Out of the vast mass of the great order of the gnawing animals of the world it is possible here to consider only half a dozen types. However, these will serve to blaze a trail into the midst of the grand army. The White-Footed Mouse, or Deer Mouse. On the wind-swept divides and coulees of the short-grass region of what once were the Buffalo Plains of Montana, only the boldest and most resourceful wild mice can survive. There in 1886 we found a white-footed mouse species (_Peromyscus leucopus_), nesting in the brain cavities of bleaching buffalo skulls, on divides as bare and smooth as golf links. In 1902, while hunting mule deer with Laton A. Huffman in the wildest and most picturesque bad-lands of central Montana, we pitched our tent near the upper waterhole of Hell Creek. [Footnote: A few months later, acting upon the information of our fossil discoveries that we conveyed to Professor Henry Fairfield Osborn, an expedition from the American Museum of Natural History ushered into the scientific world the now famous Hell Creek fossil bed, and found, about five hundred feet from the ashes of our camp-fire, the remains of _Tyrannosaurus rex._]For the benefit of our camp-fire, our cook proceeded to hitch his rope around a dry cottonwood log and snake it close up to our tent. When it was cut up, we found snugly housed in the hollow, a nest, made chiefly of feathers, containing five white-footed mice. Packed close against the nest was a pint and a half of fine, clean seed, like radish seed, from some weed of the Pulse Family. While the food-store was being examined, and finally deposited in a pile upon the bare ground near the tent door, the five mice escaped into the sage-brush. Near by stood an old-fashioned buggy, which now becomes a valuable piece of stage property. The next morning, when Mr. Huffman lifted the cushion of his buggy-seat, and opened the top of the shallow box underneath, the five mice, with their heads close together in a droll-looking group, looked out at him in surprise and curiosity, and at first without attempting to run away. But very soon it became our turn to be surprised. We found that these industrious little creatures had gathered up every particle of their nest, and every seed of their winter store, and carried all of it up into the seat of that buggy! The nest had been carefully re-made, and the seed placed close by, as before. Considering the number of journeys that must have been necessary to carry all those materials over the ground, plus a climb up to the buggy seat, the industry and agility of the mice were amazing.