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 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 sexually mature, but usually they
are far from full grown.
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
