2i 4 SCIENCE PROGRESS 



ground — a stone, a tuft of grass or a tree trunk — but rather 

 towards reproducing on the animal's surface the effect of a 

 mixed background — of vegetation, of water, of stone or sand 

 or soil. The animal is not merely coloured ; it is painted. 

 Moreover, the way in which dashes or gradations of colours 

 ire distributed on the animal's coat is used to help forward the 

 work of countershading— to emphasise the illusion of flatness, 

 to make the animal resemble not an object but a background 

 seen in perspective. 



" Patterns on animals' coats " are thus " the utmost that 

 Nature can do" against what Thayer calls the " patent vicissi- 

 tudes of silhouetting" which follow from the animal moving 

 about out-of-doors against a variety of backgrounds. As we 

 have seen, natural selection works to pick out those species 

 whose colour-scheme is an averaging of their normal back- 

 grounds. But the really protective scheme goes farther still 

 and definitely aims, so to speak, at merging itself into the 

 background so that the outline of the animal is completely 

 obliterated. It is not enough that the living creature should 

 resemble its inanimate background : it must merge with and 

 fade away into it. Thus a new purpose is found by Thayer 

 for the very daring of those patterns, stripes and colour con- 

 trasts the developing and fixing of which have so often been 

 traced to sexual selection or again, in some cases of gregarious 

 species, to their efficacy as warning signs or danger signals to 

 others. The peacock's tail, according to Thayer, is not ex- 

 clusively to please the peahen or the rabbit's to guide its young 

 or warn its fellows. The object of both is to break up the 

 continuous outline of the creature's silhouette ; such markings 

 are classified by Thayer as " ruptive " or "secant" for this 

 reason. It is one of his cardinal principles that a scheme of 

 colouration may be at once exceedingly bold and most effective 

 as a disguise. What Thayer does is to extend to a whole 

 variety of similar cases what has long been recognised of the 

 tiger in the jungle : that markings, which against a background 

 of a uniform hue make their possessor exceedingly conspicuous, 

 completely conceal him amid the varied jungle in which he 

 hunts. Anything which breaks up or cuts into sections the 

 surface of the animal's form makes against the possibility of 

 recognising it as what it is. 



It follows too from this that Thayer finds a new meaning too 



