birds of other orders, are obliteratively shaded, from pure white to dusky 

 brown or gray, with or without connecting middle tones. Though often very 

 inconspicuous against the sea, such dark-backed birds are of course less well 

 equipped for 'vanishment' against either sea or sky than are the beautiful 

 white and pearl-gray guUs and terns. These have, indeed, the very acme of 

 oceanic obliterative coloration. 



