Bats, at the beginning of cold weather, begin to huddle together in bunches in hollow trees, dark corners in deserted houses, and in caves and crevices in the rocks. They gradually lose all sensibility, and continue in a comatose state until the return of genuine warm weather. When you see the first bat of the season fluttering at nightfall you can be sure that warm weather has come to stay. The little hooks at the end of one of the joints of each wing are what the bat hangs itself up by when it goes to sleep, whether for a day or for months. When the bats are clustering for hibernation one of the number hangs itself up by its hooks, head downward, and the others cling to it. It is on record that sixty bats have been found in one cluster, the entire weight of the lot being sustained by the one bat clinging with its hooks to whatever it had fastened them to at the start--a weight of at least ten pounds. The position of the central bat in such a cluster would be like that of a man hanging by his thumb-nails and supporting the weight of fifty-nine other men. So completely is animation suspended in the bat during the cold months that no test yet applied has induced it to show the least sign of life. Torpid bats have been inclosed by the hour in air-tight glass jars and not a particle of oxygen in the jars has been exhausted when they were taken out, showing that the bats had not breathed. As cold drives certain animals, insects, and reptiles to a state of torpidity, so heat and lack of water bring about the same condition in others. The animal or reptile that hibernates, or goes to sleep in cold weather, arranges its body so that it will conduce to the greatest warmth, while those that estivate, or become torpid in warm weather, place themselves in positions that show that they want all the coolness the climate will permit. The tenric, a tropical animal, carnivorous and insectivorous, becomes torpid during the greatest heat, and lies on its back with its body drawn to its greatest length, and its limbs spread wide apart. Snakes estivate in the South, all kinds together, just as snakes hibernate in the North, but instead of rolling themselves in great balls, as the northern snakes do, they lie singly, and stretched to their full length.