Mollusca. 77 



which hang the gills ; the water which has been used for respiration is 

 then forced out through the "funnel", the flap being kept closed. This 

 alternating movement serves also as means of progression, the water 

 which is being forced out, propelling the animal with its hind-end 

 foremost (Fig. 73). The arms are used for crawling and climbing, they 

 serve also to catch and hold the prey with their suckers. Food consists 

 chiefly of crabs which after being caught and carried to the mouth by means 

 of the arms, are quickly paralyzed by a poisonous fluid secreted by the 

 salivary glands. Then the juices are sucked out of the body, the solid 

 parts not being swallowed. The Octopus are strong and daring robbers, 

 lying in wait for their prey in the crevices of the rocks. In the Aquarium 

 they pile up large stones into a heap behind which they conceal themselves, 

 ready to pounce out on the unwary fishes; their power 1 of changing then- 

 colour and of producing all sorts of warts and wrinkles on their other- 

 wise smooth skin, enables them to counterfeit so closely their surroun- 

 dings, that they can only be distinguished with difficulty. They are 

 caught all round the coasts of the Mediterranean , allured by baits, upon 

 which they pounce and with which they are hauled up. They are found 

 in all Neapolitan fish markets, as they are often eaten, and the arms of 

 young specimens are especially esteemed. 



A very near ally of Octopus is Eledone moschata, the Musk- 

 octopus, much smaller and with only one row of suckers on each arm. 

 They are very shy and try to hide themselves from view. When taken 

 out of the water they give out a strong odour of musk. As they are 

 frequent in occurrence they are often brought to market , but are gene- 

 rally only eaten by the common people. 



One of the most interesting and most important of the Cephalopods 

 is the Sepia or Cuttlefish (Sepia offlcinalis , Fig. 78). Their body is 

 oval, somewhat flattened, and with a membranous fin running down both 

 sides. Beneath the dorsal skin is the "cuttle-bone", found often on the 

 English coast and given to captive canaries to sharpen their beaks. 

 The eight arms are much shorter than those of the Octopus and are 

 generally carried closely applied together; between them is hidden an- 

 other much longer pair of arms which can be shot out to catch crabs 

 or fish. 



The most noticeable characters in Sepia are the excretion of an 

 inky fluid and the change of colouring in the skin. Both of these they 

 have in common with the other Cephalopods, but they make more fre- 

 quent use of them. The sepia used by artists is the product of a gland, 

 the so-called ink-sack, the contents of which can be squirted out through 

 the funnel; a small quantity is enough to suddenly envelope the animal 

 in a black cloud, which hides it from its pursuer. The ink is extracted, 

 dried and brought to market; even that of fossil forms can still be used. 

 - The wonderful play of colours on the living animal is due to large 

 cells (chromatophores) which are situated in the skin and are filled with 

 finely divided dark colouring matter ; as these cells contract (become glo- 

 bular) and expand (become flat), a continuous change of colours takes 

 place; stripes, spots and markings make their appearance and disappear 

 according as the animal is at rest or is irritated. The Cuttlefish have 



