POCKET GOPHERS—GRINNELL 355 
with the ccntributing agency of more or less impassable barriers 
here and there, each of the many and diverse “ gopher differentia- 
tion areas” thus formed in California has impressed its occu- 
pant with its stamp, namely, a peculiar combination of adaptive 
characters best fitting that gopher to carry on successfully existence 
in that restricted area. One more inference, of far-reaching impli- 
cations, fairly forces itself upon us—that evolution of habitats 
(differentiation areas) must have preceded and guided differentia- 
tion of the gopher stocks which came eventually under their impress. 
