Lest in the text of these volumes credit may not always have been given where credit is due, grateful acknowledgment is here made to Professor Hugo Miinsterbergy Professor Walter Dill Scott, Dr. James H. Hyslop, Dr. Ernst Haeckel, Dr. Frank Channing Haddock, Mr. Frederick W. Taylor, Professor Morton Prince, Professor F. H. Gerrish, Mr. Waldo Pondray Warren, Dr. J. D. Luackenbos, Professor C. A. Strong, Professor Paul Dubois, Professor Joseph Jastrow, Professor Pierre Janet, Dr. Bernard Hart and Professor G. M. Whipple, of the indebtedness to them incurred in the preparation of this work.