I must conclude these notes about sleep by relating a very curious case of sleep, resembling the winter-sleep of higher animals, on the part of a snail. This was the case of a desert snail from Egypt, which was withdrawn into its shell, the mouth of the shell being closed with a glistening film secreted by the snail, as is usual with snails in this country in winter when they sleep. The desert snail in question was affixed to a tablet of wood in a glass case in the natural history department of the British Museum on March 25, 1846. On March 7, 1850, that is four years afterwards, it was noticed by a visitor looking at the case that the snail had emerged from his shell and discoloured the paper around, but had again retired. So the officials unlocked the case and removed the snail from the tablet and placed him in tepid water. He rapidly and completely recovered, crawled about as a wide-awake snail should, and sat for his portrait. This may be regarded as an instance of unusually long sleep, natural to this species of snail, and related probably to the frequently prolonged dryness of the snail’s surroundings. We are led by such a case as this on to what are called examples of “suspended animation.” Wheel-animalcules, and some other minute creatures which are found living in tiny pools of water, on the bark of trees, and in the hollows of leaves, naturally dry up when the water evaporates. You may dry them yourself in a watchglass; they appear as nothing more than shapeless dust particles mixed with the dried mud of a drop of dirty water. They may be kept in this state for months—even years. I do not know that any limit has been ascertained. But when you add pure rain-water to the dust in the watchglass, it softens, and in less than an hour the little wheel-animalcules have softened too, and expanded into life, swimming about whilst the delicate spikes on their “wheels” vibrate regularly as though they had never ceased to do so, and as though the animalcules had not for years been dried-up little mummies.