52 THE SEA-SHORE 



rocks, like the piddocks, it bores into timber, such 

 as the hulls of ships, and the posts which support 

 jetties and piers. Very often it cuts away more 

 than half the wood in a great beam, leaving only 

 the thinnest walls between its tunnels. And as it 

 works along it lines these tunnels with a curious 

 shelly substance, which strengthens them and pre- 

 vents them from breaking down. 



By burrowing into timber in this way the ship- 

 worm often does most terrible damage. But it 

 seems to dislike the taste of iron rust very much 

 indeed. So when a beam of timber has to be pro- 

 tected from its attacks, a number of iron nails 

 with very broad, flat heads are driven into the 

 surface, with only the space of an inch or two 

 between them. The salt water acts upon these 

 very quickly, and the result is that the whole of 

 the beam is very soon covered over with a thin 

 coating of rust, so that no shipworm will attempt 

 to touch it. 



When the shipworm is quite small it is not in 

 the least like the perfect animal. Indeed, if you 

 were to see a baby shipworm, I do not think that 

 you would ever guess what it was. It is really 

 a kind of shipworm caterpillar. In shape it is 

 nearly round, and is covered almost all over with 

 tiny hair-like organs, by means of which it swims 

 in the water. But the odd thing about it is that 

 it keeps on changing its form. After about thirty- 

 six hours it becomes oval. A few hours later, if 



