The existence of these isolated groups of burrowing animals, dwelling together in communities, was made the subject of observation by the expeditions sent by the United States Government to explore these regions, and it was reported that it was not unusual to find rattlesnakes living in the same holes as the prairie dogs. Captain Stansfield, the leader of one of these exploring parties, stated that the holes were generally guarded by a rattlesnake, and that when the hand was about to be thrust into the hole to draw out the prairie dog which had been shot at, but had got into its burrow, the ominous rattle of the reptile was heard within. Twenty years had elapsed since that time, and many changes had taken place in the conditions of animal life upon these plains. I thrust my stick down various holes but there were no rattlesnakes in them. I afterwards heard that in these districts the reptiles, which had been so numerous, had disappeared. Another group of these village communities which I examined was placed to the south of the Platte. Although it covered a comparatively small area it was more fully tenanted and the dwellings were closer together, each mound almost touching its neighbour. One of the young occupiers of this village had been captured and tamed by a squatter living near the settlement in which I was then stopping. As it rarely happens that the habits of these marmots can be regularly observed, this creature’s actions were noticed with great curiosity. It was the daily habit of this prairie dog to sit for hours upon its haunches, with its fore-paws held steadily in front of him, continuously maintaining a careful watch upon everything that was happening. I observed that although the method of sitting was that of the squirrel tribe, the shape and appearance of the body was of a different type, and like that of a large guinea-pig. The most attractive point about the little animal was its keen manner of keeping guard like a sentinel. Nothing seemed to escape its vigilance. [Illustration: PRAIRIE AND BOULDERS, NORTH IOWA.] [Illustration: PRAIRIE DOGS, NEBRASKA. (THE MOUNDS ARE ABOUT EIGHTEEN INCHES HIGH.)] When the fact of rattlesnakes living in the same holes as the prairie dogs was originally made known, there were several theories advanced upon the subject; but, in the absence of any direct evidence as to the nature of the apparent alliance or friendship, nothing could be positively proved. It was however subsequently discovered that young marmots were occasionally found inside the bodies of rattlesnakes which had been killed near the mounds. It is therefore probable that the reptiles used the burrows for their winter residences, after having expelled the previous inhabitants.