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.
FIVE-FINGERED JACK ON THE OYSTER.
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.