of the Action of the Siphtincle in the Pearly Nautilus, 505 



with the branchial chamber c, by two apertures h h, through 

 each of which a bristle is passed to indicate the channels ol 



conimunication. From this arrangement it is evident that 

 the pericardial bag has three openings, one behind which 

 conducts the fluid into the siphon, and two before which 

 open into the branchial chamber, into which the sea water is 

 constantly flowing to bathe the respiratory organs. With 

 this mechanism before me, I humbly submit whether it is not 

 a reasonable inference to suppose that the sea water alone is 

 the ballast by which the nautilus is retained at the bottom^ and 

 its ejection the means by which the animal is enabled to rise to 

 the surface at pleasure. 



Thus by relaxing the anterior orifices, h //, that commu- 

 nicate with the common branchial chamber, the water would 

 flow into the pericardial sac, and from thence into the si- 

 phon 5: during this distended condition of the apparatus 

 the animal and shell would be specifically heavier, and the 

 nautilus, in obedience to a prescribed law, would remain 

 at the bottom without any muscular effort on the part of the 



