HE present volume consists of two parts; the first of these deals with the theory of hyperelliptic functions of two variables, the second with the reduction of the theory of general multiply-periodic functions to the theory of algebraic functions; taken together they furnish what is intended to be an elementary and self-contained introduction to many of the leading ideas of the theory of multiply-periodic functions, with the incidental aim of aiding the comprehension of the importance of this theory in analytical geometry.