CEPHALOPODS. 481 



structure of which is quite characteristic of this genus. It is known 

 as the cuttle-bone (Fig. 325). This bone is used for many purposes ; 

 among others, it is used in a powdered state as a dentifrice. It is 

 sometimes suspended in the cage with captive birds, that they may 

 whet their beaks on it, and collect phosphate of lime for the forma- 

 tion and repair of their bones. The shell is oval or oblong, some- 

 times provided with a slightly salient point. The upper part is 

 surrounded with a horny or cretaceous margin, and it presents in the 

 centre a combination of open cells. 



Some of the Cephalopods secrete a blackish, inky fluid, the uses 

 of which, in the economy of the animals, is imperfectly known. 

 The cuttles have considerable quantities of this liquor, which is con- 

 tained in a sort of sac or ink-bag, placed low down in the abdomen. 

 When the animal is pursued or threatened with danger it discharges 

 a jet of the fluid, which renders the water thick and muddy, and 

 permits it to escape in the obscurity from its pursuers. It appears 

 that the cuttle-fish avails itself of this stratagem when left accidentally 

 ashore. It is related of an English officer, that, having dressed for 

 dinner, and having some time to spare, he proceeded along the shore 

 on his favourite search for objects of natural history. He reached a 

 hollow rock in which a cuttle-fish had established its quarters ; he 

 soon detected the animal, which looked at him for some time with 

 its great prominent eyes ; and for a little they watched each other 

 with fixed attention. This mute contemplation came to a sudden 

 and unexpected termination by the discharge of a voluminous jet of 

 inky fluid, that covered the officer, which was the more unfortunate, 

 since he was in his summer dress of white trousers. 



The ink of the cuttle-fish is a favourite pigment, used in water- 

 colour painting under the name of sepia. It is truly indestructible ; 

 and the hard and black substance found in the sac of fossil species o 

 cuttle-fish when diluted with water produces a brilliant sepia. This 

 property of the inky fluid was well known to the Romans, who used 

 it in making ink. It was long supposed to be the chief ingredient 

 in Indian ink ; but a recent traveller, Mr. Siebold, who has visite.l 

 the manufactory, and investigated the subject, has revealed the true 

 process by which Indian ink is prepared. 



The species of the genus Septa affect the sea-shore ; they are 

 along-shore molluscs. The flattened form of their bodies is favourable 

 to a coasting life, by permitting them to rest easily on the bottom. 

 Still they do not remain all the year round upon the coast. The 

 cold in temperate regions, and the extreme heat in warm regions, lead 

 them to withdraw from the shore, to which they only return in the 



