MAMMALIA. _(Mammals)--continued_.
Let us continue to pass in review the different orders of the class
Mammalia. We may meet elsewhere with facts more important to science,
but nowhere with any so personally interesting to ourselves.
ORDER 5. _Insectivora (insect-eaters)_.
This order devours insects, as their name tells you plainly enough.
They feed in the same manner as the bats; consequently they have molars
like theirs, as was necessary. It is an unimportant little family, and
we will not waste much time upon it. The chief of the order is the
hedgehog, a native of our country--not very large, about nine inches
long--which lives in the woods, and which when rolled up into a ball,
with all its quills standing out, looks very much like an enormous
horse-chestnut in its shell. Its canines have not much work to do,
consequently they are very small; but, on the other hand, its two front
incisors are prolonged beyond the others, the better to seize its prey,
which creeps upon the ground. Internally there is nothing to remark
upon.
Next to the hedgehog I will mention as a curiosity the shrew or
sand-mouse, which, in spite of its name, is no mouse at all, but has
the honor, if honor it be, of being the smallest animal known of the
class Mammalia.
It is about two inches in length altogether; and if you carefully
examine its little body, you will find that it contains all the organs
you possess yourself--oesophagus, stomach, liver, intestines, veins,
arteries, heart, lungs--nothing is wanting: the machinery is absolutely
the same.
ORDER 6. _Rodentia (rodents)_.
Were we to translate this word into its meaning, namely, the _Gnawers_,
there would be some comfort in it, for we would at once know what it
means: but no matter. Rodents, or Gnawers, are rats, hares, rabbits,
beavers, marmosets, squirrels, in fact all the creatures which _nibble_.
To _nibble_, if you do not exactly understand the word, means to chew
with the points of the teeth. The rodents have no other way of eating
but by filing, if one may so say, their food with the points of two
incisors with which both the jaws are provided; these incisors are very
long, much longer even than those of the hedgehog. The next time you see
a rabbit at table, ask to see the head; and you will find that it has
four pretty little teeth, very sharp, shaped like a joiner's chisel;
that is to say, with a "bevelled edge," to use the received expression;
in other words, with one edge thinner than the other.
Here, then, we begin to diverge from the old model. First, there is a
different fastening, or _articulation_, as it is called, of the jaw. Its
_condyles_, which we saw just now in the _Carnivora_ enlarged
transversely and deeply embedded in the _fossae_ or cavity of the
temporal bone, extend here longitudinally; an arrangement which enables
the jaw to move backward and forward at pleasure, like the arm of the
locksmith when using the file. Furthermore, those little teeth, which
are constantly rubbing against each other, would be very soon worn out,
if, like our own, they were made once for all; accordingly their germ,
or _pulp_, to use the proper term, instead of perishing, as with us,
when the tooth has once come, retains its life, and works on throughout
the life of the animal. They sometimes say of a man who has not eaten
for a long while, that his teeth have grown long. This is a joke with
us; but in the case of a _rodent_ would be too serious a matter to be a
joke; for, as their incisors are always growing, like our nails, they
would soon become too long if the animal ceased for any length of time
to wear them down by eating. It is for this reason that rats and mice
have such incessant appetites, and that with them "all is fish that
comes to the net;" old books, rags, and even planks of wood, which they
will gnaw for want of something better. Come what may, they must keep up
at an equal rate the wear and tear of the incisors, and the internal
growth of the pulp beneath, which is always pushing the tooth forward.
This dull continuous work might otherwise have a terrible result, which
you would never suspect. It is very disastrous for a young lady to lose
a front tooth, as it is called, for it sadly spoils a pretty face; but
for a _rodent_ such a loss is much worse; in fact, it is a
death-warrant. The corresponding tooth, having no longer anything to rub
against, ceases to wear out; and as it does not stop growing on this
account, it lengthens indefinitely, until at last it pushes out beyond
the mouth, and places itself like a bar between the two Remaining teeth
and the food of the animal, who, poor beast, being unable to eat,
ceases to live.
The canines, whose duty it is to pierce the food, have, of course, no
use in a jaw that grinds, nor are they to be found there. Between the
incisors and the molars there is a large vacant space, which you will
easily detect if you examine a rabbit's head.
Finally, animals which can fall back in time of need on a plank for
their dinner, require a very different-sized cooking apparatus to that
of the _Carnivora_. Thus the rat, the most perfect sample of the
rodent order, possesses a digestive tube of a prodigious length, through
which the scrapings of wood have plenty of time for travelling, while
the minute nutritive particles they contain are being thoroughly
disengaged; and as every part of the animal organization tends towards
keeping our insatiable rodents in the constant state of voracity
required by its inexorable pulps, nature has given it an enormous heart
whose size exceeds even that of its stomach.
Perhaps you do not catch at once the connection which exists between
the size of the heart and of the appetite; yet it is very simple. Large
barrels are requisite for those who brew a great deal of beer, and
large hearts for those who make a great deal of blood. Now, it is the
blood, as you know, which carries heat; in other words, life, throughout
the body; when it pours in in torrents, the fire goes twice as fast,
and, consequently, the feeding must be kept up. A medical friend of
mine told me that he once had some rats sent to him--a boxful in
fact--for one of those scientific experiments which one would venture
to condemn more earnestly if their results were not sometimes
beneficial. Next morning there were only two or three animals to be
found, and these had eaten up the others. See the consequence of having
too much heart!
ORDER 7. _Pachydermata (thick-skinned)_.
In Greek _pachus_ means thick, and _derma_ skin. _Pachyderms_,
therefore, are thick-skinned animals. It is rather a vague denomination,
as you perceive, and does not tell us much about them; but it appears
that it was not very easy to find a better term. For my own part I
should be very much puzzled to find a name really suitable for such an
irregular company as this, in which all the huge beasts of the
earth--the elephant, the rhinoceros, the hippopotamus--are heaped one
upon the other, side by side with the horse, the ass, and the hog;
begging your pardon for an ugly word.
All these creatures live on vegetables, with the exception of the hog,
to whom nothing comes amiss; or who, in other words, is _omnivorous_,
like the bear, and also another member of the class _Mammalia_, which I
do not name for fear of making you blush at your companionship. This
assures you that, in the order of the _Pachydermata_, the digestive
apparatus is very fully developed. The horse, for instance, has a very
voluminous stomach, which extends much farther back than the point at
which the oesophagus empties itself; and in which, on close examination,
a sort of contraction is observed which appears to divide it in half,
producing the false effect of there being two stomachs. But, after all,
we do not find, even in this case, any essential difference to remark
upon in the internal arrangements; it is always the teeth we must look
at if we want to have something to say. There, indeed, we have only to
choose; nature has indulged herself in all manner of fantastic freaks.
To begin with the elephant, the grand master of the order, he presents
us with one of the most oddly-furnished jaws in existence. Every one
knows those two enormous tusks which protrude from his mouth, and which
furnish human industry with nearly the whole store of ivory it has
need of. Those two teeth are the largest, beyond comparison, of any
in the animal kingdom; yet they are two merely ornamental teeth,
perfectly useless in the operation of eating, and very ruinous into
the bargain to the proprietor. All those stores of the blood which
furnish the materials for ivory pass into these tusks, and, as often
happens to people who give way to a taste for luxuries, there is nothing
left wherewith to provide the animal with serviceable teeth. Those
tusks of the elephant are nothing but his upper incisors, the only
ones, observe, which curve in coming out of his jaw. In the lower jaw
he has no incisors at all; canine teeth are entirely wanting; and by
way of dental apparatus, this meagerly-furnished mouth possesses on
each side of either jaw one or two molars, enormous in size, but not
of ivory. They are composed of a number of enamelled upright layers
of tooth-substance (_dentine_), soldered together with a bony
cement; and these are our giant's only resource for chewing the grass,
young shoots, and leaves of trees, which are his natural food.
[Footnote: These teeth are nevertheless very efficient grindstones.]
As a consolation, he has the glory of knowing that he possesses the
very finest teeth in the world, the terror of all who approach him;
and I can compare him to nothing so well as to a vain woman, who is
contented to live on potatoes that she may wear fine clothes and excite
the envy of her neighbors.
The hippopotamus also has incisors in the upper jaw, which curve as
they come out of the mouth; but these never attain anything like the
size of the elephant's tusks, neither do they hinder the development
of the other teeth, of which this animal has a very respectable
collection. The upper incisors bend downward; those in the lower jaw
stand out horizontally, and terminate in sharp points like
plough-shares; and indeed the hippopotamus uses them for tearing up
the ground in order to get at the roots which form its nutriment. These
are, besides, formidable weapons, with which when enraged the animal
can tear even boats in pieces; for, as you are aware, the hippopotamus
is almost amphibious, and browses on water-plants, and lives in the
great rivers of Africa, its native country. Its name alone would have
told you this had you understood Greek; [Footnote: _Ippos_, a horse, and
_potamos_, a river. The Greeks, who had seen the hippopotamus in the
Nile, in Egypt, named it the river-horse; as afterwards the Romans
called the elephant the ox of Lucania, because they first saw it in
Lucania during the war with Pyrrhus.] but I have no complaint to make
this time, for it was the Greeks themselves who gave it. You would find
it very awkward, would you not? if you had to breakfast at the bottom of
the Thames, and could not swallow a morsel without having your nose
filled with water? But the hippopotamus labors under no such
inconvenience. Its nostrils are provided with two little doors, which it
closes at will, and behind this screen the lungs keep quite quiet while
the animal goes backwards and forwards in the water. There is generally
a hippopotamus in every large menagerie. The next time you visit one
look at him. You will see him with a large stomach almost trailing on
the ground: and no wonder; he needs plenty of room in which to stow away
all the canes, reeds, and water-plants from the bottoms of rivers, which
are not very nutritious food. Accordingly the stomach of the river-horse
presents the appearance not only of two compartments, like that of the
true horse, but looks as if it were divided into three or four.
To conclude my account of this animal, I must add that the ivory of
its teeth is even more beautiful than that of the elephant's tusks,
and that dentists carve it into very magnificent teeth for their
patients. This is not a matter to interest you much at present, but
we never know what may happen. I advise you, however, never to make
use of hippopotamus's teeth; they turn yellow very quickly, and, when
people are driven to buy teeth, the least they can try for, is to get
good-looking ones for their money.
I should like to say something about the rhinoceros while we are on
the colossal tribes, but it is a very unsatisfactory subject. The
animal has no canines, sometimes no incisors even; sometimes it has
as many as thirty-six teeth, according to the species, as naturalists
aver; and this is all I have to say about this great lump of flesh,
so misshapen outside, yet so regularly formed within. He it is who
especially deserves the title _pachydermata_, his skin being so
hard and thick that bullets glance off its surface. But this has nothing
to do with our present subject, any more than the horn upon his nose,
whose turn for description may come if I ever give you the history of
the skin and all connected with it.
The hog also has canines, and very strong ones; but it is in the wild
state, when it is called a boar, that these appear in their real form.
There we find them projecting out of the mouth with a curve, as is so
commonly seen among the _pachydermata_, forming those terrible,
sharp, and pointed tusks which have been so often fatal to the hunter.
The wild boar of the forest is supposed to be the original ancestor
of the domestic pig; and if, as is probable, this is really the case,
we have here a remarkable instance of the effect of man's treatment
upon the organisation of the animals he collects around him. The wild
boar lives only on fruits and roots, which, like the hippopotamus, he
tears up with his tusks, those safeguards of his, amid the many perils
of his life in the woods. In the service of man, on the contrary, he
becomes lazy, cowardly, and greedy; unlearns his energy and
combativeness, eats all that is offered to him in the trough, even
meat, when it happens to be thrown in; and, in order to do this
moreeasily, has recalled toward his mouth those formidable war-tusks of
his, so tremendous as weapons, so useless as teeth; has, in fact,
turned his sword into a fork. It is the case of a Tartar degenerated
into a Chinaman. [Footnote: China, about which we have heard a great
deal of late years, has been several times invaded by the warrior
hordes of Tartary. But at each time, unto the second and third
generations, the vanquishers have taken the effeminate manners, the
costume and the usages of the vanquished, and so many conquests have
only resulted in converting millions of Tartars into Chinese.]
This suggests to me an idea relative to the horse, the last important
member of the _pachydermata_ which remains to be spoken of. It
also has its canines, but very small ones; they disappear, so to speak,
in a large vacancy between the incisors and the molars, where man
inserts the bit, by means of which the animal has been subdued. Small
as these are, however, these canines indicate that the horse might eat
flesh, canine teeth being the distinctive attribute of the carnivorous
mammals. I have read somewhere, but I do not remember where, that an
unusual development of strength could be produced in the horse by
feeding it on flesh; and the old Greek poets write of a king [Footnote:
Diomed, King of Thrace] in the barbarous ages who gave his horses,
men for food. If I knew some rich professor who was inclined to spend
money in the investigation of a curious fact, I would advise him to
set apart a sum for putting horses on a meat diet, from sire to son,
gradually increasing the quantity; and I would boldly warrant that in
the course of successive generations the canines would become so large
as to impede the entrance of the bit into the mouth, and, moreover,
would make it rather a ticklish office for the groom to place it there.
But let us set aside the teeth the horse might possibly have, in order
to examine those it has already. There are six incisors in each jaw;
these are long and rather projecting teeth, by examining which, the
age of the horse can be detected from certain marks which appear in
them from year to year. The molars are flat, square, furrowed with
bars of enamel, marking out more or less distinct crescents; perfectly
constructed, in short, for chewing hay and oats. Nevertheless, I should
never be surprised to see the enamel crescents become sharp-cutting
in our rich professor's stable; so skillful is the unseen Architect
who created animals, in altering the house when the tenant changes his
habits.