Il6 THE MEANING OF EVOLUTION 



away from the light, is so shaded as to mark a dis- 

 tinct boundary between the stone and the board. An- 

 other cobblestone was colored on its upper side like 

 the board, but the color faded into a lighter and 

 lighter tint until the bottom of the stone was nearly 

 white. This stone, placed upon the board, was at 

 a short distance nearly invisible. In other words, al- 

 though the pigment was actually lighter on the under 

 side, it was so much less intensely illuminated, that 

 the result was the same in tint as the other side un- 

 der the clear sharp light of the sky. 



Many a person, looking down into the water from 

 a bridge, sees nothing whatever of the fish in the wa- 

 ter below, because their backs are exactly like the 

 bottom of the stream. Suddenly one of the fish, by a 

 quick movement, turns its lighter under side over in 

 such a way that it is clearly illuminated from the sky. 

 Immediately a flash as of silver strikes the eye of the 

 onlooker and makes him aware of the presence of the 

 fish which had previously been undetected. If ren- 

 dered thus suspicious, the observer will carefully ex- 

 amine the bottom of the water, he may quite likely 

 find dozens of fish which had previously escaped his 

 attention. 



Nature is very versatile. So many of her ap- 

 parently chance ventures have proved successful that 

 she has retained many devices by which her children 



