The science of life : fully illustrated in tone and line and including many diagrams

THE SECOND GREAT PHYLUM: THE ARTHROPODS

FOR. Biscmrwern,

Fig. 83. The Cockroach

alone than of all other animals taken together. Butterflies, moths, dragon-flies, beetles, gnats, mosquitoes, house-flies, blowflies, bot-flies, daddy-long-legs, bees, wasps, ants, fleas, bugs, lice, termites, grasshoppers, earwigs, cockroaches—these are the most familiar forms, but there are many others. For the most part they are mere nuisances. Some, it must be admitted, are esthetically satisfying, and a few, such as bees and cochineal bugs and those insects which eat weeds or other insects or those which fertilize flowers, have been found actually useful to man; but these are the few bright exceptions in a yast family of bloodsuckers, stingers, spreaders of disease, and devourers of crops. They are a distressful aspect of reaction. They are a hard problem for the theologian.

Some of these animals live in water—the larve of gnats and dragon-flies, for example, or the air-breathing water-beetles—but the greater number are land-living forms, and like the spiders they breathe by means of a system of air-tubes or trachee. They may be distinguished from other land arthropods by their possession of three pairs of walking legs; in addition, the great majority of insects have a highly characteristic feature in their wings. Alone among invertebrates, the insects have conquered the air, unless we consider that the gossamer spider who

cleans himself and flies away.

floats along parachute or balloon fashion on his slender threads is also a conqueror.

‘The wings do not correspond to any of the appendages of a crustacean; they are different structures, sprouting, not from the belly, but from the back. ‘Typically there are two pairs of wings—as for example in the dragon-flies, where the wings are transparent and delicately veined, in the butterfliesand moths, where they are coloured and dusted over with prettily constructed scales, and in the bees, where the front and back pairs are fastened together by hooks so that they may beat together more accurately—but this arrangement may be departed from. In the beetles only the hinder pair is used for flying; the front pair of wings forms a hard, opaque casing that covers and protects the delicate second pair when the latter are not in use. In the mosquitoes and commoner flies, on the other hand, the front pair are the ones which are used as wings or should be used ;_the hind pair are developed as tiny knob-like structures, the so-called ‘“‘ balancing organs.” Finally, many insects, such as the fleas and the spring-tails, have no wings at all.

A second respect in which the insects excel over other invertebrates is the surprisingly efficient degree of communal organization to which many of their species attain. There is only one other animal—

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