_Relative position of the internal organs._—As has been shown in the preceding pages, the body-wall serves as a skeleton, being hard and giving support to the other organs of the body, which are contained within it.

The accompanying diagram (Plate XXV, 1), which represents a vertical longitudinal section of the body of the larva of an insect, will enable the reader to gain an idea of the relative positions of some of the more important organs. The parts shown in the diagram are the following: The body-wall or skeleton (_s_); this is made up of a series of overlapping segments; that part of it which is between the segments is thinner, and is not hardened, this remaining flexible and allowing for the movements of the body. Just within the body-wall, and attached to it, are represented a few of the muscles (_m_); it will be seen that these muscles are so arranged that the contraction of those on the lower side of the body would bend it down, while the contraction of those on the opposite side would act in the opposite direction. The alimentary canal (_a_) occupies the centre of the body and extends from one end to the other. The heart (_h_) is a tube open at both ends, and lying between the alimentary canal and the muscles of the back.

The central part of the nervous system (_n_) is a series of small masses of nervous matter, connected by two longitudinal chords; one of these masses, the brain, lies above the alimentary canal; the others are situated, one in each segment, between the alimentary canal and the ventral wall of the body; the two chords connecting these masses, or ganglia, pass one on each side of the œsophagus to the brain. The reproductive organs (_r_) lie in the cavity of the abdomen and open near the hind end of the body. The respiratory organs are omitted from this diagram for the sake of simplicity.

_The respiratory system._—The most striking peculiarity in the structure of insects is the form of their organs for breathing, for they do not breathe through the mouth as we do. If an insect be carefully examined, there can be found along the sides of the body, a series of openings; these are the openings through which the air passes into the respiratory system, and are termed spiracles. The spiracles of the honey-bee are small, and are not easily found by one not trained to look for such things; but if the reader will examine the sides of one of our larger caterpillars, he will have no trouble in seeing them. Typically, there is a pair of spiracles, one on each side of the body, in each of the body-segments, but they are lacking in the head and in some of the other segments. The spiracles lead into a system of air tubes, termed tracheæ, which carry the air to all parts of the body. When the body of an insect is opened, the tracheæ appear as silvery threads, on account of the contained air. In the adult honey-bee certain of the tracheæ are greatly expanded so as to form large air sacs. (Plate XXVI _b_, 2).

_The glands._—Those glands found in the body of the honey-bee that are of most interest to the practical bee-keeper are the following:

In the larva there is a pair of long, tubular glands, which secrete the silk of which the cocoon is made. These glands open through a common duct, which has its outlet near the mouth.

In the adult worker bee there are four pairs of glands opening into the mouth, which have been much discussed by students of this subject. These glands are designated both by number and by name as follows: System I. or supracerebral glands; system II. or postcerebral glands; system III. or thoracic glands; and system IV. or mandibulary glands.

The supracerebral glands or system I. (Plate XXV, Fig. 4, 1) are situated in the head above the brain. They open by two openings in the floor of the mouth cavity, one on each side.

The postcerebral glands or system II. (Plate XXV, Fig. 4, 2) are situated in the head behind the brain; their outlets unite into a common duct which opens on the middle line of the anterior end of the œsophagus at the base of the tongue.

The thoracic glands or system III. (Plate XXV, Fig. 4, 3) are situated in the thorax; their outlets unite into a common duct, which joins the ducts from the postcerebral glands, the two systems of glands opening through a common opening.

The mandibulary glands or system IV. are two small glands one on each side opening at the base of the mandible.

There has been much discussion regarding the function of these different glands; and even now any statement of conclusions must be regarded as provisional.

The supracerebral glands are large in nurse bees and shrunken in the old bees that no longer nurse the brood; they are normally found only in the workers. It is therefore believed that they secrete the milky food, commonly called royal jelly, which is fed to all larvæ during the first days of their development, to the queen larvæ throughout their development, and to the adult queen during the egg-laying period. The food fed worker and drone larvæ during the latter part of their development is produced in the chyle-stomach of the nurse bees, and is semi-digested food.

The other systems of glands enumerated above produce the saliva, which is supposed to perform a great variety of functions. “It helps the digestion; it changes the chemical condition of the nectar harvested from the flowers; it helps to knead the scales of wax of which the combs are built, and perhaps the propolis with which the hives are varnished. It is used also to dilute the honey when too thick, to moisten the pollen grains, to wash the hairs when daubed with honey, etc.”

The wax glands are found only in the worker. There are four pairs of them. They are situated on the ventral wall of the second, third, fourth and fifth abdominal segments, and on that part of the segment which is overlapped by the preceding segment. Each gland is simply a disc-like area of the hypodermis, the cells of which take nourishment from the blood and transform it into wax. The cuticle covering each gland is smooth and delicate, and is known as a wax plate. The wax exudes through these plates and accumulates, forming little scales. (Plate VI, X, also Plate XXV, Fig. 5.)

_The alimentary canal._—The form of the alimentary canal of the adult honey-bee is shown in Plate XXVI. The following parts can easily be recognised: the œsophagus, a slender tube, beginning at the mouth and extending through the head and thorax to the base of the abdomen. Here there is a sac-like enlargement of the canal, which is termed the honey-stomach; it is in this that the nectar accumulates as it is collected by the bee, and is carried to the hive. Behind the honey-stomach lies the true stomach, the chief digestive organ. Closely applied to the true stomach are several small tubes, which open into it; which are known as the Malpighian tubes; they were named after one of the early anatomists who described them; they are the urinary organs. Next to the true stomach is the small intestine; and behind this, the large intestine.

_The reproductive organs._—The internal reproductive organs are situated in the abdomen; there is a set on each side, but the two sets open by a common duct, whose outlet is at the hind end of the body.

The reproductive organs of the female are shown on Plate XXVI (_a_), Fig. 1. There are two ovaries (_o_), one on each side of the body. Each ovary consists of a large number of parallel egg-tubes, within which the eggs are developed. The egg-tubes of each ovary open into an oviduct (_od_). The two oviducts unite and form a single tube on the middle line of the body; this is the _vagina_; the _vagina_ leads to the external opening of the system. Communicating with the _vagina_, there is a sac-like pouch, the _spermatheca_, which is the reservoir for the seminal fluid; this is filled at the time of pairing, and the _spermatozoa_ may remain alive in it for several years.

Each egg-tube produces many eggs. As the eggs increase in size, they pass towards the oviduct. When the egg is fully developed a shell is formed about it. This shell has a minute opening through it at one end; this is the micropyle. At the time the egg is laid a _spermatozoon_ may pass from the _spermatheca_, where thousands of them are stored, into the egg through the micropyle, and thus the egg is fertilised.

With most animals, the egg must be fertilised in order that it may develop. But with bees, both fertilised and unfertilised eggs develop, the former into females, that is, workers or queens, the latter into males, that is, drones.

PLATE XXVI. (_a._) The reproductive organs of the honey-bee. (From Leuckart, slightly modified.) FIG. 1.—Reproductive organs of a queen; _o_, _o_, ovaries; _od_, oviduct; _s_, spermatheca; _g_, gland; _p_, poison sac connected with the sting. FIG. 2.—Reproductive organs of a drone; _t_, _t_, testes; _v_, vas deferens; _s_, _s_, seminal sacs; _m_, _m_, mucous glands; _ed_, ejaculatory duct; _b_, pouch or bulb. The bulb and the following parts are everted through the outer opening at the time of pairing.]

PLATE XXVI. (_b._) FIG. 1.—The internal anatomy of the honey-bee (after Cheshire). _o_, œsophagus; _hs_, honey sac; _p_, stomach-mouth; _cs_, true stomach or chyle-stomach; _m_, malpighian tubes; _si_, small intestine; _li_, large intestine; _h_, heart or dorsal vessel; _n_, central nervous system; _1_, supracerebral glands; _2_, postcerebral glands; _3_, thoracic glands. The respiratory system and the reproductive organs are not shown in this figure (after Cheshire). FIG. 2.—The respiratory system of the honey-bee. _s_, _s_, _s_, spiracles; _a_, enlarged trachea or air sac (adapted from Leuckart).]

_Courtesy of Ginn & Company_

PLATE XXVII. AN OLD-FASHIONED APIARY]

Closely associated with the reproductive organs of the female is the sting; this is a barbed dart connected with a poison gland, whose use is well known.

In the abdomen of the male there is a pair of organs, the testes, in which the _spermatozoa_ are developed. These correspond in position to the ovaries of the female, but are much smaller. From each testis there extends a tube corresponding to the oviduct, this is the _vas deferens_. The two _vasa deferentia_ unite and form the single ejaculator duct. Each _vas deferens_ is enlarged just before it joins the ejaculatory duct, forming a reservoir for the accumulation of _spermatozoa_; these reservoirs are termed the seminal sacs. Appended to each seminal sac there is a large glandular sac, which adds mucus to the seminal fluid. Near the outer end of the ejaculatory duct there is a pouchlike enlargement into which the _spermatozoa_ pass. Here they are massed into a compact body, known as the spermatophore, which is transferred to the female at the time of pairing. The terminal part of the reproductive organs of the male, the intermittent organ, has several appendages, which are firmly grasped in the opening of the reproductive organs of the female and are torn from the male when the two pairing individuals separate. This causes the death of the male. The male has no sting. (Plate XXVI, Fig. 2.)