The History of a Mouthful of Bread
by
Jean Mace
Part 5 out of 6
old-fashioned sort, like the three others; it is called the _reed_ or
_rennet-bag_, from the property it possesses, in the calf, of turning
milk into curds: and of his four stomachs this is the only one which the
ruminant makes use of at first. As long as the young animal is nursed by
its mother, the other compartments remain inactive and small in size;
they neither grow nor exercise their functions until it begins to eat
grass. Indeed, they would probably entirely disappear, if any one would
go to the expense of keeping the animal on milk all its life. If it
ceased to have anything to ruminate, nature would certainly lose no time
in relieving it of its useless workshop of rumination.
As it is right to give every one his due, I will mention that we owe
our accurate knowledge of this simple and ingenious mechanism of
_rumination_ to the labors of Flourens, a scientific Frenchman,
who is still alive, and who has made a great many interesting inquiries
into the subject we are now considering, _i. e._, the life of
animals. He is a very clever man into the bargain--so perfect a master
of his own language, that the French Academy has felt itself justified
in opening its doors to him--an unheard-of honor for a member of the
Academy of Sciences. And yet, in spite of all this, I heartily
congratulate you that the discovery of the _paunch_, the _cap_, the
_leaf_, and the _rennet-bag_, was not delayed for his arrival. He is
just the man who might have been tempted, in his capacity of profound
scholar, to have hunted up for them in the _Jardin des racines grecques_
[Footnote: Your brother can tell you about the _Jardin des racines
grecques_. It is a charming little book, of which every generation of
collegians has learnt, by heart, the commencement; but I have never
known one, even among the most intrepid, who had ever been to the end of
it.], four magnificent names, which would only have bewildered you.
Beyond the rennet-bag there is no change of conformation to note,
except that the intestinal tube is naturally much longer than ours,
on account of the difference of food: as a general rule, it is ten or
twelve times the length of the body. The sheep, who is able to pick
up a living in the poorest pastures, is indebted for this inestimable
power, which makes him the special blessing of dry and barren countries,
to a still further peculiarity of organization; with him the intestinal
tube is twenty-eight times the length of the body.
We have seen among the _Carnivora_, whose jaws have so much work
to do, that the condyles of the jawbone are sunk deeply into the fossa
of the temporal bone. The ruminant, whose peaceful mouth is formed for
contending only with grass, is organized quite differently.
Here the condyle is flattened, and the fossa of the temporal bone very
shallow, presenting to the condyle an almost flat surface, so that the
jawbone is enabled to revolve with ease for the better mastication of
the pellets of grass. This conformation is also to be seen in the
_pachydermata_ who feed upon vegetables. In the horse, especially,
whose food is almost the same as that of the ox, the _articulation_
(as this joining of the condyle to the temporal bone is called) of the
jaw, is also nearly identical; and it is the same with the teeth, with
very trifling variations, those of all ruminants are constructed on
the same plan as in the horse. The canines only require a separate
notice.
But first I must tell you that, by some special privilege, the reason
for which I do not undertake to explain, the order of ruminants is the
only one containing animals with horns on their foreheads. Stags,
goats, reindeer, chamois, gazelles, roebucks, oxen, buffaloes, all the
beasts with horned foreheads, belong to the ruminants. Indeed, this
fact would form a very convenient mark of distinction between them and
other animals, were there not exceptions to it. Some ruminants have
no horns; and then, as if in compensation for the deficiency, we find
them provided with canines in the upper jaw, in addition to those
below.
The ruminant which has the most beautiful canines is the musk-deer,
a pretty little animal inhabiting the highlands of Central Asia, like
the chamois of the Alps. But now that you know who he is, you will
probably often be tempted to wish he had never existed; for it is from
a small pouch below his belly that people obtain that odious musk of
which Oriental beauties are so fond, and which even certain
strong-nerved ladies of our own country are guilty of using in public,
to the great detriment of general health. But enough of this; our
business is with the canines of the musk-deer. They project with a
descending curve from the upper jaw, and would give the animal the
very false appearance of a small wild boar, but for the great delicacy
of its legs, which are more slender than even those of our roebuck,
to whom, with the exception of the horns, it bears a close resemblance,
as its name implies.
After the musk-deer comes the large family of camels and llamas, which
represent--the former in Asia and Africa, the latter in America--the
irregular groups of ruminants which have canines instead of horns, and
which seem to be placed as intermediates between true ruminants and
the pachydermata. They form the connecting link between the horse and
the ox, and men prefer employing them as beasts of burden to using
them as butcher's meat; though one could eat them in their own country
with less disgust than Europeans feel in making a meal of horseflesh;
so that they might be a very acceptable resource in many cases. The
real fact is, that ruminants with horns and without upper canines have
more delicate flesh than the others, and seem more especially destined
to be eaten. Yet if one had only to look at the stomach, which is,
after all, the distinctive characteristic of the order, camels and
llamas would stand in the first rank as ruminants. Besides the usual
character of four stomachs, their paunch and honeycomb-bag are furnished
with large cells which act as reservoirs, and fill with water whenever
the animal has the chance of drinking freely, and from whence in time
of drought he draws it up into his mouth and swallows it. This is what
makes the camel so valuable to the wandering tribes in the great deserts
of Africa and Asia. He is the only animal who can pass several days
under the burning sun of Sahara without drinking--or rather without
appearing to do so--for he carries his provision of water concealed
from all eyes in the recesses of his body. I dare say you have often
heard stories of Arabs dying of thirst who have opened the stomachs
of their camels in search of a last draught of water. It must be a
terrible thirst to drive a man to such an extremity; for, as you may
imagine, one could not expect the water there to be either fresh or
clear, to say nothing of the great risk there would generally be of
finding the reservoir empty. Such an extreme is never resorted to till
water has failed for a long time, and all the goatskin bottles have
been emptied; and in such a ease it is but too likely that the camel
has followed his master's example, and emptied his water-skins for his
own use. But this is only half the internal fittings of the "ship of
the desert," as the Arabs call him. In the desert it is often as
difficult to find food as water; and nature has equally provided for
this. The hump you see rising upon the camel's back in your
picture-books is his safeguard against starvation. It is a huge mass
of fat. I need say no more. You will remember Mr. Liebeg's pig, which
lived 160 days upon its own bacon. Without going quite such lengths
as that, the camel can keep up his fire for a long time upon the fuel
which the blood obtains from this blessed hump. Since we are talking
of this animal, and he takes a remarkable place in a history of
nutrition, I ought to tell you that camels are classed into two families
by their hump: there is the camel, properly so called, which has two
humps, and the dromedary, which has but one. This latter did not require
such a supply of provisions as the other, for he is very much swifter
of foot, and consequently his journeys are more speedily performed.
I have nothing particular to say to you about the other ruminants, in
the matter of their organs of nutrition; but I will not quit the subject
without reminding you of one thing which concerns nutrition, not theirs,
however, but ours. It was by the taming of the domestic ruminants--that
unfailing dinner-material which now follows everywhere at the heels
of his master--that human civilisation began. Before that event, man,
driven to depend for his living upon the hazards of the chase, spent
his whole time in seeking for food, and had none to spare for the
pursuit of any other branch of industry.
Far as we may ascend in the history of ages we shall find shepherd
races. Beyond them there is no history at all, nor could there be. The
first leisure hours of man, and, consequently, his first efforts in
art and literature, date from the period when the ruminant animals,
those special fabricators of nutritive aliments, were gathered around
mankind, and worked out their destiny under the shadow of his tent,
by his direction, and for his benefit. But all this is so distant from
us now, that it is scarcely worth the trouble of thinking about. The
human race is somewhat like those old people who have lost all
recollection of their childhood; and young people are not required to
know what their elders have forgotten. It is well, however, that they
should not be quite ignorant on the subject. When you hear that the
Society for the Prevention of Cruelty to Animals has taken up the cause
of some barbarously-used ox or sheep, do not turn it into ridicule.
Those humble species have supported ours from the first; and you should
recollect, now and then, that human society made its first step forward
when it began to keep flocks and herds.
LETTER XXXIII.
MAMMALIA--_continued_.
We come now to animals less familiar to you, and none of which inhabit
Europe. We shall therefore pass 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 classed 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 noble 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 assigned 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 class 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 illustrious 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 classification--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
title 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 classed 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 space between the
two canines, which thus form a sort of passage in which it manoeuvres
freely. As you may suppose, the walrus cannot insert prey of any great
size into this contracted passage; but that is no matter, as he lives
partly on seaweeds, and partly--indeed principally--on shell-fish; his
molars being specially adapted for breaking shells. They are short
massive 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 grass
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 assure 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 Linnæus 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 passed 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 classify 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 passage 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 mass 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_, classable with the
ant-eater, if one dared, and some people have dared, which by this
time will not surprise you. A classifying 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
classify 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, horny 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
mass 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 horny 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 classed 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 analogies 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 eggshells
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 classification
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 mass only the more important changes which lead from one class
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 XXXIV.
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 space, 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 mass:
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 quantity 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-glass, 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 class? 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 horny armour, which makes their edges sharp and cutting.
At the same time were we to review the birds in detail, as we have
done the mammals, you would see that there are almost more modifications
to be observed in this one single instrument than in our thirty-two
teeth. All birds have a beak, but each has his own, organized expressly
with reference to the kind of food needed by its owner. The eagle's
beak, which mangles living prey, is pointed, bent, and hard as steel;
the bill of the duck, which laps up water from ponds and puddles, in
order to get worms and half-decomposed refuse out of it, is soft, and
flattened like a shovel. The woodpecker's, which has to pierce the
trunks of trees, is like a pickaxe; that of the humming-bird, which
has to suck up the juice of flowers from the bottom of their corollas,
is slender as a needle. The swallow feeds on flies, which it snaps up
on the wing, and has a soft bill, which opens like a little oven. The
stork picks up reptiles in the mud of the marshes; its beak is
straight-pointed, cutting as a knife, and resembles a long pair of
pincers. The sparrow feeds especially on hard grains, difficult to
break; accordingly its beak is stumpy, short, and thick, and is arched
on the upper side for still further solidity. But I should never end
if I began to enumerate all the thousand varieties in the bills of
birds. Each variety, too, corresponds with some peculiar sort of life,
and consequently with a general conformation (easily ascertained) of
the animal in which it appears. Give a naturalist the bill of a bird
--only its bill remember--and he will tell you half its history without
fear of being mistaken.
On the other hand, we must not deceive ourselves as to the real value
of this complaisant bill. Let it transform itself as it pleases into
all manner of forms for the better fulfilment of its task, it makes,
at the best, but a very poor instrument for mastication; nay, to say
the truth, it breaks, cuts, and tears, but it never masticates at all.
Thus the bird's mouthful is far from undergoing as perfect a preparation
as ours does. It is no sooner taken in than it is swallowed, and the
salivary glands, which are still to be found under the tongue, seem
only to be there as a matter of form; what little saliva they produce
is thick and sticky, and has none of the qualities necessary for making
that liquid paste which our tongue sweeps up from every corner of the
mouth. Besides, it must be owned that a bird's tongue would be a very
awkward implement in such a task. Open a hen's bill and you will see
therein a very inferior sort of porter. It is merely a dry hard lance,
as it were, armed with prickles at the point, as ill-qualified for
tasting as for sweeping. So the hen does not waste her time in finding
out the flavor of what is thrown to her. She picks up and swallows
over and over again, without appearing to experience any other pleasure
than that of satisfying her appetite. Birds of prey, it is true, have
rather more convenient tongues, capable, moreover, of tasting up to
a certain point; and the parrot, who is a complete epicure, and chews
his food philosophically, has a charming-little black one, thick,
fleshy, and susceptible--a true porter, in fact-who enables Polly
thoroughly to enjoy her breakfast. But certain birds who live on insects
surpass even the hen in the dryness and hardness of their tongues.
That of the woodpecker, especially, is a model of the kind, and deserves
a few words more than the others. Picture to yourselves a long pin,
terminated by an iron point with barbs like those of fish-hooks. An
ingenious mechanism enables the bird to dart it out with the rapidity
of lightning, far beyond his bill, upon the insects to which he gives
chase. The point pierces them, and the hooks retain them, without any
need of assistance from the bill. I have just told you that this bill
pierces the bark of trees; but it only plays the part of gamekeepers
on grand sporting occasions, who beat the bushes to make the game rise.
The woodpecker's bill routs up the insects by destroying their shelter;
but the real sportsman is the tongue. Good-bye to any notion of a cosy
little chat in such a porter's lodge as that! What could a harpoon
have to say for itself?
Do not, however, let this miserable entrance-hall alarm you, at the
same time, for the fate of the mouthful thus presented half-dressed
to the œsophagus. You will find it only so much the better treated
within. In the first place, the œsophagus, when half-way down to the
stomach, swells out suddenly and forms a pocket, which is generally
particularly well developed in birds who feed on grain; this is called
the _crop_ in English, in French _jabot_; whence comes the application
of that word to those full shirt-frills which have sometimes been the
fashion. It is the pigeon's _crop_ that gives him the rounded chest over
which he bridles so prettily. The crop is a receptacle where the food
makes a halt: it is something between the pouch of the monkey and the
paunch of the ox; a preparatory stomach, which does not, it is true,
send back the grain to the bill, for the bill could do it no good, but
in which that grain lies until there is room for it further on.
Prom thence it resumes its journey; but, before reaching the true
stomach, it passes through a second enlargement of the oesophagus,
whose walls are pitted with numberless little cavities, from which
pour over it the juices destined to supply the place of the saliva
that was wanting above.
It reaches its destination at last, but still hard, and generally
whole. No matter, however. The stomach which receives it, and which
is called the gizzard, is quite a different sort of thing from a useless
membrane, thin and delicate like ours. It is a thick muscle of enormous
power, lined inside with a kind of horny skin, so tough that nothing
can break through it. You may form some idea of the prodigious strength
of this organ, when I tell you that turkey-fowls have been made to
swallow hollow balls of glass, so thick as not to break when dropped
to the ground, and that at the end of a few days they have been found
reduced almost to powder in the uninjured stomach. No fear of
indigestion with such an apparatus as that. Though the grain may not
have been masticated in the bill, what does it signify? There is a
power here, as you see, quite equal to carrying the whole work through.
Thanks, indeed, to the invaluable horn which lines it, fowls which
have no teeth of their own can safely present themselves with as many
and as hard ones as they please. They swallow small pebbles, which rub
against the grain, during the contractions of the gizzard, and act
just as effectually as if they were fixed in the jawbone. Well, this
terrible gizzard performs its crushing work with such energy, that not
only the grain but the pebbles themselves are ground down there, and
end by being pounded into fine sand. When you rear fowls, do not forget,
if you keep them shut up, to put within their reach a store of small
pebbles, so that they may have teeth to run to in time of need.
You remember the _pylorus_--the porter down below, who keeps the
door of egress from our stomach? He is as badly provided for here as
his fellow-workmen up above; worse in fact. It is a gaping hole, and
we cannot expect a very strict supervision from it. Birds who feed on
fruits profit by this fact to carry vegetables from one country to
another. With such an easy opening, seeds have a good many chances of
passing from the stomach unaltered; and then they drop from the clouds,
as is supposed, hap-hazard, and germinate afterwards, when circumstances
prove favorable, to grow up before the astonished eyes of the natives
into plants of which they have never even heard. The French
Acclimatization Society, which I spoke of lately, and which, though
so modern, has correspondents all over the globe, is at this moment
laboring to effect an exchange between all countries of the natural
productions of their soil. But here you see that nature had thought
of this before, and established her acclimatization society long ago.
To complete the internal work of digestion, so feebly begun in the
bill, an extremely large liver pours torrents of bile into the duodenum,
and the manufacture of chyle proceeds with that wild rapidity which
characterizes all the living actions of birds. But speaking of this
liver, I think I ought to give you an account of a celebrated dish,
considered a great dainty by epicures, called _pâtés de foies
gras_--_fat liver patties_, to translate it into its meaning.
Very likely you will not care to eat them after hearing my story; but
that will be no great loss to you, for it is a very indigestible sort
of food, and not at all good for children.
You remember my telling you about Englishmen going to India and coming
back with a liver-complaint, from having eaten and drunk more than the
climate allowed? By an imitation of this process, human
ingenuity--occasionally so cruel--has created the _pâtés de foies
gras_, the glory of Strasburg. I have been in the country, and can
tell you how it is managed. They shut a goose up in a square box, where
there is just room for his body. They open his bill at feeding-time,
and cram down with the finger as much food as can be got in. This is
throttling rather than feeding it. The poor beast, who can use no
resistance, since it cannot move, and who is kept in the dark to prevent
excitement; the poor beast is quite unable to burn all the mass of
combustibles with which the blood soon finds itself loaded. This carries
them to the liver to be turned into bile; but the liver is not equal
to the work, becomes loaded in its turn by unemployed materials, and
grows and grows, till at last, having filled up all the space around
it, it stops the play of the heart and lungs. When the animal is
nearly suffocated they kill it; and this is how we come to have _pâtés
de foies gras_ to eat! If they give us a fit of indigestion
afterwards, it is a vengeance we richly deserve. At Toulouse, where
the same trade is carried on on a large scale, they used formerly to
go even beyond this. They fastened the goose by the feet before the
fire-place, after having put out its eyes. The imitation of the
Englishman's proceeding was still more perfect here, for the fire acted
the part of the Indian sun to perfection. I do not know that part of
the country well enough to tell you whether they have quite given up
this piece of wicked ingenuity; all I can say is, I devoutly hope so.
The intestine of birds is much shorter than that of mammals. Here
everything is done at full gallop, and the chyle has not to go far
before it is absorbed. I have before me a book, in which I am told
that the wagtails eaten in France can be fattened in twenty-four hours,
if you only know how to set about it, and these birds are not rare;
they belong to the same family as the red-breasts, the tomtits, and
the nightingale. Thrushes and wheatears (ortolans) require, for the
same purpose, four or five days in the same country, left to themselves
to roam about, when the vine keeps open table for them.
This incredible quickness, not only in digesting, but, what is much
more, in transforming food into fresh living material
(_assimilating_ it, as it is called), has often a fatal result
for the bird. He is prohibited from fasting; his life is a fire of
straw, which must be replenished unceasingly, or it will die out in
the twinkling of an eye. Our own little birds--children--eat oftener
than grown-up people, and if by any accident they are kept waiting
awhile, they soon cry out with hunger. You know this, do you not? Well,
then, if any one should give you a bird to keep in a cage, remember
that you have undertaken a great responsibility, and that it will not
do to be careless with him. To neglect feeding him for one day is to
run the risk of finding him starved to death next morning. With this
warning, I will conclude my chapter on birds. I hope I have not spoken
in vain in behalf of those poor little captive songsters, whose fragile
lives are at the mercy of their young masters and mistresses.
LETTER XXXV.
REPTILIA. (_Reptiles_.)
Passing from birds to reptiles is like falling from a torrent into
still water. Life drags on as sluggishly with the second as it dashes
furiously forward with the first.
I spoke to you just now about a fire of straw: now we have a fire such
as Frenchwomen make in their _chaufferettes_, or foot-stoves. A
handful of charcoal-dust, and a few live embers between two layers of
ashes, is enough for the whole day; which is economical, is it not?
but then it throws out only just warmth enough to keep one's feet
comfortable. And so it is with reptiles. They live at very small
expense. If you feed them once a month they will not complain, for so
slow a fire does not often need replenishing with combustibles. It is
even said that the experiment has been carried so far with tortoises
that they have been made to fast for more than a year, and still the
charcoal fire kept up its languid pace. Of course, on the other hand,
there is not nearly so much oxygen consumed at once upon such a diet
as this. Where a bird would perish twenty times over in five minutes
for want of oxygen, a lizard can remain whole hours with impunity.
Moreover, the animal heat of reptiles is in proportion to their
expenditure of it. Graceful as is the snake (that living jewel so often
copied by bracelet-makers), you feel on touching it an instinctive
horror, caused by the thrill of cold it produces. All the animals we
have considered hitherto have warm blood, and bear within themselves
the source of their heat, which is pretty nearly always the same. But
reptiles are cold-blooded, and heat comes to them chiefly from without.
If, at the end of a cold winter, we go to some favorable corner to
catch the first rays of spring sunshine, we feel ourselves almost
re-born, as it were, as if a new life had come into us with the
sunbeams. Look at the little lizard you see frisking on the white
stones of the wall; upon him decidedly the sun is darting actual life
from its rays. While the cold lasted he staid squatting in his
hiding-place--not asleep, but annihilated--congealed, so to speak,
like water caught by the frost; no longer digesting, and hardly
breathing, he had ceased to live in reality: and it is no imaginary
regeneration which the return of warmth brings to him. Like those
helpless people who have not the power to carve out their own destinies,
reptiles have within them only an insufficient source of animation;
their life is at the mercy of the sun, and is high or low, according
as that rises or sets in the heavens. At Martinique, where at noonday
it darts its devouring rays perpendicularly upon the cane-fields, and
every one flies into the shade to escape its scorching heat, the
rattlesnake traverses the country, monarch of all he surveys; he strikes
rapidly with a vigorous tail upon the calcined ground; and woe then
to any one who receives his bite! All the fire of the atmosphere has
passed into his frame. Now go to the Zoological Gardens, and see him
there: he crawls languidly under the coverings that shelter him; if
by chance he bites any one, it is with an idle tooth that no longer
knows how to kill; his life was left behind with the sun of the tropics,
and it is little more than a corpse that you are looking at.
And so among ourselves, my dear child: we meet with people whose whole
power comes from without, who are brilliant and haughty in the sunshine
of good fortune, but crest-fallen, cowardly, and cringing in the cold
days of adversity. Nevertheless, they are constituted originally like
other people: they are neither greater fools as a general rule, nor
less gifted than their neighbors; where they fail is in the heart, but
that is enough to spoil everything. And so with reptiles: the heart
is their weak point also. Like us, they have lungs into which the air
pours without any difficulty, and a heart to send the blood to them;
so it seems at first sight as if there could be nothing to prevent
their resisting the changes of external temperature just as well as
ourselves. There is only one small trifle wanting, and that is a
partition in the middle of the heart; but this one defect is enough
to disorder the whole machinery.
You know that, with us, the heart is divided into two compartments:
the right ventricle, which receives the venous blood from the organs
and sends it to the lungs; the left ventricle, which receives it (now
become arterial) from the lungs and returns it to the organs. Hence
the double system of veins and arteries, the one going from the heart
to the lungs, the other from the heart to the organs. All this is found
the same in reptiles: except that the partition, which separates our
two ventricles from each other, does not exist in them; and the heart
has only one common room, in which, therefore, arterial and venous
blood become mixed together. It follows from this that, at each
contraction of the heart, it is a mixture of arterial and venous blood
which is sent in the two opposite directions at the same time, and
that the organs receive some which has been used before, while the
lungs have some returned to them which has been regenerated already.
Now, on the one hand, this mixed blood can only keep up an imperfect
combustion in the body (like the live embers between two layers of
ashes that we spoke of lately), and, on the other hand, the air in the
lungs can only act upon a part of the blood it meets with there, the
rest having already undergone the regenerating process. And this
accounts for both the feeble animal heat and the small consumption of
oxygen in reptiles.
Added to which the lungs of a reptile are coarsely constructed, and
composed of cells enormous in comparison with ours, so that the blood
does not find nearly as many little chambers to rush into for a taste
of air as with us. Moreover, you must understand that there is no such
thing as a diaphragm here: the lungs float loosely in the form of
elongated bags in the one only cavity of the body, and the slight
movement of the ribs does not allow them to dilate sufficiently to
take in much air at a time.
All these things, taken together, make the reptile a very poor stove,
and render him incapable of any prolonged exertion. The serpent darts
like an arrow upon his prey; but he could not pursue it for half a
mile without stopping, not even over the burning soil of the equator.
The lizard is very nimble, is it not? and the quickness of its movements
rather reminds one of the agility of a bird. But watch it, and you
will see it only moves in jerks, and keeps stopping every minute; it
cannot escape you if there is no hole near into which it can disappear.
In France there is a large green lizard that runs among the vine trees.
If you pursue him he is off like lightning for a second; then he stops
suddenly short. You return to the charge, and he starts afresh, but
only to stop again. At the fourth or fifth attack he is quite out of
breath; you poke him with the stick with which you have been hunting
him, but in vain; there he lies motionless, in spite of his alarm. A
few steps have brought him to the end of his powers, like a man whose
heart is diseased and who cannot go far. This, however, is a peculiarity
common to all reptiles. Each of the three orders of which this third
class of Vertebrata is composed has its own particular history besides.
You must excuse my mentioning the barbarous names that have been given
them, and allow me to call them _tortoises_, _lizards_, and _serpents_,
like other people. The hard names mean no more than these; but they are
Greek, which is always more imposing.
The slowness of the tortoise has passed into a proverb, which is not
to be wondered at; for they cannot inhale the air, because their ribs
(which are a reptile's only resource for breathing) are condemned to
absolute immobility. The _carapace_, or shell, which the tortoise
carries on his back, and under which it retreats upon the least alarm,
as under a shield, is really formed of its ribs, each of which has
widened itself so as to join on to its neighbor, like the boards of
an inlaid floor, which run one into another. Of course there is no
question of moving up and down with such ribs, and the poor bellows
cannot work at all. How does the tortoise get out of this difficulty
then, you will ask? I answer, it swallows air, as we should swallow
a glass of water. You see its mouth open and then shut again, thereby
taking in an actual mouthful of air, which the sides of the mouth, by
contracting themselves, send straight to the lungs. These, which are
very large, get filled in this way by degrees, and, when they are quite
inflated, they expel the overplus by collapsing, like an over-stretched
spring. You may imagine that this does not produce a very active
respiration, and that a tortoise would be puzzled to run at even a
moderate trot. To be sure, when he has once filled his great lungs
with air, he has enough for a long time. Most tortoises are aquatic,
and, as divers, leave the cetaceans far behind. Méry, an obscure French
naturalist of the days of the Empire, pretended that he had kept in
his house, _for a month_, some tortoises, whose breathing he had
completely stopped. Only imagine from this how far their life must be
below ours, although it is the result of similar actions, performed by
organs which after all are copies (imperfect ones, it is true) of our
own.
Some tortoises feed on vegetable substances, and some upon fish or
small soft-bodied animals. Like birds, they mash their food with
difficulty, by means of a real bill. Their jawbones are generally
arched forward toward the front, and are furnished with sharp horny
plates, in which a fairly-marked denticulation or notching may sometimes
be traced, as in the bills of birds of prey. Indeed there is one, the
_caretta_, whose hooked and notched beak so completely recalls
the warlike bill of a hawk, that it is usually known by the name of
the "Hawk's-bill Turtle." You ought to know about this tortoise, for
it is the one which furnishes tortoise-shell, that nice material which
is so smooth to the touch, so pretty to look at, and so very fragile,
that it seems only fit for the use of ladies' hands. I could hardly
speak of tortoises without saying something of this one, out of
whose back was carved the handle of your own pretty little penknife.
Behind this bill of the hawk's-bill there is a tongue, but of the
character of a whale's tongue, and it is fastened underneath to the
bottom of the mouth. At the base of it there is a sort of fleshy pad
or cushion, which serves instead of a soft palate, that being another
detail which is about to disappear from our history. We are now really
entering upon the simplification of the digestive tube, which will,
I forewarn you, end by being nothing more than a perfectly straight
pipe, without any appendages whatever. In tortoises the intestine is
still tolerably long, and is doubled up backwards and forwards many
times in the abdomen; but it is already beginning to lose that variety
of form which its different parts assumed in the higher animals. The
large intestine can no longer be clearly distinguished from the smaller
one, nor this from the stomach, which itself seems to be a continuation
of the oesophagus, without any very distinct boundary line between them.
The porter, who with us keeps the door of the stomach, does his duty
here so badly, that there are certain kinds of tortoises whose
oesophagus is covered with spines, the points inclined backward, to
prevent the food from rising up into the mouth whilst the oesophagus is
driving it down by its contractions.
In the gray lizards of our walls we find teeth again, but very different
from any that we have hitherto seen. In the first place, they are not
content with their usual place on the edge of the jaws, but encroach
upon the surface of the palate, where they stretch out in close lines.
Besides, they are even still less like teeth than the great nails in
the jaws of the cetaceans. They are little ivory prongs, with the
points turned inwards, analogous to the thorns of the oesophagus in the
tortoise, and serve the lizard solely to retain and bruise his prey.
He lives on insects, especially flies, which he seizes on the wing
with the greatest skill, hastily catching and engulphing them in his
open jaw; they pierce themselves on the little prongs, and are swallowed
promiscuously. The tongue of the lizard has also a curious peculiarity,
which is shared by that of the serpent: it is divided at the end into
two threads, which dart in and out of its mouth, and by means of which
it laps, like a dog, the few drops of water it requires to satisfy its
thirst. I have seen lizards which had been tamed by children greedily
sucking up the saliva from their lips by drawing across them those
little forked tongues of theirs, which, after all, are very soft, and
perfectly inoffensive.
The tongue of the chameleon, another species of lizard, is still more
curious. You must know that the chameleon is a lumbering lazy animal,
who feeds on flies and other swift insects, and who would, therefore,
be constantly liable to go without his dinner but that his tongue
serves him for a hunting weapon, like those of the wood-pecker and the
ant-eater. When at rest, it is an oval spongy mass, lying comfortably
in the mouth, with nothing formidable in its appearance; but let the
prey come frisking round the chameleon, as if despising so helpless
an enemy, and this great soft tongue is transformed into an active
dart. It shoots forth like an arrow, and will sometimes seize the rash
intruder at half a foot's distance, transferring it with equal rapidity
to the motionless mouth. The blow is so soon struck, that it is very
difficult to see how it all happens. Some say that the chameleon curves
the tip of his tongue by a sudden effort, and then catches his flies
with it, just as you would catch them with your hand. Others maintain
(and this is the general opinion) that the tongue of the chameleon is
terminated by a sort of sticky cushion, on which the flies are caught,
like birds with birdlime. This singular dart is always out-jerked with
such force that, if it strikes against a glass (the experiment has
been tried with chameleons in captivity), it makes a sound as loud as
that of a pea from a pea-shooter; so you may judge if it is not strong
enough to stun a fly. Besides this, too, the chameleon (who is
by-the-by, a hideous little beast) has given endless trouble to
naturalists on another and very different point. It is he who is
so celebrated for his faculty of changing color when any emotion
agitates him; and ever since the days of Aristotle, who lived more than
two thousand years ago, people have been trying to explain this, without
any one being able to flatter himself that he has found out the exact
answer to the riddle.
But there is a lizard more interesting still, and that is the crocodile.
He stands alone among reptiles. His heart has two ventricles, and you
would think that he ought to be included in the class of warm-blooded
animals. But, no. The separation of the two kinds of blood takes place
in the heart, it is true, and it is really true arterial blood which
the aorta carries away from the left ventricle. But the right ventricle
has two doors of exit. One communicates with the lungs, the other with
the aorta; and the latter has hardly performed its distribution in the
upper part of the body when it meets, as it descends, with a treacherous
tube bringing to it a current of venous blood. In this way only half
the blood that comes from the veins passes on to be regenerated by
contact with the air, and all the hinder part of the body receives
nothing but the mixed blood common to reptiles, while the head and
fore members enjoy the privilege of the superior orders. After this
go and lay down your laws of classification! Nature, while maintaining
amongst all animals the same principle of life--the regeneration of
the blood by oxygen--has in their construction followed many systems
leading to the same result by different combinations, and which seem
to permit the establishment of essential distinctions among them. Here
is an animal who, if I may so express myself, is climbing up from one
system to the other, and you would have to cut him in two before you
could classify him properly, since his fore-quarters have risen to the
warm-blooded animals, while his hind ones are left behind among the
cold-blooded reptiles!
But there is something which even outdoes this.
On dry land the crocodile is timid, faltering, a bad walker, incapable
of regular combat, and a man can manage him with a stick. One feels
that he is betrayed by the hinder half of his body, through which
circulates the only half-oxygenized blood. But when once he has plunged
into the water his whole behavior suddenly alters; he is a ferocious
being, high-mettled, indomitable, a savage enemy, redoubling his
exertions, as if the entire mass of his blood had suddenly become
arterial. Geoffroy St. Hilaire, who followed Bonaparte as a scientific
explorer when he set out for the conquest of Egypt, the country of
crocodiles, was deeply struck by studying on the spot this double life,
which seems in a way to maintain two beings in the same body. He
afterwards gave an extremely curious explanation of it in his work on
the crocodiles of Egypt. Here it is; but I forewarn you that you will
not understand it:
"The crocodile, when it is under water, receives by two canals into
the cavity of the abdomen, a considerable quantity of water, which the
animal can renew at will."
You are not much the wiser, are you? But wait a moment. We are soon
coming to the fishes, and you will then see what an unlimited scope
nature has allowed herself here. Not satisfied with two systems in one
animal, she appears to have got hold of three.
If we continue the examination of this privileged reptile, we shall
find many other infractions of the usual rules of his class. His tongue,
certainly, is fastened to his mouth like that of the tortoise, so much
so that the ancient Egyptians told the Greeks he had not got one; but
his set of teeth clearly approach those of the lower mammals. You have
probably heard a great deal of the strength of the crocodile's
formidable teeth. Travellers have given them this reputation; but we
have nothing to do with that now. They stand in battle array, in a
single line, along the whole length of the jaws, into which they are
sunk with genuine fangs, whilst the prongs of our little lizard are
merely fastened to the surface of the bones which support them. Indeed,
in one way, the crocodile is even better provided than the mammals.
He possesses under each tooth one or two germs, the life of which lasts
as long as that of the animal, and which are always there ready
toreplace the previous one should it chance to fall out. There are many
ladies, and (not to be rude) gentlemen as well, who would, I am sure,
give a great deal to have as many teeth at their service. Indeed, they
may possibly think Dame Nature very unjust to have selected this great
villanous beast rather than us as the object of a gift which they would
have been so well able to appreciate. But we must not blame nature too
quickly: she had her reasons. We, during our infancy, have teeth in
reserve. Now, a reptile may be considered as an imperfect rough draft
of a mammal; and the crocodile gives one thoroughly the idea of a
mammal half-finished and fixed for life in a state of childhood. I am
sorry that I cannot enter into full details, that you might see how
far the idea is a just one. Moreover, in his character of a perpetual
child, he is always growing bigger all his life long, and never seems
able to die but by accident, hardly ever, I may really say, from old
age. By specimens kept in captivity, it has been ascertained that
their growth is very slow. Well, imagine their being only from seven
to eight inches long when they come out of the shell, and that
full-grown crocodiles have been found thirty feet in length, and
calculate accordingly. You will not account for it under a century;
and I should like to know what would become of this venerable child
of more than a hundred years old if kind Mother Nature had not left
him our system of milk-teeth to the end?
A curious peculiarity of these persistent teeth is, that they are
hollow inside, so much so, that the bowls of tobacco-pipes are said
to be made from them in Europe. I mention the fact, although of no
great interest to you, for the benefit of any pipe-merchants who have
not yet thought of sending for such things to Cairo.
But let us return to the efforts perceptible in the organization of
the crocodile to raise itself to a higher level. The soft palate, as
we called it (Letter VII.), is wanting in other reptiles; but here
there is one which completely closes the entrance of the windpipe (the
larynx). I announced, too, the disappearance of the diaphragm; and we
bewailed together the loss of that servant of the good old times, whose
touching history you must, I am sure, remember. But I reckoned without
this wretched crocodile, who seems determined to give the lie to all
we have been saying. He has a diaphragm, and one which acts well enough
in the main, although it is pierced right through the middle, as if
it were rather ashamed of being there, and wished to make up for
dividing the body into two compartments, against all proper reptile
regulations, by opening a door of communication between them. What
shall I tell you besides? The lungs, not to be behind the rest of this
aristocratic reptile's organization, are hollowed into cells much more
complicated than those of his fellows. You find here no end of nooks
and corners, which multiply opportunities of contact between the air
and the blood, and so give the crocodile almost the respiration of the
mammals, as he has already got pretty nearly their system of
circulation.
With serpents, again, we fall very low. When we were speaking of the
tortoises I told you that, in proportion as we come down in the scale,
the digestive tube has a tendency to get rid of its accessories, and
to assume the appearance of a perfectly straight tube. If any one were
to cut open a serpent before you, you would see this final condition
almost reached already. In the first place, the soft palate is entirely
suppressed, and the mouth extends straight into the oesophagus, whose
tube seems to run through the whole length of the body without
interruption, with just four or five doublings towards the base, in
that part which represents the intestines. An imperceptible swelling
indicates the place where the real stomach lies within; but in another
sense one may call the oesophagus, and I might almost add the mouth
itself, its stomach. You shall see how.
The jaws of serpents are even in a more unfinished state than those
of other reptiles. Nature has not taken the time to weld the different
parts of them together; but these begin by not being very firmly joined,
remember, in young mammals. The bones of the head, which support the
jaws, are themselves movable, and can be detached from the skull if
necessary, so as to allow the throat to open extraordinarily wide;
thus it is not uncommon to see a serpent swallow animals much larger
than itself. You will be horrified when I tell you that the anaconda,
one of the giants of the family, swallows large quadrupeds at a single
mouthful. What are our mouthfuls in comparison with his? however, it
must be confessed, that his often take several days to go down. When
the animal has rolled up his prey in his terrible folds, he pounds and
kneads it till it is reduced to a kind of long roll, which he moistens
with a copious slaver to make it slip down more easily. Then, attacking
it at one end, he fastens this very expansive jaw upon it, and the
gigantic mouthful slowly begins its journey; what was left outside the
mouth, advancing little by little, in proportion as the digestion
reduces what has entered to pulp, and sends it farther down. This is
on great occasions; but in the case of more modest prey--a rabbit, for
instance--the mouthful goes in whole at one gulp and remains stationary,
partly in the oesophagus, partly in the stomach, while the powerful
juices distilled by the walls of the latter are dissolving it.
You can see that a soft palate would have been quite useless here, and
that the serpent has not much need of teeth to chew his food.
Accordingly, his are nothing but simple prongs, like those of the
lizard, and, like his, they extend over the palate, the more effectually
to cut off the return of the swallowed masses of food. About a hundred
and twenty have been counted in the throat of the boa-constrictor; but
their number varies considerably in the different species. They are
not organs of the highest order, and nature is not very particular
about the quantity.
There is only one tooth among serpents of which she takes any particular
care, and that is the venomous tooth which she has bestowed on certain
species, and which serves them for striking down, as it were, the
animals on which they feed. Let us study it in the rattlesnake, the
most celebrated of this odious race. On each side of the upper jaw you
may see, isolated from the others, and exceeding them all in length,
a very sharp fang pierced through by a tiny canal, which opens into
a gland placed at the root of the tooth. The bone which supports this
little apparatus is very flexible, and when at rest, the fang, falling
back, hides itself in a fold of the gum. When the animal wishes to
bite, it springs up again, and the gland, compressed by the action of
biting, sends into the little canal a jet of poison, which runs through
it into the wound. As far as can be ascertained, this poison paralyses
the victim and disorders the blood, which at once loses its power,
and no longer acts upon the organs as before; still it is only injurious
when it has been carried by the current of circulation into the mass
of the blood; if swallowed, it has no effect whatever on the stomach.
Now do not look at me with such incredulous eyes, as if it were quite
impossible any one should think of swallowing such a thing. You have
no idea what a scientific man is capable of when he comes to close
quarters with nature, for the purpose of extracting one of her secrets.
He has his own fields of battle, where very often as much courage is
displayed as on any other.
These two fangs, in which lie all the power of the animal, are of the
greatest importance to him, and their want of solidity makes them
liable to remain in the wounds which they have made. In consequence
of this, they enjoy the same privilege as the teeth of the crocodile,
and in a still greater degree even. Behind each poison fang lie in
wait, not one nor two, but several sentinel germs, ready at the first
alarm of a loss to set to work and re-supply the disarmed serpent with
his venomous needle. So the serpent also lives in a state of perpetual
childhood: he is always growing; and I could not tell you the exact
natural limits of his life any more than of that of the crocodile.
They are gentlemen who do not allow themselves to be very closely
studied in a state of freedom. But these also grow very slowly, and
some have been met with whose size had extended quite enormously from
their first start. I ought to tell you, once for all, that this
indefinite growth, joined to extreme longevity, is found in many of
the inferior species whom we have yet to consider. It seems the portion
of these unfinished creatures, in which nature has only as it were
sketched in her work, and who seem vowed to endless youth, in testimony
of the state of childhood they represent, a state transitory among the
superior animals, but permanent with them. It belonged of right,
therefore, to the serpent, which is the most unfinished animal we have
yet met with, and who, at the first glance, seems almost reduced to
a mere digestive tube, lodged between a vertebral column and a series
of small ribs, whose number sometimes reaches three hundred. The liver,
which, with us, presents such a distinct and bulky mass, is here
elongated into a thin cord, which runs the whole length of the
oesophagus
and intestine, to the walls of which it is, to some extent, attached.
It is the same with the lungs. There is rarely room for the full
development of two in this narrow conduit, where everything has to
follow the shape of the master of the house: one, therefore, is often
merely indicated by a very slight protuberance; the other, presenting
the appearance of a long tube, which extends nearly half-way down the
body, and whose feeble action halts periodically at each of those
monstrous repasts, after which the torpid animal becomes nothing but
a huge digesting machine. We have now reached the extreme limits of
that organization, the most perfect model of which we find in man, and
which is no longer to be recognized in fishes.
LETTER XXXVI.
PISCES. (_Fishes._)
We are becoming terribly learned, my poor child, and I am half afraid
you will be getting tired of me. When I was little myself, I had rather
a fancy for breaking open those barking pasteboard dogs you know so
well; to see what was inside them. Why should you not, then, feel a
certain amount of interest in looking with me into the insides of real
animals? Still I cannot conceal from myself that the subject grows
very serious at last, and that while I am busied in struggling to make
myself intelligible through the endless crowd of facts which surround
me, I am apt to neglect chatting with you as we go along. Happily,
however, here is an opportunity for so doing.
Up to the present time we have lived, as it were, upon the explanations
I gave you whilst studying the action of life in yourself, and all the
organs we have met with since, have been only, properly speaking,
reproductions, more or less exact, of those which you yourself possess.
But, in passing over into the kingdom of fishes, we find ourselves in
the presence of something altogether new, and I must go back to our
old familiar style of talking to open the subject.
Take a water-bottle half-filled with water, and shake it well, and you
will see a quantity of white froth come to the surface of the liquid.
This is the air which having been drawn in by the water, as it went
up and down in the bottle, is now struggling to fly off again in bubbles
as fast as it can. But the whole of it does not get away; a small
portion remains behind, and melts, as it were, into the water, as a
morsel of sugar would do, taking up its abode therein. This seems odd
to you, but I will tell you how you may convince yourself of the fact.
Get a small white glass bottle, slightly rounded, and thin at the
bottom, if possible; fill it with water, and hold it for a short time
over a lighted taper. If you do this carefully there is no danger. You
will soon see tiny little balls, looking like drops of silver, rise
from the bottom of the bottle, come up to the surface, and burst. This
is the air which was installed in the water, as I described above, and
which is now running away from the heat of the candle, as the
inhabitants run away from a house on fire. After a time the whole will
have passed off, and the little balls will cease to rise.
But what has all this to do with fishes? you ask.
A very great deal, I assure you, dear child. If there had been a little
fish in your bottle, before it was exposed to the flame, it would have
found means to make use of that air, whose original presence in the
water you cannot refuse to believe after having seen it come out. It
is with this air that fishes breathe in the water. They do so rather
feebly, I admit; but, as if to make up to them for the small amount
of the air placed at their disposal, it contains more oxygen than that
we breathe ourselves, because oxygen, dissolving more readily in water
than nitrogen, is there in greater proportion. Of course, you do not
suppose that fishes have lungs like ours? I dare say you know the two
large openings on each side of their head, called _gills_, by which the
fishermen string them together to carry them away more easily? It is
there you will find their lungs, to which the name of _branchiae_, or
gills, has been given, because they are so different from other organs
of respiration that it was impossible to use one word for the two. The
arrangement of the gills varies considerably in the different species,
but their general form is the same everywhere. They are composed of a
number of plates, consisting of an infinitude of leaflets, arranged like
a fringe, and suspended by bony arches, into which plates and leaflets
the blood pours from a thousand invisible canals.
First of all, then, we must see how blood circulates in fishes.
Like reptiles, their heart has only one ventricle, and yet the arterial
and venous blood go each its separate way without the slightest risk
of being mixed; but this is because fishes have not that double system
of veins and arteries which hitherto we have always met with. The
venous blood goes to the heart, which drives it into the gills, from
whence it passes forward of its own accord, as arterial blood into the
organs, under the remote influence of the original impetus from the
heart, the newly-arrived blood incessantly driving the other before
it into the vessels of circulation. It does not flow very quickly, as
you may suppose; and as the heart is close to the head, its action is
but very feebly felt at the extremity of the body, when this happens
to be very long. Nature has, in consequence, taken pity on the eel,
whose tail is so far from its heart, and provided accordingly. Dr.
Marshall Hall has discovered near the tip a second, reinforcing heart,
so to speak, which has its own pulsations, independent of the pulsations
of the one above, and gives a fresh impetus to the sluggish blood,
[Footnote: Many observers refer this to the lymphatic system.--TR.]
which otherwise, as it would seem, would scarcely be able to accomplish
the long return journey. Finally, even with an additional heart in
thetail, the circulation among fishes is quite on a par with their
respiration. They have a melancholy steward, whose legs are very heavy,
and his pockets very light, and their life comes down a peg lower in
consequence. It is always the same life nevertheless--you must never
lose sight of that fact: it gets low in consequence of the imperfection
of the machine, but without changing its nature, any more than the
light in our different sorts of lighting apparatus. You remember that
comparison of the lamp with which I began my story, and which you could
not at the time see the full value of? From a dungeon lamp up to a
candle, you have always grease burning in the air at the end of the
threads of a wick. It does not burn equally well everywhere, and does
not always give the same amount of light; but that is all the
difference. From the mammal to the fish, it is always hydrogen and
carbon (as we have said of the grease) which oxygen sets on fire in
the human body at the fine-drawn extremities of the blood-vessels;
only the fire is lower in some than others, and the life with it. Let
us now look at the circulation of water in the fish's body.
The gills communicate with the mouth by a sort of grating, formed by
the bony arches to which the gill-plates are suspended. The fish begins
by swallowing water, which then passes through the grating and
circulates round the innumerable leaflets of which each plate is
composed, and among which creep the blood-vessels. It is through the
thin coats of these leaflets that the mysterious exchange is made of
the unemployed oxygen in the water and the carbonic acid in the blood.
When this is over, the cover which closes the gills opens to let out
the water, and a fresh gulp takes its place; and so on continually.
When the fish is out of the water its gills fall together and dry up;
the course of the blood, already so weak, is interrupted by the breaking
down and shrinking of the vessels, and the animal can no longer breathe;
so that we have here the curious instance of a creature breathing
oxygen like ourselves, who is drowned, if we may use the expression,
in the air in which we find life, and lives in the water in which we
are drowned. While he is in the water matters take another course, and
his gills, moistened and supported, accommodate themselves perfectly
to the contact of the air, which desires nothing better than to give
up its oxygen to the blood, through the coats of the capillaries.
Accordingly you will often see fishes--carps, for example--come to
the surface of the water to inhale the air like a mammal or a reptile.
This is a valuable resource, which supplements the parsimonious
allowance of air given out to them by the water. There are even certain
fishes whose gills, more firmly closed than those of others, have, in
addition, a number of cells, which retain for a considerable time a
sufficient quantity of water to preserve the gills in their natural
state. These fishes can easily take an airing on land, where they
breathe the air as you or I do, and are downright amphibians.
The most celebrated of these is the _Anabas_, or "climbing-fish."
an Indian fish, which not only can remain many days out of the water,
but also amuses itself by climbing up the palm trees--it is hard to
say how--and establishing itself in the little pools of water left by
the rain at the roots of the leaves. But we need not go to India to
find those wandering fishes. There is one of them living among ourselves
who can walk about in the grass, and I was talking to you about him
only just now--that is the eel. If you ever put eels in a fish-pond
you must, I assure you, try to make it agreeable to them, otherwise
they will have no scruple in setting politeness at defiance and moving
off to seek their fortune elsewhere. In a country walk, when the dew
is on the ground, you yourself may chance to come across one or two
of these gentlemen, who have had their reasons for changing their
residence, and whom you will see gliding so briskly along that they
will deceive you into taking them for snakes if you have not a very
experienced eye; so much so, that in certain parts of France where the
peasants ate snakes formerly, they reconciled themselves to the sickly
idea by christening them _hedgerow-eels_.
On the other hand, fishes may be drowned in water just as easily as
ourselves if it does not contain air. The little fish who could have
lived very well in the bottle we were just now talking about before
you exposed it to the flame of the taper, would have died in it after
all the air-bubbles had gone off; and I hope I need not tell you why.
In the same way, if you leave fishes too long in a small quantity of
water without renewing it, they suffer exactly as we do if the air
which we breathe is not changed often enough. As soon as they have
consumed what oxygen is in the water, it can no longer keep them alive.
It is then, especially, you will see them come gasping to the surface
to call upon the air for help. Those who keep gold fish in a glass
bowl ought to know this, and to change their water oftener than is
generally done. When we take poor little creatures from their natural
way of life, and set a human providence over them in the place of the
Divine one which has hitherto been their safeguard, the least we can
do is to acquaint ourselves with the laws of their existence, so that
we may not expose them to the risk of suffering by our ignorance.
Finally, there are fishes whose gills, still more greedy of oxygen,
will not act well except in thoroughly aerated water, and who would
soon die in our tanks. This is the case with the trout, who is only
happy in the waters of hilly countries; rich with all the air they
have carried along with them as they fell from rock to rock. Now that
people are beginning to do with fishes what has long since been done
with sheep and oxen--keep them in flocks to have them always ready for
use--you may perhaps hear a good deal said about vessels made expressly
for the carriage of trout, with a thousand inventions besides for
sending air into the water, and you will not have to ask the meaning
of this now.
I promised last time that I would revert in the chapter of fishes to
that marvellous transformation of the crocodile which has been explained
by the torrent of water he draws into his stomach. You could understand
nothing about it the other day; but after what we have just seen the
explanation suggests itself. Just as the extraordinary activity of
life in birds is explained by that double oxygenization of blood, of
which part takes place in the lungs and part in the reservoirs of air
placed everywhere in the way of the capillaries, so this sudden increase
of energy in the crocodile the moment it plunges into water may be
explained by a second respiration suddenly established in the vast
cavity of the abdomen, by the contact of the capillaries with the water
which penetrates there. Hence the crocodile would then have, like the
bird, a double respiration: only with him the one would be permanent
and from the lungs, the other temporary and from the stomach. By this,
on the one hand, he would rise up to the birds, since the blood
encounters air twice over in its course, while, at the same time, he
would plunge into the world of fishes, since the blood has to seek air
in the water. The above, be it remembered, is only a supposition, and
I ought to add that in this case there would be a good deal of danger
in observing nature at work, for in front of the laboratory, where she
is toiling in secret, stands on guard a row of teeth, by no means
encouraging to indiscreet intruders. At the same time, if there ever
were a legitimate conjecture, this is it. Everything seems to confirm
it; and if it be true, we should have in the crocodile a specimen of
each of the four systems adopted by nature for the mammal, the bird,
the reptile and the fish. At first I spoke of two, then of three; so
that even in my addition I was modestly below the mark, and had really
some grounds for recommending our friends the classifiers to beware
what they asserted in this case.
Talking of puzzling classifications, this is just the place for
mentioning the _batrachians_, who have been made into a class by
themselves, but who most distinctly belong to two classes at the same
time; not like the crocodile by details borrowed from each, but by a
fundamental change which takes place at a certain period in their
organization. The batrachians are in reality reptiles, but they are
reptiles which begin by being fishes, and real fishes too.
If you have ever strolled about in the country, you must have often
come across those great pools of water which collect at rainy seasons
in the ruts of deep lanes. Amuse yourself by looking into them in
early summer, and unless the land is too parched and dry, the chances
are that you will see quantities of little black fishes, almost entirely
composed of a long tail joined to a large head, playing jovially in
the muddy waters, and looking as if they had dropped there from the
skies. These are young frogs--_tadpoles_, as we call them--and
they are beginning their apprenticeship of life. Enclosed in each side
of those great heads, they have gills, and they breathe in the same
manner as fishes. Presently the two hind feet begin to bud out and
grow, little by little; then the fore feet; finally, the tail wastes
away till it disappears; and thus insensibly the tadpole is transformed
into a frog. Observe here that the tadpole's gills share the same fate
as his fish-tail; they wither and disappear by slow degrees, and
gradually as they do so, his lungs are developed. The animal changes
his class very quietly, and without ceasing to be genuinely the same,
although it would be impossible at last to recognize the old individual
in the new if you had not heard its history beforehand. This is one
of the most striking exemplifications I know of the mysterious process
by which nature has insensibly raised animals from one class to another,
always improving upon her original plan without ever abandoning it.
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 _tracheæ_, 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
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