Gratefully, and with this expression of my thanks, I acknowledge my
indebtedness to Professor Hugo Muensterberg for placing at my command the
resources of the Harvard Psychological Laboratory and for advice and
encouragement throughout my investigation; to Professor Edwin B. Holt for
valuable assistance in more ways than I can mention; to Professor Wallace
C. Sabine for generous aid in connection with the experiments on hearing;
to Professor Theobald Smith for the examination of pathological dancers;
to Miss Mary C. Dickerson for the photographs of dancing mice which are
reproduced in the frontispiece; to Mr. Frank Ashmore for additional
photographs which I have been unable to use in this volume; to Mr. C. H.
Toll for the drawings for Figures 14 and 20; to Doctors H. W. Rand and C.
S. Berry for valuable suggestions on the basis of a critical reading of
the proof sheets; and to my wife, Ada Watterson Yerkes, for constant aid
throughout the experimental work and in the preparation of this volume.

R. M. Y.

CAMBRIDGE, MASSACHUSETTS,

August, 1907.





CONTENTS


LIST OF ILLUSTRATIONS