MOLLUSKS. 321 
cling to rocks or retain its hold upon its prey. It has a 
powerful parrot-like beak, with which it can crush the 
shell-fish and the crustacea that it captures. It can man- 
age even a large Crab in this way. Winding its long 
arms around it, and holding it, both body and claws, with 
its numerous suckers, it deliberately crushes its various 
parts with its strong mandibles, and picks out the flesh. 
In the Indian seas this animal attains so large a size as to 
be a dangerous enemy even to man. The color called 
sepia comes from the Cuttle-fish. It is used by the ani- 
mal for darkening the water with an inky cloud, that it 
may more easily escape from a pursuing enemy. The 
so-called cuttle-fish bone is a chalky substance secreted 
from the mouth of the fish, and is composed of almost in- 
numerable plates united by myriads of little pillars. 
553. The Argonaut, Fig. 253, called the Paper Nau- 
tilus, from its thin, 
white, delicate shell, 
has, like the Cuttle- 
fish, eight arms with 
suckers. Two of 
these are expanded 
into broad membra- 
nous fiaps. From ear- 
ly times it has been 
said that this animal 
uses its membranous 
arms for sails, and its 
other arms for oars. 
It has been found, 
however, that the 
membranes are not 
used at all as sails, 
but are usually spread 
over the sides of the shell, meeting along its keel. It is 
from them, and not from the surface of the body, that 
the calcareous secretion is poured forth for the enlarge- 
O.2 | 
Fig. 253.—Argonaut, or Paper Nautilus. 
