212 SCIENCE PROGRESS 



of animals the effectiveness of whose disguise was the very 

 reason for the failure to understand its working. Until you 

 can learn to detect the concealed animal you cannot of course 

 appreciate the laws of its concealment ; if you only see the 

 magpie on the road, you cannot understand how it hides itself 

 in the wood. 



What then has enabled Thayer to detect a system of 

 obliteration so efficient as to conceal its own methods from 

 practised naturalists? Simply his artist's training. He has 

 approached the problem from the standpoint not of the zoologist 

 but of the painter ; and not the least significant feature of his 

 work is the fact that his knowledge of the means by which Art 

 aims at reproducing Nature would seem to have given him a 

 new insight into the working of natural laws. Briefly his con- 

 clusion is that in the matter of animal colouration Nature works 

 as does the artist. What the art student has first to learn is 

 to make a drawing or picture on a flat surface look like a solid 

 figure or a landscape. He has to make a flat surface look the 

 reverse of flat. This he is taught to do by three chief means— 

 by drawing, by modelling and by colouring. To produce on 

 flat paper the illusion of a rounded form he first learns to draw 

 the outline of that form ; then he shades it in such a way as to 

 give the effect of the play of light and shade on a solid object; 

 lastly he colours it. As a result it appears to stand out in sharp 

 relief against the flat background. Now, Thayer's contention is 

 that in the matter of animal colouration the forces of natural 

 selection are at work to create an optical illusion in precisely 

 the opposite direction. Just as the student cultivates accuracy 

 of drawing and an appreciation of line so as to be able to draw 

 what looks like an animal, so Nature, aiming at creating what 

 does not look like an animal, works as far as possible to 

 obliterate the outline. Just as the student has even to accentuate 

 the play of light and shade on a convex or concave body in his 

 reproduction of it, so in nature the concealment of that body 

 is attained by somehow neutralising or counteracting the same 

 play of light and shade. Just as the student uses colour to give 

 the last touch of individuality to his figures, so in Nature colour 

 serves the opposite purpose: to blur instead of to define, to 

 obliterate instead of to characterise. In a word, in Nature those 

 varieties have survived which most completely fade into their 

 background. 



