of these, as well as many other insects, must be referred to the
laborious and interesting memoirs of Reaumur. Happy if he should, like
De Geer, be induced thereby to follow the steps of so great a master; he
will derive from thence a continual source of new pleasures and
increasing delights; and the more he extends the boundaries of his
observations, the more he will be convinced that INFINITY is, as it
were, impressed on all the works of the CREATOR.
Different species of caterpillars are often to be found in great numbers
on the same tree or plant; but then as they seem to have no connection
with each other, and the actions of the one have no influence on the
rest, they may be considered as solitary; but there are others who seem
still more independent of each other, and greater friends to solitude,
constructing a lodging formed of leaves tied together with considerable
ingenuity, in which they live as in a hermitage. The operation by which
these tie the leaves together, is far surpassed by another kind, who
fold and bend one part of the leaf till it meets the other. These are
again exceeded by those who roll the leaves which they inhabit. For this
purpose the caterpillar chooses a part of a leaf which it finds in some
degree bent; here it establishes its abode, and begins its work, moving
the head with great velocity in a curved line, or rather vibrating it
like a pendulum, the middle of the body being the center on which it
moves. At each motion of the head a thread is spun, and fixed to that
part to which the head seems to be applied. The threads are extended
from the bent to the flat part of the leaf, being always adjusted both
in length and strength to the nature of the leaf, and the curvature
which is to be given to it.
De Geer attending to the operations of a species of this kind of
caterpillar, observed that at each new thread it spun, the edges of the
leaf insensibly approached to each other, and were bent more and more,
in proportion as the caterpillar spun new threads; when the last thread
that was spun was tight, that which preceded it was loose and floating
in the air. To effect this, the caterpillar, after it has fixed a thread
to the two edges of the leaf, and before it spins another, draws it
towards itself by the hooks of its feet, and by these means bends the
leaf; it then spins another thread, to maintain the leaf in this
position, which it again pulls towards itself, and repeats the
operation, till it has bent the leaf in its whole direction. It now
begins again, placing the threads further back upon the bent part of the
leaf, and by proceeding in this manner, it is rolled up; when it has
finished this business, it strengthens the work, by fastening the ends
of the leaf together. The habitation thus formed is a kind of hollow
cylinder, open to the light at both ends, the sides of it affording the
insect food and protection, for within it the creature feeds in safety.
In the same case they are also transformed; at the approach of the
change the caterpillar lines the rolled leaf with silk, that the rough
parts of it may not injure the chrysalis.
A great number of the smaller larvæ require an artificial covering, to
protect them from the open air. Among these, some inhabit the interior
parts of leaves, making their way between the superior and inferior
membranes, living upon the parenchymous parts of the leaf; and as they
are exceedingly small, a leaf affords them a spacious habitation. If the
distance between the membranes be not large enough for them, they
enlarge the space by forming different folds in one of them, in which
they can move with ease: from these circumstances they have been named
by Reaumur miners of leaves. This illustrious author has described these
larvæ, the flies into which they are changed, and all the Various
methods made use of by them in performing this work. Some mine a large
oval or circular space; others form a kind of gallery, which is
sometimes straight, sometimes crooked. They only leave a thin membrane
on the upper side of the leaf; but they leave the under side more
substantial. One species of moth which proceeds from these larvæ is very
small but exceedingly beautiful.
The larvæ of the phryganea mostly live in little cases of their own
building, which are formed of a variety of materials, that they train
after them in the water wherever they go. These cases are generally
cylindrical, and open at both ends; the inside is lined with silk spun
by the larva, the outside formed of different substances, as bits of
reed, stone, gravel, and some entirely of small shells, &c. which they
arrange and manage with singular dexterity: they never quit this case.
When they walk, they put out the head, and a few of the first rings of
the body, training the case after them.
Having lived in the water for some time, they become inhabitants of the
air. They assume the pupa form in the water, closing up the two ends of
the case with bars of silk, by which it is secured from the attacks of
its enemies; and at the same time there is a free passage for the water,
which is still necessary for its existence. At a proper period the pupa
forces its way through the case, and makes for the land, where its
further change instantly commences, and is soon completed.
We shall close these specimens of the industry of insects with an
account of that which is displayed by the larvæ of the tineæ. The
greatest part of the body of these little creatures, except the head and
six fore feet, is covered over with a thin tender skin; the body of the
insect is cylindrical, and lodged in a tube which is open at both ends.
Soon after they are born, they begin to cover themselves, and are,
therefore, seldom to be found but in these tubes or cases. They are in
general so small, that it is not easy to distinguish the cases without a
magnifier; but as the body lengthens, the case becomes too short; it is,
therefore, part of its daily employ to lengthen it. For this purpose it
extends the head beyond the tube, and having found the materials which
answer its purpose, it tears it off, and brings it to the end of the
tube, and fixes it there, repeating this manoeuvre till it has
sufficiently lengthened it. After it has finished one end, it turns
itself round within the case, and performs the same operation at the
other.
This does not terminate their labours, for the tube must also be
increased in diameter, as it soon becomes too small for the body; the
means they make use of to enlarge it, is precisely the same as we
ourselves should adopt under similar circumstances. The insect slits the
tube at the two opposite sides, at the same end, and inserts in the slit
two pieces of the required size; it then performs the same at the other
end. By these means they soon enlarge it sufficiently, without exposing
themselves to the air during the operation. The outside of these cases
is made of silk, hair, &c. the inside is of silk only. Their covering
always partakes of the colour of the cloth or tree, &c. from whence it
was taken; if it pass over a red piece, the colour will be red. When
they are come to their perfect growth, they abandon the cloth, and seek
for a proper place wherein they may pass from their present to a more
perfect state.
I cannot conclude this long chapter better than in the words of Mr.
Stillingfleet. “Many are apt to treat with contempt any man whom they
see employed in poring over a moss, or examining an insect, from day to
day, thinking that he spends his time and his life in unimportant and
barren speculations; yet were the whole scene of nature laid open to our
views, were we admitted to behold the connections and dependences of
every thing on every other, and to trace the œconomy of nature through
the smaller, as well as greater parts of this globe, we might, perhaps,
be obliged to own that we were mistaken; that the Supreme Architect had
contrived his works in such a manner, that we cannot properly be said to
be unconcerned in any one of them; and, therefore, that studies, which
seem upon a slight view to be quite useless, may in the end appear of no
small importance to mankind. Nay, were we only to look back into the
history of arts and sciences, we must be convinced that we are apt to
judge over hastily of things of this nature. We should there find many
proofs that he who gave this instinctive curiosity to some of his
creatures, gave it for good and great purposes, and that he rewards with
useful discoveries all these minute researches.
“It is true, this does not always happen to the searcher, or his
contemporaries, nor even sometimes to the immediate succeeding
generation; but I am apt to think, that advantages of one kind or other
always accrue to mankind from such pursuits; some men are born to
observe and record what perhaps by itself is perfectly useless, but yet
of great importance to another who follows and goes a step further,
still as useless; to him another succeeds, and thus by degrees, till at
last one of a superior genius comes, who laying all that has been done
before this time together, brings on a new face of things, improves,
adorns, exalts human society.
“All those speculations concerning lines and numbers, so ardently
pursued, and so exquisitely conducted by the Grecians, what did they aim
at? or what did they produce for ages? a little arithmetic, and the
first elements of geometry, were all they had need of. This Plato
asserts; and though, as being himself an able mathematician, and
remarkably fond of these sciences, he recommends the study of them; yet
he makes use of motives that have no relation to the common purposes of
life.
“When Kepler, from a blind and strong impulse, merely to find analogies
in nature, discovered that famous one between the distance of the
several planets from the sun, and the periods in which they complete
their revolutions, of what importance was it to him or the world?
“Again; when Galileo, pushed on by the same irresistible curiosity,
found out the law by which bodies fall to the earth, did he, or could he
foresee that any good would come from his ingenious theorems; or was any
immediate use made of them?
“Yet had not the Greeks pushed their abstract speculations so far, had
not Kepler and Galileo made the above-mentioned discoveries, we never
could have seen the greatest work that ever came from the hands of man,
Sir Isaac Newton’s Principia.
“Some obscure person, whose name is not so much as known, diverting
himself idly, as a stander-by would have thought, with trying
experiments on a seemingly contemptible piece of stone, found out a
guide for mariners on the ocean, and such a guide as no science, however
subtil and sublime its speculations may be, however wonderful its
conclusions, would ever have arrived at. It was mere curiosity that put
Sir Thomas Millington upon examining the minute parts of flowers; but
his discoveries have produced the most perfect and most useful system of
botany that the world has yet seen.
“Other instances might be produced to prove, that bare curiosity in one
age, is the source of the greatest utility in another; and what has
frequently been said of chemists, may be applied to every other kind of
vertuosi. They hunt, perhaps, after chimeras and impossibilities; they
find something really valuable by the bye. We are but instruments under
the Supreme Director, and do not so much as know, in many cases, what is
of most importance for us to search after; but we may be sure of one
thing, viz. that if we study and follow nature, whatever paths we are
led into, we shall at last arrive at something valuable to ourselves and
others, but of what kind we must be content to remain ignorant.”
CHAP. VI.
A GENERAL VIEW OF THE INTERNAL PARTS OF INSECTS, AND MORE PARTICULARLY
OF THE CATERPILLAR OF THE PHALÆNA COSSUS---A DESCRIPTION OF SUNDRY
MISCELLANEOUS OBJECTS.
The interior part of insects includes four principal viscera; the spinal
marrow, the intestinal bag, the heart, and tracheal vessels.
The spinal marrow, or principal trunk of the nerves of insects, is a
whitish thread, extended the whole length from the head to the
hindermost part, furnished at intervals with small knots or ganglions.
From these knots proceed the nervous threads that are supposed to be the
instruments of sensation and motion.
On the medullary thread is placed the intestinal bag, which is equal to
it in length; it is a long gut, in which are contained the oesophagus,
the stomach, and intestines.
Along the back, and parallel to the intestinal bag, runs a long thin
vessel, in which may be perceived through the skin of the insect
alternate contractions and dilatations; this part is supposed to perform
the functions of the heart.
The tracheal vessels of insects are very similar to those of plants; are
of the same structure, colour, and elasticity, and are, like them,
dispersed through the whole body.
A clearer idea of these parts will be obtained by the short extract I
shall give of M. Lyonet’s work; which, at the same time that it displays
the wonderful organization of insects, shews how worthy it is of the
attention of a rational being; and, though this description is confined
to a particular species, it will be found to accord in general with a
great number.
Of all the modifications of which matter is susceptible, the most noble
is undoubtedly the organization thereof. In the structure of animals,
the Sovereign Wisdom is exhibited to our view in the most striking
manner. The body of an animal is a little particular system more or less
complicated, and which, like the system of the universe at large, is the
result of the combination and connection of a multitude of different
parts, which all conspire to produce one general effect, the
manifestation of the principle which we term life. So wonderful are
these combinations that we are incapable of comprehending, or even of
admiring sufficiently the astonishing apparatus of springs, levers,
counter-weights, tubes of different diameters, &c. which constitute
these organical machines. The interior parts of the insect, the most
despicable in appearance, would absorb all the powers of the most able
anatomist. He would be lost in the labyrinth as soon as he attempted to
explore all its windings. A truth that will be evident to every one who
considers only the small portion here introduced of the anatomy of the
caterpillar inhabiting the trunk of the willow-tree. This caterpillar
produces the phalæna cossus, or goat-moth. M. Lyonet in his admirable
work entitled, “Traite Anatomique de la Chenille qui ronge le Bois de
Saule,” has given an ample and minute description of this insect. In the
following concise abstract enough will appear to convince the reader of
the utility of microscopic glasses, in displaying the wonders of the
creation, and to afford additional proof that the attention of the
Almighty is not confined merely to objects of magnitude.
In a former edition of this work, I entered into a more minute detail of
the several parts contained in the figures exhibited in plate XII. This
account I have now omitted, as after all it could not convey a clear
idea of the muscles alone, much less of the different parts of the
caterpillar, without a reference to other plates of M. Lyonet’s work. I
therefore concluded it would be better to let the figures speak for
themselves, and then give a general description of the interior parts of
the caterpillar; referring the reader for full particulars to the
original.
Figures 1 and 2 represent the muscles of the caterpillar, when it is
opened at the belly. Fig. 3 and 4 exhibit a view of the muscles when it
is opened at the back. Fig. 5 and 6, an anatomical delineation of the
head; so complex is this organ, that in order to give an adequate idea
of its structure, M. Lyonet has employed no less than twenty figures.
Fig. 7 is an out-line of the head more magnified than in the last
figures. In order to obtain the views here exhibited, the muscles were
freed as well from fat, as from the nerves and other vessels.
The BODY of the caterpillar in the Plate Fig. 2 and 3, is divided into
twelve parts, corresponding to its rings marked by the numbers 1 to 12;
to the first number the word RING is affixed. Each of these rings is
distinguished from that which follows, and that preceding it, by a kind
of neck or small hollow part. By conceiving a line to pass through these
necks, and forming boundaries to the rings, we acquire twelve more
divisions, Fig. 1 and 4; these are also marked with the numbers 1 to 12;
to the first the word DIVISION is annexed. The several parts exhibited
in the divisions, Fig. 1, are the muscles; those in Fig. 2, under the
word ring, are also muscles, which appear when those in Fig. 1 are
removed, lying under them.
The anatomical delineation of the muscles of the head, Fig. 5 and 6,
should be considered as consisting of two figures, which join in the
middle, being terminated by the superior and inferior lines. The head,
as here represented, is magnified about three-hundred times. H H are the
two palpi: the truncated muscles d, belong to the lower lip, and form a
part of those which give it motion: K, the two ganglions of the neck
united: I I, the two silk vessels: L, the oesophagus: M, the two
dissolving vessels: the Hebrew letters denote the continuation of the
cephalic arteries: S T U W and X are the ten abductor muscles of the
jaw: under e e and f f are seen four occipital muscles: a a, a nerve of
the first pair, belonging to the ganglion of the neck; b, a branch of
this nerve.
Fig. 7 is an outline of the head magnified considerably more than in the
last figure, exhibiting the nerves as seen from the under part.
Excepting in two or three instances, only one nerve of each pair is
shewn, as a greater number would have occasioned confusion. The nerves
of the first ganglion of the neck are designed by capital letters; those
of the ganglion a, are distinguished by Roman letters; those of the
small ganglion, by Greek characters; and those of the frontal ganglion,
except one, by numbers.
A GENERAL VIEW OF THE INTERIOR PARTS OF THE CATERPILLAR.
The MUSCLES have neither the exterior form, nor the colour of those of
larger animals. In their natural state they are soft, and have the
appearance of a jelly; they are of a greyish blue, and the
silver-coloured appearance of the aerial or pulmonary vessels, which
creep over and penetrate their substance, exhibits under the microscope
a most beautiful spectacle. When the caterpillar has been soaked for
some time in spirit of wine, they lose their elasticity and
transparency, and become firm, opake, and white; the aerial vessels
disappear. At first sight they might be taken for tendons, as they are
of the same colour and possess almost the same lustre. They are
generally flat, and of an equal size throughout; the middle seldom
differs either in colour, substance, or size, from the extremities. The
ends are fixed to the skin; the rest of the muscle is generally free and
floating; several of them branch out considerably; the branches extend
sometimes so far, that it is not always easy to discover whether they
are distinct and separate muscles, or parts of another. They are of a
moderate strength; those that have been soaked in spirit of wine, when
examined by the microscope, will be found to be covered with a membrane
which may be separated from them; they then appear to consist of several
parallel bands, disposed according to the length of the muscle. These,
when divided by the assistance of very fine needles, appear to be
composed of still smaller bundles of fibres, in the same direction;
which, when examined by a very deep magnifier, and in a favourable
light, appear twisted like a small cord. The muscular fibres of the
spider, which are much larger than those of the caterpillar, are found
on examination to consist of two substances, one soft, and the other
hard; the last is twisted round the former spirally, and thus gives to
it the afore-mentioned cord-like appearance. If the muscles are
separated by means of very fine needles, in a drop of some fluid, we
find that they are not only composed of fibres, membranes, and aerial
vessels, but also of nerves; and, from the drops of oil that may be seen
floating on the fluid, that they are also furnished with many unctuous
particles. The muscles in a caterpillar are very numerous, exceeding by
much those of the human body; the reader may form some idea of their
number by inspecting Fig. 1 2 3 and 4 of Plate XII. They occupy the
greatest part of the head; there is an amazing number at the oesophagus,
the intestines, &c. the skin is as it were lined by different beds of
them, placed one under the other, and ranged with very great symmetry.
The number of muscles that our observer has been able to distinguish is
truly astonishing; he found 228 in the head, 1647 in the body, and 2066
in the intestinal tube, making in all 3941!
The SPINAL MARROW, and the brain of the caterpillar, if it can be said
to have any, seem to have very little relation to those of man; in the
last, the brain is inclosed in a bony cavity; it occupies the greatest
part of the head, and is anfractuose, and divided into lobes. There is
nothing similar to this in the caterpillar; we find indeed in the head
of that which we are describing, a part which seems to answer the
purpose of the brain, because the nerves that are disseminated through
the head are derived from it; but then this part is unprotected, and so
small, that it does not occupy one-fifth part of the head; the surface
is smooth, and has neither lobes nor anfractuousness; and if we must
call this a brain, the caterpillar may be said to have thirteen, as
there are twelve more such parts following each other in a line; they
are nearly of the same size with that in the head, and of the same
substance, and it is from them that the nerves are distributed through
the whole body. Lest the idea of thirteen brains might be disagreeable
to his readers, Lyonet has called these parts ganglions. The spinal
marrow in the human species descends down the back, inclosed in a bony
case; is large with respect to its length, and not divided into
branches, diminishing in thickness in proportion as it is removed
further from the brain. In the caterpillar, the spinal marrow goes along
the belly, is not inclosed in any tube, is very small, forks out at
intervals, and is nearly of the same thickness throughout, except at the
ganglions. For a description of the numerous vessels, and curious
texture of these parts, reference must be had to the original work of
Lyonet. The substance of the spinal marrow, and of the ganglions, is not
near so tender and easily separated as in man; it has a very great
degree of tenacity, and does not break without considerable tension. The
substance of the ganglions differs from that of the spinal marrow, as no
vessels can be discovered in the latter, whereas the former are full of
very delicate ones. The patient anatomist of the caterpillar has counted
forty-five pair of nerves, and two single ones; so that there are
ninety-two principal nerves, whose ramifications are innumerable.