344 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
pocket gophers are of squirrel-like ancestry. But that was in very 
remote times, geologically speaking: for the particular genus 
Thomomys has been in existence since the Miocene period. Despite 
this long lapse of time, then, the group of rodents here under con- 
sideration has not found its way beyond certain geographic limits, 
and yet within those limits it is exceedingly abundant and wide- 
spread, in other words, successful. What was the place for itself 
that the nascent ancestral race, just becoming gopher-like, discovered, 
and which its descendants, continually specializing, have found so 
favorable ? 
Superficial examination of a garden gopher shows the animal to 
be remarkably formed throughout for existence underground. Ob- 
servation of its habits shows that in all probability each individual 
spends fully 99 per cent of its time underground. Its world is lim- 
ited by the earthen walls of a burrow which the animal is equipped 
to dig for itself through the soil. In one direction this burrow leads 
to safety for itself and young from enemies; at the other end it leads 
to food supply. Thus the conditions of existence for any vertebrate 
animal, safe refuges and breeding places, and food of right kind and 
sufficient amount, are met. _ 
But this discovery of a previously unappropriated means of sub- 
sistence, by adoption of the subterranean mode of life, has brought 
with it deficiencies in certain faculties not bound up with proficiency 
in digging. To dig, the animal must have short legs and a muscular 
body, especially anteriorly. The head of a pocket gopher is larger - 
in proportion to its body than is that of any other land mammal in 
California; there is no obvious neck constriction, and the shoulders 
are broad. The musculature having to do with the operation of the 
front feet is massive; and so also are the bones of the skull to which 
are attached the big muscles which operate the relatively heavy 
incisor teeth, these being the chief tools with which the gopher 
loosens the soil as it advances along its underground routes of ex- 
ploration for food, or digs to greater depths for more secure refuge. 
Obviously, the acquisition of all these modifications for burrowing 
has necessitated the loss of that litheness of body and length of limb 
which would enable it to move freely over the surface of the ground 
in search of food or in escape from enemies. -The pocket gopher is, 
indeed, well-nigh lacking in powers of locomotion overland. 
I‘urthermore, the pocket gopher is deficient relatively to other 
rodents with respect to eyesight and probably also with respect to 
hearing. It is almost as helpless outside of its burrow as a fish out of 
water. There may be some compensation in a heightened sense of 
touch, especially as localized in the nose and surrounding vibrissae 
and in the tip of the tail. While the animal has little need of being 
