In these heydays of popular zoology, when eager young naturalists are coming to the front in crowds, and fine new scientific museums are starting up on every hand, there is small need to apologize for the appearance of a work designed expressly for the naturalist and museum-builder. Had justice been done, some one would have written this book ten years ago. The rapid and alarming destruction of all forms of wild animal life which is now going on furiously throughout the entire world, renders it imperatively necessary for those who would build up great zoological collections to be up and doing before any more of the leading species are exterminated. It is already too late to collect wild specimens of the American bison, Californian elephant seal, West Indian seal, great auk, and Labrador duck. Very soon it will also be too late to collect walrus, manatee, fur seal, prong-horn antelope, elk, moose, mountain sheep, and mountain goat. All along the Atlantic coast and in Florida the ducks are being exterminated for the metropolitan markets, and the gulls, terns, herons, egrets, ibises, and spoonbills are being slaughtered wholesale for the equally bloodthirsty goddess of Fashion. If the naturalist would gather representatives of all these forms for perpetual preservation, and future study, he must set about it at once. This work is offered as my contribution to the science of zoology and the work of the museum-builder. It is entirely "an affair of the heart," and my only desire in regard to it is that it may be the means of materially increasing the world's store of well-selected and well-preserved examples of the beautiful and interesting animal forms that now inhabit the earth and its waters. The sight of a particularly fine animal, either[viii] alive or dead, excites within me feelings of admiration that often amount to genuine affection; and the study and preservation of such forms has for sixteen years been my chief delight.