A SHORT ESSAY ON LEGS--TAKING A WALK--BRITISH FAKIRS--INSECT
LIFE--DEVELOPMENT--THE TIGER MOTH--GROWTH OF THE
CATERPILLAR--HOW TO DISSECT INSECTS--PLAN OF CATERPILLAR
ANATOMY--SILK ORGANS--ORGANS OF RESPIRATION--SPIRACLES AND
THEIR USE--WONDERS OF NATURE--THE CHRYSALIS--SCIENTIFIC
LANGUAGE.
As, in common with many other animals, mankind are furnished with legs,
and the power to move them, it is universally acknowledged that those
limbs ought to be put to their proper use. But while men agree respecting
the importance of the members alluded to, they differ greatly in the mode
of employing them.
To the tailor, for example, legs are chiefly valuable as cushions,
whereon to lay his cloth. For the jockey, the same members form a
bifurcated or pronged apparatus, by the help of which he sticks on a
horse. The legs of the acrobat are mostly employed to show the extent of
ill-treatment to which the hip-joint can be subjected without suffering
permanent dislocation. The dancer values his leg solely on account of the
“light fantastic toe” which it carries at its extremity. The turner sees
that two legs are absolutely necessary to mankind--_i.e._, one to stand
upon, and the other to make a wheel run round. The surgeon views legs--on
other people--as objects affording facilities for amputation. The boxer
professionally regards his legs as “pins,” upon which the striking
apparatus is kept off the ground. The soldier’s opinion of his legs is
modified according to the temperament of the individual, and the position
of the enemy. Some people employ their legs in continually mounting the
same stairs, and never getting any higher; while others use those limbs
in continually pacing the same path and never going any farther.
And of all these modes of employing the legs, the last, which is called
“taking a walk,” is the dreariest and least excusable.
For, in the preceding cases, the owners of the legs gain their living,
or at all events their life, by such employment of those members; and
in the case of the interminable stairs, the individual is not acting by
his own free will. But it does seem wonderful that a being possessed of
intellectual powers should fancy himself to be the possessor of a right
leg and a left one, merely that the right should mechanically pass the
left so many thousand times daily and in its turn be passed by the left;
while the sentient being above was occupied in exactly the same manner as
if both legs were at rest, snugly tucked under a table.
Sad to relate, such is the general method of taking recreation.
A man who has been over-tasking his brain all the early part of the day,
rises corporeally from his work at a certain time, places his hat above
his brain, buttons his coat underneath it, and sallies forth to take a
walk.
Whatever subject he may be working upon he takes with him, and on
that subject he concentrates his attention. Supposing him to be a
mathematician, and that the prevalent idea in his mind is to prove that △
A B C = (∠ D E F + ∠ G H I). He takes one final look at his Euclid while
drawing on his gloves, and sets off with A B C before his eyes.
As he walks along, he sees nothing but A B C, hears nothing but D E F,
feels nothing but G H I, and thinks of nothing but the connection of all
three.
An hour has passed away and he re-enters his room without any very
definite recollection of the manner in which he got there. He has
mechanically paced to a certain point, mechanically stopped and turned
round, mechanically retraced his steps, and mechanically come back again.
He has not the least recollection of anything that happened during his
walk; he don’t know whether the sky was blue or cloudy, whether there
was any wind, nor would he venture to say decidedly whether it was
night or day. He _does_ recollect seeing a tree on a hill and a spire
in a valley, because, together with himself, they formed an angle that
illustrated the proportions of the triangle A B C; but whether the tree
had leaves or not he could not tell. But he is happy in the consciousness
of having performed his duty;--he has taken a walk, he has been for a
“constitutional”.
O deluded and misguided individual! The walking powers are meant to carry
yourself--not only your corporeal body--into other scenes, to give a
fresh current to your thoughts, and to give your brain an airing as well
as your nose. The mind requires variety in its food, as does the body;
and to obtain that change of nutriment is the proper object of taking a
walk.
That a rational being can condemn himself to walk three miles along a
turnpike road, and three miles back again, at one uniform pace, his eyes
directed straight ahead, and his thoughts at home with his books, seems
incredible to ordinary personages.
Yet, such British fakirs may be seen daily in all weathers, on the roads
leading from university towns, going at the rate of four miles per hour,
their hats tilted towards the back of their heads, their bodies inclining
forward at an angle of eighty degrees, their lips muttering polysyllabic
language, and their eyes as beaming as those of a boiled cod-fish.
Now the real use of taking a walk is to get away from one’s self, and to
change the current of the thoughts for a while, by changing the locality
of the individual.
In order so to do, he should cast his senses abroad instead of
concentrating them all within himself; and from sky, air, water, and
earth draw a new succession of images wherewith to relieve the monotony
within. There are various modes of attaining this object; and each man
will follow that mode which most accords with his own character.
For example, if he is an astronomer, he will look to the heavenly
bodies; if a geologist, his eyes will be directed to the earth; if a
botanist, his mind seeks employment among the vegetable productions; if
a meteorologist, the wind’s temperature and atmospheric phenomena will
claim his attention; if an entomologist, he will find recreation in
watching the phases of insect life, and so on.
It is evident enough that to treat of all these subjects would render
necessary a volume that numbered its pages by thousands, and its volumes
by at least tens; and therefore, in a work of this nature, it must be
sufficient to lay particular stress on one portion, to treat slightly of
others, and to leave many entirely untouched. And that portion on which
I shall lay the chief stress is that which is brought more constantly
before the eye and ear than any other, namely, the entomological
department.
As, when approaching cities, the “busy hum of men” is the first
indication that meets the ear, so in the country the busy hum of insects
is, next to the song of the birds, the sound that gives strongest
evidence of a life untrammelled by the artificial rules of society.
Not only do insects make their presence known to the ear, but they also
address themselves to the eye. Their forms may be seen flitting through
the air, running upon the ground, or making their abode on the various
examples of vegetable life. Comparatively small as insects are, they are
of vast importance collectively; and there is hardly a leaf of a tree, a
blade of grass, or a square inch of ground, where we may not trace the
work of some insect. Nearly all strange and curious objects that are
noticed by observant eyes in the woods or fields are caused by the action
of insects, and are often the insects themselves, in one or other of the
phases of their varied life. Certain examples of insect life, and its
effects, will now be given. No particular order will be observed, no long
scientific terms will be used, and every creature that is mentioned will
be so common that it may be found almost in every field.
The first creature that we will notice is that caterpillar which is so
abundantly found at several seasons of the spring and summer, and, from
the long hairy skin in which it is enveloped, goes by the popular name
of the “Woolly Bear!” A figure of this creature may be seen in plate B,
fig. 5 _a_. This creature is the larva of the common Tiger-moth, which is
represented on the same plate, fig. 5.
It will be necessary to pause here a little, before proceeding to the
description and histories of the various insects, because in the course
of description certain terms must be used, which must be explained in
order to make the description intelligible.
In the first place, let it be laid down as a definite rule, that
INSECTS NEVER GROW.
Many people fancy that a little fly is only little because it is
young, and that it will grow up in process of time to be as big as a
blue-bottle. Now this idea is entirely wrong; for when an insect has once
attained to its winged state, it grows no more. All the growing, and most
part of the eating, is done in its previous states of life; and, indeed,
there are many insects, such as the silkworm-moth, which do not eat at
all from the time that they assume the chrysalis state to the time when
they die.
It is a universal rule in nature, that nothing comes to its perfection
at once, but has to pass through a series of changes, which if carefully
examined can mostly be reduced to three in number. Sometimes these
changes glide imperceptibly into each other, but mostly each stage of
progress is marked clearly and distinctly. Such is the case with the
insect of which we are now considering; and when we have examined the
development of the Tiger-moth through its phases of existence, we have
the key to the remainder of the insects.
After an insect has left the egg, and entered upon the world as an
individual being, it has to pass through three stages, which are called
larva, pupa, and imago.
The word “larva,” in Latin, signifies “a mask,” and this word is used
because the insect is at that time “masked,” so to speak, under a
covering quite different from that which it will finally assume. In the
present instance, the Tiger-moth is so effectually masked under the
Woolly Bear, that no one who was ignorant of the fact would imagine two
creatures so dissimilar to have any connection with each other.
Throughout this work the word “larva” will be always understood to
signify the first of the three states of insect life, whether it be a
“caterpillar,” a “grub,” or a “worm”.
In its next stage the insect becomes a “pupa,” which word means a
“mummy,” or a body wrapped in swaddling clothes. This name is employed
because in very many insects the pupa is quite still, is shut up without
the power of escape, and looks altogether much like a mummy, wrapped
round in folds of cloth. In the moths and butterflies the insect in
this stage is called a “chrysalis,” or “aurelia,” both words having the
same import, the first Greek and the other Latin, both derived from a
word meaning “gold”. Several butterflies--that of the common cabbage
butterfly, for example--take a beautiful golden tinge on their pupal
garments, and from these individual instances the golden title has been
universally bestowed.
The last, and perfected state, is called the “imago,” or image, because
now each individual is an image and representative of the entire species.
The Woolly Bear, then, is the larva of the Tiger-moth; and if any
inquiring reader would like to keep the creature, and watch it through
its stages, he will find it an interesting occupation. There is less
difficulty than with most insects, for the creature is very hardy, and
the plant on which it mostly feeds is exceedingly common.
Generally, the Woolly Bear is found feeding on the common blind nettle,
but it may often be detected at some distance from its food, getting over
the ground at a great rate, and reminding the spectator of the porcupine.
In this case it is usually seeking for a retired spot, whither it resorts
for the purpose of passing the helpless period of pupa-hood.
If it is captured on such an occasion, there will be little trouble in
feeding, as it will generally refuse food altogether, and, betaking
itself to a quiet corner, prepare for its next stage of existence.
If taken at an earlier period of its life, it feeds greedily on the
nettle above-mentioned, and the amount of nutriment which one caterpillar
will consume is perfectly astounding. I once had nearly four hundred
of them all alive at the same time, and they used to be furnished with
nettles by the armful. Of course so large a number is not necessary for
ordinary purposes; but this regiment was required for the purpose of
watching the development and anatomy of the creature through its entire
life.
As the skins of caterpillars are not capable of growth, and the creature
itself grows with singular rapidity, it is evident that the skins
themselves must be changed, as is the case with many other animals of a
higher class, such as the snakes, newts, &c.
For this purpose the skin of the caterpillar splits along the back of the
neck, and by degrees the creature emerges, soft, moist, and helpless. A
very short time suffices for the hardening of the new envelope; and as
the caterpillar has been obliged to fast for a day or two, previously to
changing the skin, it sets to work to make up for lost time, and does
make up effectually.
In the case of the Woolly Bear, and several others, the cast skin retains
nearly the same shape and appearance as when it formed the living
envelope of the caterpillar; and, consequently, if any number of these
insects are kept, the interior of their habitation soon becomes peopled
with these imitation caterpillars. Each individual changes its skin some
ten or eleven times, each time leaving behind it a model of its former
self, so that caterpillars seem to multiply almost miraculously.
Although even the exterior appearance of an insect is very wonderful,
yet its interior anatomy is, if possible, even more wonderful, and, if
possible, should be examined. The mode of doing so is simple and easy.
If the Woolly Bear, for example, is to be dissected, the easiest mode of
doing so is as follows:--
Get a shallow vessel, glass if possible, about an inch or so in depth;
load a flat piece of cork with lead, put it at the bottom of the vessel,
and fill it nearly to the top with water. Now take the caterpillar, which
may be killed by a momentary immersion in boiling water, or by being
placed in spirits of wine, and with a few minikin pins fasten it on its
back on the cork. The pins of course must only just run through the skin,
and two will be sufficient at first, one at each end.
Now take a pair of fine scissors, and carefully slit up the skin the
entire length of the creature, draw the skin aside right and left, and
pin it down to the cork.
The creature will now exhibit portions of organs of different shapes and
characters, the remainder being concealed under the mass of fat that is
collected in the interior. This fat must be carefully removed in order
to show the vital organs; and this object is best attained by using a
fine needle stuck into a handle. I generally use a common crochet-needle
handle, so that needles of various sizes can be used at pleasure.
Now will appear a number of organs closely packed together, and mostly
stretching along the entire length of the creature. In order to assist
the inquirer, I here present a plan or chart of the interior of the
caterpillar when thus opened. It must be understood that the drawing is
not meant to represent the particular anatomy of any one species, but
to give a general view, by means of which the anatomical details of any
caterpillar may be recognised. And in order to give greater distinctness,
only one of each organ is seen, though with the exception of the
intestinal canal, there is a double set of each organ, one on each side.
Running in a straight line from head to tail is seen the digestive
apparatus, consisting of throat, stomach, and intestines, with their
modifications; and this apparatus is marked A A in the cut.
[Illustration: INTERIOR OF CATERPILLAR.]
On the surface of the digestive apparatus, and straight along its centre,
lies the nervous system, represented by tiny white threads dotted at
regular distances by rather larger spots of the same substance. If the
nerve is examined closely, it will be seen to be composed of _two_ very
slender threads, lying closely against each other, but easily separable:
in which state they are shown. And the little knobs are called
“ganglia,” each forming a nervous centre, from which smaller nerves
radiate to the different portions of the body.
As for brains, the caterpillar dispenses with them almost entirely; and
instead of wearing one large brain in the head, is furnished with a row
of lesser brains, or ganglia, extending through its whole length. This is
the reason why caterpillars are so tenacious of life. If a man loses his
head, he dies immediately; but an insect is not nearly so fastidious, and
continues to live for a long time without any head at all. Indeed, there
are some insects, which, if beheaded, die, not so much on account of the
head, but of the stomach: for, having then no mouth, they cannot eat, and
so die of hunger. And some insects there are which positively live longer
if decapitated than if left in possession of their head.
On the right hand may be seen a curiously twisted organ, marked C,
swelling to a considerable size in the middle, and diminishing to a mere
thread at each end. This is one of the vessels that contain the silk, or
rather the substance which becomes silk when it is spun.
If this organ be cut open in the middle, it will be seen filled with a
gummy substance of curious texture, partly brittle and partly tough.
From this substance silk is spun, by passing up the tube, through
the thread-like portion, and so at last into a tiny tube, called the
spinneret, which opens from the mouth, and wherefrom it issues in a fine
thread.
There are two of these silk-making organs, and both unite in the
spinneret. Consequently, if silk is examined in the microscope, the
double thread can clearly be made out, both threads adhering to each
other, but still distinguishable. If the threads lie parallel to each
other, the silk is good; if not so, it is of an inferior quality, and
liable to snap.
Most caterpillars possess this silk-factory, but some have it much more
largely developed than others--the silk-worm, for instance. It is of
considerable size in the larva which we are examining, because the Woolly
Bear has to spin for itself a silken hammock in which to swing while it
is in the sleep of its pupal state. Just before it begins to spin, the
organ is of very large size, and distended with the liquid silk; but
after the hammock is completed, the organ diminishes to a mere thread,
and is soon altogether absorbed.
At the left hand of the drawing may be seen a curious structure, marked
B B. This is the chief portion of the respiratory system, and may be at
once recognised by the ringed structure of the tube. Indeed it is quite
analogous to that of the windpipe in animals.
The mode in which insects breathe differs much from that of the higher
animals. In them the breathing apparatus is gathered into one mass,
called lungs or gills, as the case may be; but with insects, the
respiratory system runs entirely over, round, and through the body, even
to the tips of the claws, and the end of the feelers or antennæ.
Every internal organ is also surrounded and enveloped by the breathing
tubes; and this often to such an extent, that the dissector is sadly
perplexed how to remove the tracheal tubes, as they are called, without
injuring the organs to which they so tightly cling. Sometimes they are so
strongly bound together, that they may be removed like a net, but mostly
each must be taken away separately. The mode in which these tracheal
tubes supply the digestive apparatus may be seen at _b b_; and as there
is a double set of them, it may be seen how closely they envelop the
organ to which they direct their course.
The ringed structure runs throughout the entire course of the air tubes,
and is caused by a thread running spirally between the two membranes of
which the tube is composed. The object of this curious thread is to keep
the tube always distended, and ready for the passage of air. Otherwise,
whenever the insect bends its flexible body, it would cut off the supply
of air in every tube which partook of the flexure of the body.
The structure is precisely similar to that of a spiral wire bell-spring;
and so strong is the thread, that I have succeeded in unwinding nearly
two inches of it from the trachea of a humble bee.
The air obtains entrance into these tubes, not through the mouth or
nostrils, but through a set of oval apertures arranged along the sides of
the insect, which apertures are called “spiracles”; and two of them are
indicated at _b* b*_.
In order to prevent dust, water, or anything but air, from entering,
the spiracles are defended by an elaborate _chevaux de frise_ of hair,
or rather quill, so disposed as to keep out every particle that could
injure. So powerful are these defences, that, even under the air-pump, I
was unable to force a single particle of mercury through them, though a
stick will be entirely permeated by the metal, so that if cut it starts
from every pore. I kept the creature in a vacuum for three days, then
plunged it under mercury, and let in the air. Even then no effect was
produced, except that the whole of the stomach and intestinal canal were
charged with mercury.
But, though the spiracles are such excellent defences against obnoxious
substances, they are not capable of throwing off any substance that
may choke them. Consequently, nothing is easier than to kill an insect
humanely, if one only knows how; and few things more difficult, if one
does not know.
For example, if ladies catch a wasp they proceed to immolate it by
snipping it in two with their scissors; a dreadfully cruel process, for
the poor creature has still some four or five brains left intact, and
lives for many hours. But if a feather is dipped in oil and swept across
the body of the creature, it collapses, turns on its back, and dies
straightway. For the oil has stopped up the spiracles, and so the supply
of air is cut off from every portion of the body at once. The same rule
holds good with all insects.
There is yet one more organ to which I must draw attention, and that is
the curious bag-shaped object marked E.
Just as the silk is contained in the vessel C, so the saliva is contained
in E, and is developed according to the character and habits of the
insect. Some insects require a large supply of that liquid, which is
used for various purposes, and others require comparatively little. The
caterpillar in which these receptacles may be found best developed is the
larva of the Goat-moth, which may be easily found within the substance of
decaying trees. Of the Goat-moth we may speak in a future page.
If the reader will again refer to the engraving on p. 100, he will see
that between the tracheal tube and the digestive apparatus is a curiously
waved line, forming two loops in its upper portion, and running into
a confused entanglement below. This entanglement, however, is only
apparent, for in nature there is no entangling; all is perfect in order.
This wavy line represents one of the numerous thread-like vessels that
surround this portion of the digestive apparatus, and are called the
biliary vessels, being, in fact, the insect’s liver. There is a large
mass of these biliary vessels, and they are found so closely entwined
among each other, and so encircled with the air tubes, that to separate
them is no easy matter. Their microscopic structure is curious, and will
repay a careful examination.
In examining the creature for the first time, the dissector will be
tolerably sure to damage the organs and unfit it for preservation, and
therefore it is best to take such a course for granted, and to make the
best of it.
Removing all these vital organs, he should then examine the wonderful and
most complicated muscular structure, by which the caterpillar is enabled
to lengthen, shorten, twist, and bend its body in almost any direction,
and that with such power that many caterpillars are enabled to stretch
themselves horizontally into the air, and there to keep themselves
motionless for hours together.
Few people have any idea of the wonders that they will find inside even
so lowly a creature as a caterpillar--wonders, too, that only increase in
number and beauty the more closely they are examined. When the outer form
has been carefully made out, there yet remains the microscopical view,
and after that the chemical, in either of which lie hidden innumerable
treasures.
A very forcible and unsophisticated opinion was once expressed to me,
after I had dissected and explained the anatomy of a silk-worm to an
elderly friend. He remained silent for some time, and then uttered
disconnected exclamations of astonishment.
I asked him what had so much astonished him.
“Why,” said he, “it’s that caterpillar. It is a new world to me. I always
thought that caterpillars were nothing but skin and squash.”
Having now seen something of the exterior and interior of the
caterpillar, we will watch it as it prepares for its next state of
existence.
Hitherto it has been tolerably active, and if alarmed while feeding, it
curls itself round like a hedgehog and falls to the ground, hoping to lie
concealed among the foliage, and guarded from the effects of the fall
by its hairy armour, which stands out on all sides, and secures it from
harm. But a time approaches wherein it will have no defence and no means
of escape, so it must find a means of lying quiet and concealed. This
object it achieves in the following manner.
It leaves its food, and sets off on its travels to find a retired spot
where it may sling its hammock and sleep in peace. Having found a
convenient spot, it sets busily to work, and in a very short time spins
for itself a kind of silken net, much like a sailor’s hammock in shape,
and used in the same manner. It is not a very solid piece of work,
for the creature can be seen through the meshes; but it is more than
sufficiently strong to bear the weight of the inclosed insect, and to
guard it from small foes.
On plate B, and fig. 5 _b_, the silken hammock is represented, the form
of the pupa inside being visible. It casts off its skin for the last
time, and instead of being a hirsute and active caterpillar, becomes a
smooth and quiescent chrysalis. In this state it abides for a time that
varies according to the time of year and the degree of temperature, and
at last bursts its earthly holdings, coming to the light of the sun a
perfect insect.
When first the creature becomes a chrysalis, its colour is white, and its
surface is bathed in an oily kind of liquid, which soon hardens in the
air, and darkens in the light.
On one occasion, I watched a Woolly Bear changing its skin, and, seizing
it immediately that the task was accomplished, put it into spirits of
wine, intending to keep it for observation.
Next day, the spirit was found to have dissolved away the oily coating,
and all the limbs and wings of the future moth were standing boldly out.
Before closing this chapter, I must just remark that the absence of
scientific terms throughout the work will be intentional, from a wish to
make the subject intelligible, instead of imposing. It would have been
easy enough to speak of the Woolly Bear as the larva of Arctia Caja;
to describe it as a chilognathiform larva, with a subcylindrical body,
and no thoracic shield: passing through an obtected metamorphosis, and
becoming a pomeridian lepidopterous imago; and to have proceeded in the
same style throughout. But as nearly every one who has taken a country
walk has seen Woolly Bears, and hardly any one knows what is meant by
“chilognathiform,” the subject is treated of for the benefit of the many,
even at the risk of incurring the contempt of the few.