LETTER x.x.xIII.
MAMMALIA--_continued_.
We come now to animals less familiar to you, and none of which inhabit Europe. We shall therefore pa.s.s more quickly over them.
ORDER 9. _Marsupialia (pouched)_.
_Marsupium_ is Latin for purse, pouch, or pocket. The marsupials are distinguished from other animals by a pouch which the mother has under her belly, and in which the little ones take refuge at the slightest alarm. You would be very much interested with their whole story; but it has nothing to do with our present subject, which we should soon lose sight of if we once began to wander away. This order, so easily distinguished otherwise by that singular pouch, unfortunately for us, offers nothing new for observation. It includes several species, differing entirely from one another on the subject of nutrition, and closely resembling some already described. Some are both carnivorous and insectivorous, and are therefore armed with powerful canines, and with molars like those of the hedgehog. Others are herbivorous, like hares, and have almost the jaws of a rodent. Among the former we have the opossum, celebrated by Florian in one of his prettiest fables. The opossum inhabits South America. Charming little marsupials are to be found in the Molucca Isles, whence come the nutmeg and the clove; these are very like our squirrels, and live as they do, in trees, hunting after fruit and insects. But the greatest number of marsupials belong to Australia, the real native land of the order. They form by far the larger portion of the mammalia with which that country is enriched; the most celebrated amongst them being the kangaroo; an animal which is now becoming common in European menageries, and which, excepting in the matter of its pouch, is nothing but a magnified rabbit, as tall as a man, and with a tail almost as long as itself. As a rabbit, you know what its eating apparatus must be; and some day, no doubt, the French Acclimatisation Society will enable us to judge of its flavor.
It is a kind of meat very likely to be seen on our dinner-tables by-and-by; and, as you have plenty of time before you, probably you may eat of it before you die.
ORDER 10. _Edentata (toothless)_.
These come more directly within our limits. They are cla.s.sed according to their teeth; yet if their name were to be trusted, they ought to have no teeth at all. Whereas, alas! almost all of them have some, and I am heartily ashamed of their scientific designation; but how can we help it? The only really _Edentata, i. e_. toothless animals, amongst them are the ant-eaters, who, considering the nature of their food, are not much in want of teeth. They feed among the ant-hills, whence they get their name; and as they are a tolerable size (from two to three feet in length), it would really have been quite a hardship upon them to have been forced to crunch the ants one by one at every meal. To get on rapidly they catch them with their tongue; but what a tongue! Imagine a kind of long earthworm, lodged in a snout which is elongated like a bird"s beak, and has a very small opening at the extremity. The ant eater inserts this long, string-like tongue into the crowded ranks of its victims, and, as its surface is glutinous, they stick to it by hundreds at a time, and are swallowed at one gulp without a chance of escape. This tongue, perfectly unique in its character, stretches out in its murderous exertions to nearly three times the length of the animal"s long head. What a distance there seems between such a tongue as this and your own little doorkeeper! But no wonder: we have now reached the confines of the kingdom of _Mammalia,_ and the face of nature is beginning to change.
The Armadillo, for instance, which comes next to the ant-eater, looks far more like the tortoise or lizard than its n.o.ble mammalian brethren.
It is covered with scales; and, to look at it, you would say it was a reptile, in spite of its higher internal organization. As for teeth, it has certainly enough of them to give the lie to its name of _edentata;_ but they are not very serviceable ones. They are called molars, however, because they are situated in that part of the mouth which is always a.s.signed to molars; but they are miserable grindstones, very unlike any of which we have hitherto treated. They are all of them flattened cylinders, with no enamel bars to strengthen them; are small and poor, and are placed at rather wide intervals from one another. The poor armadillo munches with these, as best he can, slugs, tender roots, and other prey of the same sort, with which he is obliged to content himself, and which do not require very formidable tools.
The most questionable member of this cla.s.s is the Unau, or Two-toed Sloth. It only wants incisors to be as toothless as ourselves! and the first time I saw it I took it for a little bear. It is true I was then younger than you are now; for the bear, who is one of our nearest neighbors, ought not to have been confounded with the unhappy being before us, one of the drudges of the animal creation; though M. de Blainville (who had not my excuse) proposed placing it still nearer to us, namely, amongst the _Quadrumana_. Observe that instead of hands it has at the end of its fore-limbs only two enormously curved claws, which have somewhat the appearance of a gigantic fork accidentally twisted. Accordingly its ill.u.s.trious sponsor offered it to the world as an _irregular quadrumane_. I believe so, indeed! This _quadrumane_ without hands--this _edentate_ whose molars are preceded by magnificent canines--this enigma of nature, created for the confusion and despair of all cla.s.sification--does, I must in all humility confess, completely upset the rule I laid down so stringently when speaking of the horse, as to the objects for which canine teeth were framed. The canine teeth of the sloth are more developed than its molars, and yet I cannot tell you what they are there for at all. It feeds upon the leaves of trees; and old travellers in South America, where it inhabits, have told us that, when it has once hoisted itself up a tree, it will strip it to its last leaf, and afterwards drop to the ground to avoid the trouble of crawling down. This was what first obtained for it the villanous name of sloth, a t.i.tle which is certainly justified by its gait when on the ground; for it is so ill-made that it cannot stand upright on its legs, but moves clumsily forward by dragging itself on its elbows. It seems, however, that when once in a tree it is a different creature altogether, and can scramble lightly from branch to branch. Moreover, if its claws cannot reasonably be reckoned as hands, they are at all events excellent hooks; and when it is springing about thus in the forest, suspended to the branches by its long arms, one might be tempted, while watching it from below, to decide in favor of M. de Blainville"s opinion. I saw it originally myself in a cage.
As to the sloth"s relationship to the armadillo, this rests upon a detail which bears directly upon our subject. The molars in both animals are cylindrical and smooth, this is a trifle, but what would you have?
The animal had to be cla.s.sed somehow; since naturalists have not had the wit to make detached companies, as they do in regiments of soldiers.
ORDER 11. _Amphibia (two-lived)_.
We are going farther and farther away. Here are animals who are nearly half fishes (_amphis_, _double_, and _bios_,_life_). The _Amphibia_ have two lives: one in the water, which is their true life, and where they are in their element; the other upon land, where they can only crawl; for their paws, which are but half developed, are destined to perform the office of fins, and the hinder ones are extended flatly behind them, and act like a fish"s tail. They are divided into two families, the seal and the walrus. The first feed on fish, and have the same internal organization as the _Carnivora_, as well as the same dental conformation. Some species have even exactly thirty-two teeth, as we have. The jaw of the walrus is the least regular, and the incisors are generally wanting, especially in the full-grown animal; for it appears they lose them very young, as you lost your milk teeth, only, unluckily for the walrus, his never grow again. On the other hand, he has two canines in his upper jaw, which, next to the elephant"s tusks, are the largest we have yet met with. They are sometimes as much as two feet long, and incline downwards with a curve, like the two bars of a pick-axe. They would play the walrus the same trick that the incisors of rodents are apt to do when they have not work enough to wear them down; that is, stop up the entrance of its mouth, were it not that the lower jaw is contracted in front, in order to fit into the s.p.a.ce between the two canines, which thus form a sort of pa.s.sage in which it manoeuvres freely. As you may suppose, the walrus cannot insert prey of any great size into this contracted pa.s.sage; but that is no matter, as he lives partly on seaweeds, and partly--indeed princ.i.p.ally--on sh.e.l.l-fish; his molars being specially adapted for breaking sh.e.l.ls. They are short ma.s.sive cylinders--the upper ones fitting into the lower as a pestle into a mortar.
After the walrus comes a strange animal which has been ranked among Cetaceans (we shall see why presently), but which it would be better not to separate from the Amphibians, since an Amphibian order has been made, for it crawls from time to time upon land: this is the Manatee, or Sea-cow. It comes still nearer a fish than the others. Its forelimbs are absolute fins, with mere vestiges of nails at their edges; it has no hind ones, and its body, which is quite cylindrical, ends in a fin tail in the shape of a shovel. The sea-cow feeds on plants and herbage, and lives at the mouths of great rivers, going up them occasionally to great distances, their banks serving it for pasture ground. In some respects it is half brother to the hippopotamus and the great gra.s.s eating _Pachydermata_, to whom it comes so near in internal organization, and above all in the structure of its molars, that M.
de Blainville seriously proposed ranking it among the elephants, though as an _irregular elephant_, as you may suppose. But then Cuvier had even placed the seal among the _Carnivora_, by the side of the cat, whose whiskers it possessed, and of the dog, whom it resembled in the formation of its head. A naturalist"s office is sometimes very perplexing, I a.s.sure you; and as we are touching on this subject, I cannot resist telling you that the sea-cow laid claim to, on so many sides, had by right a free admission to the celebrated order of _Primates_, although it looks exactly like a large barrel elongated at the two ends. It suckles its young at the breast like man and the monkey; and if Linnaeus flinched from this rather too absurd parentage, old navigators were less scrupulous. Observing this creature in the distance, sporting on the waves, the upper part of its body quite out of the sea, the sailors, whose eye is not of the most refined, and who have no objections generally to the marvellous, imagined they saw a new species of human beings; and hence arose those stories of mermaids and sirens which have been told from the days of Homer downwards, and the traditions of which have not yet quite died out in seaport towns.
To have been pa.s.sed from man to the whale, touching the elephant on the road, is a long way to travel, especially when, after all, one is only a huge barrel of amphibious fat; and you may judge from this that it is not always an easy thing to cla.s.sify animals.
ORDER 12. _Cetacea (whale-kind)_.
Cetaceans are whales; and if I had been consulted on the matter, I should have joined this order and the last together, under whatever name was thought most appropriate. The pa.s.sage from the seal to the whale through the walrus and the sea-cow is an easy and natural one, the two latter being obviously the connecting links; and in spite of certain diversities of food, they form in reality one family-party, as do the marsupials.
But it is too late in the day to talk of this, my dear child, and you and I cannot pretend to alter what is taught in the schools.
But you are astonished, are you not? to hear that the whale is not a fish: and no wonder. It is with it, however, as with the armadillo; it is a fish with a higher organisation inside. The interior of this enormous ma.s.s is a faithful reproduction, as a whole, of that of the shrew-mouse; and when we come to talk of fishes you will have some faint idea of the prodigious distance which this places between the whale and his countrymen of the ocean.
As far as we are concerned, the chief difference is in their way of breathing. The cetaceans breathe like ourselves, and are obliged to come to the surface of the water to take air; while fishes have a special apparatus, which I will explain to you presently, which enables them to breathe in the water. This is a disadvantage to the cetacean in his fish life; nevertheless, of all the mammals (as may easily be imagined) he is the one who can remain longest under the water. With us, for instance, the best divers one ever heard of, those who go to the bottom of the sea after the pearl-oyster, can scarcely stay below longer than two minutes; and even during that short time the veins of the head become so overcharged with the blood, which cannot return to the lungs owing to its forced inactivity, that when the diver comes back to the surface it is by no means unusual to see him streaming with blood from both nose and ears. The cetaceans remain under water for half an hour at a time without seeming to suffer in the least; and Breschet, a clever French naturalist, has given a very satisfactory explanation of this wonderful faculty. In dissecting a cetacean, he discovered all along the vertebral column an extensive network of large veins, which are not found in other mammals, and which seemed designed to serve as a refuge place for the blood during the time the animal remains submerged. According to him, this network would act as a reservoir, to which any overplus in the head or important organs would flow through vessels communicating therewith, and which might swell out as it pleased, without any risk to the inert bed of fat against which it lies. From thence the blood rushes to the lungs, as soon as the animal"s return to the air enables them to play as usual. It must be admitted, at the same time, that all this involves the necessity of a much less active life than that of land mammals, that is to say, a consumption of oxygen much smaller in proportion than theirs; for were you to be furnished down your back with the finest network reservoir in the world for venous blood, it would still not enable you to remain half an hour without breathing.
There is nothing remarkable in the digestive apparatus of the cetaceans except about the mouth, which is, as you know, the essentially variable point among animals. To begin with, the cetacean tongue has the most original appearance possible. Indeed, it is not a tongue, but a large carpet, spread over the floor of the animal"s mouth, and bears not the faintest trace of resemblance to that nimble delicate porter, who does you such good service. Imagine a thick soft lump absolutely crammed with fat, and completely immovable, because it is glued down along its whole length to the bottom of the mouth, and you will have a good idea of this strange tongue, which in the whale, the largest of the cetaceans, attains to the length of twenty-five feet and the width of twelve, and of itself alone furnishes the whale-fishers with from five to six tons of oil. This is a great deal farther from us than even the long string which serves as a tongue to the ant-eater; and you feel at once that we are getting among strangers.
With respect to teeth, I have now a melancholy piece of news to tell you. We have done with them; we have seen the last of incisors, canines, and molars, henceforth you will hear no more about those valuable instruments. The teeth of the cetaceans, with whom this painful falling-off begins, are no more teeth than his tongue is a tongue.
They are like so many nails set in a row in the jaw, and can only be of use in retaining prey, not in grinding it; so that of the many processes your bit of bread has to go through before it becomes a part of yourself, there is one which is dispensed with here altogether, namely, mastication. Cetaceans swallow their food without chewing it.
Besides, they have not got a whole set even of these unmasticating teeth. Dolphins and porpoises, those faithful companions of the sailor, around whose vessel they come playing and tumbling in the seas of all countries, are the only ones who have them in both jaws. And these are the small fry of the order; they do not usually exceed six or ten feet in length.
The Cachalot, or Spermaceti Whale, an enormous cetacean, which rivals the true whale in size, and whose head alone forms nearly the half of its body, has teeth in the lower jaw only. This lower jaw, whose two sides are joined together for half their length (a new deviation, very unlike anything we have found before), is so little proportioned to the gigantic head which contains it, that it is almost lost to sight, and seems like a small plank slipped under a great square block.
Such as it is, however, it possesses many very respectable teeth, of which some weigh as much as two pounds; and with these the cachalot, whose ferocity is tremendous, tears in pieces everything that comes near it, sometimes even the boats of the fishermen who risk their lives in the dangerous pursuit of capturing them. By a singular arrangement, of which this is the only known instance, there is, opposite each of the cachalot"s teeth, a corresponding cavity in the upper jaw, into which they fit closely, turning the monster"s muzzle into the most formidable pair of pincers to be found in the animal kingdom. Another curiosity in the order is the tooth of the Narwhal, a modest cetacean, who is not much more than twenty feet long!
I speak of _the tooth_, because the creature has commonly but one; a cylindrical-pointed tooth, spirally furrowed, whose length varies from six to ten feet, and which comes straight out from the extreme front of the upper jaw, like a soldier"s pike. There are two sockets at this extremity of the jaw, each furnished with a tooth-germ; but as a general rule the germ on the left side is the only one which develops, the other lying asleep in its socket, where it is choked up and never appears. Behind this long pike, which, like the tusk of the elephant, attracts to itself all the ivory in the body, lies a completely unfurnished mouth; so that the owner of this magnificent weapon, invaluable as a war-tool, but quite inapplicable to the purpose of supporting life, is obliged to feed on small fishes and _mollusks_. We have not yet spoken about these latter, but if you have ever seen slugs and snails you will know what a _mollusk_ is.
The same wretched food falls to the lot of the whale also, that giant of the ocean, whose open mouth forms an aperture twenty feet in extent.
Geoffroy St. Hilaire, in his indefatigable endeavors to trace out points of resemblance connecting together animals the most unlike in outward appearance, discovered, along the lower jaw of a young whale, certain traces of teeth, indicating a last effort on the part of nature to carry out her usual plan in furnishing the jaws of mammals; but, like the right-hand tooth of the narwhal, these vain attempts soon disappear, overgrown and lost in the tissue of the bone, so that the whale offers us a true type of an _edentate_, cla.s.sable with the ant-eater, if one dared, and some people have dared, which by this time will not surprise you. A cla.s.sifying professor is utterly merciless, whether he gets hold of the poor beasts by the mouth or by the paw: they may protest with all the rest of their body against the peg on which they are hung; so much the worse for them! If one were to listen to what they have all got to say, it would be impossible to cla.s.sify even one.
To return to the whale. As a compensation for the teeth which she found herself unable to give him, nature has manufactured on the two sides of his upper jaw the most extraordinary apparatus without exception to be found in the mammal mouth. You know what is called the _whalebone_ used in stay-making, &c. The name is quite correct; for those little flexible black strips, which support the figure so nicely, began life in wandering over the polar or Australasian seas, fastened to the palate of some monstrous whale.
On the two sides of the upper jaw the membrane which covers the palate sends out rows of broad, thin, h.o.r.n.y plates, which are from eight to ten feet long (they have sometimes been seen twenty-five feet) in the centre of each side, but which decrease gradually towards the extremities. These are plates of whalebone (sometimes called whale"s whiskers), and the industry of man has turned them to a thousand different uses; and you will open your eyes in astonishment when I tell you that 800 or 900 of them have been sometimes counted on each side of one mouth. Think of the number of stays that could be furnished from the whalebone plates of one whale! It is true, they were not exactly designed for this purpose originally. At the tips and on the edges of these plates, the elastic fibres of which they are composed unravel and peel off, and hang down from the lip like tufts of horsehair. The Arctic seas, which the whale inhabits, are, like other seas, full of innumerable troops of various little sea-animals, and it is these which are destined to the honor of nourishing this gigantic ma.s.s of flesh. When the colossus wishes to take a meal, he stretches his mouth to its utmost width, and the salt water rushing in as into a gulf, carries with it the imprudent little fry, who disappear then and there for ever, being retained by the fringe-like sieve of the whalebone. But as, in this way of eating, the stomach of the whale, however large, would be terribly overgorged with water, he is furnished with another apparatus for preventing the inconvenience. All the superfluous water is rejected by the _pharynx_, and springs up in spouts of fifteen or twenty feet high, through the nostrils, _i.e._ the nasal openings, sometimes called "vents," sometimes "blow-holes," which are pierced exactly at the top of the head. This is a peculiarity common to all cetaceans, who have thence received the name of "blowers," alluding to the powerful blast which is necessary to send those majestic columns of water into the air; but it takes a much milder form with the lesser cetaceans, such as dolphins and porpoises. There is but a slight jet with them: the water escapes comparatively quite quietly from the nostril-vents, trickling away down the animal"s sides.
I hope you consider that I have told you something new this time, my dear child, and that our machine is beginning to change its appearance very materially. I told you before that we had reached the outskirts of the mammal kingdom. When we got to the armadillo we were within a stone"s throw of the reptiles, and here, one step more would take us to the fishes. But we must first consider the birds, who are a very superior set of animals to either of the latter; and we have accordingly an order of mammals (Monotremes) which, as you will now find, opens the road on that side also.
There are but two sorts, and both of them are natives of Australia, which is, as you may have heard, the land of the wonderful in natural history, and their existence was unknown to the learned men of Europe till within the last sixty years. The most extraordinary of the two is the _Ornithorhynchus_, or, to translate the hard Greek word into English, the _Duck-bill_. Its mouth is a true duck"s bill, a downright h.o.r.n.y beak, and its short paws sprawling sideways with a membrane joining the toes together below, and coming a good deal beyond them in front, seem intermediate between the flippers of the seal and the webbed feet of a water-bird. The first naturalist who had anything to do with the ornithorhynchus, Blumenbach the German, who gave it its pretty name, did not think it was able to suckle its young, so much did it differ from mammals in some respects, though looking so like them on the whole. And presently a report arose in the learned world that the new animal which had been cla.s.sed at all risks among mammals (it having the close fur and almost the body of the otter), a report arose, I say, that this ornithorhynchus of Blumenbach laid eggs like a real duck. The uproar in the Academies was tremendous. As early as 1829, indeed, a learned Englishman, Sir Everard Home had sent over to France an authenticated drawing, as he said, of an ornithorhynchian egg, to the delight of the hunters after a.n.a.logies among animal races; while Cuvier looked sadly askance at the intruder, whose arrival threw his animal outlines into confusion, there being no place in them for such a beast. Happily for the poor animal, he has ended by almost settling the matter for himself. The ornithorhynchian egg has never turned up. But in the animal"s nest have been found baby ornithorhynchuses, newly born, under two inches long (the full-grown animal being more than a foot and a half), and not a trace of eggsh.e.l.ls near. Further investigations showed that the mother ornithorhynchus nursed her young with milk, for curdled milk was found in their stomachs; so the Australian phenomenon has been restored triumphantly to the Mammalian order, whence Geoffroy St. Hilaire had excluded both it and its companion, the _echidna_, a sort of hedgehog, provided like the ornithorhynchus with a bird-like bill, only more of the canary-bird sort; and like it, also, approximating to the bird tribe by other details which do not belong to our subject. And so the matter stands at present; and all we venture to say is that cla.s.sification had a very lucky escape.
And now, my dear child, that I have made you acquainted in detail with your nearest neighbors, the last of whom, nevertheless, are strangely unlike you outside, however they may resemble you within, I shall take the liberty of going more quickly over the ground, and shall point out in the ma.s.s only the more important changes which lead from one cla.s.s of animals to another. I should be found fault with if I tried to make you too learned, and you yourself might be tempted to tell me, to my sorrow, that you had heard about enough.
LETTER x.x.xIV.
AVES. (_Birds._)
Tell me, my dear child, when you have seen birds taking their flight into the air, and going boldly to their object, without a thought of all the barriers, ditches, rivers, and mountains, which hinder man at every step in his travels, did it never strike you to wish for their wings, and imagine how you would fly off if you had them? If you ever dreamt this dream, do not apologise for it; it is one as old as the world. "Oh that I had wings like a dove!" cried the Prophet, nearly 3,000 years ago; and the dialogue of the swallow and the prisoner, so often sung by poets, has been repeated in prose behind all the prison-bars on the globe since prisons were first invented.
Now you will not think it kind on my part, but I must undeceive you about this fancy, as you will be undeceived some day about many others.
The wings of a dove or swallow would be of no use to you if you had them, any more than the formidable swords of the middle ages would be to our modern gentlemen, were any one to put such into their hands.
We are not adapted for them, nor they for us.
You saw, some time ago, what an amount of muscular exertion was required for running--what a violent flow of blood, what hurried play of the lungs. Now in flying it is still worse; for the earth, at any rate, holds us up quite naturally, whereas the air will not hold up the bird unless it is beaten vigorously and unremittingly by an untiring wing.
If we men, constructed as we are, had to do such work, we should be out of breath at once; the heart would cry out immediately for quarter, and the diaphragm turn red with anger. And only just imagine in what a critical position a poor wretch launched into the air on the wings of a swallow would find himself when, at the end of five minutes, his servants should refuse point-blank to go on working at a height of 500 feet above the ground!
But a bird has not these internal rebellions to fear. In the first place, it has no diaphragm; so here is another friend to whom we must say good-bye. We shall not meet with him again anywhere. The journey we are taking together, my dear, is somewhat like the journey of life.
One sets off, surrounded by friends and acquaintances, but whoever travels on to the end is apt to find himself alone at last; this is what is happening to the digestive tube, which we shall see losing all its accessories, one by one, as we gradually advance in our study.
Even now here is one essential fundamental difference in the internal machinery. The body has only one compartment instead of two; and the lungs, masters of the whole s.p.a.ce, extend freely to its utmost depths.
When a fowl is cut up at table, look along the body, and you will find lodged in the cavity of the ribs, a long, blackish, and spongy ma.s.s: this is the lungs. There is not, therefore, the same danger of a bird"s getting out of breath as with us; that delicate board which is found in our bellows is wanting in his. His is set in action solely by the to-and-fro movement of the ribs, which is produced by muscular exertions, which are greatly increased during the action of the wings.
From which it follows, that the rapidity of flight itself regulates the arrival of air, and consequently the expenditure of strength, or, if you like better, the activity of the fire, since the energy of the muscles depends, as we have seen, upon the quant.i.ty of oxygen that feeds the internal stove.
This is not all. These elongated lungs are still not sufficient to furnish the blood with all the oxygen demanded by this excessive labor of flight. They are pierced with holes, through which issue pipes which carry the air all over the body. You know what is said of spendthrifts?-that they burn the candle at both ends. It is so with the blood of birds. That fillip which in our case it receives in the lungs, and which sends it back full of vigor into the arteries, is repeated in the bird at the other end of the arteries as well. The capillaries, those delicate vessels at the end of the arteries, plunge from all sides into little reservoirs of air-lungs, therefore-where the blood renews its provision of oxygen, and relights its half-extinguished fire, so that it sends the combustion afresh into the muscles on its return back to the heart, and sets them going a second time.
The natural consequence of this prodigality of combustion is, that there must be, in proportion, much more oxygen in birds than in us; and that of all animals a bird is the one most quickly poisoned by his own carbonic acid when the air is not renewed around him. Therefore, let me beg you never to think of putting a poor little bird under a wine-gla.s.s, as a child of my acquaintance once did, that she might examine her little friend more closely. In the twinkling of an eye he would consume all the oxygen inside his prison, and you would soon see him fall upon his side and die.
On the other hand, the temperature of these flying machines, which consume so much oxygen, is very much higher than ours. It rises to 41, 42 (centigrade), and sometimes to 44, 7 higher than with us.
If ever you have taken hold of a little bird, you will have remarked how warm it makes your hand: this is quite natural, since there is always a double fire going on within him, to meet the extraordinary expenditure of strength that is required of him whenever he takes wing.
Besides, do but look at the poor little creature when you have imprisoned it in a cage! How it goes up! How it comes down! How it hops from one perch to another, with a quick sudden movement, like that of a spring when it unbends. There is no apparent cause for this state of continual agitation; and yet there is a cause, and only too serious a one. Its fire is not slackened because you have put it into a cage, and its muscles, lashed furiously on by the double-oxygenized blood, drive it hap-hazard into a thousand movements, in which it expends, as best it can, a superabundance of power, which no longer finds natural employment. Little children, who are the real singing-birds of our homes, and whose blood also drives much more energetically along than ours--little children I say--often fare no better than caged birds in those larger cages we call schools; and schoolmasters and governesses would scold rather less if they thought rather more about this. It is right, I do not deny it, that the rebellious young rogues should be taught in good time not to abandon themselves, like wild birds, to the mere animal impulses of the blood: but, in dealing with them, one must also make allowances, as they say, for the fire within, and know how to open the cage now and then. It is not for you, however, that I say this, young lady: you are no longer a little child; but it may happen that you may have some to take care of some day. Believe me, then, you must not expect too much wisdom from them, and you must allow them to change their perch every now and then. It is a law of our Almighty Father that little children, and little birds, should not stay too long in one place.
The mechanism of the circulation is here the same as with us, and does not offer any important peculiarity. Only the left ventricle of the heart has walls of extreme thickness, which enable it to launch the blood into the members with greater vigor and rapidity; and the blood itself, although it is composed of precisely the same materials as that of the mammals, differs from it nevertheless as regards the globules. In the first place, they are more numerous; secondly, they are larger; and finally, instead of being round like a plate, they are drawn out ovally, and are almost shaped like those long dishes on which fish is usually served. I shall not attempt to give you the reason of their size and form. This is hidden from us in the same mystery which envelopes all the microscopic population of the blood; but is it not a curious thing, this strange persistency of form in the globules ofall animals of one cla.s.s? In all birds they are oval; in all mammals they are round. In all? Nay, I am wrong. As if the better to hide from us the key to this riddle, nature has amused herself by making an exception. Camels and llamas, I forgot to tell you, have also globules in the form of long dishes, like the hen and the chaffinch. Find out why, if you can. As to the reason of the number, it is a very simple one. Since the energy of the blood resides in the globules, it follows that the most energetic blood will contain the largest amount of globules. Looking at you, for instance, little monkey, running and jumping about the garden, I would lay a wager, without counting first, that there are, in one drop of your blood, some millions more globules than in one of mine.
Let us now go on to the digestion, with which, properly, we ought to have begun; but I preferred pointing out to you, first, the particular character which is the chief mark of distinction in the organization of the bird.
"When hens grow teeth," says a shrewd proverb, meaning of course, _never_. Birds have no teeth, and in this respect there is no variety among them. All, from the first to the last, have uniformly the same tool to eat with--the bill, that is--which is, in all cases, composed of the same elements, two jawbones elongated to a point, and clothed in a h.o.r.n.y armour, which makes their edges sharp and cutting.