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THE POPULAR SCIENCE MONTHLY 



background, and, as now proves to be the case with practically the whole 

 animal kingdom, wear Us colors (or some of them). 



Bark moths, terrestrial animals in general, terrestrial habited birds, 

 etc., all such species, when thus in actual contact with their back- 

 grounds, share its varying illumination from minute to minute. The 

 patch of sunlight that falls on the squatting woodcock illumines also 



Pig. 5 shows the revealing-effect of being seen against a contrasting back- 

 ground, and illustrates the fact that no aerial creature can go about at all without 

 constantly passing across both revealing and concealing backgrounds. 



the surrounding ground, so that the bird continues to seem a part of it ; 

 and the same is of course true of the rest of this great class of animal. 

 But a very different fate attends the life of aerial species destined con- 

 stantly to appear against more or less distant backgrounds which do not 

 share their particular momentary illumination, and which constantly 

 show, now light, when the flying bird or butterfly is dark, and the next 

 instant dark when he is light. This fate causes all aerial species, in a 

 very vital sense, to be conspicuous. Fig. 5 illustrates this. On the 

 white of the sky a white butterfly has been pasted, which, of course, 

 does not show. In the same way, a black one has been placed upon 

 the darkest part of the tree's shadow, and a ground-colored one on the 

 ground. Both of these, like the white one, are, of course, practically 

 invisible, and, could they be always seen against these same back- 

 grounds, they might be classed as cryptic. But their habits preclude 

 the possibility of this, their own changes of position, not to speak of 

 those of the spectator, bringing them, as they fly about, across, often in 

 a single second, the whole gamut of backgrounds, from brightest sky to 

 deepest tree-shadow, and back. And against every one, except the 

 single one which they match, they are clearly visible. The black one 

 shows against the sky, the ground, etc., the white one against the various 



