986 
Journal of Agricultural Research 
Vol. XXVIII, No. 10 
institute another mode. After all, it is a very simple matter, though perhaps 
less satisfactory, to ascertain the head-and-body length by subtracting that of 
the tail from the total length, as has been done in the present instance. 
As mentioned previously, an arrangement of the series of skins with reference 
to the length of head and body does not give results that are as satisfactory as 
could be desired. Individual variation, of course, can not be escaped, but, still, 
this arrangement does not appear as natural to the orderly sequence of pelages 
and cranial development as does the arrangement according to the condylo- 
Fig. 2.—Graph showing external measurements and weights of both sexes of Microtus m. yosemite reduced 
to percentages and arranged according to the condylo-basilar length of the skulls, with largest skull of 
either sex taken as par 
basilar length of the skull. When thus disposed, the accompanying graph indi¬ 
cates that there is considerable individual variation; also that the average trend 
with age is for the head-and-body length to increase at a faster rate than the 
condylo-basilar length; in other words, the skull of the juvenile is proportionately 
larger with reference to the body of the animal than is that of the adult, roughly 
estimated 8 per cent larger. However, this relative disparity practically disap¬ 
pears as soon as sexual maturity has been attained. In taking the average of the 
external measurements and weights, several of the oldest and youngest specimens, 
judged by the condylo-basilar dimensions, were eliminated from consideration, 
even though there are but few in the present series. This was done for the purpose 
