COLOUR AND PATTERN IN ANIMALS 69 



of the chemical processes of the body is retained. This grade is to 

 be expected in primitive animals and in the young stages of animals, 

 and, whether it be brilliant or dull, is retained in higher types when 

 it is not disadvantageous. The second grade is the smoothing over 

 and partial obliteration of growth-pattern and the toning down of 

 natural colours. This condition is the simplest mode of producing 

 concealment by inconspicuousness, in conditions where the first 

 grades of colour and pattern are disadvantageous. The third and 

 highest grade is when the structural pattern is overlaid by a new 

 pattern, often with very little relation to the natural growth and 

 symmetry of the animal, and where the colours do not appear to 

 be the direct result of the ordinary physiological processes of the 

 body. This third grade is found in the higher groups of animals, and 

 is more frequent in adults than in the young, and in males than in 

 females. As we shall see, even although it may be vivid and brilliant, 

 it may yet secure inconspicuousness in the natural environment of 

 the animals. These three grades must be taken as a help to remember 

 and understand coloration, and not as an absolute set of divisions 

 into which the facts fall, or into one of which any particular fact can 

 be placed with complete certainty. 



As the cases in which it appears to be an advantage to animals to 

 be conspicuous are relatively few, I shall begin with them. Many 

 animals, and especially males, wear their bravest livery as a marriage 

 dress, and however they may be coloured at other times, are 

 resplendent at the approach of the breeding season. Differences 

 in coloration of the sexes are not frequent amongst mammals, 

 although the males are more usually distinguished by their powerful 

 weapons of aggression. But the coloured patches on the skin 

 in many monkeys are brighter and more conspicuous in males, 

 and differences in colour and pattern mark the males of many 

 deer, antelopes and small carnivores. These male ornaments 

 are usually intensified during the breeding season. In birds 

 such differences are almost the rule, and are directly associated 

 with the breeding season, which in many cases is preceded by 

 a moult, after which the sexual plumage is assumed, or the colour 

 of the naked parts intensified. Every one knows that the 

 cocks are most highly ornamented in such familiar examples 

 as the fowls and pheasants (see Plate IV), the peacocks, drakes, 

 male ostriches, birds-of-paradise, and so on. But there are also 

 birds in which the sexes are so much alike that it is almost 

 impossible to distinguish them except by observation of their 



