. The world of animal life. Zoology. 404 THE WORLD OF ANIMAL LIFE Where our sea-coast cliffs are composed of limestone or chalk, we may have noticed that the rocks are perforated by a great number of tunnels, each of which is sufficiently large to admit a man's thumb. These are the burrows of the Piddock or Pholas, as we have called it. Let us suppose that we have before us a piece of chalk which has been pierced by these creatures, and that we have carefully split it open with a mallet and chisel. There, lying in its tunnel, is the piddock or pholas that made it—a mollusc with a double shell,
. The world of animal life. Zoology. 404 THE WORLD OF ANIMAL LIFE Where our sea-coast cliffs are composed of limestone or chalk, we may have noticed that the rocks are perforated by a great number of tunnels, each of which is sufficiently large to admit a man's thumb. These are the burrows of the Piddock or Pholas, as we have called it. Let us suppose that we have before us a piece of chalk which has been pierced by these creatures, and that we have carefully split it open with a mallet and chisel. There, lying in its tunnel, is the piddock or pholas that made it—a mollusc with a double shell, hinged firmly together at the back. Its shell has a number of raised lines which cross and recross one another, causing its surface to resemble that of a rasp. It is by means of this shell that the tunnels are made. When boring a hole in the chalk the pholas takes Piddocks a firm hold with its " foot", or that part of the body which can be pushed out from between the shells and used in locomotion, and then begins to turn slowly from side to side. The sharp edges of the valves soon cut a hollow, which is quickly enlarged by the action of their rasp-like surfaces upon it. And before long the animal is buried in the rock. The piddock has a siphon of the same character as that of the cuttle-fish, through which a jet of water can be expelled with no little force. So, when the burrow becomes clogged by the particles of stone or chalk, all that the animal has to do is to eject a jet of water, which washes out the tunnel, and removes the obstruction. Upon some parts of our coasts the work of the pholas has been extraordinary. That the piddock or pholas has helped the sea very materially to undermine and destroy the cliffs upon its margin is unquestion- able. For it drives its tunnels through and through the rock, until it reduces them almost to the condition of a honey-comb. Then. Please note that these images are extracted from scanned page images that may have been digit
Size: 1684px × 1484px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1910
