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.