22 THE HAUNTS OF LIFE 
it does not evaporate, and the limpet is safe, 
too, from being injured by the waves. But it 
is not altogether safe from other animals, for 
some birds, especially the oyster-catcher or 
sea-pie, have discovered exactly the kind of 
sudden sharp stroke of the bill that is needed 
to knock a limpet off its rock, and once it has 
let go its hold it is a helpless victim. When 
the tide covers the limpet’s rock it relaxes its 
hold and slowly moves off on its foot to the 
nearest seaweed patch where it cuts, with the 
long, toothed, rasping ribbon or file in its 
mouth, the grassy blades on which it feeds. 
Before the tide has ebbed it makes its way 
back to its rock, if it has not wandered too far 
and lost its way, and fixes itself in the exact 
spot in which it was before. In some cases it 
keeps to this spot so persistently that a little 
pit corresponding in size and shape to its shell 
may often be seen in the rock. Where all the 
rock is smooth the limpet does not trouble to 
return to its starting-point, for every spot is 
very much the same. 
Some molluscs, whose shells are not large 
enough to enclose them comfortably, or to 
protect them effectively, have learnt to bury 
themselves in the sand, and so to secure mois- 
