MARINE MOLLUSCS 251 



tongue is also very large and fleshy, and in part armed with 

 numerous hooked spines or teeth. 



The class is usually divided into two orders, one characterised 

 by the possession of two gills, and the other of foxir ; but the 

 British species belong to the former, known technically as the 

 Dibranchiata. This order is subdivided into two sections 

 according to the number of arms ; and the divisions are called the 

 Octopoda and Decapoda respectively. 



The former section includes the Octopods, of which some species 

 inhabit our seas. They all have eight arms, of unequal size, with 

 the suckers arranged in two rows, and their round or oval bodies 



FIG. 183. OCTOPUS 



seldom have any fins, locomotion being effected by means of the 

 arms, and by the sudden expulsion of water from the siphon. The 

 shell is rudimentary, being represented merely by two short ' styles' 

 within the mantle. The species vary considerably in size, some 

 being only about an inch long when fully grown, while others measure 

 two feet or more, and are looked upon as formidable creatures by 

 man. Sometimes they are washed up on our beaches, but the best 

 way to make their acquaintance is to examine the contents of the 

 fishermen's drag nets as they are hauled on the beach. 



In the same manner we may secure various species of the 

 Decapods or Ten-footed Cephalopods, which comprise the Cala- 

 maries, Squids, and Cuttlefishes. These, too, properly speaking, 



