TEREDO NAVALIS. 375 



common with such mollusks as are unprovided with a 

 cavity for the reception of salt water,, are placed externally, 

 evinces that tlieir construction is in exact accordance with 

 their mode of life. The animals turn readily in tlieir re- 

 spective shells, to which they merely adhere by a slight 

 connection at one particular part : this arrangement is evi- 

 dently designed to prevent the tubes from being dis- 

 turbed by the motion of the inmates, which resembles that 

 of boring. 



As the T. gigantea, or Great Bifurcated Borer, burrows 

 in the mud, on which he cannot be supposed to subsist, a 

 question has arisen wdiether the T. navalis receives any 

 support from the wood which he destroys, or is solely 

 suppHed with food from the sea. The latter opinion is 

 now generally adopted, as it appears, on close investiga- 

 tion, that the saw-dust received by the animal does not 

 experience the slightest change. 



"When the hull of a vessel continues for any length of 

 time in water, the Teredines appropriate it to their own use. 

 They commence operations by making holes in the softest 

 parts of the wood, and, as they have seldom at this period 

 attained their full growth, the perforations are so small as 

 to be scarcely discoverable. As soon as they have com- 



