If now we observe the back of a bird, and view the skeleton with the wings at rest, we shall find it falls into three morphological tracts. First, the shoulder, or scapular track; second, the thigh, or pelvic; third, the tail, or caudal region; and in all these birds the several tracts are beautifully marked by sudden and contrasted change of colour. In _P. Wilsoni_ all the tracts are brilliant red, but they are separated by jet-black borders. In _Nectarinea chloropygia_ the scapular region is red, the pelvic yellow, and the caudal green. [Illustration: Plate X. SUN BIRDS.] In _P. Wilsoni_ we have a wonderful example of morphological emphasis. The head is bare of feathers, and coloured blue, except along the sutures of the skull, where lines of tiny black feathers map out the various bones. But morphological emphasis exists everywhere in birds. The wing-primaries, which attach to the hand, are frequently differently decorated from the secondaries, which feathers spring from the ulna; and the spur-feathers of the thumb, or pollux, are different in shape, and often in colour, from the others, as every fly-fisher who has used woodcock spur-feathers knows full well. The wing-coverts and tail-coverts are frequently mapped in colour; and the brain case is marked by coloured crests. The eye and ear are marked by lines and stripes; and so we might go on throughout the whole bird. We may remark that these very tracts are most valuable for the description and detection of species, and among ornithologists receive special names. Now, this distribution of colour is the more remarkable inasmuch as the feathers which cover the surface--the contour feathers--are not evenly distributed over the body, but are confined to certain limited tracts, as shown by Nitzsch; and though these tracts have a morphological origin, they are rendered quite subsidiary to the colouration, which affects the whole bird, and not these regions in particular. In fact, the colouration is dependent upon the regions on which the feathers lie, and not upon the area from which they spring. In other words, we seem to have in birds evidence of the direct action of underlying parts upon the surface. In more obscurely coloured birds, and those which seem to be evenly spotted, close examination shows that even here the decoration is not uniform, but the sizes and axes of the spots change slightly as they occupy different regions; as may be seen in Woodpeckers and Guinea-fowl. Although the same tone of colour may prevail throughout the plumage, as in the Argus Pheasant, great variety is obtained by the fusion of spots into stripes. A symmetrical effect is produced by the grouping of unsymmetrical feathers; as is so often seen in plants, where irregular branches and leaves produce a regular contour.