32 BULLETIX 1091j U. S. DEPAET-MEXT OF AGEICULTUKE. { ^^n^xo^^l 



of a fist in its interior (PL IX. Fig. I). One may sometimes 

 find tliis cavity distinctly ^varm from the rerent presence of the 

 inhai^itant. 



The walls or }jartitions Ijetween 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 fi^om two to four stories in vertical plan, 

 as shown by the transect of a mound in Plate VII. Fignre 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 I'ains and disturbances 

 from larger animals. 



Apparently there are no special pockets for deposit of feces in 

 Dipodomj/s 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. tliough 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 Ijurrows. 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 were 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, was 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 



