Various Works Read online

  things; one naturally exists prior to another. But the word 'prior' is

  used in more senses than one. For there is a difference between the

  end or final cause and that which exists for the sake of it; the

  latter is prior in order of development, the former is prior in

  reality. Again, that which exists for the sake of the end admits of

  division into two classes, (1) the origin of the movement, (2) that

  which is used by the end; I mean, for instance, (1) that which can

  generate, (2) that which serves as an instrument to what is generated,

  for the one of these, that which makes, must exist first, as the

  teacher before the learner, and the other later, as the pipes are

  later than he who learns to play upon them, for it is superfluous that

  men who do not know how to play should have pipes. Thus there are

  three things: first, the end, by which we mean that for the sake of

  which something else exists; secondly, the principle of movement and

  of generation, existing for the sake of the end (for that which can

  make and generate, considered simply as such, exists only in

  relation to what is made and generated); thirdly, the useful, that is

  to say what the end uses. Accordingly, there must first exist some

  part in which is the principle of movement (I say a part because this

  is from the first one part of the end and the most important part

  too); next after this the whole and the end; thirdly and lastly,

  the organic parts serving these for certain uses. Hence if there is

  anything of this sort which must exist in animals, containing the

  principle and end of all their nature, this must be the first to

  come into being- first, that is, considered as the moving power, but

  simultaneous with the whole embryo if considered as a part of the end.

  Therefore all the organic parts whose nature is to bring others into

  being must always themselves exist before them, for they are for the

  sake of something else, as the beginning for the sake of the end;

  all those parts which are for the sake of something else but are not

  of the nature of beginnings must come into being later. So it is not

  easy to distinguish which of the parts are prior, those which are

  for the sake of another or that for the sake of which are the

  former. For the parts which cause the movement, being prior to the end

  in order of development, come in to cause confusion, and it is not

  easy to distinguish these as compared with the organic parts. And

  yet it is in accordance with this method that we must inquire what

  comes into being after what; for the end is later than some parts

  and earlier than others. And for this reason that part which

  contains the first principle comes into being first, next to this

  the upper half of the body. This is why the parts about the head,

  and particularly the eyes, appear largest in the embryo at an early

  stage, while the parts below the umbilicus, as the legs, are small;

  for the lower parts are for the sake of the upper, and are neither

  parts of the end nor able to form it.

  But they do not say well nor do they assign a necessary cause who

  say simply that 'it always happens so', and imagine that this is a

  first principle in these cases. Thus Democritus of Abdera says that

  'there is no beginning of the infinite; now the cause is a

  beginning, and the eternal is infinite; in consequence, to ask the

  cause of anything of this kind is to seek for a beginning of the

  infinite'. Yet according to this argument, which forbids us to seek

  the cause, there will be no proof of any eternal truth whatever; but

  we see that there is a proof of many such, whether by 'eternal' we

  mean what always happens or what exists eternally; it is an eternal

  truth that the angles of a triangle are always equal to two right

  angles, or that the diagonal of a square is incommensurable with the

  side, and nevertheless a cause and a proof can be given for these

  truths. While, then, it is well said that we must not take on us to

  seek a beginning (or first principle) of all things, yet this is not

  well said of all things whatever that always are or always happen, but

  only of those which really are first principles of the eternal things;

  for it is by another method, not by proof, that we acquire knowledge

  of the first principle. Now in that which is immovable and

  unchanging the first principle is simply the essence of the thing, but

  when we come to those things which come into being the principles

  are more than one, varying in kind and not all of the same kind; one

  of this number is the principle of movement, and therefore in all

  the sanguinea the heart is formed first, as was said at the beginning,

  and in the other animals that which is analogous to the heart.

  From the heart the blood-vessels extend throughout the body as in

  the anatomical diagrams which are represented on the wall, for the

  parts lie round these because they are formed out of them. The

  homogeneous parts are formed by heat and cold, for some are put

  together and solidified by the one and some by the other. The

  difference between these has already been discussed elsewhere, and

  it has been stated what kinds of things are soluble by liquid and

  fire, and what are not soluble by liquid and cannot be melted by fire.

  The nutriment then oozes through the blood-vessels and the passages in

  each of the parts, like water in unbaked pottery, and thus is formed

  the flesh or its analogues, being solidified by cold, which is why

  it is also dissolved by fire. But all the particles given off which

  are too earthy, having but little moisture and heat, cool as the

  moisture evaporates along with the heat; so they become hard and

  earthy in character, as nails, horns, hoofs, and beaks, and

  therefore they are softened by fire but none of them is melted by

  it, while some of them, as egg-shells, are soluble in liquids. The

  sinews and bones are formed by the internal heat as the moisture

  dries, and hence the bones are insoluble by fire like pottery, for

  like it they have been as it were baked in an oven by the heat in

  the process of development. But it is not anything whatever that is

  made into flesh or bone by the heat, but only something naturally

  fitted for the purpose; nor is it made in any place or time

  whatever, but only in a place and time naturally so fitted. For

  neither will that which exists potentially be made except by that

  moving agent which possesses the actuality, nor will that which

  possesses the actuality make anything whatever; the carpenter would

  not make a box except out of wood, nor will a box be made out of the

  wood without the carpenter. The heat exists in the seminal

  secretion, and the movement and activity in it is sufficient in kind

  and in quantity to correspond to each of the parts. In so far as there

  is any deficiency or excess, the resulting product is in worse

  condition or physically defective, in like manner as in the case of

  external substances which are thickened by boiling that they may be

  more palatable or for any other purpose. But in the latter case it

  i
s we who apply the heat in due measure for the motion required; in

  the former it is the nature of the male parent that gives it, or

  with animals spontaneously generated it is the movement and heat

  imparted by the right season of the year that it is the cause.

  Cooling, again, is mere deprivation of heat. Nature makes use of

  both; they have of necessity the power of bringing about different

  results, but in the development of the embryo we find that the one

  cools and the other heats for some definite purpose, and so each of

  the parts is formed; thus it is in one sense by necessity, in

  another for a final cause, that they make the flesh soft, the sinews

  solid and elastic, the bones solid and brittle. The skin, again, is

  formed by the drying of the flesh, like the scum upon boiled

  substances; it is so formed not only because it is on the outside, but

  also because what is glutinous, being unable to evaporate, remains

  on the surface. While in other animals the glutinous is dry, for which

  reason the covering of the invertebrates is testaceous or crustaceous,

  in the vertebrates it is rather of the nature of fat. In all of

  these which are not of too earthy a nature the fat is collected

  under the covering of the skin, a fact which points to the skin

  being formed out of such a glutinous substance, for fat is somewhat

  glutinous. As we said, all these things must be understood to be

  formed in one sense of necessity, but in another sense not of

  necessity but for a final cause.

  The upper half of the body, then, is first marked out in the order

  of development; as time goes on the lower also reaches its full size

  in the sanguinea. All the parts are first marked out in their outlines

  and acquire later on their colour and softness or hardness, exactly as

  if Nature were a painter producing a work of art, for painters, too,

  first sketch in the animal with lines and only after that put in the

  colours.

  Because the source of the sensations is in the heart, therefore this

  is the part first formed in the whole animal, and because of the

  heat of this organ the cold forms the brain, where the blood-vessels

  terminate above, corresponding to the heat of the heart. Hence the

  parts about the head begin to form next in order after the heart,

  and surpass the other parts in size, for the brain is from the first

  large and fluid.

  There is a difficulty about what happens with the eyes of animals.

  Though from the beginning they appear very large in all creatures,

  whether they walk or swim or fly, yet they are the last of the parts

  to be formed completely, for in the intervening time they collapse.

  The reason is this. The sense-organ of the eyes is set upon certain

  passages, as are the other sense-organs. Whereas those of touch and

  taste are simply the body itself or some part of the body of

  animals, those of smell and hearing are passages connecting with the

  external air and full themselves of innate spiritus; these passages

  end at the small blood-vessels about the brain which run thither

  from the heart. But the eye is the only sense-organ that has a

  bodily constitution peculiar to itself. It is fluid and cold, and does

  not exist from the first in the place which it occupies later in the

  same way as the other parts do, for they exist potentially to begin

  with and actually come into being later, but the eye is the purest

  part of the liquidity about the brain drained off through the passages

  which are visible running from them to the membrane round the brain. A

  proof of this is that, apart from the brain, there is no other part in

  the head that is cold and fluid except the eye. Of necessity therefore

  this region is large at first but falls in later. For the same thing

  happens with the brain; at first it is liquid and large, but in course

  of evaporation and concoction it becomes more solid and falls in; this

  applies both to the brain and the eyes. The head is very large at

  first, on account of the brain, and the eyes appear large because of

  the liquid in them. They are the last organs to reach completion

  because the brain is formed with difficulty; for it is at a late

  period that it gets rid of its coldness and fluidity; this applies

  to all animals possessing a brain, but especially to man. For this

  reason the 'bregma' is the last of the bones to be formed; even

  after birth this bone is still soft in children. The cause of this

  being so with men more than with other animals is the fact that

  their brain is the most fluid and largest. This again is because the

  heat in man's heart is purest. His intellect shows how well he is

  tempered, for man is the wisest of animals. And children for a long

  time have no control over their heads on account of the heaviness of

  the brain; and the same applies to the parts which it is necessary

  to move, for it is late that the principle of motion gets control over

  the upper parts, and last of all over those whose motion is not

  connected directly with it, as that of the legs is not. Now the eyelid

  is such a part. But since Nature makes nothing superfluous nor in

  vain, it is clear also that she makes nothing too late or too soon,

  for if she did the result would be either in vain or superfluous.

  Hence it is necessary that the eyelids should be separated at the same

  time as the heart is able to move them. So then the eyes of animals

  are perfected late because of the amount of concoction required by the

  brain, and last of all the parts because the motion must be very

  strong before it can affect parts so far from the first principle of

  motion and so cold. And it is plain that such is the nature of the

  eyelids, for if the head is affected by never so little heaviness

  through sleepiness or drunkenness or anything else of the kind, we

  cannot raise the eyelids though their own weight is so small. So

  much for the question how the eyes come into being, and why and for

  what cause they are the last to be fully developed.

  Each of the other parts is formed out of the nutriment, those most

  honourable and participating in the sovereign principle from the

  nutriment which is first and purest and fully concocted, those which

  are only necessary for the sake of the former parts from the

  inferior nutriment and the residues left over from the other. For

  Nature, like a good householder, is not in the habit of throwing

  away anything from which it is possible to make anything useful. Now

  in a household the best part of the food that comes in is set apart

  for the free men, the inferior and the residue of the best for the

  slaves, and the worst is given to the animals that live with them.

  Just as the intellect acts thus in the outside world with a view to

  the growth of the persons concerned, so in the case of the embryo

  itself does Nature form from the purest material the flesh and the

  body of the other sense-organs, and from the residues thereof bones,

  sinews, hair, and also nails and hoofs and the like; hence these are

  last to assume their form, for they have to wait till the time when

  Nature has
some residue to spare.

  The bones, then, are made in the first conformation of the parts

  from the seminal secretion or residue. As the animal grows the bones

  grow from the natural nourishment, being the same as that of the

  sovereign parts, but of this they only take up the superfluous

  residues. For everywhere the nutriment may be divided into two

  kinds, the first and the second; the former is 'nutritious', being

  that which gives its essence both to the whole and to the parts; the

  latter is concerned with growth, being that which causes

  quantitative increase. But these must be distinguished more fully

  later on. The sinews are formed in the same way as the bones and out

  of the same materials, the Seminal and nutritious residue. Nails,

  hair, hoofs, horns, beaks, the spurs of cocks, and any other similar

  parts, are on the contrary formed from the nutriment which is taken

  later and only concerned with growth, in other words that which is

  derived from the mother, or from the outer world after birth. For this

  reason the bones on the one hand only grow up to a certain point (for

  there is a limit of size in all animals, and therefore also of the

  growth of the bones; if these had been always able to grow, all

  animals that have bone or its analogue would grow as long as they

  lived, for these set the limit of size to animals. What is the

  reason of their not always increasing in size must be stated later.)

  Hair, on the contrary, and growths akin to hair go on growing as long

  as they exist at all, and increase yet more in diseases and when the

  body is getting old and wasting, because more residual matter is

  left over, as owing to old age and disease less is expended on the

  important parts, though when the residual matter also fails through

  age the hair fails with it. But the contrary is the case with the

  bones, for they waste away along with the body and the other parts.

  Hair actually goes on growing after death; it does not, however, begin

  growing then.

  About the teeth a difficulty may be raised. They have actually the

  same nature as the bones, and are formed out of the bones, but

  nails, hair, horns, and the like are formed out of the skin, and