Life's Simplest Children: How they Live, and Move, and Build

HO are Life's simplest children, and where are they to be found? Let us try to answer the second question first, and rubbing the scales from off our eyes, peer into the hidden secrets of nature; and when we have tracked to their home the tiny beginnings of life, we will examine them and try to understand how they live.

How calm, and lovely, and still the sea looks on a warm, sunny, breezeless day of summer, and how happy we can imagine the myriads of creatures to be that float in its waters! We know many of them well, especially those which come close up to the shore. The small fry of the fish, the shrimp and the sand-hopper, the large jelly-fish, and the tiny transparent jelly-bells (see 3', Fig. 22), only to be seen by the keenest eye, as we dip out the water carefully in a glass. Surely these minute jelly-bells with their invisible hanging threads must be some of the simplest and lowest forms of life. Not so, they are really very high up in the world compared with the forms we are seeking.

If, indeed, we come out late some autumn evening when, after the sun has set and the sky is dark, the sea in some sheltered bay appears all covered with a sheet of light, we may see some of the beings of the lowest order of life with the naked eye; for when we dip the liquid fire out in a glass vessel and examine it, we find in it hundreds and thousands of tiny bags of slime giving out the bright specks of light, and these little Noctilucæ, or night-glows (2, Fig. 3), are, as we shall presently see, some of Life's simplest children, although not by any means the most simple of the order.

No; to begin at the very beginning and find the first known attempts at a living being, we must search long and carefully, not merely with our own eyes, but with the microscope. Then we may perhaps be fortunate enough to discover some wondrously small creature like that on the next page, which Professor Haeckel took out of the sunny blue waters of the Mediterranean, near Nice, in 1864. The largest specimen to be found will be smaller than the smallest pin's head, yet when seen under the microscope, this tiny speck appears with outstretched threads, a living animal (see a,  Fig. 1), floating in search of food. Examine it how we will, we can find in it no mouth, no stomach, no muscles, no nerves, no parts of any kind. It looks merely like a minute drop of gum with fine grains in it, floating in the water, sometimes with its fine threads outstretched, sometimes as a mere drop; and if we take it out and analyse the matter of which it is made, we find that is much the same as a speck of white-of-egg. Is it possible that it can be alive? How can we be sure? In the first place it breathes. If it be kept in a drop of water, it uses up the oxygen in it, and makes the water bad, by breathing into it carbonic acid; then it moves, and, as we shall see presently, can draw in and throw out its fine threads when and where it chooses; again it eats, feeding on the minute jelly-plants in the water, or even on animals higher in the world than itself; and lastly, it grows and increases, for when it is too large to be comfortable it splits in two, and each half goes its way as a living animal.

The Thread-slime. (Protogenes.)—Haeckel. a, In its natural round shape, immensely magnified ; b, spreading itself over a small animal, c (Ceratium), to suck the soft body out of the shell.

Let us see how one behaved which Professor Haeckel took out of the sea and kept in a watch-glass under a microscope. When he first looked at it he found that it was drawn up in a lump with a minute animal and a plant-cell in the middle of its slime, and close by it in the water lay a small living animal called a Ceratium (c,  Fig. I), which has a hard case or shell. After a while, as he watched, he saw the thread-slime put out its fine threads on all sides (a,  Fig. I). Soon the threads on the right side touched the shell of the Ceratium. Here was food, and the body of the Thread-slime  evidently became aware of it at once, for all the little grains in the slime began to course to and fro, and the threads touching the Ceratium lengthened out and stretched more and more over it, while all those on the other side which had not found any food were drawn in, (b,  Fig. I). Six hours later when Dr. Haeckel looked again, to his astonishment the thread-slime had disappeared, but on examining more closely he discovered it completely spread in patches over the shell of the Ceratium. It had drawn its whole body after the pioneering threads and wrapped itself round its prey. Next morning when he looked again, lo! it was back in its original place, and by its side lay the Ceratium shell quite empty,  together with the skeletons of the other two forms which had been inside the Thread-slime!

This little drop of slime without eyes or ears or parts of any kind, knew how to find its food; without muscles or limbs it was able to creep over it; without a mouth it could suck out its living body; without a stomach it could digest the food in the midst of its own slime, and throw out the hard parts which it did not want.

This is the history of one of Life's simplest children.

Here is another (Fig. 2), which lives not only in the sea but also in pools and puddles, and in the gutters of our streets and of our house-tops. Any where that water lies stagnant these little drops of slime will grow up and make it their home. Sometimes few and far between, sometimes in crowds, so that the whole pond would seem alive if we could see them, they live, and multiply, and die under our very feet. Can anything be less like an animal than this shapeless mass (a, Fig. 2)? Yet under a strong microscope it may be seen moving lazily along by putting out a thick slimy finger and then letting all the rest of its body flow after it. When it touches food it flows over it just as the Thread-slime did, and dissolving the soft parts sends out the hard refuse anywhere, it does not matter where, for it has no skin over its body, being merely one general mass of slime.

The Finger Slime. (Protamceba.)—Haeckel. a, At rest. b, Feeding on minute slime-plants.

And now, before we go on to other forms, let me ask you to pause and think what these little slime-specks tell us about the wonderful powers of Life. Can you guess at all how these creatures do their work? We are obliged to have eyes to see our food, nerves and muscles to enable us to feel and grasp it, mouths to eat it, stomachs which secrete a juice in order to dissolve it, and a special pump, the heart, to drive it into the different parts of our body. But in these tiny slime-animals life has nothing better to work with than a mere drop of living matter, which is all alike throughout, so that if you broke it into twenty pieces every piece would be as much a living being as the whole drop. And yet by means of the wonderful gift of life, this slime-drop lives, and breathes, and eats, and increases, shrinks away if you touch it, feels for its food, and moves from place to place, changing its shape to form limbs and feeling-threads, which are lost again as soon as it no longer needs them.

Nor have we yet learnt one-half of the marvels which can be wrought in living specks of slime. For, on further inquiry, we find these simple forms developing two quite different modes of life. In the one case the slime is moulded itself into delicate forms, making creatures with mouths, with suckers, and with delicate lashes to drive the body through the water; while in the other case, remaining a simple drop with delicate threads, it has learned to build a solid covering of the most exquisite delicacy.

To the first class belongs our little Noctiluca, and the forms drawn by its side in Fig. 3. To the second belong the microscopic shells (Fig. 4) which form our chalk. Look at the little wriggling creatures at 1 Fig. 3, small as they look here, they are drawn many thousand times larger than they really are in life, and yet they are much more perfectly formed than either the thread-slime or the finger-slime. They have actually a kind of skin, and do not throw out threads here and there, but are provided with a little whip of slime, which they lash to and fro, and so drive themselves through the water. These microscopic forms called monads  grow up in water in which flowers have stood for many days till their stalks begin to decay, and in infusions  of hay or straw, made by pouring hot water upon them and letting it stand and for this reason the little beings are called infusoria. In such impure water, under a powerful microscope you may see them darting along by thousands. But the whip does riot only serve them as an oar, it also sends the food they meet with into a tiny opening, one of life's first attempts at a mouth. With a little jerk, when the creature is still or fixed to the bottom, the whip drives still smaller beings than the monad itself into its wide-opened cavity, and there they are digested in a little watery bubble, which may be clearly seen in its body. The Noctiluca or night glow  (2, Fig. 3) is much larger, being often as large as the head of a small pin, and just below the outer rim of its slimy bag the sparks of light are given out. It has been reckoned that there are as many as 30,900 Noctilucæ in one cubic inch of phosphorescent water, and it is almost impossible to grasp the idea of the millions upon millions of these tiny forms which must be floating over a sea which is giving out a glow of liquid fire for miles and miles. And it is only because of this light that we realise that they are there. There are just as many other forms in the water on every side of us, while we dream nothing of this teeming life in the midst of which we live.

Infusoria, all immensely magnified. 1, A group of monads. (Monas.) 2, The Night-glow.(Noctiluca.) 3, Bell-flower.(Vorticella.)

We cannot stop here to speak of the tube-sucker  and all his relations, which have a mouth at the end of every tube; nor of the beautiful little bell-flower  which may be seen in any pond or in sea-water, with its hanging bells whirling the food in by their little fringe of hairs (a,  Fig. 3); or shutting up with the food inside, and starting back by curling up their slender stem (b);  or splitting in two (c)  and sending off buds (d, d),  which swim away to form new colonies elsewhere. All these wondrous little beings are some of life's simplest children, and one and all are made of nothing but slime, while yet they live, and move, and seek their daily food.

But all these are naked and homeless, and to a great extent unprotected. Gulped down in thousands and millions by each other, and by other animals, they are defenceless and weak against attacks. It would certainly be better for them if they could have solid shells to cover their soft bodies, and to protect them in many dangers. And so we find that even in this lowest stage of life necessity is the "mother of invention;" and drops of slime, no higher than the thread-slime (Fig. I), have learned to build shells around their delicate bodies.

These shell-builders live chiefly in the sea, and there you may find them if you search carefully by the help of a strong magnifying glass in the ooze of oyster-beds, or under the leaves of the delicate green seaweed, or in the muddy sand of the sea-shore. The most common forms will be those shown at a, e, f,  and g  in Fig. 4; and, though they are so very small, you may if you are fortunate see them clinging by their fine slime-threads to the weeds or the mud.

These animals are, as I have said, simple slime-drops like the thread-slime,  but they add to the list of wonderful things that such slime can do, for they take out of the sea-water, particle by particle, the lime which is dissolved in it, and build around their soft bodies the solid shell or skeleton in which they live. Nor is this all; even if they all built the same simple shell, it would be very puzzling to imagine how they do it, but they do much more. They build shells in many different shapes, often with the most beautiful and complicated patterns upon them. All but the simplest shells have several chambers in them, a new one being added as soon as the animal outgrows the last one; and in the partition between each chamber there is a minute hole through which a thin thread of slime passes into the next chamber, so that the whole body is joined together throughout the shell. On account of these holes these lime-builders have been called Foraminifera  from foramen  a hole, fero  I bear.

a, Miliolite, with a shell of lime, a', The same, with a shell of sand. b, Peneropolis. c, Orbitolite. In these shells the animals feed only from the edge of the shell. d, Globigerina. e, Lagena. f, Nodosarina. g, Rotalia. h, Textularia. These shells are full of holes, out of which the animal puts threads to feed.

Let us now take one of these shells (a,  Fig. 4), and see how it was built up. The grown animal as he looks when the shell is taken off him is shown in Fig. 5. In the beginning, when he is quite young, he is merely a round drop (1, Fig. 5) with a delicate transparent shell and an opening, out of which he puts his threads of slime. Then as he outgrows this first chamber he draws his slime threads together and forms a bud (2) outside the shell, and round this bud he builds a second chamber out of the end of which he again puts his threads. Then he forms the next bud (3), and goes on thus till he has built a complete shell, generally of seven chambers; and as each new compartment is so placed as to overlap the one before it, the whole when finished has the curious form a,  Fig. 4, altogether not larger than a millet-seed, from which it takes the name of Miliola. These miliolite shells may be found by the help of the microscope in the damp sand of almost any sea-shore, and while some of the shells will be empty, others will still be filled with the dark-yellow animal slime.

The jelly body of the Miliolite, a, Fig.4, showing the buds of slime, 1, 2, 3, etc., round which each chamber is built.—Carpenter.

Think of the constant manufacture of such delicate shells as these going on all over the world, and the makers but a drop of slime! And lest you should be inclined to think little of it as a mere mechanical process, the miliolite himself tells us another story, for from time to time we find miliolites with shells made,—not of lime,—but of grains of sand and tiny broken pieces of shell (a',  Fig. 4), which the little architect has used to build the walls of his house, when for some reason the ordinary material was deficient. It seems to me that the power of this living drop to choose its own materials is one of the most wonderful facts in the history of life's simplest children.

These miliolites and other Foraminifera when found clinging to sea-weed are easily placed in a saltwater aquarium, and they will then thrust their threads out of the mouth of the shell and crawl on the sides of the glass. Professor Schultze even saw a number of young miliolites born in an aquarium, and this was how it happened. He noticed one day that several of his miliolites had covered the outside  of their shells with their brown slimy body, and a few days later he could see through the microscope a number of dark-looking specks gradually loosening themselves from this slime.

There were as many as forty of these specks on one shell, and after a time he could distinguish that every speck was a tiny miliolite, having only one chamber (1, Fig. 5) to begin life in, the shell of which was so pale and transparent that he could see the slime within it. As soon as each one shook himself free from the rest of the slime, he put out his threads and crawled away on the glass to get his own living; and now when Professor Schultze examined the shell of the parent miliolite, he found it almost empty. The mother had broken herself up into her little children!

A miliolite builds generally only six or seven chambers, but other forms, such as c,  Figure 4, build hundreds of separate apartments. This particular form c,  which is called an Orbitolite, has often as many as fifteen rings, each with its numerous chambers, even when the whole shell is only as large as the head of a small pin; and in ages long gone by, the larger Orbitolites had a far greater number of rings and thousands of chambers in one single shell. The animal builds these in the same way as we have seen the Miliolite do it, only after he has made one round of chambers with a hole in each, he puts out slime-threads at every hole and joins them into a ring with swellings in it, like beads upon a string, and round these he builds the next row of chambers. So he goes on increasing his home till he reaches his full size, and then Professor Parker tells us that the slime of the outer row often breaks up into myriads of young Orbitolites just as the body of the Miliolite did. At the same time these forms can also multiply by merely breaking in half as the naked Finger-slime does, and if by accident a piece of an Orbitolite is broken off it can form a new and complete shell of its own.

If you have now understood how the Orbitolite grows, you will see that the only communication it has with the outer world is through the minute threads which stretch out of the holes of the chambers in the last  ring (see c,  Fig. 4), and that the slime in all the middle chambers can get food in no other way than by its passing from the outside right through all the other rings. This is a tedious way of getting food, and we shall find that some of the forms shown in Fig. 4 have escaped from it in a most ingenious way. These forms (d  to h,  Fig. 4) have hit upon the plan of keeping their thin threads stretched out like the thread-slime (a,  Fig. 1) all the time they are laying down their lime house. The consequence of this is that wherever a thread has been, there a minute hole like a pin-prick is left in the shell, and while the animal can draw itself quite in out of danger, it can also come out all over the shell and take in food. Here, then, we have another stratagem taught by life to these her infant children. The slime which builds the Globigerina (a)  or the Rotalia (g)  is exactly the same as far as we can see as the slime which builds the Miliolite, and yet those drops of slime have learnt a new lesson, and each one as it is born stretches out its fine threads before constructing its shell, thus providing a thousand openings for the entrance of its food in a house not bigger than a grain of sand!

And now it only remains for us to ask how long these wondrous lime-builders have been upon the earth. We ask, and ask in vain, for we have no means of counting the vast ages during which they have lived and built. One of the largest and most complicated forms called the Nummulite  (from nummus  a coin, which it resembles), lived and died in such millions before the Alps or the Carpathians had any existence, that whole beds of limestone thousands of feet thick and stretching over hundreds of miles are made entirely of its shells; while the little Globigerina (d,  Fig. 4) and its friends were living and multiplying in still more dim and distant periods till their shells accumulated into vast beds of chalk.

A Nummulite with half the shell broken open, showing the chambers. Life size.

When the ancient Egyptians raised the pyramids of Egypt, they little dreamed that every inch of the stone they used was made of the shelly palaces of the Nummulite, constructed by little drops of slime with a skill and ingenuity far surpassing their own. As little do most Parisians think now that the limestone of which their houses are built Is almost entirely made up of Orbitolite shells. And still less does the country boy as he strolls over the chalk downs of Sussex or Hampshire suspect that the chalk under his feet is largely composed of shells of the Globigerina and the other minute forms shown in Figure 4; yet so it is. These minute slime-builders have been patiently living and building for untold ages, and are doing so still, at the bottom of the Atlantic, where the Globigerina lives in such great numbers that the falling of the shells through the water down to the bottom must be like a constant shower of snow, as is proved by the freshness of those brought up in the dredge.

When a little of the chalky mud was taken tip from the bottom at the time when the Atlantic telegraph was laid down, it was found to be almost entirely composed of Globigerina shells, and this led naturalists, who had long known that chalk was formed of shelly matter, to rub down some ordinary chalk and examine it under the microscope, and there again was our little Globigerina, often crushed and worn, but still plainly recognisable. So that, astounding as it may seem, it is nevertheless true that the vast beds of chalk stretching from Ireland to the Crimea, from Sweden to Bordeaux, are in great part formed of the dead shells of these little drops of slime.

We have paused so long over the lime-builders that we can only glance at those minute specks of slime which build their skeletons of flint instead of lime. These animals are a little higher in the world than the lime—builders, for their body has within it a small bag or capsule, buried in the middle of the slime (see Fig. 7), and in this bag the solid grains lie very thickly, and have sometimes small crystals among them, while in the slime round it there are often little oil-globules floating. If you dip a glass into the quiet bays of Nice or Messina you may be fortunate enough to bring up one or more of these little sun-slimes, but they are so tiny and transparent that even when the light falls upon them you will only distinguish them as bright specks in the water. Their threads stick out stiff and straight, and for this reason they are all classed under the name Radiolaria,  or ray-like animals.

The Sun-Slime. (Physematium.)—Haeckel. Immensely magnified, its real size being not larger than a mustard seed.

Let us look for a moment at Fig. 8, and study the solid skeletons which these Radiolaria build with the flint (or silex) which they find in minute quantities in the water. We saw that the lime-builders construct shells into which they can draw back entirely if they are attacked, but the flint-builders seem very careless in this respect, for they have large holes all over their flinty skeletons. But then, on the other hand, notice how they send out sharp spikes, which must be un. comfortable for any animal trying to snap at them, although as we have seen (p. 16) the soft thread-slime manages to suck their bodies out of the shells. Still these hard spiky outside skeletons must be a great protection to them, and we find every kind of shape devised by these wonderful architects in the construction of their tiny houses, though these are so small as to look like a grain of sand when seen by the naked eye. Perhaps the most wonderful of all is the one shown at f,  Fig. 8. It is broken open to show the three balls one within another, each kept in its place by rods of flint passing through the whole. This beautiful little shell looks just like the carved balls of the Chinese, yet, instead of being the work of intelligent man, it is built by a mere mass of slime.

Flint Shells built by slime animals. (Radiolariæ or Polycistinæ. a, Petalospyris; b, Ethmosphxra; c, Diploconus; d, Dictyopodium; e, Heliosphæra; f, Actinonima.) Immensely magnified: the real sizes are from a mere speck to that of one of these letters.

We have now learned to know the simplest of all animals; how they live, and move, and the homes they build. All the forms are not quite equally simple, for some of the higher ones have a solid spot or nucleus  in the middle of the slime, and sometimes a small watery bubble, as in the Monad or the Bell-flower, which contracts and expands at intervals: and in these forms the outside of the slime is rather thicker than the inside, so that we might say that they are on the road to having a skin, while the shell-builders have a uniform slimy body. But both classes alike belong to that first and lowest branch of the children of life, called by scientific men the Protozoa  (protos  first, zoon  animal) or first animals, The still water everywhere is swarming with them, though we may see and know nothing of them. Yet we owe them something; for not only do the dead shells of many of them form our solid ground, but those now living purify our waters by feeding upon the living and dead matter in them. These tiny slime animals are the invisible scavengers of the ocean and the pools, and in earning their own living they also work for others. When you look upon a still pond in some quiet country lane, the insects you see swimming about in it, and the plants which cover it, are not the only inhabitants, but on its surface and in its silent depths minute specks of slime are living and working though no eye can see them. Beautiful and wonderful, however, as these forms are, they are yet very low in the scale of life; they live and increase in multitudes, but in multitudes also they die and are devoured. Delicate, and frail, and helpless, they are, as it were, but first attempts at the results which life can accomplish. Let us pass on and see the next step towards higher and, in many ways, more ambitious creatures.