These creatures are first-cousins, so to speak, of the acorn shells, and they are called “Ship Barnacles” because they are so very fond of fastening themselves to the bottoms of ships. Even after two or three months, indeed, the hull of a vessel is often quite covered with them below the water-line, and they check her speed so greatly that she has to be taken into dock to have them scraped off before she can set out upon another voyage.
You may generally find quite a number of these barnacles on the pieces of timber which are so often flung up by the waves after a storm. And you will notice that each of them grows, as it were, upon a kind of stalk, instead of being fastened down to the surface of the wood, as the acorn shells are upon the rocks. This stalk consists of the pillar of cement with which the little animal covered its feelers just before it changed its form for the last time.
There are a good many other kinds of barnacles, some of which are found in very odd places. There is one, indeed, which always lives on the backs of whales, and somehow manages to sink itself quite deeply into their skins!