Every visitor to the sea‐shore has observed rocks drilled with innumerable holes, almost as though by art. A few good blows with a stout hammer on the chisel‐head serve to split off a great slice of the coarse red sandstone. The holes run through its substance, but they are all empty, or filled only with the black fœtid mud which the sea has deposited in their cavities. These are too superficial; they are all deserted; the stone lies too high above low‐water mark; we must seek a lower level. Try here, where the lowest spring‐tide only just leaves the rocks bare. See! now we have uncovered the operators. Here lie snugly ensconced within the tubular perforations, great mollusca, with ample ivory‐like shells, which yet cannot half contain the whiter flesh of their ampler bodies, and the long stout yellow siphons that project from one extremity, reaching far up the hole towards the surface of the rock. We lift one from its cavity, all helpless and unresisting, yet manifesting its indignation at the untimely disturbance by successive spasmodic contractions of those rough yellow siphons, each accompanied with a forcible _jet d’eau_, a polite squirt of sea‐water into our faces; while at each contraction in length, the base swells out till the compressed valves of the sharp shell threaten to pierce through its substance. Strange as it seems, these animals have bored these holes in the stone, and they are capable of boring in far harder rock than this, even in compact limestone. The actual mode in which this operation is performed long puzzled philosophers. Some maintained that the animal secreted an acid which had the power of dissolving not only various kinds of stone, but also wood, amber, wax, and other substances in which the excavations are occasionally made. But it is hard to imagine a solvent of substances so various, and to know how the animal’s own shells were preserved from its action, while, confessedly, no such acid had ever been detected by the most careful tests. Others maintain that the rough points which stud the shell enable it to serve as a rasp, which the animal, by rotating on its axis, uses to wear away the stone or other material; but it was difficult to understand how it was that the shell itself was not worn away in the abrasion.