CEPHALOPODA. 85 
CHAPTER XXII. 
CEPHALOPODA. 
CLass IV. CEPHALOPODA.—The last and highest class of the 
Mollusca 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 downwards, by means of 
the arms (fig. 109) which surround 
the mouth, which are usually 
provided with numerous suckers, 
and which are really produced 
by a splitting up of the margins 
of the foot. It is from the pre- 
sence of these arms that the 
class derives its name (Gr, heph- 
ale, head ; and odes, feet). The 
Cuttle-fishes can also swim rap- 
idly, either by means of expan- 
sions 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 ma- 
jority of the living Cephalopods 
Fig. 109.—Sepiola Atlantica, one of 
the Cuttle-fishes (after Wood- 
ward). 
are naked, possessing only an 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, : 
