302 THE BRITISH NATURE BOOK 



It will be obvious now that bivalves that is, molluscs having their mantles 

 in two parts produce two shells, one with each half of the mantle, while those 

 molluscs that have the mantle in one piece produce one shell only, and thus 

 are called Univalves. 



Cuttle-fish. These belong to the Cephalopods, the most highly developed 

 of all the molluscs, and have a distinct head, and two large, cruel-looking eyes. 



The beak (or jaws) is an exceed- 

 ingly powerful organ, very much 

 like that of a parrot, and there is 

 a thick fleshy tongue, covered with 

 hooks, for rasping or tearing flesh. 

 The Common Cuttle, or SEPIA 

 (Sepia officinalis), is most familiar 



Side view of a Cuttle-fish swimming as an ex- to us from the SO - C alled " bones r ' 

 ample of the division of Mollusca called Cephalo- ,., , u. .'"'' i. 



poda : ff, fore-foot, produced into arms bearing which are found on the beach, and 



suckers; hf, hind-foot or funnel the dotted line are Sold by bird dealers for cage 

 shows upper edge of foot; m, mantle; s, concealed birdSj and> j believe, are also used 



by chemists for producing tooth 



powder. The animal itself is from 6 to 10 inches long, with a flattened 

 body, shaped rather like a shield with a pointed end, and pale grey or brown in 

 colour. It is not very likely to be found close to the shore, though sometimes 

 it may be seen in a rock pool or caught in a net. None the less, it is an occupant 

 usually of shallow waters. Enclosing the body is the mantle, a tough and 

 muscular sac, expanding along the sides into a narrow fin. Inside the body, 

 just under the skin of the back, is the " cuttle-bone," an internal shell (sepio- 

 staire), which acts as a shield, and also as a float. Protruding from the front 

 of the head are ten arms, eight of which are covered with tremendously powerful 

 suckers, four rows on each arm ; the remaining pair are " tentacles," twice 

 as long as the others, swollen at the ends into a kind of club, covered with 

 similar suckers. They can be entirely withdrawn into pockets below the eyes 

 when not engaged in seizing upon their prey. When disturbed, the Sepia dis- 

 charges a deep brown fluid from an " ink bag," which darkens the water 

 around effectually ; from this the paint known as sepia is prepared. 



These animals are free swimmers, moving by means of their fins, but in 

 addition they possess a means of discharging water through an organ known as 

 a siphon, and by the recoil send themselves backwards at great pace through 

 the water. 



One other most interesting feature may be recorded : they can change colour 

 with great rapidity. The cells under the skin contain various minute grains of 

 pigment, and by expanding or contracting these cells the colour is concentrated 

 or diffused, so that there is frequently a remarkable play of colour over the 

 whole body, and the animal can match its surroundings with ease. 



The Sepia's eggs, by-the-bye, are like clusters of grapes, and are frequently 

 found on the shore cast up by storms. 



