Aristotle

by Various Works [lit]

  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,r />
  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