Encyclopaedia Britannica > Volume 3, Anatomy-Astronomy

ANIMAL KINGDOM.
172
Animal every function. Nutrition exhausts its principles, diges-
Kingdom. tion repairs them, respiration elaborates and renders it
perfect, and the action of the heart gives it circulation.
All these elements united and variously combined com¬
pose the different organs of animated beings, the harmo¬
nious action of which organs forms the essence of our
wellbeing, physically considered, in the present stage of
our existence. The human race possesses the attributes
of animal life in common with the brute creation; but we
must ever bear about with us a firm conviction that these
are “ the accidents, not the essentials of our nature j”1 and
that however proper it may be to mention them as the
technical statements of physiology, yet that they are to¬
tally inadequate to the description of a being who bears
about with him the germ of immortal life, and knows that
he was created “ but a little lower than the angels.”
“ Those persons,” says Buffon, “ who see, hear, or smell
imperfectly, are of no less intellectual capacity than others;
an evident proof that in man there is something more
than an internal sense. This is the soul of man, which is
an independent and superior sense, a lofty and spiritual
existence, entirely different in its essence and action from
the nature of the external senses.”
It is easy to perceive that one set of organs may be so
related to another as constantly to require its co-exist¬
ence. Thus, circumscribed respiratory organs are always
accompanied by a heart, which causes the blood to flow
through them ; and a brain is never found without nerves
and muscles, which serve it as faithful ministers and at¬
tendants. The brain receives impressions, and is enabled
to judge of them through the medium of nervous sensa¬
tions : this is the first mode of the functions of relation.
But the order is inverse so far as relates to the pheno¬
mena of the will as connected with the exercise of the
voice and the organs of movement. The brain wills or
commands, the nerves transmit the order, and the muscles
execute it.
There are other co-existences in the animal economy
as apparent as those above alluded to, the motives of
which are not, however, so easily comprehended. We are
still ignorant why the viscus called the liver should al¬
ways exist where there is a heart; and why all orthop¬
terous insects should have the forehead furnished with a
broad plate.
It will readily be conceived that the diversified circum¬
stances pf life in the various tribes of animals necessitate
an infinite variety of phenomena in their functions and
faculties. An animal which respires, and has its dwelling
in the waters, can neither feel nor move after the manner
of one which breathes in the pure air; and wherever there
are bianchiae or gills instead of lungs, we are sure also to
find oviparous generation, an incomplete circulation, an
absence of voice, and imperfect organs of hearing and
of smell. But the existence of lungs alters the relation
of the whole of these functions.
The same principle may be applied to the different
kinds of aliment. A carnivorous animal is endowed with
force and courage : it has a strait stomach, short intes¬
tines, and a lank or somewhat slender form. Herbivorous
animals, on the contrary, are usually mild and timid, dull
in action, of a sluggish nature, and unapt to self-defence :
their intestines are spacious, and their external forms
more or less massive. “ The disposition of the alimen¬
tary canal determines, in a manner perfectly absolute, the
kind of food by which the animal is nourished; but if the
animal did not possess, in its senses and organs of motion,
the means of distinguishing the kinds of aliment suited to
its nature, it is obvious that it could not exist. An animal Ani
therefore, which can only digest flesh, must, to preserve Kingdm,
its species, have the power of discovering its prey, of pur-
suing it, of seizing it, of overcoming it, and of tearino- it
in pieces. It is necessary then that this animal should
have a penetrating eye, a quick smell, a swift motion,
address and strength in the jaws and talons. Agreeably
to this necessity, a sharp tooth, fitted for cutting flesh, is
never co-existent in the same species with a hoof cover¬
ed with horn, which can only support the animal, but
with which it cannot grasp any thing : hence the law ac¬
cording to which all hoofed animals are herbivorous, and
also those still more detailed laws, which are but corol¬
laries of the first, that hoofs indicate molar teeth with
flat crowns, a very long alimentary canal, a capacious or
multiplied stomach, and several other relations of the
same kind.’2 In short, such harmony exists between the
different organs, according to the leading forms after
which they are modelled, that an experienced anatomist,
from an inspection of a very limited portion of a body’
can form an accurate opinion regarding the entire charac¬
ters of an animal. It is thus that Cuvier, combining pro¬
found knowledge of detail with a commanding power of
generalization, has, as it were, called back into existence
those long-extinguished races whose scattered and im¬
perfect remains attest the wonderful revolutions to which
our planet has of old been subjected.
The aid which natural history has derived from the
sister sciences of anatomy and physiology, is in nothing
more apparent than in the improved systems of modern
classification. It wras formerly the practice to adopt, as
the basis of arrangement, the modifications of some single
organ, chosen arbitrarily and at hazard. Of course it did
not follow that all the other organs would resemble each
other in all the animals in which the likeness of this one
organ might be preserved. Nothing, therefore, could be
affirmed respecting the other organs belonging to the
whole of a class or genus of animals, which we should
have attempted to distinguish by characters taken from
this unimportant organ. “ Suppose, for example,” says
Cuvier, “ that we had made three divisions of animals,
the aerial, terrestrial, and aquatic, as they were anciently
classed ; there would be included in the first class, besides
what are commonly called birds, some mammiferous ani¬
mals, such as bats—some reptiles, as the dragon—some
fishes, as the flying fish—and an infinite multitude of in¬
sects. Similar difficulties would occur, in a greater or less
degree, in the other two classes.” “ This example is well
calculated to show how important it is that the characters
of our divisions should be well chosen ; for, though in the
formation of methods and systems of natural history, er¬
rors so flagrant as the above are not now committed, se¬
veral naturalists, even in modern times, have adopted di¬
visions which, in the detail, tend to similar results.”3
It is both interesting and important to trace the dif¬
ferent systems of organs in the animal kingdom, from
their first feeble rudiments, through a gradual and long-
continued chain of increasing manifestation, to their com¬
plete development in some particular class or order, in
which the perfect exercise of a special function is indis¬
pensable to its wellbeing. It is in accordance with such
development that the improved classifications of recent
times have been established; and it is now admitted as
an axiom, that a natural and philosophical arrangement of
animals can have no other foundation than a knowledge
inore or less perfect of anatomical structure. It does not
follow from this that every naturalist must be a profound
1 Grinfield’s Letters to Laurence.
2 Lectures on Comparative Anatomy, vol. i. p. 56.
1 Loc. cit. p. 62.