ing * and almost all are subject to dangerous and deadly attacks from smaller 

 marine animals,— ^uch for instance as the Grampus or Killer {Orca gladiator). 



Sea-cows or manatees, and dugongs (order Sirenia), those uncouth sur- 

 vivors of an ancient race of littoral-marine and fiuviatile herbivorous mam- 

 mals, are not pronouncedly equipped with obliterative shading. They are 

 colored like grayish mud and dingy water, however, and tend to be palest 

 underneath. 



The predatoi-y and semi-predatory land beasts which nearly or quite lack 

 obliterative shading are few in number, and, as has been said, they are chiefly 

 nocturnal.t Almost all belong to the group Arctoidea, or bearlike animals. 

 Good examples are the black and brown bears of Europe and America, the 

 Polar Bears {Ursus marUimus) the Wolverine {Gvlo luscus), and several ex- 

 clusively American beasts, the skunks {Mephitis and Conepatus), and the 

 Fisher or Pennant's Martin {Mustela pennanti). But, though largely without 

 counter shading, some of these animals are obliteratively colored to a high de- 

 gree. The Polar Bear, like the boreal foxes, hares, weasels and ptarmigans 

 in their winter dress, is immaculate white, above and below; and, as has been 

 explained in connection with ptarmigans (Chapter VII), this uniform white- 

 ness is about the nearest approach to perfect obliterative coloration that an 

 inhabitant of realms of glaring snow and ice can have, because there the 

 monotonous, perfect whiteness makes counter shading inadmissible, since 

 it would involve making the beast's top darker than the surrounding 

 scene. J The shadowed and therefore too dark underside cannot be light- 

 ened, but neither must the fitly illuminated white back be darkened to 

 match it, for then there would be a monochrome, complete (although flat- 

 seeming) beast-form to silhouette against the background. The skunks, 

 and in less degree the wolverine, are equipped with wonderfully efficient 



* Those whales which prey, more or less, on forms that have both sight and power of locomotion, 

 must be quite as much hel{)ed by obliterative coloration in their approach to such prey, as any of the 

 beautifully counter shaded fishes that hunt in the same waters. — A. H. T. 



• t The slight counter shading of black nocturnal animals has apparently the exact degree to defeat 

 the very small illumination of night. — A. H. T. % See also p. 151. 



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