This volume is an outline of the principles of mythology, chiefly with reference to its more modern developments. Hand in hand with the sister sciences of folklore and comparative religion, it has advanced so rapidly within the last twenty years and altered so greatly from its ancient aspect that it seems an entirely new science. Thirty years ago, if a student of myth had been asked who Janus was, he would probably have replied: "A Roman god of origins." To-day he might see in him a development of the 'kirn-baby.' So does the study of collected facts and analogies enable us to make broad generalizations.