(1) To give themselves buoyancy several families of squid and crustaceans accumulate large amounts of NH<latex>$^+_4$</latex> ions in special compartments within their bodies. This is often in high concentration, approximately 0.5 mol/l, and very acid; sometimes two-thirds of the body weight consists of such strong ammoniacal solutions. Possible mechanisms for the accumulation of NH<latex>$^+_4$</latex> are discussed. (2) Cephalopods using chambered shells for buoyancy once dominated the seas, they included the nautiloids, ammonites and belemnites. Three types of such shells can still be found in living Sepia, Spirula and Nautilus. They differ greatly in morphology but all function in the same way. While being formed a chamber is full of a liquid isosmotic with sea water, later this liquid is pumped out against the hydrostatic pressure of the sea. It is shown that gases play no role in this pumping of salts and water and an account of our knowledge of the processes involved in the pumping is given.