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1 I 
found them nearrj b foot above the ground. Sometimes thej are 
place. I under flat stones or logs or under shocks of grain. The struc 
tures are so slight thai a day's sunshine will «h\ them out after b 
storm, and yet they are so compact that the animals pass the coldest 
weather snugly housed in them under the snow. 
The nests arc admirably located with respect to drainage, being 
placed that the\ arc not likely to be flooded during excessive rains, 
and often being in depressions of mounds made l>\ the mice, well 
above the genera] surface of the meadows. 
Trails, often of great length and worn smooth by constant use, 
lead to neighboring feeding grounds. A.s far as possible they are 
under shelter of old grass, fallen weed-, leaves, and other material. 
The trails of some species are almost entirely below the surface of the 
ground, and short tunnels are common with most species. At inter- 
vals burrows of varying depth occur, usually but a few inches below 
the surface. These lead to underground nests, to the root- of food 
plant-, or serve only for refuge from enemies. 
BREEDING HABITS. 
While most surface nests are for shelter only, sometimes the young, 
especially of swamp species, are produced in them. However, the 
young of most kinds are born in underground nests and are rarely 
seen unless uncovered by accident. They are at first hairless and 
blind. When discovered in the, nest the mother vole slips noise- 
lessly away, sometimes carrying the young attached to her mammae. 
The breeding season includes most months of the year, except mid- 
winter in cold latitude- and period- 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. Even the 
same species in different localities differs much in this particular. 
That the number of young in a litter varies with the different species 
may be inferred from the variation in the number of teats. Some 
species produce normally from two to four young, other- from four 
to eight; but the variation in the same species is remarkable, and 
depend- partly upon climate, but probably more on the -cat-city or 
abundance of food. The largest litter recorded by the held natural- 
ists of the Biological Survey is thirteen, the species being the dwarf 
vole (J/, nanus). The period of gestation is not positively known, 
hut probably i> about twenty day-. Members of the Biological Sur- 
vey have recorded finding young of the American species in the 
nests, or female- containing embryo-, in wvvy month of the year 
except January and February. 
European testimony proves conclusively that, like the Lemmings, 
vole- at time- increase in number- abnormally, but the causes are 
