Natural History, Mollusca/Cephalopoda

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Natural History, Mollusca by Philip Henry Gosse
Cephalopoda

CLASS I. CEPHALOPODA.

(Head-footed Mollusks.)


If we were to take a Poulpe or a Cuttle-fish from some hole or tide-pool in the rocks, and look upon its many flexible arms studded with sucking disks, its sack-like body, its green staring eyes, and its bird-like beak, we should be ready to say that such an animal presents but a slight analogy with the sluggish and almost shapeless creatures familiar to us under the name of shell-fish. And, in truth, the former do possess a higher rank in the scale of animal life, having their senses developed into greater perfection, and forming, indeed, the link by which the latter take hold of the races which, from their elaborate organization, are placed at the summit of the scale—the Vertebrata.

We shall better understand the connexion between the present Class and other Mollusca, by considering, with Cuvier, that "the mantle unites beneath the body, and thus forms a muscular sac which envelopes all the viscera. This body, or trunk, is fleshy and soft, varying in form, being either spherical, elliptical, or cylindrical, and the sides of the mantle are in many of the species extended into fleshy fins. The head protrudes from the muscular sac, and is distinct from the body: it is gifted with all the usual senses, and the eyes, in particular, which are either pedunculated or sessile, are large and well developed. The mouth is anterior and terminal, armed with a pair of horny or calcareous mandibles, which bear a strong resemblance to the bill of a parrot, acting vertically one upon the other. Its situation is the bottom of a subconical cavity, formed by the base of the numerous fleshy tentacular appendages which surround it, and which have been termed arms by some naturalists, and feet by others."

These fleshy flexible feet are characteristic of the Class, and give to it its systematic appellation of Cephalopoda, signifying head-footed. They are instruments of locomotion; the animal being enabled to crawl awkwardly upon this circle of feet, head downwards. But their chief use to the animal is as organs for the seizing and holding of prey; and for this purpose they are eminently qualified. Each arm is furnished with a double row of sucking disks, each of which on being applied to any surface adheres to it at the will of the animal with immense force, so that it is easier to tear away the substance of the limb while the creature maintains its hold, than to release it from its attachment; and even after death, the suckers continue to retain a considerable power of adhesion.

The manner in which these suckers act, will be understood by a reference to the principle of a cupping-glass. Each one consists of a firm fleshy or cartilaginous ring, across which a disk of muscular membrane is stretched, with a circular aperture in the centre. A cone-shaped mass of flesh fills this aperture, like a piston, capable of being drawn backward. The membranous disk itself can also be drawn in. Now, let us suppose that one of the sucking disks of a tentacle touches any object fit for prey, such as a fish, for example, gliding by. The instant that the Cuttle feels the contact, instinctively, and with the speed of lightning, it retracts the fleshy piston; a vacuum is thus created, and the edges of the disk are pressed against the surface of the victim, with a force equal to the weight of the water that is above it, added to the weight of the atmosphere. If need be, as when the victim makes strenuous efforts to escape, the vacuum, and consequently the adhesion, is increased by the withdrawal of the membranous disk.

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STRUCTURE OF SUCKER.

This apparatus, powerful as it is, is but one out of a thousand instruments of the same kind with which the animal is furnished. Our common Poulpe (Octopus vulgaris) has eight tentacular arms, and every one of these carries one hundred and twenty pairs of sucking disks. The struggles of the unhappy victim once touched by the fatal spell, only ensure its speedy destruction; for as it writhes and darts to and fro, it ever comes into contact with others of the disks in succession, each of which adheres. Others of the arms now entwine themselves about it, and thus it is surely dragged to the central mouth, where the sharp and horny beak soon cuts it to pieces in spite of its scaly armour. The effective power of this apparatus is graphically described by Mr. Broderip:—

"We well remember, in our youth, going far out with an old fisherman of Dawlish, to visit his floating nets which he had laid for the pilchards. As we looked down into the clear blue water, we could see that the number of fish entangled was great; but, to the great discomfiture of the fisherman, who was eloquent on the occasion, almost every other fish was locked in the embraces of a cuttle-fish, plying his parrot-like mandibles to some purpose. The fisherman, who seemed to regard these unbidden guests as an incarnation of all evil, carried a capacious landing-net, but so quick was the sight of these Cephalopods, so ready were they in letting go, and agile in darting back or sideways clear of the net, that, though the greedy creatures held on to the last moment, the fisherman did not secure above three out of the crowds that had spoiled his haul. Upon mentioning this to Mr. Owen, he informed us that the muscular arrangement enabled the animal, when it was disposed to let go its hold, to push forward the piston, and thus in a moment destroy the vacuum which its retraction had produced."[1]

These highly endowed and repulsive creatures are formidable even to man. We may pass by, until better authenticated, the stories told by old naturalists, of Cuttles inhabiting the Indian Seas, with tentacles as long and thick as a ship's mast, which they are said to throw over vessels and drag them under water. But Mr. Beale, who has so largely increased our knowledge of the Sperm Whale, recounts a sufficiently fearful rencontre which he had with a species of Octopus, while searching for shells upon the rocks at the Bonin Islands. He was much astonished at seeing at his feet a most extraordinary looking animal crawling towards the surf, which it had only just left. It was creeping on its eight legs, which, from their soft and flexible nature, bent considerably under the weight of its body; so that it was lifted by the efforts of its tentacula only a small distance from the rocks. It appeared much alarmed at seeing him, and made every effort to escape. Mr. Beale endeavoured to stop it by pressing on one of its legs with his foot; but although he used considerable force for that purpose, its strength was so great that it several times liberated its member, in spite of all the efforts he could employ on the wet and slippery rocks. He then laid hold of one of the tentacles with his hand, and held it firmly, so that the limb appeared as if it would be torn asunder by the united efforts of himself and the creature. He then gave it a powerful jerk, wishing to disengage it from the rocks, to which it clung so forcibly by its suckers. This effort it effectually resisted; but the moment after, the apparently enraged animal lifted its head with its large projecting eyes, and, loosing its hold of the rocks, suddenly sprang upon Mr. Beale's arm, which he had previously bared to the shoulder for the purpose of thrusting it into holes in the rocks after shells, and clung with its suckers to it with great power, endeavouring to get its beak, which Mr. Beale could now see, between the roots of its arms, in a position to bite. Mr. Beale declares that a sensation of horror pervaded his whole frame, when he found that this monstrous animal had fixed itself so firmly on his arm. He describes its cold slimy grasp as extremely sickening; and he loudly called to the captain, who was also searching for shells at some distance, to come and release him from his disgusting assailant. The captain quickly came, and taking Mr. Beale down to the boat, during which time the latter was employed in keeping the beak of the cuttle away from his hand, quickly released him by destroying his tormentor with the boat-knife, when he disengaged it by portions at a time. Mr. Beale states that this Cephalopod must have measured across its expanded arms about four feet, whilst its body was not bigger than a large clenched hand.[2]

In one genus of this Class the action of the suckers is increased by a strong and sharp hook which projects from the centre of each. During action these hooks are plunged into the flesh of the victim, securing a yet firmer hold; added to which the two long arms, which are so endowed, and which are over and above the eight possessed by the Poulpe, are capable of being firmly locked together, and thus can be made "to cooperate in dragging to the mouth such powerful or refractory prey as singly the arms might be unable to subdue."

Most of the species of the Class are destitute of any external covering, but a few are protected by a shell. An immense number of fossil species, however, belonged to the latter division, known by the names of Belemnite, Nummulites, Orbulites, Ammonites, &c. The most important existing species possessing a shell, are te Pearly Nautilus of the tropical seas, and the Paper Nautilus of the Mediterranean. The former of these possesses four gills, a peculiarity which distinguishes it from all its fellows: Professor Owen, therefore, proposes to divide the Class into two Orders; the one including the Pearly Nautilus, called Tetrabranchiata, or four-gilled; the other including the rest of the existing species, named Dibranchiata, or two-gilled.

As the animals belonging to the Molluscous Division are very numerous, I propose to limit this volume to those families which are represented by species existing in and around the British Islands, contenting myself with an occasional slight notice of such foreign kinds as have anything particularly interesting in their history. I shall therefore at once proceed to the second of these Orders.


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