MAMMALS OF THE REGION 69 



CAVE MOUSE 



Peromyscus leucopus tornillo {Fig. 22) 



The only mammals living their entire lives, being born 

 and reaching old age, in the dark depths of the great 

 cavern, are the cave mice, or the west Texas form of the 

 white-footed mice, near relatives of our eastern white- 

 footed or deer mice. They are rather large, heavy 

 bodied mice with not very long tails, and specimens 

 from the cave seem to differ from those outside only in 

 larger size and better development, differences easily 

 accounted for by protection from natural enemies, long 

 life, and abundance of food. Evidently they have not 

 been restricted to the cave long enough to have under- 

 gone important physical changes. They may origi- 

 nally have fallen in, and not being expert climbers were 

 unable to climb out, and so adapted themselves to cave 

 life and wandered to the farthest rooms. If so, their 

 imprisonment would probably extend back only about 

 twenty-four years, or to the time when the guano came 

 up much nearer to the entrance and must have made 

 the exit comparatively easy. 



These mice are fairly common in the King's Palace 

 and especially in the lunch room beyond, all through 

 the great south room, and in the deep room below it, 

 reached by a hundred-foot wire ladder, as well as in 

 the guano rooms and large halls near the entrance to 

 the cavern. Their little round tracks and well-worn 

 trails usually follow the edge- of the walls, or cut across 

 from one point of rocks to another, taking the shortest 

 lines of travel from one protecting cover to another. 



