412 SUPPLEMENT 
its solidity, the nature of the ligneous body, and the perfectly 
smooth state of the hole which is excavated, will not permit 
us to doubt that it is done by mechanical action, aided, how- 
ever, by the maceration of the wood. It appears that the 
thick adductor muscle, which passes from one valve to the 
other, is in reality the power which puts the shell in play, 
supports it at the bottom of the hole, and causes it to turn in 
the wood like a real gimlet. ‘There is here no necessity to 
have recourse to the presence of a solvent acid, which we 
have already observed is so doubtful as to the other terebrat- 
ing shells. The relation of cause and effect is too evident. 
In proportion as the little animal grows, it excavates its hole, 
which it also carpets in proportion as it goes on, with the 
cretaceous exhalation of the parts of its body not covered by 
the shell, and there buries itself until it has arrived at its full 
size. 
From the singular habits of the teredines, it is evident that 
they must be very formidable animals to the human species, 
for they very considerably hasten the ruin of all constructions 
in wood, established in or near the sea, such as piles, dykes, 
moles, barricades, and even vessels. Piles are in general 
completely untouched by them, as far as they are discoverable 
at the lowest sea; but from a certain point which is constantly 
immerged, to a very considerable depth, the holes of the 
teredines are so numerous, that the thickest piles give way to 
the slightest efforts. Holland is the country where the results 
of this are most fatal. Vessels have been known to spring 
leaks in consequence of the holes made in them by teredines. 
Means have been devised to obviate such serious accidents, 
either in the selection of the wood, or in securing it from the 
attacks of these animals. No European wood is certainly 
secure against the terebrating action of these mollusca. It 
has been asserted that there are some American timbers which 
they will not attack, either in consequence of their hardness, 
