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 foetuses — giving 



an average of nearly six per litter. Barrett- Hamilton observed 



ten in a family born at Kilmanock in September 19 10, 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 {Gerbillus) gave birth to one on 24th August 



and to four young on the following 5 th September, also 



mentions that a similar period of twelve days was once 



observed in common fancy mice. Bonhote (in lit.) 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 Meriones, 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 



> Field, 8th February 1913, 283 ("Dabchick" and "Ed."). 



' Quite a good though brief account of this species was given by Oken 

 [AUgem. 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. 



' J. L. Bonhote, Proc. Zool. Soc, 191 1, 5. 



• W. R. Temple, Field, 13th September 1913, 620. 



