348 SCIENCE FROM AN EASY CHAIR 



sawdust, and others do not swallow any of the material 

 into which they bore. So, too, the Pholas and marine- 

 boring mussels do not swallow the material which they 

 loosen. It is a very slow process, the boring in rock, and 

 the fine particles rubbed away by incessant movement are 

 carried off in the sea-water. 



To some extent the marine creatures which bore in 

 rocks seem to be helped by chemical action, since they 

 show a preference for chalk and limestone, easily dissolved 

 by weak acid secreted by the borer, though, clearly 

 enough, they are not dependent on such chemical aid 

 since we find them also boring in insoluble granite rock 

 and shale and clay. There is one true worm-borer which 

 perforates hard limestone pebbles and chalk rocks, so as 

 to give them the appearance which we call " worm-eaten " 

 when caused by another sort of worm and observed in 

 a very different material, namely, old furniture and 

 woodwork. At Tenby, in South Wales, the limestone 

 pebbles on the beach are quite commonly riddled with 

 these worm-holes, truly "worm-eaten." When they are 

 not too abundant one can see that the holes are 

 arranged in pairs like a figure 8, about half the size here 

 printed. On splitting the rock or stone one finds a 

 deeply-running U-shaped double tube excavated in the 

 stone. In this the little worm lived. It is easiest to get 

 at the worms in a fresh and living state on a coast where 

 there are chalk-rocks and sea-washed lumps of chalk. 

 The chalk is easy to split and cut at low tide, and then 

 the little key-hole apertures can be broken across and the 

 soft red worm extracted. It is a beautiful red-blooded 

 little worm little more than half an inch long with two 

 tactile horns on its head and little bristles and gills on the 

 rings of its annulated body. It is a true " worm," like the 

 earth-worm, what naturalists call by the not displeasing 

 name an " annelid." It seems at first sight impossible 



