Then, while he looks at this figure from nearly as far off as he can distinguish 

 it from its background, let some one place a bit of bright white paper, likewise 

 smooth and flat, in the middle of the end part of one of the butterfly's wings. 

 (The white spot should be about one third the wing's diameter.) The wing 

 so treated, if it was very dimly distinguishable before, will now prove wholly 

 invisible, in the vicinity of the white spot. This beautiful principle is of course 

 a constant factor in the effect of all animals' patterns, — snakes, wasps, butter- 

 flies, birds, etc. — and, in the sense that counter shading merely prepares 

 animals' bodies, as it were, to be painted upon, this other principle is almost the 

 leading one of all. Such a butterfly as Heliconius amaryllis is a fine example. 

 Against the dark of shadows that nearly match its own dark ground-color, 

 its red spots 'obliterate' its adjacent outlines, and the sharp gold stripe that 

 crosses the hind wings does the same for that part of the insect. The bright 

 bar also illustrates the importance of the direction of such marks on animals. 

 Being continuous (with very slight interruption) right across the insect's very 

 body, it not only 'obliterates' it as a body, but, by its own conspicuousness, — 

 in view of the fact that two things can't occupy the same space, — prevents one's 

 suspecting the existence at that point of anything but a yellow grass-stem, or 

 more often a sunlit twig, further off. 



Students -Once convinced of the real function of all such markings, will be 

 delighted to discover the wonder- world they constitute. 



THE COOPERATION OF INTERPOSED VEGETATION WITH CONCEALING- COLORS 



Here is another fact of the greatest importance: Species that live amidst 

 vegetation are looked at through a certain average amount oj interposed foliage 

 and twiggery. 



Let us imagine a man or other predatory animal stationed at some point 

 in the forest. Obviously there is some limit to the distance to which he can 

 see through the surrounding thicket, some point beyond which the last inter- 

 stice is masked by leaves or branches. A little nearer than this limit begins 

 the distance at which our observer can see, on an average, some small portion 



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