Page:The Zoologist, 4th series, vol 4 (1900).djvu/326

296 launched itself off from it; and, after moving about with a sort of swimming or rolling motion in a horizontal direction for some time, lowered itself gradually. During the descent, the flexible leaf was bent with an undulating motion, corresponding with every movement of the Snail, and making it clear that the animal had an attachment to the extremity of the leaf. Proof of the existence of a thread was obtained also by means of an experiment which the observer often repeated with Limnæa stagnalis, L. auricularia, and Amphipeplea glutinosa. When the Snails were some inches from the supposed point of attachment, a rod was introduced, and slowly drawn on one side in a horizontal direction; and, by this means, the Snails were made to undulate to and fro, obeying exactly the movement of the rod. This had to be done gently, for when too much force was used the thread broke, and the animal rose rapidly to the surface. According to Mr. Tye's observations, Limnæa glabra spins its upward thread well and easily; L. stagnalis, when young, does the same, but the habit decreases as the animal grows older; the same is the case with L. palustris, which, however, was not seen to use a thread as often as ''L. stagnalis. L. auricularia, L. truncatula, and L. peregra,'' though kept under observation by Mr. Tye, were not seen by him to spin. Mr. R.M. Lloyd, however, had observed the habit in the last-named species. The present writer has noted L. peregra and L. palustris, presumably retained by threads, slowly rise through the water in aquaria; the L. peregra, which was extended as if crawling on a solid body, did not always keep its foot in the same plane, from which fact the writer concludes that it was not creeping up a thread already fixed. The water through which it rose was about eight inches deep; and, on arriving at its destination, the animal applied its foot to the surface-film of the water, under which it crept in the usual inverted position. In L. auricularia, the use of a thread was observed, as we have just seen, by Mr. Warington. Mr. Taylor, also, has seen this species spin, and has recently published a figure of an individual using a thread. This figure (Fig. 1) shows the animal, moderately extended from its shell, suspended from the surface of the water upon a downward-spun thread. The drawing was at first supposed by the writer to be