. Outlines of zoology. Zoology. 302 PERIPATUS, MYRI0P0DS, AND INSECTS. clawed and hairy at their tips, and differ greatly according to their uses, as may be seen by comparing, for instance, the hairy feet by aid of which the fly runs up the smooth window pane, the muscular limbs of grasshoppers, the lank length of those which characterise " daddy- long-legs," the bees' legs with their pollen baskets, the oars of water- beetles. Wings.—These arise as flattened hollow sacs, which grow out from the two posterior segments of the thorax. They are moved by muscles, and traversed by "v
. Outlines of zoology. Zoology. 302 PERIPATUS, MYRI0P0DS, AND INSECTS. clawed and hairy at their tips, and differ greatly according to their uses, as may be seen by comparing, for instance, the hairy feet by aid of which the fly runs up the smooth window pane, the muscular limbs of grasshoppers, the lank length of those which characterise " daddy- long-legs," the bees' legs with their pollen baskets, the oars of water- beetles. Wings.—These arise as flattened hollow sacs, which grow out from the two posterior segments of the thorax. They are moved by muscles, and traversed by "veins " or "nervures," which include air-tubes, nerves, and vessel-like continuations of the body cavity. Most insects have two pairs, but many sluggish females and parasites, like lice and fleas, have lost them. On the other hand, there is no reason to believe that the very simplest wingless insects, known as Collembola and Thysanura, ever had wings. There are many interesting differ- ences in regard to wings in the various orders of Insects. Thus in beetles the front pair form wing-covers or elytra ; in the little bee parasites—Strepsiptera —they are twisted rudiments; in flies the posterior pair are small knobbed stalks (halteres or balancers); in bees the wings on each side are hooked together. When the insect is at rest the wings are usually folded neatly on the back ; but dragon-flies and others keep them expanded; butterflies laise them like a single sail on the back ; moths keep them flat. Many wings bear small scales or hairs, and are often brightly coloured. It is well known that the colours also vary with sex, climate, and surroundings. Most interesting are those cases in which the colours of an insect harmonise exactly with those of its habitat, or make it a mimetic copy of some more successfully protected neighbour. As to the origin of wings, it may be remembered that in many cases they are of some use in respiration as well as in locomotion, an
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Keywords: ., bookauthorth, bookcentury1800, bookdecade1890, booksubjectzoology
