[Illustration: Fig. 131.--Moth whose wings are developing.]
[Illustration: Fig. 132.--Moth whose wings are developed.]
Figs. 131 and 132, borrowed, like the preceding, from the 14th Memoir of Réaumur (_sur la transformation des chrysalides en papillons_), show the states through which the wings of the same moth pass, before they are thoroughly developed.
Those pupæ enclosed in cocoons free themselves entirely or in part from their old skin, in the shell itself; but the imago is still a prisoner. It has broken through a first enclosure; it must open itself a way through the second. How does it manage to bore through the often very solid walls of this second prison, so as to regain its liberty? Réaumur states that in the Lackey Moth (_Bombyx neustria_) the head is the only instrument of which the insect makes use in opening a passage, the compound eyes then acting like files. These files cut the very fine threads of which the cocoon is composed, and as soon as the end of the cocoon is pierced through, the insect uses its thorax like a wedge, to enlarge the hole. It very soon manages to get its two front legs out, fixes itself by them on to the outside, and little by little emerges from its prison.
Who does not admire the extraordinary splendour, the vivacity, the prodigious variety of colours of these brilliant inhabitants of the air? Some amateurs have devoted to the purchase of certain butterflies large sums of money. "Diamonds," says Réaumur on the subject, "have perhaps beauties no more real than those of a butterfly's wings; but they have a beauty which is more acknowledged by the world in general, and which is more recognised in commerce." The essential character of butterflies and moths makes them very easily recognisable among all other insects. All have four wings, which are covered with scales, that communicate to them the brilliant colours with which they are decorated. It is these scales which adhere to the fingers when we seize one of these charming creatures.
[Illustration: Fig. 133.--Different forms of the scales of Butterflies, after Réaumur.]
For a long time this dust was thought to be formed of very small feathers, but Réaumur showed that it is composed of little scales. Their form varies singularly, as we may see in Fig. 133, borrowed from the Memoirs of Réaumur,[45] which represents the different forms of the scales which cover the wings of Lepidoptera. M. Bernard Deschamps has closely studied them. According to this naturalist, they are composed of three membranes, or plates, superposed one on the other, of which the first is covered with granulations of a rounded form, which give to these scales their splendid and varied colours; the second plate is covered with silk, forming sometimes curious designs; the third plate, viz., that which is applied to the membrane of the wing, has the peculiar property of reflecting colours the most brilliant and the most varied, although the surface of the scales visible to the eye is often dull and colourless.