Frequently upon the fronds of the large olive sea-weeds may be found a tiny shell shaped something like that of the Common Limpit; it is of an olive green colour, with blue streaks, and is called, from its clearness, the Pellucid Limpit, P. pellucida. There is also another much like it in appearance, which naturalists call P. lœvis. To the labours of these little mollusks, according to Dr. Harvey, may be partly attributed the destruction of the gigantic Algæ, (sea-weed.) Eating into the lower part of the stems, and destroying the branches of the roots, they so far weaken the base, that it becomes unable to support the weight of the frond; and thus the plant is detached and driven on shore by the waves.
“And so the forest tall that groweth,
Underneath the waters clear,
Does the little woodman mollusk,
Level every year;
From small causes, great results—
Teaching you to persevere.”
ROCK-BORERS.
The family Pholadæ comprises a group of mollusks, the boring habits of which have long been known; they penetrate wood, hard clay, chalk, and rocks, and devastate the labours of man; they attack the hulls of ships, the piles which form the foundations of piers and break-waters, and they force themselves upon our attention by the loss of property, as well as of life, which results from their hidden depredations. Of this family, those belonging to the genus Pholus may be more especially likened to the Edomites of Scripture, because they take up their abode in the rock, and hollow out for themselves dwellings therein. With a shell as thin as paper, and brittle as glass, the wonder is how these Rock-borers work their way into and through hard stones. Some naturalists assert that they effect this by means of an acid which decomposes the substance of the rock, and renders it soft; others, that the animal keeps turning round and round like an instrument called an auger, and so gradually rasps away the surface of the stone with the angles of its shell, but we question whether the shell would not be worn out first in such a process. The generic name of these “stone-piercers,” comes from the Greek word Pholeo—to hide, and the rocky chambers which they hollow out for themselves, are as snug hiding-places as can well be imagined; yet, however deep they may go into these gloomy caverns, as we should be apt to suppose them, they need not be in darkness, for it appears that these Pholades emit a most remarkable light, whether phosphorescent or not does not appear to be determined; so strong is it, that it is said to illuminate the mouth of the person who eats the mollusk; and it is remarked by Dr. Priestly, that “contrary to the nature of most fish, which give light when they tend to putrescence, this is more luminous the fresher it is, and when dried its light will revive on being moistened with water.” So that in more respects than one these rock-borers are mysteries. The most common of them, perhaps, is the Prickly Pidduck, or Peckstone, (P. dactylus,) which is much used by the fishermen of our coasts as bait; the specific name is the Latin for a fruit shaped like a finger, which is something like the shape of this mollusk, as will be seen by the annexed engraving.
