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  therefore women and mares are the only animals which admit the male

  during gestation, the former for the reason stated, and mares both

  because of the barrenness of their nature and because their uterus

  is of superfluous size, too large for one but too small to allow a

  second embryo to be brought to perfection by superfoetation. And the

  mare is naturally inclined to sexual intercourse because she is in the

  same case as the barren among women; these latter are barren because

  they have no monthly discharge (which corresponds to the act of

  intercourse in males) and mares have exceedingly little. And in all

  the vivipara the barren females are so inclined, because they resemble

  the males when the semen has collected in the testes but is not

  being got rid of. For the discharge of the catamenia is in females a

  sort of emission of semen, they being unconcocted semen as has been

  said before. Hence it is that those women also who are incontinent

  in regard to such intercourse cease from their passion for it when

  they have borne many children, for, the seminal secretion being then

  drained off, they no longer desire this intercourse. And among birds

  the hens are less disposed that way than the cocks, because the uterus

  of the hen-bird is up near the hypozoma; but with the cock-birds it is

  the other way, for their testes are drawn up within them, so that,

  if any kind of such birds has much semen naturally, it is always in

  need of this intercourse. In females then it encourages copulation

  to have the uterus low down, but in males to have the testes drawn up.

  It has been now stated why superfoetation is not found in some

  animals at all, why it is found in others which sometimes bring the

  later embryos to birth and sometimes not, and why some such animals

  are inclined to sexual intercourse while others are not.

  Some of those animals in which superfoetation occurs can bring the

  embryos to birth even if a long time elapses between the two

  impregnations, if their kind is spermatic, if their body is not of a

  large size, and if they bear many young. For because they bear many

  their uterus is spacious, because they are spermatic the generative

  discharge is copious, and because the body is not large but the

  discharge is excessive and in greater measure than is required for the

  nourishment wanted for the embryo, therefore they can not only form

  animals but also bring them to birth later on. Further, the uterus

  in such animals does not close up during gestation because there is

  a quantity of the residual discharge left over. This has happened

  before now even in women, for in some of them the discharge

  continues during all the time of pregnancy. In women, however, this is

  contrary to Nature, so that the embryo suffers, but in such animals it

  is according to Nature, for their body is so formed from the

  beginning, as with hares. For superfoetation occurs in these

  animals, since they are not large and they bear many young (for

  they have many toes and the many-toed animals bear many), and they

  are spermatic. This is shown by their hairiness, for the quantity of

  their hair is excessive, these animals alone having hair under the

  feet and within the jaws. Now hairiness is a sign of abundance of

  residual matter, wherefore among men also the hairy are given to

  sexual intercourse and have much semen rather than the smooth. In

  the hare it often happens that some of the embryos are imperfect while

  others of its young are produced perfect.

  6

  Some of the vivipara produce their young imperfect, others

  perfect; the one-hoofed and cloven-footed perfect, most of the

  many-toed imperfect. The reason of this is that the one-hoofed produce

  one young one, and the cloven-footed either one or two generally

  speaking; now it is easy to bring the few to perfection. All the

  many-toed animals that bear their young imperfect give birth to

  many. Hence, though they are able to nourish the embryos while newly

  formed, their bodies are unable to complete the process when the

  embryos have grown and acquired some size. So they produce them

  imperfect, like those animals which generate a scolex, for some of

  them when born are scarcely brought into form at all, as the fox,

  bear, and lion, and some of the rest in like manner; and nearly all of

  them are blind, as not only the animals mentioned but also the dog,

  wolf, and jackal. The pig alone produces both many and perfect

  young, and thus here alone we find any overlapping; it produces many

  as do the many-toed animals, but is cloven-footed or solid-hoofed

  (for there certainly are solid-hoofed swine). They bear, then, many

  young because the nutriment which would otherwise go to increase their

  size is diverted to the generative secretion (for considered as a

  solid-hoofed animal the pig is not a large one), and also it is

  more often cloven-hoofed, striving as it were with the nature of the

  solid-hoofed animals. For this reason it produces sometimes only

  one, sometimes two, but generally many, and brings them to

  perfection before birth because of the good condition of its body,

  being like a rich soil- which has sufficient and abundant nutriment

  for plants.

  The young of some birds also are hatched imperfect, that is to say

  blind; this applies to all small birds which lay many eggs, as crows

  and rooks, jays, sparrows, swallows, and to all those which lay few

  eggs without producing abundant nourishment along with the young, as

  ring-doves, turtle-doves, and pigeons. Hence if the eyes of swallows

  while still young be put out they recover their sight again, for the

  birds are still developing, not yet developed, when the injury is

  inflicted, so that the eyes grow and sprout afresh. And in general the

  production of young before they are perfect is owing to inability to

  continue nourishing them, and they are born imperfect because they are

  born too soon. This is plain also with seven-months children, for

  since they are not perfected it often happens that even the

  passages, e.g. of the ears and nostrils, are not yet opened in some of

  them at birth, but only open later as they are growing, and many

  such infants survive.

  In man males are more often born defective than females, but in

  the other animals this is not the case. The reason is that in man

  the male is much superior to the female in natural heat, and so the

  male foetus moves about more than the female, and on account of moving

  is more liable to injury, for what is young is easily injured since it

  is weak. For this same reason also the female foetus is not

  perfected equally with the male in man (but they are so in the

  other animals, for in them the female is not later in developing

  than the male). For while within the mother the female takes longer

  in developing, but after birth everything is perfected more quickly in

  females than in males; I mean, for instance, puberty, the prime of

  life, and old age. For females are weaker and colder in nature, and we

  must look upon the female character as being a sort of natur
al

  deficiency. Accordingly while it is within the mother it develops

  slowly because of its coldness (for development is concoction, and it

  is heat that concocts, and what is hotter is easily concocted); but

  after birth it quickly arrives at maturity and old age on account of

  its weakness, for all inferior things come sooner to their

  perfection or end, and as this is true of works of art so it is of

  what is formed by Nature. For the reason just given also twins are

  less likely to survive in man if one be male and one female, but

  this is not at all so in the other animals; for in man it is

  contrary to Nature that they should run an equal course, as their

  development does not take place in equal periods, but the male must

  needs be too late or the female too early; in the other animals,

  however, it is not contrary to Nature. A difference is also found

  between man and the other animals in respect of gestation, for animals

  are in better bodily condition most of the time, whereas in most women

  gestation is attended with discomfort. Their way of life is partly

  responsible for this, for being sedentary they are full of more

  residual matter; among nations where the women live a laborious life

  gestation is not equally conspicuous and those who are accustomed to

  work bear children easily both there and elsewhere; for work

  consumes the residual matter, but those who are sedentary have a great

  deal of it in them because not only is there no monthly discharge

  during pregnancy but also they do no work; therefore their travail

  is painful. But work exercises them so that they can hold their

  breath, upon which depends the ease or difficulty of child-birth.

  These circumstances then, as we have said, contribute to cause the

  difference between women and the other animals in this state, but

  the most important thing is this: in some animals the discharge

  corresponding to the catamenia is but small, and in some not visible

  at all, but in women it is greater than in any other animal, so that

  when this discharge ceases owing to pregnancy they are troubled

  (for if they are not pregnant they are afflicted with ailments

  whenever the catamenia do not occur); and they are more troubled as a

  rule at the beginning of pregnancy, for the embryo is able indeed to

  stop the catamenia but is too small at first to consume any quantity

  of the secretion; later on it takes up some of it and so alleviates

  the mother. In the other animals, on the contrary, the residual matter

  is but small and so corresponds with the growth of the foetus, and

  as the secretions which hinder nourishment are being consumed by the

  foetus the mother is in better bodily condition than usual. The same

  holds good also with aquatic animals and birds. If it ever happens

  that the body of the mother is no longer in good condition when the

  foetus is now becoming large, the reason is that its growth needs more

  nourishment than the residual matter supplies. (In some few women

  it happens that the body is in a better state during pregnancy;

  these are women in whose body the residual matter is small so that

  it is all used up along with the nourishment that goes to the foetus.)

  7

  We must also speak of what is known as mola uteri, which occurs

  rarely in women but still is found sometimes during pregnancy. For

  they produce what is called a mola; it has happened before now to a

  woman, after she had had intercourse with her husband and supposed she

  had conceived, that at first the size of her belly increased and

  everything else happened accordingly, but yet when the time for

  birth came on, she neither bore a child nor was her size reduced,

  but she continued thus for three or four years until dysentery came

  on, endangering her life, and she produced a lump of flesh which is

  called mola. Moreover this condition may continue till old age and

  death. Such masses when expelled from the body become so hard that

  they can hardly be cut through even by iron. Concerning the cause of

  this phenomenon we have spoken in the Problems; the same thing happens

  to the embryo in the womb as to meats half cooked in roasting, and

  it is not due to heat, as some say, but rather to the weakness of

  the maternal heat. (For their nature seems to be incapable, and

  unable to perfect or to put the last touches to the process of

  generation. Hence it is that the mola remains in them till old age

  or at any rate for a long time, for in its nature it is neither

  perfect nor altogether a foreign body.) It is want of concoction that

  is the reason of its hardness, as with half-cooked meat, for this

  half-dressing of meat is also a sort of want of concoction.

  A difficulty is raised as to why this does not occur in other

  animals, unless indeed it does occur and has entirely escaped

  observation. We must suppose the reason to be that woman alone among

  animals is subject to troubles of the uterus, and alone has a

  superfluous amount of catamenia and is unable to concoct them; when,

  then, the embryo has been formed of a liquid hard to concoct, then

  comes the so-called mola into being, and this happens naturally in

  women alone or at any rate more than in other animals.

  8

  Milk is formed in the females of all internally viviparous

  animals, becoming useful for the time of birth. For Nature has made it

  for the sake of the nourishment of animals after birth, so that it may

  neither fail at this time at all nor yet be at all superfluous; this

  is just what we find happening, unless anything chance contrary to

  Nature. In the other animals the period of gestation does not vary,

  and so the milk is concocted in time to suit this moment, but in

  man, since there are several times of birth, it must be ready at the

  first of these; hence in women the milk is useless before the

  seventh month and only then becomes useful. That it is only

  concocted at the last stages is what we should expect to happen also

  as being due to a necessary cause. For at first such residual matter

  when secreted is used up for the development of the embryo; now the

  nutritious part in all things is the sweetest and the most

  concocted, and thus when all such elements are removed what remains

  must become of necessity bitter and ill-flavoured. As the embryo is

  perfecting, the residual matter left over increases in quantity

  because the part consumed by the embryo is less; it is also sweeter

  since the easily concocted part is less drawn away from it. For it

  is no longer expended on moulding the embryo but only on slightly

  increasing its growth, it being now fixed because it has reached

  perfection (for in a sense there is a perfection even of an embryo).

  Therefore it comes forth from the mother and changes its mode of

  development, as now possessing what belongs to it; and no longer takes

  that which does not belong to it; and it is at this season that the

  milk becomes useful.

  The milk collects in the upper part of the body and the breasts

  because of the original plan of the organism. For the part above the

&nb
sp; hypozoma is the sovereign part of the animal, while that below is

  concerned with nourishment and residual matter, in order that all

  animals which move about may contain within themselves nourishment

  enough to make them independent when they move from one place to

  another. From this upper part also is produced the generative

  secretion for the reason mentioned in the opening of our discussion.

  But both the secretion of the male and the catamenia of the female are

  of a sanguineous nature, and the first principle of this blood and

  of the blood-vessels is the heart, and the heart is in this part of

  the body. Therefore it is here that the change of such a secretion

  must first become plain. This is why the voice changes in both sexes

  when they begin to bear seed (for the first principle of the voice

  resides there, and is itself changed when its moving cause changes).

  At the same time the parts about the breasts are raised visibly

  even in males but still more in females, for the region of the breasts

  becomes empty and spongy in them because so much material is drained

  away below. This is so not only in women but also in those animals

  which have the mammae low down.

  This change in the voice and the parts about the mammae is plain

  even in other creatures to those who have experience of each kind of

  animal, but is most remarkable in man. The reason is that in man the

  production of secretion is greatest in both sexes in proportion to

  their size as compared with other animals; I mean that of the

  catamenia in women and the emission of semen in men. When,

  therefore, the embryo no longer takes up the secretion in question but

  yet prevents its being discharged from the mother, it is necessary

  that the residual matter should collect in all those empty parts which

  are set upon the same passages. And such is the position of the mammae

  in each kind of animals for both causes; it is so both for the sake of

  what is best and of necessity.

  It is here, then, that the nourishment in animals is now formed

  and becomes thoroughly concocted. As for the cause of concoction, we

  may take that already given, or we may take the opposite, for it is