CHAPTER IX.

PARTS OF AN INSECT (CONTINUED).

62. THE pupils have learned that the abdomen is divided into rings or segments, and the division between these segments is plainly seen in most insects.

The thorax is divided in a similar manner, only the lines which divide the thorax are not so plainly seen.

The number of segments in the thorax is three. To the first segment, the head and first pair of legs are attached; to the second segment, the second pair of legs and the first pair of wings are attached; and to the third segment, the hind pair of legs, the hind pair of wings, and the abdomen, are attached. The three segments of the thorax have special names: the prothorax, this being the forward segment, next to the head; mesothorax, being the middle segment; and metathorax, being the last segment. Arranging these segments with the appendages attached to them in a table, they would appear as follows:

THE THORAX IS COM-
POSED OF THREE SEG-
MENTS.

1st Segment, Prothorax,
2d Segment, Mesothorax,

3d Segment, Metathorax,

Has attached to it the first pair of legs.

Has attached to it the second pair of legs and the first pair of wings. Has attached to it the third pair of legs and the second pair of wings.

63. Let the pupils now endeavor to dissect a beetle, carefully separating the segments of the thorax, and, if possible, the minute jaws and other mouth-parts, and stick them on

F

55. Thus far we have learned that an insect proper, or true insect, has the body divided into three parts or regions, called the head, the thorax, and the abdomen.

Let the pupil take a dead fly, and first pull off carefully the legs and wings, and afterward separate the head from the thorax, and the thorax from the abdomen. Having separated the parts in this way, they may be pasted to a card in this manner, writing the correct name beside each part, or region, as shown in Fig. 58.

Head.
Thorax.

Abdomen.

FIG. 58.-CARD, WITH REGIONS OF AN INSECT GLUED TO IT, AND MARKED.

The principal parts of the head are the mouth-parts, compound eyes, simple eyes, and antennæ.

56. In studying the thorax, the pupil may select some common insect (a large fly, or a bee, will answer the purpose), and pull off the head and abdomen. A common house-fly separated in this way may be stuck upon a card. By experimenting with a number of insects in this manner, the pupil will soon learn that insects not only have the body divided into three sections, but that the thorax invariably has attached to it the legs and wings-the legs being at

tached to the under side of the thorax, while the wings are attached to the upper side thereof.

head. c

thorax.

abdomen.

FIG. 59.-Head, having mouth-parts, antennæ, compound eyes, c; and simple eyes, 8.
Thorax, having legs and wings.

Abdomen, never having legs or wings, but having certain appendages at the extremity.

57. The wings of insects are never more than four in number, and these are arranged in two pairs.

The group of insects to which the house-fly belongs has but two wings, or a single pair, and in this group (and other groups of insects as well) there are some which have no wings.

The wings are very different in shape and structure in distinct kinds of insects. In the common fly they are quite small, and transparent. In the butterflies they are large and broad, and are covered with minute scales which rub off on the fingers like dust. In the dragon-fly the wings are long and narrow.

In all these wings the pupil will observe a net-work of lines, which stiffen the wing and support the delicate membrane constituting the wing, just as the frame of a kite stiffens and supports the paper that is stretched upon it. These lines are called veins, or nervures. To study the vena

FIG. 60.-AN IN- FIG. 61.-AN INSECT WITH FIG. 62.-AN INSECT WITH FOUR WINGS.
SECT WITHOUT
Two WINGS.

WINGS.

tion of the wings, is to study the way in which these veins are arranged. It would be well for the pupils to stick upon a card a number of different kinds of wings, such as those of the grasshoppers, beetles, flies, wasps, and label them accordingly.

58. In many insects the forward and hinder pair of wings are of the same nature, as in the butterflies, moths, bees, wasps, and dragon-flies. In other insects, however, the forward-wings differ in character from the hind-wings. Thus, in the grasshopper the forward pair of wings are more dense in structure than the hind-wings, though the little veins may be seen closely crowded together. They differ as well in form. (See Fig. 64.)

In other insects, as in the squash-bug, the front-wings

have the half nearer the body dense and stiff, while the remaining portion of the wing is very thin, or membranous.

In the beetles the front wings are hard throughout, and in most of them are bent and moulded to the shape of the body, and, when closed, form a tight cover over the hindwings.

The forward-wings of a beetle are so unlike ordinary wings, that they are not called wings, but are known as elytra, a single one being called an elytron.

59. When insects are at rest, they generally bring their wings into a position different from that taken by them in flight. In certain dragon-flies, however, the wings when

Butterfly at rest with wings

meeting over the back.

Moth at rest with the wings sloping on the sides of the body.

FIG. 63.-INSECTS AT REST.

at rest assume the same position as they do when flying. In the butterfly the wings are brought together over the back when at rest, while the moths with few exceptions rest them sloping over the abdomen, the front-wings covering the hinder-wings.