by Aristotle
nature in the tail and hinder portion of the body.
In fishes there are no limbs attached to the body. For in accordance
with their essential constitution they are swimming animals; and
nature never makes anything superfluous or void of use. Now inasmuch
as fishes are made swimming they have fins, and as they are not made
for walking they are without feet; for feet are attached to the body
that they may be of use in progression on land. Moreover, fishes
cannot have feet, or any other similar limbs, as well as four fins;
for they are essentially sanguineous animals. The Cordylus, though
it has gills, has feet, for it has no fins but merely has its tail
flattened out and loose in texture.
Fishes, unless, like the Batos and the Trygon, they are broad and
flat, have four fins, two on the upper and two on the under side of
the body; and no fish ever has more than these. For, if it had, it
would be a bloodless animal.
The upper pair of fins is present in nearly all fishes, but not so
the under pair; for these are wanting in some of those fishes that
have long thick bodies, such as the eel, the conger, and a certain
kind of Cestreus that is found in the lake at Siphae. When the body is
still more elongated, and resembles that of a serpent rather than that
of a fish, as is the case in the Smuraena, there are absolutely no
fins at all; and locomotion is effected by the flexures of the body,
the water being put to the same use by these fishes as is the ground
by serpents. For serpents swim in water exactly in the same way as
they glide on the ground. The reason for these serpent-like fishes
being without fins is the same as that which causes serpents to be
without feet; and what this is has been already stated in the
dissertations on the Progression and the Motion of Animals. The reason
was this. If the points of motion were four, motion would be
effected under difficulties; for either the two pairs of fins would be
close to each other, in which case motion would scarcely be
possible, or they would be at a very considerable distance apart, in
which case the long interval between them would be just as great an
evil. On the other hand, to have more than four such motor points
would convert the fishes into bloodless animals. A similar explanation
applies to the case of those fishes that have only two fins. For
here again the body is of great length and like that of a serpent, and
its undulations do the office of the two missing fins. It is owing
to this that such fishes can even crawl on dry ground, and can live
there for a considerable time; and do not begin to gasp until they
have been for a considerable time out of the water, while others,
whose nature is akin to that of land-animals, do not even do as much
as that. In such fishes as have but two fins it is the upper pair
(pectorals) that is present, excepting when the flat broad shape of
the body prevents this. The fins in such cases are placed at the head,
because in this region there is no elongation, which might serve in
the absence of fins as a means of locomotion; whereas in the direction
of the tail there is a considerable lengthening out in fishes of
this conformation. As for the Bati and the like, they use the marginal
part of their flattened bodies in place of fins for swimming.
In the Torpedo and the Fishing-frog the breadth of the anterior part
of the body is not so great as to render locomotion by fins
impossible, but in consequence of it the upper pair (pectorals) are
placed further back and the under pair (ventrals) are placed close
to the head, while to compensate for this advancement they are reduced
in size so as to be smaller than the upper ones. In the Torpedo the
two upper fins (pectorals) are placed on the tail, and the fish uses
the broad expansion of its body to supply their place, each lateral
half of its circumference serving the office of a fin.
The head, with its several parts, as also the organs of sense,
have already come under consideration.
There is one peculiarity which distinguishes fishes from all other
sanguineous animals, namely, the possession of gills. Why they have
these organs has been set forth in the treatise on Respiration.
These gills are in most fishes covered by opercula, but in the
Selachia, owing to the skeleton being cartilaginous, there are no such
coverings. For an operculum requires fish-spine for its formation, and
in other fishes the skeleton is made of this substance, whereas in the
Selachia it is invariably formed of cartilage. Again, while the
motions of spinous fishes are rapid, those of the Selachia are
sluggish, inasmuch as they have neither fish-spine nor sinew; but an
operculum requires rapidity of motion, seeing that the office of the
gills is to minister as it were to expiration. For this reason in
Selachia the branchial orifices themselves effect their own closure,
and thus there is no need for an operculum to ensure its taking
place with due rapidity. In some fishes the gills are numerous, in
others few in number; in some again they are double, in others single.
The last gill in most cases is single. For a detailed account of all
this, reference must be made to the treatises on Anatomy, and to the
book of Researches concerning Animals.
It is the abundance or the deficiency of the cardiac heat which
determines the numerical abundance or deficiency of the gills. For,
the greater an animal's heat, the more rapid and the more forcible
does it require the branchial movement to be; and numerous and
double gills act with more force and rapidity than such as are few and
single. Thus, too, it is that some fishes that have but few gills, and
those of comparatively small efficacy, can live out of water for a
considerable time; for in them there is no great demand for
refrigeration. Such, for example, are the eel and all other fishes
of serpent-like form.
Fishes also present diversities as regards the mouth. For in some
this is placed in front, at the very extremity of the body, while in
others, as the dolphin and the Selachia, it is placed on the under
surface; so that these fishes turn on the back in order to take
their food. The purpose of Nature in this was apparently not merely to
provide a means of salvation for other animals, by allowing them
opportunity of escape during the time lost in the act of turning-for
all the fishes with this kind of mouth prey on living animals-but also
to prevent these fishes from giving way too much to their gluttonous
ravening after food. For had they been able to seize their prey more
easily than they do, they would soon have perished from
over-repletion. An additional reason is that the projecting
extremity of the head in these fishes is round and small, and
therefore cannot admit of a wide opening.
Again, even when the mouth is not placed on the under surface, there
are differences in the extent to which it can open. For in some
cases it can gape widely, while in others it is set at the point of
<
br /> a small tapering snout; the former being the case in carnivorous
fishes, such as those with sharp interfitting teeth, whose strength
lies in their mouth, while the latter is its form in all such as are
not carnivorous.
The skin is in some fishes covered with scales (the scale of a
fish is a thin and shiny film, and therefore easily becomes detached
from the surface of the body). In others it is rough, as for
instance in the Rhine, the Batos, and the like. Fewest of all are
those whose skin is smooth. The Selachia have no scales, but a rough
skin. This is explained by their cartilaginous skeleton. For the
earthy material which has been thence diverted is expended by nature
upon the skin.
No fish has testicles either externally or internally; as indeed
have no apodous animals, among which of course are included the
serpents. One and the same orifice serves both for the excrement and
for the generative secretions, as is the case also in all other
oviparous animals, whether two-footed or four-footed, inasmuch as they
have no urinary bladder and form no fluid excretion.
Such then are the characters which distinguish fishes from all other
animals. But dolphins and whales and all such Cetacea are without
gills; and, having a lung, are provided with a blow-hole; for this
serves them to discharge the sea-water which has been taken into the
mouth. For, feeding as they do in the water, they cannot but let
this fluid enter into their mouth, and, having let it in, they must of
necessity let it out again. The use of gills, however, as has been
explained in the treatise on Respiration, is limited to such animals
as do not breathe; for no animal can possibly possess gills and at the
same time be a respiratory animal. In order, therefore, that these
Cetacea may discharge the water, they are provided with a blow-hole.
This is placed in front of the brain; for otherwise it would have
cut off the brain from the spine. The reason for these animals
having a lung and breathing, is that animals of large size require
an excess of heat, to facilitate their motion. A lung, therefore, is
placed within their body, and is fully supplied with blood-heat. These
creatures are after a fashion land and water animals in one. For so
far as they are inhalers of air they resemble land-animals, while they
resemble water-animals in having no feet and in deriving their food
from the sea. So also seals lie halfway between land and water
animals, and bats half-way between animals that live on the ground and
animals that fly; and so belong to both kinds or to neither. For
seals, if looked on as water-animals, are yet found to have feet; and,
if looked on as land-animals, are yet found to have fins. For their
hind feet are exactly like the fins of fishes; and their teeth also
are sharp and interfitting as in fishes. Bats again, if regarded as
winged animals, have feet; and, if regarded as quadrupeds, are without
them. So also they have neither the tail of a quadruped nor the tail
of a bird; no quadruped's tail, because they are winted animals; no
bird's tail, because they are terrestrial. This absence of tail is the
result of necessity. For bats fly by means of a membrane, but no
animal, unless it has barbed feathers, has the tail of a bird; for a
bird's tail is composed of such feathers. As for a quadruped's tail,
it would be an actual impediment, if present among the feathers.
14
Much the same may be said also of the Libyan ostrich. For it has
some of the characters of a bird, some of the characters of a
quadruped. It differs from a quadruped in being feathered; and from
a bird in being unable to soar aloft and in having feathers that
resemble hair and are useless for flight. Again, it agrees with
quadrupeds in having upper eyelashes, which are the more richly
supplied with hairs because the parts about the head and the upper
portion of the neck are bare; and it agrees with birds in being
feathered in all the parts posterior to these. Further, it resembles a
bird in being a biped, and a quadruped in having a cloven hoof; for it
has hoofs and not toes. The explanation of these peculiarities is to
be found in its bulk, which is that of a quadruped rather than that of
a bird. For, speaking generally, a bird must necessarily be of very
small size. For a body of heavy bulk can with difficulty be raised
into the air.
Thus much then as regards the parts of animals. We have discussed
them all, and set forth the cause why each exists; and in so doing
we have severally considered each group of animals. We must now pass
on, and in due sequence must next deal with the question of their
generation.
-THE END-
.
350 BC
ON THE SOUL
by Aristotle
translated by J. A. Smith
Book I
1
HOLDING as we do that, while knowledge of any kind is a thing to
be honoured and prized, one kind of it may, either by reason of its
greater exactness or of a higher dignity and greater wonderfulness
in its objects, be more honourable and precious than another, on
both accounts we should naturally be led to place in the front rank
the study of the soul. The knowledge of the soul admittedly
contributes greatly to the advance of truth in general, and, above
all, to our understanding of Nature, for the soul is in some sense the
principle of animal life. Our aim is to grasp and understand, first
its essential nature, and secondly its properties; of these some are
taught to be affections proper to the soul itself, while others are
considered to attach to the animal owing to the presence within it
of soul.
To attain any assured knowledge about the soul is one of the most
difficult things in the world. As the form of question which here
presents itself, viz. the question 'What is it?', recurs in other
fields, it might be supposed that there was some single method of
inquiry applicable to all objects whose essential nature (as we are
endeavouring to ascertain there is for derived properties the single
method of demonstration); in that case what we should have to seek for
would be this unique method. But if there is no such single and
general method for solving the question of essence, our task becomes
still more difficult; in the case of each different subject we shall
have to determine the appropriate process of investigation. If to this
there be a clear answer, e.g. that the process is demonstration or
division, or some known method, difficulties and hesitations still
beset us-with what facts shall we begin the inquiry? For the facts
which form the starting-points in different subjects must be
different, as e.g. in the case of numbers and surfaces.
First, no doubt, it is necessary to determine in which of the
summa genera soul lies, what it is; is it 'a this-somewhat, 'a
substance, or is it a quale or a quantum, or some other of the
remaining kinds of predicates which we have distinguished? Further,
does soul belong to the class of potential existents, or is it not
rather an actuality? Our answer to this question is of the greatest
importance.
We must consider also whether soul is divisible or is without parts,
and whether it is everywhere homogeneous or not; and if not
homogeneous, whether its various forms are different specifically or
generically: up to the present time those who have discussed and
investigated soul seem to have confined themselves to the human
soul. We must be careful not to ignore the question whether soul can
be defined in a single unambiguous formula, as is the case with
animal, or whether we must not give a separate formula for each of it,
as we do for horse, dog, man, god (in the latter case the
'universal' animal-and so too every other 'common predicate'-being
treated either as nothing at all or as a later product). Further, if
what exists is not a plurality of souls, but a plurality of parts of
one soul, which ought we to investigate first, the whole soul or its
parts? (It is also a difficult problem to decide which of these
parts are in nature distinct from one another.) Again, which ought
we to investigate first, these parts or their functions, mind or
thinking, the faculty or the act of sensation, and so on? If the
investigation of the functions precedes that of the parts, the further
question suggests itself: ought we not before either to consider the
correlative objects, e.g. of sense or thought? It seems not only
useful for the discovery of the causes of the derived properties of
substances to be acquainted with the essential nature of those
substances (as in mathematics it is useful for the understanding of
the property of the equality of the interior angles of a triangle to
two right angles to know the essential nature of the straight and
the curved or of the line and the plane) but also conversely, for
the knowledge of the essential nature of a substance is largely