342 ANNUAL. REPORT SMITHSONIAN INSTITUTION, 1923 



ture connected with them, comprise the ohief engine of digging. Its 

 operation results in cutting away, and in part transporting, the 

 earth, as the animal extends its underground system of passageways. 

 But there are also supplementary digging structures. Instead of the 

 hind feet being larger than the forefeet, as in most mammals, the 

 reverse is the case in the pocket gopher. We find the forefeet are 

 larger and provided with long stout curved claws ; and the forearm 

 and shoulder are heavily muscled. Through and through, the adap- 

 tations of the pocket gopher are seen to be concentrated for the 

 digging function. 



I have excavated several tunnel systems of gophers and have re- 

 corded the diameters in various portions of their courses, and the 

 volumes of the earth removed. I will not take space to give the 

 figures here. Suffice it to say that the ordinary runs maintain a 

 remarkably uniform diameter and depth below the surface of the 

 ground. The depth varies from 4 to 8 inches, depending upon the 

 consistency of the soil — clayey and coherent, or sandy and loose. 

 The deeper extensions of the burrows, down to a depth of 20 inches, 

 lead to the breeding chambers where the nests are located. 



As already intimated, pocket gophers appear above ground rather 

 seldom; they do so, as a rule, only as necessary to push out surplus 

 earth loosened in the extension of their tunnels or to forage in the 

 near vicinity of the open burrows. While gophers are active 

 throughout the entire 24 hours of the day, new surface workings, 

 marked by dark damp soil, are to be found chiefly in the morning. 



The typical mound is of a fan shape, the opening of the burrow 

 from which the earth was pushed, although closed, being clearly 

 indicated at the base of the fan. The upraised surface of the fan 

 is marked by more or less sharply indicated concentric " moraines," 

 each registering the terminus of an operation from the mouth of 

 the burrow. The rim of the mound is often irregular, the earth 

 having been pushed farther out at some points on the periphery than 

 at others. The mouth of the burrow is plainly outlined in a perfect 

 circle of raised earth 2 to 3 inches in diameter, but this small 

 circle is always lower than the preponderance of the heap. 



However, a great deal of the gophers' activity at the surface of 

 the ground is not marked by the presence of mounds. Especially 

 during the dry season, one will find at frequent intervals circular 

 openings in the ground which have been filled with loose earth, nearly 

 or quite to the level of the surrounding surface. Examination will 

 show that these burrows have been used as exits from short side 

 branches of the main tunnels. They are used for the purpose of 

 exploring the immediately adjacent surface for food. 



A gopher is loath to leave its shelter and ordinarily does not 

 venture as far even as the length of its body from the open mouth 



