202 ROYAL NORTON CHAPMAN 
This then was his way of life—this little inter world between 
the floor and carpet was for him; and thus I learned why he had 
bartered his eyesight for keener powers of smell and touch.” 
Shull (07) concluded from his observations in the field and 
laboratory that shrews, like moles, push the earth aside as they 
burrow. We may therefore class the moles and shrews together 
with respect to the forces which have developed their narrow 
horizontal pelves lacking the symphysis. 
Brief attention should be given to those forms in which the 
conditions are less specialized. Some of the meadow mice 
(Microtinae) possess habits similar to those of the shrews which 
live in the litter over the surface of the ground. Seton (’09) 
may again be quoted with regard to the habits of some of the 
mice: 
“Tf we make of our six common mice a ladder to show their 
chosen elevations, we shall put Peromyscus arcticus (the deer 
mouse) at the top, far above the ground, next Evotomys (the 
red-backed wood-mouse) very near the ground, next Microtus 
minor (the small meadow mouse or vole) a little below, and 
lowest of all, much of the time below the surface, we find the 
present subterranean group (the common meadow mouse, 
Microtus pennsylvanicus).”’ 
The modification of the pelves in these mice conforms in a 
remarkable way to the elevations as given in this account of 
their habits. The deermouse (Peromyscus) possesses a sym- 
physis and the pubic bones converge posteriorly, while the 
meadow mouse (Microtus pennsylvanicus) is without the 
symphysis and the ventral margins of the pubic bones are 
parallel. Other forms with less specialized pelves have not been 
studied sufficiently to determine all the correlations between 
their habits and structure. Mice in general live more under 
cover, where they crowd under and between obstacles, than in 
the open where their action is free and unimpeded, and their 
progress, between and under the litter and under the vegetation 
which covers the ground, may have to do with the approach of 
the pelvis to the position parallel to the sacrum and the shortening 
of the symphysis pubis, as in the typical burrowers. 
