Chapter III: The Silver Crown (3)

The animal kingdom consists, first, of a sub-kingdom of animals which possess a spinal column, or backbone, and which are known as vertebrate animals. Such are all beasts, birds, reptiles, and fishes. There are also a variety of remotely allied marine organisms known as tunicates, sea-squirts, or ascidians (Fig. 2). There is, further, an immense group of arthropods, consisting of all insects, crab-like creatures, hundred-legs and their allies, with spiders, scorpions, tics and mites. We have also the sub-kingdom of shell-fish or molluscs, including cuttle-fishes, snails, whelks, limpets, the oyster, and a multitude of allied forms. A multitudinous sub-kingdom of worms also exists, as well as another of star-fishes and their congeners. There is yet another of zoophytes, or polyps, and another of sponges, and, finally, we have a sub-kingdom of minute creatures, or animalculæ, of very varied forms, which may make up the sub-kingdom of _Protozoa_, consisting of animals which are mostly unicellular.

Multitudinous and varied as are the creatures which compose this immense organic world, they nevertheless exhibit a very remarkable uniformity of composition in their essential structure. Every living creature from a man to a mushroom, or even to the smallest animalcule or unicellular plant is always partly fluid, but never entirely so. Every living creature also consists in part (and that part is the most active living part) of a soft, viscid, transparent, colorless substance, termed protoplasm, which can be resolved into the four elements, oxygen, hydrogen, nitrogen and carbon. Besides these four elements, living organisms commonly contain sulphur, phosphorus, chlorine, potassium, sodium, calcium, magnesium and iron.

In the fact that living creatures always consist of the four elements, oxygen, hydrogen, nitrogen and carbon, we have a fundamental character whereby the organic and inorganic (or non-living) worlds are to be distinguished, for as we have seen, inorganic bodies, instead of being thus uniformly constituted, may consist of the most diverse elements and sometimes of but two or even of only one.

Again, many minerals, such as crystals, are bounded by plain surfaces, and, with very few exceptions (spathic and hematite iron and dolomite are such exceptions) none are bounded by curved lines and surfaces, while living organisms are bounded by such lines and surfaces.

Yet, again, if a crystal be cut through, its internal structure will be seen to be similar throughout. But if the body of any living creature be divided, it will, at the very least, be seen to consist of a variety of minute distinct particles, called "granules," variously distributed throughout its interior.

All organisms consist either--as do the simplest, mostly microscopic, plants and animals--of a single minute mass of protoplasm, or of a few, or of many, or of an enormous aggregation of such before-mentioned particles, each of which is one of those bodies named a "cell" (Fig. 3). Cells may, or may not, be enclosed in an investing coat or "cell-wall." Every cell generally contains within it a denser, normally spheroidal, body known as the nucleus.

Now protoplasm is a very unstable substance--as we have seen many substances are whereof nitrogen is a component part--and it possesses active properties which are not present in the non-living, or inorganic world. In the latter, differences of temperature will produce motion in the shape of "currents," as we have seen with respect to masses of air and water. But in a portion of protoplasm, an internal circulation of currents in definite lines will establish itself from other causes.

Inorganic bodies, as we have seen, will expand with heat, as they may also do from imbibing moisture; but living protoplasm has an apparently spontaneous power of contraction and expansion under certain external conditions which do not occasion such movements in inorganic matter.

Under favoring conditions, protoplasm has a power of performing chemical changes, which result in producing heat far more gently and continuously than it is produced by the combustion of inorganic bodies. Thus it is that the heat is produced which makes its presence evident to us in what we call "warm-blooded animals," the most warm-blooded of all being birds.

Protoplasm has also the wonderful power of transforming certain adjacent substances into material like itself--into its own substance--and so, in a sense, creating a new material. Thus it is that organisms have the power to nourish themselves and grow. An animal would vainly swallow the most nourishing food if the ultimate, protoplasmic particles of its body had not this power of "transforming" suitable substances brought near them in ways to be hereinafter noticed.

Without that, no organism could ever "grow." The growth of organisms is utterly different from the increase in size of inorganic bodies. Crystals, as we have seen, grow merely by external increment; but organisms grow by an increment which takes place in the very innermost substance of the tissues which compose their bodies, and the innermost substance of the cells which compose such tissues; this peculiar form of growth is termed _intussusception_.

Protoplasm, after thus augmenting its mass, has a further power of spontaneous division, whereby the mass of the entire organism whereof such protoplasm forms a part, is augmented and so growth is brought about.

The small particles of protoplasm which constitute "cells" are far indeed from being structureless. Besides the nucleus already mentioned there is a delicate network of threads of a substance called _chromatin_ within it, and another network permeating the fluid of the cell substance, which invest the nucleus often with further complications. These networks generally perform (or undergo) a most complex series of changes every time a cell spontaneously divides. In certain cases, however, it appears that the nucleus divides into two in a more simple fashion, the rest of the cell contents subsequently dividing--each half enclosing one part of the previously divided nucleus. It is by a continued process of cell division that the complex structures of the most complex organisms is brought about.

The division of a cell, or particle of protoplasm, is indeed a necessary consequence of its complete nutrition.

For new material can only be absorbed by its surface. But as the cell grows, the proportion borne by its surface to its mass, continually decreases; therefore this surface must soon be too small to take in nourishment enough, and the particle, or cell, must therefore either die or divide. By dividing, its parts can continue the nutritive process till their surface, in turn, becomes insufficient, when they must divide again, and so on. Thus the term "feeding" has two senses. "To feed a horse," ordinarily means to give it a certain quantity of hay, oats or what not; and such indeed is one kind of feeding. But obviously, if the nourishment so taken could not get from the stomach and intestines into the ultimate particles and cells of the horse's body, the horse could not be nourished, and still less could it grow. It is this latter process, called assimilation, which is the real and essential process of feeding, to which the process ordinarily so called is but introductory.

Protoplasm has also the power of forming and ejecting from its own substance, other substances which it has made, but which are of a different nature to its own. This function, as before said, is termed secretion; and we know the liver secretes bile, and that the cow's udder secretes milk.

Here again we have an external and an internal process. The milk is drawn forth from a receptacle, the udder, into which it finds its way, and so, in a superficial sense, it may be called an organ of secretion. Nevertheless the true internal secretion takes place in the innermost substance of the cells or particles of protoplasm, of the milk-land, which particles really form that liquid.

But every living creature consists at first entirely of a particle of protoplasm. Therefore every other kind of substance which may be found in every kind of plant or animal, must have been formed through it, and be, in fact, a secretion from protoplasm. Such is the rosy cheek of an apple, or of a maiden, the luscious juice of the peach, the produce of the castor-oil plant, the baleen that lines the whale's enormous jaws, as well as that softest product, the fur of the chinchilla. Indeed, every particle of protoplasm requires, in order that it may live, a continuous process of exchange. It needs to be continuously first built up by food, and then broken down by discharging what is no longer needful for its healthy existence. Thus the life of every organism is a life of almost incessant change, not only in its being as a whole, but in that of all its protoplasmic particles also.

The clear space within it is a contractile vesicle. The dark body is the nucleus. In the right-hand figure there is shown a particle of food, passing through the external surface.]

Prominent among such processes is that of an interchange of gases between the living being and its environment. This process consists in an absorption of oxygen and a giving-out of carbonic acid, which exchange is termed respiration.

Lastly, protoplasm has a power of motion when appropriately acted on. It will then contract or expand its shape by alternate protrusions and retractions of parts of its substance. These movements are termed amoebiform, because they quite resemble the movements of a small animalcule which is named amoeba. (See Fig. 4.)

Such is the ultimate structure, and such are the fundamental activities or functions of living organisms, as far as they can here be described, from the lowest animalcule and unicellular plant, up to the most complex organisms and the body of man himself.

INHABITANTS OF MY POOL

(FROM MAGIC GLASSES.)

BY ARABELLA B. BUCKLEY.

The pool lies in a deep hollow among a group of rocks and boulders, close to the entrance of the cove, which can only be entered at low water; it does not measure more than two feet across, so that you can step over it, if you take care not to slip on the masses of green and brown seaweed growing over the rocks on its sides, as I have done many a time when collecting specimens for our salt-water aquarium. I find now the only way is to lie flat down on the rock, so that my hands and eyes are free to observe and handle, and then, bringing my eye down to the edge of the pool, to lift the seaweeds and let the sunlight enter into the chinks and crannies. In this way I can catch sight of many a small being either on the seaweed or the rocky ledges, and even creatures transparent as glass become visible by the thin outline gleaming in the sunlight. Then I pluck a piece of seaweed, or chip off a fragment of rock with a sharp-edged collecting knife, bringing away the specimen uninjured upon it, and place it carefully in its own separate bottle to be carried home alive and well.

Now though this little pool and I are old friends, I find new treasures in it almost every time I go, for it is almost as full of living things as the heavens are of stars, and the tide as it comes and goes brings many a mother there to find a safe home for her little ones, and many a waif and stray to seek shelter from the troublous life of the open ocean.

You will perhaps find it difficult to believe that in this rock-bound basin there can be millions of living creatures hidden away among the fine feathery weeds; yet so it is. Not that they are always the same. At one time it may be the home of myriads of infant crabs, not an eighth of an inch long, another of baby sea-urchins only visible to the naked eye as minute spots in the water, at another of young jelly-fish growing on their tiny stalks, and splitting off one by one as transparent bells to float away with the rising tide. Or it may be that the whelk has chosen this quiet nook to deposit her leathery eggs; or young barnacles, periwinkles, and limpets are growing up among the green and brown tangles, while the far-sailing velella and the stay-at-home sea-squirts, together with a variety of other sea-animals, find a nursery and shelter in their youth in this quiet harbor of rest.

And besides these casual visitors there are numberless creatures which have lived and multiplied there, ever since I first visited the pool. Tender red, olive-colored, and green seaweeds, stony corallines, and acorn-barnacles lining the floor, sea-anemones clinging to the sides, sponges tiny and many-colored hiding under the ledges, and limpets and mussels wedged in the cracks. These can be easily seen with the naked eye, but they are not the most numerous inhabitants; for these we must search with a magnifying glass, which will reveal to us wonderful fairy-forms, delicate crystal vases with tiny creatures in them whose transparent lashes make whirlpools in the water, living crystal bells so tiny that whole branches of them look only like a fringe of hair, jelly globes rising and falling in the water, patches of living jelly clinging to the rocky sides of the pool, and a hundred other forms, some so minute that you must examine the fine sand in which they lie under a powerful microscope before you can even guess that they are there.

(Natural size.)

1, _Ulva Linza._ 2, _Sphacelaria filicina._ 3, _Polysiphonia urceolata._ 4, _Corallina officinalis._]

So it has proved a rich hunting-ground, where summer and winter, spring and autumn, I find some form to put under my magic glass. There I can watch it for weeks growing and multiplying under my care; moved only from the aquarium, where I keep it supplied with healthy sea-water, to the tiny transparent trough in which I place it for a few hours to see the changes it has undergone. I could tell you endless tales of transformations in these tiny lives, but I want to-day to show you a few of my friends, most of which I brought yesterday fresh from the pool, and have prepared for you to examine.

s, Spores in the cells, _ss_, Spores swimming out. _h_, Holes through which spores have escaped.]

Let us begin with seaweeds. I have said that there are three leading colors in my pool--green, olive, and red--and these tints mark roughly three kinds of weed, though they occur in an endless variety of shapes. Here is a piece of the beautiful pale green seaweed, called the Laver or Sea-Lettuce, _Ulva Linza_ (1, Fig. 1),[1] which grows in long ribbons in a sunny nook in the water. I have placed under the first microscope a piece of this weed which is just sending out young seaweeds in the shape of tiny cells, with lashes very like those we saw coming from the moss-flower, and I have pressed them in the position in which they would naturally leave the plant. You will also see on this side several cells in which these tiny spores are forming, ready to burst out and swim; for this green weed is merely a collection of cells, like the single-celled plants on land. Each cell can work as a separate plant; it feeds, grows, and can send out its own young spores.

[Footnote 1: The slice given in Fig. 2 is from a broader-leaved form, _U. lactuca_, because this species, being composed of only one layer of cells, is better seen. _Ulva Linza_ is composed of two layers of cells.]

This deep olive-green feathery weed (2, Fig. 1), of which a piece is magnified under the next microscope (2, Fig. 3), is very different. It is a higher plant, and works harder for its living, using the darker rays of sunlight which penetrate into shady parts of the pool. So it comes to pass that its cells divide the work. Those of the feathery threads make the food, while others, growing on short stalks on the shafts of the feather, make and send out the young spores.

Lastly, the lovely red threadlike weeds, such as this _Polysiphonia urceolata_ (3, Fig. 1), carry actual urns on their stems like those of mosses. In fact, the history of these urns (see 3, Fig. 3), is much the same in the two classes of plants, only that instead of the urn being pushed up on a thin stalk as in the moss, it remains on the seaweed close down to the stem, when it grows out of the plant-egg, and the tiny plant is shut in till the spores are ready to swim out.

2, _Sphacelaria filicina._ 3, _Polysiphonia urceolata._ 4, _Corallina officinalis._]

The stony corallines (4, Figs. 1 and 3), which build so much carbonate of lime into their stems, are near relations of the red seaweeds. There are plenty of them in my pool. Some of them, of a deep purple color, grow upright in stiff groups about three or four inches high; and others, which form crusts over the stones and weeds, are a pale rose color; but both kinds, when the plant dies, leaving the stony skeleton (1, Fig. 4), are a pure white, and used to be mistaken for corals. They belong to the same order of plants as the red weeds, which all live in shady nooks in the pools, and are the highest of their race.

1, _Corallina officinalis._ 2, _Sertularia filicula._]

My pool is full of different forms of these four weeds. The green ribbons float on the surface rooted to the sides of the pool, and, as the sun shines upon it, the glittering bubbles rising from them show that they are working up food out of the air in the water, and giving off oxygen. The brown weeds lie chiefly under the shelves of rocks, for they can manage with less sunlight, and use the darker rays which pass by the green weeds; and last of all, the red weeds and corallines, small and delicate in form, line the bottom of the pool in its darkest nooks.

And now if I hand round two specimens,--one a coralline, and the other something you do not yet know,--I am sure you will say at first sight that they belong to the same family, and, in fact, if you buy at the seaside a group of seaweeds gummed on paper, you will most likely get both these among them. Yet the truth is; that while the coralline (1, Fig. 4) is a plant, the other specimen (2), which is called _Sertularia filicula_, is an animal.

This special sertularian grows up right in my pool on stones or often on seaweeds, but I have here (Fig. 5) another and much smaller one which lives literally in millions hanging its cups downwards. I find it not only under the narrow ledges of the pool sheltered by the seaweed, but forming a fringe along all the rocks on each side of the cove near to low-water mark, and for a long time I passed it by thinking it was of no interest. But I have long since given up thinking this of anything, especially in my pool, for my magic glass has taught me that there is not even a living speck which does not open out into something marvellous and beautiful. So I chipped off a small piece of rock and brought the fringe home, and found, when I hung it up in clear sea-water as I have done over this glass trough (Fig. 5) and looked at it through the lens, that each thread of the dense fringe, in itself not a quarter of an inch deep, turns out to be a tiny sertularian with at least twenty mouths. You can see this with your pocket lens even as it hangs here, and when you have examined it you can by and by take off one thread and put it carefully in the trough. I promise you a sight of the most beautiful little beings which exist in nature.

Come and look at it. It is a horny-branched stem with a double row of tiny cups all along each side. Out of these cups there appear a row of tiny cups all along each side (see Fig. 5), Out of these cups there appear from time to time sixteen minute transparent tentacles as fine as spun glass, which wave about in the water. If you shake the glass a little, in an instant each crystal star vanishes into its cup, to come out again a few minutes later; so that now here, now there, the delicate animal-flowers spread out on each side of the stem, and the tree is covered with moving beings. These tentacles are feelers, which lash food into a mouth and stomach in each cup, where it is digested and passed, through a hole in the bottom, along a jelly thread which runs down the stem and joins all the mouths together. In this way the food is distributed all over the tree, which is, in fact, one animal with many feeding-cups. Some day I will show you one of these cups with the tentacles stretched out and mounted on a slide, so that you can examine a tentacle with a very strong magnifying power. You will then see that it is dotted over with cells, in which are coiled fine threads. The animal uses these threads to paralyze the creatures on which it feeds, for at the base of each thread there is a poison gland.

In the larger Sertularia the whole branched tree is connected by jelly threads, running through the stem, and all the thousands of mouths are spread out in the water. One large form called _Sertularia cupressina_ grows sometimes three feet high and bears as many as a hundred thousand cups, with living mouths, on its branches.

The next of my minute friends I can only show to the class in a diagram, but you will see it under the fourth microscope by and by. I had great trouble in finding it yesterday, though I know its haunts upon the green weed, for it is so minute and transparent that even when the weed is in a trough a magnifying-glass will scarcely detect it. And I must warn you that if you want to know any of the minute creatures we are studying, you must visit one place constantly. You may in a casual way find many of them on seaweed, or in the damp ooze and mud, but it will be by chance only; to look for them with any certainty you must take trouble in making their acquaintance.

1, _Thuricolla_ erect. 2, Retracted. 3, Dividing. 4, _Chilomonas amygdalum. hc,_ Horny carapace, _cv_, Contractile vesicle. _v_ Closing valves.]

Turning then to the diagram (Fig. 6) I will describe it as I hope you will see it under the microscope--a curious, tiny, perfectly transparent open-mouthed vase standing upright on the weed, and having an equally transparent being rising up in it and waving its tiny lashes in the water. This is really all one animal, the vase _hc_ being the horny covering or carapace of the body, which last stands up like a tube in the centre. If you watch carefully, you may even see the minute atoms of food twisting round inside the tube until they are digested, after they have been swept in at the wide open mouth by the whirling lashes. You will see this more clearly if you put a little rice-flour, very minutely powdered and colored by carmine, into the water; for you can trace these red atoms into some round spaces called _vacuoles_ which are dotted over the body of the animal, and are really globules of watery fluid in which the food is probably partly digested.

You will notice, however, one round clear space _(cv)_ into which they do not go, and after a time you will be able to observe that this round spot closes up or contracts very quickly, and then expands again very slowly. As it expands it fills with a clear fluid, and naturalists have not yet decided exactly what work it does. It may serve the animal either for breathing, or as a very simple heart, making the fluids circulate in the tube. The next interesting point about this little being is the way it retreats into its sheltering vase. Even while you are watching, it is quite likely it may all at once draw itself down to the bottom as in No. 2, and folding down the valves _w_ of horny teeth which grow on each side, shut itself in from some fancied danger. Another very curious point is that, besides sending forth young ones, these creatures multiply by dividing in two (see No. 3, Fig. 6), each one closing its own part of the vase into a new home.

There are hundreds of these Infusoria, as they are called, in my pond, some with vases, some without, some fixed to weeds and stones, others swimming about freely. Even in the water-trough in which this Thuricolla stands, I saw several smaller forms, and the next microscope has a trough filled with the minutest form of all, called a Monad. These are so small that two thousand of them could lie side by side in an inch; that is, if you could make them lie at all, for they are the most restless little beings, darting hither and thither, scarcely even halting except to turn back. And yet though there are so many of them, and as far as we know they have no organs of sight, they never run up against each other, but glide past more cleverly than any clear-sighted fish. These creatures are mostly to be found among decaying seaweed, and though they are so tiny, you can still see distinctly the clear space contracting and expanding within them.

_a, Cocconema lanceolatum. b, Bacillaria paradoxa. c, Gomphonema marinum. d, Diatoma hyalina_.]

But if there are so many thousands of mouths to feed, on the tree-like Sertulariæ as well as in all these Infusoria, where does the food come from? Partly from the numerous atoms of decaying life all around, and the minute eggs of animals and spores of plants; but besides these, the pool is full of minute living plants--small jelly masses with solid coats of flint which are moulded into most lovely shapes. Plants formed of jelly and flint! You will think I am joking, but I am not. These plants, called Diatoms, which live both in salt and fresh water, are single cells feeding and growing just like those we took from the water-butt, only that instead of a soft covering they build up a flinty skeleton. They are so small, that many of them must be magnified to fifty times their real size before you can even see them distinctly. Yet the skeletons of these almost invisible plants are carved and chiselled in the most delicate patterns. I showed you a group of these in our lecture on magic glasses, and now I have brought a few living ones that we may learn to know them. The diagram (Fig. 7) shows the chief forms you will see on the different slides.

The first one, _Sacillaria paradoxa_ (_b_, Fig. 7), looks like a number of rods clinging one to another in a string, but each one of these is a single-celled plant with a jelly cell surrounding the flinty skeleton. You will see that they move to and fro over each other in the water.

The next two forms, _a_ and _c_, look much more like plants, for the cells arrange themselves on a jelly stem, which by and by disappears, leaving only the separate flint skeletons. The last form, _d_, is something midway between the other forms, the separate cells hang on to each other and also on to a straight jelly stem.

_a, b,_ Flint skeleton inside the jelly-cell. _a, c_ and _d, b_, Two flint skeletons formed by new valves, _c_ and _d_, forming within the first skeleton.]

Another species of Diatoma (Fig. 8) called _Diatoma vulgare_, is a very simple and common form, and will help to explain how these plants grow. The two flinty valves _a, b_ inside the cell are not quite the same size; the older one _a_ is larger than the younger one _b_ and fits over it like the cover of a pill-box. As the plant grows, the cell enlarges and forms two more valves, one _c_ fitting into the cover _a_, so as to make a complete box _ac_, and a second, _d_, back to back with _c_, fitting into the valve _b_, and making another complete _bd_. This goes on very rapidly, and in this plant each new cell separates as it is formed, and the free diatoms move about quite actively in the water.

If you consider for a moment, you will see that, as the new valves always fit into the old ones, each must be smaller than the last, and so there comes a time when the valves have become too small to go on increasing. Then the plant must begin afresh. So the two halves of the last cell open, and throwing out their flinty skeletons, cover themselves with a thin jelly layer, and form a new cell which grows larger than any of the old ones. These, which are spore-cells, then form flinty valves inside, and the whole thing begins again.

Now, though the plants themselves die, or become the food of minute animals, the flinty skeletons are not destroyed, but go on accumulating in the waters of the ponds, lakes, rivers, and seas, all over the world. Untold millions have no doubt crumbled to dust and gone back into the waters, but untold millions also have survived. The towns of Berlin in Europe and of Richmond in the United States are actually built upon ground called "infusorial earth," composed almost entirely of valves of these minute diatoms which have accumulated to a thickness of more than eighty feet! Those under Berlin are fresh-water forms, and must have lived in a lake, while those of Richmond belong to salt-water forms. Every inch of the ground under those cities represents thousands and thousands of living plants which flourished in ages long gone by, and were no larger than those you will see presently under the microscope.

These are a very few of the microscopic inhabitants of my pond, but, as you will confuse them if I show you too many, we will conclude with two rather larger specimens, and examine them carefully. The first, called the Cydippe, is a lovely, transparent living ball, which I want to explain to you because it is so wondrously beautiful. The second, the Sea-mat or Flustra, looks like a crumpled drab-colored seaweed, but is really composed of many thousands of grottos, the homes of tiny sea-animals.

1, Animal with tentacles _t_, bearing small tendrils _t'_. 2, Body of animal enlarged. _m_, Mouth. _c_, Digestive cavity. _s_, Sac into which the tentacles are withdrawn. _p_, Bands with comb-like plates. 3, Portion of a band enlarged to show the moving plates _p_.]

Let us take the Cydippe first (1, Fig. 9). I have six here, each in a separate tumbler, and could have brought many more, for when I dipped my net in the pool yesterday such numbers were caught in it that I believe the retreating tide must just have left a shoal behind. Put a tumbler on the desk in front of you, and if the light falls well upon it you will see a transparent ball about the size of a large pea marked with eight bright bands, which begin at the lower end of the ball and reach nearly to the top, dividing the outside into sections like the ribs of a melon. The creature is so perfectly transparent that you can count all the eight bands.

At the top of the ball is a slight bulge which is the mouth (_m_ 2, Fig. 9), and from it, inside the ball hangs a long bag or stomach, which opens below into a cavity, from which two canals branch out, one on each side, and these divide again into four canals which go one into each of the tubes running down the bands. From this cavity the food, which is digested in the stomach, is carried by the canals all over the body. The smaller tubes which branch out of these canals cannot be seen clearly without a very strong lens, and the only other parts you can discern in this transparent ball are two long sacs on each side of the lower end. These are the tentacle sacs, in which are coiled up the tentacles, which we shall describe presently. Lastly you can notice that the bands outside the globe are broader in the middle than at the ends, and are striped across by a number of ridges.

In moving the tumblers the water has naturally been shaken, and the creature being alarmed will probably at first remain motionless. But very soon it will begin to play in the water, rising and falling, and swimming gracefully from side to side. Now you will notice a curious effect, for the bands will glitter and become tinged with prismatic colors, till, as it moves more and more rapidly these colors, reflected in the jelly, seem to tinge the whole ball with colors like those on a soap-bubble, while from the two sacs below come forth two long transparent threads like spun glass. At first these appear to be simple threads, but as they gradually open out to about four or five inches, smaller threads uncoil on each side of the line till there are about fifty on each line. These short tendrils are never still for long; as the main threads wave to and fro, some of the shorter ones coil up and hang like tiny beads, then these uncoil and others roll up, so that these graceful floating lines are never two seconds alike.

We do not really know their use. Sometimes the creature anchors itself by them, rising and falling as they stretch out or coil up; but more often they float idly behind it in the water. At first you would perhaps think that they served to drive the ball through the water, but this is done by a special apparatus. The cross ridges which we noticed on the bands are really flat comb-like plates (_p_, Fig. 9), of which there are about twenty or thirty on each band; and these vibrate very rapidly, so that two hundred or more paddles drive the tiny ball through the water. This is the cause of the prismatic colors; for iridescent tints are produced by the play of light upon the glittering plates, as they incessantly change their angle. Sometimes they move all at once, sometimes only a few at a time, and it is evident the creature controls them at will.

This lovely fairy-like globe, with its long floating tentacles and rainbow tints, was for a long time classed with the jelly-fish; but it really is most nearly related to the sea-anemones, as it has a true central cavity which acts as a stomach, and many other points in common with the _Actinozoa_. We cannot help wondering, as the little being glides hither and thither, whether it can see where it is going. It has nerves of a low kind which start from a little dark spot (_ng_) exactly at the south pole of the ball, and at that point a sense-organ of some kind exists, but what impression the creature gains from it of the world outside we cannot tell.

I am afraid you may think it dull to turn from such a beautiful being as this, to the gray leaf which looks only like a dead dry seaweed; yet you will be wrong, for a more wonderful history attaches to this crumpled dead-looking leaf than to the lovely jelly-globe.

1, Natural size. 2, Much magnified, _s_, Slit caused by drawing in of the animal _a_.]

First of all I will pass round pieces of the dry leaf (1, Fig. 10), and while you are getting them I will tell you where I found the living ones. Great masses of the Flustra, as it is called, line the bottom and sides of my pool. They grow in tufts, standing upright on the rock, and looking exactly like hard gray seaweeds, while there is nothing to lead you to suspect that they are anything else. Yesterday I chipped off very carefully a piece of rock with a tuft upon it, and have kept it since in a glass globe by itself with sea-water, for the little creatures living in this marine city require a very good supply of healthy water and air. I have called it a "marine city," and now I will tell you why. Take the piece in your hand and run your finger gently up and down it; you will glide quite comfortably from the lower to the higher part of the leaf, but when you come back you will feel your finger catch slightly on a rough surface. Your pocket lens will show you why this is, for if you look through it at the surface of the leaf you will see it is not smooth, but composed of hundreds of tiny alcoves with arched tops; and on each side of these tops stand two short blunt spines, making four in all, pointing upwards, so as partly to cover the alcove above. As your finger went up it glided over the spines, but on coming back it met their points. This is all you can see in the dead specimen; I must show you the rest by diagrams, and by and by under the microscope.

First, then, in the living specimen which I have here, those alcoves are not open as in the dead piece, but covered over with a transparent skin, in which, near the top of the alcove just where the curve begins, is a slit (_s_ 2, Fig. 10) Unfortunately, the membrane covering this alcove is too dense for you to distinguish the parts within. Presently, however, if you are watching a piece of this living leaf in a flat water-cell under the microscope, you will see the slit slowly open, and begin to turn as it were inside out, exactly like the finger of a glove, which has been pushed in at the tip, gradually rises up when you put your finger inside it. As this goes on, a bundle of threads appears, at first closed like a bud, but gradually opening out into a crown of tentacles, each one clothed with hairs. Then you will see that the slit was not exactly a slit after all, but the round edge where the sac was pushed in. Ah! you will say, you are now showing me a polyp like those on the sertularian tree. Not so fast, my friend; you have not studied what is still under the covering skin and hidden in the living animal. I have, however, prepared a slide with this membrane removed and there you can observe the different parts, and learn that each one of these alcoves contains a complete animal, and not merely one among many mouths, like the polyp on Sertularia.

1, Animal protruding. 2, Animal retracted in the sheath, _sh_, Covering sheath, _s_, Slit. _t_, Tentacles. _m_, Mouth. _th_, Throat, _st_, Stomach. _i_, Intestine, _r_, Retractor muscle, _e_, Egg-forming parts. _g_, Nerve-ganglion.]

Each of these little beings (_a_, Fig. 10) living in its alcove has a mouth, throat, stomach, intestine, muscles, and nerves starting from the ganglion of nervous matter, besides all that is necessary for producing eggs and sending forth young ones. You can trace all these under the microscope (see 2, Fig. 11) as the creature lies curiously doubled up in its bed, with its body bent in a loop; the intestine _i_, out of which the refuse food passes, coming back close up to the slit. When it is at rest, the top of the sac in which it lies is pulled in by the retractor muscle _r_, and looks, as I have said, like the finger of a glove with the top pushed in. When it wishes to feed this top is drawn out by muscles running round the sac, and the tentacles open and wave in the water (1, Fig. 11).

Look now at the alcoves, the homes of these animals; see how tiny they are and how closely they fit together. Mr. Gosse, the naturalist, has reckoned that there are six thousand, seven hundred and twenty alcoves in a square inch; then if you turn the leaf over you will see that there is another set, fixed back to back with these, on the other side, making in all, thirteen thousand, four hundred and forty alcoves. Now a moderate-sized leaf of flustra measures about three square inches, taking all the rounded lobes into account, so you will see we get forty thousand, three hundred and twenty as a rough estimate of the number of beings on this one leaf. But if you look at this tuft I have brought, you will find it is composed of twelve such leaves, and this after all is a very small part of the mass growing round my pool. Was I wrong, then, when I said my miniature ocean contains as many millions of beings as there are stars in the heavens?

You will want to know how these leaves grew, and it is in this way. First a little free swimming animal, a mere living sac provided with lashes, settles down and grows into one little horny alcove, with its live creature inside, which in time sends off from it three to five buds, forming alcoves all round the top and sides of the first one, growing on to it. These again bud out, and you can thus easily understand that, in this way, in time a good-sized leaf is formed. Meanwhile the creatures also send forth new swimming cells, which settle down near to begin new leaves, and thus a tuft is formed; and long after the beings in earlier parts of the leaf have died and left their alcoves empty, those round the margin are still alive and spreading....

If you can trace the spore-cells and urns in the seaweeds, observe the polyps in the Sertularia, and count the number of mouths on a branch of my animal fringe (Sertularia tenella); if you make acquaintance with the Thuricolla in its vase, and are fortunate enough to see one divide in two; if you learn to know some of the beautiful forms of diatoms, and can picture to yourself the life of the tiny inhabitants of the Flustra; then you will have used your microscope with some effect, and be prepared for an expedition to my pool, where we will go together some day to seek new treasures.

NOTES

AGASSIZ, J.L.R., naturalist, born in Switzerland, 1807; died, Cambridge, Mass., 1873. In 1846 he came to America, after having gained a high reputation in Europe, to deliver a course of lectures in Boston "On the Plan of the Creation," and met with such success that he spent the rest of his days there, declining an invitation to return to his native country and to Paris. In 1848 he was elected to the chair of Natural History at Harvard. In 1850-51 he went on an expedition to the Florida Reefs. In 1858 he founded and organized the Museum of Comparative Zoölogy at Cambridge--and, later on, went on his important voyage to Brazil. In 1872 he founded and organized the summer school of Natural History at Buzzard's Bay. He wrote "The Fishes of Brazil," "A Study of Glaciers," "Natural History of the Fresh Water Fishes of Central Europe," "Contributions to the Natural History of the United States" (unfinished), and with his wife, "A Journey in Brazil."

BALL, PROF. SIR R.S., English astronomer, born in Dublin, 1840. Was appointed Lord Ross's astronomer in 1865. Professor of mathematics and mechanics at the Royal Irish College of Science in 1873, and is now astronomer royal for Ireland. He is the author of "The Story of the Heavens," "Starland," etc., and is well known as a successful lecturer on astronomical subjects in this country.

DARWIN, CHARLES R., English naturalist, born, 1809; died, 1882. He first formulated what is known as the principle of Natural Selection. In 1831 he went in the famous scientific voyage of the _Beagle_ as naturalist, and afterwards published an account of it. He was one of the most thorough, careful, and painstaking scientific men of this or any age. He is the author of many famous books. "The Origin of Species," "The Descent of Man," "Insectivorous Plants," "The Power of Movement in Plants," "The Structure and Distribution of Coral Reefs," "Geological Observations on Volcanic Islands." "The Formation of Vegetable Mould" was his last published work.

FLAMMARION, C., famous French astronomer, born, 1842. He has written many popular works on astronomy, most of which have been translated into English. "The Stars," "The World Before the Creation," "Uranus," "Comets," "Popular Astronomy," are among his best known.

HOLDEN, PROF. E.S., American astronomer, born at St. Louis, 1846. Lieutenant engineers, U.S.A., 1870-73; professor mathematics, U.S.N., 1873-81; director Washburn Observatory, 1881-85; president University of California, 1883-88; director Lick Observatory, 1888-98. Is a member of several learned societies of Europe. Is the author of a "Life of William Herschel," "A Hand-book of the Lick Observatory," "Earth and Sky," "Primer of Heraldry," "Elementary Astronomy," "Family of the Sun," "Essays in Astronomy," "Stories of the Great Astronomers," etc.

HUXLEY, T.H., English biologist, born, 1825; died, 1895. Went on an exploring expedition on the _Rattlesnake_, and devoted himself to the study of marine life. For his scientific researches he received many honors. His lectures were models of clearness, and he could simplify the most difficult subjects. He strongly advocated Darwin's views and evolutionist doctrines. His writings are numerous and many of them technical. Among some of the most popular are "Man's Place in Nature," his "Lay Sermons," "Critiques and Addresses," "American Addresses," "Physiography," "Science and Culture," "Lessons in Elementary Physiology," etc.

KINGSLEY, C., English clergyman and author, born, 1819; died, 1875. Wrote "Westward, Ho!" which every boy should read, "Hypatia," "Alton Locke," "Hereward the Wake," etc., and a charming book of travel, entitled, "At Last." His "Water Babies" is exceedingly popular, and his "Heroes" is a book much appreciated by the boys and girls alike.

PROCTOR, R.A., English astronomer, born, 1834; died, 1888. He was a very popular writer, and lectured on astronomical subjects in this country, and in England and her colonies. A memorial teaching observatory is erected in his honor near San Diego, Cal. He was a man of untiring industry, an athlete, a musician, and a chess-player. His books are numerous. Among them are "Half Hours with the Telescope," "Other Worlds than Ours," "Light Science for Leisure Hours," "The Expanse of Heaven," "The Moon," "The Borderland of Science," "Our Place Among Infinites," "Myths and Marvels of Astronomy," "The Universe of Suns," "Other Suns than Ours," etc.

SHALER, N.S., professor of geology at Harvard. Born Newport, Ky., 1841. Served in the Union Army during the Civil War. Instructor zoölogy, geology, and paleontology, Lawrence Scientific School, till 1887. Since then at Harvard. Is the author of "Kentucky a Pioneer Commonwealth," "The Story of Our Continent," "The Interpretation of Nature," "Feature of Coasts and Oceans," "Domesticated Animals," "The Individual," "Study of Life and Death," etc.

THOMPSON, SIR C. WYVILLE, English zoölogist, born, 1830; died, 1882. He conducted scientific dredging expeditions in the _Lightning_ and _Porcupine_, 1868-69, and was the scientific head of the famous voyage of 68,900 miles in the _Challenger_ for deep-sea explorations (1872-76). His books are "The Depths of the Sea," and "The Voyage of the Challenger."

TYNDALL, JOHN, English physicist, born, 1820. Began his original researches in 1847, when teacher of physics in Queenwood College. He and Professor Huxley visited the Alps together, and they wrote a work on the structure and nature of glaciers. It is impossible to detail the work he has done; but his inquiries and experiments in connection with light, heat, sound, and electricity have all had practical results. He is a popular lecturer, and devoted the proceeds of a lecturing tour in this country to founding scholarships at Harvard and Columbia Colleges, for students devoting themselves to original research. Among his books are "Glaciers of the Alps," "Mountaineering," "Heat as a Mode of Motion," "On Radiation," "Hours of Exercise in the Alps," "Fragments of Science," "The Floating Matter of the Air," and volumes on Light, Sound, Electricity, and the forms of water.

WALLACE, A.R., English naturalist and traveller, born 1822; was educated as land surveyor and architect, but afterwards devoted himself entirely to Natural History. He explored the Valley of the Amazon and Rio Negro, 1848-52, and travelled in the Malay Archipelago and Papua, 1854-62, publishing the results of his explorations later on. He also wrote "Contributions to the Theory of Natural Selection," "Miracles and Modern Spiritualism," "Geographical Distribution of Animals," "Tropical Nature," "Island Life," etc.

GIBERNE, AGNES, English author--living. Began to write at seven years old. Her first story for children was published when she was only seventeen. Her stories for children have not been so popular as her scientific writings, "Sun, Moon, and Stars," "The Starry Skies," "Among the Stars," "The Ocean of Air," "The World's Foundations," "Radiant Suns," etc.

WILSON, ANDREW, English physiologist and lecturer, born, 1852. Is the author of "Studies on Life and Sense," "Leisure Time Studies," "Science Stories," "Chapters on Evolution," "Wild Animals," "Brain and Nerve," etc., and is a constant contributor on scientific subjects to the magazines and newspapers, contributing weekly "Science Jottings" to the "Illustrated London News"

WONDERS OF EARTH, SEA, AND SKY

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