The work Of Parts I and III covers a period of eight years. Out of the material accumulated by Dr. Sidis and his collaborators, some experiments and observations of functional psychopathic cases have been utilized in the last part of this volume. Another portion of the work of Parts I and III has been accomplished in the Psycho pathological Laboratory of the New York Infirmary for Women and Children, and sincere thanks are therefore due to the Trustees and especially to Dr. Alexander Lambert and Julia B. De Forest.