THE TEREDO. 93 



and stones are thus penetrated is not satisfactorily as- 

 certained. The foot is large, broad, and flat, and con- 

 stitutes a sort of sucker, by which the animal firmly 

 attaches itself to the walls of its chamber, which fits 

 the size of the shell. Whether this foot bores mechani- 

 cally, (an impossibility as it would appear,) or whether 

 it applies some solvent to the stone, and thus works by 

 chemical agency, has yet to be ascertained. The for- 

 midable teredo, which has more than once threatened 

 Holland with destruction, penetrates the wood-work of 

 dams, breakwaters, and other structures on the shore, 

 beneath the water, as well as the undefended hulls of 

 ships, and by its unceasing labours makes a complete 

 sieve or riddle of the mass attacked. As the animals 

 grow, they enlarge the gallery, as it is supposed, by 

 the aid of the valves of the shell ; but this is not certain. 

 The position of the teredo in its gallery is with the 

 tubes toward the entrance of the gallery, for the sake 

 of water and food; and the walls of its habitation are 

 lined with a calcareous incrustation, produced by the 

 mollusk, and which constitutes a sort of extra shell of 

 a tubular form. 



We have said that the hinge of bivalve shells 

 is so constructed, and possesses such elasticity, as to 

 act as a spring, opening the shell without any eff'ort 



