V. Memmler 1943 Perognathus californicus June 18, M.V.Z. After weighing + measuring the mice this a.m. Dr. Benson examined their fur under the microscope. The shoulder regions appear greayer than formerly. In this region it also seems that additional hair are coming out at the old follicles. These are coarser than those already present. An area about 18 mm. in diameter was clipped from Mike's back, also the vibrissae on one side were cut to within about 6mm of their bases. Hair on the end of the tail was also cut. P.M. At noon when I left the mice had just constructed a new burrow in the ground. It starts in the corner behind the nest and runs around the corner clock-wise and down the long side of the box. A hole started earlier was passed under and made an opening to the outside. This was soon plugged from within. When I left the main exit hole was not yet closed, as the mice were still pushing out dirt and clearing their way back in. When I returned at 1:00'clock the main hole was plugged too and more dirt was thrown out on the surface. During the afternoon I accidentally broke into a piece of the tunnel. I set the nest over this place; during the afternoon Pat came out for seeds & filth