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