ACEPHALA. 257 



Pholas, the Stone-borer. 



Which is able in some manner, hardly yet under- 

 stood, to excavate solid rocks into deep holes, in 

 which it dwells. The shell is much lengthened 

 transversely, and the outer surface is roughened by 

 ridges crossing each other like a rasp. It has been 

 said that the animal fixing itself by the foot, which 

 expands at the tip into a sucker-like disk, keeps per- 

 petually turning partly round, to and fro, and thus 

 wears away, or files, the substance of the rock. 

 When we consider, however, the very fragile texture 

 of the shell, and that it is destitute of LIFE, which 

 would resist the "wear and tear" of mechanical 

 action, we cannot help thinking that some fluid is 

 secreted, which aids the process, by dissolving or 

 softening the stone. As the minute fragments 

 abraded would soon fill up the hole and stifle the 

 animal, it is endued with the power of sucking them 

 in, and expelling them through one of its orifices, in 

 a forcible jet of water. 



Teredo, f the Shipworm. 



This is closely allied to the last genus, in its in- 

 stincts, but chooses a field for the display of its ener- 

 gies, which renders it formidably obnoxious to man. 

 It attacks timber when permanently beneath the 



ptiolas, living in a cave. 

 y, teredon, a borer. 



