HotFreeBooks.com
The History of a Mouthful of Bread - And its effect on the organization of men and animals
by Jean Mace
Previous Part     1  2  3  4  5  6  7  8     Next Part
Home - Random Browse

On the shores of certain subterranean lakes which exist in Carniola, a country subject at this time to Austria, there are to be found batrachians far more ambitious than our frog—namely, the proteans. These cumulate rather than change: they become reptiles without ceasing to be fishes, if I may so express it; they develop lungs as they grow up, and yet keep their gills. I could tell you a thousand other particulars about these batrachians if I were to examine them all in succession; for it is a very motley family, in the bosom of which the transition from reptiles to fishes is in some imperceptible manner accomplished; from the frog, which the unanimous consent of mankind has always ranked among reptiles, to the axolotl or siren, who lives in Mexican lakes; and who, feature for feature, is exactly like a carp, with four little feet fastened under him. To be quite in order, the batrachians ought to have followed the reptiles, for their interior organization is the same; but how could I tell you about their gills without explaining that there was air in the water? and I did not want, for the sake of these intruders, whose babyhood-gills only just appear and disappear, to rob the history of the fishes of its most interesting points.

Let us be satisfied, then, with this passing glance at a dubious class, whose history is only a repetition of two others, and let us return to our friends the fishes. We have seen how they breathe, now let us look how they eat.

The modifications of the digestive apparatus are endless among fishes. The lampreys, who are placed in the lower ranks of the class, carry out to its fullest extent the type which we have already seen indicated in the serpent. The digestive tube is quite straight, without any perceptible swelling, and does not even go the whole length of the body. It comes to an end at some distance from the tail. Among some fishes an odd tendency begins to display itself, which we shall meet with again farther on. The digestive tube, after going downwards towards the bottom of the body, as we have seen it do so constantly hitherto, doubles back, and comes up again to the throat, under which it empties itself. In most cases the stomach is distinct; but it assumes a thousand different forms; as if nature had wished to try her hand in all sorts of ways in the construction of these imperfect vertebrates, before adopting the definite model which was to serve for the others.

The liver is enormous, and generally contains a great quantity of oil, the taste of which you will know if you have ever swallowed a spoonful of cod-liver oil; but in most fishes its old companion, the pancreas, has disappeared. In its stead you will find, close by the outlet of the pylorus, the open ends of certain small tubes, which are shut in at their upper extremity like a "blind alley," and through which descends into the interstices a thick glairy fluid, given out from their sides or walls. The result is the same, you see, although the organ is different; and, remarkably enough, these little tubes are wanting among fishes, which, like carp, have a species of salivary glands in their mouths, of which the others show no trace; from which one may fairly conclude that these glands and tubes mutually supply each other's places. Here, then, you see an instance of the light which different animal organisations throw upon each other when they are compared together. In fact, this one establishes pretty clearly the real office of the pancreas in the higher races, exhibiting it to us as an internal salivary gland, intended to complete the work only begun by those in the mouth, in the case of lazy people who swallow their food too quickly.

There is the same diversity in the mouth as in the intestine. Some fishes, like the skate, have no tongue at all. Others, instead of a tongue, have a hard dry filament, very nearly immovable, and which one would think was put there like a stake, to show the place where the tongue is to be found in the more perfect organisations. There are even fishes, like the perch and the pike, whose tongue is furnished with teeth, or rather fangs; an evident sign that it has forfeited the confidential position occupied by your own good little porter. You must know also that the perch and the pike, like many other of their fellows, have teeth all over the mouth. This invasion of the palate by teeth, which began in the lizard and the serpent, assumes alarming proportions here. It is not merely the roof of the palate which is spiked with teeth: above, below, at the sides, everywhere to the very limits of the oesophagus, the little fangs triumphantly stick out their slender points. It is impossible, therefore, to state their number. Nature has scattered them broadcast without counting, just as she has done with the hairs of the beard round the human mouth; and the comparison is not so impertinent as you may think. They sometimes form an actual internal beard, even thicker than our outer one, and which sprouts from the skin into the bargain. There is one fish whose teeth are so delicate and so close together that, in passing your finger over them, you would think you were touching velvet. This does not refer to the shark, mind. His teeth are sharp-cutting notched blades, hard as steel, arranged in threatening rows round the entrance of his mouth, and cut a man in two as easily as your incisors do a piece of apple. Others, such as the skate, have their mouths paved—that is the proper term—with perfectly flat teeth. The first time your mamma is sending to buy fish beg her to let you have a skate's head to look at. You will be interested to see the small square ivory plates laid close adjoining each other, like the tiles of a church floor. It is in fact a regular hall-pavement, over which the visitors glide untouched, and are then swallowed down in the lump; thus entering straight into the house without having been stopped by the inscription nature has placed over your door and mine—"Speak to the Porter."

But all this is nothing compared to the lamprey's entrance-hall, which differs from ours in quite another way. The lamprey, as I have already told you, ranks almost lowest among fishes, and consequently among vertebrate animals, of which fishes form the rear-guard. Indeed, it is almost stretching a point to consider her worthy to bear the proud title of a vertebrate at all; for the vertebral column, so clearly marked in other fishes, where it forms the large central bone, is only faintly indicated in certain species of lampreys, by a soft thread (or filament), which is rather a membrane than a bony chaplet, and at the top of this mockery of a vertebral column is the creature's mouth. If you ever had leeches on, you will remember the sharp sting you felt when the little beasts bit you. Well, the lamprey feeds herself just in the same way as the leech does. Her mouth forms a completely circular ring, which sticks to the prey, and through which runs backward and forward a small tongue armed with lancets. This darts out to pierce the skin, and draws in the blood as it retreats. Round your lips well; dip them so into a glass of water, and draw back your tongue, and you will at once feel the water rise into your mouth. It is by a similar sort of proceeding that leeches relieve people of the blood they want to get rid of; and in the same way the lamprey draws out the blood of the animals upon which she fastens.

What a long way we have come already! How very far we find ourselves here from the little mouths we first talked about as chewing their eatables so prettily! With the lamprey we bid adieu to the class Vertebrata—the nobility of the animal kingdom—among whom nevertheless we must distinguish between the peer, who approaches nearest the person of his sovereign, and the inferior provincial lords who live at a hundred miles' distance. There is only one step from the lamprey to the mollusks or soft-bodied animals, and this is the course which animal organisation seems really to have taken in its progress. But nature never moves forward in a single straight line. In passing from the mollusk to the fish to get thence to the higher vertebrates, she turned aside in another direction toward a class of animals which rises far above mollusks, but which leads to nothing beyond.

One would think there had been a check here, as if the creative power, having discovered that it was going in a wrong direction, had retraced its steps; if it be allowable to apply common ideas and expressions to our conceptions of that Great Intelligence which has arranged the plan of the mysterious ladder of animal life.

The animals we must examine next, on account of their superiority to the rest, are insects. Small as the ant is, it would not be right to let her be preceded by the oyster.



LETTER XXXVII.

INSECTA. (Insects.)

Before speaking of insects, my dear child, it will be necessary, in the first place, to tell you to what primary division they belong and on what characters this division has been established. And here I find myself in a difficulty. We have been but too learned already, and now we run the risk of becoming still more so, if we commence an attack on the three primary divisions which follow the vertebrates. We shall have to encounter terrible names and tedious details, besides having to take into account a thousand things of which we have not yet spoken. We are going on quietly with the history of the feeding machine which occupies the middle of the body, and learned men never looked in that direction for the establishment of their divisions; between ourselves, it was not accommodating enough. They have fallen back upon the locomotive apparatus (movement machine) which affects the body all over, and which they have proclaimed to be the leading feature of the animal organization, without noticing however that it is, after all, but the servant of the other. It is true that the great divisions are more easily established upon this point than the other, because the differences are more decided. It separates what the other unites, and thus it is that nature carries on that beautiful combination which the Germans have so accurately named "Unity in Variety" that is to say, she is always at work, as I have already told you, on the same canvas, but always embroidering it with a different pattern. Wait! I have something to promise, if you are very good, and if this history (that of the feeding machine) should have given you a taste for inquiry. I will tell you another time the history of the movement machine, and there the classification of our learned men will come in naturally very well. In the meantime we will do as they do, and just shut our eyes to their divisions, in which the feeding machine can have no interest, because they were established without reference to it. We will content ourselves, then, without further pretension to science, with modestly examining the last transformations of our pet machine in the principal groups of the inferior animals; of which groups I will now tell you the names in their proper order. They are as follows: Insects, Crustaceans, Mollusks, Worms, and Zoophytes. You must take these names on trust; those which you do not understand will be explained in their places.

1. Insects.—I know not where it was I once read that there are said to be something like a hundred thousand different species of insects; and I verily believe this is not all. Of course we shall not attempt to review the whole of this formidable battalion. Let us take one of those you are most familiar with—the cockchafer, for instance— and examine what goes on in his inside. The history is nearly that of all the others.

"Fly away, cockchafer, fly!" says the song; and surely it is a bird that we have here, and a bird which will appear to you even more wonderful than those of which I have already spoken, when you have considered the simplicity, and at the same time the strength, of his organization. His mode of flight is rather lumbering, it is true; he is, in comparison with the large flies, what the ox is to the deer; but when you contrast the weight of his thick body with the delicacy and narrow dimensions of the two membranes which sustain him in the air, you may well ask yourself how those little morsels of wings, thin as gold-beater's skin, can carry such a mass along. In fact, they only accomplish this feat of strength by dint of an excess of activity almost startling to think of. When you run as fast as you can, how many times, think you, do you move your legs in one second? You would be somewhat puzzled to say; and so should I: but I defy you to count ten. Now the bird makes his wing move much oftener when he beats the air with rapid blows as he flies; but even he does not strike a hundred strokes in a second: and what is this to the feats of the cockchafer's wing? It is not hundreds but thousands of times that he flaps his wings in a second; and here let me hint, by-the-by, that when people seriously wish to find out a method of travelling in the air, they will lay aside balloons, of which they can make nothing in their present condition, and will set to work to fabricate machines with wings which shall beat the air as fast as those of the cockchafer. This sounds extravagant, but I have seen an electric pile fixed in a stand with glass feet, which caused a little hammer to beat thousands of times in a second: and surely the hammer could have been made to communicate its movement to a small wing! Forgive me this little castle in the air! The idea came into my head a long while ago, and the cockchafer has just reminded me of it. I will not, however, pursue the subject, neither will I offer to explain the method used for counting the beats of an insect's wing. That would carry us farther than would be desirable.

To return to our little animal. I leave you to imagine the enormous amount of strength required for such precipitate motion. We have spoken of the rapid course of the blood in birds during flight: who shall calculate its comparative rate in this fabulously wonderful locomotive, the cockchafer? And if we lift up the cuirass which encases it, what do we behold? Not a single trace of all the complicated circulation-apparatus you have learnt to know so well; neither heart nor veins nor arteries; only a quantity of whitish liquid, equally distributed throughout the whole internal cavity. Not a trace of lungs, nor any apparent means of renovation for this seemingly motionless blood; for blood it is, in spite of its color, or, at any rate, blood in its first stage of formation. It also has its globules—ill-formed, it is true, and altogether in balls—like those found in the chyle with us; which chyle, be it observed, is the same color as the blood of insects, and may also be considered blood in its apprenticeship. By what magic, then, is this raw, imperfectly-formed steward, who seems altogether stationary, enabled to accomplish exploits which would stagger his higher-bred compeers, agile and perfected as they are? Where does he pick up the oxygen necessary for such repeated movements, it being an established fact that no animal can move at all without consuming oxygen, and that the quantity consumed is in proportion to the rate of motion? Look under his wings for an answer. There, all along his body, you will observe a number of small holes, pierced in a line, at regular distances, and furnished with shutters of two kinds. They are the mouths of what are called tracheae, or breathing tubes: and from them branch out a multitude of little canals, which, spreading in endless ramifications through every part of the body, convey to the whole mass of the blood, from all directions, the air which makes its way into them through the tracheal holes. In this case, you see, it is not the blood which seeks the air, but the air which seeks the blood; whence arises a new system of circulation, whose action is all the more energetic because it is unintermitting, and makes itself felt everywhere at the same time. A little while ago we were wondering at the twofold respiration of birds; yet this is far less surprising than the universally-diffused respiration of insects, who may well be able to do without lungs, seeing that their whole body is one vast lung in itself.

For the rest, do not trust to appearances, nor imagine that the blood of our friend the cockchafer in reality remains motionless around the air-tubes, idly drinking in the oxygen which is brought to it. Though not flowing in enclosed canals, it is not the less continually displaced by regular currents, which sweep through and renew this apparently stagnant pool. Nor is this the only instance of such a current presented to us by nature.

Guess, however, if you can, where you will have to look for the counterpart to the circulation of the cockchafer. In ocean itself! But, remember, nothing is absolutely little or great in nature, who applies her laws indifferently to a world as to an atom. The blood of our world is water, which contains in itself all the germs of fertility, and without which, as I have already told you, life is impossible either in the animal or vegetable kingdom. The water of brooks, streams, and rivers, flows along in channels, which, when figured in a map, present to the eye of the beholder an exact picture of the system of circulation found in the vertebrated animals. But the waters of the sea are borne along, like the blood of insects, by a secret circulation, which cannot be represented on the map; i.e. by immense currents everlastingly in action, some on the surface, some in the mid-heart of the ocean, which drive it in ceaseless course from the equator to the poles, from the poles to the equator; so that the Supreme Intelligence, in His overruling providence, has ordained the same law to set in movement the immensity of ocean, and to effect circulation in the cockchafer's few drops of blood. In the latter we find the moving agent to be a long tube, which runs the whole length of the back, and is called the dorsal vessel (from the Latin dorsum, back). I told you that the cockchafer had no heart under his cuirass, but I spoke too hastily. The dorsal vessel is a true heart, but a heart devoid of veins or arteries, and thrown into the midst of the blood. It dilates and contracts like ours, sucks in the blood by means of side-valves, which act as our own do, and drives it back again into the mass by that valve at its extremities, which opens near the head. From thence arises a continued to-and-fro movement, which sends the blood from the head to the tail, and brings it back again from the tail to the head. But who would recognise, in this simple primitive organisation, where all seems to go on of its own accord, as it were, the same machine, with all its complicated movements, that we have been so long considering?

Well, in this apparently universal shipwreck of all the organs we know so well, there is yet one which survives, and remains the same as ever, namely, the digestive tube. I began by saying the insect is a bird. His digestive tube is formed upon the same pattern as that of birds, so that naturalists have bestowed the same names on the various parts in each of them. After the oesophagus comes a crop (jabot), very distinctly indicated; then a gizzard with thick coats, in which the food is ground down. The hen, if you remember, swallows small pebbles, which perform in her gizzard the office of the teeth in our mouths. The cockchafer has no need to swallow anything. His gizzard is furnished with little pieces of horn; real teeth, fixed in their places, which have a great advantage over the chance teeth picked up at random by the hen. I pointed out to you in birds, between the crop and the gizzard, a swelling or enlargement of the digestive tube, pitted with small holes, where the food is moistened by juices. The same enlargement is found here, covered all over with a multitude of small tubes, which might easily be mistaken for hairs, from which also falls a perfect shower of juices. The only difference is, that it comes after the gizzard, instead of before it, as in birds. Some naturalists, considering that the manufacture of chyle takes place here, have called it the chylific ventricle; [Footnote: The corresponding protuberance of the birds bears a name, somewhat similar, but stillmore barbarous. I had passed it over in silence, because, I make the confession in all humility, I do not understand it; but a remorse now seizes me: it is called the Ventricule succenturie.] a somewhat barbarous name, but one which explains itself, and might with truth be applied to the duodenum of the higher animals. Bile is poured in close to the hinder end of it, but you must not look for the liver; it has disappeared, or rather its form is entirely changed. You remember what the pancreas had become in fishes; i.e. a row of tubes giving out a salivary fluid. Such is exactly the appearance of the liver in the cockchafer.

Instead of that fleshy substance on which hitherto the office of preparing the bile had devolved, you see nothing but a floating bundle of long loose tubes, which, opening into the intestines, pour in their bile. The organ is transformed, but we recognise it again by the office it performs, which continues the same. As to the pancreas it is wanting here, as in the fish with salivary glands; but in its place in many insects other tubes, acting also as glands, pour saliva into the pharynx; i. e., the cavity at the back of the throat.

As you see, therefore, everything is found complete in this tube of a few inches long; and you can also distinguish there a small and a large intestine. We are speaking of the cockchafer, which feeds on the leaves of trees; and it is for this reason I name some inches as the length of the digestive tube. This would not be longer than the body itself, had it been destined, as in the case of many other insects, to receive animal food. In fact, the law which we have shown to exist with regard to the ox and the lion, rules also over the insect-world; and whilst a radical change seems to have been made in the rest of the organisation, here everything is in its place, and we find ourselves in the same system.

Was I not justified in asserting that the unity of the animal plan is to be found in the digestive tube? and that this is the unchanging basis upon which the Creator of the animal world had raised his varied constructions?

How would it be, then, if we were to take the insect from its starting-point when it is only a worm, that is to say, merely and simply a digestive tube? for I am only telling you a small portion of its history here; a history you must know, which reveals a miracle still more wonderful than the transformation of the little tadpole into the frog! There is a brilliant-colored fly which comes buzzing about the meat-safe—the bluebottle—do you know her? It is on her account that we put large covers of iron wire over the dishes of meat; but, perhaps, you never troubled yourself to think why.

But the truth is, she only comes there to deposit her eggs in the good roast-meat; and if she could get near enough to do so, you would soon afterwards see it swarming with little white worms, which would entirely take away all your appetite. These worms are only flies out at nurse, and they will find their wings by-and-by if you only give them time enough. Disgusting as they may appear on a dining-table, I assure you they deserve more interest than you may think. When we come to speak of worms, we will ask of them to let out the secret of the mysterious transformations of animals.

In the meantime, let us finish the observations we were making on the perfect insect, as this little creature is called when he has passed through the intermediate stages which separate him from the undeveloped condition. Forgive me, my dear child, here I am speaking to you as if you were a grown-up woman! This is because it is so difficult to explain things of this sort in any other way. And now that you have been introduced into the midst of the wonders of creation, you ought to familiarise yourself with the ideas and terms they have suggested to mankind. I began with you as a child, and great would be my triumph if I could leave you a grown-up girl! And I flatter myself that I have so far set your brain, to work, under pretence of amusing you, that this hope is not altogether unfounded. I found it necessary to say this to you in confidence, because I have just read over our first conversations, and perceive that I have insensibly put you on a different diet from the one I began with. I am obliged to comfort myself by remembering that you have grown older since, and that you are now acquainted with a great many things which you had never heard spoken of then. And this is the secret of all transformations. We crept on at first over ground that was quite unknown to us; but as we went along, our wings must have begun to grow, and we are now able to fly a little!

Do not be afraid, however; I will exercise your tiny butterfly-wings very carefully just at present. We have only to examine what becomes of the chyle of the cockchafer after it has been prepared in the pretty little tube so finely wrought. We men have chyliferous vessels which draw up chyle from the intestines and throw it within a short distance of the heart, into the torrent of blood, where its education is completed. But the cockchafer, who has no other vessels than his air-pipes, and the dorsal tube, which has no communication with the intestines, what is he to do? Do not distress yourself about him. Make a tube of a bit of linen, well sewn together, and fill it with water. Sew it together as firmly as you may on all sides, the water will have no difficulty in escaping through the meshes. And this is just what happens with the little tubes found in animals, the coats of which are formed of interwoven fibres. By-the-by, from thence comes their name of "tissue," which they share in common with all the solid substances of the body, for all were once supposed to have the same general structure. The intestine of the cockchafer floats, did I not say? in the lake of blood which fills the whole cavity of the body. Well, then, the chyle has only to penetrate through these coats, to go where it is wanted. Hence it is not at all surprising that this blood should be white; and I have very good reasons just now for comparing it to our chyle. It is, indeed, chyle arriving directly from the place of its manufacture, without undergoing any other process; by which you may see that this little machine (of the digestive organs of the cockchafer), though differing in appearance so entirely from our own, is reducible to the same elements of construction, and that life is maintained by the same process as with us; namely, by the action of the air upon the albumen extracted from food. The cockchafer, it is true, is much further removed from being a fellow-creature of ours than even the horse; but the principle of life is the same with him as with us. And this is quite enough to cause children, who can feel and reason, to think twice before they begin to torture, by way of amusement, a creature whose life the God of goodness has subjected to the same conditions as our own. I speak this to those miserable little executioners who make toys of suffering animals: but the case is different with agriculturists, who have necessarily to contend with the devourers of their harvests, and whom, I admit, it would not be reasonable to bind down by the maxim of Uncle Toby.

[Footnote: I have introduced my Uncle Toby, who really has nothing to do here, in order to make you acquainted with a few lines of Sterne, which I wish I could place before the eyes of every child in the world.

"Go!" said he, one day at table, to an enormous fly which had been buzzing around his nose and had cruelly tormented him all dinner time. After many attempts, he finally caught him in his hand. "Go! I will not do thee any harm," said my Uncle Toby, rising and crossing the room with the fly in his hand; "I would not hurt a hair of your head. Go!" said he, opening the window and his hand at the same moment, to let the fly escape; "go, poor little devil; away with you; why should I do you any harm? the world is certainly large enough to contain both of us!"]

But now to finish with the cockchafer. We have got to examine one very important part of his body, that which in other animals has been the one most talked about ever since we began our study: I mean the mouth. You know that this is the essentially variable point in the digestive tube; so that you will not be much surprised, should we find he has something altogether new. The mouth of the cockchafer is composed of a great number of small pieces placed externally round the entrance to the alimentary canal; but the names of these, as they would not interest you, I will not enter upon with you; more especially as they refer to such tiny morsels, that you would have great difficulty in finding them again on the owner. Of these pieces only two are worth our attention. These are two bits of extremely hard horn, placed one on each side of the animal, which are called "mandibles" and which serve the cockchafer to cut up the leaves which he eats. Fancy your share of teeth being two huge things fixed in the two corners of your mouth, each advancing alone against the other till they meet under the nose! You would then attack your tarts with the weapons of the cockchafer! You would not, however, be able to bite them straight through from the top to the bottom, as is done by all the animals whom we have yet seen. It is this which so peculiarly distinguishes the insect's manner of feeding; for we have already been taught by the bird and the tortoise, that it is possible to eat with two pieces of horn. The cockchafer now shows us how to eat sideways; but this is merely an accessory detail. It does not affect what happens after the mouthful is swallowed. All insects, however, have not this peculiarity. The cockchafer belongs to the category of grinding insects as they are called, who bite their food: but there is the category of the sucking insects (or suckers), whose food consists of liquids; and these insects are furnished in a different manner.

In the innocent butterfly, who lives on the juice of flowers, the digestive tube terminates externally in a sort of trunk, twisted in several convolutions, which is nothing more than an exaggerated elongation of the two jaws, which become hollow within, and form a tube when joined together. When the insect alights on a flower, he suddenly unrolls this trunk, and sucks in the juices from the depth of its "corolla," as you would drink up liquid with a straw from the bottom of a small vial. Amuse yourself some summer's day by watching a butterfly in his labors amongst the flowers: sometimes he stops still, but oftener he is contented to hover over them; and, as he does so, you will see a little loose thread, as it were, move backwards and forwards as fast as possible: this is his trunk, which he darts out, while flying, into the corolla of the flowers, but which scarcely seems to touch them, so delicate is its approach.

Less inoffensive far is the trunk of the mosquito-gnat, and of all the detestable troop of blood-sucking flies. It is always a tube; but this tube is no longer a simple straw, but a sheath furnished with stilettos of such exquisite delicacy and temper, that nothing is comparable to them; and these, as they play up and down, pierce the skin of the victim, like the lancets of the lamprey, and, like them, draw in blood as they retreat.

Finally, amongst the parasites, the last and lowest group of insects, the stiletto-sheath is reduced to the size of a kind of little tube-shaped beak, which, when not in use, folds down like the fangs of the rattlesnake.

You do not know, perhaps, what a parasite is. The word comes from the Greek, and signifies literally, "that which moves round the corn." The Greeks applied it to those shameless paupers who, to escape honest labor, made their way into the houses of the great, and enjoyed themselves at their expense. These parasites are little animals which settle themselves on large ones, to suck in, without having worked for it, the blood which the others have manufactured. The wolf hunts, fights, and tears its victim in pieces; and then, by means of that interior labor which I have spent so much time in describing, transforms it into nourishing liquid: and when all this is accomplished, the little flea, who lives hidden among his hairs, coolly draws out for his own use the valuable blood obtained with so much effort. There are many parasites in the world, my dear child—yourself, for instance, to begin with—who are perfectly happy to chew your bread without asking where the corn comes from which made it. But you have heart enough to see plainly that this indifference ought not to last, and that it is not honorable to go on living in this indefinite manner at other people's cost only.

You will some day have duties to fulfil, which you should accustom yourself to think of now, in order that you may prepare yourself for them beforehand, so that it may never hereafter be said of you that you passed through the midst of human society, taking from it all you needed, without giving it back anything in return, I advise you to conjure up this idea when the time comes to leave off playing and begin preparing to be of use. The sort of thing is not always very amusing, I admit, but you must look upon it as the ladder by which you will be enabled to rise from the degradation of a parasitical life. If you were in a well, and some one were to let down a real ladder for you to get up by, I do not think you would complain of the difficulty of using it. It is for you, then, to consider whether you would like to remain for ever in your present condition; for those who learn nothing, who submit to nothing, who are good for nothing, but to show off and amuse themselves—these remain parasites all their lives in reality, however little they may sometimes seem to suspect it.

At your age, however, there is still no disgrace in the matter. God shows us by the insects that little things are allowed to be parasitical; but on this subject I must return to a point in the history of animals which I touched upon before. I told you, in speaking of the crocodile, that the perfect state of the inferior animals is found represented in the infancy or less perfect state of those above them: and I may say the same again with regard to insects. All the young of the mammalia begin life as parasites, at least, as sucking animals: for they all live at first on their mother's milk, which is nothing more than blood in a peculiar state. But the name of parasite among insects is generally confined to those which take up their abode on the bodies of their hosts; though in common justice it might equally well be applied to the gnat and his relations, who, when once full, make their bow and are off, like the kitten when he has finished sucking. Well, without meaning to find fault, if we descend to the lower ranks of the mammals, we shall find among them many parasites in the received sense of the word. You remember the pouch to which the marsupials owe their odd name. The young kangaroo remains hidden for months in the pouch of its mother, feeding continually all the time; and it is then a strict parasite. During the four following months it goes in and out, and strolls about between meals, like other young ones of its class, and is then an animal at nurse affording thus a twofold example of the tendency of the great Creator to repeat Himself in His conceptions, here using for the infancy of the mammal the system invented for adult insects—elsewhere repeating the butterfly in the humming-bird, who may fairly be called a vertebrated butterfly, and reproducing the gnat in the vampire-bat, which I look upon as an enlarged and perfected revise of the original pattern, whence comes the scourge of our sweet summer nights.

And now, surely, I have said enough about these parasites, whose very name, I suspect, will make you shudder after my impertinent application of it. Never mind: it depends entirely upon yourself to get rid of whatever you find humiliating in the position I have hinted at. Do all you can to bring happiness to the parents on whom you live at present, and who give their life-blood so willingly for your good. God has made you very different from those little animals who have neither heart nor reason to guide them. Do not be like them, then, in conduct. By a little obedience and love—child as you are—you can pay them back what you owe, and they will never complain of the bargain.



LETTER XXXVIII.

CRUSTACEA—MOLLUSCA. (Crustaceans and Mollusks.)

Crustaceans.

Crustaceans consist of cray-fish, crabs, lobsters, and prawns, who may be considered cousins-german of insects, among which more than one naturalist has thought they ought to be placed. Like them they are divided into grinders, having the same action of the mandibles; and suckers, who are also parasites, and have tubular sheaths containing stilettos. Mammals and birds are the victims of parasitical insects; fishes have been reserved for the crustaceans, who do not disdain also to fasten upon their humble neighbors, the mollusks; and even among themselves the little ones settle down on the great. A few live on land, but an immense majority in water, and seem destined to represent, in the aquatic world, the aerial class of insects, from whom, however, they differ in many ways.

The first difference is in that stony crust with which they are enveloped, like the cockchafer in his horny cuirass, and which you must know well enough if you have ever eaten lobster. Wherever we meet with horn in insects, we find stone in crustaceans. The jaws are stony, and the teeth of the stomach also. They are constructed on the same plan, only the materials are changed.

The digestive tube is less complicated, and consists merely of one large stomach, instead of that series of stomachs by which insects approach the organisation of birds. On the other hand, if among some of them the liver is reduced to simple tubes, floating loosely in the body, as we have just seen it in the cockchafer among insects, these tubes are generally so profusely multiplied, and press so closely against each other, that they form a large compact lump—a true liver, to sum up all—from which issues, as from ours, a choledochian canal, a bile duct, i. e., which passes out into the intestine at the entrance of the pylorus.

You recollect that canal of the liver which I was afraid to tell you the name of because it was so ugly? Well, this is that formidable name! Now that you have swallowed so many others, you must be strong enough to digest this.

No chyliferous vessels have been found in crustaceans, whence one may conclude that the chyle leaves the intestine by oozing from it, just as it does in insects. There it gives rise to an almost transparent sort of blood, a kind of sap, or lymph, which is put in motion by a genuine circulation-apparatus; a real heart, with all its canals. This heart has only one ventricle, and only sends blood in one direction, as in the case of fishes; but there is an essential difference between them, which we must point out. The heart of fishes may be called a venous heart, since it only receives venous blood, which passes thence to the gills, while that of crustaceans is an arterial heart. It receives the blood directly it leaves the respiratory organ, and sends it, not into one aorta, but into several arteries, which set out at once, each in its own direction, to nourish the various quarters of the body. This greatly resembles the system of circulation, with which we are already acquainted. The veins only are unsatisfactory. They form a kind of transition between the uncertain currents which convey the blood of insects from one end to the other of the cavity in which these strange organs lie bathed, and the closed canals of the higher animals. But they are not canals, properly speaking. The irregular intervals which separate the organs, more numerous here, are enclosed by membranes, between which the venous blood pours, and naturally the chyle also. The whole thus arrives at certain excavations formed at the place where the legs are jointed on to the body—reservoirs, so to speak—where the real canals come to carry it off and convey it away into the gills.

It is, in fact, by means of gills that crustaceans breathe in their character of aquatic animals. These gills are made nearly upon the same model as we have already seen in those of fishes; and although their form and arrangement differ in different species, yet the principle is always the same: they are tufts of leaflets springing from stems, up and down which run two tubes; one which brings the blood from the venous reservoirs, the other which carries it to the heart. Crabs, lobsters, and crayfish, who are the "file-leaders" of the crustacean tribe, have gills enclosed in the body, as fishes have; but the circulation of the water goes in a contrary direction to theirs, as does that of the blood. Instead of entering at the mouth and going out at the sides, as we have seen, it enters at the edge of the bony shell which covers over the body and comes out near the mouth—a merely accidental detail which does not in any way alter the play of the apparatus. All these animals are equally adapted for swimming and for walking, crabs especially, their gills accommodating themselves without difficulty to contact with the outer air, as we have seen among certain fishes; so that one might class them with amphibians. There is even one crab who has acquired the name of land-crab, because, although he has got gills, he dies in water, the small amount of air he can get out of it at a time being insufficient for him, and who, therefore, lives constantly on land. It is true that he seeks out damp spots, for his gills would also fail him if they became parched, and, like the fishes who make excursions on dry land, he is provided with an internal reservoir, which is always filled with a certain quantity of water.

Some aquatic crustaceans have the labor simplified by external gills, which hang down into the water, sometimes depending from the stomach, sometimes from the legs. In France you sometimes see at a table certain little animals, very like shrimps (squillae), the bases of whose hinder legs are fringed by slender tufts, which are in fact their gills. They find themselves placed there just within reach of the venous blood; for in the body opposite the bases of the legs are little cavities in which it accumulates. Now these gills can only act when under water, and so the squillae dies as soon as he is removed from that protecting element. For the same reason they cannot be kept long, nor travel far, much to the regret of those who like them and live at some distance from the sea.

There are other crustaceans, next-door neighbors of the squilla, whose gills are still more simplified. Here the legs themselves are turned into extremely thin plates, which play the part of gills, and are thus organs for two purposes, serving at the same time to swim and breathe with.

We have in our house one little crustacean, the only one I know of who associates with men, and that is the wood-louse. You must know the little grizzly beast, which rolls itself up into a ball whenever it thinks itself in danger, and who would be taken for an insect by anyone who was not taught otherwise. The wood-louse has neither gills hanging down outside, nor anything inside her body which resembles the breathing apparatus of her great relations. But, on examining her closely, you will perceive all along her stomach a series of little plates, which are her breathing-organs, and which come under the class of gills, because, like other gills, they require a certain degree of moisture to make them act properly. You will never, therefore, see a wood-louse strutting about in the sunshine, where he would dry up far too quickly; but if ever you get into a dark, damp corner, there you have every chance of finding one.

Animals who breathe through their legs and through their stomachs! You are astonished, and ask, What are we coming to? What would you say, then, if I were to go really to the depths of the crustacean world? We should find there such extraordinary beings as you can form no notion of, for they all live down below in the sea, and have no special breathing-organ at all, inasmuch as they breathe through the whole surface of the body. Do not exclaim yet! I will soon show you one whom you know perfectly well, and who has no other way of breathing.

But we must keep to the higher crustaceans, if we want to judge of the class. By going too low, we run the risk of not seeing clearly. Animal creation is here on a system of experiments: and they are so endlessly multiplied, and exhibit such a profusion both of deceptive resemblances, and of differences which disappear by transformations, that classification no longer knows which way to turn. Worms, crustaceans, mollusks; to which group do these and those belong? To which ever we like to refer them, for these groups represent nothing definitely determined in the plan of creation; and though easy to be distinguished from each other in the higher branches, they become confused together in the lower, like mountain summits which spring from a common base, at the foot of which they are all united together.

On this account, my dear child, you will, I am sure, excuse me now and henceforth, from entering into details of all the horrible beasts which swarm in the shallows of the animal world, and whom learned men have in their wonderful wisdom muffled up in terrible names, in order to prevent children from coming near them! What would you have thought of the poor little squilla, so prettily baptised by the fishermen, if I had taught you that it belonged to the order of Stomatopoda? You will scarcely be able to pronounce the word; but that is no fault of mine, it is spelt so.

We will content ourselves, then, with having taken a glance at the most clearly marked individuals; and as I said to you just now, it is by them that we will arrange our inventory of the groups. Here, as you may have already remarked, instead of continuing to wander from the original model whose gradual deterioration we have been following all this time from one class to another, it would seem that we are retracing our steps, and regaining some portion of the lost ground. This is because insects, as I have already stated, are an exceptional case—an idea apart from the great general plan—a by-lane turning off from one side of the great line of animal creation.

The crustacean, less perfectly worked out than the insect assuredly, but more regular, forms, so to speak, the connecting line between that tiny masterpiece of fancy, so incomplete in its exquisite organisation, and the shapeless but better constituted lump of the mollusk, who conceals under his heavy shell the sacred deposit of real organs, those which we expect to find always and everywhere. An insect outside, though less refined it is true, a mollusk within, the crustacean reminds me of what among us is called an amateur—that mild lover of the arts who holds a middle place, as it were, between the artist and the common citizen.

I regret that you are not at present quite able to appreciate my comparison fully: but put it by, in reserve, if possible, in your memory; you will find out hereafter how just it is, and it will, perhaps, help to prevent you from always setting the lively, noisy artist, above the quiet and silent citizen. Let this, however, be between you and me. If they could hear us talking, neither artist nor citizen would forgive me, and the amateur still less.

Mollusks.

There is one mollusk universally well known—namely, the oyster—so we will choose him for discussion. To look on one's plate at that little mass of soft, compact substance, one feels inclined to ask what there can possibly be in common between it and us; and if you were to declare that there was not the faintest trace of resemblance between the organization of the oyster and our own, I should not be surprised. Wiser people than you have been caught tripping there; not that they were ignorant of the points in which the oyster resembled us, but they paid no attention to them. Viewing it in other respects, they declared that it was of a structure completely different to our own; and that, in the construction of this machine, the Creator had worked upon a particular plan, laid aside afterwards as useless for any other purpose.

I should like to get hold of one of those Academicians, with thirty-six plans, and confound him before you, in proof of his relationship to the oyster, by showing you at one sitting that there is an oyster in himself; nay, further, that he is nothing but an oyster, revised, amended, and considerably enlarged. And do not imagine that I am only using a figure of speech here, as the professors of rhetoric call it; which would be in bad taste: I am speaking literally, and to prove the existence of the oyster in question in our Academician, I shall only ask permission to perform a slight operation upon him. You exclaim at this; but do not alarm yourself, for it is only an operation on paper, he will not die from it. See now, I cut off his head, his two arms, and his legs; I take out of his body the vertebral column and the ribs; I gently place what remains between two shells; and ... there is my oyster. I willingly admit that it is more carefully elaborated and richer in details than its sisters in the oyster beds; but all the principal organs are to be found in them also, and they positively are beings of a similar construction: you shall judge for yourself.

The mouth—for there is a mouth, though one must look closer than the oystermen do to discover it—the mouth is exactly what the gullet (oesophagus) would be in a man whose head had been cut off; that is, a truncated tube. Then comes the stomach, situated in the very midst of the liver; which latter may easily be distinguished, even by the most cursory glance at luncheon, from its dark color. The intestine also goes right through the liver, doubling backwards and forwards several times: and thus the digestive tube supplies itself with bile from the cask (to borrow a commercial expression); and this saves the expense of a bile-duct (choledochian canal), which would be an unnecessary mode of conveyance in this case. The animal lives in water; consequently, instead of lungs he has gills: [Footnote: The land-snail has lungs.] these are those thin, finely-streaked plates which make a fringe at the very edge of the shell. Finally, on leaving the gills the blood is received by an arterial heart, with only one ventricle like that of the crustaceans, in the shape of a small pear, similar to ours, having an auricle, and an aorta, branching out so as to distribute the blood throughout the whole body. And now what do we find here, let me ask you, in this mutilated man, reduced to the soft portions of the trunk, whom I have been imagining? A heart, with its arteries; lungs; a liver; an intestine; a stomach and an oesophagus: that is to say, merely and simply the organs of nutrition. That is all, or very nearly so.

As you perceive, then, all the elements of our own feeding-machine lie between the two shells of a mollusk; in a rough state as yet, it is true; incomplete, and unruly; as in the case of the intestine, for instance, which in many of these creatures passes without ceremony through the heart: but even so they are quite sufficiently indicated to prevent their being mistaken. Now this machine, it is in vain to deny it, is the animal itself; but it lives at first, and it is this which dies in it last. The other matter (the locomotive power), important as it may seem to us in higher races, only holds a secondary position in reality: the proof of which is, that here is an animal reduced absolutely to a mere feeding-machine, who still lives, whilst there yet remains to be found one who has nothing left but his movement-machine, and who can yet exist. We cannot disown this primitive animal, for we have it within ourselves; lost, so to speak, in the midst of the accessory organs which are successively added to it in proportion as we rise in the animal scale, but still preserving its own life, its personality, if I may use the expression. Listen to this, for here is a history well worth hearing.

I will explain to you, hereafter, how all the actions of the movement-machine are performed by means of a network of nervous threads (filaments), whose centre of impulsion is in the brain. How our will acts upon the brain, and gives its orders to the muscles through the nervous fibres, I will not offer to explain: it is a fact, let that suffice us. You say to your foot, "Forward!" and off it starts; "Halt!" and it stops. Here is an organ under command, a servant of the brain, where we rule ourselves: with or without explanation, no one will ever dispute this. The oyster, who has neither head nor brain, has, as his only instrument of action, certain little masses of nervous substance scattered right and left, which are called ganglions. These communicate with each other and with the organs by nervous cords, which are interlaced in all directions, without having any common centre, and which give the impetus to all parts of the animal.

Well, the human oyster presents to us exactly the same nervous organisation. It has its ganglions and its nerves to itself, which are put into communication with the brain by some threads strayed among his own, but which are not under its orders, and which treat with it on equal terms. You remember, perhaps, the little republic talked about when we first entered the digestive tube; you have now the explanation of it. This republic is the original animal; it is the feeding-machine. I cannot describe it, and the kingdom of which you are queen, better than by comparing them to two States having diplomatic relations with each other, who exchange dispatches and reciprocal influences; and as to the importance of these respective influences, if one were to compare them I scarcely know to which side the balance could incline.

We shall return elsewhere to this detail, one of the most interesting of our organisation, and which here finds its natural explanation. For the present I will content myself with reminding you that, since the earliest days of human civilisation, all philosophers, all poets, and all moralists, whether sacred or profane, have borne witness to that double life within us, that inward being, blind and deaf, whose disordered impulses so often carry trouble into those higher regions where will and reason sit enthroned. Behold him taken in his lair at last, this mysterious being. I have just unveiled his origin to you. And here, dear child, I must shelter myself behind a profession of faith. There will not be wanting people to tell you that it is degrading man far too much to look so low for the sources of his organisation, and that this sentence—the human oyster—which expresses my idea so well, is neither more nor less than blasphemy. Let them talk, but adopt their opinion only when they have proved to you that man had a special Creator, and that the oyster came from a different hand from ourselves. I should like to know with what face we could venture to complain, poor worms that we are, because it has seemed good to our common Father to carry forward in us his previous creations, and in what respect human dignity would suffer from this contact with a being who, like us, is one of the works of God. That human pride may suffer thereby, I admit, and I am glad it should; but if God has included all creation in His love, we may well include it all in our respect. Whence comes our superiority at all, but from the gratuitous gifts of Him who has made us what we are? Is it to lose it, then, to find ourselves side by side with inferiors whom the Divine benevolence has visited like ourselves? Surely not. But enough of the oyster, who has never, that I am aware of, heard such strange discussions sounding in his ears before. I have no time nor courage now to speak of the other mollusks, who offer more or less the same system of organs which I have just described. I must hasten on to the Worms, who give us the last clue to the great enigma of the animal machine.



LETTER XXXIX.

VERMES—ZOOPHYTA. (Worms and Zoophytes).

Worms.

The worm of worms, the one you know best, is the earthworm: so he shall have the honor of representing his group.

He will not take much time to describe. He is, in brief, a tube, open at both ends, so as to allow food to come in and go out. That is all.

I talked to you before about the ruminants, those food-manufacturers who are employed in cooking victuals for the stomach, and in disengaging albumen from the coarse materials among which it is apparently lost, so as to give it out again in a more acceptable form. The ruminant has other workmen under him, whom I keep in store for you as the last of the eaters, and who prepare the raw material for him*. These are the vegetables, who seek out the elements of albumen in earth, water, and air, those final sources of all alimentation. The earthworm also is a preparer, but in a peculiar way. Look along the garden-walks in summer-time, after rainy weather: you will see here and there, little heaps of earth moulded into small sticks, like dough which has been passed through a tube. [Footnote: M. Mace's account of the earthworm's life seems founded on the assumption that it extracts its nourishment from the earth itself, i.e., from inorganic matter, as vegetables do, to use his own words. But this notion is so entirely at variance with present received opinions, and also with the fact that the animal possesses a gizzard for digesting, as well as an intestinal canal, that it has been necessary to make considerable alterations in the description. To dismiss his theory of the primitive animal, etc., altogether, was, however, impossible, without omitting the whole chapter; but as young heads are not likely to trouble themselves about it, and it is very innocent in itself, it will do no harm; subject to this warning, that M. Mace has taken the earthworm for a more simply organised creature than it really is.—TR.] This is the damp soil which the worm has passed through his tube, after extracting from it, during its passage, the various elements of fertility he requires for the support of his life. This is what makes him so particularly fond of garden soil, because it is richer in animal and vegetable matter than common earth, and proves therefore more nourishing food. The worm, then, feeds on the fat of the earth, which he converts into azotic aliment for the use of moles, hens and Chinese. It only figures, it is true, for want of something better, in Chinese cookery, so profusely hospitable for all that; but the hen doats upon it, and you do not despise it yourself when it comes back to you in the form of a chicken's wing, that second transformation of the matter of which the soil of your garden is composed. It is told of certain savage tribes, the victims of constant scarcity, that they swallow little balls of clay in order to keep down their hunger; and during the great famines in India the distracted inhabitants may, we are told, be seen digging up the banks of the rivers to feed on the fertile clay in which the splendid vegetation of their country is developed. This is a desperate trial of that primeval system of alimentation which answers perfectly with the worm, but becomes a cruel mockery in the case of an organisation as exacting as that of man. Let us examine a little more closely, then, this wonderful tube.

At first sight one notices, to begin with, that it is composed of perfectly distinct rings, all quite alike. Inside as well as out each of these rings is an exact repetition of the other. They are all formed of circular muscles, enclosed between two coats, which extend from one to the other. A series of ganglions, arranged in the form of a necklace along the whole length of the body, set in motion the muscular system of the rings, each of which possesses its local centre of impulsion. Each feeds itself in its place from the nourishing juices with which it is in contact, the interior coat enjoying the double property of distilling digestive juices and absorbing digested ones. These juices pass through the muscular partition, and proceed to bathe the outer coat, which plays, at the same time, the part of coat and lung, and affords a passage to the air through its soft, damp surface, like that of gills. From all this results a fine red blood, such as we have not met with since we left the reptiles, and which is manufactured in all parts of the body at once.

Each of these rings, then, the worm's only organs, is a little eating machine to and for itself, and at the same time a little movement machine also; in fact, a complete animal. Each one could, if necessary, nourish itself and live apart; and this is what he really does. Learn hence, to despise nothing in nature. One tramples an earthworm under foot, and there below one's heel lies a little revealer of secrets, whose organisation throws the most unexpected light upon one of the greatest mysteries in our own life.

I said to you before, and I felt at the time that it was rather beyond you, that "each one of our organs is a distinct being, which has its particular nature and special office, its separate life consequently; and our individual life is the sum total of all these lesser lives, independent one of the other, but which nevertheless blend together, by a mysterious combination, into one common life, which is diffused everywhere, but can be apprehended nowhere in particular."

The study of the worm admirably explains this out-of-the-way sentence. And here observe my adjective—my out-of-the-way—for it is a case in point. We may call it a literary worm; a worm of four rings, each perfect in itself, but yet compounded together into a whole with its own idea.

That which makes this idea of life most difficult to comprehend is, that one cannot prove it by a direct experiment, since there is not one of our organs which could exist separately from the others. Although independent in their special action, yet these multiplied lives are nevertheless in a state of absolute and mutual dependence, from the imperative need they have of each other to make them act, each having for its share only one particular function, the effect of which extends to all the others. This is called the division of labor; and if you still do not understand me clearly, I will explain it in another way. The heart sends to all the organs—does it not?—the blood, without which they could not live: separated from the heart, the lungs would die immediately. It is to the lungs the blood goes to find the air, without which it could not maintain life. Separated from the lungs, the heart would die immediately. There is nothing belonging to us which can avoid the inexorable requirements of blood and air; consequently, there is nothing which can live an isolated life.

I will borrow a simile from human society which you will understand at once. In civilised countries, where division of labor is established, the tailor makes clothes, the mason makes houses, and the baker makes bread. If you could throw them each alone by himself into a wood, the mason would not be able to dress himself, the baker would sleep in the open air, and the tailor would not know how to make bread. Or rather, as not one of them can carry on his trade without the co-operation of a multitude of hands, they could none of them do anything at all. Each completely independent in his work, yet each dependent upon the others, both for living, and even for being able to work, our workmen can only act when they remain bound in close union with the vast society of which they form a part; and our organs—those other laborers whom you have seen working for so long—our organs are just in the same predicament. But in the primitive societies, among savage tribes, where each man can make his clothes, his house, his bread (when he has any), and everything else for himself, you might take such an individual if you liked, and separate him from the rest of the tribe, and he would go on living as before. And so with the rings of the worm, that primitive society of organs. Each of them is a universal workman, who knows how to make everything. Separate him from his fellows, it will not disturb him at all, and he will go on living as if nothing was thematter.

I still remember some profound reflections I indulged in one day some years ago whilst leaning on my spade and looking at a worm that I had just cut in two, and whose two halves were walking off one on each side.

"There was only one creature here just now," I said to myself, "and now there are two! Have I had power, then, to create one with a stroke of the spade?"

I had not then got hold of the key which I now give you, and to which no possible objection can be raised. If there are two beings after the stroke of the spade it is because there were two before. Nay, there were even many more, if we may trust to the "Manual of Zoology" by Milne Edwards, a very good book, excellent for an old scholar like myself, and which I have found very useful in my country-home, as it has enabled me to relate to you one after another the mysterious wonders of life.

He says that, "if one cuts an earthworm across into two, three, ten, or even twenty morsels, each of these morsels will go on living in the same way as the whole, and will form a new individual."

Twenty! that seems to me a great many, because, as far as I can trust to my brief observations as a gardener, it is necessary that some of the rings should remain united together and afford each other mutual support, in order to succeed in repairing the bleeding breaches; but I would much rather believe it than try the operation. My mind is easy when I am defending the plants that I have sown in my garden from the gluttonous worm who would rob them of their food; but it would not be so if I were cutting them up on my table to learn something about them.

Besides, there is no need of an operation to convince oneself of the particular life of each ring. There is one worm, well known by name at least, though happily not to be met with every day, and that is the tape-worm, who establishes himself in the intestine of man, and lives on the chyme, as the other worm does on garden-mould. They call him the Solitary worm in France; and if ever one might suppose a creature appropriately named, it would surely be him; for certainly there is not much society to be looked for in the dwelling he chooses for himself! But it happens that this pretended solitary worm, with his unlimited chain of rings, is only a long row of perfectly distinct beings, so distinct indeed that, from time to time, some of the rings let themselves go, fall off like ripe fruit, and go away to live elsewhere, ready to become the nucleus of a new set, if a happy accident carries them into another intestine, the only place favorable to their development.

At last, then, here is a corner of the curtain raised; here we see the associated organs which constitute an animal, living for once a life positively and in all respects their own. We are now satisfied about this; and when at another time we find them bound together in the chains of a union too ingenious to be severed with impunity—which we shall discover by seeing their action stop at the moment of separation— we shall know the cause.

Do not think, my dear child, that a wretched earthworm can prove nothing as regards other creatures. The worm is the starting-point of all the organisations which come after him. Of what is he composed? Of a tubewhich is itself composed of rings. Well, it is upon this very tube that the whole animal machine has been founded: and these rings, as they expand and modify themselves in a thousand different ways, give birth to all those varieties of being which drive classifiers to despair, because they will not understand that there ought only to be one animal, since there is only one Creator of animals. Now, this animal is a digestive tube served by organs; it is a worm, i.e., which goes on constantly embellishing itself. I said to you long ago, and at a time when you scarcely knew anything, "Have you ever observed a worm or a leech in motion? You see a successive swelling up of the whole surface of its body as the creature gradually pushes forward, as if there was something in its inside rolling along from the tail to the head. Such is precisely the appearance which the oesophagus would present to you as the food passes down it, if you had the opportunity of seeing it in action; and this has been called the vermicular movement, in consequence of its resemblance to the movement of a worm."

And afterwards, in speaking of the intestine:

"If your body were made of glass, so that you could look through it to watch the intestine at work, it would appear to you like an enormous worm, coiled up into a bundle, heaving and moving with all its rings at once."

You have now got hold of the secret, namely, that from the beginning to the end of the digestive tube, its movements are those of a worm. What a wonder! and that the worm is a digestive tube which can walk. This worm, or this tube, whichever you please to call it, has never ceased crawling under our eyes since we began this study. Lost sight of in man in the midst of the riches he has picked up on his road, invisible and coiled backward and forward in his palace like an Eastern despot who leaves everything to be done by his slaves; behold him here in his first stage naked, shivering in the air, forced to go off himself and alone to his pasture—ground! But in the coarse earth with which he fills himself I can already see the delicate chyme which his numerous servants will prepare for him later on, and into which the heart-tree will one day send down its roots—the chyliferous vessels.

A short time ago I called the oyster the primitive animal, but I was in too great a hurry. The worm is the real primitive animal. He is to be found in the oyster, as the oyster is to be found in us; and that poor little beast is, by comparison, an animal of high pretension, who would be shocked, I am sure, if he could understand what we are saying, and heard us assert that he is nothing but an embellished worm.

Zoophytes.

Two centuries ago it was believed that below the worm, animal life, properly so called, ceased, and the creatures whom I am about to introduce you to were supposed to be animated plants rather than living organisms. Hence their name was especially chosen to express that double nature by which they were thought to have a share in two kingdoms at one time—viz., the animal and vegetable—zoon in Greek meaning animal, and phuton a plant. Zoophytes were set down as animal plants.

And although later discoveries have long ago established the fact of the complete animality of zoophytes, the old name is still in general use. But you must not let it deceive you. Zoophytes are animals every inch of them, however low in the organic scale, and although many of the compound ones imitate the growth of plants and shrubs so exactly in their mode of spreading that it is only by the closest observation we can persuade ourselves they do not belong to the vegetable kingdom. Of these there are the delicate buff-colored, prettily-branched, horny specimens found on the shore, which make so beautiful a variety in seaweed pictures among the red and green colors of the real seaweed; but of these also are those wonderful stony shrubs which grow on the submerged rocks of islands in warm seas, and the material which you know so well by the name of coral—the very coral of which the necklaces and bracelets in the jeweller's window are composed.

In all cases of compound zoophytes, however, there is one great point which they have in common with the worm, viz., that there is an association of distinct lives acting unanimously; or, rather, to the same end. Plainly as this is seen in the worm, it is still more obvious in the zoophyte. There is no need here either of cutting them up yourself or of taking other people's dissecting operations upon trust. It is enough to use your eyes, with the help, it is true, now and then, of the microscope's clearer sight.

You know the old oak-tree which stands on the outskirts of the wood, and is called among the country folk the patriarch? Now, this is clearly not an individual, but a nation. It is not a tree; it is a forest. Nay, may I not call it a green field? For this trunk, so truly venerable from ages of growth that one feels inclined to bow to it as one goes by, is, in fact, a collection of structures, accumulated by countless generations of fleeting herbs, i.e., leaves, not one of which has lived for the space of a whole year round. Every spring some thousands and thousands of buds open to the sun; each one, therefore, affording a passage to a little green point; and this point is an oak, who comes into the world, like the first oak, the grandfather who formerly came forth from an acorn, under the form of an herb or tender leaf, which a sheep might have browsed upon. Yet it is so thoroughly an oak, that you have only to take out the bud carefully before it has expanded and fasten it into another one's place upon a tree of the same family, though of a different species, and it will produce an oak of the same sort as its old companions, and which will, as it progresses, look quite a stranger among the indigenous branches. This is the secret of what the gardeners call grafting, and I advise you to try the operation upon rose-trees, for nothing is more amusing. When the autumnal frosts set in, all these troops of new little oaks die, and deliver up their leaves to the wind; but they leave behind, as their summer's work, a tiny morsel of new wood, upon which, if you look carefully, you will see a fresh bud dawning—the hope of the coming season. And thus the great life of the tree is perpetuated from century to century by an uninterrupted succession of transient lives, reminding one in all respects of the life of a nation; and the similitude is complete in the evergreen trees, where the new leaf makes its appearance before the old one has quitted the stem.

And such is the life of the great stone trees and shrubs of various kinds which grow under tropical seas, and whose makers and inhabitants are the coral polyps, the undoubted heads of the Zoophyte race.

But before considering the polypidom, or external dwelling (otherwise called the coeneciun, or "common house"), you must learn something of its originator, the little polyp, who lives inside, and belongs to a family so widely spread over the face of the earth, that there are scarcely any waters, whether salt or fresh, without them.

In your own neighborhood, if you know how to look for them, are to be found on the banks of ponds, or along the borders of streams which lie sleeping in roadside ditches, extraordinary beings which, a hundred years and more ago, completely bewildered the good Dutch naturalist Trembley, who had taken it into his head to study them. Picture to yourself some very tiny bags made of a kind of jelly; gray, brown, or, most commonly of all, green in color, always transparent, and fastened by their base to the stalks of carex, water-lentils, or the confervas, which grow in still water. A hunter on the watch, this bag shoots out on all sides a number of slender threads, like so many whip-lashes, arranged within a circle round the edge of its opening or mouth; and with these whip-lashes all the animalcules which come within reach are entwined, stifled, and carried away to the ever-yawning little gulf, where they are digested in less than no time. Whatever will not digest comes out afterwards by the way it went in. Of what becomes of the results of this digestion it is impossible to form an idea. Were you to cut up the bag and put little morsels of it under the best microscope possible, you would see positively nothing but solid jelly, without the least sign of any organisation whatever. But this is not all. Replace these morsels in the water, and come back tolook at them at the end of five, twenty, or thirty hours. Each one of them will have become a perfect bag, ready to multiply itself afresh if you submit it to the same operation. Sometimes, on some part of the original bag, there suddenly appears a little raised spot, like that which came on your baby brother's arm the other day after he had been vaccinated. What would you have said, if this ugly spot had grown larger and larger without stopping; if it had assumed legs, arms, and a head, and so become another baby, growing from the arm of the first one? Yet this is just what the spots do which come on the bag I have been telling you of; and people have come across bags of a larger species still—between one and two inches in size, in fact—which in this way carried twelve young ones on their backs, if one is allowed to talk of stomachs having backs. You perceive at once that this commencement of animal life is not even a digestive tube, and that nothing in it can he found but a stomach, opening straight to the air above and closed up below.

It was Reaumur, the originator of the famous thermometer, who gave a name to the wonderful bags discovered by Trembley. Aristotle had previously bestowed the title of polypus (many feet) upon a mollusk outwardly formed upon a similar model [Footnote: This is the cuttle-fish, called polypus by old naturalists. We shall speak of it fully hereafter in the history of the movement machine.] with large whips disposed regularly in a circle round the mouth, and intended for a similar use, only that they have another function besides; that of carrying the body along in the capacity of feet by clinging on to the rocks with their suckers as they go. Reaumur transferred this name to the newcomers, and called them fresh-water polyps, to the infinite amusement of Voltaire, who had declared that they were only blades of grass; a new proof, among many others, that in natural history all the intellect in the world is not worth a pair of good eyes.

But it was soon found out that, in collecting these bits of living jelly near the Hague, Trembley had laid his hands on little beings of immense importance on the surface of the globe, and that he had discovered under his microscope the explanation of a mystery which had spread itself, setting human science at defiance, over some thousands of square miles.

I talked to you just now of the jeweller's coral, of which ornaments so becoming to dark-haired people are made. That is one of the stony polypidoms I spoke of as stone trees found at the bottom of the sea, where it grows attached to the rocks in the form of a charming little shrub, stretching its red branches in all directions. The Greeks, who were never at a loss, relate that Perseus one day laid down upon the sea-shore the famous head of Medusa, the sight of which had the property of turning everything to stone, and that the nymphs, in sport, showed it to the coral shrubs; a fact which explained everything quite naturally. Without exactly holding this mythological explanation, modern philosophers had not got much farther, and coral was still a puzzle to them, which they were not fond of troubling themselves about; till, roused by Trembley's revelations, they examined it more carefully, and discovered in its soft extremities (hitherto unnoticed) those same living jelly-bags or sacs, with their circlets of legs, or rather arms, charged with supplying them with food. These were marine polyps, which grow, like those in fresh water, one upon another, but each in its own crusty cell; and like the buds of the oak, these buds of the stony tree form each its special deposit, which it bequeaths in dying to the general mass. In short, as the tender shoot of the oak is filled by degrees with the wood which forms within it, and hardens into a branch, that goes on increasing by perpetually new growths, so the jelly polyp of the polypidom hardens below into stone and dies incessantly at the base, while it lives on indefinitely above in its constantly-renewed summit.

Do not get tired of all this phantasmagoria, my dear pupil: it is a matter of the highest interest. Here is the point of junction—the bond, as it were, between the three kingdoms: an animal growing vegetable-wise produces a mineral mass, extracted from the waters of the sea by an infinity of little living crucibles, who carry on under our eyes the work begun in the first ages of the globe, and quietly manufacture continents for the use of future generations. This ought to console you, my dear child, for being little. It is by little things that God loves to effect what is truly great. He did not seek out the elephant or the whale to form these worlds; He chose workmen no bigger than a pin's head. I have spoken to you about jeweller's coral, which is made into toys or presents for ladies to adorn themselves with; but its brethren, the madrepores of the Pacific Ocean play a very different part. They have formed in front of the shores of New Holland a barrier of reefs three hundred leagues in extent and twenty wide. What are all our buildings after this?—those pyramids and cathedrals which seem so gigantic to us? This ever-increasing wave of coral polypidoms will one day shut against navigators the entrance to one part of the sea's tropical region; and lands not to be found on the map to-day will then lie stretched out under the sun, covered with plants and animals; and this in places where ships now plough the ocean. Know, also, that a great portion of the soil which we tread under foot has no other origin. It was manufactured formerly in the sea by infinite myriads of beings, often infinitely small. Each one, whether polype or shell, produced its grain of stone, and from all these grains God, who directed their work, has made our country.

But it is time to bring this chattering to a close, for it will never end if I do not force myself to stop. I leave it with regret; but all these paths through which I have threaded my way one after another without counting them, have already made a volume which may possibly be considered too large for you. There are many other zoophytes besides the coral polypes, and all of them beautiful and curious. They all inhabit the fertile depths of the waters where God has deposited the first germs of life. I cannot describe them to you now. But to make amends, I will give you a piece of advice which will perhaps make some people stare. Ask your papa to lend you Michelet's book, The Sea, and look there for what is said about the mysterious animals which lie hid beneath the waves. His book was not written for you as this one is: and if, in spite of all my good intentions, I have not always succeeded in being as comprehensible as I meant to be, Michelet, who never thought about little people when he took up his pen, will certainly startle you now and then. But do not be disheartened by a word. You will find there, that which will be forever plain to you, the poesy of nature, and children comprehend that better than learned men.



LETTER XL.

THE NOURISHMENT OF PLANTS.

One more word before we part about the last of the eaters, about Vegetables. They will furnish you with a new and very clearly marked proof of the uniformity of the fundamental conditions to which the Author of life has subjected all organised beings.

Let us look once more at this oak, of whose manner of growth I was obliged to give you a sketch beforehand, in order to show you the ties which unite it with its immediate neighbors in the animal kingdom. How does it feed? I need not tell you this. It feeds by its roots, which suck up in the bosom of the earth the water charged with the juices which form its nourishment. Are you aware that every large branch had its subterranean fellow or representative, and that the annual shoot at the top of the tree is reproduced at the base by fresh fibres, which extend themselves in the soil of the earth, in proportion as their sisters above make their way in the air? And thus, by means of organs ever young, the life and progress of the great association is kept up, while those members whose day of work is over still remain there as the supports of the edifice. It is the same with human societies. They are sustained by what is old, but they live and progress only by what is young. The sap, then, which is the name given to the moisture or water sucked in by the young roots, having once got into the cells of which the tissue of the fibres is composed, passes from one to another, and travels thus to the top of the tree, where it is wanted by the leaves.

There is no obvious machinery here, however, to impel it forward. It journeys on of itself, as it were, under the action of laws which have never been satisfactorily explained, but all of which are dependent on the vital force or life-power of the tree, inasmuch as without it there is no circulation. One agent, but by no means the principal, or it would act as well in a dead tree as a living one, is capillary attraction; and, if you wish to know what that is, you have only to think of what happens to a towel, if you hang it upon a peg, and leave the end of it soaking in water. Does not the "wet" seem to climb up it thread by thread, till it is damp from one end to the other? A little in this way—but these similes are very imperfect, and will not bear close application—the sap rises in a tree, stealing up branch by branch; and it is then called ascending sap. [Footnote: M. Mace speaks of this sap as the blood of the tree, and of the leaves only as lungs. These statements have been modified so as to meet the fact that ascending sap consists of, and conveys the raw elements of food to, the leaves; that in the leaves this food is digested, as well as brought in contact with the air, and that it is thus converted into that nourishing fluid, the descending sap, which certainly plays the part of steward to the tree as our blood does to us, and therefore may now be called the blood of the tree. It must be remembered, however, that each tree has its own sort of steward, as the case of the Euphorbia (quoted afterwards) plainly shows. The analogy with the more general substance of blood is therefore not very complete.-TR.]

It arrives at last at the leaves, which it enters as our food enters our stomachs, and for the same purpose; for in them takes place, as in all true stomachs, that process of digestion by which the elements of the crude sap-food are decomposed from their first condition, and converted into a nourishing chyle; in each tree of a sort "after its kind."

But more than this. Like the outer coat of the earthworm, the coat of the leaf affords a passage to air and moisture through its surface; and here, therefore, takes place that mysterious exchange which is everywhere the essential condition of life. Here is the charcoal-market as before, only the bargainers have changed parts. The air, which in the other case received the carbon, delivers it up, now, and receives oxygen in exchange; exactly the reverse of its traffic with animals. In other words, the tree inhales through its leaves the carbonic acid gas thrown into the atmosphere by our lungs. On its own responsibility it breaks through the alliance between the carbon and oxygen contracted in our organs; keeps the carbon for its own use, to restore it to us another day under the form of wood, or, by the aid of the charcoal-burner, in the pure and simple state of charcoal; and sets at liberty the oxygen, which once more goes off in search of new lungs and a fresh alliance. Thus a constant equilibrium is maintained in the atmosphere; and thus, by a system of perpetual rotation or everlasting merry-go-round, the same substances serve, indefinitely, to support life of every opposite description.

Now there are two things to be remembered in this inverted respiration of vegetables. In the first place, it occurs only in the parts which are green. Flowers, fruit, the root, and every part of any other color, do as we do when we breathe; i.e. deprive the air of its oxygen, charging it with carbonic acid instead. For which reason, by-the-by, we ought not to keep flowers in a bedroom at night. Charming as they are, they are poisoners, and a headache is what we may fairly expect after sleeping shut in with them in the same room. It is almost as bad to allow green boughs to remain there either, for, in the dark, even the green parts cease to purify the air, and begin like the others to manufacture carbonic acid, at the expense of course of their carbon, which thus by degrees is used up. Now, as it is the carbon which constitutes the solid fibres of plants and produces their green color, they soon become yellow and limp when deprived of light. You may, perhaps, have wondered why the gardener amused himself with smothering his poor lettuces by tying them up at top like a knot of "back hair," instead of letting them grow freely in the air and sunshine. It is, my dear, to make them more tender and delicate for you to eat; and those beautiful, crisp, yellow leaves, so delicious to the tooth, would have been green and tough, had they not slowly and quietly let out a great portion of their store of carbon in darkness during the last few days, before being gathered. Even without playing the gardener, you may assure yourself of this fact in a still more simple manner. Put a flat board upon the lawn and leave it there for three days; then take it up again, and you will find just where the board has prevented the light from reaching the grass, a yellow mark so distinctly traced as to be seen from the other end of the garden.

But to return to the sap, which we left undergoing a change from air and solar influences in the leaves. The ascending sap was to all appearance only clear water. When it returns from the leaves, charged with carbon, it is a thick juice having almost the consistency, and sometimes even the color of milk, and is possessed of properties altogether new. The most striking example that I can give you of thedifference of the two states of sap is the Euphorbia of the Canary Islands, whose digestive or descending sap is a violent poison. When the natives of the country are accidentally pressed by thirst, they carefully remove the bark in which the fatal juice circulates, and are then able to refresh themselves safely by sucking the stem, which yields only the watery sap sucked from the ground, and as yet unaltered and harmless.

Each of these two saps, in fact, has its path distinctly traced for it: the first rises through the wood, the second descends through the bark, whence it is called descending sap. If you wish to satisfy yourself of this, fasten a rather tight knot of pack-thread round a young branch, and after a time you will see it pine below the knot and become swollen above it, an unanswerable proof that the nutritive juices flowed downward through the bark; for the wood inside the branch will have been uninjured by the strangling pressure. Remember this, my dear, when you are playing in the garden, and do not injure the bark of the young trees your father likes so much to see flourishing. It is by the bark that they are nourished, and you might even kill them by treating it too roughly.

And now I must show you how the nutrition is carried on, or, if you like better, how the tree grows by means of this descending sap. See: here is a fir tree, which has just been cut down to the ground. Now, if you like, I will tell you in a moment how old it is. I will even tell you the age of every branch, little and big ones both, without making a mistake in a single year; and you know as well as I do that I am no conjuror. You see these small circles so delicately drawn, as it were, upon the face of the sawn trunk, each wider than the last, as if they were composed of a set of tubes, of unequal sizes, fitting exactly into each other. Now count them; and you will perhaps find twenty-five; and as each of these circles represents the work of one year, you will know that the tree is twenty-five years old. In spring, when the sap begins to move more briskly, it deposits everywhere between the wood and the bark, from the trunk to the farthest boughs of the tree, a uniform layer of a thick liquid, which moulds itself exactly upon the wood already formed. This layer stiffens during the year; it gets filled with the carbon left in it atom after atom, by each drop of the descending sap as it goes by, and thus insensibly becoming organised and hardened. When winter arrives to interrupt the work, it will have formed two ligneous, i.e. woody layers, as they are called. Of these, one belongs to the wood, and will never move again so long as the tree lasts, for it will be covered over, and as it were buried, by the successive layers yet to come; while, on the contrary, the other (layer) belongs to the bark, and is doomed to find itself perpetually forced outwards by the fresh layers, which will after a while insinuate themselves between it and the wood.

Previous Part     1  2  3  4  5  6  7  8     Next Part
Home - Random Browse