118 HOMES WITHOUT HANDS. 



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 specimens 

 which are covered with alga? 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. 



Our next example of the burrowing mollusks is the well-known 

 Pholas, popularly called the Piddock {Pholas dactylus), 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 locali- 

 ty. The chalk cliffs, which bound so many miles of our coast, 

 are thickly studded with the burrows of the Piddock, which takes 

 up its residence as high as the mid-water zone of the coast, and 

 in some places is so plentiful, that the hand can scarcely be laid 

 upon the rock without covering one or two of the holes. 



The shell itself is extremely fragile, and of a rather soft texture, 

 and its outer surface is covered with ridges, that sweep in the 

 most graceful curves from the hinge to the edge, and bear some 

 resemblance to the projections upon a file. Yet practical natu- 

 ralists have proved that, by means of these tiny points and ridges, 

 the Pholas is able to work its way into the rock ; for not only 

 can a similar hole be bored by using the shell as a brad-awl is 

 used to pierce wood, but the creature has actually been watched 

 while in the act of insinuating itself into the chalk rock, a feat 

 which was performed by gently turning the shell from right to 

 left, and back asrain. 



