LIMPET — PIDDOCK. 99 



mud, seldom less than three inches, and generally eleven or 

 twelve inches from its surface. In this position it would be 

 unable to respire, were it not for the elongating tube, which pro- 

 jects through the mud into the water, and just permits the ex- 

 tremities of the siphons to show themselves, surrounded by the 

 little radiating tentacles which betray them to the experienced 

 shell-hunter. These tentacles or fringes are never seen in the 

 dried specimens, and can only be partially preserved by plunging 

 the animal into spirits of wine, glycerine, or other antiseptic 

 liquid. The Gaper Shell is esteemed as an article of food by 

 man, beast and bird ; for not only do human beings dig it up 

 with tools, cook it, and eat it, but the wolves and the arctic fox 

 scratch it out of the mud and eat it raw, and the various sea 

 birds peck it out with their beaks, prize the shell open, and 

 devour the contents. 



The well-known Limpet is a kind of borer, though the holes 

 which it excavates are of very trifling depth, and are probably 

 made by the mechanical friction of the shell and foot against the 

 rock, without any intention on the part of the animal. Those 

 who have been accustomed to wander along the sea-shore must 

 have noticed that the Limpet shells always sink more or less 

 into the rocks on which they cling, and that in very old speci- 

 mens which are covered vrith algse and barnacles, the shells are 

 often sunk fully half their depth into the solid rock. Grooves, 

 too, of various depths may be seen in the same rock, showing the 

 slow and tedious track which the Limpets have made over its 

 surface, until they finally settled down into some convenient 

 situation. 



OuEnext example of the burrowing molluscs is the well-known 

 Pholas, popularly called the Piddock {Pholas dadylus), the 

 shells of which are extremely plentiful upon our coasts, whether 

 empty and thrown upon the beach, or still adhering to the living 

 animal and deeply sunken in the rock. Almost in every part of 

 our shores the Piddock is to be found wherever there is rock, 

 and its dimensions and general appearance vary together with 

 the locality. The chalk cliffs, which bound so many miles of 

 our coast, are thickly studded with the burrows of the Piddock, 

 wliich takes up its residence as high as the mid- water zone of 



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