THE FAIRY SAILOR AND HIS COUSINS. 117 



None, save the &quot; paper nautilus,&quot; have had external shells. 



The animals of the lower order are incased in shells which 



are long, tapering tabes, divided at regular intervals by 



transverse partitions. The paper nautilus and his allies 



have all lived in a later age of the 



world than that of which I have been 



speaking. The pearly nautilus&quot; is the 



only living representative of the lower 



order an order which swarmed in the 



seas of the Paleozoic and Mesozoic 



Times. The pearly nautilus is closely 



coiled (Fig. 46) ; its shell is divided at 



frequent intervals by smooth partitions 



concave anteriorly, the animal occupy 



ing only the space in front of the last 



one. A shelly tube runs through the 



middle of all these chambers to the far 



ther extremity of the shell. .Through 



this a ligament passes from the body of 



the- animal, and anchors it securely in 



the last chamber. This tube is called 



the siphon. Such is the structure of 



the pearly nautilus, which may be seen 



. T -i i n j. 



in myriads, on a calm day, floating on 

 the surface of the waters of the South 

 Pacific. 



The reader will certainly thank me for introducing here 

 a beautiful poem on &quot; the Chambered Nautilus,&quot; though the 

 author has committed the error of supposing it was this 

 species of nautilus to which the Aristotelian fable of the 

 fairy sailor applied. 



&quot; This is the ship of pearl, which, poets feign, 

 Sails the unshadowed main 

 The venturous bark that flings 



Shell (Baeulitcs ovatn-K) 



O f Mesozoic Time, be- 



