Page:Natural History, Mollusca.djvu/64

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of our workmen's files in this, that the surface keeps itself always in a proper state of roughness for trituration. This is done by an organic law, which causes the crystals to be constantly shed, and as constantly renewed.[1]

Natural History - Mollusca - Limpet.png


All the borers above alluded to are Bivalves, and I know of no other Mollusk which can properly be classed with them. A common Gasteropod, however, the familiar Limpet (Patella vulgata), excavates the rock on which it lives to the extent of making a depression, more or less deep, exactly corresponding to the shape and size of the margin of its shell. When one removes a Limpet from its firm adhesion and finds a hollow beneath it, evidently made to contain its body, one is ready to conclude that the animal is a permanent tenant of the spot, never moving from it; and when we learn that the food of the Limpet consists of sea-weeds, we wonder how it is possible that a stationary animal can find vegetable food. But the truth is,

  1. Ann. and Mag. K. H. Oct. 1848.