Part 4
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.
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.
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.
EARTH-WORMS IN HISTORY.
Earth-worms are found throughout the world. Though few in genera, and not many in species, yet they make up in individual numbers, for it has been estimated that they average about one hundred thousand to the acre. Our American species have never been monographed, which renders it impossible to judge of their probable number. Their castings may be seen on commons, so as to cover almost entirely their surface, where the soil is poor and the grass short and thin, and they are almost as numerous in some of our parks where the grass grows well and the soil appears rich. Even on the same piece of ground worms are much more frequent in some places than in others, although no visible difference in the nature of the soil is manifest. They abound in paved court-yards contiguous to houses, and on the sidewalks in country towns, and instances have been reported where they have burrowed through the floors of very damp cellars.
Beneath large trees few castings can be found during certain parts of the year, and this is apparently due to the moisture having been sucked out of the ground by the innumerable roots of the trees, an explanation which seems to be confirmed by the fact that such places may be observed covered with castings after the heavy autumnal rains. Although most coppices and woods support large numbers of worms, yet in forests of certain kinds of tree-growths, where the ground beneath is destitute of vegetation, not a casting is seen over wide reaches of ground, even during the autumn. In mountainous districts worms are mostly rare, it would seem, a circumstance which is perhaps owing to the close proximity of the subjacent rocks, into which it is impossible for them to burrow during the winter, so as to escape being frozen. But there are some exceptions to this rule, for they have been found at great altitudes in certain parts of the world, and especially is this so in India, where they have been observed to be quite numerous upon the mountains.
Though in one sense semi-aquatic animals, like the other members of the great class of Annelids to which they belong, yet it cannot be denied that earth-worms are terrestrial creatures. Their exposure to the dry air of a room for a single night proves fatal to them, while on the other hand they have been kept alive for nearly four months completely submerged in water. During the summer, when the ground is dry, they penetrate to a great depth and cease to work, just as they do in winter when the ground is frozen. They are nocturnal in their habits, and may be seen crawling about in large numbers at night, but generally with their tails still inserted in their burrows. By the expansion of this part of the body, and with the aid of the short reflexed bristles with which they are armed inferiorly, they hold so securely that they can seldom be withdrawn from the ground without being torn in pieces. But during the day, except at the time of pairing, when those which inhabit adjoining burrows expose the greater part of their bodies for an hour or two in the early morning, they remain in their burrows. Sick individuals, whose illness is caused by the parasitic larvæ of a fly, must also be excepted, as they wander about during the day and die on the surface. Astonishing numbers of dead worms may sometimes be seen lying on the ground after a heavy rain succeeding dry weather, no less than a half-hundred in a space of a few square yards, but these are doubtless worms that were already sick, whose deaths were merely hastened by the ground being flooded, for if they had been drowned it is probable, from the facts already given, that they would have perished in their burrows.
After there has been a heavy rain the film of mud or of very fine sand to be seen over gravel-walks in the morning is often distinctly marked with the tracks of worms. From May to August, inclusive, this has been noticed when the months have been wet. Very few dead worms are anywhere to be seen on these occasions, although the walks are marked with innumerable tracks, five tracks often being counted crossing a space of only an inch square, which could be traced either to or from the mouths of the burrows in the gravel-walks for distances varying from three to fifteen yards, but no two tracks being seen to lead to the same burrow. It is not likely, from what is known of the sense-organs of these animals, that a worm could find its way back to its burrow after having once left it. They leave their burrows, it would seem, on a voyage of discovery, and thus they find new sites for the exercise of their powers. For hours together they may often be seen lying almost motionless beneath the mouths of their burrows. But let the ejected earth or rubbish over their burrows be suddenly removed and the end of the worm’s body may be seen rapidly retreating.
This habit of lying near the surface leads to their destruction to an immense extent, for, at certain seasons of the year, the robins and blackbirds that visit our lawns in the country may be observed drawing out of their holes an astonishing number of worms, which could not be done unless they lay close to the surface. But what brings the worms to the surface? This is a question whose answer cannot be positively asserted. It is not probable that they behave in this manner for the purpose of breathing fresh air, for it has been seen that they can live a long time under water. That they are there for the sake of warmth, especially in the morning, is a more reasonable supposition, which seems to be confirmed by the fact that they often coat the mouths of their burrows with leaves, apparently to prevent their bodies from coming into contact with the cold, damp earth, and by the still other fact that they completely close their burrows during the winter.