Philip Henry Gosse.

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tips of which terminate at the same level and form a vel-
vety surface. Now these points are the whitish bulbous
extremities exactly answerable to those of the palms of the
fly, and doubtless they answer the very same purpose.
Only here they are set in far closer array and are a hun-
dred times more numerous; whence we may reasonably
presume a higher power of adhesion to be possessed by
the beetle. The structure is best seen -in the male, which
may be distinguished by its smaller dimensions, and by its
broader feet.

A still better example of a sucking foot is this of the
Dyticus marginalis. It is the great flat oval beetle, which
is fond of coming up to the surface of ponds, and hanging



EVENINGS AT THE MICROSCOPE

there by the tail with its pair of hind- legs stuck out on
each side at right angles; the redoubtable monster which
little boys who bathe hold in such salutary awe under the
name of Toe- biter. We have turned the tables upon the
warrior, and have bitten his toe off, and here it is. This
is the tarsus of one of the fore limbs.

The peculiarity that first strikes us is that the first three




FOOT OP WATER-BEETLE.

a, large sucker; 66, two smaller suckers;
c, small crowded suckers.



One of the last more
enlarged.



joints are as it were fused into one, and dilated so as to
make a large roundish plate. The under surface of this
broad plate is covered with a remarkable array of sucking
disks, of which one is very large, occupying about a fourth
part of the whole area. It is circular, and its face is
strongly marked with numerous fibres radiating from the
centre. Near this you perceive two others of similar form



INSECTS: THEIR FEET 141

and structure, but not more than one-tenth part of its size;
one of these, moreover, is smaller than the other. Indeed,
the size and number of these organs differ in different in-
dividuals of the same species.

The greater number of the suckers are comparatively
minute; but they are proportionally multitudinous and
crowded. Each consists of a club-shaped shaft, with a
circular disk of radiating fibres attached to its end. The
whole apparatus constitutes a very effective instrument of
adhesion.

There is a somewhat similar dilatation of the first joints
of the tarsus, but for a very different object, in the Honey-
bee; and it is particularly worthy to be observed, not only
for the interesting part which it plays in the economy of
the insect, but for the example it affords us of the adapta-
tion of one and the same organ to widely different uses,
by a slight modification of its structure.

It is the hind-foot of the Bee that we are now to ex-
amine. The first joint is, as you see, enlarged into a wide,
long, and somewhat ovate form, constituting a flattish plate,
slightly convex on both surfaces. The upper face presents
nothing remarkable, but the under side is set with about
nine stiff combs, the teeth of which are horny straight
spines, set in close array, and arranged in transverse rows
across the joint, nearly on a level with its plane, but a lit-
-tle projecting, and so ordered that the tips of one comb
slightly overlap the bases of the next. We see them in
this example very distinct, because their color, a olear red-
dish-brown, contrasts with a multitude of tiny globules of
a pale yellow hue, like minute eggs, which are entangled
in the combs.

Now these globules serve to illustrate the object of this



142 EVENINGS AT THE MICROSCOPE

apparatus. They are grains of pollen; the dust that is
discharged from the anthers of flowers, which being
kneaded up with honey forms the food of the infant
bees, and is, therefore, collected with great perseverance
by those industrious insects; and the way in which they
collect it is by raking or combing it from the anthers by
means of these effective instruments on their hind- feet.

You see that in this specimen the combs are loaded
with the grains, which lie thickly in the furrows between
one comb and another. But how do they discharge their
gatherings ? Do they return to the hive as soon as they
have accumulated a quantity such as this, which one would
suppose they could gather in two or three scrapes of the
foot? No; they carry a pair of panniers, or collecting
baskets, which they gradually fill from the combs, and
then return to deposit the results of their collecting.

One of these baskets I can show you; and, indeed, we
should be unpardonable to overlook it, for it is the com-
panion structure to the former, I make the stage forceps
to revolve on its axis, and thus bring into focus the joint
(tibia) immediately above that of the combs, and so that
we shall look at its. opposite surface; that is, the outer,
We notice at once two or three peculiarities, which distin-
guish the joint in this instance from other parts of the
same limb, and from the corresponding part in the same
limb of other insects.

First, the surface is decidedly concave, whereas it is or-
dinarily convex. Secondly, this concave surface is smooth
and polished (except that it is covered with a minute net-
work of crossed lines), not a single hair, even the most
minute, can be discerned in any part; whereas the corre-
sponding surface of the next joints, both above and below,



INSECTS. THEIR FEET 143

is studded with fine hairs, as is the exterior of insects
generally. Thirdly, the edges of this hollowed basin are
beset with long, slender, acute spines, which pursue the
same curve as the bottom and sides, expanding widely,
and arching upward.

Here, then, we have a capital collecting-basket. Its
concavity of course fits, it to contain the pollen. Then its
freedom from hairs is important: hairs would be out of
place in the concavity. Thirdly, the marginal spines
greatly increase the capacity of the vessel to receive the
load, on the principle of the sloping stakes which the
farmer plants along the sides of his wagon when he is
going to carry a load of hay or corn.

But, you ask, how can the Bee manage to transfer the
pollen from the combs to the basket ? Can she bend up
the tarsus to the tibia? or, if she can, surely she could
only reach the inner, not the outer, surface of the latter.
How is this managed?

A very shrewd question. Truth to say, the basket you
have been looking at never received a single grain from
the combs of the joint below it. But the Bee has a pair
of baskets and a pair of comb-joints. It is the right set
of combs that fills the left basket, and vice versa. She can
easily cross her hind-legs, and thus bring the tarsus of one
into contact with the tibia of the other; and if you will
pay a moment's more attention to the matter, you will dis-
cover some further points of interest in this beautiful series
of contrivances still. If you look at this living bee, you
notice that, from the position of the joints, when the in-
sect would bring one hind -foot across to the other, the un-
der surface of the tarsus would naturally scrape the edge
of the opposite tibia in a direction from the bases of the



144 EVENINGS AT THE MICROSCOPE

combs toward their tips; and, further, that the edge of
the tibia so scraped would be the hinder edge, as the leg
is ordinarily carried in the act of walking.

Now, if you take another glance at the basket-joint in
the forceps of the microscope, you will see what, per-
haps, you have already noticed that the marginal spines
have not exactly the same curvature on the two opposite
edges, but that those of the one edge are nearly straight,
or at most but slightly bowed, whereas those of the op-
posite edge are strongly curved, the arc in many of them
reaching even to a semicircle, so that their points, after
performing the outward arch, return to a position perpen-
dicularly over the medial line of the basket.

It is the outer or hinder edge of the joint that carries the
comparatively straight spines. These receive the grains from
the combs, which, then falling into the basket, are received
into the wide concavity formed partly by its bottom and
sides, but principally by the arching spines of the opposite
edge. Their curving form would have been less suitable
than the straighter one to pass through the interstices of
the combs, because it would be much more difficult to get
at their points; while, on the other hand, the straight lines
of these would have been far less effective as a receiver
for the burden. The thickness of the spines is just that
which enables them to pass freely through the interstices
of the comb-teeth, and no more.

On the whole, this combination of contrivances reads
us as instructive a lesson of the wisdom of God displayed
in creation as any that we have had brought under our
observation.

The end to be attained by all this apparatus is worthy
of the wondrous skill displayed in its contrivance; for it



INSECTS: THEIR FEET 145

is connected with the feeding of the stock, and whatever
diminishes the labor of the individual bees enables a larger
number to be supported. But valuable as is the Honey-
bee to man, there are other important purposes to be ac-
complished, which are more or less dependent, collaterally,
on this series of contrivances.

"In many instances it is only by the bees travelling
from flower to flower that the pollen and farina is carried
from the male to the female flowers, without which they
could not fructify. One species of bee would not be suffi-
cient to fructify all the various sorts of flowers were the
bees of that species ever so numerous; for it requires spe-
cies of different sizes and different constructions. M.
Sprengel found that not only are insects indispensable in
fructifying different species of Iris, but some of them, as
/. Xiphium, require the agency of the larger humble-bees,
which alone are strong enough to force their way beneath
the style-flag; and hence, as these insects are not so com-
mon as many others, this Iris is often barren, or bears
imperfect seeds. ' ' '

The legs and feet of Caterpillars are constructed on a
very different plan from those of perfect insects, as you
may see in this living Silkworm. The first three segments
of the body, reckoning from the head, are furnished each
with a pair of short curved limbs set close together on the
under side. These represent the true legs of the future
rnoth, and show, notwithstanding their shortness, four dis-
tinct joints, of which the last is a little pointed horny
claw. The whole limb resembles a short stout hook. The
two segments occur which are quite smooth beneath, and

1 "Penny Cyclop.," art. BEE.
15 SCIENCE 7



146 EVENINGS AT THE MICROSCOPE

destitute of limbs; and then on the sixth we begin to find
another series, which goes on regularly, a pair on each
segment, to the eleventh and final one, with the single
exception of the tenth segment, which is again deprived
of limbs.

But these organs are of a very peculiar character.
They have no representatives in the mature insect, but
disappear with the larva state, and they are not consid-
ered limbs proper at all, but mere accessory developments
of the skin to serve a special purpose. They are some-
times called claspers, sometimes false-legs, but more com-
monly pro-legs.

Each consists of a fleshy wart, which is capable to some
extent of being turned inside out, like the finger of a
glove. Partly around the blunt and truncate extremity are
set two rows of minute hooks, occupying the side next the
middle line of the caterpillar in a semicircle along the mar-
gin. These hooks arch outward as regards the axis of the
pro-leg, though the majority of them point toward the
medial line of the body. The double row is somewhat
interrupted at its middle point; and just there, in each
pro-leg, a clear vesicle or fleshy bladder protrudes from
the sole, which may perhaps serve as a very delicate organ
of touch, or may exude a viscid secretion helpful to prog-
ress on smooth bodies. The hooks seem adapted to catch
and hold the fine threads of silk, which most caterpillars
spin as a carpet for their steps.

In some cases the circle of hooks is complete, as in this
example, which I find in one of the slides of my drawer,
marked " Pro-leg of a Caterpillar." It is some large spe-
cies, probably a Sphinx, for the hooks are very large, of a
clear orange-brown hue, and set in a long oval ring sin-



INSECTS: STINGS AND OVIPOSITORS 147

gle as to their bases, but double as to their points com-
pletely around the extremity of the foot. These hooks are
simply cutaneous, as may be well seen in this prepared
specimen doubtless mounted in Canada balsam; for their
origins are mere blunt points, set most superficially in the
thin skin without any enlargement or apparent bulb.



CHAPTEE VIII

INSECTS: STINGS AND OVIPOSITORS

PROBABLY at some period of your life you have
been stung by a bee or wasp. I shall take it for
granted that you have, and that having tested the
potency 'of these warlike insects' weapons with one sense,
you have a curiosity to examine them with another. The
microscope shall aid your vision to investigate the mor-
bific implement.

This is the sting of the Honey-bee, which I have but
this moment extracted. It consists of a dark brown horny
sheath, bulbous at the base, but suddenly diminishing, and
then tapering to a fine point. This sheath is split entirely
along the inferior edge, and by pressure with a needle I
have been enabled to project the two lancets, which com-
monly lie within the sheath. These are two slender fila-
ments of the like brown horny substance, of which the
centre is tubular, and carries a fluid, in which bubbles are
visible. The extremity of each displays a beautiful mech-
anism, for it is thinned away into two thin blade- edges,
of which one remains keen and knife- like, while the op-
posite edge is cut into several saw teeth pointing backward.

The lancets do not appear to be united with the sheath



148 EVENINGS AT THE MICROSCOPE

in any part, but simply to lie in its groove; their basal
portions pass out into the body behind the sheath, where
you see a number of muscle-bands crowded around them:
these, acting in various directions, and being inserted into
the lancets at various points, exercise a complete control
over their movements, projecting or retracting them at
their will. But each lancet has a singular projection from
its back, which appears to act in some way as a guide
to its motion, probably preventing it from slipping aside
when darted forth, for the bulbous part of the sheath, in
which these projections work, seems formed expressly to
receive them.

Thus we see an apparatus beautifully contrived to enter
the flesh of an enemy: the two spears finely pointed, sharp-
edged, and saw- toothed, adapted for piercing, cutting, and
tearing; the reversed direction of the teeth gives the weap-
on a hold in the flesh, and prevents it from being readily
drawn out. Here is an elaborate store of power for the
jactation of the javelins, in the numerous muscle -bands;
here is a provision made for the precision of the impulse;
and finally, here is a polished sheath for the reception
of the weapons and their preservation when not in actual
use. All. this is perfect; but something still was wanting
to render the weapons effective, and that something your
experience has proved to be supplied.

The mere intromission of these points, incomparably
finer and sharper than the finest needle that was ever
polished in a Sheffield workshop, would produce no result
appreciable to our feelings; and most surely would not
be followed by the distressing agony attendant on the
sting of a bee. We must look for something more than
we have seen.



INSECTS: STINGS AND OVIPOSITORS



149



We need not be long in finding it. For "here, at the
base of the sheath, into which it enters by a narrow neck,
lies a transparent pear-shaped bag, its surface covered all
over, but especially toward the
neck, with small glands set
transversely. It is rounded
behind, where it is entered
by a very long and slender
membranous tube, which, after
many turns and windings,
gradually thickening and be-
coming more evidently glandu-
lar, terminates in a blind end.

This is the apparatus for
preparing and ejecting a pow-
erful poison. The glandular
end of the slender tube is
the secreting organ: here the
venom is prepared; the re-
mainder of the tube is a duct
for conveying it to the bag, a
reservoir in which it is stored
for the moment of use. By
means of the neck it is thrown
into the groove at the mo-
ment the sting is projected,
the same muscles, probably,
that dart forward the weapon
compressing the poison- bag
and causing it to pour forth its contents into the groove,
whence it passes on between the two spears into the
wound which they have made.




STING OF BEE.

a, Tip of Lancet, more enlarged.



150 EVENINGS AT THE MICROSCOPE

A modification of this apparatus is found throughout
a very extensive order of insects the Hymenoptera; but
in the majority of cases it is not connected with purposes
of warfare. Wherever it occurs it is always confined to
the female sex, or (as in the case of some social insects)
to the neuters, which are undeveloped females. When
it is not accompanied by a poison-reservoir, it is ancillary
to the deposition of the eggs, and is hence called an ovi-
positor, though in many cases it performs a part much
more extensive than the mere placing of the ova.

In the large tribe of Cuckoo- flies (Ichneumonidce), which
spend their egg and larva states in the living bodies of
other insects, this ovipositor is often of great length; even
many times longer than the rest of their bodies; for the
larvae' which have to be pierced by it require to be reached
at the bottom of deep holes and other recesses in which
the providence of the parent had placed them for security.
The structure of the organ may be seen in this little spe-
cies, not more than one- sixth of an inch in entire length,
of which the ovipositor projects about a line. Under the
microscope you see that this projection consists of two
black fleshy filaments, rounded without and flattened on
their inner faces, which are placed together and of the
true implement for boring, in the form of a perfectly
straight awl, of a clear amber hue, very slender and
brought to an abrupt oblique point, where there are a few
exceedingly fine reverted teeth. It is probably double,
though it refuses to open under the pressure which I bring
to bear upon it. At the base are seen within the semi-
pellucid abdomen the slender horns, on which the muscles
act in protecting the borer.

You are doubtless aware that the little berries which



INSECTS: STINGS AND OVIPOSITORS 151

look like bunches of green currants often seen growing
on the oak, are not the proper fruit of the tree, but dis-
eased developments produced by a tiny insect, for the
protection and support of her young. But perhaps you
have never paid any special attention to the living atom
whose workmanship they are, and are not familiar with
the singular mechanism by which she works. I have not
had an opportunity of seeing it myself, and therefore can-
not show it to you ; but as Gall-flies are by no means rare,
and you may easily rear a brood of flies from the galls,
you may have a chance of meeting with it. I will there-
fore quote to you what Rennie says about it.

"There can be no doubt that the mother gall-fly makes
a hole in the plant for the pur-
pose of depositing her eggs.
She is furnished with an ad-
mirable ovipositor for that ex-
press purpose, and Swammer-
dam actually saw a gall-fly
thus depositing her eggs, and

we have recently witnessed the OALL-FLY AND MECHANISM OF OVIPOSITOR.

same in several instances. In some of these insects the
ovipositor is conspicuously long, even when the insect is
at rest; but in others, not above a line or two of it is
visible, till the belly of the insect be gently pressed.
When this is done to the fly that produces the currant-gall
of the oak, the ovipositor may be seen issuing from a
sheath in form of a small curved needle, of a chestnut-
brown color, and of a horny substance, a,nd three times
as long as it at first appeared.

"What is most remarkable in this ovipositor is, that
it is much longer than the whole body of the insect, in




152 EVENINGS AT THE MICROSCOPE

whose belly it is lodged in a sheath, and, from its horny
nature, it cannot be either shortened or lengthened. It
is on this account that it is bent into the same curve as
the body of the insect. The mechanism by which this
is effected is similar to that of the tongue of the wood-
peckers (Picidce), which, though rather short, can be darted
out far beyond the beak by means of a forked bone at the
root of the tongue, which is thin and rolled up like the
spring of a watch. The base of the ovipositor of the gall-
fly is, in a similar way, placed near the anus, runs along
the curvature of the back, makes a turn at the breast, and
then, following the curve of the belly, appears again near
where it originates.

"With this instrument the mother gall-fly pierces the
part of a plant which she selects, and, according to our
older naturalists, 'ejects into the cavity a drop of her cor-
roding liquor, and immediately lays an egg or more there;
the circulation of the sap being thus interrupted, and
thrown, by the poison, into a fermentation that burns the
contiguous parts and changes the natural color. The sap,
turned from its proper channel, extravasates and flows
round the eggs, while its surface is dried by the external
air, and hardens into a vaulted form.' Kirby and Spence
tell us that the parent-fly introduces her egg 'into a punc-
ture made by her curious spiral sting, and in a few hours
it becomes surrounded with a fleshy chamber.' M. Yirey
says the gall-tubercle is produced by irritation, in the
same way as an inflamed tumor in an animal body, by
the swelling of the cellular tissue, and the flow of liquid
matter, which changes the organization, and alters the
natural external form." '

1 "Ins. Arch.," 371.



INSECTS: STINGS AND OVIPOSITORS 153

Perhaps a still more charming example of animal mechan-
ics is that furnished to us by the Saw-flies (Teuthredinidce).
These are very common four- winged insects of rather small
size, many species of which are found in gardens and along
hedges, in summer, produced from grubs which are often
mistaken for true caterpillars, as they strip our gooseberry
and rose bushes of their leaves; but may be distinguished
from them by the number of their pro- legs, and by their
singular postures; for they possess from eight to fourteen
pairs of the former organs, and have the habit of coiling
up the hinder part of their body in a spiral ring, while
they hang on to the leaf by their six true feet.

These saw-fly caterpillars are produced from eggs
which are deposited in grooves, made by the parent- fly
in the bark of the tree or shrub whose future leaves are
destined to constitute their food; and it is for the con-
struction of these grooves and the deposition of the eggs
in them, that the curious mechanism is contrived which
I am now bringing under your notice.

Almost all our acquaintance with this instrument and
the manner of its employment we owe to the eminent
French naturalist Eeaumur, and to his Italian contem-
porary Yalisnieri. Their details I shall first cite, as they
have been put into an English dress hy Eennie, and then
show you a specimen dissected out by myself, and point
out some agreements and some discrepancies between it
and them.

"In order to see the ovipositor, a female saw-fly must
be taken, and her belly gently pressed, when a narrow slit
will be observed to open at some distance from the anus,
and a short, pointed, and somewhat curved body, of a
brown color and horny substance, will be protruded. The



154 EVENINGS AT THE MICROSCOPE

curved plates which form the sides of the slit are the ter-
mination of the sheath, in which the instrument lies con-
cealed till it is wanted by the insect.

"The instrument thus brought into view is a very finely
contrived saw, made of horn, and adapted for penetrating
branches and other parts of plants where the eggs are to
be deposited. The ovipositor- saw of the insect is much
more complicated than any of those employed by our car-
penters. The teeth of our saws are formed in a line, but
in such a manner as to cut in two lines parallel to and at
a small distance from each other. This is effected by
slightly bending the points of the alternate teeth right
and left, so that one half of the whole teeth stand a little



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