THE ABDOMEN.
Respiratory Organs--Circulation of Nutritive Fluid--Digestion
and Nutrition--Secretion of Wax--Reproductive Organs--Detailed
description of Sting--Effects of Poison--Queen's Sting.
The abdomen constitutes the largest and hindmost segment of the
body, and is important as containing several structures which have
most essential functions in the economy of the insect. Among these
are the chief parts of the respiratory apparatus, the digestive, the
wax-making, the reproductive, and stinging organs.
First, it must be noted that the bee has nothing strictly analogous
to our lungs, heart, liver, and other structures making up a true
circulating-system. At the same time there is a real oxygenation of the
fluids of the body, with a consequent evolution of heat, water, and
carbonic acid gas.
The breathing apparatus has not its aperture for inspiration and
expiration situated in the head, as is the case in the higher animals;
but air is admitted and expelled through apertures along both sides
of the body. In the thorax are two pairs of such openings, and there
is a pair on each ring of the abdomen. These air-holes are called
_spiracles_, or _stigmata_, and lead into two minute chambers, one
behind the other, the outer being provided with a number of short
hairs, to prevent the entry of foreign particles likely to obstruct the
important passages.
[Illustration: Fig. 32.--Abdomen of Bee, Showing Respiratory Organs.
_a_, Air-sac. _b b b_, Spiracles.]
From these vestibules the air is conducted by tubes, or _tracheæ_,
into sacs or bladders communicating with each other. The largest pair
of these cavities is found in the abdomen, and from these two main
trunks lead, one into the thorax, and the other to the termination
of the abdomen. From the latter there branch out subsidiary tubes,
leading into the minuter chambers, called _sacculi_, or little sacs.
Those going upwards do not subdivide till they reach the head, in
which are found two air-chambers of considerable size. Reasons for this
distribution of the secreting vessels may be found, on the one hand, in
the need of the oxygenation of the tissues, especially those connected
with the nutrition of the ganglia of highest functions; and, on the
other, in the requirements of buoyancy in the segments relatively the
heaviest, and destitute of organs of support in the atmosphere, such
as the wings furnish. A confirmation of the second of these purposes
is derived from the remarkable fact, that in the queen bee, who does
not fly more than once or twice in her life, the great air-sacs of the
abdomen are almost obliterated, their space being needed for the large
ovaries.
[Illustration: Fig. 33.--Air-sacs of Worker.]
The structure of the _tracheæ_ is very remarkable. Under a powerful
microscope they are seen to consist of a double membrane, between the
two coats of which are coils of an elastic thread, which act like
the spiral wire frequently used for keeping open and strengthening
india-rubber tubing. By means of this structure the air-pipes are
maintained in a condition for the free passage of the atmosphere, and
if closed by pressure, the elastic fibre reopens them directly the
pressure is removed.
[Illustration: Fig. 34.--_a_, Air-sacs, _b_, Ovaries, of the Queen.]
With regard to the circulation of the nutritive fluid in the system,
considerable obscurity prevails. What is known is, that along the back
of the insect runs a vessel called, from its position, the _dorsal_
vessel, attached to the outer covering of the body by bands of
ligamentous tissue. The portion of this tube contained in the abdomen
is enlarged at intervals into chambers communicating with each other
by valves, which allow the fluid to go forward to the head, but not
back towards the other extremity. Passing by a simple elastic tube
through the thorax, the blood, if we may so call it, is propelled to
the anterior segment of the body. Its subsequent course is not very
clear; for, while some anatomists speak of a small vessel leading back
to the hinder part of the body, others consider that the sanguineous,
or nutritive, liquid finds its way from the cephalic parts to other
vital organs, and after bathing them, returns to the dorsal vessel by a
second set of valves permitting its ingress only.
[Illustration: Fig. 35.--_a_, Tracheæ; _b_, Elastic Spiral of Tracheæ.]
Turning next to the nutritive organs, we have already spoken at
sufficient length of the mouth and its appendages, and have mentioned
that the nectar of flowers is conveyed first to an enlargement of the
gullet, analogous to the crop of birds. From this, some is regurgitated
by the workers into the cells, for storage, while another portion
passes on to the true stomach.[4] A certain amount of nitrogenous food,
chiefly pollen, also finds its way to this cavity, and there undergoes
a second mastication by the so-called _gastric_ teeth. These consist of
silica, and are therefore very hard.
[Footnote 4: Pastor Schönfeld has recently made some most interesting
researches into the anatomy and communication of the two stomachs. A
translation of his articles may be found in _The British Bee Journal_
for July, 1883.]
After undergoing considerable digestion in the stomach, the chyle,
as we may now consider it, passes into a short intestine, where it
receives fluid from the so-called "biliary ducts." Further on is an
expansion, called the _colon_, after traversing which the portions of
food not absorbed into the system, together with the waste products
brought to the intestines, are expelled from the body. It is probable
that the nutritive parts of the aliment find their way through the
walls of the intestine, and mingling with the sanguineous liquid
returned from the cephalic extremity, pass with it into the dorsal
vessel.
Closely connected with the digestive apparatus is that which is
concerned in the making of wax. By pressing the abdomen of the bee, so
as to cause its extension, there can be seen, on the under side of the
four medial ventral segments, two trapeziform whitish pockets, one on
either side of the _carinæ_, or elevated central part. These are of a
membranous texture, and are covered with a reticulation of hexagonal
meshes, reminding one of the inner coat of the second stomach of the
sheep, and other ruminating animals. There is no direct communication
between the stomach and these pockets; but Hunter suggested that the
secreting surface is in the membrane just alluded to.
[Illustration: Fig. 36.--Under Side of Abdomen, Showing Wax Scales.]
[Illustration: Fig. 37.--Bee, Showing the Wax Scales.]
[Illustration: Fig. 38.--Scales.]
We cannot follow the process by which the change from honey to wax is
effected, any more than we can account for the elaboration of bile,
saliva, and the pancreatic liquid, from our blood by the different
organs connected with their production. All we can say is, that the
membrane of the wax-receptacles is endowed with the peculiar power of
transforming the nectar of flowers into an oil. The actual chemical
change may be stated in general terms thus: Honey and sugar contain,
roughly speaking, equal chemical equivalents of oxygen, carbon, and
hydrogen. In wax, the quantities of the first of these elements is
diminished to about an eighth part, while the carbon and hydrogen are
more than quadrupled. In other words, the saccharine material suffers
very great de-oxidation in passing into the condition of wax.
The wax-oil, when it has filled the pocket in which it is secreted,
passes out of the body of the insect in _laminæ_ or scales, which take
the shape of the bags in which they have been produced. In contact
with the air, the wax absorbs a small quantity of oxygen, and loses an
equal amount of carbon. When about to be used by the bee, it is picked
off the under segments of the body by the hind-legs, passed on to the
fore-feet, and by them is conveyed to the mouth, where, by being mixed
with saliva and well kneaded, it is rendered pliant, ductile, and more
tenacious.
The reproductive organs of the queen consist, first, of two large bags,
one on each side of the abdomen, and called ovaries, in which the eggs
are generated. When mature, these eggs pass by a tube from each ovary
to a common duct, on one side of which is found a small yellow vesicle,
called the _spermatheca_. On examination under the microscope, this is
found to be filled with a viscous fluid, in which, with a lens of high
power, may be seen moving thousands of spermatozoa derived from the
drone.
[Illustration: Fig. 39.--Ovaries and Spermatheca of Queen.]
By voluntary effort on the part of the queen, each egg, as it passes
this vesicle, may be touched with a most minute drop of the fluid
just mentioned. Then this very marvellous fact results. An egg thus
fertilised develops into a queen or a worker, according to the
conditions under which it is hatched; while those eggs which are not
brought in their passage into contact with the fluid, and receive no
spermatozoa, become drones. Herein lies the explanation of fertile
workers giving birth to drones only, and of queens, hatched after
the drones of a season are dead, also laying eggs which will develop
only into male bees. We are absolutely unable to account for these
most extraordinary circumstances, which open up interesting fields for
future investigation. Not the least wonderful point is the exercise of
will, on the part of the queen, in the production of the particular
kind of egg which, without making mistakes, she lays in the cells
specially provided for the three classes of her offspring.
The last of the abdominal organs we have now to describe, is one
which is not essential to the life of the individual, but has been
conferred by the Creator as a means of offence and defence, viz.,
the sting. Those who have frequently felt its effects have no need
to be told how formidable a weapon it is; but few probably are fully
acquainted with the structures which give it such potent force. If a
bee be irritated, and made to thrust out its sting, we observe a dark
brown and sharply-pointed dart. This, when magnified, is seen to be
the sheath, in which the true sting lies and is moved. The sheath is
divided down the centre, and between the two parts the real piercers
work, though the sheath itself is thrust into the wound. It consists of
two horny scales, smooth and closely adherent to the true darts. These
last are stiff filaments, barbed along their outer edge. They are not
quite equal in length, so that the teeth of the one do not lie exactly
opposite those of the other. They work side by side, and, possibly with
alternate motion, pierce deeper and deeper into the punctured material.
The teeth give a firm hold to the imbedded weapon, and prevent its easy
withdrawal. In fact, when plunged into human flesh, or into thick
leather gloves, these barbs hold so tightly that the insect is unable
to free itself, and if forcibly detached, or if by a vigorous effort it
escapes, the sting is left behind, and frequently attached to it are
portions of the viscera. The bee thus loses its life, and the injury it
inflicts is the more severe.
[Illustration: Fig. 40.--Sting of a Bee, greatly magnified.]
The mere puncture of the weapon, however, would be a quite unimportant
matter, were it not that, connected with the groove in which the dart
works, is a short tube leading from a bag containing a liquid of the
most acrid and poisonous nature. By powerful muscles, attached to the
upper part of the sting, the barbs are thrust out; the sheath follows
them into the pierced substance, and then, by the pressure of other
muscles, a drop of the poison-liquid runs down into the wound, and
immediately sets up a violent pain and inflammation of the surrounding
parts. So powerful is the action of the irritant, that numerous cases
are on record of death ensuing through its influence. We are, however,
bound to say that, by many authorities, such fatal consequences are
considered to result from syncope produced by fright, rather than from
the _direct_ effect of the poison on the nervous system. Still, there
is no doubt of the very formidable nature of the liquid, as may be
generally seen in the amount of swelling and discomfort caused by the
exceedingly minute portion injected by the sting of a bee.
[Illustration: Fig. 41.--Barbs of a Bee's Sting, very highly magnified.]
The most remarkable function of the sting-apparatus has, in modern
times, been discovered to be the insertion of a minute drop of the
poison in each honey-cell when filled. This acts as an anti-septic, and
prevents fermentation in the sweet liquid.
The poison is secreted by tiny glands, from which it is conveyed,
by tubes or ducts, into the reservoir, where it is stored ready for
use. Chemically, the liquid is said to have an acid reaction. Hence
the application of ammonia, and other alkaline solutions, will most
effectually counteract its effects.
The sting of the queen differs from that of the worker, in having its
barbs curved, instead of straight. This modification makes it a much
less formidable implement. Moreover, it is very seldom employed. It is,
indeed, almost impossible to make a queen sting the hand, even by great
provocation. Almost the only circumstances in which her majesty employs
the weapon are, first, for mortal combat with a rival, and second, for
murdering, if permitted by the workers, the princesses before they
emerge from the cells in which they have developed.
The drone is without a sting, and, indeed, seems never to show fight at
all. Its jaws might furnish no despicable weapons, but the insect seems
to lack spirit to use them, even in self-defence, and when attacked by
the mandibles only of the workers, manifests no inclination to employ
its own against its tormentors. Struggles to escape, and haste to flee,
seem to betray its absence of courage; though, possibly, an instinctive
knowledge that its assailants have in reserve a more deadly piece of
armour than strong jaws may make "discretion the better part of valour."
With regard to the sting of the bee, Paley aptly remarks that it
"affords a beautiful example of the union of chemistry and mechanism:
of chemistry in respect to the venom, which, in so small a quantity,
can produce such powerful effects; of mechanism, as the sting is not
a simple but a compound instrument. The machinery would have been
useless, had it not been for the chemical process, by which, in the
insect's body, honey is converted into poison; and, on the other hand,
the poison would have been ineffectual without an instrument to wound,
and a syringe to inject the fluid."