40 ANIMAL COMPETITORS 
alone could have produced and preserved the 
race of dancers.”’ 
That it originated in a ‘‘freak’’ seems very 
likely, since mere cultivation of the familiar 
white mice (albinos), beloved of children, never 
develops into a habit of whirlmg. A German 
naturalist inbred albino mice for 28 generations 
without producing any hint of such a pecul- 
larity. 
Prevalence of mice. House-mice are very 
prolific. They will begin to produce young 
when only three months old, and continue to 
breed at intervals of two or three months all 
the year round. It is not known whether any 
proper pairing takes place—probably not. 
The period of gestation is 25 days, five to ten 
young are produced at a birth—minute, pink, 
blind, hairless things—and are weaned after 
about two weeks. 
There are few houses or barns in which mice 
do not make themselves at home, racing from 
cellar to garret in the hollow walls and par- 
titions, and gnawing passageways wherever 
they think it worth while. Too often they: 
penetrate where food is kept, and besides what 
