330 REPORTS ON THE STATE OF SCIENCE.—1913. 
lets in the light. A still larger number of colours are due to pigments, blues 
and greens more rarely, reds, yellows, blacks and browns almost invariably. 
Perhaps in most cases the pigment has a direct physiological importance, as, 
for instance, the red colour of the blood, due to the presence of hemoglobin, the 
substance that carries oxygen to the tissues, or the green chlorophyll of plants, 
by which the radiant energy of sunlight is captured. Others are by-products of 
excretion, poisonous waste that has to be removed, like the brilliant derivatives 
of bile and urea. Extreme instances of the casual or accidental production of 
colour may be seen in the crimson of turacos, which is not merely a pigment, 
but one that is soluble in rain-water. The Malay tapir exudes a black sweat, and 
that of the hippopotamus is carmine-coloured. Still more suggestive is it to 
reflect that not only the visible surface of the body may be resplendent with 
vivid hues. The blood runs as red under the thick and hairy hide of an ape 
as on the fair cheek of a girl. Splashes and streaks of black, glows of yellow and 
green and scarlet, vivid contrasts of colour, diversify the internal organs and 
tissues, where they can delight the eye only of the anatomist, who, after all, is a 
small part of the economy of Nature. Ruskin once said that it was immoral if 
the back of a column, destined to be invisible to every eye from the moment it 
was put in place until the cathedral crumbled, were not carved as fairly and 
lovingly as the side that was to confront the world. In her dispersal of colour 
Nature is of the school of Ruskin, and no parsimonious utilitarian, scamping the 
invisible part of her work. Colour is lavished freely on creatures that rejoice in 
the sun and that seem consciously to flaunt their brilliance or coyly to match 
their surroundings, but it is lavished no less freely on internal parasites, 
creatures of the night, inhabitants of clefts in the rocks, or of the dim abysses 
of the ocean. 
Colouration (the combination of colour and pattern) is in a sense accidental. 
A thin slice of almost any living tissue placed under the microscope reveals 
little of its structure because of the uniform grey of protoplasm. The skilled 
microscopist stains his sections, and as the different parts react differently, the 
uniformity disappears and the structure becomes visible. In the same fashion, 
in the laboratory of Nature colour often magnifies or intensifies pattern. Differ- 
ences in texture of the component parts of the structural pattern may reflect light 
differently, so that iridescent hues map out the lines of growth. The bright 
exudations of the body reveal differences in the texture and substance of the 
tissues they reach, or the structural distribution of blood is made visible by 
the scarlet hemoglobin. The combined effect is so conspicuous that we deem it 
must have a purpose. It is curious, however, to note how much inconspicuous 
pattern exists amongst animals and plants. The black variety of leopards and 
jaguars is a familiar instance; it is just possible to see, like a faint water-mark, 
the characteristic rosettes of the leopard or the jaguar on the uniform black fur. 
It may be said that these melanistic forms are abnormal, almost pathological ; 
but there are many cases for which no such explanation can be offered. The 
young of almost all the cats, great and small, are spotted or striped, even if the 
adults are self-coloured. The kittens of cheetahs, or hunting-leopards, appear 
to be a remarkable exception. for, although the yellow fur of the adult is 
thickly set with black spots, the young are clothed with soft fur of a uniform 
pale grey; but closer examination shows that the under fur is spotted. Ray 
Lankester has called attention to the almost invisible pattern of stripes on the 
face of the young giraffe. The cony or hyrax is really a striped animal; when 
the creature is alive one can see in appropriate light that the hair is set in 
hoop-like bands running downwards from the dorsal middle line, but the uniform 
colouration masks this arrangement. I have almost no doubt but that the 
African rhinoceros is similarly a striped creature, the stripes appearing as 
structure and not as colouration. 
The striped pattern of zebras is a salient instance of the combination of 
structure and colour, and there is excellent reason to suppose that it has been 
turned to a utilitarian purpose, and helps to protect the animal by making it less 
visible against a background, or merely by breaking up its outline and so making 
it less like an animal. But it passes belief to suppose that the different types of 
pattern found in Grevy’s zebra, the Mountain zebra, and Burchell’s zebra 
have different and appropriate utilities. They are the outcrop of different 
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