and Teredo Navalis. 
287 
The teredo gigantea is imbedded in a different substance, and 
may have many other characteristic differences : although it 
appears from comparing the shells in which they are incased, 
that they are formed of exactly the same materials. 
The teredo gigantea, when arrived at its full growth closes 
up the end of the shell. This the teredo navalis does also ; 
and Sellius was induced to believe that the animal, by this 
act, formed its own tomb, since it could no longer destroy 
the wood, in which it was contained. We find, however, that 
in the teredo gigantea death is not a consequence of this 
seclusion from the substance, in which it is imbedded. 
In some of the specimens in Mr. Griffiths’s possession, 
the shell is just covered in, and that part close to the termi- 
nation is extremely thin, but in others is increased in thickness 
twenty fold : in others again the shell has not only become 
thick, but the animal has receded from its first inclosure, and 
has formed a second three inches up the tube, and afterwards 
a third two inches further on, and has made the sides thicker 
and thicker, to diminish the canal in proportion to the dimi- 
nution of its own size. 
These facts prove that the teredo gigantea, when arrived 
at its full growth, or whenever prevented from increasing its 
length, closes up the end of its shell, and lives a long time 
afterwards, furnished with food from the sea-water it receives 
like the actinece. The teredo navalis closes up its shell in the 
same manner ; it must, therefore, after that period, be sup- 
plied with food entirely through the medium of sea-water. 
The teredines in their anatomical structure are more perfect 
than many of the other vermes, and have a portion of red 
MDCCCVL P p 
