THE HOUSE MOUSE 659 
materials are usually first bitten into shreds. In comfortable 
surroundings and in the presence of abundant food, young 
are born in every month of the year, and one dam may have 
many successive litters in each year. Sometimes the young 
are dropped gregariously, several litters of different ages 
together, so that as many as fifty young mice have been 
found in a single nest... The number of young per litter 
is variable, but seems to average between five and six; ten 
pregnant females examined by Cocks between the months of 
January and May of different years, contained nine, seven 
(twice), six (four times), five, four, and two fcetuses—giving 
an average of nearly six per litter. Barrett- Hamilton observed 
ten in a family born at Kilmanock in September 1910, and 
copulation took place immediately after parturition. Lataste 
(290) observed, in his tame specimens, a short period of rut, 
never longer than half a day, immediately following parturition ; 
he found the period of gestation to vary between nineteen and 
twenty-one days normally,’ or to last thirty-one days where 
lactation caused delay in development of the embryos. Others 
have observed much shorter gestation; thus Bonhote® gives 
it as about thirteen days, and Temple* recording that a 
Desert Mouse (Gevdézllus) gave birth to one on 24th August 
and to four young on the following 5th September, also 
mentions that a similar period of twelve days was once 
observed in common fancy mice. Bonhote (zz /¢.) says that 
he does not doubt the correctness of Lataste’s notes, but since 
he knows that a large variation in the period of gestation 
exists in J/eriones, he expects that a similar variation may 
exist in the House Mouse. 
The young are born blind, naked, and pink; but, according 
to Macgillivray, they grow so rapidly that in a fortnight they 
are able to shift for themselves. Lataste (304) found, subject 
of course to individual variation, young domesticated House 
1 Field, 8th February 1913, 283 (“‘ Dabchick” and “ Ed.”). 
2 Quite a good though brief account of this species was given by Oken 
(Allgem. Naturgesch., Bd. 7, Abt. 2, 716, 1838) ; he states the period of gestation as 
three weeks, the number of young as four to six, while ten might be nourished ; and 
that the young can take care of themselves in fourteen days. 
3 J. L. Bonhote, Proc. Zool. Soc. 1911, 5. 
4 W.R. Temple, Fze/d, 13th September 1913, 620. 
