_The body-wall._—Insects differ fundamentally from man and other backboned animals. With us, the muscles and other soft parts are supported by an internal skeleton; with the insects the body-wall, that part which corresponds to our skin, is hard and serves as a skeleton. In some respects this is a better arrangement than that which obtains with us, for the skeleton of an insect serves as an armour to protect the body as well as a support for the soft parts.

This arrangement of parts holds with the appendages of the body of an insect as well as with the body itself; the legs, mouth-parts and antennæ are all tubular organs, having a firm outer skeleton supporting the inner parts.

Movement of the body and its appendages is provided for by narrow, flexible, zone-like areas in the skeleton which encircle the body and the appendages, at frequent intervals. This segmented condition of the body is easily seen in the hind part or abdomen, which appears to consist of a series of rings.

The microscopic structure of the body-wall is comparatively simple. There is an inner cellular part which consists of a single layer of cells: this is the hypodermis (Plate XXV, 2, _h_); and the outer or hard part: this is the cuticle (Plate XXV, 2, _c_).

The hypodermis is the active living part; it produces the cuticle, which receives additions from it constantly during the life of the insect. On this account, when a section of the cuticle is examined with a microscope it presents a layered appearance.

_Moulting of the cuticle._—From time to time during the growth of the insect the outer layers of the cuticle are shed; this is known as moulting. After a moult, the inner layers of the cuticle, which have now become the outer layers, but which are still soft, stretch to accommodate the increased size of the body, and then soon become hard. This moulting, or shedding of the skin, takes place about six times during the development of the bee. Several moults occur during the larval life: one when the larva changes to a pupa, and the last one when the pupa changes to the adult or winged form, just before leaving the cell in which it has been developed.

_The head._—The segments of which the body of an insect is composed are grouped into three regions: the head, the thorax, and the abdomen.

The head is the first of the three regions. It is formed of several segments grown together so as to form a compact box. It bears the eyes, the antennæ, and the mouth-parts.

The eyes are of two kinds, which are distinguished as the compound eyes and the simple eyes.

The compound eyes are two in number, one on each side of the head; they are the organs commonly recognised as the eyes. They are called compound eyes because each consists of a great number of little eyes closely pressed together. If a compound eye be examined with a microscope, it will be seen to present the appearance of a honey-comb, being composed of a great number of six-sided elements; each of these is a separate eye.

In addition to the compound eyes, the bee has three simple eyes, or _ocelli_, as they are termed. They are situated on the upper part of the head between the compound eyes.

The antennæ are two slender, many-jointed organs projecting from the front part of the head. Their use has not been fully elucidated. They are doubtless sense organs; and it is believed that certain microscopic pits, which occur in great numbers in their cuticle, are the organs of smell. It is possible, also, that the antennæ function as organs of touch, certain hairs with which they are furnished being the tactile organs.

The mouth-parts are very complicated. They consist of an upper lip, a lower lip, and two pairs of jaws between the lips.

The upper lip is known as the _labrum_. It is a flap-like projection situated above, or in front of, the other mouth-parts (Plate XXV, _u_).

The first pair of jaws, those situated nearest the labrum, are the mandibles (Plate XXV, 3, _md_). Each mandible consists of a single hard piece. They are the biting organs. Certain wild bees, distantly related to the honey-bee, dig holes in wood with their mandibles for nests for their brood. The honey-bee uses its mandibles as tools for the manipulation of wax and propolis, and as weapons in its combats.

The second pair of jaws, which are situated between the mandibles and the lower lip, are the maxillæ (Plate XXV, 3, _mx_). Each maxilla is a long blade. The maxillæ, combined with the lower lip, constitute what, in popular language, is known as the tongue, the organ by means of which the food is conveyed to the mouth, or the nectar extracted from a flower.

_Photograph by Ralph W. Curtis_

PLATE XXIV. SUMAC IN BLOSSOM AND BLOSSOM OF MOUNTAIN MAPLE

The Sumac is an excellent honey-producer.]

PLATE XXV. FIG. 1.—Vertical longitudinal section of the body of a larva of an insect; _s_, body-wall or skeleton; _m_, muscles; _a_, alimentary canal; _h_, heart; _n_, nervous system; _r_, reproductive organs. FIG. 2.—Section of the body-wall; _c_, cuticle; _h_, hypodermis; _t_, trichogen or hair-forming cell. FIG. 3.—Head of a bee and its appendages; _a_, antenna; _c_, clypens; _u_, upper lip or labrum; _m_, mandible; _mx_, maxilla; _l_, lower lip or labium; _p_, labial palpus. FIG. 4.—Glands of a honey-bee (after Girard); _1_, supracerebral glands; _2_, postcerebral glands; _3_, thoracic glands. FIG. 5.—The wax plates (after Cheshire).]

The lower lip, or labium (Plate XXV, 3, _l_), is the long central part of the so-called tongue; it bears on each side a long appendage; these are the labial _palpi_ (Plate XXV, 3, _p_).

_The thorax._—The thorax is the central region of the body. It consists of three body-segments, which are grown together so compactly in the adult insect that it is difficult to distinguish them. The thorax bears the organs of locomotion, the wings and the legs.

There are two pairs of wings; but the two wings of each side are so closely united that they appear as one. The union is accomplished by a row of hooks on the front edge of the hind wing, which fasten into a fold in the hind edge of the fore wing. The wings are strengthened by a framework of heavy lines, which extend in various but definite directions. Between these lines the wing is a thin membrane.

There are three pairs of legs, a pair borne by each of the three body-segments of which the thorax is composed.

Each leg consists of nine segments and a pair of claws at the tip of the last segment. The first two segments, the _coxa_ and the _trochanter_, are short; then follow the two principal segments, the _femur_, or thigh, and the _tibia_, or shank; the five remaining segments constitute the _tarsus_ or foot. A striking peculiarity in the _tarsi_ of bees is that the first segment differs greatly in form from the other segments and is much larger, approaching the _tibia_ in size. This enlarged tarsal segment has received the special name of _metatarsus_.

The legs serve several functions besides that of locomotion. Thus, on each fore leg there is an organ for cleaning the antennæ. The antenna cleaner consists of a circular notch near the base of the _metatarsus_, which is furnished with teeth like a comb (Plate VII, F, _a_), and a spur projecting back from the _tibia_ in such a way as to close this notch when the leg is bent. The antenna to be cleaned is drawn through this notch and thus the dirt is combed from it.

On the middle legs there is a strong spur at the distal end of the _tibia_ which is used in loosing the pellets of pollen brought to the hive on the hind legs.

The third pair of legs are furnished with three organs which deserve mention here. _First_: the wax pincers. Both the _tibia_ and the _metatarsus_ are wide; the joint uniting them is at one edge, hence by alternately bending and straightening the leg at this joint, the space between the two segments (Plate VII, B, _wp_) is opened and shut like pincers. This organ is used to loosen from the abdomen the scales of wax. _Second_: the pollen-combs. These are several comb-like series of spines, borne on the inner surface of the _metatarsus_ (Plate VII, B, _pc_). When a bee visits a flower the pollen is gathered by the tongue and fore legs and some of it becomes entangled among the hairs on the thorax. It is then combed from these parts by means of the pollen-combs and transferred to the pollen baskets. _Third_: the pollen basket. There is a pollen basket on the outer surface of the _tibia_ of each hind leg. It consists of a fringe of hairs, surrounding a smooth, concave area which occupies the greater part of the outer face of this segment of the leg. In it the pollen is packed when combed from the hairs, and transported to the hive.

_The abdomen._—The abdomen is the last of the three regions of the body. It consists of a series of comparatively simple, overlapping segments, without conspicuous appendages.