Sometimes, especially on the breast and back, the feathers of one region seem to unite so as to form one tract, so far as colour is concerned. Thus, if in _P. Wilsoni_ the black borders of the dorsal regions were suppressed, all three areas would be of one hue. This seems to have been the case in the breast region of Humming Birds, where only the throat is highly coloured. In the Toucans the breast and throat regions are often marked with colour; but sometimes the hue is the same and the boundaries of the regions marked with a band of another colour; if this boundary band be increased, the regions do not seem so well shown, for the boundary becomes as broad as the area; yet, in all these cases the dependence upon regional decoration is manifest. No doubt the few uniformly coloured birds were derived from species which were once variously hued; the gradation of colour being lost in transmission. _Mammalia._ The axial decoration of the mammalia is very definite, and nearly all species have a dorsal tract marked with colour. The dark bands on the back of the horse, ox, and ass, are cases in point. In nearly every case the dorsal is darker than the ventral surface. If we take highly decorated species, that is, animals marked by alternate dark and light bands, or spots, such as the zebra, some deer, or the carnivora, we find, first, that the region of the spinal column is marked by a dark stripe (Figs. 9 & 16); secondly, that the regions of the appendages, or limbs, are differently marked; thirdly, that the flanks are striped, or spotted, along or between the regions of the lines of the ribs; fourthly, that the shoulder and hip regions are marked by curved lines; fifthly, that the pattern changes, and the direction of the lines, or spots, at the head, neck, and every joint of the limbs; and lastly, that the tips of the ears, nose, tail, and feet, and the eye are emphasized in colour. In spotted animals the greatest length of the spot is generally in the direction of the largest development of the skeleton. This morphological arrangement can be traced even when the decoration has been modified. Thus, in the carnivora we have the lion and puma, which live in open country, with plain skins, the tiger with stripes, an inhabitant of the jungle, and the leopard, ocelot, and jaguar with spots, inhabiting the forests. But the lion has a dark dorsal stripe, and the nose, etc., are emphasized in colour, and, moreover, the lion has probably lost its marked decoration for protective purposes, for young lions are spotted. The tiger's stripes start from the vertebræ, and still follow the lines of the ribs. In the tiger the decoration changes at the neck, and on the head, and the cervical vertebræ are often indicated by seven stripes. See Fig. 5.