. Cassell's natural history. Animals; Animal behavior. NATURAL -HEAD OF SET (Vespa crabro) exlaeged, front (a) SIDE VIEW (b). tliis is usually of a blackish or brownish tint, the wing-veins become plainly marked. The mode of ram- fication of these veins is exceedingly characteristic of different groups of insects, and consequently of great importance in their classitication. In some cases the deposition of liorny material in the wing is not contined to the veins, but extends throughout the wing, which then becomes a horny or leathery organ, unfitted to assist in flight. This change u
. Cassell's natural history. Animals; Animal behavior. NATURAL -HEAD OF SET (Vespa crabro) exlaeged, front (a) SIDE VIEW (b). tliis is usually of a blackish or brownish tint, the wing-veins become plainly marked. The mode of ram- fication of these veins is exceedingly characteristic of different groups of insects, and consequently of great importance in their classitication. In some cases the deposition of liorny material in the wing is not contined to the veins, but extends throughout the wing, which then becomes a horny or leathery organ, unfitted to assist in flight. This change usually takes places in the fore wings alone, which then serve as protective cover- ings to the greatly developed and more delicate posterior wings, the true organs of flight, which in rejtose are folded up and packed away on the back of the abdomen beneath the firmer anterior pair. In the Beetles (see Fig. 1), which furnish the best examples of this modification, the horny fore wings, called elytra, when closed, meet in a straight line down the middle of the back, usually concealing the whole dorsal surface of the body, excejjt the fii'st segment of the thorax {prmwtum) and a small, .shield-shaped piece of the mesonotuni (the sciitellam) ; in other insects which possess horny or leathery fore wings, these generally overlap towards the end ; and in the Bugs only the first portion of the wing becomes horny, and the overlapping terminal parts are membranous. Such fore wings are called tegniina and liemelijtrn. Exceptionally many insects belonging to the most groups, are always wingless, or the males ate winged and the females apterous; and besides these certain entire groups, especially of parasitic insects, contain none but apterous .species. Either of the i)airs of wings may become gi-eatly reduced in size, and apparently useless, while the other pair is fully formed ; and in one -whole order the fore wings alone are developed, and the \\ ) ^\. ,U hind wings are repi'es
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Keywords: ., bookcentury1800, bookdecade1890, booksubjecta, booksubjectanimals
