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