In an erudite manner, Holt introduces his study of metapsychology with a comprehensive elucidation of Freud's concepts. It was necessary for him to use the Concordance, as the Index in the Standard Edition was inadequate to his task. Most of his paper is devoted to Freud's definition and use of metapsychology. The discussion is far-reaching and involves the influence of Darwin's, Lipps's, and Hecker's theories on Freud's thinking. Holt describes in detail how one of Freud's ever-present problems was the integration of the mechanical with the biological. Thus he shows how Freud differentiated metapsychology from clinical theory and from