208 



INVERTEBRATE ANIMALS. 



C H A 1' T E U X X I. 



C'EPHALCJPOJJA. 



Class 1\. C'Ei'HALoroDA. 



The last and highest class of tlie Mollnsca is that of tlie Cephalo- 

 jMxld, C(im]]i-ising tlie Cuttle-hshes, Calamaries, Squills, and the 

 Pearly Nautilus. They are all inhabitants of the sea, and are all 



ca,inivor(ius ; and they are possessed 

 of consideralile powers of locomo- 

 tion. At the bottom of the sea they 

 can walk about head downwards, by 

 means of the arms (tig. 148) which 

 surrounil the mouth, which are usu- 

 :dly provided with numerous suckers, 

 and which are really produced b}' a 

 s|ilitting U]) of the margins of the 

 foot. It is fi-om the jiresence of 

 these arms t^iat the class derives its 

 name (Gr. heplinla, liead ; and podes, 

 feet). The t'nttle - fishes can also 

 swim rajiidly, either by means of ex- 

 pansions of the skin constituting fins, 

 or by the forcilile exjiulsion of water 

 from the cavity of the mantle, the 

 reaction of which caiLses the animal 

 to move in the opposite direction. 

 The majority of the living Cephalo- 

 pods are nakeil, possessing only au 

 internal skeleton, and this often a 

 rudimentary one ; but the Argonaut 

 (Paper Naiitilus) and the Pearly 

 N.-uitilus are jirotecteil by an external .shell, though the nature of 

 tills is I'xtrcniely ditt'ereiiL in the two forms. 



'I lie body i]i the <_ri>liidiipiiilii is symmetrical, and is enclosed in an 



