Colouration in Animals and Plants

by Alfred Tylor

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].

The markings over the vertebræ are not in continuous lines, as in many mammals, but form a series of vertebra-like spots. This plan of decoration is continued even on the tail, which is coloured more on the upper than on the lower surface.

The spotted cats have their spot-groups arranged on the flanks in the direction of the ribs, at the shoulder and haunch in curves, at the neck in another pattern, on the back of the head in another; and the pattern changes as each limb-joint is reached, the spots decreasing in size as the distance is greater from the spine. See Figs. [9]-[15].

There is in tigers, and the cat-tribe generally, a dark stripe over the dental nerve; and the zygoma, or cheek-bone, is often marked by colour. Even the supraorbital nerve is shown in the forehead, and there are dark rings round the ears. In dissecting an ocelot at the Zoological Gardens in 1883, a forked line was found immediately over the fork of the jugular vein.

The colouration in these animals seems often to be determined by the great nerves and nerve-centres, and the change from spots, or stripes, to wrinkled lines on the head are strikingly suggestive of the convolutions of the brain, falling, as they do, into two lateral masses, corresponding with the cerebral hemispheres, separated by a straight line, corresponding with the median fissure. This is well shown in the ocelot, [Fig. 15], and in many other cats.