JOURNAL OF MAMMALOGY 
 
of northern Africa are reputed to be more tolerant, to the extent of one
or 
two days. 
Some of the Heteromyidae are probably able to withstand a greater degree

of desiccation than any other North American mammal, but within the family

there is much variation in this ability. Howell has kept many individuals
of 
several species of Dipodomys on a diet of dry rolled oats, without water,
for 
various periods of time up to three months, by which time they have usually

lost a little weight and are fairly ravenous for moisture when they sense
its 
proximity. Bailey (unpublished manuscript) attests to the fact, however,

that members of this genus will lose condition if kept on such a diet and
will 
die in a few weeks. Bailey (1923) has also reported that small, silky pocket

mice (Perognathus flavescens perniger and P. fasciatus) will also lose condition

after a few weeks of dry diet, and Benson (MS) states that P. xanthonotus
will 
suffer if deprived of water for a week. On the other hand Stephens (1906)

has reported P. fallax to have lived for three years exclusively on dry barley,

and Benson that P. penicillatus will apparently do the same. Howell kept

an individual of P. fa~lax pallidus for more than a year on a fare of dry
rolled 
oats, at the end of which time it was in good condition, but was accidently

killed. 
It seems established then that at least some pocket mice can dispense en-

tirely with both free water and succulent food. Not the least surprising
fact 
in the above evidence, however, is the ability of such animals to survive
for 
long periods in good condition on a diet of rolled oats, a food so incomplete

as to prove fatal in a far shorter space of time to a white rat, even with
access 
to water. 
Additional interesting facts may be learned from animals in captivity. For

two years C. P. Richter (MS) has studied certain aspects of two sorts of
heter- 
omyids in the laboratory. He has found that Dipodomys ordii columbianus 
consumes free water, in addition to a bit of lettuce once a week, to an amount

varying from 2 to about 10 cc. per day. Strangely enough, the rate of con-

sumption does not vary much in any particular individual; one will drink
2 to 
2.5 cc. day after day for weeks, while another animal will consistently drink

8 cc. Young white rats of equal weight regularly drink more than the above

maximum, or 10 to 12 cc. per day. The activity record of Dipodomys is quite

variable, according to Richter, but individuals may run on an exercising

wheel as far as 16 miles per night. The palm for restlessness must be accorded

to Perognathus fallax, however. This species will not drink an appreciable

amount of water at any time, Richter's records show, but it will run as far
as 
22 miles per night, an astonishing distance for such a rodent, particularly
as 
such a small species must expend energy to turn the wheel; or, in other words,

the animal is running uphill all the time. 
After a Dipodomys has been on an air-dried diet for some time its behavior

is noticeably different only in a few ways. It will reach back to receive
the