Page:Natural History, Mollusca.djvu/212

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water. But their gills are constantly moistened by a minute quantity of sea-water contained in the cavity of the body; and this is prevented from evaporation, partly by the close adhesion of the margin of the shell to the rock, and partly by the tightly-fitting operculum.

Indeed there is reason to believe that this and some other species of the genus spend the winter in the air, hybernating, like the Snails. "Mr. Gray found that many individuals of L.petræa and some of L. rudis, were in this condition, during his stay at Dawlish. They were attached to the rocks several feet above the reach of the highest autumnal tides; the foot was entirely retracted; and a membranous film was spread between the rock and the edges of the outer lip of the shell; the gills were only moist, the branchial sac being destitute of that considerable quantity of water which exists in it in those of the same species which are adherent to it by their expanded foot. In this torpid condition the individuals observed by Mr. Gray continued during the whole of his stay, which lasted for more than a week. On removing several of them, and placing them in sea-water, they recovered in a few minutes their full activity."[1]

In Sweden the common people affect to prognosticate the weather by the position of the Periwinkles; when these ascend the rocks, it is considered as a sure sign that a storm is near, as their instinct leads them to place themselves out of the reach of the dashing of the waves; on the contrary, when they descend upon the sands it is supposed to indicate calm weather. I much doubt, however, the fact of any such connexion between the habits of

  1. Proc. Zool. Soc. iii. 116.