the other hand, the application of such a principle in Nature is almost always 

 enmeshed and interwoven with that of other principles, and this case is no 

 exception to the rule. The same marks which serve to direct an enemy's at- 

 tention to the tail when the bird is in motion, also serve, as we have seen, to 

 picture the quiet background when the bird is still. Here, however, we have 

 not the blurring counter-action of two principles, but their full coordinate 

 development and perfect interadjustment. The marks on the bird's tail may 

 be, and often are, beautiful pictures of leaves and sticks and light and shadow, 

 as potently obliterative as any other picture-patterns; this is their function 

 when the bird is "lying close." But the moment he moves they are changed 

 into effective 'target marks.' The transformation is instantaneous and com- 

 plete; the picture-effect wholly ceases; for leaves and sticks and lights and 

 shadows are never seen to move off suddenly and rapidly over the ground, 

 in a compact, unchanging company. With patterns of lengthwise streaks, on 

 the contrary, there is little visible change between rest and motion, as we have 

 already seen. The longer and straighter are the streaks, the smaller is the 

 visible effect of their lengthwise motion, and vice versa. (The two extreme 

 t5^es are of course connected by all manner of intermediates.) 



Enormously developed feather-appendages are characteristic of several 

 groups of tropical birds, notably the Birds of Paradise (Paradiseidce). Hith- 

 erto, it has always been supposed that male birds of paradise represented the 

 very acme of avian conspicuousness; but this belief is curiously wide of the 

 mark. In a museum exhibition box, amid blank walls, one of these richly- 

 colored and sumptuously plumed birds is extremely shov(^ and conspicuous; 

 but why should we infer from this that he must also be conspicuous in life in 

 his native woods? They are not monochrome and blank, but, on the con- 

 trary, full to overflowing with every possible variation of form and color, 

 produced by the redundant richness of the vegetation, and the numberless 

 vivid and changeable effects of sun and shade. The eye finds it hard or im- 

 possible to unravel such a luxuriant labjnrinth, to separate and define the 

 boundaries of its individual components. Leaves and stems and trunks and 



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