XI 



PHYLUM MOLLUSCA 



299 



sented by the funnel, a wide tube through which water is 

 driven out from the mantle cavity. In the Nautili (Fig. 171), 

 (sub-class Tetrabranchiata), the place of the arms with their 

 suckers is taken by a number of lobes bearing sheathed 

 tentacles surrounding the mouth, and a funnel is also 

 present, though it does not form a complete tube. 



FIG. 172. Section of the shell of Nautilus pompilius, showing the septa (s, s), the 

 septal necks (s. ., j. n.\ the siphuncle (si, represented by dotted lines), and the 

 large body-chamber (ch.). (From the Cambridge Natural History.) 



To compare such a Cephalopod as a Cuttle-fish or Squid 

 with a Fresh-water Mussel or a Snail, it is advisable to place 

 it in a position which it quite naturally assumes when not 

 swimming, with the head and its arms downwards and the 

 body sloping away from this upwards and backwards. In 



