CUTTLE-FISHES 



395 



cuttle-fishes it is chambered. In one species (the Spirula) the 

 internal shell is a coiled tube of many chambers. 



The family of the Nautilus (the Nautilidse) is the only group of 

 the Cephalopoda that lives in shells. These are also chambered 



Nautilus 



and exquisitely constructed, the animal occupying the mouth of 

 the shell, which may be described as the open chamber, and that 

 which was last formed. 



Considerably over 400 species of living Cephalopoda are known. 



CUTTLE-FISHES (Family OCTOPODID^) 



It may be enough for us here to know that the head-footed 

 Molluscs are divided into two sub-orders — those with eight ten- 



