2. Cerripeda.
3. Crustacea.
{Coleoptera }
{Orthoptera }
{Neuroptera }
{Hymenoptera }
4. Insecta. {Strepsiptera} 9 Orders.
{Lepidoptera }
{Hemiptera }
{Diptera }
{Aptera }
5. Arachnida.
Sub-family 3.--MOLLUSCA, having Six classes.
ACEPHALA, or Headless.
1. Tunicata.
2. Brachiopoda.
3. Lamellibranchiata.
ENCEPHALA, Having a Head.
4. Pteropoda.
5. Gasteropoda.
6. Cephalopoda.
The Infusoria, the first class of the Radiata, comprise all those
microscopic organisms called "Protozoa;" they consist of a membranous
cell with fluid contents, and are very nearly allied to the Protophytes
or lowest vegetable existences. It is still a matter of discussion
amongst physiologists and microscopists as to which kingdom shall claim
certain of them, but, according to Dr. Carpenter, it appears that the
vegetable cell-beings have two envelopes, the inner one albuminous and
the outer one cellulose or starchy, and the following passage occurs
in his treatise on the Microscope (which should be in the hands of all
enquiring minds):--
"The animal cell, in its most complete form, is comparable in most
parts of its structure to that of the plant, but differs from it
in the entire absence of the 'cellulose wall' or of anything that
represents it, the cell-contents being enclosed in only a single
limitary membrane, the chemical composition of which, being albuminous,
indicates its correspondence with the primordial utricle. In its
young state it seems always to contain a semi-fluid plasma, which is
essentially the same as the protoplasm of the plant, save that it
does not include chlorophyll granules, and this may either continue
to occupy its cavity (which is the case in cells whose entire energy
is directed to growth and multiplication) or may give place, either
wholly or in part, to the special product which it may be the function
of the cell to prepare. Like the vegetable cell, that of animals very
commonly multiplies by duplicative sub-division, it also (especially
among Protozoa) may give origin to new cells by the breaking up of its
contents into several particles."
Some of these creatures are so exceedingly minute that hundreds of
millions may be contained in a drop of water. They have no organs of
any kind, but consist of single cells of a soft substance called
"sorcode;" there is no distinction of sexes, and generation takes place
by sub-division, each cell separating into two, and these again into
two more, and so on with marvellous rapidity; this is the usual method
of increase, but occasionally an act of conjugation takes place, two
cells blending into one at the points of contact, the result of which
is a nucleus or cell within the original one. These animated cells
are of all forms, having prolongations which appear to be thrown out
to absorb any particle of organic matter within reach, which then
enters within the soft substance of the animalcule and is digested or
dissolved, such are the Amboeba, the Actinophrys, &c. (see fig. 1);
a step or two higher from these, the very lowest, infusoria
are found to possess the first rudiments of organs in the form of
cilia, which consist of minute elongations having a constant vibratory
motion, for the purpose of causing a current in the water in which they
live and bringing food into their vicinity.
Some very curious and complicated changes take place in the lowest of
the animals, very similar to those in the lowest vegetables; and what
has been called the life-history of these beings, often embraces a
great number of forms before the circle of their metamorphoses comes
round to the starting-point. Some of these phases of existence are
quite different from those going before and after them, and as the
vegetable free-cell at one time is capable of motion, it has long been
mistaken for an active living animalcule (the Protococcus pluvialis,
&c.), and there can be no doubt but that it will be found that many of
the lower forms of animated life described by Ehrenberg and others, and
still considered as such, will prove to be merely different stages of
the metamorphosis of the same protozoon; or it may be not an animal at
all, but a simple vegetable or protophyte.
[Illustration: FIG. 2.--VOLVOX GLOBATOR.]
Dr. Carpenter says, "It is quite certain that the Desmidiaceæ, like
the confervoid plants in general, grow at the expense of the inorganic
elements which surround them, instead of depending upon other living
beings for their subsistence, and that they decompose carbonic acid and
give off oxygen under the influence of sunlight. They have the power
of generating from these materials the organic compounds which they
require for their own development, and these are such as are formed by
other undoubted protophytes, as is proved by the application of the
appropriate tests." These "Desmidiaceæ" were long considered to belong
to the animalculæ, as were the "Diatomaceæ," "Volvox globator" (fig.
2), &c.
[Illustration: FIG. 3.--WHEEL ANIMALCULE (Rotifer vulgaris).]
Some of the Infusoria, however, have a far higher organisation, such
as the "Rotiferæ," and especially the "wheel animalcule" (fig. 3),
which at one time was supposed, absurdly enough, to possess a living
wheel turning round rapidly on its head! This wheel, however, proved
to be nothing else than a vortex of water produced by rotatory cilia.
This and many other mistakes were owing to the imperfect construction
of the microscopes of that date. These and their fellow animalcules
possess several organs, as a stomach, &c. The protozoa at one time
were supposed to possess a number of stomachs, and were thence called
"poly-gastric infusoria," but it has now been demonstrated that these
beings merely absorb or entangle portions of organic matter into
their substance, and that there are no cysts or stomachs for their
reception. Some of the Infusoria are able to withstand enormous changes
of temperature, without losing their vitality; cold far below freezing
point, and heat equal to boiling water does not destroy them, and they
may be dried in the most complete manner which chemists can devise,
and kept in this dry state for years, and yet, on the application
of moisture, return to life. There is no doubt but every inch of air
contains the germs of some of the Infusoria in a dry state or their
ova, and make up a portion of that fine halo of dust which always
appears in the air when a gleam of sunshine is let into a dark place.
The second class of the Radiata, the Entozoa, are those beings which
inhabit, as parasites, the intestines and other parts of animals. Their
history is very obscure, but there seems to be about twenty varieties
of these creatures, and a great number of animals have their peculiar
Entozoa. The best known in the human subject are the "Ascaris" or
thread-worm, the "Lumbricus Teres" or long-worm, and the "Tænia" or
tape-worm; this last is jointed, and grows to several yards in length.
[Illustration: FIG. 4.--SERTULARIA OPERCULATA (_a_, Natural
size, _b_, magnified).]
[Illustration: FIG. 5.--FRAGMENT OF SPONGE, MAGNIFIED.]
The third class, the Zoophyta, includes four orders. The first of
these, the Hydroida, comprise the Tubularia, Sertularia (fig. 4), and
Sponges (fig. 5); these are minute gelatinous creatures, secreting a
sort of tube in which they dwell. These tubes are congregated into
masses of different forms and colours, and, with other structures
totally different, are erroneously known by the general name of
"sea-weed." The Zoophyte which dwells in these tubes is furnished with
a set of cilia forming a sort of plume. Most of these Hydroida are
phosphorescent, such are those which, scattered about on the surface of
the sea, contribute to that luminosity so frequently seen.
[Illustration: FIG. 6.--GORGONIA GUTTATA (Natural size).]
The second order of the Zoophyta, Asteroida, are those which have a
star-like shape; they are congregated into compound structures, forming
what are called sea-fans (Gorgonia, fig. 6). These Gorgonia are of all
colours, and very beautiful; the animals or "polypes" are gelatinous,
and have a gelatinous mass or stalk with branches, strengthened and
supported by a horny centre. This gelatinous mass forms the animal
itself, as well as a sort of common integument connecting the whole
family of many thousands. The Gorgonia or sea-fans usually preserved,
are dry and hard, as the gelatinous covering has so little substance
that, when dried, it forms a rough powdery covering only to the horny
support. This powdery surface, if washed off with a little water
and placed under the microscope, is found to contain and be made up
of spiculæ or crystals of carbonate of lime, of various colours and
beautiful forms (fig. 7); these, when the animal is alive, help to
support its gelatinous frame; the Tubiporæ also belong to this class.
Fig. 8 represents the Organ-coral (Tubipora musica); it is of a bright
red colour, and, when the polypes are living, is a very beautiful
object.
[Illustration: FIG. 7.--SPICULES OF GORGONIA, MAGNIFIED.]
The third order of Zoophytes is the Helianthoida, which include the
"Actinia." These Zoophytes are entirely gelatinous, and have beautiful
variations of colour. They throw out tentacles like the petals of
a flower, and form very beautiful objects; they may be seen in the
aquatic vivaria of the Zoological Gardens. To this order of Zoophytes
belong the "corals" or Zoanthoid polypes, which produce the coral
reefs, extending in some cases hundreds of miles. Dr. Baird gives the
following account of them:--
"By far the greater part of the Zoanthoid polypes, as they grow,
deposit in the cellular substance of the flesh of their back an immense
quantity of calcareous matter which enlarges as the animal increases
in size, and, in fact, fills up those portions of the substance of
the animal, which by the growth of new parts are no longer wanted
for its nourishment, and in this manner they form a hard and strong
case, amongst the folds of which they contract themselves so as to be
protected from external injury, and by the same means they form for
themselves a permanent attachment which prevents their being tossed
about by every wave of the element in which they live. The stony
substances so formed are called corals, and their mode of formation
causes them exactly to represent the animal which secretes them. The
upper surface is always furnished with radiating plates, the remains
of the calcareous particles which are deposited in the longitudinal
folds of the stomach. These, in all probability were the constructors
of all the strata of limestone rocks, which form some of our largest
mountains--they were once the beds of seas, and were up-heaved by
internal forces. The Madrepores (fig. 9) are also of this order, and
form the stony matter in the same way. These are of various patterns,
and the beautiful brain-stones in the British Museum are of their
construction."
[Illustration: FIG. 8.--TUBIPORA MUSICA.]
The fourth order of Zoophytes are the Ascidioida, including formerly
the Flustræ (fig. 10), but of late these have been shown to be closely
allied, if not identical with, the Tunicated Mollusca, and have
received the name of Polyzoa, they will therefore be noticed under that
head.
[Illustration: FIG. 9.--CORAL (Madrepora brachiata).]
[Illustration: FIG. 10.--SEA MAT (Flustra foliacea), (A,
magnified, B, natural size).]
The fourth class of the Radiata, are the Radiaria, including two
orders. The first of these are the Acalephæ; the Medusæ or Jelly-fishes
belong to this order; these creatures float about sometimes in great
numbers, they are transparent and gelatinous, of a hemispherical form,
the flat surface being fringed round with fibres, some of which sting
like nettles if brought into contact with the skin.
The second order of the Radiaria include the Echinodermata or
Sea-hedgehogs, Star-fishes, &c., these are many of them furnished with
a profusion of spines, and hence their name; they are also called
Sea-eggs or Sea-urchins (fig. 11), and are mostly of a conical or
spherical shape, divided into five segments covered with minute holes,
from which project tentaculæ serving as organs of locomotion, touch,
&c., and the surface of the body is covered with shelly spines of
various forms and thicknesses; the mouth is in the centre, and they
feed upon marine productions. The spines, if cut across and ground
thin so as to be transparent, show a most complicated and beautiful
structure when under the microscope (fig. 12).
[Illustration: FIG. 11.--SEA-URCHIN (Echinus), WITH AND WITHOUT SPINES.]
[Illustration: FIG. 12.--SPINE OF ECHINUS (A, natural size, B, a
section magnified).]
The Star-fishes are inhabitants of the sea, and have generally five
arms covered beneath with tentaculæ having small suckers at the point,
it is by means of these that they move from place to place; the mouth
is in the centre. They live upon small marine animals, and have the
power of reproducing any of the rays which happen to be broken off; and
if cut into two or more pieces, each will produce a fresh animal. There
is a species of Star-fish, so brittle, that it is quite impossible
to touch it without breaking it, or rather it breaks itself, for it
seems to have the power of casting off its arms at pleasure. These
forms complete the Radiate series of animals, they have nearly all a
somewhat regular radiated form, and some of them are very beautiful,
such as Sertularia, which grow in communities and form many beautiful
branched objects, much resembling sea-weeds and flowers, hence the name
Zoophyte, which means animal flowers.
[Illustration: FIG. 13.--EARTH WORM (Lumbricus terrestris), leech
(Hirudo medicinale).]
The Articulata form the second division of the Invertebrata. It has
five classes, the first of which is the Annellata; in this order are
included the Worms and Leeches (fig. 13), these have no hard covering
but are soft throughout, they are made up of a number of soft rings
which encircle their bodies from one end to the other, and are capable
of being shortened or elongated by the muscles which draw together the
rings (these are placed longitudinally), or by those which contract and
widen them, placed circularly; this enables them to move along, and in
so peculiar a manner that it has received the name of "vermicular," or
worm-like. The most familiar example of this class is the Earth-worm
(Lumbricus terrestris), this lowly creature lives in soft mud and clay
and bores its way into the ground, in doing so it is assisted by a
slimy secretion which covers it, its food consists of earth containing
organic matter, this it swallows constantly and extracts what is fit
for its nourishment ejecting the remainder apparently unaltered; the
curious little heaps of soft dirt which are so often seen in wet
weather on the garden-paths, &c., are formed in this way. The Leech
is another familiar example of the Annellata or Annelidæ, this little
useful creature lives in ponds and stagnant waters, and feeds by
sucking the fluids of other animals (chiefly frogs and fish) with which
it will gorge itself till it is double its original size, it will then
remain (often for months) without food till it is all appropriated,
the process going on very slowly; a full-grown Leech is perhaps twenty
years old, they grow so slowly, (hence it is, that Leeches may be kept
for months after being gorged with blood without any food, and they
will live and be healthy). They are furnished with two suckers, one at
each end, and a mouth with numerous fine teeth placed in a tri-radiate
manner, with which they pierce the skin when about to feed. They move
in the water with great rapidity by a wavy motion of their bodies, but
on solid substances their mode of progression is that of adhering by
the sucker in front, then drawing the other one close up and extending
the body to its full length, taking hold again by the front sucker and
again bringing up the hindermost.
The Cirripeda constitute the second class of the Articulata, which
comprise the "Acorn shells" and "Barnacles" (fig. 14); these little
creatures were formerly described as Molluscs, but are now considered
to be articulate animals, and by some as Crustaceans. Dr. Baird gives
the following description of them:--"The Cirripeds are articulated
animals contained within a hard covering composed of several pieces and
consisting of calcified chitine. The body of the animal is enclosed in
a sac lined with the most delicate membrane of chitine, which in one
group is prolonged into a peduncle and contains the ova; the body is
distinctly articulated and placed with the back downwards."
[Illustration: FIG. 14.--A, SEA-ACORNS; B, BARNACLES (Cirripedes).]
Dr. Carpenter describes the young of the Cirripedes as not fixed like
the adult creatures, but moving about freely, and only becoming fixed
in the form of the usual acorn shell after undergoing several strange
metamorphoses, during which stages they more resemble the ordinary
Crustaceans than they do in their fixed state.
The Crustacea form the third class of the Articulata, they comprise
animals covered with a hard shell or carapace, like a case made up of
rings, with joints allowing the pieces to move upon each other, except
where several of them are consolidated to form the principal covering.
These rings generally amount to twenty-one in number, some composing
the claws, others the legs, &c. The shell is chiefly made of carbonate
of lime (chalk) held together by animal matter. The greater part of
the Crustacea inhabit the waters, and they cast their shells from time
to time as they grow; the Lobster (Astacus marinus), is a familiar
example, it is found in the sea near rocky shores, and is capable of
rapid motion under the water, darting along (tail foremost) with great
rapidity, it has powerful claws, with one of which (the blunt one)
it holds its food and with the other (the sharp one) cuts it up into
pieces; they have the power of casting off these claws and reproducing
them; they feed upon smaller Crustacea and fish, or any animal matter
they can find. The Cray-fish is another example, it is a sort of
fresh-water Lobster, living in holes (frequently deserted rat holes) in
the banks of rivers; its shell is very rough, but otherwise somewhat
resembles the Lobster. Crabs, Shrimps, and Prawns, are members of this
class (fig. 15).
[Illustration: FIG. 15.--CRUSTACEA.
1. Lobster (Astacus marinus).
2. Cray-fish (Astacus fluviatilis).
3. Crab (Cancer pagurus).
4. Shrimp (Crangou vulgaris).
5. Prawn (Palæmon serratus).
]
[Illustration: FIG. 16.--INSECTS.
1. Dragon-fly (Libellulina depressa).
2. Grasshopper (Gryllus).
3. Bee (Apis mellifica).
4. Fly (Musca domestica).
5. Butterfly (Pontia brassicæ).
6. Musk-beetle (Cerambyx moschatus).
]
The Insects form the fourth class of this division, and by far
the most important and numerous. They come to maturity only after
undergoing successive changes from the egg to the perfect animal;
these transformations are amongst the most wonderful things connected
with them. The eggs (some of which are very beautiful) are first
deposited in some safe place, either attached to a leaf or tied up
in a small bundle by silken threads spun by the parent insect, and
in some nutritious substance, so that when it comes to life it may
at once have food; this is sometimes in manure, sometimes in flesh,
and sometimes under the skin of a living animal (few are exempt from
this infliction), where they remain for a time and then come forth as
maggots, caterpillars, &c.; in this state they are called "larvæ,"
these are generally active creatures and eat most voraciously, which
seems to be the principal act of this state of their existence. These
larvæ frequently change their skins as they grow, and at last they
assume the next stage of their life, the pupa or chrysalis state,
which is one generally of complete inactivity; many of these larvæ,
weave themselves a covering of a sort of silk, to defend them while
in the pupa state--such as the Silkworm, whose covering (cocoon) is
the source of all the silk of commerce--others merely place themselves
in a situation of security. The pupa remains dormant for a certain
time, and then becomes the imago or perfect insect (the last state
of its existence), such as a Moth, a Butterfly, a Beetle, &c. These
are of different sexes, and in due time produce a batch of eggs and
then die; these eggs are often incredible in numbers, amounting to
many thousands--fortunately but few escape the watchful eyes of other
insects and of birds who feed upon them.
[Illustration: FIG. 17.--ANTENNA OF COCK-CHAFFER (Melolontha vulgaris).]
[Illustration: FIG. 18.--FOOT OF FLY, MAGNIFIED.]
Insects have six jointed legs, a pair of antennæ or horns (as they are
called) and generally one or two pairs of wings. The head is joined
to the body by a constricted neck, the part of the body to which it
is joined is called the thorax, and to this is added the posterior
part or abdomen; this part is extremely various in form in different
insects, in some it is round and full, in others long and extended.
The antennæ arise from the head, and are generally composed of eleven
pieces variously disposed; these wonderful organs are possessed of
great sensibility, and they certainly serve to convey information to
the insect, of the nature of one of the special senses; it was formerly
thought to be simply that of touch very much refined, or of smell, but
it is now generally considered to be that of hearing, or a modification
of it. The forms of the antennæ are very various, fig. 17 represents
that of the Cockchaffer (Melolontha vulgaris). The legs proceed from
the thorax, as do the wings, the abdomen giving rise to none of the
extremities; the feet of insects are all pretty much upon the same
model, some being more developed than others, they have a pair of hooks
or claws for catching and clinging to rough surfaces, and a pair of
cushions or pads, covered in some cases with suckers. The foot of the
Fly (fig. 18) is well developed in this particular, enabling it to walk
with perfect ease even on glass or the smoothest surface, and in any
position. Insects do not breathe by lungs or gills, but by means of
branched tubes called "tracheæ," which convey the air to the interior
of the animal. On the surface of these, the blood vessels ramify,
giving out the carbonic acid of the blood and receiving oxygen; the
openings to these air-tubes are arranged along the sides of the body,
and are called "spiracles" (fig. 19). They are curious objects under
the microscope, some of them being closed by a perforated membrane,
others have a sort of sieve or network of fibres, and most of them a
contrivance to catch and exclude minute particles of matter floating in
the air, and thus prevent their entry into the tracheæ. Insects have
two eyes, one on each side of the head, which are of great size, often
forming complete hemispheres; each eye is made up of several thousand
separate eyes or "ocelli," hence they are called compound eyes; these
ocelli are placed closely together, so as to form a sort of honeycomb
arrangement; the appearance of a part of one of these eyes is shown in
fig. 20.
[Illustration: FIG. 19.--SPIRACLE.]
[Illustration: FIG. 20.--COMPOUND EYE.
(1, perpendicular section; 2, surface.)]