Chapter I: Preface

This book is the direct result of what, at the time of its occurrence, seemed to be an unimportant incident in the course of my scientific work-- the presentation of a pair of dancing mice to the Harvard Psychological Laboratory. My interest in the peculiarities of behavior which the creatures exhibited, as I watched them casually from day to day, soon became experiment-impelling, and almost before I realized it, I was in the midst of an investigation of their senses and intelligence.

The longer I observed and experimented with them, the more numerous became the problems which the dancers presented to me for solution. From a study of the senses of hearing and sight I was led to investigate, in turn, the various forms of activity of which the mice are capable; the ways in which they learn to react adaptively to new or novel situations; the facility with which they acquire habits; the duration of habits; the roles of the various senses in the acquisition and performance of certain habitual acts; the efficiency of different methods of training; and the inheritance of racial and individually acquired forms of behavior.

In the course of my experimental work I discovered, much to my surprise, that no accurate and detailed account of this curiously interesting animal existed in the English language, and that in no other language were all the facts concerning it available in a single book. This fact, in connection with my appreciation of the exceptional value of the dancer as a pet and as material for the scientific study of animal behavior, has led me to supplement the results of my own observation by presenting in this little book a brief and not too highly technical description of the general characteristics and history of the dancer.

The purposes which I have had in mind as I planned and wrote the book are three: first, to present directly, clearly, and briefly the results of my investigation; second, to give as complete an account of the dancing mouse as a thorough study of the literature on the animal and long-continued observation on my own part should make possible; third, to provide a supplementary text-book on mammalian behavior and on methods of studying animal behavior for use in connection with courses in Comparative Psychology, Comparative Physiology, and Animal Behavior.

It is my conviction that the scientific study of animal behavior and of animal mind can be furthered more just at present by intensive special investigations than by extensive general books. Methods of research in this field are few and surprisingly crude, for the majority of investigators have been more deeply interested in getting results than in perfecting methods. In writing this account of the dancing mouse I have attempted to lay as much stress upon the development of my methods of work as upon the results which the methods yielded. In fact, I have used the dancer as a means of exhibiting a variety of methods by which the behavior and intelligence of animals may be studied. As it happens the dancer is an ideal subject for the experimental study of many of the problems of animal behavior. It is small, easily cared for, readily tamed, harmless, incessantly active, and it lends itself satisfactorily to a large number of experimental situations. For laboratory courses in Comparative Psychology or Comparative Physiology it well might hold the place which the frog now holds in courses in Comparative Anatomy.

Gratefully, and with this expression of my thanks, I acknowledge my indebtedness to Professor Hugo Münsterberg 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

LITERATURE ON THE DANCING MOUSE

CHAPTER I

CHARACTERISTICS, ORIGIN, AND HISTORY

Peculiarities of the dancing mouse--Markings and method of keeping record of individuals--The dancer in China and Japan (Kishi, Mitsukuri, Hatai)-- Theories concerning the origin of the race: selectional breeding; the inheritance of an acquired character; mutation, inheritance, and selectional breeding; pathological changes; natural selection--Instances of the occurrence of dancers among other kinds of mice--Results of crossing dancer with other kinds of mice.

CHAPTER II

FEEDING, BREEDING, AND DEVELOPMENT OF THE YOUNG

Methods of keeping and caring for dancers--Cages, nest-boxes, and materials for nest--Cleansing cages--Food supply and feeding--Importance of cleanliness, warmth, and pure food--Relations of males and females, fighting--The young, number in a litter--Care of young--Course of development--Comparison of young of dancer with young of common mouse-- Diary account of the course of development of a typical litter of dancers.

CHAPTER III

BEHAVIOR: DANCE MOVEMENTS

Dancing--Restlessness and excitability--Significance of restlessness-- Forms of dance: whirling, circling, and figure-eights--Direction of whirling and circling: right whirlers, left whirlers, and mixed whirlers-- Sex differences in dancing--Time and periodicity of dancing--Influence of light on activity--Necessity for prolonged observation of behavior.

CHAPTER IV

BEHAVIOR: EQUILIBRATION AND DIZZINESS

Muscular coordination--Statements of Cyon and Zoth concerning behavior-- Control of movements, orientation, equilibration, movement on inclined surfaces, climbing--The tracks of the dancer--Absence of visual dizziness--Comparison of the behavior of the dancer with that of the common mouse when they are rotated in a cyclostat--Behavior of blinded dancers (Cyon, Alexander and Kreidl, Kishi)--Cyon's two types of dancer-- Phenomena of behavior for which structural bases are sought: dance movements; lack of response to sounds; deficiency in equilibrational ability; lack of visual and rotational dizziness.

CHAPTER V

STRUCTURAL PECULIARITIES AND BEHAVIOR

The functions of the ear--Structure of the ear of the dancer as described by Rawitz, by Panse, by Baginsky, by Alexander and Kreidl, and by Kishi-- Cyon's theory of the relation of the semicircular canals to space perception--Condition of the auditory organs--Condition of the equilibrational organs--Condition of the sound-transmitting organs--The bearing of the results of anatomical investigations upon the facts of behavior.

CHAPTER VI

THE SENSE OF HEARING

Experiments on hearing in the dancer made by Rawitz, by Panse, by Cyon, by Alexander and Kreidl, by Zoth, and by Kishi--Hearing and the voice-- Methods of testing sensitiveness to sounds--Results of tests with adults-- Importance of indirect method of experimentation--Results of tests with young--The period of auditory sensitiveness--Individual differences.

CHAPTER VII

THE SENSE OF SIGHT: BRIGHTNESS VISION

What is known concerning sight in the dancer--Brightness vision and color vision--Methods of testing brightness vision, the visual discrimination apparatus--Motives for discrimination and choice--Punishment versus reward as an incentive in animal experiments--Hunger as an incentive--An electric stimulus as an incentive--Conditions for brightness vision tests-- White-black vision--Evidence of preference--Check experiments--Conclusion.

CHAPTER VIII

THE SENSE OF SIGHT: BRIGHTNESS VISION (_Continued_)

The delicacy of brightness discrimination--Methods of testing the dancer's ability to detect slight differences in brightness--Results of tests with gray papers--Relation of intensity of visual stimuli to the threshold of discrimination--Weber's law apparatus and method of experimentation-- Results of Weber's law tests--Practice effects, the training of vision-- Description of the behavior of the dancer in the discrimination box experiments--Modes of choice: by affirmation; by negation; by comparison-- Evidence of indiscriminable visual conditions.

CHAPTER IX

THE SENSE OF SIGHT: COLOR VISION

Does the dancer see colors?--The food-box method of testing color vision-- Waugh's food-box method--Results of tests--Tests by the use of colored papers in the visual discrimination box--Yellow-red vision--Blue-orange vision--Brightness vision _versus_ color vision--Brightness check tests--Green-blue vision--Violet-red vision--Conclusions.

CHAPTER X

THE SENSE OF SIGHT: COLOR VISION (_Continued_)

The use of color filters--Testing color vision by the use of transmitted light--Green-blue vision--Green-red vision--Blue-red vision--Stimulating value of different portions of the spectrum--Does red appear darker to the dancer than to us?--Conclusions concerning color vision--Structure of the retina of the dancer and its significance.

CHAPTER XI

THE ROLE OF SIGHT IN THE DAILY LIFE OF THE DANCER.

Sight and general behavior--Behavior of blinded dancers--Experimental tests of ability to perceive form--Visual guidance in mazes--Following labyrinth paths in the dark--The relative importance of visual, olfactory, and kinaesthetic stimuli--Conditions for the acquisition of a motor habit--Conditions for the execution of an habitual act.

CHAPTER XII

EDUCABILITY: METHODS OF LEARNING

The modifiability of behavior--Educational value of experimental studies of modifiability--Methods: the problem method; the labyrinth method; the discrimination method--Relation of method to characteristics of animal-- Simple test of the docility of the dancer--Lack of imitative tendency-- Persistence of useless acts--Manner of profiting by experience--Individual differences in initiative.

CHAPTER XIII

HABIT FORMATION: THE LABYRINTH HABIT

The labyrinth method--Problems--Preliminary tests--Comparison of the behavior of the dancer in a maze with that of the common mouse--Evolution of a labyrinth method--Records of time and records of errors--Simple and effective method of recording the path--Curves of habit formation--Regular and irregular labyrinths--Points for a standard labyrinth--Values and defects of the labyrinth method.

CHAPTER XIV

HABIT FORMATION: THE DISCRIMINATION METHOD

Quantitative _versus_ qualitative results--Motives--Precautions-- Preference--Results of systematic habit-forming experiments--Curves of habit formation--Meaning of irregularity in curve--Individual differences--Comparison of curves for discrimination habits with those for labyrinth habits--Averages--The index of modifiability as a measure of docility--Reliability of the index.

CHAPTER XV

THE EFFICIENCY OF TRAINING METHODS

Importance of measuring the efficiency of educational methods--Rapidity of learning and permanency of modifications wrought by training--Results of a study of the efficiency of discrimination methods--Comparison by means of indices of modifiability--Number of tests per series versus number of series--Efficiency as measured by memory tests.

CHAPTER XVI

THE DURATION OF HABITS: MEMORY AND RE-LEARNING

Measures of the permanency of modifications in behavior--The duration of brightness and color discrimination habits--The relation of learning to re-learning--Can a habit which has been lost completely be re-acquired with greater facility than it was originally acquired?--Relation of special training to general efficiency--Does the training in one form of labyrinth aid the dancer in acquiring other labyrinth habits?

CHAPTER XVII

INDIVIDUAL, AGE, AND SEX DIFFERENCES IN BEHAVIOR

Individual peculiarities in sensitiveness, docility, and initiative--The relation of docility to age--The individual result and the average--How averages conceal facts--Sex differences in docility and initiative-- Individual differences of motor capacity which seem to indicate varieties--Is the dancer pathological?