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The Dancing Mouse by Robert M. Yerkes

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A Study in Animal Behavior



The Cartwright Prize of the Alumni Association of the College of
Physicians and Surgeons, Columbia University, was awarded, in 1907, for an
Essay which comprised the first twelve chapters of this volume.




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 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.


August, 1907.






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.



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.



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.



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.



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



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.



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.



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.



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.



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.



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.



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.



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.



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.



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.



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?



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?



Characteristics of the race--Inheritance of the tendency to whirl in a
particular way--Tests of the inheritance of individually acquired forms of



Dancing Mice--sniffing and eating _Frontispiece_


1. Color patterns of dancers. Record blanks

2. Double cage, with nest-boxes and water dishes

3. Double cages in frame

4. Photographs of dancers climbing (After Zoth)

5. Tracks of common mouse (After Alexander and Kreidl)

6. Tracks of dancer (After Alexander and Kreidl)

7. The inner ear of the rabbit (Retzius)

8. The membranous labyrinth of the ear of the dancer (After Rawitz)

9. Same

10. Same

it. Model of the ear of the dancer (After Baginsky)

12. Ear of the dancer (After Kishi)

13. Ear of the dancer (After Kishi)

14. Discrimination box

15. Ground plan of discrimination box

16. Nendel's gray papers

17. Weber's law apparatus

18. Food-box apparatus

19. Waugh's food-box apparatus

20. Color discrimination apparatus

21. Ground plan of color discrimination apparatus

22. Cards for form discrimination

23. Labyrinth B

24. Labyrinth B on electric wires

25. Labyrinth A

26. Curves of habit formation for labyrinth B

27. Plan of labyrinth C, and path records

28. Labyrinth D

29. Curve of learning for white-black discrimination, twenty individuals

30. Curve of learning for white-black discrimination, thirty individuals

31. Curve of habit formation for labyrinth D

32. Curves of learning and re-learning

33. Plasticity curves


1. ALEXANDER, G. UND KREIDL, A. "Zur Physiologie des Labyrinths der
Tanzmaus." _Archiv fuer die gesammte Physiologie_, Bd. 82: 541-552.

2. ALEXANDER, G. UND KREIDL, A. "Anatomisch-physiologische Studien ueber
das Ohrlabyrinth der Tanzmaus." II Mittheilung. _Archiv fuer die gesammte
Physiologie_. Bd. 88: 509-563. 1902.

3. ALEXANDER, G. UND KREIDL, A. "Anatomisch-physiologische Studien ueber
das Ohrlabyrinth der Tanzmaus." III Mittheilung. _Archiv fuer die
gesammte Physiologie_, Bd. 88: 564-574. 1902.

4. BAGINSKY, B. "Zur Frage ueber die Zahl der Bogengaenge bei japanischen
Tanzmaeusen." _Centralblatt fuer Physiologie_, Bd. 16: 2-4. 1902.

5. BATESON, W. "The present state of knowledge of colour-heredity in mice
and rats." _Proceedings of the Zooelogical Society of London_, Vol. 2:
71-99. 1903.

6. BREHM, A. E. "Tierleben." Dritte Auflage. Saugetiere, Bd. 2: 513-514.

7. BREHM, A. E. "Life of Animals." Translated from the third German
edition of the "Tierleben" by G. R. Schmidtlein. Mammalia, p. 338.
Marquis, Chicago. 1895.

8. CYON, E. DE. "Le sens de l'espace chez les souris dansantes
japonaises." _Cinquantenaire de la Societe de Biologie_ (Volume
jubilaire). p. 544-546. Paris. 1899.

9. CYON, E. VON. "Ohrlabyrinth, Raumsinn und Orientirung." _Archiv fuer
die gesammte Physiologie_, Bd. 79: 211-302. 1900.

10. CYON, E. DE. "Presentation de souris dansantes japonaises." _Comptes
rendus du XIII Congres International de Paris, Section de
physiologie_, p. 160-161. 1900.

11. CYON, E. VON. "Beitraege zur Physiologie des Raumsinns." I Theil. "Neue
Beobachtungen an den japanischen Tanzmaeusen." _Archiv fuer die gesammte
Physiologie_, Bd. 89: 427-453. 1902.

12. CYON, E. DE. "Le sens de l'espace." Richet's "Dictionnaire de
physiologie," T. 5: 570-571. 1901.

13. DARBISHIRE, A. D. Note on the results of crossing Japanese waltzing
mice with European albino races. _Biometrica_, Vol. 2: 101-104. 1902.

14. DARBISHIRE, A. D. Second report on the result of crossing Japanese
waltzing mice with European albino races. _Biometrica_, Vol.2:
165-173. 1903.

15. DARBISHIRE, A. D. Third report on hybrids between waltzing mice and
albino races. _Biometrica_, Vol. 2: 282-285. 1903.

16. DARBISHIRE, A. D. On the result of crossing Japanese waltzing with
albino mice. _Biometrica_, Vol 3: 1-51. 1904.

17. GUAITA, G. v. "Versuche mit Kreuzungen von verschiedenen Rassen der
Hausmaus." _Berichte der naturforschenden Gesellschaft zu Freiburg i.
B_., Bd. 10: 317-332. 1898.

18. GUAITA, G. v. "Zweite Mitteilung uber Versuche mit Kreuzungen von
verschiedenen Hausmausrassen." _Berichte der naturforschenden
Gesellschaft zu Freiburg i. B_., Bd. 11: 131-138. 1900.

19. HAACKE, W. "Ueber Wesen, Ursachen und Vererbung von Albinismus und
Scheckung und ueber deren Bedeutung fuer vererbungstheoretische und
entwicklungsmechanische Fragen." _Biologisches Centralblatt_, Bd.
15: 44-78. 1895.

19a. HUNTER, M. S. "A Pair of Waltzing Mice." _The Century Magazine_,
Vol. 73: 889-893. April, 1907.

20. KAMMERER, P. "Tanzende Waldmaus und radschlagende Hausmaus."
_Zooelogische Garten_, Bd. 41: 389-390. 1900.

21. KISHI, K. "Das Gehoerorgan der sogenannten Tanzmaus." _Zeitschrift
fuer wissenschaftliche Zooelogie_, Bd. 71: 457-485. 1902.

22. LANDOIS, H. "Chinesische Tanzmaeuse." _Jahresbericht des Westfaehschen
Provinzial-Vereins_, Munster, 1893-1894: 62-64.

22a. LOSE, J. "Waltzing Mice." _Country Life in America_, September,
1904. p. 447.

23. PANSE, R. Zu Herrn Bernhard Rawitz' Arbeit: "Das Gehoerorgan der
japanischen Tanzmaeuse." _Archiv fuer Anatomie und Physiologie_,
Physiologische Abtheilung, 1901: 139-140.

24. PANSE, R. "Das Gleichgewichts- und Gehoerorgan der japanischen
Tanzmaeuse." _Muenchener medicinische Wochenschrift_, Jahrgang 48, Bd.
I: 498-499. 1901.

25. RAWITZ, B. "Das Gehoerorgan der japanischen Tanzmaeuse." _Archiv fuer
Anatomie und Physiologie_, Physiologische Abtheilung, 1899: 236-243.

26. RAWITZ, B. "Neue Beobachtungen ueber das Gehoerorgan japanischer
Tanzmaeuse." _Archiv fuer Anatomie und Physiologie_, Physiologische
Abtheilung, 1901, Supplement: 171-176.

27. RAWITZ, B. "Zur Frage ueber die Zahl der Bogengaenge bei japanischen
Tanzmaeusen." _Centralblatt fuer Physiologie_, Bd. 15: 649-651. 1902.

28. SAINT-LOUP, R. "Sur le mouvement de manege chez les souris."
_Bulletin de la Societe Zooelogique de France_, T. 18: 85-88. 1893.

29. SCHLUMBERGER, C. "A propos d'un netzuke japonais." _Memoires de la
Societe Zooelogique de France_, T. 7: 63-64. 1894.

30. WELDON, W. F. R. Mr. Bateson's revisions of Mendel's theory of
heredity. _Biometrica_, Vol. 2: 286-298. 1903.

31. ZOTH, O. "Ein Beitrag zu den Beobachtungen und Versuchen an
japanischen Tanzmaeusen." _Archiv fuer die gesammte Physiologie_, Bd.
86: 147-176. 1901.

32. ANONYMOUS. "Fancy Mice: Their Varieties, Management, and Breeding."
Fourth edition. London: L. Upcott Gill. No date.



The variety of mouse which is known as the Japanese dancing or waltzing
mouse has been of special interest to biologists and to lovers of pets
because of its curious movements. Haacke in Brehm's "Life of Animals" (7
p. 337)[1] writes as follows concerning certain mice which were brought to
Europe from China and Japan: "From time to time a Hamburg dealer in
animals sends me two breeds of common mice, which he calls Chinese
climbing mice (Chinesische Klettermaeuse) and Japanese dancing mice
(Japanische Tanzmaeuse). It is true that the first are distinguished only
by their different colors, for their climbing accomplishments are not
greater than those of other mice. The color, however, is subject to many
variations. Besides individuals of uniform gray, light yellow, and white
color, I have had specimens mottled with gray and white, and blue and
white. Tricolored mice seem to be very rare. It is a known fact that we
also have white, black, and yellow mice and occasionally pied ones, and
the Chinese have profited by these variations of the common mouse also, to
satisfy their fancy in breeding animals. The Japanese, however, who are no
less enthusiastic on this point, know how to transform the common mouse
into a really admirable animal. The Japanese dancing mice, which perfectly
justify their appellation, also occur in all the described colors. But
what distinguishes them most is their innate habit of running around,
describing greater or smaller circles or more frequently whirling around
on the same spot with incredible rapidity. Sometimes two or, more rarely,
three mice join in such a dance, which usually begins at dusk and is at
intervals resumed during the night, but it is usually executed by a single

[Footnote 1: The reference numbers, of which 7 is an example, refer to the
numbers in the bibliographic list which precedes this chapter.]

As a rule the dancing mouse is considerably smaller than the common mouse,
and observers agree that there are also certain characteristic
peculiarities in the shape of the head. One of the earliest accounts of
the animal which I have found, that of Landois (22 p. 62), states,
however, that the peculiarities of external form are not remarkable.
Landois further remarks, with reason, that the name dancing mouse is ill
chosen, since the human dance movement is rather a rhythmic hopping motion
than regular movement in a circle. As he suggests, they might more
appropriately be called "circus course mice" (22 p. 63).

Since 1903 I have had under observation constantly from two to one hundred
dancing mice. The original pair was presented to the Harvard Psychological
Laboratory by Doctor A.G. Cleghorn of Cambridge. I have obtained
specimens, all strikingly alike in markings, size, and general behavior,
from animal dealers in Washington, Philadelphia, and Boston. Almost all of
the dancers which I have had, and they now number about four hundred, were
white with patches, streaks, or spots of black. The black markings
occurred most frequently on the neck, ears, face, thighs, hind legs, about
the root of the tail, and occasionally on the tail itself. In only one
instance were the ears white, and that in the case of one of the offspring
of a male which was distinguished from most of his fellows by the
possession of one white ear. I have had a few individuals whose markings
were white and gray instead of white and black.

The method by which I was able to keep an accurate record of each of my
dancers for purposes of identification and reference is illustrated in
Figure 1. As this method has proved very convenient and satisfactory, I
may briefly describe it. With a rubber stamp[1] a rough outline of a
mouse, like that of Figure 1 A, was made in my record book. On this
outline I then indicated the black markings of the individual to be
described. Beside this drawing of the animal I recorded its number,
sex,[2] date of birth, parentage, and history. B, C, and D of Figure 1
represent typical color patterns. D indicates the markings of an
individual whose ears were almost entirely white. The pattern varies so
much from individual to individual that I have had no trouble whatever in
identifying my mice by means of such records as these.

[Footnote 1: For the use of the plate from which this stamp was made, I am
indebted to Professor W.E. Castle, who in turn makes acknowledgment to
Doctor G.M. Allen for the original drawing.]

[Footnote 2: I have found it convenient to use the even numbers for the
males and the odd numbers for the females. Throughout this book this usage
is followed. Wherever the sex of an individual is not specially given, the
reader therefore may infer that it is a male if the number is even; a
female if the number is odd.]

All of my dancers had black eyes and were smaller as well as weaker than
the albino mouse and the gray house mouse. The weakness indicated by their
inability to hold up their own weight or to cling to an object curiously
enough does not manifest itself in their dancing; in this they are
indefatigable. Frequently they run in circles or whirl about with
astonishing rapidity for several minutes at a time. Zoth (31 p. 173), who
measured the strength of the dancer in comparison with that of the common
mouse, found that it can hold up only about 2.8 times its own weight,
whereas the common white mouse can hold up 4.4 times its weight. No other
accurate measurements of the strength, endurance, or hardiness of the
dancer are available. They are usually supposed to be weak and delicate,
but my own observations cause me to regard them as exceptionally strong in
certain respects and weak in others.

[Illustration: FIGURE I.--Typical markings of dancers. A, blank outline of
mouse for record. B, markings of No. 2 [symbol for male], born September
7, 1905, of unknown parents, died March 30,1907. C, markings of No 43
[symbol for female], born November 10, 1906, of 212 and 211. D,
markings of No. 151 [symbol for female], born February 28, 1906, of 1000
and 5, died February 26, 1907.]

What the Japanese have to say about the dancing mouse is of special
importance because Japan is rather commonly supposed to be its home. For
this reason, as well as because of the peculiar interest of the facts
mentioned, I quote at length from Doctor Kishi (21 p. 457). "The dancing
mouse has received in Europe this name which it does not bear in its own
home, because of the fact that the circular movements which it makes are
similar to the European (human) dance. Sometimes it is also called the
Japanese or Chinese mouse; originally, however, China must have been its
home, since in Japan it is mostly called '_Nankin nesumi_,' the mouse from
Nankin. When this animal came from China to Japan I shall inquire at a
later opportunity. There were originally in Japan two different species of
mouse, the gray and the white; therefore in order to distinguish our
dancing mouse from these it was necessary to use the name of its native

"In Japan, as in Europe, the animal lives as a house animal in small
cages, but the interest which is taken in it there is shown in quite
another way than in Europe, where the whirling movements, to which the
name dancing mouse is due, are of chief interest. For this reason in
Europe it is given as much room as possible in its cage that it may dance
conveniently. In Japan also the circular movements have been known for a
long time, but this has had no influence upon our interest in the animal,
for the human fashion of dancing with us is quite different from that in
Europe. What has lent interest to the creature for us are its prettiness,
its cleverness in tricks, and its activity. It is liked, therefore, as an
amusement for children. For this purpose it is kept in a small cage,
usually fifteen centimeters square, sometimes in a somewhat broader wooden
box one of whose walls is of wire netting. In this box are built usually a
tower, a tunnel, a bridge, and a wheel. The wheel is rather broad, being
made in the form of a drum and pierced with holes on one side through
which the animal can slip in and out. Running around on the inside, the
mouse moves the wheel often for hours at a time, especially in the
evening. Moreover, there are found in the box other arrangements of
different kinds which may be set in motion by the turning of the wheel. No
space remains in the box in which the animal may move about freely, and
therefore one does not easily or often have an opportunity to observe that
the animal makes circular movements, whether voluntarily or involuntarily.
This is the reason that in its home this interesting little animal has
never been studied by any one in this respect."

It is odd indeed that the remarkable capacity of the dancer for the
execution of quick, graceful, dextrous, bizarre, and oft-repeated
movements has not been utilized in America as it has in Japan. The mice
are inexhaustible sources of amusement as well as invaluable material for
studies in animal behavior and intelligence.

Concerning the origin and history of this curious variety of mouse little
is definitely known. I have found no mention of the animal in scientific
literature previous to 1890. The fact that it is called the Chinese
dancing mouse, the Japanese dancing mouse, and the Japanese waltzing mouse
is indicative of the existing uncertainty concerning the origin of the

Thinking that Japanese literature might furnish more information bearing
on the question of racial history than was available from European
sources, I wrote to Professor Mitsukuri of the University of Tokyo, asking
him whether any reliable records of the dancer existed in Japan. He
replied as follows: "I have tried to find what is known in Japan about the
history of the Japanese waltzing mice, but I am sorry to say that the
results are wholly negative. I cannot find any account of the origin of
this freak, either authentic or fictitious, and, strange as it may seem to
you, no study of the mice in a modern sense has been made, so you may
consider the literature on the mouse in the Japanese language as
absolutely _nil_." In explanation of this somewhat surprising ignorance of
the origin of the race in what is commonly supposed to be its native land,
Professor Mitsukuri adds: "The breeders of the mice have mostly been
ignorant men to whom writing is anything but easy."

In response to similar inquiries, I received the following letter,
confirmatory of Professor Mitsukuri's statements, from Doctor S. Hatai of
Wistar Institute, Philadelphia: "If I remember rightly the so-called
Japanese dancing mouse is usually called by us _Nankin-nedzumi_. _Nankin_
means anything which has been imported from China, and _nedzumi_ means
rat-like animal, or in this case mouse, or Chinese mouse. I referred to
one of the standard Japanese dictionaries and found the following
statement: 'The _Nankin-nedzumi_ is one of the varieties of _Mus
spiciosus_ (_Hatszuka-nedzumi_), and is variously colored. It was imported
from China. These mice are kept in cages for the amusement of children,
who watch their play.' _Mus spiciosus_, if I remember correctly, is very
much like _Mus musculus_ in color, size, and several other
characteristics, if not the same altogether."

In Swinhoe's list of the mammals of China, which appeared in the
_Proceedings of the Zoological Society of London_ for 1870, _Mus musculus
L_. is mentioned as occurring in houses in South China and in Formosa. It
is further stated that black and white varieties which are brought from
the Straits are often kept by the Chinese (p. 637).

The statements of Kishi, Mitsukuri, and Hatai which have been quoted,
taken in connection with the opinions expressed by various European
scientists who have studied the dancer, make it seem highly probable that
the race appeared first in China, and was thence introduced into Japan,
from which country it has been brought to Europe and America. Accepting
for the present this conclusion with reference to the place of origin of
the dancer, we may now inquire, how and when did this curious freak, as
Professor Mitsukuri has called it, come into existence? Concerning these
matters there is wide divergence of opinion.

Haacke (6 p. 514), as quoted in Brehm's "Tierleben," says that an animal
dealer with whom he discussed the question of the possible origin of the
dancer maintained that it came from Peru, where it nests in the full
cotton capsules, arranging the cotton fibers in the form of a nest by
running about among them in small circles. Hence the name cotton mouse is
sometimes applied to it. Haacke himself believes, however, that the race
originated either in China or Japan as the result of systematic
selectional breeding. Of this he has no certainty, for he states that he
failed to find any literature on the "beautiful mice of China and Japan."
Whether Haacke's description of the dancing mouse was published elsewhere
previous to its appearance in Brehm's "Tierleben" I am unable to state; I
have found nothing written on the subject by him before 1890. Zoth (31 p.
176) also thinks that the race was developed by systematic breeding, or in
other words, that it is a product of the skill of the Asiatic animal

Another account of the origin of the race is that accepted by Kishi (21 p.
481) and some other Japanese biologists. It is their belief that the forms
of movement acquired by the individual as the result of confinement in
narrow cages are inherited. Thus centuries of subjection to the conditions
which Kishi has described (p. 6) finally resulted in a race of mice which
breed true to the dance movement. It is only fair to add, although Kishi
does not emphasize the fact, that in all probability those individuals in
which the dancing tendency was most pronounced would naturally be selected
by the breeders who kept these animals as pets, and thus it would come
about that selectional breeding would supplement the inheritance of an
acquired character. Few indeed will be willing to accept this explanation
of the origin of the dancer so long as the inheritance of acquired
characters remains, as at present, unproved.

Still another mode of origin of the mice is suggested by the following
facts. In 1893 Saint Loup (28 p. 85) advanced the opinion that dancing
individuals appear from time to time among races of common mice. The
peculiarity of movement may be due, he thinks, to an accidental nervous
defect which possibly might be transmissible to the offspring of the
exceptional individual. Saint Loup for several months had under
observation a litter of common mice whose quick, jerky, nervous movements
of the head, continuous activity, and rapid whirling closely resembled the
characteristic movements of the true dancers of China. He states that
these mice ran around in circles of from 1 to 20 cm. in diameter. They
turned in either direction, but more frequently to the left, that is,
anticlockwise. At intervals they ran in figure-eights ([Symbol: figure
eight]) as do the true dancers. According to Saint Loup these exceptional
individuals were healthy, active, tame, and not markedly different in
general intelligence from the ordinary mouse. One of these mice produced a
litter of seven young, in which, however, none of the peculiarities of
behavior of the parents appeared.

In view of this proof of the occurrence of dancing individuals among
common mice, Saint Loup believes that the race of dancers has resulted
from the inheritance and accentuation of an "accidental" deviation from
the usual mode of behavior. It is scarcely necessary to say that this
opinion would be of far greater weight had he observed, instead of
postulating, the inheritance of the peculiarities of movement which he has
described. It might be objected, to the first of his so-called facts, that
the litter resulted from the mating of mice which possessed dancer blood.
Until the occurrence of dancers among varieties of mice which are known to
be unmixed with true dancers is established, and further, until the
inheritance of this peculiar deviation from the normal is proved, Saint
Loup's account of the origin of the dancing mouse race must be regarded as
an hypothesis.

The occurrence of dancing individuals among common mice has been recorded
by several other observers. Kammerer (20 p. 389) reports that he found a
litter of young wood mice (_Mus sylvaticus L_.) which behaved much as do
the spotted dancers of China. He also observed, among a lot of true
dancers, a gray individual which, instead of spinning around after the
manner of the race, turned somersaults at frequent intervals. It is
Kammerer's opinion, as a result of these observations, that the black and
white dancers of China and Japan have been produced by selectional
breeding on the basis of this occasional tendency to move in circles.
Among albino mice Rawitz (25 p. 238) has found individuals which whirled
about rapidly in small circles. He states, however, that they lacked the
restlessness of the Chinese dancers. Some shrews (_Sorex vulgaris L_.)
which exhibited whirling movements and in certain other respects resembled
the dancing mouse were studied for a time by Professor Haecker of Freiburg
in Baden, according to a report by von Guaita (17 p. 317, footnote).
Doctor G. M. Allen of Cambridge has reported to me that he noticed among a
large number of mice kept by him for the investigation of problems of
heredity[1] individuals which ran in circles; and Miss Abbie Lathrop of
Granby, Massachusetts, who has raised thousands of mice for the market,
has written me of the appearance of an individual, in a race which she
feels confident possessed no dancer blood, which whirled and ran about in
small circles much as do the true dancers.

[Footnote 1: Allen, G.M. "The Heredity of Coat Color in Mice." Proc. Amer.
Academy, Vol. 40, 59-163, 1904.]

Although it is possible that some of these cases of the unexpected
appearance of individuals with certain of the dancer's peculiarities of
behavior may have been due to the presence of dancer blood in the parents,
it is not at all probable that this is true of all of them. We may,
therefore, accept the statement that dancing individuals now and then
appear in various races of mice. They are usually spoken of as freaks,
and, because of their inability to thrive under the conditions of life of
the race in which they happen to appear, they soon perish.

Another and a strikingly different notion of the origin of the race of
dancers from those already mentioned is that of Cyon (11 p. 443) who
argues that it is not a natural variety of mouse, as one might at first
suppose it to be, but instead a pathological variation. The pathological
nature of the animals is indicated, he points out, by the exceptionally
high degree of variability of certain portions of the body. According to
this view the dancing is due to certain pathological structural conditions
which are inherited. Cyon's belief raises the interesting question, are
the mice normal or abnormal, healthy or pathological? That the question
cannot be answered with certainty off-hand will be apparent after we have
considered the facts of structure and function which this volume presents.

Everything organic sooner or later is accounted for, in some one's mind,
by the action of natural selection. The dancing mouse is no exception, for
Landois (22 p. 62) thinks that it is the product of natural selection and
heredity, favored, possibly, by selectional breeding in China. He further
maintains that the Chinese dancer is a variety of _Mus musculus L._ in
which certain peculiarities of behavior appear because of bilateral
defects in the brain. This author is not alone in his belief that the
brain of the dancer is defective, but so far as I have been able to
discover he is the only scientist who has had the temerity to appeal to
natural selection as an explanation of the origin of the race.

Milne-Edwards, as quoted by Schlumberger (29 p. 63), is of the opinion
that the Chinese dancer is not a natural wild mouse race, but instead the
product of rigid artificial selection. And in connection with this
statement Schlumberger describes a discovery of his own which seems to
have some bearing upon the problem of origin. In an old Japanese wood
carving which came into his possession he found a group of dancing mice.
The artist had represented in minute detail the characteristics of the
members of the group, which consisted of the parents and eight young. The
father and mother as well as four of the little mice are represented as
white spotted with black. Of the four remaining young mice, two are
entirely black and two entirely white. The two pure white individuals have
pink eyes, as has also the mother. The eyes of all the others are black.
From these facts Schlumberger infers that the dancer has resulted from the
crossing of a race of black mice with a race of albinos; the two original
types appear among the offspring in the carving.

Experimental studies of the inheritance of the tendency to dance are of
interest in their bearing upon the question of origin. Such studies have
been made by Haacke (19), von Guaita (17, 18), and Darbishire (13, 14, 15,
16), and the important results of their investigations have been well
summarized by Bateson (5).

By crossing dancing mice with common white mice both Haacke and von Guaita
obtained gray or black mice which are very similar to the wild house mouse
in general appearance and behavior. The characteristic movements of the
dancers do not appear. As the result of a long series of breeding
experiments, Darbishire (16 pp. 26, 27) says: "When the race of waltzing
mice is crossed with albino mice which do not waltz, the waltzing habit
disappears in the resulting young, so that waltzing is completely
recessive in Mendel's sense; the eye-color of the hybrids is always dark;
the coat-color is variable, generally a mixture of wild-gray and white,
the character of the coat being distinctly correlated with characters
transmitted both by the albino and by the colored parent." When hybrids
produced by the cross described by Darbishire are paired, they produce
dancers in the proportion of about one to five.

Bateson (5 p. 93, footnote), in discussing the results obtained by Haacke,
von Guaita, and Darbishire, writes: "As regards the waltzing character,
von Guaita's experiments agree with Darbishire's in showing that it was
always recessive to the normal. No individual in F1 [thus the first hybrid
generation is designated] or in families produced by crossing F1 with the
pure normal, waltzed. In Darbishire's experiments F1 x F1 [first hybrids
mated] gave 8 waltzers in 37 offspring, indicating 1 in 4 as the probable
average. From von Guaita's matings in the form DR x DR the totals of
families were 117 normal and 21 waltzers.... There is therefore a large
excess of normals over the expected 3 to 1. This is possibly due to the
delicacy of the waltzers, which are certainly much more difficult to rear
than normals are. The small number in von Guaita's litters makes it very
likely that many were lost before such a character as this could be

Bateson does not hazard a guess at the origin of the dancer, but merely
remarks (5 p. 86) that the exact physiological basis of the dancing
character is uncertain and the origin of this curious variation in
behavior still more obscure. "Mouse fanciers have assured me," he
continues, "that something like it may appear in strains inbred from the
normal type, though I cannot find an indubitable case. Such an occurrence
may be nothing but the appearance of a rare recessive form. Certainly it
is not a necessary consequence of inbreeding, witness von Guaita's long
series of inbred albinos." (von Guaita (17 p. 319) inbred for twenty-eight

From the foregoing survey of the available sources of information
concerning the origin and history of the race of dancing mice the
following important facts appear. There are four theories of the origin of
the race: (1) origin by selectional breeding (Haacke, Zoth, Milne-
Edwards); (2) origin through the inheritance of an acquired character
(Kishi); (3) origin by mutation, inheritance, and selectional breeding
(Saint Loup, Kammerer, Cyon); (4) origin by natural selection, and
inheritance, favored by selectional breeding (Landois). Everything
indicates that the race originated in China. It is fairly certain that
individuals with a tendency to move in circles appear at rare intervals in
races of common mice. It seems highly probable, in view of these facts,
that the Chinese took advantage of a deviation from the usual form of
behavior to develop by means of careful and patient selectional breeding a
race of mice which is remarkable for its dancing. Even if it should be
proved that the mutation as it appears among common mice is not inherited,
the view that slight deviations were taken advantage of by the breeders
would still be tenable. The dancing tendency is such in nature as to unfit
an individual for the usual conditions of mouse existence, hence, in all
probability human care alone could have produced and preserved the race of

In answer to the question, how and when did the race of dancers originate,
it may be said that historical research indicates that a structural
variation or mutation which occasionally appears in _Mus musculus_, and
causes those peculiarities of movement which are known as dancing, has
been preserved and accentuated through selectional breeding by the Chinese
and Japanese, until finally a distinct race of mice which breeds true to
the dance character has been established. The age of the race is not
definitely known, but it is supposed to have existed for several



In this chapter I shall report, for the benefit of those who may wish to
know how to take care of dancing mice, my experience in keeping and
breeding the animals, and my observations concerning the development of
the young. It is commonly stated that the dancer is extremely delicate,
subject to diseases to an unusual degree and difficult to breed. I have
not found this to be true. At first I failed to get them to breed, but
this was due, as I discovered later, to the lack of proper food. For three
years my mice have bred frequently and reared almost all of their young.
During one year, after I had learned how to care for the animals, when the
maximum number under observation at any time was fifty and the total
number for the year about one hundred, I lost two by disease and one by an
accident. I very much doubt whether I could have done better with any
species of mouse. There can be no doubt, however, that the dancer is
delicate and demands more careful attention than do most mice. In March,
1907, I lost almost all of my dancers from what appeared to be an
intestinal trouble, but with this exception I have had remarkably good
luck in breeding and rearing them.

My dancers usually were kept in the type of cage of which Figure 2 is a
photograph.[1] Four of these double cages, 70 cm. long, 45 cm. wide, and
10 cm. deep in front, were supported by a frame as is shown in Figure 3.
The fact that the covers of these cages cannot be left open is of
practical importance. A similar type of cage, which I have used to some
extent, consists of a wooden box 30 by 30 cm. by 15 cm. deep, without any
bottom, and with a hinged cover made in part of 1 cm. mesh wire netting.
Such a cage may be placed upon a piece of tin or board, or simply on a
newspaper spread out on a table. The advantage of the loose bottom is that
the box may be lifted off at any time, and the bottom thoroughly cleansed.
I have had this type of cage constructed in blocks of four so that a
single bottom and cover sufficed for the block. If the mice are being kept
for show or for the observation of their movements, at least one side of
the cages should be of wire netting, and, as Kishi suggests, such objects
as a wheel, a tower, a tunnel, a bridge, and a turntable, if placed in the
cage, will give the animals excellent opportunity to exhibit their
capacity for varied forms of activity.

[Footnote 1: This cage was devised by Professors W.E. Castle and E.L.
Mark, and has been used in the Zoological Laboratories of Harvard
University for several years.]

[Illustration: FIGURE 2.--Double cage, with nest boxes and water dishes.]

The floors of the cages were covered with a thin layer of sawdust for the
sake of cleanliness, and in one corner of each cage a nest box of some
sort was placed. During the warm months I found it convenient and
satisfactory to use berry boxes, such as appear in Figure 2, with a small
entrance hole cut in one side; and during the cold months cigar boxes,
with an entrance hole not more than 5 cm. in diameter at one end. In the
nest box a quantity of tissue paper, torn into fragments, furnished
material for a nest in which the adults could make themselves comfortable
or the female care for her young. Cotton should never be used in the nest
boxes, for the mice are likely to get it wound about their legs with
serious results. Apparently they are quite unable to free themselves from
such an incumbrance, and their spinning motion soon winds the threads so
tightly that the circulation of the blood is stopped.

[Illustration: FIGURE 3.--Double cages in frame.]

The cages and nest boxes were emptied and thoroughly cleaned once a week
with an emulsion made by heating together one part of kerosene and one
part of water containing a little soap. This served to destroy whatever
odor the cages had acquired and to prevent vermin from infesting the
nests. In hot weather far greater cleanliness is necessary for the welfare
of the mice than in cold weather. The animals attend faithfully to their
own toilets, and usually keep themselves scrupulously clean.

For water and food dishes I have used heavy watch glasses[1] 5 cm. in
diameter and 1/2 cm. deep. They are convenient because they are durable,
easily cleaned, and not large enough for the young mice to drown in when
they happen to spin into one which contains water. It is said that mice do
not need water, but as the dancers seem very fond of a little, I have made
it a rule to wash the watch glasses thoroughly and fill them with pure
fresh water daily. The food, when moist, may be placed in the cages in the
same kind of watch glass.

[Footnote 1: Minot watch glasses.]

There is no need of feeding the animals oftener than once a day, and as
they eat mostly in the evening and during the night, it is desirable that
the food should be placed in the cage late in the afternoon. For almost a
year I kept a pair of dancers on "force"[1] and water. They seemed
perfectly healthy and were active during the whole time, but they produced
no young. If the animals are kept as pets, and breeding is not desired, a
diet of "force," "egg-o-see,"[1] and crackers, with some bird-seed every
few days, is likely to prove satisfactory. As with other animals, a
variety of food is beneficial, but it appears to be quite unnecessary. Too
much rich food should not be given, and the mice should be permitted to
dictate their own diet by revealing their preferences. They eat
surprisingly little for the amount of their activity. I have had excellent
success in breeding the mice by feeding them a mixture of dry bread-
crumbs, "force," and sweet, clean oats slightly moistened with milk. The
food should never be made soppy. A little milk added thus to the food
every other day greatly increases fertility. About once a week a small
quantity of some green food, lettuce for example, should be given. It is
well, I have found, to vary the diet by replacing the bread and "force" at
intervals with crackers and seeds. Usually I give the food dry every other
day, except in the case of mice which are nursing litters. One person to
whom I suggested that lettuce was good for the dancers lost four,
apparently because of too much of what the mice seemed to consider a good
thing. This suggests that it should be used sparingly.

[Footnote 1: A cereal food.]

Success in keeping and breeding dancing mice depends upon three things:
cleanliness, warmth, and food supply. The temperature should be fairly
constant, between 60 deg. and 70 deg. Fahr. They cannot stand exposure to cold or
lack of food. If one obtains good healthy, fertile individuals, keeps them
in perfectly clean cages with soft nesting materials, maintains a
temperature of not far above or below 65 deg., and regularly supplies them
with pure water and food which they like, there is not likely to be
trouble either in keeping or breeding these delicate little creatures.
Several persons who have reported to me difficulty in rearing the young or
in keeping the adults for long periods have been unable to maintain a
sufficiently high or constant temperature, or have given them food which
caused intestinal trouble.

The males are likely to fight if kept together, and they may even kill one
another. A male may be kept with one or more females, or several females
may be kept together, for the females rarely, in my experience, fight, and
the males seldom harm the females. Unless the male is removed from the
cage in which the female is kept before the young are born, he is likely
to kill the newborn animals. When a female is seen to be building a nest
in preparation for a litter, it is best to place her in a cage by herself
so that she may not be disturbed.

The sex of individuals may be determined easily in most cases, at the age
of 10 to 12 days, by the appearance of teats in the case of females.

The period of gestation is from 18 to 21 days. The maximum number born by
my dancers in any single litter was 9, the minimum number 3. In 25 litters
of which I have accurate records, 135 individuals were born, an average of
5.4. The average number of males per litter was precisely the same, 2.7,
as the number of females.

On the birth of a litter it is well to see that the female has made a nest
from which the young are not likely to escape, for at times, if the nest
is carelessly made, they get out of it or under some of the pieces of
paper which are used in its construction, and perish. Several times I have
observed nests so poorly built that almost all of the young perished
because they got too far away to find their way back to the mother. It is
surprising that the female should not take more pains to keep her young
safe by picking them up in her mouth, as does the common mouse, and
carrying them to a place where they can obtain warmth and nourishment.
This I have never seen a dancing mouse do. For the first day or two after
the birth of a litter the female usually remains in the nest box almost
constantly and eats little. About the second day she begins to eat
ravenously, and for the next three or four weeks she consumes at least
twice as much food as ordinarily. Alexander and Kreidl (3 p. 567) state
that the female does not dance during the first two weeks after the birth
of a litter, but my experience contradicts their statement. There is a
decreased amount of activity during this period, and usually the whirling
movement appears but rarely; but in some cases I have seen vigorous and
long-continued dancing within a few hours after the birth of a litter.
There is a wide range of variability in this matter, and the only safe
statement, in the light of my observations, is that the mother dances less
than usual for a few days after a litter is born to her.

The development of the young, as I have observed it in the cases of twenty
litters, for ten of which (Table I) systematic daily records were kept,
may be sketched as follows. At birth the mice have a rosy pink skin which
is devoid of hair and perfectly smooth; they are blind, deaf, and
irresponsive to stimulation of the vibrissae on the nose. During the first
week of post-natal life the members of a litter remain closely huddled
together in the nest, and no dance movements are exhibited. The mother
stays with them most of the time. On the fourth or fifth day colorless
hairs are visible, and by the end of the week the body is covered with a
coat which rapidly assumes the characteristic black and white markings of
the race. For the first few days the hind legs are too weak to support the
body weight, and whatever movements appear are the result of the use of
the fore legs. As soon as the young mice are able to stand, circling
movements are exhibited, and by the end of the second week they are
pronounced. Somewhere about the tenth day the appearance of the teats in
the case of the females serves to distinguish the sexes plainly. Between
the tenth and fifteenth days excitability, as indicated by restless jerky
movements in the presence of a disturbing condition, increases markedly;
the auditory meatus opens, and, in the case of some individuals, there are
signs of hearing. On or after the fifteenth day the eyes open and the
efforts to escape from the nest box rapidly become more vigorous. About
this time the mother resumes her dancing with customary vigor, and the
young, when they have opportunity, begin to eat of the food which is given
to her. They now dance essentially as do the adults. From the end of the
third week growth continues without noteworthy external changes until
sexual maturity is attained, between the fourth and the sixth week. For
several weeks after they are sexually mature the mice continue to increase
in size.




152+151 5 0 4th day -- 13th day 14th day 14th day 16th day
152+151 1 3 4th day 9th day 10th day 12th day 13th day 15th day
410+415 4 1 5th day 11th day 14th day 15th day 15th day 17th day
410+415 2 4 5th day 10th day 13th day 14th day 14th day 16th day
420+425 0 2 4th day 10th day 12th day 14th day 14th day 16th day
210+215 4 1 -- -- 17th day 13th day 17th day 15th day
210+215 3 3 5th day 11th day 11th day 14th day No 16th day
212+211 1 3 4th day 10th day 15th day 14th day No 15th day
220+225 2 4 4th day 10th day 16th day 14th day No 15th day
220+225 3 3 4th day 10th day 17th day 13th day No 15th day

A course of development very similar to that just described was observed
by Alexander and Kreidl (3 p. 565) in three litters of dancing mice which
contained 3, 5, and 7 individuals respectively. These authors, in
comparing the development of the dancer with that of the common mouse, say
that at birth the young in both cases are about 24 mm. in length. The
young common mouse grows much more rapidly than the dancer, and by the
ninth day its length is about 43 mm. as compared with 31 mm. in the case
of the dancer. According to Zoth (31 p. 148) the adult dancer has a body
length of from 7 to 7.5 cm., a length from tip of nose to tip of tail of
from 12 to 13 cm., and a weight of about 18 grams. The movement of the
dancer from the first tends to take the form of circles toward the middle
of the nest; that of the common mouse has no definite tendency as to
direction. When the common mouse does move in circles, it goes first in
one direction, then in the other, and not for any considerable period in
one direction as does the true dancer. Neither the young dancer nor the
common mouse is able to equilibrate itself well for the first few days
after birth, but the latter can follow a narrow path with far greater
accuracy and steadiness than the former. The uncertain and irregular
movements of the common mouse are due to muscular weakness and to
blindness, but the bizarre movements of the young dancer seem to demand
some additional facts as an explanation.

A brief account of the development of the dancer given by Zoth (31 p. 149)
adds nothing of importance to the description given by Alexander and
Kreidl. As my own observations disagree with their accounts in certain
respects, I shall now give, in the form of a diary, a description of the
important changes observed from day to day in a normal litter. The litter
which I have selected as typical of the course of development in the
dancer grew rapidly under favorable conditions. I have observed many
litters which passed through the various stages of development mentioned
in this description anywhere from a day to a week later. This was usually
due to some such obviously unfavorable condition as too little food or
slight digestive or bowel troubles. According to the nature of the
conditions of growth the eyes of the dancer open anywhere from the
fourteenth to the twentieth day. This statement may serve to indicate the
degree of variability as to the time at which a given stage of development
is reached by different litters.

On July 14, 1906, No. 151 (female) and No. 152 (male) were mated, and on
August 3 a litter of six was born to them. The course of the development
of this litter during the first three weeks was as follows:--

_First day_ The skin is pink and hairless, several vibrissae are visible
on the nose and lips, but there is no definite response when they are
touched. The mice are both blind and deaf, but they are able to squeak
vigorously. The mother was not seen to dance or eat during the day.

_Second day_. There is a very noticeable increase in size. The vibrissae
are longer, but touching them still fails to cause a reaction. No hairs
are visible on the body. The mother danced rapidly for periods of a minute
several times while the record was being made. She ate very little to-day.

_Third day_. Scales began to appear on the skin to-day. The animals are
rapidly increasing in strength; they can now crawl about the nest easily,
but they are too weak to stand, and constantly roll over upon their sides
or backs when they are placed on a smooth surface. Because of their
inability to progress it is impossible to determine with certainty whether
they have a tendency to move in circles. The mother was seen out of the
nest dancing once to-day. She now eats ravenously.

_Fourth day_. One of the six young mice was found under a corner of the
nest this morning dead, and the others were scattered about the nest box.
I gathered them together into a nest which I made out of bits of tissue
paper, and the mother immediately began to suckle them. They are very
sensitive to currents of air, but they do not respond to light or sound
and seldom to contact with the vibrissae.

_Fifth day_. When placed on a smooth surface, they tend to move in
circles, frequently rolling over. When placed on their sides or backs,
they immediately try to right themselves. They do not walk, for their legs
are still too weak to support the weight of the body; instead they drag
themselves about by the use of the fore legs. Fine colorless hairs are
visible over the entire body surface. When the vibrissae are touched, the
head is moved noticeably. The mother dances a great deal and eats about
twice as much as she did before the birth of the litter.

_Sixth day_. Certain regions of the skin, which were slightly darker than
the remainder on the fourth and fifth days, are now almost black. It is
evident that they are the regions in which the black hair is to appear.
The movement in circles is much more definite today, although most of the
individuals are still too weak to stand on their feet steadily for more
than a few seconds at a time. Most of their time, when they are first
taken from the nest, is spent in trying to maintain or regain an upright
position. The hair is now easily visible, and the skin begins to have a
white appearance as a result.

_Seventh day_. Although they are strong enough to move about the nest
readily, none of the young has attempted to leave the nest. They huddle
together in the middle of it for warmth. The epidermal scales, which have
increased in number since the third day, are dropping off rapidly. Contact
with the vibrissae or with the surface of the body, frequently calls forth
a motor reaction but neither light nor sound produces any visible change
in behavior. The black and white regions of the skin are sufficiently
definite now to enable one to distinguish the various individuals by their
markings. The mother was seen to dance repeatedly today, and she ate all
the food that was given to her.

_Eighth day_. A fold is plainly visible where later the eyelids will
separate. The black pigment in the skin has increased markedly.

_Ninth day_. The eyelids are taking form rapidly, but they I have not
separated. The body is covered with a thick coat of hair which is either
pure white or black. Standing on the four legs is still a difficult task.

_Tenth day_. To-day teats are plainly visible in the case of four of the
five individuals of the litter. Up to this time I had thought, from
structural indications, that there were three males and two females; it is
now evident that there are four females and one male. The external ear,
the pinna, is well formed, and has begun to stand out from the head, but
no opening to the inner portion of the ear is present. The eyelids appear
to be almost fully formed.

_Eleventh day_. There are no very noticeable changes in appearance except
in size, which continues to increase rapidly. They are able to regain
their normal upright position almost immediately when they happen to roll
over. The mother dances as usual.

_Twelfth day_. It appears to-day as if the eyes were about to open. The
ears are still closed, and there is no evidence of a sense of hearing.
They squeaked considerably when in the nest, but not at all when I took
them out to note their development. The mother stays outside of the nest
box much of the time now, probably to prevent the young ones from sucking

_Thirteenth day_. One of the little mice came out of the nest box while I
was watching the litter this morning, and was able to find his way back
directly despite the lack of sight. The mice are still dependent upon the
mother for nourishment. I have not seen any of them attempt to eat the
food which is given to the mother. They are extremely neat and clean. I
watched one of them wash himself this morning. Each foot was carefully
licked with the tongue. There seems to be special care taken to keep the
toes perfectly clean.

_Fourteenth day_. An opening into the ear is visible to-day. When tested
with the Galton whistle, all five responded with quick, jerky movements of
the head and legs. They evidently hear certain tones. During the past two
days the ears have changed rapidly. In one of the females, which seems to
be a little in advance of the others in development, certain peculiarities
of behavior appeared to-day. She jumped and squeaked sharply when touched
and sprang out of my hand when I attempted to take her up. This is in
marked contrast with her behavior previously.

_Fifteenth day_. The eyes are partly opened. All of the members of the
litter came out of the nest box this morning and ran around the cage,
dancing frequently and trying to eat with the mother. Three out of the
five gave auditory reactions on first being stimulated; none of them
responded to repetitions of the stimulus. All appeared to be less
sensitive to sounds than yesterday. The quick, nervous, jerky movements
are very noticeable.

_Sixteenth day_. The eyes of all five are fully opened. They dance
vigorously and are outside the nest much of the time.

_Seventeenth day_. No reactions to sound could be detected to-day. The
sense of sight gives evidence of being well developed. The nervous jumping
movements persist.

_Eighteenth day_. The young mice continue to suck, although they eat of
the food which is given to the mother. They are now able to take care of

_Nineteenth day_. There are no noteworthy changes except increase in size
and strength.

_Twentieth day_. No auditory reactions were obtained today, but other
forms of stimulation brought about unmistakable responses.

_Twenty-first day_. They are now about half grown and there is no other
change of special interest to be recorded. Growth continues for several
weeks. The statement made by Alexander and Kreidl to the effect that the
dancer is almost full grown by the thirty-first day of life is false. At
that age they may be sexually mature, but usually they are far from full



The peculiarities of behavior of the dancing mouse are responsible alike
for the widespread interest which it has aroused, and for its name. In a
little book on fancy varieties of mice, in which there is much valuable
information concerning the care of the animals, one who styles himself "An
old fancier" writes thus of the behavior of the dancer: "I believe most
people have an idea that the waltzing is a stately dance executed on the
hind feet; this is not so. The performer simply goes round and round on
all fours, as fast as possible, the head pointing inwards. The giddy
whirl, after continuing for about a dozen turns, is then reversed in
direction, and each performance usually occupies from one to two minutes.
Whether it is voluntary or not, is difficult to determine, but I am
inclined to think the mouse can refrain if it wishes to do so, because I
never see them drop any food they may be eating, and begin to waltz in the
midst of their meal. The dance, if such it can be called, generally seizes
the mouse when it first emerges from its darkened sleeping place, and this
would lead one to suppose that the light conveys an impression of shock to
the brain, through the eyes, which disturbs the diseased centers and
starts the giddy gyrations. The mice can walk or run in a fairly straight
line when they wish to do so." Some of the old fancier's statements are
true, others are mere guesses. Those who have studied the mice carefully
will doubtless agree that he has not adequately described the various
forms of behavior of which they are capable. I have quoted his description
as an illustration of the weakness which is characteristic of most popular
accounts of animal behavior. It proves that it is not sufficient to watch
and then describe. The fact is that he who adequately describes the
behavior of any animal watches again and again under natural and
experimental conditions, and by prolonged and patient observation makes
himself so familiar with his subject that it comes to possess an
individuality as distinctive as that of his human companions. To the
casual observer the individuals of a strange race are almost
indistinguishable. Similarly, the behavior of all the animals of a
particular species seems the same to all except the observer who has
devoted himself whole-heartedly to the study of the subject and who has
thus become as familiar with their life of action as most of us are with
that of our fellow-men; for him each individual has its own unmistakable

I shall now describe the behavior of the dancing mouse in the light of the
results of the observation of scores of individuals for months at a time,
and of a large number of experiments. From time to time I shall refer to
points in the accounts of the subject previously given by Rawitz (25 p.
236), Cyon (9 p. 214), Alexander and Kreidl (1 p. 542), Zoth (31 p. 147),
and Kishi (21 p. 479).

The most striking features of the ordinary behavior of the dancer are
restlessness and movements in circles. The true dancer seldom runs in a
straight line for more than a few centimeters, although, contrary to the
statements of Rawitz and Cyon, it is able to do so on occasion for longer
distances. Even before it is old enough to escape from the nest it begins
to move in circles and to exhibit the quick, jerky head movements which
are characteristic of the race. At the age of three weeks it is able to
dance vigorously, and is incessantly active when not washing itself,
eating, or sleeping. According to Zoth (31 p. 149) the sense of sight and
especially the sense of smell of the dancer "seem to be keenly developed;
one can seldom remain for some time near the cage without one or another
of the animals growing lively, looking out of the nest, and beginning to
sniff around in the air (_windet_). They also seem to have strongly
developed cutaneous sensitiveness, and a considerable amount of curiosity,
if one may call it such, in common with their cousin, the white mouse." I
shall reserve what I have to say concerning the sense of sight for later
chapters. As for the sense of smell and the cutaneous sensitiveness, Zoth
is undoubtedly right in inferring from the behavior of the animal that it
is sensitive to certain odors and to changes in temperature. One of the
most noticeable and characteristic activities of the dancer is its
sniffing. Frequently in the midst of its dancing it stops suddenly, raises
its head so that the nose is pointed upward, as in the case of one of the
mice of the frontispiece, and remains in that position for a second or
two, as if sniffing the air.

The restlessness, the varied and almost incessant movements, and the
peculiar excitability of the dancer have repeatedly suggested to casual
observers the question, why does it move about in that aimless, useless
fashion? To this query Rawitz has replied that the lack of certain senses
compels the animal to strive through varied movements to use to the
greatest advantage those senses which it does possess. In Rawitz's opinion
the lack of hearing and orientation is compensated for by the continuous
use of sight and smell. The mouse runs about rapidly, moves its head from
side to side, and sniffs the air, in order that it may see and smell as
much as possible. In support of this interpretation of the restlessness of
the dancer, Rawitz states that he once observed similar behavior in an
albino dog which was deaf. This suggestion is not absurd, for it seems
quite probable that the dancer has to depend for the guidance of its
movements upon sense data which are relatively unimportant in the common
mouse, and that by its varied and restless movements it does in part make
up for its deficiency in sense equipment.

The dancing, waltzing, or circus course movement, as it is variously
known, varies in form from moment to moment. Now an individual moves its
head rapidly from side to side, perhaps backing a little at the same time,
now it spins around like a top with such speed that head and tail are
almost indistinguishable, now it runs in circles of from 5 cm. to 30 cm.
in diameter. If there are any objects in the cage about or through which
it may run, they are sure to direct the expression of activity. A tunnel
or a hole in a box calls forth endless repetitions of the act of passing
through. When two individuals are in the same cage, they frequently dance
together, sometimes moving in the same direction, sometimes in opposite
directions. Often, as one spins rapidly about a vertical axis, the other
runs around the first in small circles; or again, both may run in a small
circle in the same direction, so that their bodies form a living ring,
which, because of the rapidity of their movements, appears perfectly
continuous. The three most clearly distinguishable forms of dance are (1)
movement in circles with all the feet close together under the body, (2)
movement in circles, which vary in diameter from 5 cm. to 30 cm., with the
feet spread widely, and (3) movement now to the right, now to the left, in
figure eights ([Symbol: figure eight]). For convenience of reference
these types of dance may be called _whirling, circling_, and the _figure
eight dance_. Zoth, in an excellent account of the behavior of the dancer
(31 p. 156), describes "manege movements," "solo dances," and "centre
dances." Of these the first is whirling, the second one form of circling,
and the third the dancing of two individuals together in the manner
described above.

Both the whirling and the circling occur to the right (clockwise) and to
the left (anticlockwise). As certain observers have stated that it is
chiefly to the left and others that it is as frequently to the right, I
have attempted to get definite information concerning the matter by
observing a number of individuals systematically and at stated intervals.
My study of this subject soon convinced me that a true conception of the
facts cannot be got simply by noting the direction of turning from time to
time. I therefore planned and carried out a series of experimental
observations with twenty dancers, ten of each sex. One at a time these
individuals were placed in a glass jar, 26 cm. in diameter, and the number
of circle movements executed to the right and to the left during a period
of five minutes was determined as accurately as possible. This was
repeated at six hours of the day: 9 and 11 o'clock A.M., and 2, 4, 6, and
8 o'clock P.M. In order that habituation to the conditions under which the
counts of turning were made might hot influence the results for the group,
with ten individuals the morning counts were made first, and with the
others the afternoon counts. No attempt was made in the counting to keep a
separate record of the whirling and circling, although had it been
practicable this would have been desirable, for, as soon became evident to
the observer, some individuals which whirl in only one direction, circle
in both.

In Table 2 the results of the counts for the males are recorded; in Table
3 those for the females. Each number in the column headed "right" and
"left" indicates the total number of circles executed by a certain dancer
in a period of five minutes at the hour of the day named at the head of
the column. I may point out briefly the curiously interesting and entirely
unexpected new facts which this method of observation revealed to me.

First, there are three kinds of dancers: those which whirl almost
uniformly toward the right, those which whirl just as uniformly toward the
left, and those which whirl about as frequently in one direction as in the
other. To illustrate, No. 2 of Table 2 may be characterized as a "right
whirler," for he turned to the right almost uniformly. In the case of the
6 P.M. count, for example, he turned 285 times to the right, not once to
the left. No. 152, on the contrary, should be characterized as a "left
whirler," since he almost always turned to the left. From both of these
individuals No. 210 is distinguished by the fact that he turned now to the
left, now to the right. For him the name "mixed whirler" seems

Second, the amount of activity, as indicated by the number of times an
individual turns in a circle within five minutes, increases regularly and
rapidly from 9 A.M. to 8 P.M. According to the general averages which
appear at the bottom of Table 2, the average number of circles executed by
the males at 9 A.M. was 89.8 as compared with 207.1 at 8 P.M. In other
words, the mice dance more in the evening than during the day.

Third, as it appears in a comparison of the general averages of Tables 2
and 3, the females dance more than the males, under the conditions of
observation. At 9 A.M. the males circled 89.8 times, the females 151.0
times; at 8 P.M. the males circled 207.1 times, the females, 279.0 times.

Fourth, according to the averages for the six counts made with each
individual, as they appear in Table 4, the males turn somewhat more
frequently to the left than to the right (the difference, however, is not
sufficient to be considered significant); whereas, the females turn much
more frequently to the right than to the left. I do not wish to emphasize
the importance of this difference, for it is not improbable that counts
made with a larger number of animals, or even with another group of
twenty, would yield different results.



NUMBER 9 A.M 11 A.M. 2 P.M.

2 11 2 23 4 194 1
30 20 1 134 1 109 2
34 2 16 2 48 4 92
36 194 21 180 11 143 65
152 7 48 3 171 6 79
156 63 8 53 9 27 6
210 3 9 7 41 225 21
220 168 105 39 43 47 5
410 2 67 10 27 8 103
420 15 142 5 214 16 238

Averages 48.5 41.3 45.6 56.9 77.9 61.2

Gen. Av. 89.8 102.5 139.1

NUMBER 4 P.M 6 P.M. 8 P.M.

2 70 3 285 0 237 10
30 154 0 107 6 134 5
34 7 158 5 118 6 147
36 173 14 170 11 325 19
152 0 91 16 210 9 223
156 85 2 72 26 139 26
210 159 18 31 82 47 201
220 45 38 78 17 69 33
410 9 155 9 394 24 94
420 18 243 16 291 3 320

Averages 72.0 72.2 78.9 115.5 99.3 107.8

Gen. Av. 144.2 194.4 207.1



NUMBER 9 A.M. 11 A.M. 2 P.M.

29 9 18 17 30 7 22
33 287 0 329 1 352 3
35 48 15 198 46 208 14
151 13 88 7 75 3 167
157 57 6 50 45 53 12
211 218 21 31 55 66 5
215 67 216 33 105 37 226
225 46 39 72 49 143 44
415 23 0 156 0 34 3
425 43 296 12 201 12 210

Averages 81.1 69.9 90.5 60.7 91.5 70.6

Gen. Av. 151.0 151.2 162.1

NUMBER 4 P.M. 6 P.M. 8 P.M.

29 33 114 31 36 45 99
33 436 7 408 3 364 2
35 279 6 165 24 353 10
151 3 8 2 285 2 217
157 52 15 19 125 51 104
211 190 7 86 31 67 250
215 15 292 45 336 150 232
225 133 86 48 39 177 81
415 268 3 437 7 382 8
425 12 242 19 210 4 192

Averages 142.1 78.0 126.0 109.6 159.5 119.5

Gen. Av. 220.1 235.6 279.0

The most important results of this statistical study of turning are the
demonstration of the existence of individual tendencies to turn in a
particular direction, and of the fact that the whirling increases in
amount from morning to evening.

In order to discover whether the distribution of the dancers among the
three groups which have been designated as right, left, and mixed whirlers
agrees in general with that indicated by Table 4 (approximately the same
number in each group) I have observed the direction of turning in the case
of one hundred dancers, including those of the foregoing tables, and have
classified them in accordance with their behavior as is indicated below.


Males 19 19 12
Females 12 23 15

Totals 31 42 27

The left whirlers occur in excess of both the right and the mixed
whirlers. This fact, together with the results which have already been
considered in connection with the counts of turning, suggests that a
tendency to whirl in a certain way may be inherited. I have examined my
data and conducted breeding experiments for the purpose of ascertaining
whether this is true. But as the results of this part of the investigation
more properly belong in a special chapter on the inheritance of behavior
(XVIII), the discussion of the subject may be closed for the present with
the statement that the preponderance of left whirlers indicated above is
due to a strong tendency to turn to the left which was exhibited by the
individuals of one line of descent.




2 12 mo. 136.7 3.3 Right whirler
30 2 mo. 109.7 2.5 Right whirler
34 2 mo. 4.3 96.5 Left whirler
36 2 mo. 197.5 23.5 Right whirler
152 6 mo. 6.8 137.0 Left whirler
156 1 mo. 73.2 12.8 Right whirler
210 3 mo. 78.7 62.0 Mixed whirler
220 4 mo. 74.3 40.2 Mixed whirler
410 3 mo. 10.3 139.0 Left whirler
420 3 mo. 12.2 241.3 Left whirler

Average 70.4 75.8 4 Right whirlers
4 Left whirlers
2 Mixed whirlers


29 2 mo. 23.7 53.2 Left whirler
33 2 mo. 362.7 2.7 Right whirler
35 2 mo. 208.5 19.2 Left whirler
151 6 mo. 5.0 140.0 Right whirler
157 1 mo. 47.0 51.2 Left whirler
211 3 mo. 109.7 61.5 Right whirler
215 3 mo. 57.8 234.5 Mixed whirler
225 4 mo. 103.2 56.3 Mixed whirler
415 3 mo. 216.7 3.5 Left whirler
425 3 mo. 17.0 225.2 Left whirler

Average 115.1 84.7 3 Right whirlers
4 Left whirlers
3 Mixed whirlers

The tendency of the dancer's activity to increase in amount toward
evening, which the results of Tables 2, 3, and 4 exhibit, demands further
consideration. Haacke (7 p. 337) and Kishi (21 p. 458) agree that the
dancing is most vigorous in the evening; but Alexander and Kreidl (i p.
544) assert, on the contrary, that the whirling of the individuals which
they observed bore no definite relation to the time of day and apparently
was not influenced in intensity thereby. Since the results of my own
observations contradict many of the statements made by the latter authors,
I suspect that they may not have watched their animals long enough to
discover the truth. The systematic records which I have kept indicate that
the mice remain quietly in their nests during the greater part of the day,
unless they are disturbed or come out to obtain food. Toward dusk they
emerge and dance with varying intensity for several hours. I have seldom
discovered one of them outside the nest between midnight and daylight. The
period of greatest activity is between 5 and 10 o'clock P.M.

Zoth states that he has observed the adult dancer whirl 79 times without
an instant's interruption, and I have counted as many as 110 whirls. It
seems rather absurd to say that an animal which can do this is weak.
Evidently the dancer is exceptionally strong in certain respects, although
it may be weak in others. Such general statements as are usually made fail
to do justice to the facts.

The supposition that light determines the periodicity of dancing is not
borne out by my observations, for I have found that the animals continue
to dance most vigorously toward evening, even when they are kept in a room
which is constantly illuminated. In all probability the periodicity of
activity is an expression of the habits of the mouse race rather than of
the immediate influence of any environmental condition. At some time in
the history of the dancer light probably did have an influence upon the
period of activity; but at present, as a result of the persistence of a
well-established racial tendency, the periodicity of dancing depends to a
greater extent upon internal than upon external conditions. During its
hours of quiescence it is possible to arouse the dancer and cause it to
whirl more or less vigorously by stimulating it strongly with intense
light, a weak electric current, or by placing two individuals which are
strangers to one another in the same cage; but the dancing thus induced is
seldom as rapid, varied, or as long-continued as that which is
characteristic of the evening hours.

One of the most interesting results of this study of the direction of
turning, from the observer's point of view, is the demonstration of the
fact that the truth concerning even so simple a matter as this can be
discovered only by long and careful observation. The casual observer of
the dancer gets an impression that it turns to the left more often than to
the right; he verifies his observation a few times and then asserts with
confidence that such is the truth about turning. That such a method of
getting knowledge of the behavior of the animal is worse than valueless is
clear in the light of the results of the systematic observations which
have just been reported. But, however important the progress which we may
have made by means of systematic observation of the phenomenon of turning,
it must not for one moment be supposed that the whole truth has been
discovered. Continued observation will undoubtedly reveal other important
facts concerning circling, whirling, and the periodicity of dancing, not
to mention the inheritance of peculiarities of dancing and the
significance of the various forms of activity.



Quite as interesting and important as the general facts of behavior which
we have been considering are the results of experimental tests of the
dancer's ability to maintain its position under unusual spatial
conditions--to climb, cross narrow bridges, balance itself on high places.
Because of its tendency to circle and whirl, to dart hither and thither
rapidly and apparently without control of its movements, the study of the
mouse's ability to perform movements which demand accurate and delicate
muscular cooerdination, and to control its expressions of activity, are of
peculiar scientific interest.

That observers do not entirely agree as to the facts in this field is
apparent from the following comparison of the statements made by Cyon and
Zoth (31 p. 174).

Cyon states that the dancer

Cannot run in a straight line,
Cannot turn in a narrow space,
Cannot run backward,
Cannot run up an incline,
Cannot move about safely when above the ground, because of
fear and visual dizziness,
Can hear certain tones.

Zoth, on the contrary, maintains that the animal

Can run in a straight line for at least 20 cm.,
Can and repeatedly does turn in a narrow space,
Can run backward, for he has observed it do so,
Can run up an incline unless the surface is too smooth for it to
gain a foothold,
Can move about safely when above the ground, and gives no
signs of fear or dizziness,
Cannot hear, or at least gives no signs of sensitiveness to sounds.

Such contradictory statements (and unfortunately they are exceedingly
common) stimulated me to the repetition of many of the experiments which
have been made by other investigators to test the dancer's behavior in
unusual spatial relations. I shall state very briefly the general
conclusions to which these experiments have led me, with only sufficient
reference to methods and details of results to enable any one who wishes
to repeat the tests for himself to do so. For the sake of convenience of
presentation and clearness, the facts have been arranged under three
rubrics: equilibrational ability, dizziness, and behavior when blinded. To
our knowledge of each of these three groups of facts important
contributions have come from the experiments of Cyon (9 p. 220), Alexander
and Kreidl (1 p. 545), Zoth (31 p. 157), and Kishi (21 p. 482), although,
as has been stated, in many instances their results are so contradictory
as to demand reexamination. All in all, Zoth has given the most
satisfactory account of the behavior and motor capacity of the dancer.

If the surface upon which it is moving be sufficiently soft or rough to
furnish it a foothold, the dancer is able to run up or down inclines, even
though they be very steep, to cross narrow bridges, to balance itself at
heights of at least 30 cm. above the ground, and even to climb up and down
on rods, as is shown by certain of Zoth's photographs which are reproduced
in Figure 4. Zoth himself says, and in this I am able fully to agree with
him on the basis of my own observations, "that the power of equilibration
in the dancing mouse, is, in general, very complete. The seeming reduction
which appears under certain conditions should be attributed, not to visual
dizziness, but in part to excitability and restlessness, and in part to a
reduced muscular power" (31 p. 161). The dancer certainly has far less
grasping power than the common mouse, and is therefore at a disadvantage
in moving about on sloping surfaces. One evidence of this fact is the
character of the tracks made by the animal. Instead of raising its feet
from the substratum and placing them neatly, as does the common mouse
(Figure 5), it tends to shuffle along, dragging its toes and thus
producing on smoked paper such tracks as are seen in Figure 6. From my own
observations I am confident that these figures exaggerate the differences.
My dancers, unless they were greatly excited or moving under conditions of
stress, never dragged their toes as much as is indicated in Figure 6.
However, there can be no doubt that they possess less power of grasping
with their toes than do common mice. The animal is still further
incapacitated for movement on inclined surfaces or narrow places by its
tendency to move in circles and zigzags. The results of my own experiments
indicate that the timidity of the adult is greater than that of the
immature animal when it is placed on a bridge 1 or 2 cm. wide at a
distance of 20 cm. from the ground. Individuals three weeks old showed
less hesitation about trying to creep along such a narrow pathway than did
full-grown dancers three or four months old; and these, in turn, were not
so timid apparently as an individual one year old. But the younger animals
fell off more frequently than did the older ones.

[Illustration: FIGURE 4.--Zoth's photographs of dancers crossing bridges
and climbing rods. Reproduced from _Pfluger's Archiv_, Bd. 86.]

[Illustration: FIGURE 5--Tracks of common mouse Reproduced from Alexander
and Kreidl's figure in _Pfluger's Archiv_, Bd 82]

[Illustration: FIGURE 6--Tracks of dancing mouse Reproduced from Alexander
and Kreidl's figure in _Pfluger's Archiv_ Bd 82]

Additional support for these statements concerning equilibrational ability
is furnished by the observations of Kishi (21 p. 482). He built a wooden
bridge 60 cm. long, 1 cm. wide at one end, and 1/2 cm. at the other, and
supported it at a height of 30 cm. above the ground by posts at the ends.
On this bridge ten dancers were tested. Some attempted to move sidewise,
others began to whirl and fell to the ground; only one of the ten
succeeded in getting all the way across the bridge on the first trial. The
second time he was tested this individual crossed the bridge and found the
post; and the third time he crossed the bridge and climbed down the post
directly. The others did not succeed in descending the post even after
having crossed the bridge safely, but, instead, finally fell to the floor
from awkwardness or exhaustion. On the basis of these and other similar
observations, Kishi says that the dancer possesses a fair degree of
ability to orient and balance itself.

Inasmuch as equilibration occurs similarly in darkness and in daylight,
Zoth thinks that there is neither visual dizziness nor fear of heights.
But it is doubtful whether he is right concerning fear. There is no doubt
in my mind, in view of the way the mice behave when placed on an elevated
surface, that they are timid; but this is due probably to the
uncomfortable and unusual position rather than to perception of their
distance from the ground. That they lack visual dizziness seems fairly
well established.

When rotated in a cyclostat[1] the dancer, unlike the common mouse, does
not exhibit symptoms of dizziness. The following vivid description of the
behavior of both kinds of mice when rotated is given by Alexander and
Kreidl (1 p. 548). I have not verified their observations.

[Footnote 1: An apparatus consisting of a glass cylinder with a mechanism
for turning it steadily and at different speeds about its vertical axis.]

The common mouse at first runs with increasing rapidity, as the speed of
rotation of the cyclostat cylinder is increased, in the direction opposite
to that of the cylinder itself. This continues until the speed of rotation
has increased to about 60 revolutions per minute. As the rotation becomes
still more rapid the mouse begins to crawl along the floor, its body
stretched out and clinging to the floor. At a speed of 250 revolutions per
minute it lies flat on the floor with its limbs extended obliquely to the
movement of rotation, and at times with its back bent against the axis of
the cylinder; in this position it makes but few and feeble efforts to
crawl forward. When the rotation is suddenly stopped, the animal pulls
itself together, remains for some seconds with extended limbs lying on the
floor, and then suddenly falls into convulsions and trembles violently.
After several attacks of this kind, cramps appear and, despite its
resistance, the animal is thrown about, even into the air at times, as if
by an external force. This picture of the position assumed during rapid
rotation, and of cramps after the cessation of rotation (the typical
picture of rotation dizziness), is repeated with great uniformity in the
case of the common mouse. Within fifteen minutes after being returned to
its cage the animal recovers from the effects of its experience. This
description of the symptoms of rotation dizziness in the common mouse
applies equally well to the blinded and the seeing animal.

In sharp contrast with the behavior of the common mouse in the cyclostat
is that of the dancer. As the cylinder begins to rotate the dancer runs
about as usual in circles, zigzags, and figure-eights. As the speed
becomes greater it naturally becomes increasingly difficult for the mouse
to do this, but it shows neither discomfort nor fear, as does the common
mouse. Finally the centrifugal force becomes so great that the animal is
thrown against the wall of the cylinder, where it remains quietly without
taking the oblique position. When the cyclostat is stopped suddenly, it
resumes its dance movements as if nothing unusual had occurred. It
exhibits no signs of dizziness, and apparently lacks the exhaustion which
is manifest in the case of other kinds of mice after several repetitions
of the experiment. The behavior of the blinded dancer is very similar.

If these statements are true, there is no reason to believe that the
dancer is capable of turning or rotation dizziness. If it were, its daily
life would be rendered very uncomfortable thereby, for its whirling would
constantly bring about the condition of dizziness. Apparently, then, the
dancer differs radically from most mammals in that it lacks visual and
rotational dizziness. In the next chapter we shall have to seek for the
structural causes for these facts.

The behavior of the blinded animal is so important in its bearings upon
the facts of orientation and equilibration that it must be considered in
connection with them. Cyon insists that the sense of vision is of great
importance to the dancer in orienting and equilibrating itself. When the
eyes are covered with cotton wads fastened by collodion, this writer
states (9 p. 223) that the mice behave as do pigeons and frogs whose
semicircular canals have been destroyed. They perform violent forced
movements, turn somersaults forward and backward, run up inclines and fall
over the edges, and roll over and over. In a word, they show precisely the
kind of disturbances of behavior which are characteristic of animals whose
semicircular canals are not functioning normally. Cyon, however, observed
that in certain dancers these peculiarities of behavior did not appear
when they were blinded, but that, instead, the animals gave no other
indication of being inconvenienced by the lack of sight than do common
white mice. This matter of individual differences we shall have to
consider more fully later.

No other observer agrees with Cyon in his conclusions concerning vision,
or, for that matter, in his statements concerning the behavior of the
blind dancer. Alexander and Kreidl (1 p. 550) contrast in the following
respects the behavior of the white mouse and that of the dancer when they
are blinded. The white mouse runs less securely and avoids obstacles less
certainly when deprived of vision. The dancer is much disturbed at first
by the shock caused by the removal of its eyes, or in case they are
covered, by the presence of the unusual obstruction. It soon recovers
sufficiently to become active, but it staggers, swerves often from side to
side, and frequently falls over. It moves clumsily and more slowly than
usual. Later these early indications of blindness may wholly disappear,
and only a slightly impaired ability to avoid obstacles remains.

It was noted by Kishi (21 p. 484), that the dancer when first blinded
trembles violently, jumps about wildly, and rolls over repeatedly, as Cyon
has stated; but Kishi believes that these disturbances of behavior are
temporary effects of the strong stimulation of certain reflex centers in
the nervous system. After having been blinded for only a few minutes the
dancers observed by him became fairly normal in their behavior. They moved

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