Page:Popular Science Monthly Volume 39.djvu/245

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233
THE CHARACTERISTICS OF INSECTS.

legs (Fig. 13). The leg has the form of an elongated trapeze, the major base of which is often provided with spurs, while the crest is covered with teeth or rigid hairs. The tarsus is composed of joints, not exceeding and not always reaching five in number. These short joints are of different forms. They are sometimes furnished with fine balls of silk, a kind of brushes which aid in standing}} or with suckers answering the same purpose. The last joint of the tarsus, called the onychium, bears one or two nails. The joints of the tarsi are generally distributed in equal numbers upon all the legs of the insect; but there are sometimes fewer on the middle and after limbs than on the fore limbs.

The arrangements we have pointed out hold with the walking insects; with aquatic insects the rugosities of the joints are smoothed down, the nails are blunted, and the legs are transformed into ciliated paddles that permit the animal to move easily in the water.

PSM V39 D245 Foot on fly.jpg
Fig. 14. — Foot of a Fly. p, pelotes; g, nails.

The abdomen consists of a series of rings joined to one another by a fine membrane which gives them great mobility. It is by means of this disposition that the abdomens of females when distended with eggs attain such extraordinary proportions. The number of abdominal segments varies from six to nine. The last ones are sometimes transformed into accessories of the genital apparatus. The last horny arch of the abdomen is called the pygidium, as in the tail of the cockchafer.

The cutaneous envelope of insects is usually of a dull, ruddy, or pitchy color; sometimes clearer, sometimes of a metallic appearance; but that which constitutes their richest livery is the investment of their external skeleton. This investment is formed of silks, felted hairs, spines, or thin caducous scales, the overlaying of which composes most original designs. A moderate enlargement is sufficient to give some species the appearance of brilliant jewels; seen under the lens, the Curculio imperialis, a Brazilian beetle, appears like a real set of emeralds and diamonds. Nothing is more interesting than to observe the fine pubescence of our native weevils and the delicate scales of the coats of some individuals. All these ornaments are, however, so fragile that we only have to graze a butterfly's wing with the finger to scatter