Page:Natural History, Mollusca.djvu/32

20 A species of Cerithium, found at the mouths of rivers in tropical countries, has the silkworm-like habit of spinning threads, by which it suspends itself from the mangrove-roots; and our own, freshwater Snails have the power of suspending themselves in the same manner. Mr. Warington, in an interesting paper on the habits of some aquatic animals kept in confinement, thus records the curious fact:—

"In watching the movements of the Limnei, I was for some time under the impression that they had a power of swimming or sustaining themselves in the water, as they would rise from the bottom of the pond, a portion of the rockwork, or a leaf of the plants, and float for a considerable period, nearly out of their shells, without any apparent attachment, and by the contortions and gyrations of their body and shell, move some little distance, in a horizontal direction, from the point which they had left. On more carefully watching this phenomenon, however, I found they were attached by a thread or web, which was so transparent as to be altogether invisible, and which they could elongate in a similar way to the spider: they also possessed the power of returning upon this thread by gathering it up, as it were, and thus drawing themselves back to the point which they had quitted. These facts were clearly proved in the following manner: A Limneus stagnalis had glided its way along a young and short leaf of the Vallisneria, which terminated below the surface of the water, and having