the foremost pair half horny and half membraneous, the base being
horny, and the apex membraneous. They include the Bugs, some of which
are aquatic, as the Water Scorpion (Nepa), and the Water Boatman
(Natonecta), which swims on its back, rowing itself by means of a pair
of long legs, which look like oars; the common bed Bug is also of this
order, although wingless, as are also the Plant Lice (Aphides), which,
however, obtain wings in their perfect state.
8. DIPTERA (Two-winged).
[Illustration: FIG. 29.--PART OF GNAT'S WING, MAGNIFIED. ]
The Diptera include the common House Fly (fig. 16), Bluebottle Fly,
Gnat, and many others; their wings are like the Neuroptera, but they
have but one pair, the other pair being undeveloped, form little
knobs called "balancers." The wings of Flies are generally covered
with short stout hairs, as seen in fig. 29; the common Fly feeds upon
almost anything, but some of the Diptera feed exclusively on the blood
of other animals; the Gnat (Culex pipiens), of which the Mosquito is
a variety, deposits its egg in the water on any floating substance,
the larva which comes from the egg is aquatic, living with its head
downwards, the end of the abdomen only being above the water, in this
there is a spiracle or breathing orifice, which enables it to take in
the air; the Gnat, when it comes from this larva, stands on its shell
for a moment, and then flies off, for it is not suited to live in the
water; this history of the early stages of its life, accounts for Gnats
being always found in such numbers near pools of water. The Tsetse,
which Dr. Livingstone describes as being so fatal to cattle, is of
this order; he says, "It is well known that the bite of this poisonous
insect is certain death to ox, horse, or dog.... A most remarkable
feature in the bite of the Tsetse is its perfect harmlessness to man
and wild animals, and even calves, so long as they continue to suck the
cows."
9. APTERA (Wingless).
To this order belongs the Flea (Pulex irritans), which is furnished
with lancet-shaped weapons, through which it sucks the blood of other
animals, for it is entirely parasitic, and also the "Chigeo" (Pulex
penetrans), which is a troublesome and even dangerous pest in the West
Indies; it penetrates the skin of the feet, and deposits its young
beneath it.
[Illustration: FIG. 30.--FLEA (Pulex irritans)
MAGNIFIED.]
[Illustration: FIG. 31.--ARACHNIDA.1, Spider (Epeira Diadema);
2, Scorpion (Scorpio).]
[Illustration: FIG. 32--LONG-LEGGED HOUSE-SPIDER (Aranæ
domestica).]
The last class of the Articulata, the Arachnida, includes the Spiders,
Scorpions, Centipedes, and Millipedes. The Arachnida differ from
insects, in having eight or more legs, more than two eyes, no wings,
and no head; the Spiders have four pairs of legs, and six, eight, or
more, simple eyes, which appear as minute spots on the upper part of
the thorax. Spiders nearly all live by preying upon small insects,
which they catch in several ways, but by far the most general mode is
by constructing a web or net to entangle them; the threads of this
web are made of a fluid glutinous substance, which is secreted within
the abdomen, and which they project from extremely minute orifices,
several of which exist on the point of little projections called
"spinnarets," this liquid dries into a solid thread immediately it
comes into contact with the air; it is extremely strong, and so fine
that several thousand of the single fibres will only make the size of
a human hair. The Garden Spider (Epeira diadema) is often called the
Geometrical Spider, from the regularity of its web. These Spiders will
often place a thread from one spot to another, where it would seem
impossible that they could attach it, such as from the branch of a
tree to the corner of a house twenty feet or more from the ground; it
has never been accurately determined how the Spider does this, and it
is the more difficult to observe, as it is always done in the night,
but it has been supposed that a fine thread is spun, and that the wind
carries it across, when it is strengthened and afterwards made tight.
The Spider (Araneæ domestica) that makes "cobwebs" in the corners of
rooms, is called the Weaving Spider. Some Spiders are called Hunting
Spiders, they do not construct webs, but pounce upon their prey with a
leap; the Mygale avicularis of South America is one of this kind; it is
said that some grow so large that their feet spread out a foot wide.
The Long-legged Spider, often found in our houses, and of which fig. 32
is an exact copy, measures 3 1/2 inches, and is the largest species we
have. There are also aquatic Spiders, which feed upon insects in the
water and dive down for them; their surface being hairy and unctuous,
retains sufficient air to bring them up and prevent them being wetted.
The eyes of Spiders are different from those of other insects; they
appear as simple, shining spots, or "ocelli," and not compound eyes,
having a great many "ocelli" compounded into one. These "ocelli" are
arranged in a group of eight or more, and placed on the upper part of
the thorax, for Spiders have no head, although generally represented
with one. The eggs of Spiders are generally deposited in some sheltered
place, fastened together and partly covered with a net-work of a sort
of yellow silk, very much resembling the cocoon of the Silkworm. The
Scorpion, so terrible in appearance, and in its sting so deadly, and
which is sometimes a foot in length, belongs to this order. It has
eight legs, and a pair of claws like a lobster, the body is lengthened
into a sort of tail, at the end of which is a claw or sting, like the
poison fang of a serpent, with a poison bag at its root; its effects
are often fatal to man, and always so to the insects and other small
animals upon which the Scorpion feeds, its usual mode of killing which,
is to catch them with its claws and then to sting them to death. The
Centipede is a scarcely less frightful creature; in South America and
the West Indies it is sometimes found to grow to eight or ten inches in
length, it is of a long jointed form, with generally twenty-one pairs
of legs, although some have double this number; its bite is much to be
dreaded, as it is poisonous, especially the "Scolopendræ," which have
a poison gland, like the snake; in this country they are very small
indeed, and are generally found in moist places.
The Centipedes and Millipedes are, by some, placed in the class
Arachnida, but by others in a separate class called "Myriopoda,"
divided into two orders, the Chilognatha, which have rounded
cylindrical bodies, and generally more than one pair of legs to each
segment of the body, and the Chilopoda, which have a distinct flattened
head and but one pair of legs to each segment.
[Illustration: FIG. 33.--MOLLUSCA.
1, Nautilus (Argonauta); 2, Clio Borealis; 3, Mussel (Mytilus edule).]
The last of the three great divisions of the Invertebrata is formed
by the Mollusca; it is divided into six classes, (see page 218). The
Mollusca are characterised by having no internal skeleton, nor external
horny case, as in the Articulata; they are rather soft, and either void
of solid covering, or possessed of "shells" composed chiefly of earthy
matter (chalk), and in one or two pieces, called valves, hence the
names, uni-valve and bi-valve; all shells of this description belong to
the Mollusca, some of which have no means of locomotion, as Oysters;
others have a "foot" covered with a muscular expansion, called the
"mantle," by which they glide onwards, as the Snail.
1. The Tunicata have no shell or hard covering, but are of a pretty
firm consistence; they are either fixed to rocks and sea-weeds, or
float about freely, and are either solitary, social, or compound. The
"Ascidians" are united in groups, and are all connected by a common
stalk or "Stolon," from which they grow by buds.
2. The Brachiopoda. These Molluscs are furnished with a pair of
shells, within which the animal lives; one of these shells (the
ventral one) has a small hole in it, close to the hinge, and through
this a long tendinous cord passes, which fixes the creature to some
stone or rock, hence the name Brachiopodous, which means arm-footed.
The young of this Mollusc are not fixed, but float about. The Lingula
has horny shells, and the foot passes out between them; these
creatures were some of the first created, if not the very first; the
shells of Terebratula are found in vast quantities in the oldest
fossiliferous strata.
[Illustration: FIG. 34.--COCKLE (Cardium edule).]
3. The Lamellibranchiata include a great many of our most ordinary
Mollusca, commonly known as "shell fish." They have a pair of shells,
and are thence called "bivalve." The Oyster (Ostrea edulis), Mussel
(Mytilus edulis), Cockle (Cardium edule), Scallop (Pecten), belong to
this class. Oysters form a considerable article of commerce, thirty
or forty thousand bushels are brought each season to London; they are
dredged up from "beds," where they are found in great quantities. They
spawn in May and June, and are not then good. There is an old and a
well-known saying, that "Oysters are not fit to eat, unless there is
an R in the month," all the names of the months containing an R but
May, June, July, and August. The spawn is collected and placed in
artificial beds, consisting of shallow places or hollows in the sea,
where the tide will not wash them away, and whence they can be easily
removed when sufficiently grown, which is in five or six years; these
creatures have no powers of locomotion, but remain where the tide
washes them; but Scallops, Cockles (fig. 34), and Mussels (fig. 33),
have the power of fixing themselves to any substance they wish, by
means of the "byssus" or beard, which is a tuft of fibres passing out
from between the shells; and it is said, the Scallops have the power
of progression, by suddenly opening and shutting the shells.
4. The Pteropoda are Mollusca which have no shell, or a very thin one;
the Clio borealis (fig. 33), which forms the chief food of the Whale,
is found in great multitudes in the Arctic seas, it swims about by
means of two extensions, similar to wings. The Hyaloea has a small
round transparent shell.
[Illustration: FIG. 35.--SNAIL (Helix aspersa), AND
SLUG (Limax cinerius).]
[Illustration: FIG. 36.--WENTLE-TRAP SHELL (Scalaria).]
5. The Gasteropoda are extremely numerous; most of them have univalve
shells, but many of them have none, as the Garden Slug (Limax, fig.
35). The Whelk (Buccinum undatum), Perriwinkle (Littorina littoria),
Garden Snail (Helix aspersa, fig. 35), and the Wentle-trap (Scalaria,
fig. 36), are the most familiar examples of this class. These Mollusca
walk by means of the mantle, which is muscular, and capable of
alternate contraction and expansion; they breathe by means of lungs
on their back beneath the shell, and to which there is an opening in
their side. What are usually called the horns are four in number, two
short and two long; they are tentaculæ, but what is peculiar in them
is the circumstance of having the eyes placed at their ends. These
Mollusca have a sort of valve, which, when they retire into the shell,
closes it like a lid; it is called the "Operculum;" in some cases it
is horny, as in the Perriwinkle, and in others, resembles shell; the
shells of these mollusca are coiled into a spiral, this is caused by
the shell always growing by additions to the edges of the mouth, and
in nearly every case this spiral turns in the same direction that a
screw does, but in a very few it turns in the opposite direction, as
in the "Fusus contrarius."
6. The Cephalopoda include the "Cuttle-Fish," and Nautilus (fig.
33). They are furnished with eight or ten tentacula or arms, which
spring from the head, and which are covered with suckers; the mouth
is in the centre, and these tentacula are used to lay hold of their
prey and convey it to the mouth; they have two perfect eyes, and they
breathe by gills. The Nautilus has a univalve shell, which is of a
very graceful and elegant form; its interior is divided into chambers,
with a syphon running through them, by which the air is exhausted or
compressed so as to cause them to sink or swim; the animal occupies
only the outer chamber; the extinct Ammonite belonged to this class.
It is from the Cuttle-Fish (Sepiæ) that the beautiful dark brown
pigment, known as "sepia," is obtained, and also the material of which
Indian-ink is made.
THE VERTEBRATA.
The Vertebrate animals are those which have a brain and spinal cord
inclosed within a bony case, an internal skeleton, to which are
affixed the muscles, and which is moved by them; they all possess four
extremities, more or less modified in form, with the exception of the
Serpents. They are divided into four classes, Fishes, Reptiles, Birds,
and Mammals.
FISHES.
The Fishes live in water, and are unable to live in the air; they
receive oxygen from the water, but this is received much more slowly
than by air-breathing animals, and as the combination of oxygen with
the carbon of the system gives the elevated temperature of animals, so
in Fishes, the oxygen being received slowly, their temperature rises
but little above the temperature of the water they inhabit; they have
thence received the name of "cold-blooded." Fishes live upon the marine
animals which they capture, the various sea-weeds which grow in the
water, and insects which fall into, or breed there. They have fins
instead of legs, but the two pairs of fins known as "Pectoral" and
"Ventral" are analogues of them, and in a pectoral fin may be found
bones analogous to all the bones of the arm and hand of Man, or the
fore-feet of the other Vertebrata. Fishes urge themselves through the
water chiefly by the action of the tail from side to side, and in those
members which have more extended forms (as Eels), by a wavey motion of
the body itself; and the rapidity with which they swim is such, that
Sharks have been known to go round the ship they are following many
times in a very short space, although it may be sailing at a great
speed before the wind. Fishes are covered with scales, and the head is
united to the body without any constriction which can be considered as
a neck; they are mostly of a form such as can easily pass through the
water, without offering much resistance, and their specific gravity is
so nearly that of water, that, by the compression of a small vessel
filled with air, called the swimming bladder or "sound," they can rise
and sink with little effort. Many tribes of the human family, such as
the Esquimaux and Polynesians, almost live upon Fish, and even in Great
Britain, in fishing districts, it forms a great part of the food of the
inhabitants, and their capture gives employment to thousands.
Fish inhabit all kinds of water, the sea, rivers, and ponds, and many
which live habitually in the sea come into rivers at certain seasons;
and with respect to those which dwell always in the sea, some inhabit
certain tracts only, and confine themselves to them, just as quadrupeds
do to certain localities on the land. It has been a matter of wonder
how the Fish get into ponds formed by the drainage of lands; but most
ponds are supplied by springs which run underground from adjacent
lakes or rivers, or by rills running on the surface, these bring the
ova or eggs, which in favourable situations become hatched. Fish are
exceedingly prolific, the eggs in the roe of a Codfish were estimated
by Lewenhoec, to be upwards of 9,000,000, but not one in a thousand
comes to maturity; there are enemies on all sides to devour them before
they are hatched, and others to attack them afterwards. Some of the
rivers of France have lately been artificially stocked with Fish by
causing the fecundated spawn to be preserved till they are of a bulk
and strength to protect themselves. This was effected by confining
them in tanks floating in the water and perforated with holes, and
afterwards placing them in a part of the river, inclosed both above and
below by means of nets, so as to keep away their enemies--the larger
Fishes.
Fishes were the first of the Vertebrated animals created, and as a
proof of the incorrectness of the doctrine of development, these
first-created Fish were of a class corresponding to the most highly
organised Fishes of the present day.
Fishes are divided into two families: 1, Osseous Fishes (with a bony
skeleton); 2, Cartilaginous Fishes (with a cartilaginious skeleton).
The Osseous Fishes are divided into six Orders:--
1. ACANTHOPTERYGII (Thorny-fin).
[Illustration: FIG. 37.--1, PERCH (Perea fluvia
ilis). 2, MACKEREL (Scomber vulgaris). 3, GURNARD
(Trigla Gurnhardus).]
The Acanthopterygii include a great number of our ordinary useful
Fishes, as Mackerel, Perch, Tunny, Gurnard, &c. (fig. 37). The Perch
is a good example of this order, the sharp spines on its dorsal fin
being well developed, and dangerous for anglers to handle.
2. MALACOPTERYGII ABDOMINALES (Abdominal soft-fin).
The abdominal Malacopterygii include the Pilchard, Herring, Pike (fig.
38), Salmon (fig. 39), Anchovy, Trout, Roach, Chub, Tench, and many
more of the Fish which inhabit our streams and the sea.
[Illustration: FIG. 39.--THE SALMON (Salmo salar).]
The following account of the Salmon, is extracted from Dr. Baird's
Cyclopædia of the Natural Sciences:--"The Salmon is exceedingly
abundant in all the northern oceans. It is found in France, England,
Germany, Bohemia, Switzerland, Scandinavia, Iceland, and Greenland.
It exists also in Labrador and Canada, and down the American coast to
the Connecticut river, in latitude 41-1/2 deg., and either it, or a
species so closely allied as not to be distinguished except by close
comparison, abounds in the Arctic seas washing the northern shores of
the American continent. It does not frequent the rivers falling into
the Mediterranean, and, though it has been stated to be the case, it
does not occur in the Persian Gulf, or the Caspian Sea. In entering
the mouths of rivers in order to spawn, the females are always
observed to precede the males, depositing their ova in little pools
or sort of nests, which they form in the sand at the bottom, for the
males to fecundate. The young grow very rapidly, and at the present
time, the subject of the changes which they undergo in their progress
to maturity is one exciting much interest. When first hatched they
are about an inch in length, and during the first year are called
"Parr." When they remove to the sea, they receive a more brilliant
dress, and then become the "Smolt," varying from four to six inches in
length. After a residence in the sea of from two months to ten weeks,
they revisit the fresh waters, and are then from two-and-a-half to
four pounds' weight, and are called 'grilses' or 'gilses.' During the
ensuing winter they spawn, and are then known as Salmon. Salmon grow
to a large size, full-grown specimens weighing about forty pounds,
though individuals are mentioned which have weighed seventy or even
eighty pounds. Such are now excessively rare, owing to the perfection
of the means of capturing them at the mouths of our rivers, by which
the chances are very greatly against any fish escaping the various
dangers by which it is environed for such a succession of years as is
likely to admit of its attaining to its full dimensions. The power
these fish have in overcoming obstacles to their progress up large
rivers at spawning time is very great; they shoot up rapids with
the velocity of arrows, and clear considerable waterfalls, leaping
a height of ten, twelve, and even as much as twenty feet. The usual
time at which the Salmon leaves the sea is the autumn; it remains in
the rivers during the winter, and returns to the sea, after having
deposited its spawn, in the spring. The fishing of this excellent and
universally admired fish gives employment to many thousands of people,
throughout the whole of the north of Europe. Salmon fisheries, it
has been said, rank next to agriculture. In this country the Scotch
rivers supply by far the greater proportion of the salmon brought to
market. The total value of the Scotch fisheries has been calculated at
£150,000 a year."
Many salmon are caught by stake nets, and also by the practice of
"spearing;" this is a very picturesque sight, as it is conducted by
torchlight.
The Herring (Clupea Harengus) makes its visit to this country about
September, in enormous shoals, extending many miles each way; they
are caught in great quantities and salted in the boats immediately;
when brought on shore they are suspended in the smoke of wood fires,
and become "red herrings." The Herring fisheries are very important,
and afford--like the Salmon fisheries--employment to thousands; the
greatest quantities are caught off the coast of Norway, where it
is calculated about 400,000,000 are taken yearly. A great many are
caught off Lowestoffe, and Wick, in Caithness. The Pilchard (Clupea
pilchardus) is a kind of Herring, and is caught in enormous quantities
off the coasts of Cornwall. The Sprat and Whitebait are species of
"Clupea."
3. MALACOPTERYGII SUB-BRACHIALES (Sub-brachial soft fin).
The brachial Malacopterygii include most of the Flat Fish; as the
Turbot, Plaice, Sole, &c. (fig. 40). The Turbot, and Halibut are
caught out in the deep waters, but the Plaice and Flounders, chiefly
in shallows; these fish have one side dark and the other light, and
both eyes are placed on the dark side; they always swim with this
side upwards; in the Turbot this is the _left_, while in Plaice it is
the _right_ side. The Cod (fig. 40) is also included in this order; it
is a large fish, often weighing forty or fifty pounds, and three or
four feet long; it is chiefly caught in northern regions, the banks
of Newfoundland being the most celebrated for its Cod fisheries, and
supply the London market. These fish are caught by a long line and
hook let down to a great depth.
[Illustration: FIG. 40.--1, TURBOT (Rhombus maximus).
2, SOLE (Solea vulgaris). 3, PLAICE (Platessa
communis). 4, COD (Gadus morrhua).]
4. MALACOPTERYGII APODES (Footless soft fin).
[Illustration: FIG. 41.--THE EEL (Anguilla acutirostris).]
To this order belong the Eels (fig. 41). They have no abdominal fins,
and are therefore called apodial, or footless; they very much resemble
the serpent in their elongated form; they live chiefly in rivers and
ponds, in the mud of which they obtain worms, &c., upon which they
feed, they have been known to leave the water at night and travel
for some distance in search of worms, frogs, &c. These fish live a
long time after they are removed from the water, and are extremely
tenacious of life; their skins are covered with such fine small scales
that they appear quite smooth, and are extremely slimy. The Conger Eel
is much thicker in proportion than the common Eel, and has a dorsal
fin like a fringe all down the back; it grows to the weight of ninety
or a hundred pounds sometimes. Eels are often caught by thrusting
many-pronged spears (having the spears barbed) into the mud, and the
Eels are brought up sticking between the prongs. The Electrical Eel
(Gymnotus electricus) belongs to this section; it somewhat resembles
a large ordinary Eel four or five feet long, but has a broad ventral
fin running all along its lower part; it is famous for its power of
giving electrical shocks when touched, and seems to have the power of
using this influence at pleasure, but after giving a certain number
of shocks its power becomes exhausted, and it has to remain some time
before it can again give out shocks of any strength; these shocks
are sufficiently strong to prove fatal to small animals, and even
to mules and horses crossing the streams which they frequent, when
a number will attack them at once. This creature is a native of the
rivers and pools of South America, Demerara, &c.; the natives kill
them by driving in a great number of horses, and when the Eels have
exhausted their electrical powers, they are then caught and killed.
5. LOPHOBRANCHI (Tufted gill).
[Illustration: FIG. 42--HIPPOCAMPUS (From a dried specimen).]