To test its amount of vision, Le Court took a spare water-pipe, or gutter, open at both ends. Into this pipe he introduced several Moles successively. Geoffroy St. Hilaire stood by to watch the result at the further end of the tube. As long as the spectators stood motionless the introduced Mole made the best of his way through the pipe and escaped; but if they moved, or even raised a finger, the Mole stopped, and then retreated. Several repetitions of this experiment produced the same results. In the domain of the Mole, the principal point is the habitation, or fortress, constructed under a considerable hillock raised in some secure place, often at the root of a tree, or under a bank. The dome of the fortress is of earth, beaten by the Mole-architect into a compact and solid state. Inside is formed a circular gallery at the base, which communicates with a smaller upper gallery by means of five passages. Within the lower gallery is the chamber or dormitory, which has access to the upper gallery by three passages. From this habitation extends the high road by which the proprietor reaches the opposite end of the encampment; the galleries open into this road, which the Mole is continually carrying out and extending in his search for food; this has been termed the _hunting-ground_. Another road extends, first downwards, and then up into the open road of the territory. Some eight or nine other passages open out from the external circular gallery. From the habitation a road is carried out, nearly straight, and connected with the encampment and the alleys leading to the hunting-ground which open into it on each side. In diameter the road exceeds the body of a Mole, but its size will not admit of two Moles passing each other. The walls, from the repeated pressure of the animal's sides, become smooth and compact. Sometimes a Mole will lay out a second or even a third road; or several individuals use one road in common, though they never trespass on each other's hunting-grounds. If two Moles should happen to meet in the same road, one must retreat into the nearest alley, unless they fight, when the weakest is often slain. In forming this tunnel the Mole's instinct drives it at a greater or less depth, according to the quality of the soil, or other circumstances. When it is carried under a road or stream, a foot and a-half of earth, or sometimes more, is left above it. Then does the little engineering Mole carry on the subterraneous works necessary for his support, travelling, and comfort; and his tunnels never fall in. The quality or humidity of the soils which regulates the abundance of earth-worms, determines the greater or less depth of the alleys; and when these are filled with stores of food the Mole works out branch alleys.