Philip Henry Gosse.

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is perforated, and from the tip of which the glistening yel-
low filament of silk is ever drawn out, as the caterpillar
throws his head from side to side. This pointed wart is
the spinning organ; and the thread of silk is, as it issues
from the orifice, a fluid gum, which hardens immediately
on its exposure to the air. The silk -gum is secreted by
the caterpillar in two long blind tubes, which lie twisted
and coiled in the interior of the body, occupying nearly
the whole space, except that which is taken up by the
great digestive canal. These become very slender as they
approach the head, and at length terminate in a dilated
reservoir, which opens by the little pointed wart which
you have just seen.

Many caterpillars are able to suspend themselves at
pleasure by means of the thread which they are spinning,
lengthening it and 41 stopping it off" at will. This latter
operation they perform (though they cannot recall the
thread when once it has issued) by means of an angular


point formed by the two slender tubes at their junction
in the reservoir; thus compressing the thread of gum, and
so preventing any more from issuing. The gum is per-
fectly colorless in the reservoir, but as it issues forth be-
comes coated with a varnish, which is secreted in the same
organ, and which is poured out at the same time. In the
case of the common Silkworm, this varnish imparts to the
silk that brilliant yellow hue which it generally possesses,
and which, as the varnish is soluble, can be easily dis-
charged from it in the manufacture.




A VERY wide field of observation, and one easily cul-
tivated, is presented bj the organs of sense in the
insect races, and in particular by those curious
Jointed threads which proceed from the front or sides of
the head, and which are technically called antennae. These
may sometimes be confounded with the palpi, examples of
which organs we have been lately looking at; for in a car-
nivorous Beetle, for instance, both palpi and antennae are
formed of a number of oblong, polished hard joints, set
end to end, like beads on a necklace. And it is prob-
able there may be as much community in the function as
in the form of these two sets of appendages; that both are
the seats of some very delicate perceptive faculty allied to
touch, but of which we cannot, from ignorance, speak very
definitely. It is likely, indeed, that sensations of a very
variable character are perceived by them, according to their
form, the degree of their development, and the habits of
the species.

It is not impossible, judging from the very great diver-
sity which we find in the form and structure of these and
similar organs in this immense class of beings, compared
with the uniformity that prevails in the organs of sense
bestowed on ourselves and other vertebrate animals, that
a far wider sphere of perception is open to them than to
us. Perhaps conditions that are appreciable to us only by


the aid of the most delicate instruments of modern science
may be appreciable to their acute faculties, and may gov-
ern their instincts and actions. Among such we may men-
tion, conjecturally, the comparative moisture or dryness of
the atmosphere, delicate changes in its temperature, in its
density, the presence of gaseous exhalations, the proxim-
ity of solid bodies indicated by subtile vibrations of the
air, the height above the earth at which flight is per-
formed, measured barometrically, the various electrical
conditions of the atmosphere; and perhaps many other
physical diversities which cannot be classed under sight,
sound, smell, taste, or touch, and which may be altogether
unappreciable, and therefore altogether inconceivable, by
us. It is probable, however, that the antennae are the or-
gans in which the sense of hearing is specially seated; a
conclusion which has long been conjecturally held, and
which is confirmed by some observations recently made
on the analogous organs in the Crustacea, which I will
allude to more particularly presently.

The forms which are assumed by the antennce of Insects
are very diverse; and I can bring before you only a very
small selection out of the mass. One of the most simple
forms is that found in many Beetles, as in this Carabus,
for example. Here each antennce is composed of eleven
joints, almost exactly alike and symmetrical, each joint a
horny body of apparently a long oval shape, polished on
the surface, but not smooth, because covered with minute
depressed lines, and clothed with shaggy hair. There is,
however, a slight illusion in the appearance: it seems as
if the dividing point of the joints were, as I have just said,
at the termination of the oval, but when we look closely
we see that the summit of each oval is, as it were, cut off


by a line, and by comparing the basal joints with the oth-
ers, we see that this line is the real division, that the sum-
mit of the oval really forms the bottom of the succeeding
joint, and that the constricted part is no articulation at all.
The first, or basal joint (called the scapus), and the second
(called the pedicella), differ in form from the rest, here but
slightly, but often considerably. The whole of the remain-
ing joints are together termed the clavola.

You may see a considerable diversity of figure and of
aspect generally in this tiny Weevil, which may be ac-
cepted as a representative of a great family of Beetles, the
Curculionidce. The manner of their insertion strikes us at
first sight as peculiar, as is in fact the aspect of the whole
head. Instead of a thick substantial solid front, with pow-
erful widely-gaping jaws, such as we saw in the Carabus,
here projects from between the eyes a long rod- like pro-
boscis, as long as the whole animal besides, curving down-
ward, and carrying at its very extremity a minute mouth,
with all the proper apparatus of lips, jaws, and palpi.
Moreover, the antennce are planted on the two sides of
this beak, about its mid-length; and they are curiously
elbowed, each projecting horizontally at a right angle to
the beak for a considerable distance, and then with a sharp
angle becoming parallel to it for the remainder of their
length. So that, supposing the terminal half of the beak
to be broken off just behind the insertion of the antennae,
the whole would compose the letter T. Now, the first
bend of this angle is composed of a single joint, the
scapus, which is, in this family, greatly lengthened; and
then the two or three final joints are much thicker than
all the others, and are as it were fused together into a
large oval knob, called the club.


Now, a word or two in explanation of this very singu-
lar form of head and head-organs. The larva or grub
stage of these insects is destined to be passed in the in-
terior of fruits and seeds; the individual which we have
been examining (Balaninus nucum) was born one morning
in August in the interior of a hazel-nut. Its parent had
chosen a suitable nut, just then when it is set for fruit,
and as yet green and soft; and had with her proboscis, or
rather with her jaws at its tip, as with a gimlet, bored a
tiny hole through the yielding shell into the very interior;
then turning round, and inserting the extremity of her ab-
domen with its ovipositor, she had shot an egg into this
dark cavity. The juices poured forth at the wound soon
healed the orifice; the nut grew; and presently the egg
became a little white grub. He then rioted in plenty;
prolonged his darkling feast

"From night to morn, from morn to dewy eve";

'twas all "dewy eve" to him, by the way, for no ray of
light saw he, till that prosperous condition of existence
was done. No wonder he grew fat; and fat those rogues
of nut- weevils always are, as you well know. Well, when
the nut fell, in October, the kernel was all gone, com-
pletely devoured, and our little highway-robber was ready
for his winter sleep: he gnawed a fresh hole through the
now hard shell, made his way out, and immediately bur-
rowed into the earth, where he lay till June; then became
a pupa, and emerged just what you see him, a long-snouted
beetle like his mother, in the beginning of August.

Such is his "short eventful history"; and you now
see that the long beak is formed entirely with reference
to this economy; it is an auger fitted to bore holes into


shell-fruits through their envelopes, for the reception of

There is a very extensive family of Beetles known as
LcLmellicornes, because the antennal joints are singularly
flattened and applied one over the other like the leaves
of a book (lamella, a leaf). Here is a very common little
Chafer found on the droppings in pasture (Aphodius fimeta-
rius), in which the last three joints, constituting the club of
the antenna, are of an ovate form, and flattened, so as to
lie one on another quite close, like three oval cakes: and


being connected only at one end of the long axis, they
open and shut at the pleasure of the animal, like a long
pocket memorandum-book of three leaves.

But this structure is seen to still greater advantage in
the much larger Cockchafer, so abundant in May in some
seasons. For here the joints composing the club are much
more numerous (seven in the male, six in the female), and
they are proportionally longer and thinner, and therefore
more leaf-like. The insect widely expands them, evidently
to receive impressions from the atmosphere; when alarmed,
they are closed and withdrawn beneath the shield of the


head, but on the first essay toward escape, or any kind of
forward movement, the leaves are widely opened, and then,
after an instant's pause to test the perceptions on the sen-
sorium, away it travels.

In some Beetles each joint of the series has one of its
outer angles more developed than the other, and so pro-
duced as to make, with the rest of the joints, a saw-like
edge: you may see an example in this Click-beetle or
Skipjack (Elater)] but many members of the same family
show the same structure in a far higher degree, the angle
being drawn out in a long slender rod, which (with its
fellows) imparts to the antenna the appearance of a comb.

But much more curious and beautiful are the antennae
of many Moths, which often resemble feathers, particularly
in the group Bombycina, of which the Silkworm is an ex-
ample; and in the male sex, which displays this structure
more than the female. But I will show you a native

This is the antenna of a large and handsome, and not at
all uncommon moth the Oak Egger (Lasiocampa quercds).
It consists of about seventy joints, so nearly alike in
size and outline that the whole forms an almost straight
rod, slightly tapering to the tip. Each joint, however,
sends forth two long straight branches, so disposed that
the pair make a very acute angle, and the whole double
series of seventy on each side form a deep narrow groove.
These two series of branches, being perfectly regular and
symmetrical, impart to the antennae the aspect of exquisite

It is, however, when we examine the elements of this
structure in detail, using moderately high powers of en-
largement, that we are struck with the elaborateness of the


workmanship bestowed upon them. Each of the lateral
branches is a straight rod, thick at its origin, whence it
tapers to a little beyond its middle, and then thickens
again to its tip. Here two horny spines project from it
obliquely, one much stouter than the other, at such an
angle as nearly to touch the tip of the succeeding branch.
Besides this, each branch is surrounded throughout its
length with a series of short stiff bristles, very close-set,
projecting horizontally (to the plane of the axis of the


branch), and bent upward at the end candelabrum- fashion.
The mode in which they are arranged is in a short spiral,
which makes about forty-five whorls or turns about the
axis; at least in the branches which are situated about
the middle of the antenna; for these diminish in length
toward the extremity, bringing the feather to a rather
abrupt point.

The entire surface of the branch gleams under reflected
light with metallic hues, chiefly yellows and bronzy greens;
which appear to depend on very minute and closely -applied


scales that overlap each other. The main stem of the
feather that is, the primary rod or axis is somewhat
sparsely clothed with scales of another kind, thin, oblong,
flat plates, notched at the end, and very slightly attached
by means of a minute stem at the base the common cloth-
ing-scales of the Lepidoptera specimens of which we have
before examined.

We may acquire some glimpse of a notion why this
remarkable development of antennae is bestowed upon the
male sex of this moth by an acquaintance with its habits.
It has been long a practice with entomologists, when they
have reared a female moth from the chrysalis, to avail
themselves of the instincts of the species to capture the
male. This sex has an extraordinary power of discover-
ing the female at immense distances, and though perfectly
concealed; and will crowd toward her from all quarters,
entering into houses, beating at windows, and even de-
scending chimneys, to come at the dear object of their
solicitude. Collectors call this mode of procuring the
male "sembling," that is, "assembling," because the in-
sects of this sex assemble at one point. It cannot be prac-
ticed with all insects, nor even with all moths; those of
this family, Bombycidce, are in general available; and
of these, none is more celebrated for the habit than the
Oak Egger. The very individual whose antenna has fur-
nished us with this observation was taken in this way; for
having bred a female of this species the evening before
last, I put her into a basket in my parlor. One male, the
same evening, came dashing into the kitchen; but yester-
day, soon after noon, in the hot sunshine of August, no
fewer than four more males came rapidly in succession
to the parlor window, which was a little open, and, after



beating about the panes a few minutes, found their way
in, and made straightway for the basket, totally regard-
less of their own liberty.

It must be manifest to you that some extraordinary
sense is bestowed upon these moths, or else some ordinary
and well-known sense in extraordinary development. It
may be smell; it may be hearing; but neither odor nor
sound, perceptible by our dull faculties, is given forth by
the females; the emanation is far too subtile to produce
any vibrations on our sensorium, and yet sufficiently po-
tent, and widely diffused, to call these males from their
distant retreats in the hedges and woods. I think it highly
probable that the great increase of surface given to the
antennae by the plumose ramification we have been ob-
serving, is connected with the faculty: perhaps every
bristle of the spiral whorls is a perceptive organ, con-
structed to vibrate with the tender undulations that circle
far and wide from the new-born female. Surely the ways
of Grod in creation, as well as in moral government, are
1 'past finding out!"

The male Grnat presents in its antennas a pair of plumes
of equal beauty, but of a totally different character. The
pattern here is one of exceeding lightness and grace, as
you may see in this specimen. Each antenna is essentially
a very slender cylindrical stem of many joints (about four-
teen); at each joint springs out a whorl of fine hairs of
great length and delicacy, which radiate in various direc-
tions (not, however, forming a complete circle), curving
upward like the outline of a saucer, supposing the stem
to be inserted into its centre. The length of these hairs
is so great that the diameter of their sweep equals, if it
does not exceed, the whole length of the antenna.


In the tribe of two-winged insects, which we term, par
excellence, Flies (Muscadce), the antennae are of peculiar
structure. The common House-fly shall give us a good
example. Here, in front of the head, is a shell-like con-
cavity, divided into two by a central ridge. Just at the
summit of this project are the two antennae, originating
close together, and diverging as they proceed. Each an-
tenna consists of three joints, of which the first is very
minute, the second is a reversed cone, and the third, which
is large, thick, and ovate, is bent abruptly downward
immediately in front of the concavity. From the upper
part of this third joint projects obliquely a stiff bristle or
style, which tapers to a fine point. It is densely hairy
throughout; and is. more beset with longer hairs on two
opposite sides, which decrease regularly in length from the
base, making a wide and pointed plume.

Such are a few examples of what are presumed to be
the ears of Insects; let us now turn our attention to their
eyes. And we can scarcely select a more brilliant, or a
larger example, than is presented by this fine Dragon-fly
(sEshna), which I just now caught as it was hawking to
and fro in my garden. How gorgeously beautiful are these
two great hemispheres that almost compose the head, each
shining with a soft satiny lustre of azure hue, surrounded
by olive-green, and marked with undefined black spots,
which change their place as you move the insect round I

Each of these hemispheres is a compound eye. I put
the insect in the stage -forceps, and bring a low power to
bear upon it with reflected light. You see an infinite
number of hexagons, of the most accurate symmetry and
regularity of arrangement. Into those which are in the
centre of the field of view, the eye can penetrate far down,


and you perceive that they are tubes; of those which
recede from the centre, you discern more and more of the
sides; while, by delicate adjustment of the focus, you can
see that each tube is not open, but is covered with a con-
vex arch of some glassy medium polished and transparent
as crystal. There are, according to the computations of
accurate naturalists, not fewer than 24,000 of these convex
lenses in the two eyes of such a large species of Dragon-
fly as this.

Every one of these 24,000 bodies represents a perfect
eye; every one is furnished with all the apparatus and
combinations requisite for distinct vision; and there is no
doubt that the Dragon-fly looks through them all. In
order to explain this, I must enter into a little technical
explanation of the anatomy of the organs, as they have
been demonstrated by careful dissection.

The glassy convex plate or facet in front of each hex-
agon is a cornea, or corneule, as it has been called. Behind
each cornea, instead of a crystalline lens, there descends
a slender transparent pyramid, whose base is the cornea,
and whose apex points toward the interior, where it is
received and embraced by a translucent cup, answering
to the vitreous humor. This, in its turn, is surrounded by
another cup, formed by the expansion of a nervous fila-
ment arising from the ganglion on the extremity of the
optic nerve, a short distance from the brain. Each lens-
like pyramid, with its vitreous cup and nervous filament,
is completely surrounded and isolated by a coat (the
choroid) of dark pigment, except that there is a minute
orifice or pupil behind the cornea, where the rays of light
enter the pyramid, and one at the apex of the latter, where
they reach the fibres of the optic nerve.


Each cornea is a lens with a perfect magnifying power,
as has been proved by separating the entire compound
eye by maceration, and then drying it, flattened out by
pressure, on a slip of glass. When this preparation was
placed under the microscope, on any small object, as the
points of a forceps, being interposed between the mirror
and the stage, its image was distinctly seen, on a proper
adjustment of the focus of the microscope, in every one
of the lenses whose line of axis admitted of it. The focus
of each cornea has been ascertained by similar experiments
to be exactly equal to the length of the pyramid behind it,
so that the image produced by the rays of light proceeding
from any external object, and refracted by the convex
cornea, will fall accurately upon the sensitive termination
of the optic nerve-filament there placed to receive it.

The rays which pass through the several pyramids are
prevented from mingling with each other by the isolating
sheath of dark pigment; and no rays, except those which
pass along the axis of each pyramid, can reach the optic
nerve; all the rest being absorbed in the pigment of the
sides. Hence it is evident that as no two cornese on the
rounded surface of the compound eye can have the same
axis, no two can transmit a ray of light from the very
same point of any object looked at; while, as each of the
composite eyes is immovable, except as the whole head
moves, the combined action of the whole 24,000 lenses can
present to the sensorium but the idea of a single, undis-
torted, unconfused object, probably on somewhat of the
same principle by which the convergence of the rays of
light entering our two eyes gives us but a single stereo-
scopic picture.

The soft blue color of this Dragon-fly's eyes as also


the rich golden reflections seen on the eyes of other in-
sects, as the Whameflies, and many other Diptera is not
produced by the pigment which I have alluded to, but is
a prismatic reflection from the cornece.

You would suppose that, having 24,000 eyes, the
Dragon-fly was pretty well furnished with organs of vis-
ion and surely would need no more; but you would be
mistaken. It has three other eyes of quite another char-

If you look at the commissure or line of junction of
the two compound eyes on the summit of the head you
will see just in front of the point where they separate and
their front outlines diverge a minute crescent-shaped cush-
ion of a pale-green color at each angle of which is a mi-
nute antenna. Close to the base of each antenna there is
set, in the black skin of the head that divides the green
crescent from the compound eyes, a globose polished knob
of crystal-like substance, much like the "bull's-eyes" or
hemispheres of solid glass that are set in a ship's deck to
enlighten the side-cabins. On the front side of the cres-
centic cushion there is a third similar glassy sphere, but
much larger than the two lateral ones. What are these
three spherules?

They are eyes, in no important respect differing from
the individuals which compose the compound masses, ex-
cept that they are isolated. The shining glassy hemisphere
is a cornea of hard transparent substance, behind which is
situated a spherical lens, lodged in a kind of cup formed
by an expansion of the optic nerve, and which is sur-
rounded by a colored pigment-layer.

You may study these simple eyes, or stemmata, as they
are called, in many other insects, though they are not so


universally present as the compound eyes. On the fore-
head of the Honey-bee they are well seen, as three black
shining globules, placed, as in the Dragon-fly, in a tri-



IT is always interesting to trace the varied forms and
conditions under which any particular function is per-
formed; and particularly to mark, in creatures very
remote from us in the scale of being, the organs devoted
to the senses which are so requisite to our own comfort.
We have already seen some of these diversities, in exam-
ples taken from the classes Mollusca and Insects; and will
now examine some more, as they appear in the Crustacea.
If you look at the head of a Crab, a Lobster, or a
Prawn, you will see that it is furnished with jointed an-
tennae, like that of Insects ; but whereas in insects there is
never more than a single pair, in the creatures of which I
am speaking there are two pairs. In the Prawn you may
suppose, at first sight, that there are four pairs; but that
is because the internal antennae terminate each in three
many- join ted bristles, in structure and appearance exactly
like the bristles of the outer pair, two of the three being
nearly as long as the outer, while the third is short. In

Online LibraryPhilip Henry GosseEvenings at the microscope (Volume 1) → online text (page 13 of 32)