. Elements of zoology, or, Natural history of animals / ed. by Reese. Zoology. 412 ZOOLOGY. the body of the animal is enclosed within it, as in the shells of Gasteropoda, are the nautilus and the argonaut a (paper- nautilus). In the former of these the shell is spiral, and is divided by transverse partitions into chambers, in the last or outermost of which the animal lives; and, when it wishes to enlarge its shell, it prolongs the mouth of it, which widens as it is prolonged, and throws a new partition across the bottom. The shell of the argonaut has no such chambers, and the ani- mal, wh
. Elements of zoology, or, Natural history of animals / ed. by Reese. Zoology. 412 ZOOLOGY. the body of the animal is enclosed within it, as in the shells of Gasteropoda, are the nautilus and the argonaut a (paper- nautilus). In the former of these the shell is spiral, and is divided by transverse partitions into chambers, in the last or outermost of which the animal lives; and, when it wishes to enlarge its shell, it prolongs the mouth of it, which widens as it is prolonged, and throws a new partition across the bottom. The shell of the argonaut has no such chambers, and the ani- mal, when hiding within it, occupies the whole of its cavity. In the common sepia (cuttle-fish), on the other hand, the shell is reduced to the form of an oval plate, commonly known as the cut.'le-fish bone, from which pounce is derived, that may be picked up on almost every shore; and this is enclosed within a fold of the mantle, and lies upon the back of the animal. In some of the more slender and flexible species, even this is nearly wanting; all that remains of a shell in the loUgo (squid) being a narrow horny plate, somewhat resembling a feather in shape, whence it is termed the pen. 761. The nautilus is not the only Cephalopod which possess a spiral chambered shell. Such a one is found in the spirula ;. Ammonites. it does not protect the animal, however, externally, but is en- closed within it, like the bone of the cuttle-fish. There is reason to believe that this is the character of the fossils termed anmionites (commonly known as snake-stones), which abound in almost every rock containing organic remains, but of which no living representatives are known. If this be the case, the cuttle-fish to which these shells belonged must have been of enormous size, as ammonites have been found measuring four or five feet in diameter, although most of them are much smaller. No entire specimens of gigantic cuttle-fish at present living have been seen by naturalists ; but there is no doubt,
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