Читать книгу Intelligence in Plants and Animals - Thomas G. Gentry - Страница 9

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Every one knows that the long cord or thong, called the lasso, is the peculiar weapon of the South American hunter. Almost from his earliest childhood the young Gaucho learns to amuse himself with it, and as soon as he is able to walk takes great pleasure in catching young birds and other animals around his father’s hut, hurling the long lash with such dexterity that the noose drops over their bodies and brings them to his feet. Did we wish to select from among all the denizens of life the most brilliant, graceful, and sylph-like, whose very life-histories read more like the romance of poetry than sober reality, we would choose those which might be appropriately designated the lasso-throwers.

Now among animals, as is only too well known, any weapons which they could be called upon to use must develop in their own bodies, and therefore it could hardly be suspected that a simple jelly-animal could be provided with a lasso ready grown in its own flesh. Yet it is so, for in that class of animals, which ranks just above the sponges, we discover a weapon of this kind as simple and as deadly, and far more wonderful in its action than any used by man.

In fresh-water ponds, attached by its base to the under surfaces of aquatic plants, may be found a very small animal, just large enough to be seen without the aid of a lens, usually pale green, but sometimes of a brown color. This is our common hydra, technically called Hydra fusca. It is nothing more than a tube or sac, with a sucker at one end to hold on with, and a mouth at the other, surrounded with from five to eight hollow tentacles or feelers, which opens into a central cavity or stomach. Firm and muscular are the walls of the sac, so that the little creature, which is not fixed permanently to whatever it is found clinging to, may stretch itself out or draw back as its own volition dictates, or move slowly along by means of its sucker, or float easily or contentedly upon the water. But the most remarkable, as well as the most interesting thing about this odd creature is the power which it possesses of overcoming animals more powerful and active than itself.

FRESH-WATER HYDRA MOORED AND SEARCHING FOR PREY.

Groping about with its flexible arms, which are closely invested with fine jelly-hairs, with which it seemingly feels, or attached to some leaf or bit of floating stick, its tentacles reaching out in all directions, the Hydra instantly paralyzes any minute insects, young snail or infusorian that touches its feelers, and complacently closing its arms over the helpless victim, carefully tucks it away, so to speak, into its stomach, where it is speedily digested. This power of paralyzing and thus readily capturing active living creatures is due to the presence in the skin of the tentacles and body of what are called lasso-cells, or nettling-organs, which are minute, transparent cells, so small that two hundred of the largest would occupy but the distance of an inch, each being armed with a long barbed thread coiled up within its walls. This delicate thread, which is often from twenty to forty times the length of the cell, lies bathed in a poisonous fluid, and only waits for the cell-walls to burst, which they do when the Hydra touches an animal swimming near it, when thousands of these little barbed cords dart into the victim, quickly paralyzing it and rendering it an easy prey to its captor. All Cœlenterates, such as jelly-fishes and coral polyps, possess these nettling-organs.

Thus we see where the Hydra’s strength lies. He has no need to struggle, for his victim, penetrated by a multitude of darts, and made powerless by the poison instilled, becomes as manageable as an equal bulk of inert matter. It behooves the little creature to take things quietly, for a cell once burst cannot be used again, and he is therefore compelled to wait until a new one is grown to take the place of the one that has become exhausted. So he patiently bides his time till his victim is half-conquered, when he draws him gently into his body. He lives and catches his food, as must be apparent, without the necessity of moving very far from the place where he had his birth.

All the summer through the Hydra puts out buds from its side, which, when their tentacles have grown, drop from the parent-body, and settle down in life for themselves. But when winter comes, and before all life has become extinct, an egg appears near the base of the tubes of those that are living, and these eggs lie dormant till the next spring, when they are hatched, and a new generation of Hydras is produced. Budding, which is but a process of natural self-division, is carried on to a large extent, more individuals being produced in this way than from eggs. These buds are at first a simple bulging out of the body-walls, the bud enveloping a portion of the stomach, until it becomes constricted and drops off, the tentacles meanwhile budding out from the distal end, and a mouth-opening arising between them. In the Hydra, the Actinia, and other polyps, and in truth in all the lower animals, budding is simply due to an increase in the growth and multiplication of cells at a special place on the outside of the body. As in the vertebrates, man included, the Hydra arises from an egg which, after fertilization, passes through two stages, the germ consisting at first of two cell-layers, but the sexes are not separate as in the marine Hydroids, which grow in colonies that may be either male or female.

Like some other animals of simple structure, the Hydra is capable of reproducing to a most wonderful degree when cut into pieces. Divided in two, each becomes a perfect Hydra, and even when sliced into any number of thin rings each ring will grow out a crown of tentacles. You may split them into longitudinal strips and each strip will eventually become a well-shaped Hydra. Two individuals may be fastened together by a horse-hair and in a short time they will have become like Siamese twins, but there will never arise the slightest disagreement between them. A Hydra turned inside out will readily adapt itself to the change, and in a few days will be able to swallow and digest bits of meat, its former stomach-lining having now taken upon itself the condition of skin.

Hydra fusca is our simplest lasso-thrower, and the only one to be found in fresh waters in this country. Such a wonderful and deadly weapon is his, that it is easy to understand how his numerous relatives in the wide ocean have made good use of the weapon with which nature has provided them, and secured, under all kinds of shapes and forms, homes and resting-places throughout the vast waste of waters. From the Arctic to the Tropics, and from the shallow seaside pools at low tide to the fathomless abysses of the ocean, we meet the lasso-throwers. Now in the form of huge jelly-fishes, covering the sea for miles and miles, transparent domes by day and phosphorescing lights by night, and now as tiny balls of jelly, glistening by millions in some quiet bay and splintering into light upon the beach; or in the form of living animal-trees waving their graceful arms over rocks in waters deep, or creeping like delicate threads over shells and stones and seaweed on the shore, where they often lose their identity and are mistaken for plants. There is scarcely a nook or cranny in the bed of ocean where these tree-like forms, associated with the beautiful sea-anemone, whose brilliant crimson, green and purple are unmatched in color by gem and flower, are not to be found.

All these beautiful creatures, as well as the living coral that nestles in the bosom of the warm Mediterranean or the sea that lashes our Southern shores, or that struggles boldly against Pacific’s waves, are lasso-throwers. Cœlenterata, the “hollow-bodied animals,” because of the large cavity within their bodies, is the name by which they are known to science. They naturally fall into two families, the Hydrozoa, or Water Animals, and the Actinizoa, or Ray-like Animals, our little Hydra, about which so much has been written, being representative of the former and the Anemones of the latter division.