THIS VICTORIAN NATURALIST. 79 



for it, though the imitator and the imitated may belong to utterly 

 different genera. In this paper I use the term as applying also 

 to cases in which protective imitation refers to objects as well as 

 living organisms. 



By a great many people the coloration of animal life is looked 

 upon as something merely fortuitous, something of merely physical 

 significance, but the facts to which I allude further on will, I 

 think, show that the coloration of animals has a very deep 

 biological significance. 



Colours are produced either by the presence of pigment cells 

 absorbing certain rays of light and reflecting the remainder, or by 

 the interference of rays of light of certain wave-length. This is 

 the cause of the brilliant metallic colours we so often find in the 

 plumage of birds, the surface of the feather, on which the light 

 falls, being so finely divided by the lines of junction of the 

 separate pinnoe. Few animals are brilliantly coloured, but colours 

 whether brilliant or sombre are always an advantage to the 

 possessor. You will notice how uniform is the colour among 

 wild, and how varied it is among domesticated animals. The 

 reason is that protection is assured to tame animals and even the 

 most conspicuous is secure. A white rabbit, say, is an easy mark 

 to the hawk, and cannot long escape, while a grey one is pro- 

 tected by the similarity of its coat to its environment. In Arctic 

 regions the reverse of this would, of course, obtain, and there we 

 find that the animals whose defence or attack consists in conceal- 

 ment are white, imitating their snow-clad surroundings ■ while in 

 the same region we have the raven black as proverbially, because 

 " it fears no foe," so needs no protective coloration ■ it preys on 

 carrion, so its approach need be neither silent or concealed. In 

 desert regions, on the other hand, animals are mostly of a brown 

 sandy colour. Here in Australia, the kangaroo when at rest 

 among the timber will often deceive even practised eyes. You 

 would at least think that the gorgeously coloured parrots of our 

 forests would be easily seen, but I have often stood beneath a tree 

 into which I had seen rosellas and lories fly, and could not till 

 they moved distinguish them from the foliage among which they 

 were esconced. 



The change of colour in the chameleon is quite another thing. 

 This change is brought about by means of two layers of pigment 

 cells deeply seated in the skin. These can at will be forced up- 

 wards, thus changing the whole appearance, and I have heard of 

 a frog accommodating itself to its surroundings by a diffusion of the 

 pigment cells in the skin. When on a mudbank, the skin was a 

 dusky colour, owing to the equal distribution of pigment, but when 

 placed on a sandbank it became yellow, the dark pigment being 

 all aggregated into small black patches. The unconscious change 

 of colour in larvae and pupse is well known to many of you, but so 



