THE substance of this work, at least in its main outlines, was first set forth in a course of three lectures delivered before the Royal Institution in 1906, and subsequently published as a series of articles contributed, at the request of the Editor, Dr. N. H. Alcock, to Science Progress. My original intention was simply to gather these together and to republish them in book form with adequate illustration. But in the meanwhile the rapid progress of discovery had rendered necessary so many changes in the text that I 'took advantage of the opportunity to introduce a good deal of additional matter, and to enlarge the short - summaries treating of recent hunting races, especially the Australians and Bushmen.