The Dancing Mouse | Page 5

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 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 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