adaptation in
a mouse that lives as a climber.

Many animals of cavernous habitats have small eyes (see Dobzhansky,
1951:284). Some nocturnal animals (for example, owls) have large eyes.
The brush mouse has large, protuberant eyes; it lives in the deep
crevices and fissures of the cliffs on which it is found, but it is not
strictly a cave-dwelling animal. Perhaps large eyes aid the brush mouse
in performing activities in the partial darkness of a deep crevice or
hole in a cliff. Brush mice experimentally placed in what appeared to be
total darkness fed, built houses of cotton, and ran and climbed in the
usual manner.

On several occasions the captive brush mice hid surplus seeds and on
other occasions hid acorns by burying them and sometimes by placing them
in a small jar. The mice never carried the surplus food into their
house.

Black (1937:195) has claimed that the brush mouse builds a nest similar
to that of the nest of the pack rat, _Neotoma floridana_. Hall
(1955:134) doubts this to be the case. Dalquest (1953:144) described a
nest of _P. boylii_ from San Luis Potosi as seven inches in diameter,
made of leaves, and found in a hollow tree. Drake (1958:110) noted that
_P. b. rowleyi_ lives in holes and crevices in rocky bluffs in Durango,
Mexico. I have found this to be the case for _P. b. attwateri_, as did
A. Metcalf (unpublished) for _P. b. cansensis_. Nests of sticks and
leaves were taken apart by Metcalf, and all sign indicated only the
presence of the pack rat. I have observed that there are no such houses
on the cliffs along Shoal Creek, Cherokee County, and that no pack rats
have been obtained from there (pack rats have not been reported from
Cherokee County). Blair (1938) found two brush mice (_P. b. attwateri_)
in the house of a pack rat in Oklahoma. Nests of the brush mice that
occur in Kansas have not been found.

A lactating, pregnant female (KU 81833) of _P. b. attwateri_, containing
three embryos, was obtained on December 24, 1959, and shows that this
subspecies breeds in winter. Accumulated records for the subspecies
indicates year-round breeding (see Cockrum, 1952:181). Another female
obtained on March 27, 1960, was probably lactating.

Pregnant females of _P. b. cansensis_ (KU 84892, 84895, and 84890) were
obtained from the type locality on April 1-2, 1961, containing 3, 4,
and 5 embryos respectively. This indicates, perhaps, increased breeding
in spring; five was the highest number of embryo