THE THORAX.
Detailed Description--Legs--Wings--How used in Flight--Hooking
together--Employed for Ventilating.
The thorax of the bee is divided into three sections, or imperfect
rings. Of these, that nearest the head is called the _pro_-thorax,
the middle one the _meso_-thorax, and the hindmost the _meta_-thorax.
To the first of these are attached the most forward pair of legs; to
the second, another pair of legs and one pair of wings; to the third,
the last pair of legs and the other pair of wings. These organs of
locomotion constitute, in fact, all that is worthy of special interest
in this segment of the body, and we will, therefore, give a short
account of them.
The legs of all insects consist of five parts, or joints, and in the
case of the bee they are not only the means of walking or crawling,
but, like some of the head organs of which we have spoken, serve
several purposes. The first of the leg-segments is called the _coxa_,
or hip, and is short and round, appearing, indeed, to be little more
than the joint by which the limb is articulated to the body. The
second is named the _trochanter_, and is very similar to the _coxa_.
One purpose effected by these two portions is to give great freedom
of motion to the whole member. Next comes the _femur_, or thigh, a
longer and flatter division. This is followed by the _tibia_, or shank,
a stouter and thicker division, which, especially in the hind-legs,
becomes gradually wider downwards, and in the workers is adapted to
a very special use, as we shall directly see. Then in succession we
have the _tarsus_, or foot, consisting of five joints, the first very
much stouter than the rest, and as long as the remaining four. It is
terminated by a pair of hooked claws, with a cushion or _pulvillus_.
[Illustration: Fig. 28.--Lower Segments of Hind-Leg of Bee,
Considerably Enlarged.]
[Illustration: Fig. 29.--Complete Hind-leg Of Bee.]
We have already spoken of the remarkable apparatus found in the in
the hind legs, adapted to the purpose of cleansing the antennæ.
At the junction of the fourth and fifth segments (the _tibia_ and
the _tarsus_) of the hind leg of a worker a cavity is formed by the
uppermost edge of the latter and the lower of the former. The cavity
can be opened or closed at the will of the insect. Above this, on the
outside of the tibia, is a pocket, or pollen-basket, lined along its
upper edge with a row of lancet-shaped hairs, which aid in detaining
the tiny balls of pollen, as they are successively deposited on the
leg. Like a series of prong-tines, they can be pressed into the
yielding bee-bread, and keep it from falling off; while, as _they point
downwards_, they present no obstacle to the brushing off of the whole
mass by the bee, on its return to the hive. The slight hollowing of the
_tibia_ and the _tarsus_ at the approximating ends, affords more space
for the gathered pollen, and also assists in its safe carriage to the
cells.
The last joint of the _tarsus_ is armed with a pair of double claws,
and between them lies a hollow cup-shaped cushion, somewhat like that
which enables the house-fly to walk on glass or other very smooth
surfaces, only that the _pulvillus_ of the fly is double. The edge of
the cup is fringed with _ciliæ_, or very minute hairs, of such delicacy
that a powerful lens is required to see them. Under the microscope, the
object is one of great interest.
The claws serve for hanging from the roof or sides of hives, and for
clinging to each other at swarming or wax-making times, the cushion for
walking on smooth surfaces. It is worthy of remark that all the joints
of the legs are covered with hairs more or less stiff, and all pointing
downwards. Their uses are to collect pollen, and to act as brushes
and combs to all the external parts of the body, which need constant
cleansing from flower-dust, and other matters less useful to the bee.
[Illustration: Fig. 30.--Wing of Bee.]
Passing now to the wings, new marvels and beauties await our
observation. These organs are four in number, the forward pair being
considerably larger than the hinder. Each wing consists of a double
membrane, dotted all over with fine hairs, whose purposes are to
protect the delicate structure from wet, and from particles of various
kinds which would adhere to it, and injure its surface. As a support
for this expanded tissue, there is a ramification of stronger material,
constituting nervures, and acting like the ribs of an umbrella. With
these are associated air-vessels, or _tracheæ_, for the circulation
of air, and, possibly, to assist in giving buoyancy to the organ. By
another set of tubes a portion of the nutritive fluid is conveyed to
certain parts of the wing, though no general circulation seems to take
place in it. The substance of which the expanded portion, as well as
the nervures, is composed, is very tough, and, as our readers may
remember, the natural order to which the bees are assigned is named
_Hymenoptera_, from the strongly _membranous wings_ they possess.
We can readily understand the importance to these insects of having
their organs of flight powerful, and yet not weighty, tough without
being clumsy. Considering the length of their daily journeys, and the
constant and rapid movements they require to make, we easily discern
how well suited to their needs is the structure of their wings. But we
must call attention to a remarkable provision for the further utility
of these organs. Under a lens of medium power may be seen, along the
anterior edges of the hind wings, a series of booklets of hair, while
on the posterior edge of the front wings is a rib, or bar, which the
booklets can grasp. By this means the two wings, when used for flight,
become practically one, thus presenting unbroken resistance to the air,
and, in consequence, greatly increasing the power of propelling the
body. When at rest, the unhooking of the edges enables the wings to be
folded out of the way--no mean advantage in the crowded hive.
[Illustration: Fig. 31.--Hooklets of a Bee's Wing.]
But there is a further benefit thus conferred on the insect. During
hot weather, and when the population is very dense, ventilation is
constantly and vigorously carried on by the workers, who, fixing
themselves firmly by their claws to the floor-board at the entrance,
some outside and some just within their homes, direct numerous
currents of air into the hive. Of course there must issue a quantity
corresponding to what is driven in, and thus a perpetual and free
circulation is kept up. Now, if the wings worked independently, not
only would a smaller quantity of air be affected by each stroke, but
the two sets of motions would, to some extent, counteract each other.
As it is, the hooked wings act like well-constructed and well-used
fans. By the simple experiment of slitting such an implement down the
middle, the comparative advantages of a broken and an unbroken surface,
for fanning purposes, can easily be put to the proof.
Thus, again, we are struck with the fact that the more closely we
examine the organs of any segment of the body of the insect, the
more reason do we find to admire the skill, and the care for His
creatures, manifested by the infinitely wise and the infinitely good
Maker of them all. Beauty, adaptation, perfection, are the words which
are continually suggested to our minds by the contemplation of the
structure of the bee.