. Outlines of zoology. Zoology. WINGS. 309 that the very simplest wingless insects, known as Collembola and Thysanura, ever had wings. There are many interesting differences in regard to wings in the various order 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 the
. Outlines of zoology. Zoology. WINGS. 309 that the very simplest wingless insects, known as Collembola and Thysanura, ever had wings. There are many interesting differences in regard to wings in the various order 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 raise them like a single sail on the back, moths keep them flat. Many wings bear small scales or hairs and are often brightly coloured. Pro- fessor Eimer maintains that the arrange- ment of the nervures and the colouring of butterfly wings are certain marks of the progress and relationships of species. 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 ex- actly with those of its habitat, or make it a mimetic copy of some more success- fully protected neighbour. As to the origin of wings, this at least should be remembered, that in many cases they are of some use in respiration as well as in locomotion. Seeing that the power of flight is evidently an accom- plishment which the original insects did not possess, the theory seems plausible that wings were originally respiratoiy outgrowths, which ,by-and-by became useful for aerial locomotion. This view is consistent with an idea, which grows in favour with evolutionists, that new organs develop by the predominance of some new function in organs which had some prior significance. Moreover, we can fancy that an increase in respiratory efficiency brought about by the out- growths in question would quicken the whole life, and would tend to raise insects into the air, just as terrestrial insects can he.
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
