June 7, 1924 
Variation in Microtus Montanus Yosemite 
985 
siderable size which had the hip glands but very faintly indicated is the only 
specimen of the whole series that was in such condition as subsequently to stain 
the attached label with grease. Interesting inferences may be drawn from this 
case; but they are all pure speculation. All males except small juveniles have 
glands that are readily discernible from the inner surface of the pelt, and they 
apparently begin really to develop at about the time or just before sexual ma¬ 
turity is attained. 
Fully adult females usually have hip glands almost as large, though of a finer 
texture and more poorly defined, than the males; and they never attain the 
congested condition often found in old examples of the latter sex. As a rule, an 
old female has about the same glandular- development as a subadult male of 
medium size. There is some irregularity in its shape in females, however, and it 
may or may not be present to a slight degree in the smaller subadults of the 
female series. 
The fact that both sexes of the present material have hip glands indicates 
that these do not constitute a secondary sexual character in the usual meaning 
of the term, although their development is probably directly contingent upon 
the attainment of sexual maturity by the animals. The definitely slighter 
development of the glands in females than in males should point to the hypoth¬ 
eses either that this was originally a race in which both sexes were equally well 
provided with glands, but that the females are now in gradual process of losing 
them, or else that the females were first glandless, but are now in course of 
acquiring them. 
EXTERNAL MEASUREMENTS 
LENGTH OF HEAD AND BODY 
The measurement of total length of all animals in the present series was taken 
in millimeters after manipulation of the specimens so as to obviate to some 
extent the effect of rigor mortis. The measurement was taken in the usual way 
while stretching the body to a moderate degree, but with more than usual care. 
Since collecting this series the writer has experimented with Microtus cali - 
fornicus sanctidiegae to ascertain the amount of variation that one might expect 
to occur in the measurement of total length when this was secured by a single 
collector. Two specimens were taken from the traps while still kicking and 
carefully measured as soon as movement had ceased. Their respective lengths 
were 199 and 178 mm. Twelve hours later, after a cold night and while the 
bodies were still very stiff with rigor mortis , they were manipulated to remove 
some of the rigidity before measuring; the figures then were 188 and 166 mm., 
respectively, while at noon, by which time the bodies were entirely relaxed, they 
measured 194 and 175 mm. It is thus seen that even when the measurement is 
taken carefully by the same person total length varies more than 5 per cent, 
according to the length of time that has elapsed between death and time of 
measuring. There must be at least 5 per cent additional difference in this figure 
when it is taken by several collectors, making in all a possible error of 10 per 
cent in the total length as given upon the labels of the average study skin. Add 
to this the fact that there is certainly more individual variation in this than in 
any other external measurement and it is evident that this character constitutes 
a very poor criterion by which to judge the age and development of a specimen. 
The length of head and body alone is much more reliable, for then there is not 
added to the coefficient of error for this, that.for the length of tail which is 
especially subject to mutilation. The practice of taking total length, however, 
is so firmly established among American scientists that it would be difficult to 
