Various Works

  crustacea, because they are of an earthy nature, lay eggs with a

  hard integument.

  The cephalopods, having themselves bodies of a sticky nature,

  preserve in the same way the imperfect eggs they lay, for they deposit

  a quantity of sticky material about the embryo. All insects produce

  a scolex. Now all the insects are bloodless, wherefore all creatures

  that produce a scolex from themselves are so. But we cannot say simply

  that all bloodless animals produce a scolex, for the classes overlap

  one another, (1) the insects, (2) the animals that produce a scolex,

  (3) those that lay their egg imperfect, as the scaly fishes, the

  crustacea, and the cephalopoda. I say that these form a gradation, for

  the eggs of these latter resemble a scolex, in that they increase

  after oviposition, and the scolex of insects again as it develops

  resembles an egg; how so we shall explain later.

  We must observe how rightly Nature orders generation in regular

  gradation. The more perfect and hotter animals produce their young

  perfect in respect of quality (in respect of quantity this is so with

  no animal, for the young always increase in size after birth), and

  these generate living animals within themselves from the first. The

  second class do not generate perfect animals within themselves from

  the first (for they are only viviparous after first laying eggs),

  but still they are externally viviparous. The third class do not

  produce a perfect animal, but an egg, and this egg is perfect. Those

  whose nature is still colder than these produce an egg, but an

  imperfect one, which is perfected outside the body, as the class of

  scaly fishes, the crustacea, and the cephalopods. The fifth and

  coldest class does not even lay an egg from itself; but so far as

  the young ever attain to this condition at all, it is outside the body

  of the parent, as has been said already. For insects produce a

  scolex first; the scolex after developing becomes egg-like (for the

  so-called chrysalis or pupa is equivalent to an egg); then from

  this it is that a perfect animal comes into being, reaching the end of

  its development in the second change.

  Some animals then, as said before, do not come into being from

  semen, but all the sanguinea do so which are generated by

  copulation, the male emitting semen into the female when this has

  entered into her the young are formed and assume their peculiar

  character, some within the animals themselves when they are

  viviparous, others in eggs.

  There is a considerable difficulty in understanding how the plant is

  formed out of the seed or any animal out of the semen. Everything that

  comes into being or is made must (1) be made out of something, (2)

  be made by the agency of something, and (3) must become something. Now

  that out of which it is made is the material; this some animals have

  in its first form within themselves, taking it from the female parent,

  as all those which are not born alive but produced as a scolex or an

  egg; others receive it from the mother for a long time by sucking,

  as the young of all those which are not only externally but also

  internally viviparous. Such, then, is the material out of which things

  come into being, but we now are inquiring not out of what the parts of

  an animal are made, but by what agency. Either it is something

  external which makes them, or else something existing in the seminal

  fluid and the semen; and this must either be soul or a part of soul,

  or something containing soul.

  Now it would appear irrational to suppose that any of either the

  internal organs or the other parts is made by something external,

  since one thing cannot set up a motion in another without touching it,

  nor can a thing be affected in any way by another if it does not set

  up a motion in it. Something then of the sort we require exists in the

  embryo itself, being either a part of it or separate from it. To

  suppose that it should be something else separate from it is

  irrational. For after the animal has been produced does this something

  perish or does it remain in it? But nothing of the kind appears to

  be in it, nothing which is not a part of the whole plant or animal.

  Yet, on the other hand, it is absurd to say that it perishes after

  making either all the parts or only some of them. If it makes some

  of the parts and then perishes, what is to make the rest of them?

  Suppose this something makes the heart and then perishes, and the

  heart makes another organ, by the same argument either all the parts

  must perish or all must remain. Therefore it is preserved and does not

  perish. Therefore it is a part of the embryo itself which exists in

  the semen from the beginning; and if indeed there is no part of the

  soul which does not exist in some part of the body, it would also be a

  part containing soul in it from the beginning.

  How, then, does it make the other parts? Either all the parts, as

  heart, lung, liver, eye, and all the rest, come into being together or

  in succession, as is said in the verse ascribed to Orpheus, for

  there he says that an animal comes into being in the same way as the

  knitting of a net. That the former is not the fact is plain even to

  the senses, for some of the parts are clearly visible as already

  existing in the embryo while others are not; that it is not because of

  their being too small that they are not visible is clear, for the lung

  is of greater size than the heart, and yet appears later than the

  heart in the original development. Since, then, one is earlier and

  another later, does the one make the other, and does the later part

  exist on account of the part which is next to it, or rather does the

  one come into being only after the other? I mean, for instance, that

  it is not the fact that the heart, having come into being first,

  then makes the liver, and the liver again another organ, but that

  the liver only comes into being after the heart, and not by the agency

  of the heart, as a man becomes a man after being a boy, not by his

  agency. An explanation of this is that, in all the productions of

  Nature or of art, what already exists potentially is brought into

  being only by what exists actually; therefore if one organ formed

  another the form and the character of the later organ would have to

  exist in the earlier, e.g. the form of the liver in the heart. And

  otherwise also the theory is strange and fictitious.

  Yet again, if the whole animal or plant is formed from semen or

  seed, it is impossible that any part of it should exist ready made

  in the semen or seed, whether that part be able to make the other

  parts or no. For it is plain that, if it exists in it from the

  first, it was made by that which made the semen. But semen must be

  made first, and that is the function of the generating parent. So,

  then, it is not possible that any part should exist in it, and

  therefore it has not within itself that which makes the parts.

  But neither can this agent be external, and yet it must needs be one

  or other of the two. We must try, then, to solve this d
ifficulty,

  for perhaps some one of the statements made cannot be made without

  qualification, e.g. the statement that the parts cannot be made by

  what is external to the semen. For if in a certain sense they

  cannot, yet in another sense they can. (Now it makes no difference

  whether we say 'the semen' or 'that from which the semen comes', in so

  far as the semen has in itself the movement initiated by the other.)

  It is possible, then, that A should move B, and B move C; that, in

  fact, the case should be the same as with the automatic machines shown

  as curiosities. For the parts of such machines while at rest have a

  sort of potentiality of motion in them, and when any external force

  puts the first of them in motion, immediately the next is moved in

  actuality. As, then, in these automatic machines the external force

  moves the parts in a certain sense (not by touching any part at the

  moment, but by having touched one previously), in like manner also

  that from which the semen comes, or in other words that which made the

  semen, sets up the movement in the embryo and makes the parts of it by

  having first touched something though not continuing to touch it. In a

  way it is the innate motion that does this, as the act of building

  builds the house. Plainly, then, while there is something which

  makes the parts, this does not exist as a definite object, nor does it

  exist in the semen at the first as a complete part.

  But how is each part formed? We must answer this by starting in

  the first instance from the principle that, in all products of

  Nature or art, a thing is made by something actually existing out of

  that which is potentially such as the finished product. Now the

  semen is of such a nature, and has in it such a principle of motion,

  that when the motion is ceasing each of the parts comes into being,

  and that as a part having life or soul. For there is no such thing

  as face or flesh without life or soul in it; it is only equivocally

  that they will be called face or flesh if the life has gone out of

  them, just as if they had been made of stone or wood. And the

  homogeneous parts and the organic come into being together. And just

  as we should not say that an axe or other instrument or organ was made

  by the fire alone, so neither shall we say that foot or hand were made

  by heat alone. The same applies also to flesh, for this too has a

  function. While, then, we may allow that hardness and softness,

  stickiness and brittleness, and whatever other qualities are found

  in the parts that have life and soul, may be caused by mere heat and

  cold, yet, when we come to the principle in virtue of which flesh is

  flesh and bone is bone, that is no longer so; what makes them is the

  movement set up by the male parent, who is in actuality what that

  out of which the offspring is made is in potentiality. This is what we

  find in the products of art; heat and cold may make the iron soft

  and hard, but what makes a sword is the movement of the tools

  employed, this movement containing the principle of the art. For the

  art is the starting-point and form of the product; only it exists in

  something else, whereas the movement of Nature exists in the product

  itself, issuing from another nature which has the form in actuality.

  Has the semen soul, or not? The same argument applies here as in the

  question concerning the parts. As no part, if it participate not in

  soul, will be a part except in an equivocal sense (as the eye of a

  dead man is still called an 'eye'), so no soul will exist in anything

  except that of which it is soul; it is plain therefore that semen both

  has soul, and is soul, potentially.

  But a thing existing potentially may be nearer or further from its

  realization in actuality, as e.g. a mathematician when asleep is

  further from his realization in actuality as engaged in mathematics

  than when he is awake, and when awake again but not studying

  mathematics he is further removed than when he is so studying.

  Accordingly it is not any part that is the cause of the soul's

  coming into being, but it is the first moving cause from outside.

  (For nothing generates itself, though when it has come into being it

  thenceforward increases itself.) Hence it is that only one part comes

  into being first and not all of them together. But that must first

  come into being which has a principle of increase (for this nutritive

  power exists in all alike, whether animals or plants, and this is

  the same as the power that enables an animal or plant to generate

  another like itself, that being the function of them all if

  naturally perfect). And this is necessary for the reason that

  whenever a living thing is produced it must grow. It is produced,

  then, by something else of the same name, as e.g. man is produced by

  man, but it is increased by means of itself. There is, then, something

  which increases it. If this is a single part, this must come into

  being first. Therefore if the heart is first made in some animals, and

  what is analogous to the heart in the others which have no heart, it

  is from this or its analogue that the first principle of movement

  would arise.

  We have thus discussed the difficulties previously raised on the

  question what is the efficient cause of generation in each case, as

  the first moving and formative power.

  2

  The next question to be mooted concerns the nature of semen. For

  whereas when it issues from the animal it is thick and white, yet on

  cooling it becomes liquid as water, and its colour is that of water.

  This would appear strange, for water is not thickened by heat; yet

  semen is thick when it issues from within the animal's body which is

  hot, and becomes liquid on cooling. Again, watery fluids freeze, but

  semen, if exposed in frosts to the open air, does not freeze but

  liquefies, as if it was thickened by the opposite of cold. Yet it is

  unreasonable, again, to suppose that it is thickened by heat. For it

  is only substances having a predominance of earth in their composition

  that coagulate and thicken on boiling, e.g. milk. It ought then to

  solidify on cooling, but as a matter of fact it does not become

  solid in any part but the whole of it goes like water.

  This then is the difficulty. If it is water, water evidently does

  not thicken through heat, whereas the semen is thick and both it and

  the body whence it issues are hot. If it is made of earth or a mixture

  of earth and water, it ought not to liquefy entirely and turn to

  water.

  Perhaps, however, we have not discriminated all the possibilities.

  It is not only the liquids composed of water and earthy matter that

  thicken, but also those composed of water and air; foam, for instance,

  becomes thicker and white, and the smaller and less visible the

  bubbles in it, the whiter and firmer does the mass appear. The same

  thing happens also with oil; on mixing with air it thickens, wherefore

  that which is whitening becomes thicker, the watery part in it being

  separated off by the heat and turning to air. And if oxide of lead
br />   is mixed with water or even with oil, the mass increases greatly and

  changes from liquid and dark to firm and white, the reason being

  that air is mixed in with it which increases the mass and makes the

  white shine through, as in foam and snow (for snow is foam). And

  water itself on mingling with oil becomes thick and white, because air

  is entangled in it by the act of pounding them together, and oil

  itself has much air in it (for shininess is a property of air, not of

  earth or water). This too is why it floats on the surface of the

  water, for the air contained in it as in a vessel bears it up and

  makes it float, being the cause of its lightness. So too oil is

  thickened without freezing in cold weather and frosts; it does not

  freeze because of its heat (for the air is hot and will not freeze),

  but because the air is forced together and compressed, as..., by the

  cold, the oil becomes thicker. These are the reasons why semen is firm

  and white when it issues from within the animal; it has a quantity

  of hot air in it because of the internal heat; afterwards, when the

  heat has evaporated and the air has cooled, it turns liquid and

  dark; for the water, and any small quantity of earthy matter there may

  be, remain in semen as it dries, as they do in phlegm.

  Semen, then, is a compound of spirit (pneuma) and water, and the

  former is hot air (aerh); hence semen is liquid in its nature

  because it is made of water. What Ctesias the Cnidian has asserted

  of the semen of elephants is manifestly untrue; he says that it

  hardens so much in drying that it becomes like amber. But this does

  not happen, though it is true that one semen must be more earthy

  than another, and especially so with animals that have much earthy

  matter in them because of the bulk of their bodies. And it is thick

  and white because it is mixed with spirit, for it is also an

  invariable rule that it is white, and Herodotus does not report the

  truth when he says that the semen of the Aethiopians is black, as if

  everything must needs be black in those who have a black skin, and