The Dancing Mouse Part 2

_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 continuously.

_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 repet.i.tions 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 themselves.

_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 s.e.xually mature, but usually they are far from full grown.

CHAPTER III

BEHAVIOR: DANCE MOVEMENTS

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 ill.u.s.tration 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 characteristics.

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 repet.i.tions of the act of pa.s.sing 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 s.e.x. One at a time these individuals were placed in a gla.s.s 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 ill.u.s.trate, 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 appropriate.

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.

TABLE 2

NUMBER or WHIRLS TO THE RIGHT AND TO THE LEFT DURING FIVE-MINUTE INTERVALS AS DETERMINED BY COUNTS MADE AT SIX DIFFERENT HOURS, FOR EACH OF TEN MALE DANCERS

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

OF ANIMAL RIGHT LEFT RIGHT LEFT RIGHT LEFT

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.

OF ANIMAL RIGHT LEFT RIGHT LEFT RIGHT LEFT

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

TABLE 3

NUMBER OF WHIRLS TO THE RIGHT AND TO THE LEFT DURING FIVE-MINUTE INTERVALS AS DETERMINED BY COUNTS MADE AT SIX DIFFERENT HOURS, FOR EACH OF TEN FEMALE DANCERS

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

OF ANIMAL RIGHT LEFT RIGHT LEFT RIGHT LEFT

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