Page:The Zoologist, 4th series, vol 4 (1900).djvu/333

Rh freely extended into the water, and the mantle-edges expanded; when the vase was moved or otherwise shaken, the animal contracted the mantle over its back, and descended "head foremost, as it were dropping down to the bottom, leaving a mucous filament attached to the glass"; subsequently, Gray adds, it ascended by the filament, rising thus towards the surface, and becoming attached to the glass as before.

A supposed planarian-worm, Planaria variegata—probably a Limapontia —was observed by Dalyell to be liable, in crawling up the side of a vessel, to drop to the bottom, its descent being apparently retarded, the observer says, by an invisible thread.

In the whole of the Aspidobranchiata we have but a single observation, and this, it is said, requires confirmation. It is not surprising that no case of spinning occurs among the Limpet and Limpet-like families; but the absence of records for the land operculates of the order—Helicina, &c.—is less easy to understand, especially in view of the fact that several of the land operculates regarded as Pectinibranchiata are known to suspend themselves. The Aspidobranch said to be a spinner is our little fresh-water nerite (Neritina fluviatilis), whose name appears in this capacity in most of the books; its only claim to notoriety in this respect, however, rests upon the fact that it was listed by Mr. Warington (with several air-breathing Water-Snails) as having been observed by him to spin. No particulars are given, and it is supposed by Mr. Tye that the observer may have been mistaken.