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قراءة كتاب Our Common Insects A Popular Account of the Insects of Our Fields, Forests, Gardens and Houses

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Our Common Insects
A Popular Account of the Insects of Our Fields, Forests, Gardens and Houses

Our Common Insects A Popular Account of the Insects of Our Fields, Forests, Gardens and Houses

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دار النشر: Project Gutenberg
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on slight examination, and the abdomen is composed either of ten or eleven rings. The body, then, seems divided or insected into three regions, whence the name insect.

The head is furnished with a pair of antennæ, a pair of jaws (mandibles), and two pairs of maxillæ, the second and basal pair being united at their base to form the so-called labium, or under lip. These four pairs of appendages represent the four rings of the head, to which they are appended in the order stated above.

A pair of legs is appended to each of the three rings of the thorax; while the first and second rings each usually carry a pair of wings.

2. Centipede.2. Centipede.

The abdomen contains the ovipositor; sometimes, as in the bees and wasps, forming a sting. In the spiders (Fig. 1), however, there are no antennæ, and the second maxillæ, or labium, is wanting. Moreover, there are four pairs of legs. The centipedes (Fig. 2, a Myriopod) also differ from the rest of the insects in having an indefinite number of abdominal rings, each bearing a pair of legs.

On examining the arrangement of the parts within, we find the nervous cord, consisting of two chains of swellings, or nerve-knots, resting upon the floor or under side of the body; and the heart, or dorsal vessel, situated just under the skin of the back; and in looking at living caterpillars, such as the cut-worm, and many thin-skinned aquatic larvæ, we can see this long tubular heart pulsating about as often as our own heart, and when the insect is held against its will, or is agitated, the rapidity of the pulsations increases just as with us.

Insects do not breathe as in the higher animals by taking the air into the mouth and filling the lungs, but there are a series of holes or pores along the side of the body, as seen in the grub of the humble bee, through which the air enters and is conveyed to every part of the body by an immense number of air tubes. (Fig. 3, air tubes, or tracheæ, in the caudal appendage of the larva of a dragon fly). These air tubes are everywhere bathed by the blood, by which the latter becomes oxygenated.

Indeed the structure of an insect is entirely different from that of man or the quadrupeds, or any other vertebrate animal, and what we call head, thorax, abdomen, gills, stomach, skin, or lungs, or jaws, are called so simply for convenience, and not that they are made in the same way as those parts in the higher animals.

3. Caudal appendage of larva of Agrion.3. Caudal appendage of larva of Agrion.

An insect differs from a horse, for example, as much as a modern printing press differs from the press Franklin used. Both machines are made of iron, steel, wood, etc., and both print; but the plan of their structure differs throughout, and some parts are wanting in the simpler press which are present and absolutely essential in the other. So with the two sorts of animals; they are built up originally out of protoplasm, or the original jelly-like germinal matter, which fills the cells composing their tissues, and nearly the same chemical elements occur in both, but the mode in which these are combined, the arrangement of their products: the muscular, nervous and skin tissues, differ in the two animals. The plan of structure, namely, the form and arrangement of the body walls, the situation of the appendages to the body, and of the anatomical systems within, i.e., the nervous, digestive, circulatory, and respiratory systems, differ in their position in relation to the walls of the body. Thus while the two sorts of animals reproduce their kind, eat, drink and sleep, see, hear and smell, they perform these acts by different kinds of organs, situated sometimes on the most opposite parts of the body, so that there is no comparison save in the results which they accomplish; they only agree in being animals, and in having a common animal nature.

4. Different forms of jaws.4. Different forms of jaws.
5. Mouth parts of the Larva of a Beetle.5. Mouth parts of the Larva of a Beetle.
6. Maxilla of a Beetle.6. Maxilla of a Beetle.

How Insects Eat. The jaws of insects (Fig. 4) are horny processes situated on each side of the mouth. They are variously toothed, so as to tear the food, and move horizontally instead of up and down as in the horse. The act of taking the food, especially if the insect be carnivorous in its habits, is quite complex, as not only the true jaws, but the accessory jaws (maxillæ, Fig. 5, a, upper, b, under side of the head of a young beetle; at, antennæ, md, mandible, mx, maxillæ, mx[1], labium) and the feelers (palpi) attached to the maxillæ, and the under lip (labium) are of great service in enabling the insect to detect its food both by the senses of touch and smell. The maxillæ are in the fully grown beetle (Fig. 6) divided into three lobes, the outermost forming the palpus, and the two others forming sharp teeth, often provided with hairs and minute brushes for cleansing the adjoining parts; these strong curved teeth are used in seizing the food and placing it between the grinders, where it is crushed, prepared for digestion and swallowed. Fig. 7 represents the mouth parts of the humble bee. (b, upper lip; d, mandible; e, maxilla; f, maxillary palpus; g, tongue; ih, labium and tabial palpi; k, eye.)

7. Mouth parts of a Humble Bee.7. Mouth parts of a Humble Bee.

The alimentary canal passes through the middle of the body, the stomach forming usually a simple enlargement. Just before the stomach in certain insects, as the grasshopper, is a gizzard armed with rows of powerful horny teeth for finely crushing grass.

Insects eat almost incredible quantities of food when young and growing rapidly. Mr. Trouvelot tells us in the "American Naturalist" that the food taken by a single American Silk-worm in fifty-six days is equal to eighty-six thousand times its primitive weight! On the other hand, after the insect has finished its transformations, it either takes no food at all, as in the May fly, or merely sips the honey of flowers, as in the butterfly, while the June beetle and many others like it eat the leaves of trees, and the tiger and ground beetles feed voraciously on other insects.

How Insects Walk. In man and his allies, the vertebrates, the process of walking is a most difficult and apparently dangerous feat. To describe the mechanics of walking, the wonderful adaptation of the muscles and bones for the performance of this most ordinary action of life, would require a volume. The process is scarcely less

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