black; thus the change is not a violent one nor, so to say, contrary
to Nature; at least, is it not a change into another nature. But in
animals producing many young not only do the same phenomena occur, but
also the numerous embryos hinder one another from becoming perfect and
interfere with the generative motions imparted by the semen.
A difficulty may be raised concerning (1) the production of many
young and the multiplication of the parts in a single young one, and
(2) the production of few young or only one and the deficiency of
the parts. Sometimes animals are born with too many toes, sometimes
with one alone, and so on with the other parts, for they may be
multiplied or they may be absent. Again, they may have the
generative parts doubled, the one being male, the other female; this
is known in men and especially in goats. For what are called
'tragaenae' are such because they have both male and female generative
parts; there is a case also of a goat being born with a horn upon
its leg. Changes and deficiencies are found also in the internal
parts, animals either not possessing some at all, or possessing them
in a rudimentary condition, or too numerous or in the wrong place.
No animal, indeed, has ever been born without a heart, but they are
born without a spleen or with two spleens or with one kidney; there is
no case again of total absence of the liver, but there are cases of
its being incomplete. And all these phenomena have been seen in
animals perfect and alive. Animals also which naturally have a
gall-bladder are found without one; others are found to have more than
one. Cases are known, too, of the organs changing places, the liver
being on the left, the spleen on the right. These phenomena have
been observed, as stated above, in animals whose growth is
perfected; at the time of birth great confusion of every kind has been
found. Those deficiency which only depart a little from Nature
commonly live; not so those which depart further, when the unnatural
condition is in the parts which are sovereign over life.
The question then about all these cases is this. Are we to suppose
that a single cause is responsible for the production of a single
young one and for the deficiency of the parts, and another but still a
single cause for the production of many young and the multiplication
of parts, or not?
In the first place it seems only reasonable to wonder why some
animals produce many young, others only one. For it is the largest
animals that produce one, e.g. the elephant, camel, horse, and the
other solid-hoofed ungulates; of these some are larger than all
other animals, while the others are of a remarkable size. But the dog,
the wolf, and practically all the fissipeds, produce many, even the
small members of the class, as the mouse family. The cloven-footed
animals again produce few, except the pig, which belongs to those that
produce many. This certainly seems surprising, for we should expect
the large animals to be able to generate more young and to secrete
more semen. But precisely what we wonder at is the reason for not
wondering; it is just because of their size that they do not produce
many young, for the nutriment is expended in such animals upon
increasing the body. But in the smaller animals Nature takes away from
the size and adds the excess so gained to the seminal secretion.
Moreover, more semen must needs be used in generation by the larger
animal, and little by the smaller. Therefore many small ones may be
produced together, but it is hard for many large ones to be so, and to
those intermediate in size Nature has assigned the intermediate
number. We have formerly given the reason why some animals are
large, some smaller, and some between the two, and speaking generally,
with regard to the number of young produced, the solid-hoofed
produce one, the cloven-footed few, the many-toed many. (The reason
of this is that, generally speaking, their sizes correspond to this
difference.) It is not so, however, in all cases; for it is the
largeness and smallness of the body that is cause of few or many young
being born, not the fact that the kind of animal has one, two, or many
toes. A proof of this is that the elephant is the largest of animals
and yet is many-toed, and the camel, the next largest, is
cloven-footed. And not only in animals that walk but also in those
that fly or swim the large ones produce few, the small many, for the
same reason. In like manner also it is not the largest plants that
bear most fruit.
We have explained then why some animals naturally produce many
young, some but few, and some only one; in the difficulty now stated
we may rather be surprised with reason at those which produce many,
since such animals are often seen to conceive from a single
copulation. Whether the semen of the male contributes to the
material of the embryo by itself becoming a part of it and mixing with
the semen of the female, or whether, as we say, it does not act in
this way but brings together and fashions the material within the
female and the generative secretion as the fig-juice does the liquid
substance of milk, what is the reason why it does not form a single
animal of considerable size? For certainly in the parallel case the
fig-juice is not separated if it has to curdle a large quantity of
milk, but the more the milk and the more the fig-juice put into it, so
much the greater is the curdled mass. Now it is no use to say that the
several regions of the uterus attract the semen and therefore more
young than one are formed, because the regions are many and the
cotyledons are more than one. For two embryos are often formed in
the same region of the uterus, and they may be seen lying in a row
in animals that produce many, when the uterus is filled with the
embryos. (This is plain from the dissections.) Rather the truth is
this. As animals complete their growth there are certain limits to
their size, both upwards and downwards, beyond which they cannot go,
but it is in the space between these limits that they exceed or fall
short of one another in size, and it is within these limits that one
man (or any other animal) is larger or smaller than another. So also
the generative material from which each animal is formed is not
without a quantitative limit in both directions, nor can it be
formed from any quantity you please. Whenever then an animal, for
the cause assigned, discharges more of the female secretion than is
needed for beginning the existence of a single animal, it is not
possible that only one should be formed out of all this, but a
number limited by the appropriate size in each case; nor will the
semen of the male, or the power residing in the semen, form anything
either more or less than what is according to Nature. In like
manner, if the male emits more semen than is necessary, or more powers
in different parts of the semen as it is divided, however much it is
it will not make anything greater; on the contrary it will dry up
the ma
terial of the female and destroy it. So fire also does not
continue to make water hotter in proportion as it is itself increased,
but there is a fixed limit to the heat of which water is capable; if
that is once reached and the fire is then increased, the water no
longer gets hotter but rather evaporates and at last disappears and is
dried up. Now since it appears that the secretion of the female and
that from the male need to stand in some proportionate relation to one
another (I mean in animals of which the male emits semen), what
happens in those that produce many young is this: from the very
first the semen emitted by the male has power, being divided, to
form several embryos, and the material contributed by the female is so
much that several can be formed out of it. (The parallel of
curdling milk, which we spoke of before, is no longer in point here,
for what is formed by the heat of the semen is not only of a certain
quantity but also of a certain quality, whereas with fig-juice and
rennet quantity alone is concerned.) This then is just the reason why
in such animals the embryos formed are numerous and do not all unite
into one whole; it is because an embryo is not formed out of any
quantity you please, but whether there is too much or too little, in
either case there will be no result, for there is a limit set alike to
the power of the heat which acts on the material and to the material
so acted upon.
On the same principle many embryos are not formed, though the
secretion is much, in the large animals which produce only one young
one, for in them also both the material and that which works upon it
are of a certain quantity. So then they do not secrete such material
in too great quantity for the reason previously stated, and what
they do secrete is naturally just enough for one embryo alone to be
formed from it. If ever too much is secreted, then twins are born.
Hence such cases seem to be more portentous, because they are contrary
to the general and customary rule.
Man belongs to all three classes, for he produces one only and
sometimes many or few, though naturally he almost always produces one.
Because of the moisture and heat of his body he may produce many [for
semen is naturally fluid and hot], but because of his size he
produces few or one. On account of this it results that in man alone
among animals the period of gestation is irregular; whereas the period
is fixed in the rest, there are several periods in man, for children
are born at seven months and at ten months and at the times between,
for even those of eight months do live though less often than the
rest. The reason may be gathered from what has just been said, and the
question has been discussed in the Problems. Let this explanation
suffice for these points.
The cause why the parts may be multiplied contrary to Nature is
the same as the cause of the birth of twins. For the reason exists
already in the embryo, whenever it aggregates more material at any
point of itself than is required by the nature of the part. The result
is then that either one of its parts is larger than the others, as a
finger or hand or foot or any of the other extremities or limbs; or
again if the embryo is cleft there may come into being more than one
such part, as eddies do in rivers; as the water in these is carried
along with a certain motion, if it dash against anything two systems
or eddies come into being out of one, each retaining the same
motion; the same thing happens also with the embryos. The abnormal
parts generally are attached near those they resemble, but sometimes
at a distance because of the movement- taking place in the embryo, and
especially because of the excess of material returning to that place
whence it was taken away while retaining the form of that part
whence it arose as a superfluity.
In certain cases we find a double set of generative organs [one
male and the other female]. When such duplication occurs the one is
always functional but not the other, because it is always
insufficiently supplied with nourishment as being contrary to
Nature; it is attached like a growth (for such growths also receive
nourishment though they are a later development than the body proper
and contrary to Nature.) If the formative power prevails, both are
similar; if it is altogether vanquished, both are similar; but if it
prevail here and be vanquished there, then the one is female and the
other male. (For whether we consider the reason why the whole
animal is male or female, or why the parts are so, makes no
difference.)
When we meet with deficiency in such parts, e.g. an extremity or one
of the other members, we must assume the same cause as when the embryo
is altogether aborted (abortion of embryos happens frequently).
Outgrowths differ from the production of many young in the manner
stated before; monsters differ from these in that most of them are due
to embryos growing together. Some however are also of the following
kind, when the monstrosity affects greater and more sovereign parts,
as for instance some monsters have two spleens or more than two
kidneys. Further, the parts may migrate, the movements which form
the embryo being diverted and the material changing its place. We must
decide whether the monstrous animal is one or is composed of several
grown together by considering the vital principle; thus, if the
heart is a part of such a kind then that which has one heart will be
one animal, the multiplied parts being mere outgrowths, but those
which have more than one heart will be two animals grown together
through their embryos having been confused.
It also often happens even in many animals that do not seem to be
defective and whose growth is now complete, that some of their
passages may have grown together or others may have been diverted from
the normal course. Thus in some women before now the os uteri has
remained closed, so that when the time for the catamenia has arrived
pain has attacked them, till either the passage has burst open of
its own accord or the physicians have removed the impediment; some
such cases have ended in death if the rupture has been made too
violently or if it has been impossible to make it at all. In some boys
on the other hand the end of the penis has not coincided with the
end of the passage where the urine is voided, but the passage has
ended below, so that they crouch sitting to void it, and if the testes
are drawn up they appear from a distance to have both male and
female generative organs. The passage of the solid food also has
been closed before now in sheep and some other animals; there was a
cow in Perinthus which passed fine matter, as if it were sifted,
through the bladder, and when the anus was cut open it quickly
closed up again nor could they succeed in keeping it open.
We have now spoken of the production of few and many young, and of
the outgrowth of superfluous parts or of their deficiency, and also of
monstrosities.
5
Superfoetation does not occur at all in some animals but does in
others; of the former some are able to bring the later formed embryo
to birth, while others can only do so sometimes. The reason why it
does not occur in some is that they produce only one young one, for it
is not found in solid-hoofed animals and those larger than these, as
owing to their size the secretion of the female is all used up for the
one embryo. For all these have large bodies, and when an animal is
large its foetus is large in proportion, e.g. the foetus of the
elephant is as big as a calf. But superfoetation occurs in those which
produce many young because the production of more than one at a
birth is itself a sort of superfoetation, one being added to
another. Of these all that are large, as man, bring to birth the later
embryo, if the second impregnation takes place soon after the first,
for such an event has been observed before now. The reason is that
given above, for even in a single act of intercourse the semen
discharged is more than enough for one embryo, and this being
divided causes more than one child to be born, the one of which is
later than the other. But when the embryo has already grown to some
size and it so happens that copulation occurs again, superfoetation
sometimes takes place, but rarely, since the uterus generally closes
in women during the period of gestation. If this ever happens (for
this also has occurred) the mother cannot bring the second embryo
to perfection, but it is cast out in a state like what are called
abortions. For just as, in those animals that bear only one, all the
secretion of the female is converted to the first formed embryo
because of its size, so it is here also; the only difference is that
in the former case this happens at once, in the latter when the foetus
has attained to some size, for then they are in the same state as
those that bear only one. In like manner, since man naturally would
produce many young, and since the size of the uterus and the
quantity of the female secretion are both greater than is necessary
for one embryo, only not so much so as to bring to birth a second,