Another group of researches which predominates in our laboratory is that on comparative psychology. Three rooms of the laboratory are reserved for psychological experiments on animals, under the special charge of Dr. Yerkes. The work is strictly psychological, not vivisectional; and it is our special purpose to bring animal psychology more in contact with those methods which have found their development in the laboratories for human psychology. The use of the reaction-time method for the study of the frog, as described in the fifteenth paper, may stand as a typical illustration of our aim. All the work of this volume has been done by well-trained post-graduate students, and, above all, such advanced students were not only the experimenters but also the only subjects. It is the rule of the laboratory that everyone who carries on a special research has to be a subject in several other investigations. The reporting experimenters take the responsibility for the theoretical views which they express. While I have proposed the subjects and methods for all the investigations, and while I can take the responsibility for the experiments which were carried on under my daily supervision, I have left fullest freedom to the authors in the expression of their views. My own views and my own conclusions from the experiments would not seldom be in contradiction with theirs, as the authors are sometimes also in contradiction with one another; but while I, of course, have taken part in frequent discussions during the work, in the completed papers my rôle has been merely that of editor, and I have nowhere added further comments. In this work of editing I am under great obligation to Dr. Holt, the assistant of the laboratory, for his helpful coöperation. * * * * * CONTENTS. Preface: Hugo Münsterberg ...................................... i STUDIES IN PERCEPTION. Eye-Movement and Central Anæsthesia: Edwin B. Holt ........... 3 Tactual Illusions: Charles H. Rieber ......................... 47 Tactual Time Estimation: Knight Dunlap ....................... 101 Perception of Number through Touch: J. Franklin Messenger .... 123 The Subjective Horizon: Robert MacDougall .................... 145 The Illusion of Resolution-Stripes on the Color-Wheel: Edwin B. Holt .............................................. 167 STUDIES IN MEMORY. Recall of Words, Objects and Movements: Harvey A. Peterson ... 207 Mutual Inhibition of Memory Images: Frederick Meakin ......... 235 Control of the Memory Image: Charles S. Moore ................ 277 STUDIES IN ÆSTHETIC PROCESSES. The Structure of Simple Rhythm Forms: Robert MacDougall ...... 309 Rhythm and Rhyme: R.H. Stetson ............................... 413 Studies in Symmetry: Ethel D. Puffer ......................... 467 The Æsthetics of Unequal Division: Rosewell Parker Angier .... 541 STUDIES IN ANIMAL PSYCHOLOGY.