978 
Journal of Agricultural Research 
Vol. XXVIII, No. 10 
MATERIAL 
The series herein discussed is from Long Valley, Mono County, Calif. Here, 
at an altitude of 6,800 feet, Convict Creek meanders through miles of open, 
marshy, pasture land to join near by the upper reaches of Owens River. The 
conditions at this spot are very uniform. The trapping ground was far from any 
other association (except dry sage), and the growth, although exceedingly lush, 
consisted almost wholly of a half dozen predominating grasses and small sedges, 
with the local Iris in drier situations. As there are here few kinds of foods, there 
can not be great variation in the shaping influences that particular fare may have 
upon various parts of the skull. It is known that the stresses and strains developed 
by the different major muscles of the skull have the greatest influence upon its 
exact configuration, and much—perhaps most—of the individual variation therein 
is probably due to such cause. Where great diversity of food, such as grains, 
grasses, alfalfa, root crops, fruit, and the like, is available, there must be a corre¬ 
sponding diversity in the developmental stimuli of'the skull muscles, according to 
whether an animal lives in a situation where one or another type of food predomi¬ 
nates. In the Long Valley association such variety of food is practically at a 
minimum. 
Disturbing influences as well are here very slight. The topography precludes 
the danger from severe floods, while the presence of the snow-fed creek, coupled 
with the fact that a part of its waters are so led as constantly to irrigate the 
meadows, minimizes the possibility of pronounced drought. Too, there is ample 
range for cattle in the valley, so that there is no overgrazing, with consequent 
destruction of favorable cover. Haw T ks are very few, and local indications sug¬ 
gest that the only furred predatory animals likely to exact appreciable toll upon 
the mice would be an occasional foraging coyote or mink. The only mammal 
which could compete with them ecologically to the slightest extent is the small 
shrew Sorex vagrans amoenus y which uses the runways of the rodents. Hence, 
theoretically, the meadow mice lead an existence that is unusually free from erratic 
influences, where all must eat substantially the same fare, and we are justified 
in assuming that there occurs less than the usual amount of individual variation 
among the specimens themselves. 
From July 9 to 17, 170 voles were trapped within a territory extending along 
the bank of the creek for about one-third of a mile. Of these, all specimens 
with damaged skulls and a majority of the juveniles were discarded. Each 
specimen retained was weighed and carefully relaxed by manual manipulation 
before taking the three measurements of total length, tail, and hind foot. The 
mammae were then examined and notes taken on the number and size of the 
tubercles upon the soles of the hind feet. While skinning the specimens, observa¬ 
tions were made upon the development and condition of both the outer and inner 
surfaces of the hip glands and upon the number and size of embryos when 
present. The skulls, after being labeled, were immersed in water to draw the 
blood, usually for 48 hours; the brains were then removed by syringing and 
placed in a 70 per cent solution of alcohol. 
Forty-eight hours before cleaning, the skulls were placed in water, and were 
then heated in a solution of soap, soda, and ammonia, the cooking having been 
regulated with such care that it was possible to bring them to a point at which 
the saponified flesh could be removed by means of a fine stream of water without 
recourse to scraping or brushing, hence obviating the usual danger of damaging 
the finer processes wdiile manipulating the scraper and brush. There has thus 
resulted a series consisting of 66 skins with skulls, besides a number of alcoholic 
specimens, collected within nine days in virtually the same spot by a single 
collector. In addition, every skull has been thoroughly cleaned and is perfect 
