Whether Leuwenhoek actually took the trouble to count so many, or arrived at the result from calculation after counting those on a given space, we do not know, but he declares that he found more than four hundred thousand on the wings of the silk-worm moth; and in those of larger moths and butterflies the number must greatly exceed this. They are generally arranged like the tiles on a house-roof; and if they are scraped off, the minute dots where each was attached becomes distinctly visible. The term used to indicate the tribe of insects to which the moth and butterfly appertain, is, as has been before remarked, _Lepidoptera_, or "scale-winged," from this very fact. Some membranaceous wings are clothed with fine hairs. [Illustration: _Blight-Beetle. Natural size and magnified._] If we take up a beetle, and look for its wings, for the first time, we shall probably fail in detecting them, that is, of course, if the insect has not been observed in the act of flying. On examining the body we see, indeed, a pair of shining horny plates on its back; but surely these are not wings? Presently, the insect having mounted to the top of our finger, prepares for flight; its two hard cases fly up, and, behold! from beneath them appears a pair of the most beautiful gauze-like wings, which it quickly unfolds, puts into motion, and then flies away. The two thick and horny covers for these delicate organs are called _elytra_, or "wing-cases." They are really the first pair of wings, much thickened; and their use is to protect the delicate membranous wings of the hinder pair, beneath them. When the insect flies, they open like a box-lid, and are carried out of the way of the other wings; when the insect rests it carefully folds up its other wings, and then these close over them, and preserve them from all injury. As the insects in which they are found frequent places of danger, burrow underground, or take up their abode under stones, it is manifest how admirable a contrivance this is for such purposes, and how efficiently the fragile wings will be covered and protected by such shields. The first pair of wings is sometimes thickened to the consistence of parchment as a cover to the other wings; and they are then called _tegmina_, or "wing-covers."