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.
"Supposing," says M. Bernard Deschamps, "that a painter was possessed of colours rich enough to represent on canvas with all their splendour, gold, silver, the opal, the ruby, the sapphire, the emerald, and the other precious stones which the East produces, that with these colours he formed all the shades which could result from their combination, one might affirm without the chance of contradiction, that he would have none of these colours and of their various shades, whatever might be the number, which could not be discovered by the microscope on part of the scales of the Lepidoptera, which Nature has been pleased to conceal from our gaze."
Fig. 134.—Portion of the wing of a Moth (Saturnia pavonia major), magnified.
Each of these scales adheres to the membrane of the wing by a small tube, which is solidly fixed to it. Réaumur has called our attention to the admirable arrangement of these scales, which are disposed like those of fish, that is to say, in such a manner that those of a row shall partially overlap those in the following one.
In [Fig. 134], representing a portion of the wing of the Saturnia pavonia major, magnified, which we borrow from Réaumur's Memoir, the scales are arranged in rows; isolated scales, and the points where other scales were fixed before they were taken off, are represented.
The membranous frame which supports the coloured scales of butterflies and moths is well worth a moment's consideration. It consists of two membranes intimately united by their interior surfaces, and divided into many distinct parts by horny, fistulous threads, more or less ramified, which seem intended to support the two membranes mentioned above, and which branch out from the base to the edge of the wing. Their number, counting from the exterior edge, is not always the same in the upper and lower wings. It varies from eight to twelve.
With its large and light wings, the butterfly can fly for a long time. But this flight is not in the least regular; it is not made in a straight line. When the insect has to go some distance, it flies alternately up and down. The line it takes is composed of an infinity of zig-zags, going up and down, and from right to left. This irregularity of flight saves the little insect from falling a prey to birds. "I saw one day with pleasure," says Réaumur, "a sparrow which pursued in the air a butterfly for nearly ten minutes without being able to catch it. The flight of the bird was nevertheless considerably more rapid than that of the butterfly, but the butterfly was always higher or lower than the place to which the bird flew, and where it thought it would catch it."
But let us leave the wings to pass on to the other parts of the butterfly. These other parts are the thorax or chest, the body or abdomen, and the head.