68 CHILDHOOD OF ANIMALS 



scopists are examining the structure of animal tissues, one of their 

 difficulties is that the pale grey tone of the material they are investi- 

 gating is almost uniform. And so they have learned to treat it 

 with various dyes, some of which make the differences in structure 

 visible merely because certain parts stain more deeply than other 

 parts, whilst invisible chemical differences become visible by the 

 parts of the tissue accepting, refusing or changing the colour with 

 which they are bathed. And as the red blood shining through the 

 pale skin suffuses the surface with tints of different intensity, so 

 the pigments which are being excreted through the skin become 

 differently entangled in different parts of the structure, make new 

 combinations of colour chemically or physically, and the varied 

 structure itself shines differently under the same beams of light. 



Colour, pattern, and the combination of colour and pattern that 

 we call coloration are to be expected everywhere in the animal 

 kingdom, as indeed in the living world. They are the visible 

 expression of the complex nature and of the mode of growth of 

 living things. All organisms increase in size by the multiplication 

 of parts, and the simpler they are the more mechanically geometrical 

 we must expect them to be. As they become more complex in 

 structure, the primitive and yet more startling symmetry of their 

 patterns becomes altered by irregular growth, by excess in some 

 parts, retardation in others, and by interference of the growth of 

 different systems or centres. Structurally every body is a mosaic, 

 but it is a mosaic which has grown by the growth and multiplication 

 of the separate pieces at different rates. It must have pattern. 

 The different pieces and systems of pieces must have colour, and as 

 they become different in their functions, inherent differences in 

 colour, and differences due to different reactions to the coloured 

 fluids and substances that pervade the whole, cause a still greater 

 diversity. And so coloration is an inevitable outcrop, which may 

 or may not be useful. 



And now, having fenced the tables, we pass to consideration of 

 the uses to which colours and patterns may be put and of the ad- 

 vantages they may confer on their owners, with a clear conscience. 



In natural history all general rules are dangerous, but there is 

 none safer than that it is seldom an advantage to an animal to be 

 conspicuous. It is a hungry world, and there is nothing more 

 generally useful than not to attract attention. The lowest grade in 

 the evolution of coloration is when pattern that is the direct 

 expression of structure and colour that is to say, the direct result 



