Part 2 — Note IV. Page 23. Fossil Nautili.
Reading edition
Note IV. Page 23. Fossil Nautili.
The beauty, elegant form, and remarkable internal structure of the shell of the Nautilus, have rendered it in all ages an object of curiosity and admiration: yet an accurate knowledge of the organization of the animal to which it belongs, has but recently been obtained. The Nautili may be regarded as Cuttle-fish or Sepiæ, inhabiting shells furnished with an apparatus to impart buoyancy, and enable the animals to swim on the surface, or sink to the profound depths of the ocean. A few explanatory remarks on the nature of the recent Sepia may be necessary to render the subject intelligible to the unscientific reader.
RECENT NAUTILUS.
The Sepia or Cuttle-fish of our seas is of an oblong form, and composed of a soft substance covered with a tough integument or skin: it varies from a few inches to a foot or more in length. The mouth is placed in the centre of one extremity of the body, and has a pair of powerful, curved, horny mandibles, much resembling the beaks of a parrot: it is surrounded by eight long arms like the rays of a star-fish, and these are beset with rows of little cups which act as suckers, and enable the animal to secure its prey, and attach itself with great firmness to any object.[AC] It has a distinct head, with two eyes as perfect as in the vertebrated animals, and complicated organs of hearing: and below the head there is a tube or funnel which acts as a locomotive instrument, and propels the animal backwards by the forcible ejection of the water which has served the purpose of respiration, and can be thrown out with considerable force by the contraction of the body. The soft parts are supported by a large internal bone or osselet of a very curious structure, which, when dried and reduced to powder, forms the substance used by scriveners, termed pounce. These naked mollusca also possess a membranous bag or sac, containing a dark-coloured fluid resembling ink in appearance, which they eject into the surrounding water upon the approach of danger, and by the obscurity thus induced foil the pursuit of their enemies. This fluid, when inspissated, forms the base of the colour termed sepia by artists.
The body of the Nautilus resembles in its essential characters that of the Cuttle-fish, and occupies the large outer receptacle of the shell; maintaining a connection with the inner compartments by means of the membranous siphunculus or tube, which is only partially invested with shell. The internal chambers are air-cells, and the animal can fill the siphunculus with fluid, or exhaust it at will; the difference thus effected in its specific gravity enables it to rise to the surface or sink to the bottom with facility. Now if' we imagine a Cuttle-fish placed in the outer chamber of a Nautilus-shell, and provided with a siphuncule, but having neither ink-bag nor osselet—these organs being unnecessary to an animal possessing a chambered shell—we shall have a general idea of the nature of the recent species.
The Nautilus is essentially an inhabitant of deep water: it creeps along the ground at the bottom of the sea, with its shell upwards like the snail; and by means of its arms can proceed with considerable speed.[AD]
A large and splendid species of fossil Nautilus is not uncommon in the London Clay of the Isle of Sheppey, Sussex, and Hampshire. The chambers are often lined with spar or other brilliant mineral matter; and polished sections, like those of the Ammonites, admirably display the internal structure.[AE]