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_. The thorax is solidly put together, so as to bear the movements of the wings and legs. These latter are composed, as in other insects, of five parts: the coxa, the trochanter, the thigh, the shank, and the tarsus. Many butterflies have all their six legs of equal length. In others, the two fore legs are very small, and are not suited for walking. In others, again, they are rudimentary, being deprived of hooks, very hairy, and applied on to the front of the breast. [Illustration: Fig. 135.--Leg of Butterfly armed with hooks.] [Illustration: Fig. 136.--Leg not suitable for walking.] This difference of structure may be seen in Figs. 135 and 136, one of which represents, after Réaumur, a leg unsuited for walking, very hairy, and terminated in a sort of brush resembling the tail on a tippet; and the other a leg furnished with hooks. The abdomen has the form of an elongated, or--in the majority of species--an almost cylindrical oval. It is composed of five segments, each formed of an upper and a lower ring, joined together by a membrane. The first are larger than the others, and generally overlap the edges, which gives to this part of the body the power of dilating considerably.