CHAPTER XXII. 



CBPHAI,OPODA. 



Class IV. Cephalopoda. — The last and highest class of 

 the JtfoUusca is that of the Cephalopoda, comprising the 

 Cuttle-fishes, Calamaries, Squids, and the Pearly Nautilus. 

 They are all inhabitants of the sea, 

 and are all carnivorous ; and they are 

 possessed of considerable powers 

 of locomotion. At the bottom of 

 the sea they can walk about, head 

 downward, by means of the arms 

 (Fig. 89), which surround the 

 mouth, which are usually provided 

 with numerous suckers, and which 

 are really produced by a splitting 

 up of the margin of the foot. It is 

 from the presence of these arms 

 that the class derives its name (Gr. 

 Rephale,hea.d; a,ndpodes,ieet). The 

 Cuttle-fishes can also swim rapid- 

 ly, either by means of expansions 

 of the skin constituting fins, or by 

 the forcible expulsion of water 

 from the cavity of the mantle, the 

 reaction of which causes the animal 

 to move in the opposite direction. 



The majority of the living Cephalo- ^^_ sS.-Sepiola Atlantiea, one of 



pods are naked, possessmg only an the Cuttie- fishes (after Wood- 

 internal skeleton, and this often a ™'^'^^' 

 rudimentary one ; but the Argonaut (Paper Nautilus) and the 

 Pearly Nautilus are protected by an external shell, though 

 the nature of this is extremely different in the two forms. 



