Before speaking of insects, my dear child, it will be necessary, in
the first place, to tell you to what primary division they belong and
on what characters this division has been established. And here I find
myself in a difficulty. We have been but too learned already, and now
we run the risk of becoming still more so, if we commence an attack
on the three primary divisions which follow the vertebrates. We shall
have to encounter terrible names and tedious details, besides having
to take into account a thousand things of which we have not yet spoken.
We are going on quietly with the history of the feeding machine which
occupies the middle of the body, and learned men never looked in that
direction for the establishment of their divisions; between ourselves,
it was not accommodating enough. They have fallen back upon the
locomotive apparatus (_movement machine_) which affects the body
all over, and which they have proclaimed to be the leading feature of
the animal organization, without noticing however that it is, after
all, but the servant of the other. It is true that the great divisions
are more easily established upon this point than the other, because
the differences are more decided. It separates what the other unites,
and thus it is that nature carries on that beautiful combination which
the Germans have so accurately named "_Unity in Variety_" that
is to say, she is always at work, as I have already told you, on the
same canvas, but always embroidering it with a different pattern.
Wait! I have something to promise, if you are very good, and if this
history (that of the feeding machine) should have given you a taste
for inquiry. I will tell you another time the history of the movement
machine, and there the classification of our learned men will come in
naturally very well. In the meantime we will do as they do, and just
shut our eyes to their divisions, in which the feeding machine can
have no interest, because they were established without reference to
it. We will content ourselves, then, without further pretension to
science, with modestly examining the last transformations of our pet
machine in the principal groups of the inferior animals; of which
groups I will now tell you the names in their proper order. They are
as follows: Insects, Crustaceans, Mollusks, Worms, and Zoophytes. You
must take these names on trust; those which you do not understand will
be explained in their places.
1. _Insects._--I know not where it was I once read that there are
said to be something like a hundred thousand different species of
insects; and I verily believe this is not all. Of course we shall not
attempt to review the whole of this formidable battalion. Let us take
one of those you are most familiar with--the cockchafer, for
instance--and examine what goes on in his inside. The history is nearly
that of all the others.
"Fly away, cockchafer, fly!" says the song; and surely it is a bird
that we have here, and a bird which will appear to you even more
wonderful than those of which I have already spoken, when you have
considered the simplicity, and at the same time the strength, of his
organization. His mode of flight is rather lumbering, it is true; he
is, in comparison with the large flies, what the ox is to the deer;
but when you contrast the weight of his thick body with the delicacy
and narrow dimensions of the two membranes which sustain him in the
air, you may well ask yourself how those little morsels of wings, thin
as gold-beater's skin, can carry such a mass along. In fact, they only
accomplish this feat of strength by dint of an excess of activity
almost startling to think of. When you run as fast as you can, how
many times, think you, do you move your legs in one second? You would
be somewhat puzzled to say; and so should I: but I defy you to count
ten. Now the bird makes his wing move much oftener when he beats the
air with rapid blows as he flies; but even he does not strike a hundred
strokes in a second: and what is this to the feats of the cockchafer's
wing? It is not hundreds but thousands of times that he flaps his wings
in a second; and here let me hint, by-the-by, that when people seriously
wish to find out a method of travelling in the air, they will lay aside
balloons, of which they can make nothing in their present condition,
and will set to work to fabricate machines with wings which shall beat
the air as fast as those of the cockchafer. This sounds extravagant,
but I have seen an electric pile fixed in a stand with glass feet,
which caused a little hammer to beat thousands of times in a second:
and surely the hammer could have been made to communicate its movement
to a small wing! Forgive me this little castle in the air! The idea
came into my head a long while ago, and the cockchafer has just reminded
me of it. I will not, however, pursue the subject, neither will I offer
to explain the method used for counting the beats of an insect's wing.
That would carry us farther than would be desirable.
To return to our little animal. I leave you to imagine the enormous
amount of strength required for such precipitate motion. We have spoken
of the rapid course of the blood in birds during flight: who shall
calculate its comparative rate in this fabulously wonderful locomotive,
the cockchafer? And if we lift up the cuirass which encases it, what
do we behold? Not a single trace of all the complicated
circulation-apparatus you have learnt to know so well; neither heart
nor veins nor arteries; only a quantity of whitish liquid, equally
distributed throughout the whole internal cavity. Not a trace of lungs,
nor any apparent means of renovation for this seemingly motionless
blood; for blood it is, in spite of its color, or, at any rate, blood
in its first stage of formation. It also has its globules--ill-formed,
it is true, and altogether in balls--like those found in the chyle
with us; which chyle, be it observed, is the same color as the blood
of insects, and may also be considered blood in its apprenticeship.
By what magic, then, is this raw, imperfectly-formed steward, who seems
altogether stationary, enabled to accomplish exploits which would
stagger his higher-bred compeers, agile and perfected as they are?
Where does he pick up the oxygen necessary for such repeated movements,
it being an established fact that no animal can move at all without
consuming oxygen, and that the quantity consumed is in proportion to
the rate of motion? Look under his wings for an answer. There, all
along his body, you will observe a number of small holes, pierced in
a line, at regular distances, and furnished with shutters of two kinds.
They are the mouths of what are called _tracheæ_, or breathing
tubes: and from them branch out a multitude of little canals, which,
spreading in endless ramifications through every part of the body,
convey to the whole mass of the blood, from all directions, the air
which makes its way into them through the tracheal holes. In this case,
you see, it is not the blood which seeks the air, but the air which
seeks the blood; whence arises a new system of circulation, whose
action is all the more energetic because it is unintermitting, and
makes itself felt everywhere at the same time. A little while ago we
were wondering at the twofold respiration of birds; yet this is far
less surprising than the universally-diffused respiration of insects,
who may well be able to do without lungs, seeing that their whole body
is one vast lung in itself.
For the rest, do not trust to appearances, nor imagine that the blood
of our friend the cockchafer in reality remains motionless around the
air-tubes, idly drinking in the oxygen which is brought to it. Though
not flowing in enclosed canals, it is not the less continually displaced
by regular currents, which sweep through and renew this apparently
stagnant pool. Nor is this the only instance of such a current presented
to us by nature.
Guess, however, if you can, where you will have to look for the
counterpart to the circulation of the cockchafer. In ocean itself!
But, remember, nothing is absolutely little or great in nature, who
applies her laws indifferently to a world as to an atom. The blood of
our world is water, which contains in itself all the germs of fertility,
and without which, as I have already told you, life is impossible
either in the animal or vegetable kingdom. The water of brooks, streams,
and rivers, flows along in channels, which, when figured in a map,
present to the eye of the beholder an exact picture of the system of
circulation found in the vertebrated animals. But the waters of the
sea are borne along, like the blood of insects, by a secret circulation,
which cannot be represented on the map; _i.e._ by immense currents
everlastingly in action, some on the surface, some in the mid-heart
of the ocean, which drive it in ceaseless course from the equator to
the poles, from the poles to the equator; so that the Supreme
Intelligence, in His overruling providence, has ordained the same law
to set in movement the immensity of ocean, and to effect circulation
in the cockchafer's few drops of blood. In the latter we find the
moving agent to be a long tube, which runs the whole length of the
back, and is called the dorsal vessel (from the Latin _dorsum_,
back). I told you that the cockchafer had no heart under his cuirass,
but I spoke too hastily. The dorsal vessel is a _true heart_, but
a heart devoid of veins or arteries, and thrown into the midst of the
blood. It dilates and contracts like ours, sucks in the blood by means
of side-valves, which act as our own do, and drives it back again into
the mass by that valve at its extremities, which opens near the head.
From thence arises a continued to-and-fro movement, which sends the
blood from the head to the tail, and brings it back again from the
tail to the head. But who would recognise, in this simple primitive
organisation, where all seems to go on of its own accord, as it were,
the same machine, with all its complicated movements, that we have
been so long considering?
Well, in this apparently universal shipwreck of all the organs we know
so well, there is yet one which survives, and remains the same as ever,
namely, the digestive tube. I began by saying the insect is a bird.
His digestive tube is formed upon the same pattern as that of birds,
so that naturalists have bestowed the same names on the various parts
in each of them. After the oesophagus comes a crop (_jabot_), very
distinctly indicated; then a gizzard with thick coats, in which the
food is ground down. The hen, if you remember, swallows small pebbles,
which perform in her gizzard the office of the teeth in our mouths.
The cockchafer has no need to swallow anything. His gizzard is furnished
with little pieces of horn; real teeth, fixed in their places, which
have a great advantage over the chance teeth picked up at random by
the hen. I pointed out to you in birds, between the crop and the
gizzard, a swelling or enlargement of the digestive tube, pitted with
small holes, where the food is moistened by juices. The same enlargement
is found here, covered all over with a multitude of small tubes, which
might easily be mistaken for hairs, from which also falls a perfect
shower of juices. The only difference is, that it comes after the
gizzard, instead of before it, as in birds. Some naturalists,
considering that the manufacture of chyle takes place here, have called
it the _chylific ventricle;_ [Footnote: The corresponding
protuberance of the birds bears a name, somewhat similar, but stillmore
barbarous. I had passed it over in silence, because, I make the
confession in all humility, I do not understand it; but a remorse now
seizes me: it is called the _Ventricule succenturie._] a somewhat
barbarous name, but one which explains itself, and might with truth
be applied to the _duodenum_ of the higher animals. Bile is poured
in close to the hinder end of it, but you must not look for the liver;
it has disappeared, or rather its form is entirely changed. You remember
what the _pancreas_ had become in fishes; _i.e._ a row of tubes giving
out a _salivary fluid._ Such is exactly the appearance of the liver in
the cockchafer.
Instead of that fleshy substance on which hitherto the office of
preparing the bile had devolved, you see nothing but a floating bundle
of long loose tubes, which, opening into the intestines, pour in their
bile. The organ is transformed, but we recognise it again by the office
it performs, which continues the same. As to the _pancreas_ it is
wanting here, as in the fish with salivary glands; but in its place
in many insects other tubes, acting also as glands, pour saliva into
the _pharynx; i. e._, the cavity at the back of the throat.
As you see, therefore, everything is found complete in this tube of
a few inches long; and you can also distinguish there a small and a
large intestine. We are speaking of the cockchafer, which feeds on the
leaves of trees; and it is for this reason I name some inches as the
length of the digestive tube. This would not be longer than the body
itself, had it been destined, as in the case of many other insects,
to receive animal food. In fact, the law which we have shown to exist
with regard to the ox and the lion, rules also over the insect-world;
and whilst a radical change seems to have been made in the rest of the
organisation, here everything is in its place, and we find ourselves
in the same system.
Was I not justified in asserting that the unity of the animal plan is
to be found in the digestive tube? and that this is the unchanging
basis upon which the Creator of the animal world had raised his varied
constructions?
How would it be, then, if we were to take the insect from its
starting-point when it is only a worm, that is to say, merely and
simply a digestive tube? for I am only telling you a small portion of
its history here; a history you must know, which reveals a miracle
still more wonderful than the transformation of the little tadpole
into the frog! There is a brilliant-colored fly which comes buzzing
about the meat-safe--the bluebottle--do you know her? It is on her
account that we put large covers of iron wire over the dishes of meat;
but, perhaps, you never troubled yourself to think why.
But the truth is, she only comes there to deposit her eggs in the good
roast-meat; and if she could get near enough to do so, you would soon
afterwards see it swarming with little white worms, which would entirely
take away all your appetite. These worms are only flies out at nurse,
and they will find their wings by-and-by if you only give them time
enough. Disgusting as they may appear on a dining-table, I assure you
they deserve more interest than you may think. When we come to speak
of worms, we will ask of them to let out the secret of the mysterious
transformations of animals.
In the meantime, let us finish the observations we were making on the
_perfect insect_, as this little creature is called when he has
passed through the intermediate stages which separate him from the
undeveloped condition. Forgive me, my dear child, here I am speaking
to you as if you were a grown-up woman! This is because it is so
difficult to explain things of this sort in any other way. And now
that you have been introduced into the midst of the wonders of creation,
you ought to familiarise yourself with the ideas and terms they have
suggested to mankind. I began with you as a child, and great would be
my triumph if I could leave you a grown-up girl! And I flatter myself
that I have so far set your brain, to work, under pretence of amusing
you, that this hope is not altogether unfounded. I found it necessary
to say this to you in confidence, because I have just read over our
first conversations, and perceive that I have insensibly put you on
a different diet from the one I began with. I am obliged to comfort
myself by remembering that you have grown older since, and that you
are now acquainted with a great many things which you had never heard
spoken of then. And this is the secret of all transformations. We crept
on at first over ground that was quite unknown to us; but as we went
along, our wings must have begun to grow, and we are now able to fly
a little!
Do not be afraid, however; I will exercise your tiny butterfly-wings
very carefully just at present. We have only to examine what becomes
of the _chyle_ of the cockchafer after it has been prepared in
the pretty little tube so finely wrought. We men have _chyliferous_
vessels which draw up chyle from the intestines and throw it within
a short distance of the heart, into the torrent of blood, where its
education is completed. But the cockchafer, who has no other vessels
than his air-pipes, and the _dorsal tube_, which has no communication
with the intestines, what is he to do? Do not distress yourself about
him. Make a tube of a bit of linen, well sewn together, and fill it with
water. Sew it together as firmly as you may on all sides, the water will
have no difficulty in escaping through the meshes. And this is just what
happens with the little tubes found in animals, the coats of which are
formed of interwoven fibres. By-the-by, from thence comes their name of
"_tissue_," which they share in common with all the solid substances of
the body, for all were once supposed to have the same general structure.
The intestine of the cockchafer floats, did I not say? in the lake of
blood which fills the whole cavity of the body. Well, then, the chyle
has only to penetrate through these coats, to go where it is wanted.
Hence it is not at all surprising that this blood should be white; and I
have very good reasons just now for comparing it to our _chyle_. It is,
indeed, chyle arriving directly from the place of its manufacture,
without undergoing any other process; by which you may see that this
little machine (of the digestive organs of the cockchafer), though
differing in appearance so entirely from our own, is reducible to the
same elements of construction, and that life is maintained by the same
process as with us; namely, by the action of the air upon the albumen
extracted from food. The cockchafer, it is true, is much further removed
from being a fellow-creature of ours than even the horse; but the
principle of life is the same with him as with us. And this is quite
enough to cause children, who can feel and reason, to think twice before
they begin to torture, by way of amusement, a creature whose life the
God of goodness has subjected to the same conditions as our own. I speak
this to those miserable little executioners who make toys of suffering
animals: but the case is different with agriculturists, who have
necessarily to contend with the devourers of their harvests, and whom,
I admit, it would not be reasonable to bind down by the maxim of Uncle
Toby.
[Footnote: I have introduced my Uncle Toby, who really has nothing
to do here, in order to make you acquainted with a few lines of Sterne,
which I wish I could place before the eyes of every child in the world.
"Go!" said he, one day at table, to an enormous fly which had been
buzzing around his nose and had cruelly tormented him all dinner time.
After many attempts, he finally caught him in his hand. "Go! I will
not do thee any harm," said my Uncle Toby, rising and crossing the
room with the fly in his hand; "I would not hurt a hair of your head.
Go!" said he, opening the window and his hand at the same moment, to
let the fly escape; "go, poor little devil; away with you; why should
I do you any harm? the world is certainly large enough to contain both
of us!"]
But now to finish with the cockchafer. We have got to examine one very
important part of his body, that which in other animals has been the
one most talked about ever since we began our study: I mean the mouth.
You know that this is the essentially variable point in the digestive
tube; so that you will not be much surprised, should we find he has
something altogether new. The mouth of the cockchafer is composed of
a great number of small pieces placed externally round the entrance
to the _alimentary canal_; but the names of these, as they would
not interest you, I will not enter upon with you; more especially as
they refer to such tiny morsels, that you would have great difficulty
in finding them again on the owner. Of these pieces only two are worth
our attention. These are two bits of extremely hard horn, placed one
on each side of the animal, which are called "_mandibles_" and
which serve the cockchafer to cut up the leaves which he eats. Fancy
your share of teeth being two huge things fixed in the two corners of
your mouth, each advancing alone against the other till they meet under
the nose! You would then attack your tarts with the weapons of the
cockchafer! You would not, however, be able to bite them straight
through from the top to the bottom, as is done by all the animals whom
we have yet seen. It is this which so peculiarly distinguishes the
insect's manner of feeding; for we have already been taught by the
bird and the tortoise, that it is possible to eat with two pieces of
horn. The cockchafer now shows us how to eat sideways; but this is
merely an accessory detail. It does not affect what happens after the
mouthful is swallowed. All insects, however, have not this peculiarity.
The cockchafer belongs to the category of grinding insects as they are
called, who bite their food: but there is the category of the sucking
insects (or suckers), whose food consists of liquids; and these insects
are furnished in a different manner.
In the innocent butterfly, who lives on the juice of flowers, the
digestive tube terminates externally in a sort of _trunk,_ twisted
in several convolutions, which is nothing more than an exaggerated
elongation of the two jaws, which become hollow within, and form a
tube when joined together. When the insect alights on a flower, he
suddenly unrolls this trunk, and sucks in the juices from the depth
of its "corolla," as you would drink up liquid with a straw from the
bottom of a small vial. Amuse yourself some summer's day by watching
a butterfly in his labors amongst the flowers: sometimes he stops
still, but oftener he is contented to hover over them; and, as he does
so, you will see a little loose thread, as it were, move backwards and
forwards as fast as possible: this is his trunk, which he darts out,
while flying, into the corolla of the flowers, but which scarcely seems
to touch them, so delicate is its approach.
Less inoffensive far is the trunk of the mosquito-gnat, and of all the
detestable troop of blood-sucking flies. It is always a tube; but this
tube is no longer a simple straw, but a sheath furnished with stilettos
of such exquisite delicacy and temper, that nothing is comparable to
them; and these, as they play up and down, pierce the skin of the
victim, like the lancets of the lamprey, and, like them, draw in blood
as they retreat.
Finally, amongst the _parasites,_ the last and lowest group of
insects, the stiletto-sheath is reduced to the size of a kind of little
tube-shaped beak, which, when not in use, folds down like the fangs
of the rattlesnake.
You do not know, perhaps, what a parasite is. The word comes from the
Greek, and signifies literally, "_that which moves round the
corn._" The Greeks applied it to those shameless paupers who, to
escape honest labor, made their way into the houses of the great, and
enjoyed themselves at their expense. These parasites are little animals
which settle themselves on large ones, to suck in, without having
worked for it, the blood which the others have manufactured. The wolf
hunts, fights, and tears its victim in pieces; and then, by means of
that interior labor which I have spent so much time in describing,
transforms it into nourishing liquid: and when all this is accomplished,
the little flea, who lives hidden among his hairs, coolly draws out
for his own use the valuable blood obtained with so much effort. There
are many parasites in the world, my dear child--yourself, for instance,
to begin with--who are perfectly happy to chew your bread without
asking where the corn comes from which made it. But you have heart
enough to see plainly that this indifference ought not to last, and
that it is not honorable to go on living in this indefinite manner at
other people's cost only.
You will some day have duties to fulfil, which you should accustom
yourself to think of now, in order that you may prepare yourself for
them beforehand, so that it may never hereafter be said of you that
you passed through the midst of human society, taking from it all you
needed, without giving it back anything in return, I advise you to
conjure up this idea when the time comes to leave off playing and begin
preparing to be of use. The sort of thing is not always very amusing,
I admit, but you must look upon it as the ladder by which you will be
enabled to rise from the degradation of a parasitical life. If you
were in a well, and some one were to let down a real ladder for you
to get up by, I do not think you would complain of the difficulty of
using it. It is for you, then, to consider whether you would like to
remain for ever in your present condition; for those who learn nothing,
who _submit_ to nothing, who are good for nothing, but to show
off and amuse themselves--these remain parasites all their lives in
reality, however little they may sometimes seem to suspect it.
At your age, however, there is still no disgrace in the matter. God
shows us by the insects that little things are allowed to be
parasitical; but on this subject I must return to a point in the history
of animals which I touched upon before. I told you, in speaking of the
crocodile, that the perfect state of the inferior animals is found
represented in the infancy or less perfect state of those above them:
and I may say the same again with regard to insects. All the young of
the mammalia begin life as parasites, at least, as sucking animals:
for they all live at first on their mother's milk, which is nothing
more than blood in a peculiar state. But the name of parasite among
insects is generally confined to those which take up their abode on
the bodies of their hosts; though in common justice it might equally
well be applied to the gnat and his relations, who, when once full,
make their bow and are off, like the kitten when he has finished
sucking. Well, without meaning to find fault, if we descend to the
lower ranks of the mammals, we shall find among them many parasites
in the received sense of the word. You remember the pouch to which the
marsupials owe their odd name. The young kangaroo remains hidden for
months in the pouch of its mother, feeding continually all the time;
and it is then a strict parasite. During the four following months it
goes in and out, and strolls about between meals, like other young
ones of its class, and is then an animal at nurse affording thus a
twofold example of the tendency of the great Creator to repeat Himself
in His conceptions, here using for the infancy of the mammal the system
invented for adult insects--elsewhere repeating the butterfly in the
humming-bird, who may fairly be called a vertebrated butterfly, and
reproducing the gnat in the vampire-bat, which I look upon as an
enlarged and perfected revise of the original pattern, whence comes
the scourge of our sweet summer nights.
And now, surely, I have said enough about these parasites, whose very
name, I suspect, will make you shudder after my impertinent application
of it. Never mind: it depends entirely upon yourself to get rid of
whatever you find humiliating in the position I have hinted at. Do all
you can to bring happiness to the parents on whom you live at present,
and who give their life-blood so willingly for your good. God has made
you very different from those little animals who have neither heart
nor reason to guide them. Do not be like them, then, in conduct. By
a little obedience and love--child as you are--you can pay them back
what you owe, and they will never complain of the bargain.