32 BULLETIN 1091, U. S. DEPARTMENT OF AGRICULTURE. {b^LNoTi, 
of a fist in its interior (PL IX, Fig. 1). One may sometimes 
find this cavity distinctly warm from the recent presence of the 
inhabitant. 
The walls or partitions between the chambers and tunnels are in 
places surprisingly thin, and it is no wonder that one is almost cer- 
tain to break through in stepping on a mound, since the whole is a 
honeycomblike structure of from two to four stories in vertical plan, 
as shown by the transect of a mound in Plate VII, Figure 1. As 
Bailey writes, these partition walls are a mixture of earth and old 
food and nest material discarded years ago, resembling the adobe 
walls of the Mexican houses built of chopped earth and straw. This 
is the result of the continual ejection of refuse and earth as before 
mentioned, combined with the caving action of rains and disturbances 
from larger animals. 
Apparently there are no special pockets for deposit of feces in 
Dipodomys burrows; such matter may be found throughout the den. 
and is more or less mixed with the food refuse which carpets prac- 
tically the entire tunnel system. The nest and food stores are, how- 
ever, clean and neat, the droppings being dry and, though present on 
the floor of a storage chamber, not actually mingled with the food. 
Evidently the animal does not clean up the floor litter before stor- 
ing food material. 
The entire system for any one den seems to consist not only of the 
burrows within the mound itself, as described, but of those small out- 
lying ones which we have referred to as subsidiary burrows. These 
are two to four in number, and are connected with the main mound 
by the runways already mentioned. They often seem to be way 
stations on the runways connecting main mounds, and there is seldom 
any mound of earth whatever in connection with them. One entire 
den system, the home mound and three subsidiaries, was mapped 
after being excavated (Fig. 3), all having been carefully gassed with 
carbon bisulphide. The subsidiaries were simple and contained no 
storage. Two of them Avere shallow, while in the third a depth of 
48 centimeters was reached. They appear to be merely places of 
refuge, though the well-worn trails connecting them with the main 
mound indicate regular use. These runways are conspicuous on the 
Range Reserve, and are apparently characteristic of mounds through- 
out the range of the animal. Dwellers in different mounds must have 
rather extensive social contacts, notwithstanding the enmity of in- 
dividuals toward each other in captivity. The main mound, in 
this instance very complicated, Avas in one place three stories high, 
and we have found as many as four utilized stories; but as a rule 
there are two or three only. 
Since collapses are rather frequent during rainy seasons, aside 
from the trampling previously referred to, the kangaroo rats, where 
