These creatures have much more powerful means of boring than the solens, for not only do they imbed themselves in hard clay, but even in stone and lava. In what manner this is effected has been the subject of much dispute; it is almost certain that the process is not mechanical, for their soft body, and the fragile nature of their shells, seem an insuperable bar to such a proceeding. Some authors have asserted that the hole is formed by means of an acid secreted by the animal, which acts chemically on the stone; but there are two reasons against this solution of the difficulty; first, no acid liquid has been discovered in the living animal, and, secondly, although acid would act upon stone, it would have no effect whatever on lava.
Another curious part of the history of these shell-fish is their phosphorescence, which is so bright, that it has been asserted, if eaten in the dark without their being cooked, it appears as if the person devouring them was swallowing phosphorus.
Pholas dactyloides.
Although not used as food in this country, they are not uncommonly eaten on the shores of the Mediterranean, where some large species are found.
The species represented in the engraving is found on the British coasts, imbedded in clay; its shell is of a delicate white, beautifully carved. The projecting piece at the lower part of the shell in the engraving is the long foot of the animal; on the right hand, the hole from which a shell has been removed is shown.
The Ship-Worm, ([Teredo navalis].)
Before the anatomy of this destructive creature had been carefully examined, there was as much difficulty in guessing at the means it employed in penetrating the solid timbers in which it is found, as there is with regard to the operations of the Pholas; but subsequent observation shows that the hard parts, of which the mouth is formed, are fully equal to the task.