Читать книгу Intelligence in Plants and Animals - Thomas G. Gentry - Страница 10

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Quite as infinite in number, variety and form is the life of the sea as that of the land. But of all marine animals, however, there is none more curious than the echinoderm, a name derived by science from two Greek words, indicating an animal bristling with spines like the hedgehog. These creatures are sometimes free, but quite as often attached by a stem, flexible or otherwise, and radiate after the fashion of a circle or star, or are of the form of a star, with more or less elongated arms. They are covered with shell-like plates, which they secrete for themselves, and are still further protected by spines or scales.

Perhaps the most common of the echinoderms is the Star-fish, or Five-fingered Jack, as it is called by sailors. Whoever has spent any time on the seashore has doubtless made the acquaintance of this animal, for it is readily distinguishable by its shape, its upper surface being rough and tuberculous, and armed with spine-like projections, while the under portion is soft, containing the essential organs of life and locomotion.

When first seen stranded on the shore the Star-fish, by the uninitiated, is thought to be a creature incapable of movement of any kind. But this is far from being the case, for in its native element it moves along the bottom of the sea with the greatest ease, being provided with an apparatus specially adapted for the purpose. Ordinarily its arms are kept upon the same level, but in passing over obstacles that lay in its path, the animal has the power of raising any one of its several arms. Elevations are ascended with the same ease and facility as progression on plane surfaces is effected. Perforating the arms, or rays, and issuing from apertures, will be found large numbers of membranous tubes, which prove to be the feet of the animal. Upon careful examination the latter will be found to consist of two parts, a bladder-like portion, resident within the body, and a tubular outlying projection, ending in a disk-shaped sucker, thus showing the feet to be muscular cylinders, hollow in the centre, and very extensible. In progression the animal extends a few of its feet, attaches its suckers to the rocks or stones and then, by retracting its feet, draws the body forward. Like that of the tortoise, its pace is slow and sure. But the most singular thing about this singular animal is its manner of overcoming obstructions, which it must certainly perceive, judging from the preparations to surmount them which it makes at the opportune moment.

In addition to organs of locomotion Star-fishes possess blood-vessels, digestive and respiratory apparatus, and a nervous system of a very low order, an inference to which its seeming capacity of enduring vivisection without pain unmistakably leads.

Interesting as its manner of progression, even under the most trying circumstances, must be, yet there is nothing in the life of this lowly-organized animal that has half the charm to the true lover and student of nature than the mother Star’s devotion to her young. Her eggs she carries in little pouches placed at the base of the rays. When emitted through an opening, which occasionally and unintentionally occurs, the mother does not abandon them to the cruel charities of the ocean world, but gathers them together, forming a kind of protecting cover of them, very much like a hen brooding over her chickens. Her actions bespeak an anxiety which could only be born of an affection, as real and sympathetic as that which a human mother feels for the loss of any of her offspring. No matter how often the eggs become accidentally scattered, the mother does not grow weary of her charges and leave them to themselves, but gathers them to the maternal fold with the same tender, patient solicitude as characterized her first efforts. Confined to a tank, when with ova, the mother Star has been known to traverse the entire length of the vessel until she has found and recovered her scattered treasures.

Reproduction by eggs is not the only means of generation in vogue. In common with other sea animals the Star-fish has the strange capacity of detaching one or more of its arms, each of the cast-off members becoming in time a perfect creature of its own kind, while a new arm, fully equipped to perform all necessary functions, will grow out in place of the lost member. From twelve to fifteen weeks are required to reproduce a lost ray, the animal meanwhile seeming not the least discontented, but acting as utterly unconscious of any changes in its anatomy.

As found upon the shore, Star-fishes appear dead when really they are alive. Put one of these perfectly still creatures into fresh sea-water, and in a short time it will probably be disporting itself as freely as ever it did. But as the dead and the living, when stranded by the tide, present nearly the same appearance, some certain test seems necessary to distinguish them apart. If a Star-fish hangs loose and limp, it is dead; but, however dead it may look, if on touching it there are manifest a firmness and consistency in its substance, one may feel reasonably sure that it is playing the ’possum and will revive when placed in the water. Quite as certain a mode of ascertaining whether your starry friend is living or dead, is to lay it upon its back, when, if alive, a number of semi-transparent globular objects will be seen to move, reaching this way and that, as though feeling for something to lay hold of wherewith to restore it to its normal position. These globular appendages are the ambulacra, or locomotory organs, seeking to acquire this end. If, however, no movement is manifested, you can wisely conclude that your animal is dead.

The Star-fish, not unlike all other animals of the sea, has an appetite that is never satisfied. Dinner is always welcome. The procurement of food seems its chief concern in life. It is a scavenger of no mean importance, keeping up an incessant chase after all kinds of dead animal matter, and thus largely contributing, it is probable, towards the maintaining of the waters of the ocean in a state of purity. But its feeding is not exclusively restricted to decaying matters. Any species of mollusk, from the humble whelk, not more than five-eighths of an inch in length, to the lordly oyster, so esteemed by epicures, constitutes a dainty tidbit. No more inveterate ravager and brigand, not even excepting man himself, have the oyster-beds to disturb the equanimity and serenity of their existence than the audacious, insinuating Star-fish.

With its five arms, and apparently without any other organ, this comparatively insignificant little being accomplishes a work which man, without the aid of extraneous appliances, is quite unable to execute. It opens an oyster as deftly and effectually as an expert oysterman would do, and that, too, without the habitual oyster-knife, and swallows the slimy bivalve in the same manner as the lords of creation do. Man, with all his genius and skill, were he deprived of all other means of subsistence than the oyster, and having no implement with which to open it, would be severely puzzled to get at the savory morsel shut up in its obstinate valves, yet the Star-fish performs the task seemingly without the least difficulty.

How the Star-fish manages the problem was at first a matter of guess-work. For a long time it was confidently believed that the animal waited for the moment when the oyster opened its shell to introduce one of its arms into the opening. This much gained, the other four arms were got in without much trouble, and the whole business ended with the devouring of the inmate. This belief is no longer tenable. Careful observation has revealed to us the true inwardness of the proceeding. The oyster is seized between the arms of the Star-fish and held under its mouth by the aid of its suckers. Thus secured, the Asterias, or Star-fish, everts its stomach, and envelops the whole oyster in its interior recesses, distilling a poisonous fluid, a secretion from its mouth, which causes the oyster to open its shell, when the robber, as it were, crawls in and takes its dessert. Incredible numbers of oysters are destroyed by Star-fishes, but the oystermen fail to see that their own barbaric ignorance is largely to blame. Star-fishes drawn up in nets, rakes and dredges in immense quantities are tied into bundles, but the cords are made so tight that the pile is cut in twain, the result being that all the pieces, when afterwards thrown overboard, become new and perfect Star-fishes.

STAR-FISH OPENING AN OYSTER.

Not often has one the pleasure of meeting with these animals on the New Jersey coast, but yet they are occasionally seen, more frequently, perhaps, in the North. Asterias berylinus, the commoner form, is a fairly large species, of a more or less greenish color, sometimes waning to brown, and roughly covered with tubercles. Its five arms, at the extremity of each of which is situated a single red-eye speck, are somewhat irregularly arranged, and not rarely one is stumpy through breakage or unequal development.

When a Star-fish is alarmed, or finds itself in strange quarters, it will be seen to curl up the tips of its rays, and there under the point of each ray will be found a thick red spot seated on the extremity of a nerve, and having in it as many as from one hundred to two hundred crystal lenses surrounded by red cells. With such a highly-developed eye, which is far better than the jelly-fish enjoys, it is no wonder that the Star-fish is so quick in discerning food, or enrages the fisherman by the discovery of the bait which he had intended for other animals, for it turns out that this stupid-looking animal is more wide-awake than it is given credit for. Sometimes, as in the beautifully delicate Star-fish, called the “Lingthorn,” a soft lid, or feeler, hangs over the eye-spot, which gives to the creature a curiously intelligent look, but in the case of our common form this lid is notably absent.

From all that has been written it must be evident that our first walking animal is by no means a poor or feeble creature. He has a chain armor woven into his leathery skin, with sharp, pointed spines, and snapping, beak-like claws to protect him; an excellent digestion and a capacious mouth to feed his greedy stomach, and a fine array of nerves, quick feeling and eyesight, and a wonderful apparatus for moving over the ground. When it is added to all these possessions the ability to close over the wound in the case of a lost ray and the growing of a new one, we see that his powers of living satisfactorily are by no means insignificant. But this curious walking apparatus of the Star-fish is far from being perfect in all his relations. They do not all walk by means of suckers any more than all sponge-animals build toilet sponge, or all slime-animals make chambered shells. Sure, the Rosy Feather-stars, for example, have no use for feet-tubes, as their lives are generally spent upon the rocks or nestled in bunches of sea-weed. Brittle-stars, as these are called, though closely related to the Star-fishes, are not easily confounded with them, for their arms are found to radiate from a clearly defined central disk, and there is no prolongation of their stomachs and ovaries into their interiors. The tube-feet pass out from the plates along the sides of the arms, instead of from the under surface as in the Star-fishes proper, and probably serve merely as a help for breathing, locomotion over the sands being effected by their long flexible arms. Their home is chiefly among the tangle and eel-grass, where their protecting covering affords them security from their many enemies.