The work of Murie and Murie (1931: 200-209, 1932: 79) is enlightening in this respect. These authors found that mice residing in a locality tended to remain in that locality; individuals trapped and marked were retaken in the same locality a year later. Individuals released some distance from the point of capture remained where released or returned to the point of capture. Transported individuals did not spread at random. The home instinct was developed in young as well as in old mice. Two mice in the gray pelage, four to eight weeks old, returned to their home ranges from distances one and two miles away. The authors fix the home range of an individual _Peromyscus m. artemisiae_ in Teton County, Wyoming, at approximately one hundred yards in diameter. This home-range instinct is essentially a lack of incentive for individual mice to emigrate to new localities where mice of the same species are already established. This may partly account for the microgeographic races of deer mice in Washington. Dice (1939: 21) pointed out that, except in color, the differences in nine stocks of mice from southeastern Washington could not be correlated with environmental factors. We have found this to be true of microgeographic races throughout the state of Washington. Of the four subspecies of deer mice that occupy extensive geographic ranges in Washington, one, _oreas_, is a long-tailed form that seems not to intergrade with _austerus_, a neighbor in western Washington that has a tail of moderate length. These two and _gambelii_, a short-tailed form with which _oreas_ intergrades, are easily distinguished. In eastern Washington two short-tailed subspecies, _gambelii_ and _artemisiae_, are currently recognized. The taxonomic relationships of these two subspecies are complex. The subspecies _gambelii_ has an extensive geographic range in Oregon and California. These mice, with short tails, occur in the Wallula Water Gap of southeastern Washington and on the Columbian Plateau. To the west the desert conditions of the Columbian Plateau fade into the Transition Life-zone forests of the eastern Cascade Mountains. The pale, short-tailed desert mice (_gambelii_) gradually change to the dark, long-tailed subspecies, _oreas_, that occupies the Cascade Mountains. North of the Columbian Plateau, in northeastern Washington, the deer mice are darker and relatively longer-tailed than on the Columbian Plateau. Some populations are distinctly reddish, almost as reddish as _oreas_. Although assigned to _artemisiae_, they are almost identical with populations of deer mice from the eastern Cascade Mountains, known to be intergrades between _oreas_ and _gambelii_. This fact, and the presence of surprisingly _oreas_-like characters in some microgeographic races in extreme northeastern Washington, may indicate that the race called _artemisiae_ is a group of intergrades between _gambelii_ and an _oreas_-like mouse that has become extinct.