538 



MoTlusca. 



THE NAUTILUS, OK PEARLY NAUTILUS, 



(Nautilus Pompilius,) 



Is a very different creature, and instead of the eight 

 arms of the Argonaut has its head surrounded by 

 numerous ringed and sheathed tentacles. It is remark- 

 able for the structure of its shell, the cavity of which is 

 divided into numerous chambers by transverse parti- 

 tions ; these chambers, of which the outermost alone is 

 occupied by the animal, are filled with air, but a narrow 

 tube passes through the whole of them, and communi- 

 cates with the cavity of the body. By this arrangement 

 the Nautilus is enabled to alter his specific gravity so as 

 either to rise to the surface or sink to the bottom of the 

 water. The few existing species of Nautilus are all 

 found in the Indian and South Pacific Oceans. 



