Page:The common shells of the sea-shore (IA commonshellsofse00wood 0).pdf/21

Rh substances, such as decayed wood, red sandstone, and chalk, the last-mentioned substance seeming to be its favourite. Although its natural hue is white, the Pholas is. often stained with the colour of the substance in which it is imbedded; and when it lives in the red sandstone, the stain is often so deep that it might easily be taken for the natural colour of the shell.

In common with the rest of its kin, the Piddock has the power of evolving a phosphorescent light; and if the reader can manage to procure some living specimens, he will be most gratified by watching them in an aquarium. There is not the least use in procuring an elaborate glass aquarium for a visit to the sea-side. I always buy a flat earthenware pan, which answers every purpose, is very cheap, and can be left behind if the observer does not care to pursue the experiments in his own house.

To procure living specimens is not a very easy task, common as the creatures are. The simplest plan is to take a strong crowbar, prise up a large piece of rock into which the animals have bored, carry it above high-water mark, and then, with the aid of a mallet and cold chisel, chip out the inhabitants.

There are several species of British Piddocks, at least five being acknowledged. There is, for example, the (Pholas candida), which has only one accessory valve. This species is shown in fig. 5, where the accessory valve is seen in its place. At fig. 4 are drawn the two siphons, or tubes, of another species, the (Pholas parva), in order to show the manner in which they project from the gaping end of the shell; and at fig. 4'*, the same siphons are again seen, as they appear when viewed from the front. The observer who keeps these creatures alive should be careful to mark the flow of the water through the animal, entering at one siphon tube, and being ejected at the other.

The Little Piddock is, as its name implies, of small