VO !s t /, 111 ] Thayer on Protective Coloration. I 27 



The reason of her visibility is that I have artificially extended 

 her top colors down her sides, thereby destroying her counter- 

 gradation and forcing her solidity to manifest itself. 



The reader, I think, must try these experiments for himself 

 before he can believe that in Fig. 3 and Fig. 9 I tinted the 

 under surfaces exactly as dark as the upper, and no darker. But 

 I beg him to look at any horizontal branch in the woods which 

 is either on the level of his eye or below it. He will see that 

 although it has exactly the color of its surroundings, it is not in 

 the least concealed, because, being of uniform color above and 

 below, like the birds after I had painted their under sides, it 

 wears that universal attribute of a solid, namely, a gradation of 

 shading from its light side to its dark side. 



I leave to the reader the pleasure of discovering for himself 

 that this principle of gradation in color is almost universal in the 

 animal kingdom In certain classes of birds and of flying insects, 

 however, the principle gives place, more or less, to the device 

 pointed out by Bates ; namely, the employment of strong arbitrary 

 patterns of color which tend to conceal the wearer by destroying 

 his apparent continuity of surface. This makes, for instance, the 

 Mallard's dark green head tend to detach itself from his body, 

 and to join the dark green of the shady sedge: or the ruby of the 

 Hummingbird to desert him and to appear to belong to the 

 glistening flower which he is searching. Vet many other cases 

 of color applied apparently at random conform essentially to the 

 law stated above. The dark patches are on top, the light ones 

 beneath. 1 The dark breast-mark, so widely used by nature on 

 birds, usually has the effect of putting out a conspicuous and 

 shining rotundity of some bright or light color, as in the Meadow- 

 lark and the Flicker; because it comes just where the breast, in 

 its usual position, rounds upward and faces the sky. The dark 

 collars of the males of most species of Duck are absolute 

 counter-shading to the light from the sky, when the birds sit 

 in their characteristic positions. For most female Ducks 



1 I have proved, by experiments with painted decoys, that even brilliant top- 

 colors, however strongly contrasted to surroundings, scarcely tend to betray 

 the wearer, if his ensemble be a gradation from dark above to light below. 



