158 EDIBLE BRITISH MOLLUSKS. 



and appear likely to continue so. Some thought that 

 by means of its foot it perforated the soft clay or stone 

 which hardened round it; and a Dutch philosopher 

 named Sellius, nearly 130 years ago, published an ac- 

 count of the Teredo, wherein he showed that its shell 

 could not be the instrument of perforation ; and asked 

 how it was possible that the extremely tender shell of 

 the young Teredo could make a hole in solid oak — a 

 material ten times harder than itself. He also observed 

 that the form of the tube is evidently not the result of 

 an auger-like instrument, because it is broader at the 

 bottom than at the top and sides. 



Mr. Jeffreys, who quotes the above in his ' British 

 Conchology/ agrees with Sellius that the foot or mus- 

 cular disk and not the shell is " the sole instrument of 

 perforation by the mollusca of stone, wood, and other 

 substances, which is closely applied to the concave end 

 of the hole, and is constantly supplied with moisture 

 through the glandular tissues of the body." He adds, 

 "By this simple, yet gradual process, the fibres of wood 

 or grains of sand-stone may easily be detached or disin- 

 tegrated, time and patience being allowed for the opera- 

 tion." Some naturalists believe that it is accomplished 

 by means of an acid contained in the fish, by which it 

 dissolves the calcareous rocks; while others maintain 

 that the Pholas bores by using its shell as a rasp. This 

 mechanical process is fully described by " Astur," who, 

 from his own observations, has endeavoured to solve the 

 problem, and who, to quote Mr. Buckland's words, is 

 apparently the only person " who has ever seen the 

 Pholas at work" In the ' Field/ "Astur" published 

 some time since an interesting description of the me- 

 thod by which this mollusk bores its habitation. He 



