light, by which the deep-sea fishes hunt and flee one another, is not such as 

 could favor any system of obliterative shading. For it has no prevalent direc- 

 tion relative to the fishes, but is erratic and forever shifting, striking all their 

 sides and planes with equal frequency. Accordingly, though colored, they 

 are mainly monochrome, and as dark below as above. But aside from these 

 little-known fishes that inhabit the remote abysmal depths of open ocean, 

 and the few kinds of blind fresh-water cave fish, practically all the species 

 known to man live in water permeated by the descending light of day. 

 Fishes, in fact, as man knows them, are, typically, inhabitants of the bright 

 upper and outermost border of the water, just as birds and butterflies are 

 dwellers in the bright-colored upper and outermost fringe of the earth. These 

 normal daylight fishes may be grouped, for our present purpose, in two main 

 classes,* namely, the Free-swimmers of open water, and the Haunters of sub- 

 merged land. This second class is again divisible into many general types, 

 whereas the first is wonderfully homogeneous and simple. Wherever the 

 element of land enters into the case, there begin the chances of almost limit- 

 less diversification in the adaptive development of the fishes' habits and col- 

 oration. But the conditions and aspects of water alone (especially beneath 

 the surface) are, comparatively, fixed, few, and simple. Correspondingly 

 constant and simple is the color system of the free-swimming fishes, both 

 fresh-water and marine. Their smooth, regular forms, monotonous habits, 

 and single method of locomotion all work in the same direction — all lend 

 themselves fully to plain obliterative coloration, founded on pure and perfect 

 obliterative counter shading. The gradation of shades and tints — ^from sil- 

 very-white bellies to dusky backs — on almost all free-swimming pelagic and 

 fresh-water fishes, is true and delicate and exquisite beyond description. 

 Among fishes of the same general form and habits, however distantly related, 

 this obliterative shading varies scarcely at all from species to species. Even 

 their color-tones differ but little. They almost all wear exquisite, soft, water- 



* Corresponding to the divisions called "Pelagic" and "Shore" fishes in ichthyological classi- 

 fication of the fishes of salt water. 



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