MOLLUSKS 93 



the bottom of its burrow, it extends its slender siphons up 

 the tube and out of the entrance for its food supply. 

 Often hundreds of individuals enter the same piece of 

 wood, which becomes thoroughly riddled within a short 



FIG. 52. The piddock (Zirp/uza crispata), a rock-boring mollusk. Natural size, 



from life. 



time, and though giving no outward sign of weakness may 

 collapse with its own weight. Incalculable damage is thus 

 rendered to the shipping interests, and in consequence 

 much has been done to check their ravages, but they are 

 fax from being completely overcome. 



87. Other stationary species. A large number of other 

 species, while small and inconspicuous, are also free to 



