202 



CONCHIFERA. 



rises suddenly to get rid of the nuisance. The vigilant human enemy watches 

 the moment, and seizes the opportunity and the Solen if he can catch it ; 

 bift unless very quick in his movements, those of the Solen may be quicker, 

 and once aware of the impending danger, the sensible shell-fish will not come 

 up again, but submits patiently to be salted alive rather than run the risk of 

 being caught and roasted, or else cut up for a bait. PROFESSOR FORBES. 

 The Pholades* are likewise borers. They excavate for themselves the 



dens in which they re- 

 side, in stone, clay, wood, 

 or other substances, and 

 in these excavations they 

 live a sedentary life. 

 Their shell is generally 

 thin and brittle, but it is 

 extremely hard, and co- 

 vered externally with file- 

 like teeth, that seem to 

 constitute the tools em- 

 ployed in their boring 

 operations. 



The Ship-Worm 

 (Teredo}^ well charac- 

 terized by Linnaeus as 

 the " calcunitas navium" 

 seems to have been spe- 

 cially appointed by Pro- 

 vidence for the removal 

 of floating timber, which 

 otherwise, by its accu- 

 mulation, might impede 

 the navigation of the sea. 

 The mantle is excessive- 

 ly lengthened into a sort 

 of tube, while the valves 

 are minute, so that the 

 appearance of these bi- 

 valves is rather that of a 

 worm than of a Mollusk. 

 It bores holes in all di- 

 rections through wood 

 lying in the sea, lining 

 the interior of its excava- 

 tions with a shelly crust. 

 The piles of piers and 

 wharves, the gates of 

 docks, and the bottoms 



FIG. 207. SHIP-WORM AND ITS SHELL. 



of ships are soon riddled 

 and pierced by these 



animals, insomuch that serious fears have been more than once entertained 



* 0wXeuw, pholeuo, to lie in a hole. 



t reptu, tereo, to bore. 



