GREAT NAUTILUS, 
errors occasioned by confusing the accounts of 
these two very different classes. 
Da Costa seems of opinion, that the animal 
resides in the uppermost or open chamber only ; 
leaving the rest no otherwise occupied, than by 
an appendage, or tail, like a got, or string, that 
fills the pipe, or siphimculus, which commu- 
nicates from chamber to chamber. The si- 
phimcrJus he describes as a dilatable tube under 
the command of the animal: which, when it is 
dilated, like the sv/imming -bladder of a h^h, 
renders the Nautilus buoyant ; but, when it is 
contracl:ed, the nsh and shell sink, and just to 
such a degree as the animal requires. " I be- 
lieve,'^ says he, " no water ever enters this tube." 
Mr. Hooke, in his Pinilcsophical Experiments 
and Observations, expresses, an opinion, that 
the animal uses it's tail or gut, which occupies 
the pipe or siphuncums, as it's necessities re- 
quire, to exhaust tiie air or water from the 
chambers, or to fill them with either; by 
wliich aifions, it renders itself of more or less 
specific gravity, to sink or swim. These opi- 
nions, however, are to be regarded as merely 
speculative ; since we do not appear to have 
acnuirtd any accurate history of this animal: 
for 3 
