THE "SAILING" OF THE NAUTILUS. 279 



domicile is borne lightly above the body of the Nautilus, 

 without in any way impeding its progress. 



The chambers are all connected by a membranous tube 

 slightly coated with nacre, which is connected with a large 

 sac in the body of the animal, near the heart, and passes 

 through a circular orifice and a short projecting tube in the 

 centre of each partition wall, till it ends in the smallest 

 chamber at the inner extremity of the shell. Dean 

 Buckland believed this " syphon " to be an hydraulic ap- 

 paratus acting as a " fine adjustment " of the specific gravity 

 of the shell, by admitting water within it when expanded, 

 and excluding it when contracted. As it contains an 

 artery and vein near its origin at the mantle, Professor 

 Owen has regarded it as subservient to the maintenance of 

 a low vitality in the vacated portion of the shell. Dr. 

 Henry Woodward is of the opinion that, whilst in the 

 early life of the Nautilus this siphuncle forms the main 

 point of attachment between the animal and its shell, it 

 is in the adult " simply an aborted embryonal organ whose 

 function is now filled by the shell-muscles, but which in the 

 more ancient and straight-shelled representatives of the 

 group (the Orthoceratites) was not merely an embryonal 

 but an important organ in the adult." 



Every one knows the shell of the Pearly Nautilus. It 

 may be purchased at any shell-shop in a seaside watering- 

 place, and is imported by hundreds every year from 

 Singapore.* It is abundant in the waters of the Indian 

 Archipelago, especially about the Molucca and Philippine 

 Islands, and on the shores of New Caledonia and the Fiji 



* I need hardly say that before the nacreous layer of the shell 

 from whicu this animal takes its name is made visible, an outer deposit 

 of dense calcareous matter has to be removed by hydrochloric acid : 

 the pearly ourtace thus exposed is then easily polished. 



