MISCHIEF OF MEADOW-MOUSE 57 



shallow burrows, or supported on grass stems 

 of brush-piles above the ground. Sometimes 

 they are placed under flat stones or logs or 

 under shocks of grain. The structures are so 

 slight that a day's sunshine will dry them out 

 after a storm, and yet they are so compact that 

 the animals pass the coldest weather snugly 

 housed in them under the snow. The young of 

 most kinds are born in underground nests and 

 are at first hairless and blind. When discov- 

 ered in the nest the mother vole slips noise- 

 lessly away, sometimes carrying the young at- 

 tached to her mammae. 



The breeding-season includes most months 

 of the year, except mid-winter in cold latitudes 

 and periods of long-continued drought. The 

 number of litters in a year thus depends on 

 climate, and especially upon the character and 

 length of the winter. In temperate latitudes 

 in normal seasons from four to six litters are 

 produced ; but the variation in the same species 

 is remarkable, and depends partly upon climate, 

 but probably more on the scarcity or abundance 

 of food. The period of gestation is about 

 twenty days. 



