NAUTILI AND AMMONITES. 209 



Cuttlefishes resemble Squids, but have two of the 

 arms or tentacles much lengthened and expanded at 

 their tips ; and they have a broad, internal shell, called 

 cuttle bone. This is the cuttle bone which is given 

 to canary birds. On the coasts of the Eastern Mediter- 

 ranean, Cuttlefishes are so abundant that the cuttle 

 bones are thrown up by the waves into ridges miles in 

 length. Like other Cephalopods, Cuttlefishes have the 

 power of clouding the water by ejecting an inky fluid 

 into it when they wish to escape. This ink, when 

 dried and prepared, is the sepia used in painting. 



Spirula. 



The Spirula resemble those just described, but have 

 a coiled shell inside. Figure 360, and the shell is divided 

 by partitions into chambers. 



Nautili and Ammonites. 



The Nautilus is the only living Cephalopod which 

 has an external chambered shell. Figure 361 shows 

 the Nautilus as it appears when cut open ; the animal 

 lives in the outer chamber, which communicates with 

 all the others by means of a tube called the siphuncle. 

 It has occupied each chamber in turn, making a parti- 

 tion behind as often as it outgrew its old home. 



The Nautilus lives in moderately deep water about 

 the islands of the East Indian Archipelago. 



Ammonites, Figure 359, are chambered-shelled Ceph- 

 alopods that lived in the seas ages ago ; hundreds of 

 kinds of these, from an inch to a yard in diameter, are 

 found imbedded in the rocks. 



NAT. HIST. AN.— I4 



