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 euttles 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 sefza. It is truly indestructible ; 
and the hard and black substance found in the sac of fossil species of 
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 visited 
the manufactory, and investigated the subject, has revealed the true 
process by which Indian ink is prepared. 
The species of the genus Sefza 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 
FEF 
