110 WESTERN SERIES OF READERS. 



almost everything. A little one 

 called the Teredo bores into 

 pieces of submerged wood, like 

 the bottoms of ships and the 

 piles on which wharves and 

 bridges are built. They are 

 very destructive, and to protect 

 the wood it is sometimes poi- 

 soned or covered with sheets of 

 copper. 



But the common piddocks are 

 larger than the teredo, though 

 they do not bore quite so deep 

 Figure 75. holeg Those that look like Fig- 



ure 73 bore holes into the stiffest blue clay, from 

 which they can be dug out by the use of a pickax. 

 Others, like the shells shown in Figures 74 and 

 75, attack harder substances, and even make their 

 burrows in solid rock. Sometimes a reef gets so 

 full of holes that great pieces are broken off by 

 the waves during a storm, and rolled up on the 

 beach. You can find such pieces at old Monte- 

 rey, with the dead shells still remaining in the 

 burrows. 



When the creatures begin to bore they are 

 very small, and as they go on, the diameter of the 

 burrow must increase, to allow for their growth. 



