Several persons who have reported to me difficulty in rearing the young or
in keeping the adults for long periods have been unable to maintain a
sufficiently high or constant temperature, or have given them food which
caused intestinal trouble.

The males are likely to fight if kept together, and they may even kill one
another. A male may be kept with one or more females, or several females
may be kept together, for the females rarely, in my experience, fight, and
the males seldom harm the females. Unless the male is removed from the
cage in which the female is kept before the young are born, he is likely
to kill the newborn animals. When a female is seen to be building a nest
in preparation for a litter, it is best to place her in a cage by herself
so that she may not be disturbed.

The sex of individuals may be determined easily in most cases, at the age
of 10 to 12 days, by the appearance of teats in the case of females.

The period of gestation is from 18 to 21 days. The maximum number born by
my dancers in any single litter was 9, the minimum number 3. In 25 litters
of which I have accurate records, 135 individuals were born, an average of
5.4. The average number of males per litter was precisely the same, 2.7,
as the number of females.

On the birth of a litter it is well to see that the female has made a nest
from which the young are not likely to escape, for at times, if the nest
is carelessly made, they get out of it or under some of the pieces of
paper which are used in its construction, and perish. Several times I have
observed nests so poorly built that almost all of the young perished
because they got too far away to find their way back to the mother. It is
surprising that the female should not take more pains to keep her young