154 SEA-SHORE LIFE 



ill France, Italy and Japan. They are also preyed upon hy 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 Avhich the Cej^halopoda are descended. 

 The mouth is provided with a pair of powerful, parrot-like 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 tabe 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 spinda of the tropical Atlantic and Pacific has also a 

 chambered cell, luit 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 to a mere remnant popularly called the 

 "pen," in allusion to its peculiar shape, while in the octojnis the 

 shell has disappeared entirely in the adult animal. 



The so-called shell of the paper nautilus or Argonanta 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 



