The first indication of colour is in the eyes, whose horny facets pass successively from white to tawny, then to a slaty hue, and lastly to black. The simple ones at the top of the forehead share in their turn in this coloration before the rest of the body has at all lost its whitish tint. It should be noted that this precocity in the most delicate of organs, the eye, is general in animals. Later a smoky line appears in the furrow separating the mesothorax from the metathorax, and four-and-twenty hours later the whole back of the mesothorax is black. At the same time the division of the prothorax grows shaded, a black dot appears in the central and upper part of the metathorax, and the mandibles are covered with a rusty tint. Gradually a deeper and deeper shade spreads over the last segments of the thorax, and finally reaches the head and sides. One day suffices to turn the smoky tint of the head and the furthest segments of the thorax into deep black. Then the abdomen shares in the rapidly increasing coloration. The edge of the anterior segments is tinted with daffodil, while the posterior segments acquire a band of ashy black. Then the antennæ and feet take a darker and darker tint, till they become black, all the base of the abdomen turns orange-red, and the tip black. The livery would then be complete, but that the tarsi and mouthpieces are transparent red and the stumps of wings ashy black. Four-and-twenty hours later the chrysalis will burst its bonds. It only takes six or seven days to acquire its permanent tints; the eyes have done so a fortnight before the rest of the body. From this sketch the law of chromatic evolution is easily apprehended. We see that, omitting the eyes and ocelli, whose early perfection recalls what takes place in the higher animals, the starting-point of coloration is a central one, the mesothorax, whence it invades progressively by centrifugal progression—first the rest of the thorax, then the head and abdomen, and finally the various appendages, antennæ, and feet. The tarsi and mouthpieces take colour later still, and the wings only on coming out of their cases.