Hatfield -1934 Colo. R., Yuma, Nev. Calib.-Nev. Monument, 500ft, Clark Co, Nev. 334 February 8, 1934. and branching in all directions when they reached short grass or barren mud flats. The rats are apparently not at all averse to running through water, since some of the runways were under an inch of water in some places. One which we followed out was situated so that it was broken by a small stream, though the water was only about an inch deep. In one tall grass area we found that the rats had cut all the stems just above the ground, laying the grass as though with a revolver. However, in another place, they had packed down a layer of grass to run upon. Perhaps it is of significance that in the latter area the ground was damper, often under water. In several instances runways were traceable to the edge of a tall grass area, where they would end abruptly, the water being 3 or 4 inches deep beyond. There is little doubt that such runways are in constant use, since fresh droppings and grass cuttings were present in them.