Part 3

It is called Amœba (Fig. 1), and although it is hardly a hundredth of an inch in diameter, yet if we devote some time to it we shall find that it is a very remarkable animal. Thus if it wishes to move in any given direction, a portion of the body becomes a seeming leg and protrudes in that direction, the rest of the body following, drawn along in some mysterious manner. If it wishes to eat, it is not obliged to twist around to bring the food or victims opposite the mouth, as a mouth forms there and then; the Amœba merely glides around it and covers it up.

We may even notice a difference in the parts. Thus the center calls to mind ground glass; it is blurred or granular, while around the edges is a little border which is transparent, like ordinary window glass. So the Amœba is a minute mass of jelly inclosed in a layer a little clearer.

Floating in the granular portion is seen a minute round body called the nucleus, clearer than the fluid in which it rests, and not far away another clear, circular body, which from time to time contracts or sometimes disappears in a marvelous fashion, but always returns. This is called the contracting vesicle, and here our discoveries end, so far as organs and structure are concerned, as these are nearly all that have been found; yet the Amœba eats, doubtless sleeps, and grows.

We may watch it at its dinner. When a victim is found, an animal smaller than itself, out shoots a little cape or extension from the clear rim, creeping slowly up the side of the animal; and if we watch very closely, we shall see the thicker portion of the Amœba, that which calls to mind ground glass, running or flowing into it. Then another false foot, as it is called, slowly creeps out on the opposite side and joins its companion, more of the ground-glass matter slides or pours into this, filling it out, and, presto! the two arms merge one into the other. The victim has been swallowed and is now being digested (Fig. 2, d).

That this minute atom has its likes and dislikes is evident, for if the food is too large, or not to its taste, it retracts, or even draws away from it after it has swallowed it. The shells of its victim, if it has them, are rejected in a manner equally simple; the Amœba flows away from them. Jar it with a needle point and it contracts, showing that it can be irritated. At times the body is seen to divide and two Amœbæ are formed (Fig. 3), each of which has a separate existence from then on. Such is one of the lowest of all animals. It is made up of but a single cell. All the members of the other great branches of the animal kingdom and the higher plants are made up of many cells; hence we see that the Amœba is the simplest and lowest of all animals.

In looking into our drop of water our attention has perhaps been distracted by other animals. In point of fact, it is very difficult to keep the eye on this mass of slime in its slow movements, for about it, over it, and constantly bumping into it are countless other forms whose motions convey the impression that life to them is very active. The most numerous are little objects (Fig. 4) resembling hats or bells, which go rushing along, bumping aimlessly into all others, and always in a hurry. Around the edge of the bell or hat are numerous hairs (cilia) which are really locomotive organs by which the little animals whirl themselves along. Near them we see numbers of similar objects, each one forming the cup of a seeming flower, each having a long stem. These are Bell Animalcules (Fig. 5) or Vorticellæ, among the most beautiful and graceful of all the minute animals, but much higher in the scale of life, as they have a permanent mouth and form. Among them, swimming rapidly, comes a giant by contrast, the Paramœcium (Fig. 6) or Slipper Animalcule, so called from its resemblance to a slipper. It, too, is a higher form than Amœba, as it has a permanent shape; yet in other ways it is as simple as Amœba. The Paramœcium has a marvelous array of oars which cover its body. Under the glass they look like eyelashes or whips, and by their rapid movements they drive the animal along. On the side is the mouth opening, into which the animal fans minute animals, and they can be seen swept along by the irresistible current, caught by the mouth if desirable, or tossed off if not to the taste of the wonderful living slipper. After glancing at the drop of water for a few moments the observer is convinced that here is a world in itself, with a population growing, increasing, developing, devouring its prey, and in such multitudes that the mind can not grasp the figures.

If the reader visits Egypt and climbs the pyramids, he will be impressed by these the greatest works of mankind. If a small portion of the stone from which they are constructed is placed under the glass, it will be found in many instances made up almost entirely of beautiful shells (Fig. 7). These are the shells of an amœba-like animal known as a Nummulite, which lived millions of years ago, and whose fossil remains formed the stone from which the early Egyptians in turn built the great piles or monuments of their kings. Man is powerful, but in this instance one of the most insignificant of animals made his work possible. These shells are of great beauty and variety (Fig. 8). Many are perforated, and through the minute holes are seen the false feet of the Amœba reaching out for food. They illustrate the boundless resources of nature, and suggest that the very lowest of creatures are not too insignificant to be dressed in most beautiful garbs, as all these forms vie with one another in the delicacy of their designs (Fig. 9) and the grace of their shapes. Some of these shelled forms are giants two inches across. All these minute shells perform a marvelous work in building up the crust of the earth, forming the bottom of deep seas and the platforms of coral reefs. The chalk cliffs of England are composed of shells of unestimated millions (Fig. 10), which were once dropped upon the bottom of a deep sea and piled upward until some were crushed into a shapeless mass of lime, others retained their shapes (Fig. 11); and all, by some convulsion, were afterward lifted high into the air.

The entire ocean is as thickly populated with these atoms as the drop of fresh water. The shelled forms are as constantly dying, the shells falling or sinking in a continual rain of shells upon the bottom, piling up eternally. Who shall estimate their countless numbers? It is believed that these minute shells are as abundant down to a depth of six hundred feet as they are at the surface. There are more than sixteen tons of limy shells floating in the uppermost one hundred fathoms of every square mile of the ocean. These facts convey an idea of one way in which the earth is growing--increasing in size but not in weight, as these delicate creatures merely secrete the carbonate of lime which forms their shells. They take it from the surrounding water of which it has been a part.

It would be of great interest to learn exactly how these humble creatures take lime from the water and produce shells of such marvelous beauty: to learn why one is of lime and others, like the Radiolarians, are of silica; why some live at the surface and are free swimmers, while others creep about in the ooze. When the deep-sea explorers first began to dredge, they found over vast areas a peculiar mud or ooze, and investigation showed that it was formed almost entirely of the shells of a certain minute shell maker, from which it was named the Globigerina ooze. Finding these vast banks or beds of mud at this depth is suggestive that the deepest seas may yet be filled by the dropping of this invisible rain; but as the average depth of the ocean is nearly if not quite three miles, many centuries must pass before this will be accomplished.

The marvelous phosphorescent light previously described came from a minute armored form known as Peridinium, but even this is exceeded by the glories of a little monad called Noctiluca (Fig. 12). It is a giant of the tribe, and is visible to the naked eye, being almost as large as the head of a pin, and resembling a currant in shape. It has a single hairlike organ or lash, supposed to be a locomotive organ, by which it whirls itself through the water. Of all the light givers of the sea this is the most common, some of its species being found in every sea, and where they are, it is necessary only to splash the water to cause a blaze of light to follow. A French naturalist placed on record the fact that so brilliant was the light occasioned by this minute organism in African waters that he read by their light standing on a beach where a heavy surf came pounding in upon the sand. The light of this little creature is remarkable not only for its vividness but for its many different tints. Now it is a fitful vivid green, again the water is a blaze of yellow light, or orange. At such times, when a ship is plowing along, the light is so brilliant that the sails and rigging are brilliantly illumined, casting weird shadows.

Some Noctilucæ emit a clear blue light, but when the same animal is disturbed it appears white with green and blue flashes of great beauty and intensity--a telling illustration of the boundless, and marvelous, resources of nature. Many interesting experiments have been tried with these dainty light givers. A tube fifteen millimeters in diameter was filled with them, and by shaking this novel lamp a printed page was read a foot distant; yet when a delicate thermometer was thrust into the fiery mass, the mercury was not affected in the slightest, showing that here was that wonder of wonders--vivid light without heat--a secret which man has vainly endeavored to wrest from nature. The vast number of these minute creatures can be realized when it is said that the ship Magenta sailed nearly five hundred miles among swarms of Noctilucæ, which gave splendid displays of phosphorescent light at night. Sometimes the light emitted was milky white; again it was green, or blue, the different species possessing different colors.

II. THE SPONGES

Almost every day, for several years, I devoted one or more hours to the pastime of floating or drifting over a part of the great coral reef which constitutes the most westward portion of Florida where it reaches out in the direction of Yucatan. The islands composing the group are the Tortugas Keys, and are just above water; indeed some disappeared when a particularly heavy hurricane came, and in the center of the island upon which I lived, the water at very high tide appeared above the surface.

Among the commonest objects seen on the reef were huge vases (Fig. 13). They were found in water from a foot to fifteen feet or more in depth, and were attached so strongly to the bottom that it required considerable strength to lift them up. Some were three feet high, and I have often dived down to them and for a few seconds sat upon them as a jest for the edification of my companions in the boat above. A common name for them on the reef was "Neptune's Seats." The seats were sponges, and their collection on the Florida reef has for many years constituted an important industry, vessels being fitted out from Key West and other places for this purpose. This industry is also followed in the Mediterranean Sea, where the finest sponges known are found. To take them, men go out in small boats, and in shallow water bring them up with hooks. In the greater depths a water box is used, a box with a glass bottom, which placed over the water makes everything visible, and by this the sponger secures the sponge. Other collectors, especially those of Syria, dive for them and wrench them from the bottom, then ascend to the surface with the load. There are many different kinds of sponges, those commonly used being divided into grades, from the delicate face sponge to the coarse specimens used for washing carriages. Then there are hundreds of kinds of sponges which have no value but to form veritable mimic forest growths at the bottom of the sea (Fig. 14). Some grow upon stones or sea mud and are brilliantly colored; others again are like glass, and all represent one of the lowest forms of animal life, yet one of the most beautiful, and one that is very useful.

In handling a sponge the most indifferent person has not failed to observe two peculiarities, one that the sponge is soft, another that it is filled with holes, small and large, and has a marvelous faculty of retaining water, in which property lies its value to man. Now if we take a sponge and cut down through it, making a section, we shall find that these holes are nothing more or less than doors or mouths which lead into the interior of the sponge. If we are so fortunate as to have a live sponge to study, we shall see that water is being forced through all the small pores and out into the larger ones; and if we could examine the water, we should see that the water which passed in, is laden with living creatures which have been described in a previous chapter, while the water which is discharged contains little or no living matter. The reader will have suspected what this in-going and out-coming is. It is the operation of eating on the part of the sponge, which, while it looks very much like a plant and appears to be growing from the ground, is an animal, or a community of many cells--a many-celled animal.

In our section of a sponge we may follow the winding channels which connect one part of the sponge with the other, and we see that the body is a mass of fibers made up of curious and beautifully shaped objects called spicules (Fig. 15). The spicules are the bones of sponges, the hard portion, the framework. In the sponge we find here and there little oval rooms, and in these are packed, side by side, minute objects with tails (Fig. 16). Each little cell has its tail upon the outside, which is really a whip or lash, used for capturing passing food. In these rooms the cells congregate and are fed by the constant onward flow of water laden with food. The food is in the shape of minute animals and plants which these little whips catch as they pass by. The whips have another purpose; their constant motion serves to force the water along through the canals, carrying air as well as food.

Some of the sponges have very singular shapes. One is called the finger sponge, and often takes the form of a hand. Others are very long and slender (Fig. 17). Some are perfectly round; others creep over stones and form a brilliant red matting, a charming object in the water.

The great vase or seat sponges are often the habitations of animals of various kinds--shrimps, crabs, and fishes. After a hurricane I have found a windrow of them on the beaches. When the sponge is taken from the water it is fleshy and seems covered with a reddish colored mass of jelly, or it is black, brown, or yellow, as the case may be. The sponge of commerce is the skeleton, the mass of living spicules after all the animal matter has been removed and the framework, elastic and soft, thoroughly bleached.

The variety in shape, color, and size in sponges is remarkable and can not be appreciated until a collection of these lowly animals is seen with the individuals side by side. In such a collection one sponge, shown in Figure 18, will attract the observer for its remarkable beauty; indeed few would consider it anything but a beautiful glass vase. Some years ago one was brought to England from the South Pacific and sold for several hundred dollars. It was believed to be the work of some skilled native artist in glass. But finally some one discovered that the natives did not make them, but hooked them up from the bottom of the ocean, when they had no resemblance to the glass vases of commerce sold for enormous sums under the title of Venus's flower basket. When first brought up the vase was dark and covered with mud; then it was found that it was a sponge, and that the so-called glass was merely the interior, the framework over which was drawn the ugly exterior animal matter. It is needless to say that the enormous price of the Venus's flower basket dropped, and it can now be bought for a few cents.

No more beautiful object can be imagined than this sponge, known as the Euplectella. It has great wisps of glasslike matter at the bottom, which anchor it in the sand or mud, and the framework appears to rise upward in whirls, the surface being made up of squares or basket work, so artificial that it is difficult to believe that it is not of human make. This vase has a top to it. It is perforated with squares, and is often a prison for various small animals, as crabs, which have passed into the interior when very small and which are now too large to escape, only their claws or feelers being seen protruding through the little portholes.

The sponges in their habits show a variety of tastes. Many grow in the mud, the majority upon rocks. On the New England shores there is one of a yellowish hue which lives in the sand. It is very light, and the pores are so fine that the sand does not enter them. After a storm on Cape Cod thousands are found on the beaches, blown far inshore. Black and pure white sponges are found in fresh water as well as in salt. They increase by depositing eggs. In one stage of their development the young (Fig. 14, V.) are free-swimming animals.

III. THE JELLYFISHES

Among the most beautiful and fragile of all animals are the singular forms which we call jellyfishes (Fig. 19). They are so delicate that we can not lift them, and in many instances they have ninety-five per cent of water in their composition. They would almost seem to be purely ornamental did we not know that they fill an important niche in the hall of nature, constituting almost the sole food of many whales.

The jellyfishes are found in all waters, salt and even fresh. They may be seen floating near or at the surface, often in vast numbers. Sometimes they are found deep in the heart of the upper part of the ocean, often in such quantities that the water appears to be filled with their graceful shapes.

In the Santa Catalina Channel a beautiful lavender-hued form is common, the water being alive with them at times, and I have seen specimens with tentacles streaming behind them an estimated length of twenty feet, the entire animal appearing like a huge comet in the blue sky of the ocean. Mrs. Agassiz describes a jellyfish called Cyanea which was six feet across its disk and which had tentacles over one hundred feet in length. Specimens have been seen in East Indian waters which were much larger, having an estimated weight of several tons. An English naturalist describes one which stranded in India and gave out so vivid a light at night that the natives were afraid to approach it; yet large as was this monster, a few hours in the sun caused it to disappear or literally evaporate, water forming so large a part of its make-up.

In appearance the jellies resemble umbrellas, dinner plates, or inverted bowls, from which depend streamers or tentacles of various kinds and shapes, often richly colored, especially the very minute forms. The mouth is in the center, the eyes are around the edge of the disk, while the huge tentacles, which can be lifted or lowered as fancy dictates, are so many fishing lines by which this jelly finds its food. I have often watched them floating near the surface, the delicate vermilion-tinted tentacles floating gracefully about, and serving as so many tempting baits. Should a sardine or other small fish venture to attack this tempting lure, we can almost imagine it struck by an electric shock, as it rolls over dead. The secret is very easily discovered. Lift the tentacles with the hand and a burning sensation will be experienced, in some cases very painful. The tentacles of the jellyfish are armed with stings.

The weapons are known as lassos (Fig. 20). Under the microscope the tentacles appear to be filled with little cells or oblong objects, which when examined are found to be capsules (C) resembling long glasslike bodies in which is coiled a thread. This latter is a miniature javelin, and when the tentacle of a jellyfish is seized by a fish or an enemy, tens of thousands of these cells literally explode (D) and the javelin springs out like a Jack-in-the-box (A) and penetrates the intruder. With many jellyfishes the effect of this bombardment is a stinging sensation. It paralyzes small fishes which, when benumbed, are lifted up by the tentacles and eaten.

The jellies develop in various ways. In Figure 21 we see a common and very beautiful form resting on the rocks. Near by are various little plantlike creatures, the young jellies, which undergo a remarkable series of changes in their growth from the egg to the adult form. Minute eggs are deposited in the autumn, which drop into the crevices of the rocks and soon change to pear-shaped objects which attach themselves to the bottom. Each little jelly pear (Fig. 22) divides after a while until it looks like a pile of platters one upon the other. The upper one dies, and the rest break away, each becoming a separate jellyfish, which ultimately grows to be a giant.