The Dancing Mouse.

by Robert M. Yerkes.

PREFACE

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

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

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

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

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

Gratefully, and with this expression of my thanks, I acknowledge my indebtedness to Professor Hugo Munsterberg 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 a.s.sistance 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. d.i.c.kerson for the photographs of dancing mice which are reproduced in the frontispiece; to Mr. Frank Ashmore for additional photographs which I have been unable to use in this volume; to Mr. C. H.

Toll for the drawings for Figures 14 and 20; to Doctors H. W. Rand and C.

S. Berry for valuable suggestions on the basis of a critical reading of the proof sheets; and to my wife, Ada Watterson Yerkes, for constant aid throughout the experimental work and in the preparation of this volume.

R. M. Y.

CAMBRIDGE, Ma.s.sACHUSETTS,

August, 1907.

CHAPTER I

CHARACTERISTICS, ORIGIN, AND HISTORY

The variety of mouse which is known as the j.a.panese 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 j.a.pan: "From time to time a Hamburg dealer in animals sends me two breeds of common mice, which he calls Chinese climbing mice (Chinesische Klettermause) and j.a.panese dancing mice (j.a.panische Tanzmause). 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 j.a.panese, however, who are no less enthusiastic on this point, know how to transform the common mouse into a really admirable animal. The j.a.panese 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 individual."

[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 ill.u.s.trated 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, s.e.x,[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 s.e.x 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.

[Ill.u.s.tration: 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 j.a.panese have to say about the dancing mouse is of special importance because j.a.pan 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 j.a.panese or Chinese mouse; originally, however, China must have been its home, since in j.a.pan it is mostly called '_Nankin nesumi_,' the mouse from Nankin. When this animal came from China to j.a.pan I shall inquire at a later opportunity. There were originally in j.a.pan 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 city.

"In j.a.pan, 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 j.a.pan 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 amus.e.m.e.nt 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 s.p.a.ce 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 j.a.pan. The mice are inexhaustible sources of amus.e.m.e.nt 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 j.a.panese dancing mouse, and the j.a.panese waltzing mouse is indicative of the existing uncertainty concerning the origin of the race.

Thinking that j.a.panese 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 j.a.pan. He replied as follows: "I have tried to find what is known in j.a.pan about the history of the j.a.panese 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 fict.i.tious, 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 j.a.panese 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 Inst.i.tute, Philadelphia: "If I remember rightly the so-called j.a.panese 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 j.a.panese 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 amus.e.m.e.nt 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 j.a.pan, 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 j.a.pan 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 j.a.pan."

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 breeders.

Another account of the origin of the race is that accepted by Kishi (21 p.

481) and some other j.a.panese 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 p.r.o.nounced 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 j.a.pan 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 Hacker 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, Ma.s.sachusetts, 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 j.a.panese 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).