154 SEA-SHORE LIFE 
in France, Italy and Japan. They are also preyed upon by sea 
lions and sperm whales. 
In the octopi there are eight, and in the squids and sepia ten 
long, flexible arms that surround the mouth, and in many species 
the rims of the suckers are beset with hooks, thus increasing the 
tenaciousness of their grasp. A careful study has shown that these 
arms are derived from what was once the fore part of the foot in 
the ancestral mollusk, from which the Cephalopoda are descended. 
The mouth is provided with a pair of powerful, parrot-lke beaks, 
while the tongue is beset with sharp, rasping teeth. In all forms 
the teeth and jaws are horny, but in Nautilus the beaks are coated 
externally with calcareous matter. 
The chambered nautilus of the tropical Pacific and Indian 
Ocean is the only living species whose shell is wholly external. 
This graceful shell is composed of a series of chambers filled with 
gas, and coiled in the form of a regular spiral. These chambers 
are separated one from another by shelly partitions, but each par- 
tition is pierced at its centre to allow of the passage of a tube called 
the siphuncle, which runs through the compartments, and is 
attached to the back of the body of the nautilus. The animal itself 
lives in the largest and last formed chamber, into which it can 
almost completely withdraw its head and tentacles. 
The spirula of the tropical Atlantic and Pacific has also a 
chambered cell, but this is largely covered by the mantle, and is 
small in comparison with the size of the animal, and curiously 
enough the shell of spirula is coiled in a manner opposite to that 
of nautilus. These graceful cream-colored little spirals are found 
cast up upon the sands of every coral island, but the living animal 
is exceedingly rare, and almost nothing is known concerning its 
habits. 
In the squids the shell is also internal and imbedded in the 
mantle, and is reduced toa mere remnant popularly called the 
“pen,” in allusion to its peculiar shape, while in the octopus the 
shell has disappeared entirely in the adult animal. 
The so-called shell of the paper nautilus or Argonauta is not 
to be compared with the shell of other mollusks, for it is merely a 
shell-shaped capsule secreted by broad, flat expansions of two of the 
arms. Its resemblance to a shell is merely accidental, and it serves 
