and ostriches are considered to
form distinct orders, called respectively _Columbæ_ and _Cursores_.

THE REPTILIA,

Or Reptiles, have neither hair, wool, nor feathers, and their bodies are either naked, or covered with scales. Some lay eggs, and some bring forth their young alive. Some have gills, and others lungs, but the latter have only a portion of the blood passing through them; and thus the blood of reptiles is cold, as it is respiration which gives the blood heat. The senses of reptiles are dull, and their movements are either slow or laborious. The following are the four orders into which this class is divided:--

1. _Chelonian Reptiles._ These animals have four legs. The body is
enclosed in an upper buckler, called the carapace, and an under
one, called the plastron. They have lungs which are much expanded;
but they have no teeth, though they have hard horny jaws. The
females lay eggs covered with a hard shell. The principal animals
belonging to this division are the tortoises, which live on land or
in fresh waters, and the turtles, which inhabit the sea.

2. _The Saurian Reptiles._ These animals have also expanded lungs,
and generally four legs, but some have only two. Their bodies are
covered with scales, and their mouths filled with teeth. This order
includes all the crocodiles and lizards. The crocodiles have broad
flat tongues, attached throughout to the jaws, and the lizards have
long narrow tongues, which many of them can extend to a great
distance from the mouth.

3. _The Ophidian Reptiles_ are the snakes and serpents. The body is
covered with scales, but it is destitute of feet. The lungs are
generally well developed, only on one side. Serpents are frequently
furnished with poison-bags at the base of some of their teeth.

4. _The Batrachian Reptiles_ include the frogs and toads. The body
is naked. The greater part of these reptiles undergo a transition
from a fish-like tadpole furnished with gills to a four-legged
animal with lungs. Others never lose their gills, though they
acquire lungs, and of this kind are the siren and the proteus.

THE PISCES,

Or Fishes, are defined by Cuvier to be vertebrated animals with red blood, breathing through the medium of water by means of their branchiæ or gills. To this definition may be added, that fishes have no neck, and that the body generally tapers from the head to the tail; that most of the species are furnished with air-bladders which enable them to swim; and that their bodies are generally covered with scales. The heart has only one auricle, and the blood is cold. The gills require to be kept moist to enable the fish to breathe, and as soon as they become dry, the fish dies. Thus fishes with large gill openings die almost as soon as they are taken out of the water; while those with very small openings, like the eel, live a long time. Fishes have no feet, but are furnished with fins. The scientific knowledge of Fishes is called Ichthyology. Fishes are first divided into two great series, viz. the Bony Fishes, and the Cartilaginous Fishes, and these are again subdivided into nine orders, as follows:--

OSSEOUS OR BONY FISHES.

1. _Acanthopterygii_, or fishes with hard fins.

2. _Malacopterygii abdominales_, or soft-finned fishes, with the
ventral fins on the abdomen behind the pectorals.

3. _Malacopterygii sub-brachiati_, or soft-finned fishes, with the
ventral fins under the gills.

4. _Malacopterygii apodes_, or soft-finned fishes, without ventral
fins.

5. _Lophobranchii_, or fishes with tufted gills.

6. _Plectognathii_, or fishes with the upper jaw fixed.

CHONDROPTERYGII, OR CARTILAGINOUS FISHES.

7. _Cyclostomi_, or fishes with jaws fixed in an immovable ring,
and with holes for the gills.

8. _Selachii_, or fishes with movable jaws and holes for the gills.

9. _Sturiones_, with the branchiæ in the usual form.

Of the bony fishes the _Acanthopterygii_, or fishes with hard spiny fins, are divided into fifteen families, the principal of which are the perch family, the mailed cheek fishes, including the gurnards, the flying fish of the Mediterranean, and the sticklebacks, or jack banticles; the mackerel family, including the tunny, bonito, and sword-fish; the pilot-fish, the dolphin of the Mediterranean, so celebrated for the beauty of its dying tints, and the John Dory. Among the _Malacopterygii abdominales_, or soft-finned fishes, that have their ventral fins suspended from the abdomen, the most interesting are the carp family, the pike family, the flying-fish of the ocean, the salmon family, and the herring family, including the sprat, pilchard, and anchovy.

_The Malacopterygii sub-brachiati_ are soft-finned fishes, with the ventral fins beneath the pectorals; the principal of which are the cod family, including the haddock, whiting, and ling; the flat-fish family, including soles, turbots, plaice, and flounders; and the suckers or lump-fish.

_The Malacopterygii apodes_ are confined to the eel family.

_The Lophobranchii_ include the pipe fish, and other fishes of similar form.

_The Plectognathi_ comprise the very singular forms of the balloon-fish, the sun-fish, and other similar fishes.

_The Chondropterygii, or Cartilaginous fishes_, are divided into three orders, viz. _the Sturiones_, or sturgeon family; _the Selachi_, or sharks and rays, including the torpedo; and _the Cyclostomi_, or lamprey family. The last two orders were included by Cuvier in a single one.

THE MOLLUSCOUS ANIMALS

Have no bones except their shells. Their sense of feeling appears to be very acute, but the organs for the other senses are either wanting or very imperfect. The blood is cold and white, and the heart often consists of only one ventricle; a few of them have imperfect lungs, but the greater number breathe through gills. They have all the power of remaining a long time in a state of rest, and their movements are either slow or violently laborious. Some of them appear incapable of locomotion. They produce their young from eggs, but some lay their eggs on a part of their own body, where the young are hatched. The following are Cuvier’s six classes:--

1. _Cephalopoda, or Head-footed Mollusca._ These animals are
furnished with long fleshy arms or feet, proceeding from the head,
which is not distinct from the body, and on which they crawl. There
is only one order, which includes the cuttle-fish, nautilus, and
belemnites.

2. _Pteropoda, or Wing-footed Mollusca._ These animals have two
membranous feet or arms, like wings, proceeding from the neck.
There is only one order, which contains six genera, the best known
of which is the Hyalæa, the shell of which is commonly called
Venus’s chariot.

3. _Gasteropoda, or Body-footed Mollusca._ All these animals crawl
with the flat part of the body, which acts as a kind of sucker.
There are nine orders in Cuvier’s system. The common snail will
give an idea of the habits of the class.
4. _Acephala, or Headless Mollusca._ These animals have no apparent
head, and breathe by means of branchiæ, which are generally
ribbon-shaped. Most of them are enclosed in a bivalve shell, but
some are naked; the former are the _Testacea_ of Cuvier, and the
_Conchifera_ of Lamarck; the latter are the _Tunicata_ of Lamarck.
They form two orders.

5. _Brachiopoda, or Arm-footed Mollusca._ These animals also have a
bivalve shell; but they have no true branchiæ, and their
respiration is effected by the agency of the mantle. They have two
spiral arms.

6. _Cirrhopoda, or Curled-footed Mollusca._ These are generally
attached, and enclosed in a shell of several pieces; they are
furnished with a mouth, armed with jaws, and with several pairs of
jointed and fringed organs, called cirri, by the protrusion and
retraction of which they capture their prey. Examples of this class
are the Barnacles and Acorn shells. These animals have long ceased
to be regarded as Mollusca, the investigations of modern
naturalists having proved them to be true articulated animals most
nearly related to the Crustacea.

THE ARTICULATED ANIMALS

Have no back-bone. The covering of the body is sometimes hard and sometimes soft, but it is always divided into segments by a number of transverse incisions. The limbs, when the body is provided with any, are jointed; and they can be separated from the body without any serious injury being sustained by the animal, new limbs being shortly after formed to replace them. The senses of tasting and seeing are more perfect than those of the Mollusca, though that of feeling seems much less acute. In other respects the four classes differ considerably from each other.

[_The Entozoa, or Intestinal Worms_, placed by Cuvier and others among the Radiata, are now arranged amongst the lowest forms of articulated animals, as are also those animalcules known as _Rotifera_.]

I. _The Annelida, or Red-blooded Worms_, have no heart, properly so
called, but have sometimes one or more fleshy ventricles. They
breathe through branchiæ. Their bodies are soft, and more or less
elongated, being divided into numerous rings or segments. The head,
which is at one extremity of the body, can scarcely be
distinguished from the tail, except by having a mouth. These
animals have no feet, properly so called, but they are furnished
with little fleshy projections, bearing tufts of hairs or bristles,
which enable them to move. They are generally of carnivorous
habits. They lay eggs, but the young are frequently hatched before
exclusion, and hence these creatures are said to be ovoviviparous.
Their study is called Helminthology. As examples of the three
orders of this class may be mentioned the serpulæ or worm-like
animals, often found on shells, the common earthworm, and the leech
family.

II. _The Crustacea_ comprise the shell-fish commonly called crabs,
lobsters, shrimps, and prawns. They have a distinct head, furnished
with antennæ, eyes, and mouth; and their bodies are covered with a
crust or shell, divided into segments by transverse incisions, the
segments being united by a strong membrane. Once a year the larger
species of these animals moult, throwing off their old crust or
shell, and forming a new one, the animal remaining in a naked and
greatly weakened state during the intermediate time. Many of the
Crustacea swim with great ease, but on land their motions are
generally cramped and awkward; and they are confined to crawling,
or leaping by means of the tail. When a limb is injured they
possess the extraordinary power of throwing it off, and forming a
new one. The Crustacea lay eggs, and the young of some of the
species undergo a transformation before they attain their full
size. The Crustacea were divided into two sections and seven orders
by Latreille, which are as follow:--

SECTION I. _Malacostraca._

Shell solid, legs ten or fourteen, foot-jaws six or ten, mandibles two, maxillæ four; mouth with a labrum.

Sub-section I. _Podophthalma_, eyes on foot-stalks.

ORDER 1. _Decapoda_, legs ten.

Sub-order 1. _Brachyura_, the crabs.

Sub-order 2. _Macroura_, the lobsters.

ORDER 2. _Stomapoda_, legs more than ten.

Sub-section II. _Edriophthalma_, eyes not on foot-stalks.

ORDER 3. _Amphipoda_, body compressed; mandibles palpigerous.

ORDER 4. _Læmodipoda_, abdomen rudimental, with only the rudiments
of one or two pairs of appendages.

ORDER 5. _Isopoda_, body depressed; abdominal appendages flat;
mandibles not palpigerous.