The Mutual Relations of Stimuli in the Frog _Rana Clamata_ Daudin: Robert M. Yerkes 545 The Temporal Relations of Neural Processes: Robert M. Yerkes 575 The Mental Life of the Domestic Pigeon: John E. Rouse 581 Reactions of the Crayfish: J. Carleton Bell 615 PLATES _Frontispiece_ 3 I 60 II 64 III 78 IV 80 V 269 VI 271 VII 273 VIII 293 IX 295 EMERSON HALL [Illustration: HARVARD PSYCHOLOGICAL LABORATORY] EMERSON HALL BY HUGO MÜNSTERBERG I. EXPERIMENTAL PSYCHOLOGY IN HARVARD On the 27th of December, 1905, Harvard University opened its new house of philosophy, Emerson Hall. The presence of the American Philosophical and Psychological Associations gave national significance to the completion of this building. The psychologist will find quarters in all parts of Emerson Hall. The general courses in psychology will be held on the first floor in the large lecture-room, which has nearly four hundred seats; and close by are the psychological seminary-room and smaller lecture-rooms for the advanced psychological courses. On the second floor the psychologist finds his special library as a wing of the large library hall. But the exclusive domain of the psychologist is the third floor,--a psychological laboratory with twenty-five rooms. A large attic hall for laboratory purposes on the fourth floor completes the psychologist's allotment. The work to be reported in future in the Harvard Psychological Studies will be work done in this new building, and while the researches reported in the following pages were completed in the smaller quarters of the old laboratory, it seems natural that this volume, which appears at this new epoch of our work, should give an account both of our psychological past and of the development and purpose of Emerson Hall. The Harvard Psychological Laboratory was founded in 1891 by Professor William James, who had introduced some experimental features into his psychological lecture courses for some time before the formal opening of a regular workshop. Professor James started with two large rooms on the second floor of Dane Hall, and secured an excellent equipment, especially for the study of the psychology of the senses. He was assisted by Dr. Herbert Nichols, and at once gathered a number of graduate students for research.