The first outlines of colour show on the eyes, whose faceted cornea changes successively from white to fawn, next to slate-grey, lastly to black. The simple eyes at the top of the forehead, the ocelli, share in this colouring, in their turn, before the rest of the body has yet lost any of its neutral, white tint. It should be remarked that this early development of the most delicate organ, the eye, is general in all animals. Later, a smoky line appears on the upper part of the groove separating the mesothorax and the metathorax; and, twenty-four hours later, the whole back of the metathorax is black. At the same time, the edge of the prothorax becomes shaded, a black dot appears in the central and upper part of the metathorax, and the mandibles assume a rusty tinge. Gradually a deeper and deeper shade creeps over the two end segments of the thorax and finally reaches the head and the hind-quarters. A day is enough to turn the smoky hue of the head and of the end segments deep black. Thereupon the abdomen begins to share in the rapidly-increasing coloration. The edge of its front segments is tinted saffron; and its hinder segments acquire a dull-black border. Lastly, the antennæ and legs, after passing through darker and darker shades, turn black; the lower part of the abdomen is now entirely orange-red and the tip black. The livery is complete except for the tarsi and the mouth-parts, which are a transparent red, and the wing-stumps, which are dull black. In four-and-twenty hours the nymph will burst its fetters. It takes the nymph only six or seven days to don its final tints, omitting the eyes, whose colouring precedes that of the rest of the body by fourteen or fifteen days. The law governing the insect’s chromatic evolution is easily gathered from this brief sketch. We see that, with the exception of the eyes and the ocelli, whose early development recalls what takes place in the higher animals, the starting-point of the coloration is a central spot, the mesothorax, whence it gradually invades, by centrifugal progression, first the rest of the thorax, then the head and abdomen, lastly the different appendages, the legs and antennæ. The tarsi and the mouth-parts colour later still; and the wings do not assume their hue until after they are taken from their cases.