1 · We have now discussed the other parts of animals, both generally and [715a1] with reference to the peculiarities of each kind, explaining how each part exists on account of such a cause, and I mean by this the cause for the sake of something.
There are four causes: first, the final cause, that for the sake of which; secondly, the definition of essence (and these two we may regard pretty much as one [5] and the same); thirdly, the material; and fourthly, that from which the source of movement comes.
We have then already discussed the other three causes, for the definition and the final cause are the same, and the material of animals is their parts—of the whole animal the non-homogeneous parts, of these again the homogeneous, and of [10] these last the so-called elements of bodies. It remains to speak of those parts which contribute to the generation of animals and of which nothing definite has yet been said, and to explain what is the moving cause. To inquire into this last and to inquire into the generation of each animal is in a way the same thing; and, therefore, my plan has united them together, arranging the discussion of these parts last, and the [15] beginning of the question of generation next to them.
Now some animals come into being from the union of male and female, i.e. all those kinds of animal which possess the two sexes. This is not the case with all of them; though in the sanguinea with few exceptions the creature, when its growth is [20] complete, is either male or female, and though some bloodless animals have sexes so that they generate offspring of the same kind, yet other bloodless animals generate indeed, but not offspring of the same kind; such are all that come into being not from a union of the sexes, but from decaying earth and excrements. To speak [25] generally, if we take all animals which change their locality,1 some by swimming, others by flying, others by walking, we find in these the two sexes, not only in the sanguinea but also in some of the bloodless animals; and this applies in the case of [715b1] the latter sometimes to the whole class, as the cephalopoda and crustacea, but in the class of insects only to the majority. Of these, all which are produced by union of animals of the same kind generate also after their kind, but all which are not [5] produced by animals, but from decaying matter, generate indeed, but produce another kind, and the offspring is neither male nor female; such are some of the insects. This is what might have been expected; for if those animals which are not produced by parents had themselves united and produced others, then their offspring must have been either like or unlike themselves. If like, then their parents [10] ought to have come into being in the same way; this is only a reasonable postulate to make, for it is plainly the case with other animals. If unlike, and yet able to copulate, then there would have come into being again from them another kind of creature and again another from these, and this would have gone on to infinity. But [15] nature flies from the infinite; for the infinite is imperfect, and nature always seeks an end.
But all those creatures which do not move, as the testacea and animals that live by clinging to something else, inasmuch as their nature resembles that of plants, have no sex any more than plants have, but as applied to them the word is only used [20] in virtue of a similarity and analogy. For there is a slight distinction of this sort, since even in plants we find in the same kind some trees which bear fruit and others which, while bearing none themselves, yet contribute to the ripening of the fruits of those which do, as in the case of the fig-tree and caprifig.
[25] The same holds good also in plants, some coming into being from seed and others, as it were, by the spontaneous action of nature, arising either from decomposition of the earth or of some parts in other plants; for some are not formed [716a1] by themselves separately but are produced upon other trees, as the mistletoe. Plants, however, must be investigated separately.
2 · Of the generation of animals we must speak as various questions arise in order in the case of each, and we must connect our account with what has been said. [5] For, as we said above, the male and female principles may be put down first and foremost as origins of generation, the former as containing the efficient cause of generation, the latter the material of it. The most convincing proof of this is drawn from considering how and whence comes the semen; for it is out of this that those creatures are formed which are produced in the ordinary course of nature; but we [10] must observe carefully the way in which this semen actually comes into being from the male and female. For it is just because the semen is secreted from the two sexes, the secretion taking place in them and from them, that they are first principles of generation. For by a male animal we mean that which generates in another, and by a female that which generates in itself; that is why in the macrocosm also, men [15] think of the earth as female and a mother, but address heaven and the sun and other like entities as progenitors and fathers.
Male and female differ in their definition by each having a separate faculty, [20] and to perception by certain parts; by definition the male is that which is able to generate in another, as said above; the female is that which is able to generate in itself and out of which comes into being the offspring previously existing in the generator. And since they are differentiated by a faculty and by their function, and since instruments are needed for all functioning, and since the bodily parts are the instruments to serve the faculties, it follows that certain parts must exist for union [25] and production of offspring. And these must differ from each other, so that consequently the male will differ from the female. (For even though we speak of the animal as a whole as male or female, yet really it is not male or female in virtue of the whole of itself, but only in virtue of a certain faculty and a certain part—just as [30] with sight or locomotion—which part is also plain to sense-perception.)
Now as a matter of fact such parts are in the female the so-called uterus, in the male the testes and the penis, in all the sanguinea; for some of them have testes and others the corresponding passages. There are corresponding differences of male and female in all the bloodless animals also which have this division into opposite sexes. [716b1] But if in the sanguinea the parts concerned in copulation differ in their forms, we must observe that a small change in a first principle is usually attended by changes in many of the things depending on it. This is plain in the case of castrated animals; [5] for, though only the generative part is disabled, yet pretty well the whole form of the animal changes in consequence so much that it seems to be female or not far short of it, and thus it is clear that an animal is not male or female in virtue of any random part or faculty. Clearly, then, the distinction of sex is a first principle; at any rate, [10] when that which distinguishes male and female suffers change, many other changes accompany it, as would be the case if a first principle is changed.
3 · The sanguinea are not all alike as regards testes and uterus. Taking the former first, we find that some of them have not testes at all, as the classes of fish [15] and of serpents, but only two spermatic ducts. Others have testes indeed, but internally by the loin in the region of the kidneys, and from each of these a duct, as in the case of those animals which have no testes at all; these ducts unite also as with [20] those animals; this applies (among animals breathing air and having a lung) to all birds and oviparous quadrupeds. For all these have their testes internal near the loin, and two ducts from these in the same way as serpents; I mean the lizards and tortoises and all the scaly reptiles. But all the vivipara have their testes in front; [25] some of them inside at the end of the abdomen, as the dolphin, not with ducts but with a penis projecting externally from them as in the ox-fish; others outside, either pendent as in man or towards the fundament as in swine. They have been [30] discriminated more accurately in the History of Animals.2
The uterus is always double, just as the testes are always two in the male. It is situated either near the pudendum (as in women, and all those animals which bring forth alive not only externally but also internally, and all fish that lay eggs [717a1] externally) or up towards the hypozoma (as in all birds and in viviparous fishes). The uterus is also double in the crustacea and the cephalopoda; for the membranes which include their so-called eggs are of the nature of a uterus. It is particularly [5] hard to distinguish in the case of the octopus, so that it seems to be single, but the reason of this is that the bulk of the body is everywhere similar.
It is double also in the larger insects; in the smaller it is indistinct owing to the [10] small size of the body.
Such is the description of the aforesaid parts of animals.
4 · With regard to the difference of the spermatic organs in males, if we are to investigate the causes of their existence, we must first grasp the final cause of the [15] testes. Now if nature makes everything either because it is necessary or because it is better so, this part also must be for one of these two reasons. But that it is not necessary for generation is plain; for in that case it would have been possessed by all creatures that generate, but as it is neither serpents have testes nor have fish; for [20] they have been seen uniting and with their ducts full of milt. It remains then that it must be because it is somehow better so. Now it is true that the business of most animals is, you may say, nothing else than to produce young, as the business of a plant is to produce seed and fruit. But still as, in the case of nutriment, animals with straight intestines are more violent in their desire for food, so those which have not [25] testes but only ducts, or which have them indeed but internally, are all quicker in accomplishing copulation. But those which are to be more temperate in the one case have not straight intestines, and in the other have their ducts twisted to prevent their desire being too violent and hasty. It is for this that the testes are contrived; for [30] they make the movement of the spermatic secretion steadier, preserving the folding back of the passages in the vivipara, as horses and the like, and in man. (For details see the History of Animals.)3 For the testes are no part of the ducts but are only attached to them, as women fasten stones to the loom when weaving; if they are [717b1] removed the ducts are drawn up internally, so that castrated animals are unable to generate; if they were not drawn up they would be able, and before now a bull mounting immediately after castration has caused conception in the cow because [5] the ducts had not yet been drawn up. In birds and oviparous quadrupeds the testes receive the spermatic secretion, so that its expulsion is slower than in fishes. This is clear in the case of birds, for their testes are much enlarged at the time of copulation, and all those which pair at one season of the year have them so small when this time is past that they are almost indiscernible, but during the season they are very large. When the testes are internal the act of copulation is quicker, for [10] when the testes are external the semen is not emitted before the testes are drawn up.
5 · Besides, quadrupeds have the organ of copulation, since it is possible for [15] them to have it, but for birds and the footless animals it is not possible, because the former have their legs under the middle of the abdomen and the latter have no legs at all; now the penis depends from that region and is situated there. (That is why the [20] legs are strained in intercourse, both the penis and the legs being sinewy.) So that, since it is not possible for them to have this organ, they must necessarily either have no testes also, or at any rate not have them there, as those animals that have both penis and testes have them in the same situation.
Further, with those animals at any rate that have external testes, the semen is collected together before emission, and emission is due to the penis being heated by its movement; it is not ready for emission at immediate contact as in fishes. [25]
All the vivipara have their testes in front, internally or externally, except the hedgehog; he alone has them near the loin. This is for the same reason as with birds, because their union must be quick, for the hedgehog does not, like the other [30] quadrupeds, mount upon the back of the female, but they conjugate standing upright because of their spines.
So much for the reasons why those animals have testes which have them, and why they are sometimes external and sometimes internal.
6 · All those animals which have no testes are deficient in this part, as has been said, not because it is better to be so but simply because of necessity, and secondly because it is necessary that their copulation should be speedy. Such is the nature of fish and serpents. Fish copulate throwing themselves alongside of the [718a1] females and separating again quickly. For as men and all such creatures must hold their breath before emitting the semen, so fish at such times must cease taking in the sea-water, and then they perish easily. Therefore they must not mature the [5] semen during copulation, as viviparous land-animals do, but they have it all matured together at the time, so as not to be maturing it while in contact but to emit it ready matured. So they have no testes, and the ducts are straight and simple. [10] There is a small part similar to this connected with the testes in the system of quadrupeds, for part of the folded duct is sanguineous and part is not; the fluid is already semen when it is received by and passes through this latter part, so that once it has arrived there it is soon emitted in these quadrupeds also. Now in fishes the whole passage resembles the last section of the folded part of the duct in man and [15] similar animals.
7 · Serpents copulate twining round one another, and, as said above, have neither testes nor penis, the latter because they have no legs, the former because of their length, but they have ducts like fish; for on account of their extreme length the [20] seminal fluid would take too long in its passage and be cooled if it were further delayed by testes. (This happens also if the penis is large; such men are less fertile than when it is smaller because the semen, if cold, is not generative, and that which is carried too far is cooled.) So much for the reason why some animals have testes [25] and others not. Serpents intertwine because of their inaptitude to cast themselves alongside of one another. For they are too long to unite closely with so small a part and have no organs of attachment, so they make use of the suppleness of their [30] bodies, intertwining. That is why they seem to be slower in copulation than fish, not only on account of the length of the ducts but also of this elaborate arrangement in uniting.
[35] 8 · It is not easy to state the facts about the uterus in female animals, for there are many points of difference. The vivipara are not all alike in this part; women and all the vivipara with feet have the uterus low down by the pudendum, [718b1] but the viviparous selachia have it higher up near the hypozoma. In the ovipara, again, it is low in fish (as in women and the viviparous quadrupeds), high in birds [5] and all oviparous quadrupeds. Yet even these differences are on a principle. To begin with the ovipara, they differ in the manner of laying their eggs, for some produce them imperfect, as fishes whose eggs increase and are finally developed outside of them. The reason is that they produce many young, and this is their [10] function as it is with plants. If then they perfected the egg in themselves they must needs be few in number, but as it is, they have so many that each uterus seems to be an egg, at any rate in the small fishes. For these are the most productive, just as with the other animals and plants whose nature is analogous to theirs, for the increase of [15] size turns with them to seed.
But the eggs of birds and the quadrupedal ovipara are perfect when produced. In order that these may be preserved they must have a hard covering (for their envelope is soft so long as they are increasing in size), and the shell is made by heat [20] squeezing out the moisture from the earthy material; consequently the place must be hot in which this is to happen. But the part about the hypozoma is hot, as is shown by that being the part which concocts the food. If then the eggs must be within the uterus, then the uterus must be near the hypozoma in those creatures which produce their eggs in a perfect form. Similarly it must be low down in those which produce them imperfect, for it is advantageous that it should be so. And it is [25] more natural for the uterus to be low down than high up, when nature has no other business in hand to hinder it; for its end is low down, and where is the end, there is the function, and the uterus itself is naturally where the function is.
9 · We find differences in the vivipara also as compared with one another. Some produce their young alive, not only externally, but also internally, as men, [30] horses, dogs, and all those which have hair, and among aquatic animals, dolphins, whales, and such cetacea.
10 · But the selachia and the vipers produce their young alive externally, but first produce eggs internally. The egg is perfect, for so only can an animal be generated from an egg, and nothing comes from an imperfect one. It is because they [35] are of a cold nature, not hot as some assert, that they do not lay their eggs externally.
11 · At least they certainly produce their eggs in a soft envelope, the reason being that they have but little heat and so their nature does not complete the process of drying the egg-shell. Because, then, they are cold they produce soft-shelled eggs, [719a1] and because the eggs are soft they do not produce them externally; for that would have caused their destruction.
When an animal is produced from an egg, the process is for the most part the same as in birds, for the egg descends and the young is hatched from it near the vagina, where the young is produced in those animals which are viviparous from the beginning. Therefore in such animals the uterus is dissimilar to that of both the [5] vivipara and ovipara, because they participate in both classes; for it is at once near the hypozoma and also stretching along downwards in all the selachia. But the facts about this and the other kinds of uterus must be gathered from the Anatomies and [10] from the History.4 Thus, because they are oviparous, laying perfect eggs, they have the uterus placed high, but, as being viviparous, low, participating in both classes.
Animals that are viviparous from the beginning all have it low, nature here having no other business to interfere with her, and their production having no double character. Besides this, it is impossible for animals to be produced alive near the hypozoma, for the foetus must needs be heavy and move, and that region in the [15] mother is vital and would not be able to bear the weight and the movement. Thirdly, parturition would be difficult because of the length of the passage to be traversed; even as it is there is difficulty with women if they draw up the uterus in parturition by yawning or anything of the kind, and even when empty it causes a feeling of [20] suffocation if moved upwards. For if a uterus is to hold a living animal it must be stronger than in ovipara, and therefore in all the vivipara it is fleshy, whereas when the uterus is near the hypozoma it is membranous. And this is clear also in the case of the animals which produce young by the mixed method, for their eggs are high up [25] and sideways, but the living young are produced in the lower part of the uterus.
So much for the reason why differences are found in the uterus of various animals, and generally why it is low in some and high in others near the hypozoma. [30]
12 · Why is the uterus always internal, but the testes sometimes internal, sometimes external? The reason for the uterus always being internal is that in this is contained the offspring which needs guarding, shelter, and concoction, while the outer surface of the body is easily injured and cold. The testes vary in position because they also need shelter and a covering to preserve them and to mature the [719b1] semen; for it would be impossible for them, if chilled and stiffened, to be drawn up and discharge it. Therefore, whenever the testes are visible, they have a cuticular covering known as the scrotum. If the nature of the skin is opposed to this, being too [5] hard to be adapted for enclosing them or for being soft like a true skin,5 as with the scaly integument of fish and reptiles, then the testes must be internal. Therefore they are so in dolphins and all the cetacea which have them, and in the oviparous [10] quadrupeds among the scaly animals. The skin of birds also is hard so that it will not conform to the size of anything and enclose it neatly. (This is another reason with all these animals for their testes being internal besides those previously mentioned as arising necessarily from the details of copulation.) For the same reason they are internal in the elephant and hedgehog, for the skin of these, too, is not well suited to [15] keep the protective part separate.
The position of the uterus differs in animals viviparous within themselves and those externally oviparous, and in the latter class again it differs in those which have [20] the uterus low and those which have it near the hypozoma, as in fishes compared with birds and oviparous quadrupeds. And it is different again in those which produce young in both ways, being oviparous internally and viviparous externally. For those which are viviparous both internally and externally have the uterus placed [25] on the abdomen, as men, cattle, dogs, and the like, since it is expedient for the safety and growth of the foetus that no weight should be upon the uterus.
13 · The passages also are different through which the solid and liquid [30] excreta pass out in all the vivipara. That is why both males and females in this class all have a part whereby the urine is voided, and this serves also for the issue of the semen in males, of the offspring in females. This passage is situated above and in front of the passage of the solid excreta. Those ovipara that produce imperfect eggs; [720a1] e.g. the oviparous fish, have their uterus not under the abdomen but near the loin; for the growth of the egg does not hinder this, since the growing creature is perfected and develops externally.6 The passage is the same as that of the solid [5] nutriment in all those animals that have no penis, in all the ovipara, even those of them that have a bladder, as the tortoises. For it is for the sake of generation, not for the evacuation of the urine, that the passages are double; but because the semen is naturally liquid, the liquid excretion also shares the same passage. This is clear [10] from the fact that all animals produce semen, but all do not void liquid excrement. Now the spermatic passages of the male must be fixed and must not wander, and the same applies to the uterus of the female, and this fixing must take place at either the front or the back of the body. To take the uterus first, it is in the front of the [15] body in vivipara because of the foetus, but at the loin and the back in ovipara. All animals which are internally oviparous and externally viviparous are in an intermediate condition because they participate in both classes, being at once oviparous and viviparous. For the upper part of the uterus, where the eggs are [20] produced, is under the hypozoma by the loin and the back, but as it advances7 is low at the abdomen; for it is in that part that the animal is viviparous. In these also the passage for solid excrement and for copulation is the same, for none of these, as has been said already, has a separate pudendum.
[25] The same applies to the passages in the male, whether they have testes or no, as to the uterus of the ovipara. For in all of them, the ducts adhere to the back and the region of the spine. For they must not wander but be settled, and that is the character of the region of the back, which gives continuity and stability. Now in [30] those which have internal testes, the ducts are fixed from the first, and they are fixed in like manner if the testes are external; then they meet together towards the region of the penis.
The like applies to the ducts in the dolphins, but they have their testes hidden [35] under the abdominal cavity.
We have now discussed the situation of the parts contributing to generation, and the causes thereof. [720b1]
14 · The bloodless animals do not agree either with the sanguinea or with each other in the fashion of the parts contributing to generation. There are four classes still left to deal with, first the crustacea, secondly the cephalopoda, thirdly [5] the insects, and fourthly the testacea. We cannot be certain about all of them, but that most of them do not copulate is plain; in what manner they unite must be stated later.
The crustacea copulate like the retromingent quadrupeds, fitting their tails to [10] one another, the one supine and the other prone. For the fins attached to the sides of the tail being long prevent them from uniting with the belly against the back. The males have fine spermatic ducts, the females a membranous uterus alongside the intestine, cloven on each side, in which the egg is produced. [15]
15 · The cephalopoda entwine together at the mouth, pushing against one another and enfolding their tentacles. This attitude is necessary, because nature has bent backwards the end of the intestine and brought it round near the mouth, as has been said before in the treatise on Parts of Animals8 The female has a part [20] corresponding to the uterus, plainly to be seen in each of these animals, for it contains an egg which is at first indistinct but afterwards splits up into many; each of these eggs is imperfect when deposited, as with the oviparous fishes. In the cephalopoda (as also in the crustacea) the same passage serves to void the [25] excrement and leads to the part like a uterus,† for the male discharges the seminal fluid through this passage. And it is†9 on the lower surface of the body, where the mantle is open and the sea-water enters the cavity. Hence the union of the male with the female takes place at this point, for it is necessary, if the male discharges either [30] semen or a part of himself or any other force, that he should unite with her at the uterine passage. But the insertion, in the case of the octopus, of the tentacle of the male into the funnel of the female, by which tentacle the fishermen say the male copulates with her, is only for the sake of attachment, and it is not an organ useful [35] for generation, for it is outside the passage and indeed outside the body.
Sometimes also cephalopoda unite by the male mounting on the back of the female, but whether for generation or some other cause has not yet been [721a1] observed.
16 · Some insects copulate and the offspring are produced from animals of the same name, just as with the sanguinea; such are the locusts, cicadae, spiders, wasps, and ants. Others unite indeed and generate; but the result is not a creature of [5] the same kind, but only a grub, and these insects do not come into being from animals but from putrefying matter, liquid or solid; such are fleas, flies, and cantharides. Others again are neither produced from animals nor unite with each [10] other; such are gnats, mosquitoes, and many similar kinds. In most of those which unite the female is larger than the male. The males do not appear to have spermatic passages. In most cases the male does not insert any part into the female, but the female from below upwards into the male; this has been observed in many cases (as [15] also that the male mounts the female),10 the opposite in few cases; but observations are not yet comprehensive enough to enable us to make a distinction of classes. And generally it is the rule with most of the oviparous fish and oviparous quadrupeds that the female is larger than the male because this is expedient in view of the [20] increase of bulk in conception by reason of the eggs. In the female the part analogous to the uterus is cleft and extends along the intestine, as with the other animals; in this are produced the results of conception. This is clear in locusts and [25] all other large insects whose nature it is to unite—most insects are too small.
Such is the character of the generative organs in animals which were not spoken of before. It remains now to speak of the homogeneous parts concerned, the seminal fluid and milk. We will take the former first, and treat of milk afterwards.
[30] 17 · Some animals manifestly emit semen, as all the sanguinea, but whether the insects and cephalopoda do so is uncertain. Therefore this is a question to be considered, whether all males do so, or not all; and if not all, why some do and some not; and whether the female also contributes any semen or not; and, if not semen, [721b1] whether she does not contribute anything else either, or whether she contributes something else which is not semen. We must also inquire what those animals which emit semen contribute by means of it to generation, and generally what is the nature [5] of semen, and of the menstrual flow in all animals which discharge this liquid.
Now it is thought that all animals are generated out of semen, and that the semen comes from the parents. That is why it is part of the same inquiry to ask whether both male and female produce it or only one of them, and to ask whether it comes from the whole of the body or not from the whole; for if the latter is true it is [10] reasonable to suppose that it does not come from both parents either. Accordingly, since some say that it comes from the whole of the body, we must investigate this question first.
The proofs from which it can be argued that the semen comes from each and every part of the body11 may be reduced to four. First, the intensity of the pleasure [15] of coition; for the same state of feeling is more pleasant if multiplied, and that which affects all the parts is multiplied as compared with that which affects only one or a few. Secondly, the argument that mutilated parents produce mutilated offspring; for they argue that since the parent is deficient in this part the semen does not come from thence, and the result is that the corresponding part is not formed in the [20] offspring. Thirdly, the resemblances to the parents; for the young are born like them part for part as well as in the whole body; if then the coming of the semen from the whole body is cause of the resemblance of the whole, so the parts would be like because it comes from each of the parts. Fourthly, it would seem to be reasonable to say that as there is some first thing from which the whole arises, so it is also with [25] each of the parts, and therefore if semen is cause of the whole so each of the parts would have a seed peculiar to itself. And these opinions are plausibly supported by such evidence as that children are born with a likeness to their parents, not only in congenital but also in acquired characteristics; for before now, when the parents [30] have had scars, the children have been born with a mark in the form of the scar in the same place, and there was a case at Chalcedon where the father had a brand on his arm and the letter was marked on the child, only confused and not clearly articulated. That is pretty much the evidence on which some believe that the semen comes from all the body.
18 · On examining the question, however, the opposite appears more likely; [722a1] for it is not hard to refute the above arguments and besides the view involves impossibilities. First, then, the resemblance of children to parents is no proof that the semen comes from the whole body, because the resemblance is found also in voice, nails, hair, and way of moving, from which nothing comes. And men generate [5] before they yet have certain characters, such as a beard or grey hair. Further, children are like their more remote ancestors from whom nothing has come; for the resemblances recur at an interval of many generations, as in the case of the woman in Elis who had intercourse with a negro; her daughter was not negroid but the son [10] of that daughter was. The same thing applies also to plants; for it is clear that if this theory was true the seed would come from all parts of plants also; but often a plant does not possess one part, and another part may be removed, and a third grows afterwards. Besides, the seed does not come from the pericarp, and yet this also comes into being with the same form as in the parent plant. [15]
We may also ask whether the semen comes from each of the homogeneous parts only, such as flesh and bone and sinew, or also from the heterogeneous, such as face and hands. For if from the former only, we object that the resemblance exists rather in the latter; if then it is not because of the semen coming from all parts that children resemble their parents in these, what is there to stop the homogeneous [20] parts also from being like for some other reason than this? If the semen comes from the heterogeneous alone, then it does not come from all parts; but it is more fitting that it should come from the homogeneous parts, for they are prior to the heterogeneous which are composed of them; and as children are born like their [25] parents in face and hands, so they are in flesh and nails. If the semen comes from both, what would be the manner of generation? For the heterogeneous parts are composed of the homogeneous, so that to come from the former would be to come from the latter and from their composition. Similarly, take a written name: if anything came from the whole of it, it would be from each of the syllables, and if [30] from these, from the letters and their composition. So that if really flesh and bones are composed of fire and the like elements, the semen would come rather from the elements; for how can it come from their composition? Yet without this composition there would be no resemblance. If again something creates this composition later, it [722b1] would be this that would be the cause of the resemblance, not the coming of the semen from every part of the body.
Further, if the parts of the future animal are separated in the semen, how do they live? and if they are connected, they would form a small animal.
[5] And what about the generative parts? For that which comes from the male is not similar to what comes from the female.
Again, if the semen comes from all parts of both parents alike, the result is two animals; for the offspring will have all the parts of both. That is why Empedocles seems to say what agrees pretty well with this view (if we are to adopt it), to a [10] certain extent at any rate, but to be wrong if we think otherwise.12 For he declares that there is a sort of tally in the male and female, and that the whole offspring does not come from either, ‘but sundered is the fashion of limbs, some in man’s . . .’13 For why does not the female generate from herself if the semen comes from all parts [15] alike and she has a receptacle? But, it seems, either it does not come from all the parts, or if it does it is in the way Empedocles says, not the same parts coming from each parent, which is why they need intercourse with each other.
Yet this also is impossible, just as much as it is impossible for the parts when full grown to survive and have life in them when torn apart, as Empedocles accounts [20] for the creation of animals in the time of his Reign of Love, saying that ‘many heads sprang up without necks’,14 and later on these isolated parts combined into animals. Now that this is impossible is plain, for neither would the separate parts be able to survive without having any soul or life in them, nor if they were living things, so to say, could several of them combine so as to become one animal again. Yet those who [25] say that semen comes from the whole of the body really have to talk in that way, and as it happened then in the earth during the Reign of Love, so it happens according to them in the body. Now it is impossible that the parts should be united together when they come into being and should come from different parts of the parent, meeting together in one place. Then how can the upper and lower, right and left, front and [30] back parts have been sundered? All these points are unintelligible. Further, some parts are distinguished by possessing a faculty, others by being in certain conditions; the heterogeneous, as tongue and hand, by the faculty of doing something, the homogeneous by hardness and softness and the other similar conditions. Blood, then, will not be blood, nor flesh flesh, in any and every state. It is clear, then, that that which comes from any part, as blood from blood or flesh from [723a1] flesh, will not be synonymous with that part. But if it is something different from which the blood comes, the coming of the semen from all the parts will not be the cause of the resemblance, as is held by the supporters of this theory. For if blood is formed from something which is not blood, it is enough that the semen come from [5] one part only; for why should not all the parts be formed from one part? Indeed, this theory seems to be the same as that of Anaxagoras, that none of the homogeneous parts come into being, except that these theorists assume, in the case of the generation of animals, what he assumed of everything.
Then, again, how will these parts that came from all the body grow? It is true [10] that Anaxagoras plausibly says that flesh out of the food is added to the flesh. But if we do not say this (while saying that semen comes from all parts of the body), how will the foetus become greater by the addition of something else if that which is added remain unchanged? But if that which is added can change, then why not say that the semen from the very first is of such a kind that blood and flesh can be made [15] out of it, instead of saying that it itself is blood and flesh? Nor can we say that it is increased later by a process of mixing, as wine when water is poured into it. For in that case each element would be itself at first while still unmixed, but the fact rather is that flesh and bone and each of the other parts is such later. And to say [20] that some part of the semen is sinew and bone is quite above us, as the saying is.
Besides all this there is a difficulty if the sex is determined in conception (as Empedocles says: ‘it is shed in clean vessels; some wax female, if they fall in with [25] cold’).15 Anyhow, it is plain that both men and women change not only from infertile to fertile, but also from bearing female to bearing male offspring, which looks as if the cause does not lie in the semen coming from all the parent or not, but in the mutual proportion or disproportion of that which comes from the woman and [30] the man, or in something of this kind. It is clear, then, if we are to put this down as being so, that the female sex is not determined by the semen coming from any particular part, and consequently neither is the special sexual part so determined (if really the same semen can become either a male or female child, which shows that the sexual part does not exist in the semen). Why, then, should we assert this of this part any more than of the others? For if semen does not come from the uterus, the [723b1] same account may be given of the others.
Again, some creatures come into being neither from parents of the same kind nor from parents of a different kind, as flies and the various kinds of what are called [5] fleas; from these are produced animals indeed, but not in this case of similar nature, but a kind of grub. It is plain in this case that the young of a different kind are not produced by semen coming from all parts of the parent, for they would then resemble them, if indeed resemblance is a sign of its coming from all parts.
Further, even among animals some produce many young from a single coition (and something like this is universal among plants, for it is plain that they bear all [10] the fruit of a whole season from a single movement). And yet how would this be possible if the semen were secreted from all the body? For from a single coition and a single segregation must follow only a single secretion. Nor is it possible for it to be separated in the uterus; for this would no longer be a separation of semen, but, as it [15] were, a severance from an animal.
Again, the cuttings from a plant bear seed; clearly, therefore, even before they were cut, they bore their fruit from their own mass alone, and the seed did not come from all the plant.
But the greatest proof of all is derived from observations we have sufficiently established on insects. For, if not in all, at least in most of these, the female in the [20] act of copulation inserts a part of herself into the male, This, as we said before, is the way they copulate; for the females manifestly insert this from below into the males above, not in all cases, but in most of those observed. Hence it seems clear that, [25] when the males do emit semen, then also the cause of the generation is not its coming from all the body, but something else which must be investigated hereafter. For even if it were true that it comes from all the body, as they say, they ought not to claim that it comes from all parts of it, but only from the creative part—from the [30] workman, so to say, not the material he works in. Instead of that, they talk as if one were to say that the semen comes from the shoes; for, generally speaking, if a son is like his father, the shoes he wears are like his father’s shoes.
As to the vehemence of pleasure in sexual intercourse, it is not because the semen comes from all the body, but because there is a strong friction (wherefore if this intercourse is often repeated the pleasure is diminished in the persons [724a1] concerned). Moreover, the pleasure is at the end of the act, but it ought, on the theory, to be in each of the parts, and not at the same time, but sooner in some and later in others.
If mutilated young are born of mutilated parents, it is for the same reason as [5] that for which they are like them. And the young of mutilated parents are not always mutilated, just as they are not always like their parents; the cause of this must be inquired into later, for this problem is the same as that.
Again, if the female does not produce semen, it is reasonable to suppose it does not come from all the body of the male either. And if it does not come from all the male it is not unreasonable to suppose that it does not come from the female, but [10] that the female is cause of the generation in some other way. Into this we must next inquire, since it is plain that the semen is not secreted from all the parts.
In this investigation and those which follow from it, the first thing to do is to [15] understand what semen is, for then it will be easier to inquire into its operations and the phenomena connected with it. Now the object of semen is to be of such a nature that from it as their origin come into being those things which are naturally formed,† not because there is any agent which makes them from it as . . . but simply [20] because this is the semen.†16 Now we speak of one thing coming from another in many senses; it is one thing when we say that night comes from day or a man becomes man from boy, meaning that the one comes after the other; it is another if we say that a statue is made from bronze and a bed from wood, and so on in all the other cases where we say that the thing made is made from a material, meaning [25] that the whole is formed from something pre-existing, which is put into shape. In a third sense a man becomes unmusical from being musical, sick from being well, and generally in this sense contraries arise from contraries. Fourthly, as in the ‘climax’ [30] of Epicharmus; thus from slander comes railing and from this fighting, and all these are from something in the sense that it is the efficient cause.17 In this last class sometimes the efficient cause is in the things themselves, as in the last mentioned (for the slander is a part of the whole trouble), and sometimes external, as the art is external to the work of art or the torch to the burning house.
[35] Now the semen plainly falls under one of the two following senses—either the semen is the material from which it is made, or it is the first efficient cause. For assuredly it is not in the sense of one thing being after another, as the voyage comes [724b1] from the Panathenaea; nor yet as contraries come from contraries, for then one of the two contraries ceases to be, and a third substance must exist as an immediate underlying basis from which the new thing comes into being. We must discover, then, in which of the two other classes the semen is to be put, whether it is to be [5] regarded as matter, and therefore acted upon by something else, or as a form, and therefore acting upon something else, or as both at once. For perhaps at the same time we shall see clearly also how all the products of semen come into being from contraries, since coming into being from contraries is also a natural process, for some animals do so, i.e. from male and female, others from only one parent, as is the [10] case with plants and all those animals in which male and female are not separately differentiated. Now that which comes from the generating parent is called the seminal fluid, being that which first has in it a principle of generation, in the case of all animals whose nature it is to unite; semen is that which has in it the principles from both united parents (as in the case of plants and of those animals in which [15] male and female are not separated), as the first mixture which arises from the union of male and female, be it a foetus or an egg, for these already have in them that which comes from both. (Semen and fruit differ only in the one being earlier and the other later, fruit in that it comes from something else, and seed in that something [20] else comes from it, for both are really the same thing.)
We must again take up the question what the primary nature of what is called semen is.18 Everything which we find in the body must either be one of the natural parts, whether homogeneous or heterogeneous, or an unnatural part such as a [25] growth, or a residue or waste-product, or nutriment. (By residue I mean what is left of the nutriment, by waste-product that which is given off from the growth by an unnatural decomposition.)
Now that semen cannot be a part of the body is plain; for it is homogeneous, but from it nothing is composed, as things are from sinew or flesh; nor is it separated [30] as are all the other parts. But neither is it contrary to nature nor a defect; for it exists in all alike, and the natural organism comes from it. Nutriment, again, is obviously introduced from without.
It remains, then, that it must be either a waste-product or a residue. Now the ancients seem to think that it is a waste-product; for when they say that it comes [35] from all the body by reason of the heat of the movement, they imply that it is a kind of waste-product. But these are contrary to nature, and from such arises nothing [725a1] according to nature. So then it must be a residue.
But every residue is either of useless or useful nutriment; by ‘useless’ I mean that from which nothing further is contributed to natural growth, but which is [5] particularly mischievous to the body if too much of it is consumed; by ‘useful’ I mean the opposite. Now it is evident that it cannot be of the former character, for such is most abundant in persons of the worst condition of body through age or sickness; semen, on the contrary, is least abundant in them, for either they have [10] none at all or it is not fertile, because a useless and morbid residue is mingled with it.
Semen, then, is part of a useful residue. But the most useful is the last and that from which finally is formed each of the parts of the body. For residues are either earlier or later; of the nutriment in the first stage the residue is phlegm and the like, [15] for phlegm also is a residue of the useful nutriment, an indication of this being that if it is mixed with pure nutriment it is nourishing, and that it is used up in cases of illness. The final residue is the smallest in proportion to the quantity of nutriment. But we must reflect that the daily nutriment by which animals and plants grow is [20] but small; for if a very little added of the same thing is the size of it will become excessive.
So we must say the opposite of what the ancients said. For whereas they said that semen is that which comes from all the body, we shall say it is that whose nature is to go to all of it, and what they thought a waste-product seems rather to be [25] a residue. For it is more reasonable to suppose that the last extract of the nutriment which goes to all parts resembles it, just as part of a painter’s colour is often left over resembling that which he has used up. Waste-products, on the contrary, are always due to corruption and to a departure from nature.
[30] A further proof that it is not a waste-product, but rather a residue, is the fact that the large animals have few young, the small many. For the large must have more waste and less residue, since the great size of the body causes most of the nutriment to be used up, so that the residue is small.
Again, no place has been set apart by nature for waste-products but they flow [725b1] wherever they can find an easy passage in the body, but a place has been set apart for all the natural residues; thus the lower intestine serves for the excretion of the solid nutriment, the bladder for that of the liquid; for the useful part of the nutriment we have the upper intestine, for the spermatic secretions the uterus and pudenda and breasts, for it is collected and flows together into them.
[5] And the resulting phenomena are evidence that semen is what we have said, and these result because such is the nature of the residue. For the exhaustion consequent on the loss of even a very little of the semen is conspicuous because the body is deprived of the ultimate gain drawn from the nutriment. With some few persons, it is true, during a short time in the flower of their youth the loss of it, if it be excessive in quantity, is an alleviation (just as in the case of the nutriment in its [10] first stage, if too much have been taken, since getting rid of this also makes the body more comfortable), and so it may be also when other residues come away with it, for in that case it is not only semen that is lost but also other influences come away [15] mingled with it,19 and these are morbid. That is why, with some men at least, that which comes from them proves sometimes incapable of procreation because the seminal element in it is so small. But still in most men and as a general rule the result of intercourse is exhaustion and weakness rather than relief, for the reason [20] given. Moreover, semen does not exist in them either in childhood or in old age or in sickness—in the last case because of weakness, in old age because their constitution does not concoct enough, and in childhood because they are growing and so all the nutriment is used up too soon—for in about five years, in the case of human beings at any rate, the body seems to gain half the height that is gained in all the rest of life. [25]
In many animals and plants we find a difference in this connexion not only between kinds as compared with kinds, but also between similar individuals of the same kind as compared with each other, e.g. man with man or vine with vine. Some have much semen, others little, others again none at all, not through weakness but [30] the contrary, at any rate in some cases. This is because the nutriment is used up to form the body, as with some human beings, who, being in good condition and developing much flesh or getting rather too fat, produce less semen and are less desirous of intercourse. Like this is what happens with those vines which ‘play the goat’, that is, luxuriate through too much nutrition, for he-goats when fat are less inclined to mount the female; for which reason they thin them before breeding from [726a1] them, and say that the vines ‘play the goat’, so calling it from the condition of the goats. And fat people, women as well as men, appear to be less fertile than others from the fact that the residue when in process of concoction turns to fat with those [5] who are too well-nourished. For fat also is a healthy residue due to good living.
In some cases no semen is produced at all, as by the willow and poplar. This condition is due to each20 of the two causes, weakness and strength; the former prevents concoction of the nutriment, the latter causes it to be all consumed, as said above. In like manner other animals produce much semen through weakness as well [10] as through strength, [when a great quantity of a useless residue is mixed with it; this sometimes results in actual disease when a passage is not found to carry off the impurity, and though some recover of this, others actually die of it. For they are affected by waste-products here as in the urine, which also has been known to cause [15] disease.
Further, the same passage serves for residue and semen; and whatever animals have both kinds of excrement, that of liquid and that of solid nutriment, discharge the semen by the same passage as the liquid excrement (for it is a residue of a liquid, since the nutriment of all animals is rather liquid than solid), but those which have [20] no liquid excrement discharge it at the passage of the solid residua. Moreover, waste-products are always morbid, but the removal of the residue is useful; now the discharge of the semen participates in both characteristics because it takes up some of the non-useful nutriment. But if it were a waste-product it would be always harmful; as it is, it is not so.]21 [25]
From what has been said, it is clear that semen is a residue of useful nutriment, and that in its last stage, whether it is produced by all or no.
19 · After this we must distinguish of what sort of nutriment it is a residue, and must discuss the menstrual discharges which occur in certain of the vivipara. [30] For thus we shall make it clear whether the female also produces semen like the male and the foetus is a mixture of two semens, or whether no semen is secreted by the female, and, if not, whether she contributes nothing else either to generation but only provides a receptacle, or whether she does contribute something, and how and [726b1] in what manner she does so.
We have previously stated that the final nutriment is the blood in the sanguinea and the analogous fluid in the other animals. Since the semen is also a residue of the nutriment, and that in its final stage, it follows that it will be either blood or that which is analogous to blood, or something formed from this. But since [5] it is from the blood, when concocted and somehow divided up, that each part of the body is made, and since the semen if properly concocted is quite of a different character from the blood when it is separated from it, but if not properly concocted has been known in some cases to issue in a bloody condition if one forces oneself too [10] often to coition, therefore it is plain that semen will be a residue of the nutriment when reduced to blood, being that which is finally distributed to the parts of the body. And this is the reason why it has so great power, for the loss of the pure and healthy blood is an exhausting thing; for this reason also it is natural that the offspring should resemble the parents, for that which goes to all the parts of the [15] body resembles that which is left over. So that the semen which is to form the hand or the face or the whole animal is already the hand or face or whole animal undifferentiated, and what each of them is actually such is the semen potentially, either in virtue of its own mass or because it has a certain power in itself. (For we have not yet made it clear from the distinctions drawn hitherto whether it is the [20] matter of the semen that is the cause of generation, or whether it has in it some faculty and efficient cause thereof). For the hand also or any other bodily part is not hand or other part in a true sense if it be without soul or some other power, but is only called by the same name.
[It is clear also that in cases where seminal waste-products occur, they too are [25] residues. This happens when it is dissolved into what preceded it—as when plaster falls away at once from the wall; for what comes away is the same as what was at first applied. In the same way, the last residue is the same as the first wasteproduct.]22
[30] On this subject, then, so much may be laid down. But since it is necessary that the weaker animal also should have a residue greater in quantity and less concocted, and that being of such a nature it should be a mass of sanguineous liquid, and since that which has by nature a smaller portion of heat is weaker, and since it has already been stated that such is the character of the female—it is necessary that the [727a1] sanguineous matter discharged by the female is also a residue. And such is the discharge of the so-called menstrual fluid.
It is plain, then, that the menstrual discharge is a residue, and that it is analogous in females to the semen in males. The circumstances connected with them [5] are evidence that this view is correct. For the semen begins to appear in males and to be emitted at the same time of life that the menstrual flow begins in females, and that they change their voice and their breasts begin to develop. So, too, in the decline of life the generative power fails in the one sex and the menstrual discharge in the other. [10]
The following signs also indicate that this discharge in females is a residue. Generally speaking women suffer neither from haemorrhoids nor bleeding at the nose nor anything else of the sort except when the menstrual discharges are ceasing, and if anything of the kind occurs the flow is interfered with because the discharge is diverted to it. [15]
Further, the blood-vessels of women stand out less than those of men, and women are rounder and smoother because the residue which in men goes to these vessels is drained away with the menstrual discharge. We must suppose, too, that the same cause accounts for the fact that the bulk of the body is smaller in females [20] than in males among the vivipara, since this is the only class in which menstrual fluids are discharged from the body. And in this class the fact is clearest in women, for the discharge is greater in women than in the other animals. That is why her pallor and the absence of prominent blood-vessels is always most conspicuous, and the deficient development of her body compared with a man’s is obvious. [25]
Now since this is what corresponds in the female to the semen in the male, and since it is not possible that two seminal discharges should be found together, it is plain that the female does not contribute semen to the generation of the offspring. For if she had semen she would not have the menstrual fluid; but, as it is, because she has the latter she has not the former. [30]
It has been stated then that the menstrual fluids are a residue as the semen is, and confirmation of this view may be drawn from some of the phenomena of animals. For fat creatures produce less semen than lean ones, as observed before. The reason is that fat also, like semen, is a residue and is in fact concocted blood, [35] only not concocted in the same way as the semen. Thus, if the residue is consumed to form fat the semen is naturally deficient. And so among the bloodless animals the [727b1] cephalopoda and crustacea are in best condition about the time of producing eggs, for, because they are bloodless and no fat is formed in them, that which is analogous in them to fat is at that season drawn off to form the seminal residue. [5]
And a sign that the female does not emit similar semen to the male, and that the offspring is not formed by a mixture of both, as some say, is that often the female conceives without the sensation of pleasure in intercourse, and if again the pleasure is experienced by her no less than by the male and the two sexes reach their goal together, yet often no conception takes place unless the liquid of the menstrual [10] discharge is present in a right proportion. Hence the female does not produce young if the discharge is absent altogether, nor often when, it being present, the efflux still continues; but she does so after the purgation. For in the one case she has not the nutriment or material from which the foetus can be framed by the power coming [15] from the male and inherent in the semen, and in the other it is washed away with the discharge because of its abundance. But when after its occurrence the greater part has been evacuated, the remainder is formed into a foetus. Cases of conception when the discharge does not occur at all, or of conception during the discharge instead of after it, are due to the fact that in the former instance there is only so [20] much liquid to begin with as remains behind after the discharge in fertile women, and no greater quantity is secreted so as to come away from the body, while in the latter instance the mouth of the uterus closes after the discharge. When, therefore, the quantity already expelled from the body is great but the discharge still continues, only not on such a scale as to wash away the semen, then it is that [25] conception accompanies coition. Nor is it at all strange that the discharges should still continue after conception (for even after it they recur to some extent, but are scanty and do not last during all the period of gestation; this, however, is a morbid phenomenon, and that is why it is found only in a few cases and seldom, whereas it is [30] that which happens as a regular thing that is according to nature).
It is clear then that the female contributes the material for generation, and that this is in the substance of the menstrual discharges, and that they are a residue.
20 · Some think that the female contributes semen in coition because the [35] pleasure she experiences is sometimes similar to that of the male, and also is attended by a liquid discharge. But this discharge is not seminal; it is merely proper [728a1] to the part concerned in each case. For there is a discharge from the uterus which occurs in some women but not in others. It is found in those who are fair-skinned and of a feminine type generally, but not in those who are dark and of a masculine appearance. The amount of this discharge, when it occurs, is sometimes on a [5] different scale from the emission of semen and far exceeds it. Moreover, different kinds of food cause a great difference in the quantity of such discharges; for instance some pungently-flavoured foods cause them to be conspicuously increased. And as to the pleasure which accompanies coition it is due to emission not only of [10] semen, but also of a breath, the coming together of which precedes the emission. This is plain in the case of boys who are not yet able to emit semen, but are near the proper age, and of men who are impotent, for all these are capable of pleasure by rubbing. And those who have been injured in the generative organs sometimes [15] suffer from diarrhoea because the residue, which they are not able to concoct and turn into semen, is diverted into the intestine. Now a boy is like a woman in form, and the woman is as it were an impotent male, for it is through a certain incapacity that the female is female, being incapable of concocting the nutriment in its last [20] stage into semen (and this is either blood or that which is analogous to it in animals which are bloodless) owing to the coldness of her nature. As then diarrhoea is caused in the bowels by the insufficient concoction of the blood, so are caused in the blood-vessels all discharges of blood, including the menstrual blood, for this also is such a discharge, only it is natural whereas the others are morbid.
[25] Thus it is clear that it is reasonable to suppose that generation comes from this. For the menstrual blood is semen not in a pure state but in need of working up, just as in the formation of fruits the nutriment is present, when it is not yet sifted thoroughly, but needs working up to purify it. Thus the menstrual blood causes generation by mixture with the semen, as this impure nutriment in plants is [30] nutritious when mixed with pure nutriment.
And a sign that the female does not emit semen is the fact that the pleasure of intercourse is caused by touch in the same region of the female as of the male; and yet is it not from thence that this flow proceeds. Further, it is not all females that have it at all, but only the sanguinea, and not all even of these, but only those whose [35] uterus is not near the hypozoma and which do not lay eggs; it is not found in the animals which have no blood but only the analogous fluid (for what is blood in the [728b1] former is represented by another fluid in the latter). The reason why neither the latter nor those sanguinea mentioned (i.e. those whose uterus is low and which do not lay eggs)23 have this effluxion is the dryness of their bodies; this allows but little [5] matter to be secreted, only enough for generation but not enough to be discharged from the body. All animals that are viviparous without producing eggs first (such are man and all quadrupeds which bend their hind-legs inwards; for all these are viviparous without producing eggs)—all these have the menstrual flow, unless they [10] are defective in development as the mule, only the efflux is not abundant as in women. Details of the facts in each animal have been given in the History of Animals.24
The menstrual flow is more abundant in women than in the other animals, and men emit the most semen in proportion to their size. The reason is that the [15] composition of their bodies is liquid and hot compared to others, for more matter must be secreted in such a case. Further, man has no such parts in his body as those to which the superfluous matter is diverted in the other animals; for he has no great quantity of hair in proportion to his body, nor outgrowths of bones, horns, and [20] teeth.
There is evidence that the semen is in the menstrual blood, for, as said before, this residue appears in the male at the same time of life as the menstrual flow in the female; this indicates that the parts destined to receive each of these residues are differentiated at the same time in both sexes; and as the neighbouring parts in both [25] become swollen the hair of puberty springs forth in both alike. As the parts in question are on the point of differentiating they are distended by the breath; this is clearer in males in the testes, but appears also about the breasts; in females it is more marked in the breasts, for it is when they have risen two fingers’ breadth that [30] the menstrual flow generally begins.
Now, in all living things in which the male and female are not separated the semen is a sort of embryo; by embryo I mean the first mixture of male and female; hence, from one semen comes one body,—for example, one stalk of wheat from one [35] grain, as one animal from one egg (for twin eggs are really two eggs). But in whatever kinds the sexes are distinguished, in these many animals may come from [729a1] one emission of semen, showing that the semen differs in its nature in plants and animals. A sign of this is that animals which can bear more than one young one at a time do so in consequence of only one coition. Hence, too, it is plain that the semen [5] does not come from the whole of the body; for neither would the different parts of the semen already be separated as soon as discharged from the same part, nor could they be separated in the uterus if they had once entered it all together; but what does happen is just what one would expect, since what the male contributes to [10] generation is the form and the efficient cause, while the female contributes the material. In fact, as in the coagulation of milk, the milk being the material, the fig-juice or rennet is that which contains the curdling principle, so acts the secretion of the male, being divided into the parts in the female. Why it is sometimes divided [15] into more or fewer parts, and sometimes not divided at all, will be the subject of another discussion. But because it does not differ in kind at any rate, several offspring are produced provided only that the divided semen is proportionate to the material, being neither too little to concoct it and fix it into form, nor too much so as to dry it up; and from this first formative semen, if it remains one, and is not divided, [20] only one young one comes into being.
That, then, the female does not contribute semen to generation, but does contribute something, and that this is the matter of the menstrual flow, or that which is analogous to it in bloodless animals, is clear from what has been said, and also from a general survey of the question. For there must needs be that which [25] generates and that from which it generates; even if these be one, still they must be distinct in form and their essence must be different; and in those animals that have these powers separate in two sexes the body and nature of the active and the passive sex must also differ. If, then, the male stands for the effective and active, and the [30] female for the passive, it follows that what the female would contribute to the semen of the male would not be semen but material for the semen to work upon. This is just what we find to be the case, for the menstrual blood has in its nature an affinity to the primitive matter.
21 · So much for the discussion of this question. At the same time the answer to the next question we have to investigate is clear from these considerations, [729b1] I mean how it is that the male contributes to generation and how it is that the semen from the male is the cause of the offspring. Does it exist in the body of the embryo as a part of it from the first, mingling with the material which comes from [5] the female? Or does the semen communicate nothing to the material body of the embryo but only to the power and movement in it? For this power is that which acts and makes, while that which is made and receives the form is the residue of the secretion in the female. Now the latter alternative appears to be the right one both a priori and in view of the facts. For, if we consider the question on general grounds, [10] we find that, whenever one thing is made from two of which one is active and the other passive, the active agent does not exist in that which is made; and, still more generally, the same applies when one thing moves and another is moved. But the female, as female, is passive, and the male, as male, is active, and the principle of the movement comes from him. Therefore, if we take the highest genera under [15] which they each fall, the one being active and motive and the other passive and moved, that one thing which is produced comes from them only in the sense in which a bed comes into being from the carpenter and the wood, or in which a ball comes into being from the wax and the form. It is plain then that it is not necessary that anything at all should come away from the male, and if anything does come away it does not follow that this gives rise to the embryo as being in the embryo, but only as that which imparts the motion and as the form; so the medical art cures the [20] patient.
This a priori argument is confirmed by the facts. For it is for this reason that some males which unite with the female do not, it appears, insert any part of themselves into the female, but on the contrary the female inserts a part of herself into the male; this occurs in some insects. For the effect produced by the semen in [25] the female is produced in the case of these insects by the heat and power in the male animal itself when the female inserts that part of herself which receives the residue. And therefore such animals remain united a long time, and when they are separated the young are produced quickly. For the union lasts until that which is analogous to [30] the semen has done its work, and when they separate the female produces the embryo quickly; for the young is imperfect inasmuch as all such creatures give birth to grubs.
What occurs in birds and oviparous fishes is the greatest proof that neither does the semen come from all parts of the male nor does he emit anything of such a [730a1] nature as to exist within that which is generated, as part of the material embryo, but that he only makes a living creature by the power which resides in the semen (as we said in the case of those insects whose females insert a part of themselves into the male). For if a hen-bird is in process of producing wind-eggs and is then trodden by the cock before the egg has begun to whiten and while it is all still yellow, then they [5] become fertile instead of being wind-eggs. And if while it is still yellow she be trodden by another cock, the whole brood of chicks turn out like the second cock. Hence some of those who are anxious to rear fine birds act thus; they change the [10] cocks for the first and second treading, not as if they thought that the semen is mingled with the egg or exists in it, or that it comes from all parts of the cock; for if it did it would have come from both cocks, so that the chick would have all its parts doubled. But it is by its force that the semen of the male gives a certain quality to the material and the nutriment in the female, for the second semen added to the [15] first can produce this effect by heat and concoction, as the egg acquires nutriment so long as it is growing.
The same thing happens in the generation of oviparous fishes. When the female has laid her eggs, the male sprinkles the milt over them, and those eggs are fertilized which it reaches, but not the others; this shows that the male does not [20] contribute anything to the quantity but only to the quality of the embryo.
From what has been said it is plain that the semen does not come from the whole of the body of the male in those animals which emit it, and that the [25] contribution of the female to the generative product is not the same as that of the male, but the male contributes the principle of movement and the female the material. This is why the female does not produce offspring by herself, for she needs a principle, i.e. something to begin the movement in the embryo and to define the form it is to assume. Yet in some animals, as birds, the nature of the female [30] unassisted can generate to a certain extent, for they do form something, only it is incomplete; I mean the so-called wind-eggs.
22 · For the same reason the development of the embryo takes place in the female; neither the male himself nor the female emits semen into the male, but the [730b1] female receives within herself the share contributed by both, because in the female is the material from which is made the resulting product. Not only must the mass of material exist there from which the embryo is formed in the first instance, but further material must constantly be added that it may increase in size. Therefore [5] the birth must take place in the female. For the carpenter must keep in close connexion with his timber and the potter with his clay, and generally all workmanship and the ultimate movement imparted to matter must be connected with the material concerned, as, for instance, architecture is in the buildings it makes.
From these considerations we may also gather how it is that the male [10] contributes to generation. The male does not emit semen at all in some animals, and where he does this is no part of the resulting embryo; just so no material part comes from the carpenter to the material, i.e. the wood in which he works, nor does any part of the carpenter’s art exist within what he makes, but the shape and the form [15] are imparted from him to the material by means of the motion he sets up. It is his hands that move his tools, his tools that move the material; it is his knowledge of his art, and his soul, in which is the form, that move his hands or any other part of him with a motion of some definite kind, a motion varying with the varying nature of the [20] object made. In like manner, in the male of those animals which emit semen, nature uses the semen as a tool and as possessing motion in actuality, just as tools are used in the products of any art, for in them lies in a certain sense the motion of the art. Such, then, is the way in which these males contribute to generation. But when the [25] male does not emit semen, but the female inserts some part of herself into the male, this is parallel to a case in which a man should carry the material to the workman. For by reason of weakness in such males nature is not able to do anything by any secondary means, but the movements imparted to the material are scarcely strong enough when nature itself watches over them. Thus here nature resembles a [30] modeller in clay rather than a carpenter, for she does not touch the work she is forming by means of tools, but with her own hands.
23 · In all animals which can move about, the sexes are separated, one individual being male and one female, though both are the same in species, as with [731a1] man and horse. But in plants these powers are mingled, female not being separated from male. That is why they generate out of themselves, and do not emit semen but produce an embryo, what is called the seed. Empedocles puts this well in the line: [5] ‘and thus the tall trees lay their eggs; first olives …’25 For as the egg is an embryo, a certain part of it giving rise to the animal and the rest being nutriment, so also from a part of the seed springs the growing plant, and the rest is nutriment for the shoot and the first root.
[10] In a certain sense the same thing happens also in those animals which have the sexes separate. For when there is need for them to generate the sexes are no longer separated any more than in plants, their nature desiring that they shall become one; and this is plain to view when they copulate and are united [that one animal is made out of both].26
It is the nature of those creatures which do not emit semen to remain united a [15] long time until the male element has formed the embryo, as with those insects which copulate. The others so remain only until the male has discharged from the parts of himself introduced something which will form the embryo in a longer time, as among the sanguinea. For the former remain paired some part of a day, while the semen forms the embryo in several days. And after emitting this they cease their [20] union.
And animals seem to be almost like divided plants, as though one should separate and divide them, when they bear seed, into the male and female existing in them.
In all this nature acts like an intelligent workman. For to the essence of plants [25] belongs no other function or business than the production of seed; since, then, this is brought about by the union of male and female, nature has mixed these and set them together in plants, so that the sexes are not divided in them. Plants, however, have been investigated elsewhere. But the function of the animal is not only to [30] generate (which is common to all living things), but they all of them participate also in a kind of knowledge, some more and some less, and some very little indeed. For they have sense-perception, and this is a kind of knowledge. (If we consider the value of this we find that it is of great importance compared with the class of lifeless objects, but of little compared with the use of the intellect. For against the latter the [731b1] mere participation in touch and taste seems to be practically nothing, but beside plants and stones it seems most excellent; for it would seem a treasure to gain even this kind of knowledge rather than to lie in a state of death and non-existence.) Now it is by sense-perception that an animal differs from those organisms which have only life. But since, if it is a living animal, it must also live; therefore, when it is [5] necessary for it to accomplish the function of that which has life, it unites and copulates, becoming like a plant, as we said before.
Testaceous animals, being intermediate between animals and plants, perform the function of neither class as belonging to both. As plants they have no sexes, and [10] one does not generate in another; as animals they do not bear fruit from themselves like plants; but they are formed and generated from a liquid and earthy concretion. However, we must speak later of the generation of these animals.27
1 · That the male and female are the principles of generation has been previously stated, as also what is their power and their essence. But why is it that [20] one thing becomes and is male, another female? It is the business of our discussion as it proceeds to try and point out that the sexes arise from necessity and the first efficient cause, from what sort of material they are formed. That they exist because it is better and on account of the final cause, takes us back to a principle still further remote.
Now some existing things are eternal and divine whilst others admit of both [25] existence and non-existence. But that which is noble and divine is always, in virtue of its own nature, the cause of the better in such things as admit of being better or worse, and what is not eternal does admit of existence and non-existence, and can partake in the better and the worse. And soul is better than body, and the living, having soul, is thereby better than the lifeless which has none, and being is better [30] than not being, living than not living. These, then, are the reasons of the generation of animals. For since it is impossible that such a class of things as animals should be of an eternal nature, therefore that which comes into being is eternal in the only way possible. Now it is impossible for it to be eternal as an individual—for the substance of the things that are is in the particular; and if it were such it would be eternal—but it is possible for it as a species. This is why there is always a class of [732a1] men and animals and plants. But since the male and female are the first principles of these, they will exist in those things that possess them for the sake of generation. Again, as the first efficient or moving cause, to which belong the definition and the form, is better and more divine in its nature than the material on which it works, it is [5] better that the superior principle should be separated from the inferior. Therefore, wherever it is possible and so far as it is possible, the male is separated from the female. For the first principle of the movement, whereby that which comes into being is male, is better and more divine, and the female is the matter. The male, [10] however, comes together and mingles with the female for the work of generation, because this is common to both.
A thing lives, then, in virtue of participating in the male and female principles; that is why even plants have some kind of life; but the class of animals exists in virtue of sense-perception. The sexes are divided in nearly all of these that can move [15] about, for the reasons already stated, and some of them, as said before, emit semen in copulation, others not. The reason for this is that the higher animals are more independent in their nature, so that they have greater size, and this cannot exist without vital heat; for the greater body requires more force to move it, and heat is a [20] motive force. Therefore, taking a general view, we may say that sanguinea are of greater size than bloodless animals, and those which move about than those which remain fixed. And these are just the animals which emit semen on account of their heat and size.
[25] So much for the cause of the existence of the two sexes. Some animals bring to perfection and produce into the world a creature like themselves, as all those which bring their young into the world alive; others produce something undeveloped which has not yet acquired its own form; in this latter division the sanguinea lay eggs, the bloodless animals give birth to a grub. The difference between egg and grub is this: [30] an egg is that from a part of which the young comes into being, the rest being nutriment for it; but the whole of a grub is developed into the whole of the young animal. Of the vivipara, which bring into the world an animal like themselves, some are internally viviparous (as men, horses, cattle, and of marine animals dolphins and the other cetacea); others first lay eggs within themselves, and only after this are externally viviparous (as the selachia). Among the ovipara some produce the [732b1] egg in a perfect condition (as birds and all oviparous quadrupeds and footless animals, e.g. lizards and tortoises and most snakes; for the eggs of all these do not increase when once laid). The eggs of others are imperfect; such are those of fishes, [5] crustaceans, and cephalopods, for their eggs increase after being produced.
All the vivipara and ovipara are sanguineous, and the sanguinea are either viviparous or oviparous, except those which are altogether infertile. Among bloodless animals the insects produce a grub, both those that are generated by [10] copulation and those that copulate themselves though not so generated. For there are some insects of this sort, which though they come into being by spontaneous generation are yet male and female; from their union something is produced, only it is imperfect; the reason of this has been previously stated.
These classes admit of much cross-division. Not all bipeds are viviparous (for [15] birds are oviparous), nor are they all oviparous (for man is viviparous), nor are all quadrupeds oviparous (for horses, cattle, and countless others are viviparous), nor are they all viviparous (for lizards, crocodiles, and many others lay eggs). Nor does the presence or absence of feet make the difference between them, for not only are [20] some footless animals viviparous, as vipers and the Selachia, while others are oviparous, as the other fishes and serpents, but also among those which have feet many are oviparous and many viviparous, as the quadrupeds above mentioned. And some which are bipeds, as man, and some which have no feet, as the whale and [25] dolphin, are internally viviparous. By this character then it is not possible to divide them, nor is any of the locomotive organs the cause of this difference, but it is those animals which are more perfect in their nature and participate in a purer element which are viviparous, for nothing is internally viviparous unless it receives and [30] breathes out air. But the more perfect are those which are hotter in their nature and have more moisture and are not earthy in their composition. And the measure of natural heat is the lung when it has blood in it, for generally those animals which have a lung are hotter than those which have not, and in the former class again those whose lung is not spongy nor solid nor containing only a little blood, but soft and full of blood. And as the animal is perfect but the egg and the grub are imperfect, so the [733a1] perfect is naturally produced from the perfect. If animals are hotter as shown by their possessing a lung but drier in their nature, or are colder but have more moisture, then they either lay a perfect egg or are viviparous after laying an egg [5] within themselves. For birds and scaly reptiles because of their heat produce a perfect egg, but because of their dryness it is only an egg; the Selachia have less heat than these but more moisture, so that they are intermediate, for they are both oviparous and viviparous within themselves, the former because they are cold, the [10] latter because of their moisture; for moisture is vivifying, whereas dryness is furthest removed from what has life. Since they have neither feathers nor scales such as either reptiles or other fishes have, all which are signs rather of a dry and earthy nature, the egg they produce is soft; for the earthy matter does not come to [15] the surface in their eggs any more than in themselves. This is why they lay eggs in themselves, for if the egg were laid externally it would be destroyed, having no protection.
Animals that are cold and rather dry than moist also lay eggs, but the egg is imperfect; at the same time, because they are of an earthy nature and the egg they produce is imperfect, therefore it has a hard integument that it may be preserved by [20] the protection of the shell-like covering. Hence fishes, because they are scaly, and 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.
[25] All insects produce a grub. Now all the insects are bloodless, which is why all creatures that produce a grub from themselves are so. But we cannot say simply that all bloodless animals produce a grub; for there is an overlap between the insects that produce a grub and those animals that lay their egg imperfect, as the scaly fishes, the crustacea, and the cephalopoda. For the eggs of these latter resemble a [30] grub, in that they increase after oviposition, and the grub 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. [733b1] 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 [5] 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 [10] 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 grub first; the grub after developing becomes egg-like (for the so-called chrysalis is [15] equivalent to an egg); then from this it is that a perfect animal comes into being, reaching the end of its development in the third 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 [20] 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.1
There is a considerable difficulty in understanding how the plant is formed out [25] of the seed or any animal out of the semen. Everything that comes into being or is made must be made out of something, be made by the agency of something, and 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 grub or an egg; others receive it [30] 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. [734a1]
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 anything that 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 [5] 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 [10] 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. 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 [15] 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 [20] 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 [25] 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 [30] 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 [734b1] 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 difficulty, for perhaps some one of the [5] 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 [10] B move C; that, in fact, the case should be the same as with the automatic puppets. For the parts of such puppets 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 puppets 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 [15] 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 [20] 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 soul in it; [25] it is only homonymously 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 [30] 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 [35] 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 [735a1] 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.
[5] 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 homonymously (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 [10] actuality, just as a sleeping geometer is further away than one awake and the latter than one actually 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 [15] 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 [20] 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. [25]
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 [30] 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, [35] 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 [735b1] 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 [5] are hot. If it is made of earth or a mixture of earth and water, it ought not to liquefy entirely.
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 [10] 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 [15] separated off by the heat and turning to air. And if oxide of lead is mixed with water or even with oil and stirred, 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 [20] 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 [25] (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 [30] is hot and will not freeze), but because the air is forced together and compressed the oil becomes thicker by the cold. 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 [35] 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.
[736a1] Semen, then, is a compound of breath and water, and the former is hot air; 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 [5] 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 breath, for it is also an [10] invariable rule that it is white, and Herodotus does not report the truth when he says that the semen of the Ethiopians is black, as if everything must needs be black in those who have a black skin, and that too when he saw their teeth were white. The reason of the whiteness of semen is that it is a foam, and foam is white, especially [15] that which is composed of the smallest parts, small in the sense that each bubble is invisible, which is what happens when water and oil are mixed and stirred, as said before. (Even the ancients seem to have noticed that semen is of the nature of foam; [20] at least it was from this they named the goddess who presides over union.)2
This then is the explanation of the problem proposed, and it is plain too that this is why semen does not freeze; for air will not freeze.
3 · The next question to raise and to answer is this. If, in the case of those [25] animals which emit semen into the female, that which enters makes no part of the resulting embryo, where is the material part of it diverted if (as we have seen) it acts by means of the power residing in it? It is not only necessary to decide whether what is forming in the female receives anything material, or not, from that which has entered her, but also concerning the soul in virtue of which an animal is so called [30] (and this is in virtue of the sensitive part of the soul)—does this exist originally in the semen and in the embryo or not, and if it does whence does it come? For nobody would put down the embryo as soulless or in every sense bereft of life (since both the semen and the embryo of an animal have every bit as much life as a plant), and it is productive up to a certain point. That then they possess the nutritive soul is plain [35] (and plain is it from the discussions elsewhere about soul why this soul must be acquired first). As they develop they also acquire the sensitive soul in virtue of [736b1] which an animal is an animal, . . .3 For e.g. an animal does not become at the same time an animal and a man or a horse or any other particular animal. For the end is developed last, and the peculiar character of the species is the end of the generation in each individual. Hence arises a question of the greatest difficulty, which we must strive to solve to the best of our ability and as far as possible. When and how and [5] whence is a share in reason acquired by those animals that participate in this principle? It is plain that the semen and the embryo, while not yet separate, must be assumed to have the nutritive soul potentially, but not actually, until (like those [10] embryos that are separated from the mother) it absorbs nourishment and performs the function of the nutritive soul. For at first all such embryos seem to live the life of a plant. And it is clear that we must be guided by this in speaking of the sensitive and the rational soul. For all three kinds of soul, not only the nutritive, must be possessed potentially before they are possessed in actuality. And it is necessary [15] either that they should all come into being in the embryo without existing previously outside it, or that they should all exist previously, or that some should so exist and others not. Again, it is necessary that they should either come into being in the material supplied by the female without entering with the semen of the male, or come from the male and be imparted to the material in the female. If the latter, then either all of them, or none, or some must come into being in the male from [20] outside.
Now that it is impossible for them all to pre-exist is clear from this consideration. Plainly those principles whose activity is bodily cannot exist without a body, e.g. walking cannot exist without feet. For the same reason also they cannot enter from outside. For neither is it possible for them to enter by themselves, being [25] inseparable from a body, nor yet in a body, for the semen is only a residue of the nutriment in process of change. It remains, then, for the reason alone so to enter and alone to be divine, for no bodily activity has any connexion with the activity of reason.
Now it is true that the faculty of all kinds of soul seems to have a connexion with a matter different from and more divine than the so-called elements; but as one [30] soul differs from another in honour and dishonour, so differs also the nature of the corresponding matter. All have in their semen that which causes it to be productive; I mean what is called vital heat. This is not fire nor any such force, but it is the [35] breath included in the semen and the foam-like, and the natural principle in the breath, being analogous to the element of the stars. Hence, whereas fire generates [737a1] no animal and we do not find any living thing forming in either solids or liquids under the influence of fire, the heat of the sun and that of animals does generate them. Not only is this true of the heat that works through the semen, but whatever other residue of the animal nature there may be, this also has still a vital principle in [5] it. From such considerations it is clear that the heat in animals neither is fire nor derives its origin from fire.
Let us return to the material of the semen, in and with which is emitted4 the principle of soul. Of this principle there are two kinds; the one is not connected with matter, and belongs to those animals in which is included something divine (to wit, [10] what is called the reason), while the other is inseparable from matter. This material of the semen dissolves and evaporates because it has a liquid and watery nature. Therefore we ought not to expect it always to come out again from the female or to form any part of the embryo that has taken shape from it; the case resembles that of [15] the fig-juice which curdles milk, for this too changes without becoming any part of the curdling masses.
It has been settled, then, in what sense the embryo and the semen have soul, and in what sense they have not; they have it potentially but not actually.
Now semen is a residue and is moved with the same movement as that in virtue [20] of which the body increases (this increase being due to subdivision of the nutriment in its last stage). When it has entered the uterus it puts into form the corresponding residue of the female and moves it with the same movement wherewith it is moved itself. For the female’s contribution also is a residue, and has all the parts in it potentially though none of them actually; it has in it potentially even those parts [25] which differentiate the female from the male, for just as the young of mutilated parents are sometimes born mutilated and sometimes not, so also the young born of a female are sometimes female and sometimes male instead. For the female is, as it were, a mutilated male, and the menstrual fluids are semen, only not pure; for there is only one thing they have not in them, the principle of soul. For this reason, [30] whenever a wind-egg is produced by any animal, the egg so forming has in it the parts of both sexes potentially, but has not the principle in question, so that it does not develop into a living creature, for this is introduced by the semen of the male. When such a principle has been imparted to the residue of the female it becomes an embryo.
[35] Liquid by corporeal substances become surrounded by a solid layer like that which forms on boiled foods when cooling. All bodies are held together by the [737b1] glutinous; this quality, as the embryo develops and increases in size, is acquired by the sinewy substance, which holds together the parts of animals, being actual sinew in some and its analogue in others. To the same class belong also skin, blood-vessels, [5] membranes and the like, for these differ in being more or less glutinous and generally in excess and deficiency.5
4 · In those animals whose nature is comparatively imperfect, when a perfect embryo (which, however, is not yet a perfect animal) has been formed, it is cast out [10] from the mother, for reasons previously stated. An embryo is then complete when it is either male or female, in the case of those animals who possess this distinction; for some (i.e. all those which are not themselves produced from a male or female parent nor from a union of the two) produce an offspring which is neither male nor female. Of the generation of these we shall speak later. [15]
The perfect animals, those internally viviparous, keep the developing embryo within themselves and in close connexion until they give birth to a complete animal and bring it to light.
A third class is externally viviparous but first internally oviparous; they develop the egg into a perfect condition, and then in some cases the egg is set free as with creatures externally oviparous, and the animal is produced from the egg within [20] the mother’s body; in other cases, when the nutriment from the egg is consumed, development is completed by connexion with the uterus, and therefore the egg is not set free from the uterus. This character marks the Selachian fish, of which we must speak later by themselves.6
Here we must make our first start from the first class; these are the perfect or [25] viviparous animals, and of these the first is man. Now the secretion of the semen takes place in all of them just as does that of any other residual matter. For each is conveyed to its proper place without any force from the breath or compulsion of any [30] other cause, as some assert, saying that the generative parts attract the semen like cupping-glasses, aided by the force of the breath, as if it were possible for either this residue or that of the solid and liquid nutriment to go anywhere else than they do without the exertion of such a force. Their reason is that the discharge of both is attended by holding the breath, but this is a common feature of all cases when it is necessary to move anything, because strength arises through holding the breath. [738a1] For even without this force the residues are discharged in sleep if the parts concerned are full of them and are relaxed. One might as well say that it is by the breath that the seeds of plants are always segregated to the places where they are [5] wont to bear fruit. No, the real cause, as has been stated already, is that there are special parts for receiving all the residues, alike the useless (as the residues of the liquid and solid7 nutriment), and the blood, which has the so-called bloodvessels.
To consider now the region of the uterus in the female—the two blood-vessels, the great vessel and the aorta, divide higher up, and many fine vessels from them [10] terminate in the uterus. These become over-filled from the nourishment they convey, nor is the female nature able to concoct it, because it is colder than man’s; so the blood is excreted through very fine vessels into the uterus, these being unable on account of their narrowness to receive the excessive quantity, and the result is a sort [15] of haemorrhage. The period is not accurately defined in women, but tends to return during the waning of the moon. This we should expect, for the bodies of animals are colder when the environment happens to become so, and the time of change from one month to another is cold because of the absence of the moon, whence also it [20] results that this time is stormier than the middle of the month. When then the residue of the nourishment has changed into blood, the menstrual discharges tend to occur at the above-mentioned period, but when it is not concocted a little matter at a [25] time is always coming away, and this is why ‘whites’ appear in females while still small, in fact mere children. If both these discharges of the residues are moderate, the body remains in good health, for they act as a purification of the residues which are the causes of a morbid state of body; if they do not occur at all or if they are [30] excessive, they are injurious, either causing illness or pulling down the patient; hence whites, if continuous and excessive, prevent girls from growing. This residue then is necessarily discharged by females for the reasons given; for, the female nature being unable to concoct the nourishment thoroughly, there must not only be [35] left a residue of the useless nutriment, but also there must be a residue of the blood in the blood-vessels, and this filling the channels of the finest vessels must overflow. [738b1] Then nature, aiming at the best and the end, uses it up in this place for the sake of generation, that another creature may come into being of the same kind as the former was going to be, for the menstrual blood is already potentially such as the body from which it is discharged.
In all females, then, there must necessarily be such a residue, more indeed in [5] those that have blood and of these most of all in man, but in the others also some matter must be collected in the uterine region. The reason why there is more in those that have blood and most in man has been already given; but why, if all [10] females have such a residue, have not all males one to correspond? For some of them do not emit semen but, just as those which do emit it fashion by the movement in the semen the mass forming from the material supplied by the female, so do the animals in question bring the same to pass and exert the same formative power by [15] the movement within themselves in that part from which the semen is secreted. This is the region about the diaphragm in all those animals which have one, for the heart or its analogue is the first principle of a natural body, while the lower part is a mere addition for the sake of it. Now the reason why it is not all males that have a generative residue, while all females do, is that the animal is a body with soul; the [20] female always provides the material, the male that which fashions it, for this is the power that we say they each possess, and this is what it is for them to be male and female. Thus while it is necessary for the female to provide a body and a material mass, it is not necessary for the male, because it is not within what is produced that [25] the tools or the maker must exist. While the body is from the female, it is the soul that is from the male, for the soul is the substance of a particular body. For this reason if animals of a different kind are crossed (and this is possible when the periods of gestation are equal and conception takes place nearly at the same season and there is no great difference in the size of the animals), the first cross has a [30] common resemblance to both parents, as the hybrid between fox and dog, partridge and domestic fowl, but as time goes on and one generation springs from another, the final result resembles the female in form, just as foreign seeds produce plants varying in accordance with the country in which they are sown. For it is the soil that [35] gives to the seeds the material and the body of the plant. And hence the part of the female which receives the semen is not a mere passage, but the uterus has a [739a1] considerable width, whereas the males that emit semen have only passages for this purpose, and these are bloodless.
Each of the residues becomes such at the moment when it is in its proper place; before that there is nothing of the sort unless with much violence and contrary to nature.
We have thus stated the reason for which the generative residues are formed in [5] animals. But when the semen from the male (in those animals which emit semen) has entered, it puts into form the purest part of the female residue (for the greater part of the menstrual flow is useless, being fluid, as is the most fluid part of the male secretion, i.e. in a single emission, the earlier discharge being in most cases apt to be [10] infertile rather than the later, having less vital heat through want of concoction, whereas that which is concocted is thick and of a more material nature).
If there is no external discharge, either in women or other animals, on account of there not being much useless residue in the secretion, then the quantity forming [15] within the female altogether is as much as what is retained within those animals which have an external discharge; this is put into form by the power of the male residing in the semen secreted by him, or, as is clearly seen to happen in some insects, by the part in the female analogous to the uterus being inserted into the male.
It has been previously stated that the discharge accompanying sexual pleasure [20] in the female contributes nothing to the embryo. The chief argument for the opposite view is that what are called wet dreams occur by night with women as with men; but this is no proof, for the same thing happens to young men also who do not [25] yet emit semen, and to those who do emit semen but whose semen is infertile.
It is impossible to conceive without the emission of the male in union and without the residue of the female, whether it be discharged externally or whether there is only enough within the body. Women conceive, however, without experiencing the pleasure usual in such intercourse, if the part chance to be in heat [30] and the uterus to have descended. But generally speaking the opposite is the case, because the mouth of the uterus is not closed when the discharge takes place which is usually accompanied by pleasure in women as well as men, and when this is so there is a readier way from the semen of the male to be drawn into the uterus. [35]
The actual discharge does not take place within the uterus as some think, the mouth being too narrow, but it is in the region in front of this, where the female discharges the moisture found in some cases, that the male emits the semen. [739b1] Sometimes it remains in this place; at other times, if the uterus chance to be conveniently placed and hot on account of the purgation, it draws it within itself. A proof of this is that pessaries, though wet when applied, are removed dry. Moreover, [5] in all those animals which have the uterus near the hypozoma, as birds and viviparous fishes, it is impossible that the semen should be so discharged as to enter it; it must be drawn into it. This region, on account of the heat which is in it, attracts the semen. The discharge and collection of the menstrual blood also excite heat in [10] this part. Hence it acts like cone-shaped vessels which, when they have been washed out with hot water, their mouth being turned downwards, draw water into themselves. And this is the way things are drawn up, but some say that nothing of the kind happens with the organic parts concerned in copulation. Precisely the [15] opposite is the case of those who say the woman emits semen as well as the man, for if she emits it outside the uterus this must then draw it back again into itself if it is to be mixed with the semen of the male. But this is a superfluous proceeding, and nature does nothing superfluous.
[20] When the material secreted by the female in the uterus has been fixed by the semen of the male (this acts in the same way as rennet acts upon milk, for rennet is a kind of milk containing vital heat, which brings into one mass and fixes the similar material, and the relation of the semen to the menstrual blood in the same, milk and [25] the menstrual blood being of the same nature)—when, I say, the more solid part comes together, the liquid is separated off from it, and as the earthy parts solidify membranes form all round it; this is both a necessary result and for the sake of something, the former because the surface of a mass must solidify on heating as well as on cooling, the latter because the foetus must not be in a liquid but be separated [30] from it. Some of these are called membranes and others choria, the difference being one of more or less, and they exist in ovipara and vivipara alike.
When the embryo is once formed, it acts like the seeds of plants. For seeds also [35] contain the first principle of growth in themselves, and when this (which previously exists in them only potentially) has been differentiated, the shoot and the root are [740a1] sent off from it, and it is by the root the plant gets nourishment; for it needs growth. So also in the embryo all the parts exist potentially in a way, but the first principle is furthest on the road to realization. Therefore the heart is first differentiated in [5] actuality. This is clear not only to the senses (for it is so) but also on theoretical grounds. For whenever the young animal has been separated from both parents it must be able to manage itself, like a son who has set up house away from his father. Hence it must have a first principle from which comes the ordering of the body at a later stage also, for if it is to come in from outside at a later period to dwell in it, not [10] only may the question be asked at what time it is to do so, but also we may object that, when each of the parts is separating from the rest, it is necessary that this principle should exist first from which comes growth and movement to the other parts. (That is why all who say, as did Democritus, that the external parts of animals are first differentiated and the internal later, are much mistaken; it is as if [15] they were talking of animals of stone or wood. For such as these have no principle of growth at all, but all animals have, and have it within themselves.) Therefore it is that the heart appears first distinctly marked off in all the sanguinea, for this is the first principle of both homogeneous and heterogeneous parts, since from the [20] moment that the animal or organism needs nourishment, from that moment does this deserve to be called its principle. For that which exists grows, and the nutriment, in its final stage, of an animal is the blood or its analogue, and of this the blood-vessels are the receptacle, and that is why the heart is the principle of these also. (This is clear from the Histories8 and the Anatomies.)
Since the embryo is already potentially an animal but an imperfect one, it must [25] obtain its nourishment from elsewhere; accordingly it makes use of the uterus and the mother, as a plant does of the earth, to get nourishment, until it is perfected to the point of being now an animal potentially locomotive. So nature has first designed the two blood-vessels from the heart, and from these smaller vessels branch off to the uterus, forming what is called the umbilicus. For the umbilicus is a [30] blood-vessel, consisting of one or more vessels in different animals. Round these is a skin-like integument, because the weakness of the vessels needs protection and shelter. The vessels join on to the uterus like the roots of plants, and through them the embryo receives its nourishment. This is why the animal remains in the uterus, [35] not, as Democritus says, that the parts of the embryo may be moulded in conformity with those of the mother. This is plain in the ovipara, for they have their parts [740b1] differentiated in the egg after separation from the matrix.
Here a difficulty may be raised. If the blood is the nourishment, and if the heart, which first comes into being, already contains blood, and the nourishment comes from outside, whence did the first nourishment enter? Perhaps it is not true that all of it comes from outside. Just as in the seeds of plants there is something of [5] this nature, the substance which at first appears milky, so also in the material of the animal embryo the superfluous matter of which it is formed is its nourishment from the first.
The embryo, then, grows by means of the umbilicus in the same way as a plant by its root, or as animals themselves, when separated, from the nutriment within [10] themselves—of this we must speak later at the time appropriate for discussing them. But the parts are not differentiated, as some suppose, because like is naturally carried to like. Besides many other difficulties involved in this theory, it results from [15] it that the homogeneous parts ought to come into being each one separate from the rest, as bones and sinews by themselves, and flesh by itself, if one should accept this cause. The real cause why each of them comes into being is that the residue of the female is potentially such as the animal is naturally, and all the parts are potentially [20] present in it, but none actually. It is also because when the active and the passive come in contact with each other in that way in which the one is active and the other passive (I mean in the right manner, in the right place, and at the right time), straight-way the one acts and the other is acted upon. The female, then, provides matter, the male the principle of motion. And as the products of art are made by [25] means of the tools of the artist, or to put it more truly by means of their movement, and this is the activity of the art, and the art is the form of what is made in something else, so is it with the power of the nutritive soul. As later on in the case of mature animals and plants this soul causes growth from the nutriment, using heat [30] and cold as its tools (for in these is the movement of the soul and each comes into being in accordance with a certain formula), so also from the beginning does it form the product of nature. For the material by which this latter grows is the same as that from which it is constituted at first; consequently also the power which acts upon it [35] is identical with that at the beginning (but greater than it); thus if it is the nutritive soul, it is also the generative soul, and this is the nature of every organism, existing [741a1] in all animals and plants. But the other parts of the soul exist in some living things and not in others. In plants, then, the female is not separated from the male, but in those animals in which it is separated the female needs the male besides. [5]
5 · And yet the question may be raised why it is that, if indeed the female possesses the same soul and if it is the residue of the female which is the material of the embryo, she needs the male besides instead of generating entirely from herself. The reason is that the animal differs from the plant by having sense-perception; if the sensitive soul is not present, either actually or potentially, and either with or [10] without qualification, it is impossible for face, hand, flesh, or any other part to exist; it will be no better than a corpse or part of a corpse. Thus if it is the male that has the power of making the sensitive soul, then where the sexes are separated it is [15] impossible for the female to generate an animal from itself alone, for the process in question was what being male is. Certainly that there is a good deal in the difficulty stated is plain in the case of the birds that lay wind-eggs, showing that the female can generate up to a certain point unaided. But this still involves a difficulty; in what way are we to say that their eggs live? It is neither possible that they should [20] live in the same way as fertile eggs (for then they would produce a chick actually alive), nor yet can they be called eggs only in the sense in which an egg of wood or stone is so called, for the fact that these eggs go bad shows that they previously participate in some way in life. It is plain, then, that they have some soul potentially. What sort of soul will this be? It must be the lowest surely, and this is the nutritive, [25] for this exists in all animals and plants alike. Why then does it not perfect the parts and the animal? Because they must have a sensitive soul, for the parts of animals are not like those of a plant. And so the female animal needs the help of the male, for in these animals we are speaking of the male is separate. This is exactly what we [30] find, for the wind-eggs become fertile if the male tread the female in a certain space of time. About the cause of these things, however, we shall enter into detail later.
If there is any kind of animal which is female and has no male separate from it, it is possible that this may generate a young one from itself. No instance of this worthy of credit has been observed up to the present at any rate, but one case in the [35] class of fishes makes us hesitate. No male of the so-called erythrinus has ever yet been seen, but females, and specimens full of roe, have been seen. Of this, however, we have as yet no proof worthy of credit. Again, some members of the class of fishes [741b1] are neither male nor female, as eels and a kind of mullet found in stagnant waters. But whenever the sexes are separate the female cannot generate perfectly by herself alone, for then the male would exist in vain, and nature makes nothing in vain. [5] Hence in such animals the male always perfects the work of generation, for he imparts the sensitive soul, either by means of the semen or by himself. Now the parts of the embryo already exist potentially in the material, and so when once the principle of movement has been imparted to them they develop in a chain one after another, as in the case of the automatic puppets. When some of the natural [10] philosophers say that like is brought to like, this must be understood, not in the sense that the parts are moved as changing place, but that they stay where they are and the movement is a change of quality (such as softness, hardness, colour, and the other differences of the homogeneous parts); thus they become in actuality what [15] they previously were in potentiality. And what comes into being first is the first principle; this is the heart in the sanguinea and its analogue in the rest, as has been often said already. This is plain not only to the senses (that it is first to come into being), but also in view of its end; for life fails in the heart last of all, and it happens in all cases that what comes in to being last fails first, and the first last, nature [20] running a double course, so to say, and turning back to the point from whence she started. For the process of becoming is from the non-existent to the existent, and that of perishing is back again from the existent to the non-existent.
6 · After this, as said already, the internal parts come into being before the [25] external. The greater become visible before the less, even if some of them do not come into being before them. First the parts above the hypozoma are differentiated and are superior in size; the part below is both smaller and less differentiated. This happens in all animals in which exists the distinction of upper and lower, except in [30] the insects; the growth of those that produce a grub is towards the upper part, for this is smaller in the beginning. The cephalopoda are the only locomotive animals in which the distinction of upper and lower does not exist. What has been said applies to plants also, that the upper portion is earlier in development than the lower, for the [35] roots push out from the seed before the shoots.
The agency by which the parts of animals are differentiated is air, not however that of the mother nor yet of the embryo itself, as some of the physicists say. This is manifest in birds, fishes, and insects. For some of these are separated from the [742a1] mother and produced from an egg, within which the differentiation takes place; other animals do not breathe at all, but are produced as a grub or an egg; those which do breathe and whose parts are differentiated within the mother’s uterus yet [5] do not breathe until the lung is perfected, and the lung and the preceding parts are differentiated before they breathe. Moreover, all polydactylous quadrupeds, as dog, lion, wolf, fox, jackal, produce their young blind, and the eyelids do not separate till after birth. Manifestly the same holds also in all the other parts; as the qualitative, [10] so also the quantitative differentia comes into being, pre-existing potentially but being actualized later by the same causes by which the qualitative distinction is produced, and so the eyelids become two instead of one. Of course air must be present, because heat and moisture are present, the former acting and the latter [15] being acted upon.
Some of the ancient nature-philosophers made an attempt to state which part comes into being after which, but were not sufficiently acquainted with the facts. It is with the parts as with other 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 [20] of development, the former is prior in essence. Again, that which exists for the sake of the end admits of division into two classes, first the origin of the movement, and then that which is used by the end; I mean, for instance, that which can generate, and 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 [25] 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, [30] 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 [35] 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 [742b1] 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 [5] 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 [10] 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 [15] 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. [20] Thus Democritus of Abdera says that there is no beginning of the infinite;9 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 [25] 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 [30] seek a beginning 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 [35] 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 [743a1] anatomical diagrams which are represented on the walls, 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 [5] 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 [10] 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, [15] 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 [20] 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 out of anything whatever; the carpenter would not make a box except out [25] of wood, nor will a box be made out of the wood without the carpenter. The heat exists in the seminal residue, 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 [30] 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 is 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 is the [35] 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 [743b1] 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 [5] 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 [10] reason the covering of the bloodless animals is testaceous or crustaceous, in the sanguinea 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 [15] 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 [20] 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.
[25] 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 [30] 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 [35] 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 [744a1] 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 breath; these passages end at the small blood-vessels about the brain which [5] 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 [10] 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 [15] 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—and so does the size of the eyes. The head is very large at first, on account of the brain, and the eyes [20] 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 anterior fontanelle is the last of the bones to be formed; even after birth this bone is still soft in children. The cause of this [25] 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 babies [30] 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 [35] 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 [744b1] 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 [5] such is the nature of the eyelids, for if the head is affected by the slightest 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 [10] developed.
Each of the other parts is formed out of the nutriment, the noblest and those 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, [15] 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 [20] intellect acts thus from outside 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 [25] 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 residue. As the animal grows the bones also grow from the natural nourishment, being the same as that of the sovereign parts,4 but of this they only [30] 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 brings into being both the whole and the parts; the latter is concerned with growth, being that which causes quantitative increase. But these must be distinguished more fully [35] 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 [745a1] 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 [5] 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 [10] 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 [15] 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 [20] as the bones, and are formed out of the bones, but nails, hair, horns, and the like are formed out of the skin, and that is why they change in colour along with it, for they become white, black, and all sorts of colours according to that of the skin. But the teeth do nothing of the sort, for they are made out of the bones in all animals that [25] have both bones and teeth. Of all the bones they alone go on growing through life, as is plain with the teeth which grow out of the straight line so as no longer to touch each other. The reason for their growth, as a final cause, is their function, for they [30] would soon be worn down if there were not some means of saving them; even as it is they are altogether worn down in old age in some animals which eat much and have not large teeth, for they are worn away faster than they grow. And so nature has contrived well to meet the case in this also, for she causes the failure of the teeth to synchronize with old age and death. If life lasted for a thousand or ten thousand years the original teeth would have had to be very large indeed, and many sets of them would have had to have been produced, for even if they had grown [745b1] continuously they would still have been worn smooth and become useless for their work. The final cause of their growth has been now stated, but besides this as a matter of fact the nature of the teeth is not the same as that of the other bones. The latter all come into being in the first formation of the embryo and none of them [5] later, but the teeth do so later. Therefore it is possible for them to grow again after the first set falls out, for though they touch the bones they are not naturally connected to them. They are formed, however, out of the nutriment distributed to the bones, and so have the same nature, even when the bones have their own number complete.
[10] Other animals are born in possession of teeth or their analogue (unless in cases contrary to nature), because when they are set free from the parent they are more perfect than man; but man (also unless in cases contrary to nature) is born without them.
The reason will be stated later why some teeth are formed and fall out but [15] others do not fall out.
It is because such parts are formed from a residue that man is the most naked in body of all animals and has the smallest nails in proportion to his size; he has the least amount of earthy residue, but what is not concocted is the residue, and the earthy part in the bodies of all animals is the least concocted. We have now stated [20] how each of the parts is formed and what is the cause of their generation.
7 · In viviparous animals, as said before, the embryo gets its growth through the umbilical cord. For since the nutritive power of the soul, as well as the others, is present in animals, it straightway sends off this cord like a root to the uterus. The [25] cord consists of blood-vessels in a sheath, more numerous in the larger animals as cattle and the like, one in the smallest, two in those of intermediate size. Through this cord the embryo receives its nourishment in the form of blood, for the uterus is the termination of many blood-vessels. All non-ambidentates and all ambidentates [30] whose uterus has not one great blood-vessel running through it but many close together instead—all these have in the uterus the so-called cotyledons with which the umbilical cord connects and is closely united; for the vessels which pass through the cord run backwards and forwards and split up all over the uterus; where they terminate, there are found the cotyledons. Their convexity is turned towards the uterus, the concavity towards the embryo. Between uterus and embryo are the chorion and the membranes. As the embryo grows and approaches perfection the cotyledons become smaller and finally disappear when it is perfected. For nature [746a1] sends the sanguineous nutriment for the embryo into this part of the uterus as it were into breasts, and because the cotyledons are gradually aggregated from many into a few the body of the cotyledon becomes like an eruption or inflammation. So [5] long as the embryo is comparatively small, being unable to receive much nutriment, they are plain and large, but when it has increased in size they shrink.
But most of the animals which are stunted and ambidentate have no cotyledons in the uterus, but the umbilical cord runs to meet one blood-vessel, which [10] is large and extends throughout the uterus. Of such animals some produce one young at a time, some more than one, but the same description applies to both these classes. (This should be studied with the aid of the examples drawn in the Anatomies and the Histories.) For the young are attached each to its umbilical [15] cord, and this to the blood-vessel; they are arranged next to one another along the stream of the blood-vessel as along a canal; and each embryo is enclosed in its membranes and chorion.
Those who say that children are nourished in the uterus by sucking some lump [20] of flesh or other are mistaken. If so, the same would have been the case with other animals, but as it is we do not find this (and this can easily be observed by dissection). Secondly, all embryos alike, whether of creatures that fly or swim or walk, are surrounded by fine membranes separating them from the uterus and from the fluids which are formed in it; but neither in these themselves is there anything of [25] the kind, nor is it possible for the embryo to take nourishment by means of any of them. And it is plain that all creatures developed in eggs grow when separated from the uterus. Thus those, e.g. Democritus, who put forward this view are mistaken.
Copulation takes place naturally between animals of the same kind. However, [30] those also unite whose nature is near akin and whose form is not very different, if their size is much the same and if the periods of gestation are equal. In other animals such cases are rare, but they occur with dogs and foxes and wolves and jackals; the Indian dogs also spring from the union of a dog with some wild dog-like [746b1] animal. A similar thing has been seen to take place in those birds that are salacious, as partridges and hens. Among birds of prey hawks of different form are thought to unite, and the same applies to some other birds. Nothing worth mentioning has been [5] observed in the inhabitants of the sea, but the so-called ‘rhinobates’ especially is thought to spring from the union of the rhinè and the batus. And the proverb about Libya, that Libya is always producing something new, is said to have originated from animals of different species uniting with one another in that country, for it is [10] said that because of the want of water all meet at the few places where springs are to be found, and that even different kinds unite in consequence.
Of the animals that arise from such union all except mules are found to copulate again with each other and to be able to produce young of both sexes, but [15] mules alone are sterile, for they do not generate by union with one another or with other animals. The problem why any individual, whether male or female, is sterile is a general one, for some men and women are sterile, and so are other animals in their [20] several kinds, as horses and sheep. But this kind, that of mules, is universally so. The causes of sterility in other animals are several. Both men and women are sterile from birth when the parts useful for union are imperfect, so that men never grow a beard but remain like eunuchs, and women do not attain puberty; the same thing [25] may befall others as their years advance, sometimes on account of the body being too well nourished (for in men who are in too good condition and women who are too fat the seminal residue is taken up into the body, and the former have no semen, the latter no menstrual discharge); at other times by reason of sickness men emit the [30] semen in a cold and liquid state, and the discharges of women are bad and full of morbid residues. Often, too, in both sexes this state is caused by deformities in the parts and regions contributory to copulation. Some such cases are curable, others incurable, but the subjects especially remain sterile if anything of the sort has happened in the first formation of the parts in the embryo, for then are produced [747a1] women of a masculine and men of a feminine appearance, and in the former the menstrual discharge does not occur, in the latter the semen is thin and cold. Hence it is with good reason that the semen of men is tested in water to find out if it is infertile, for that which is thin and cold is quickly spread out on the surface, but the [5] fertile sinks to the bottom, for that which is well concocted is hot indeed, but that which is firm and thick is well concocted. They test women by pessaries to see if the smells permeate from below upwards to the breath from the mouth, and by colours [10] smeared upon the eyes to see if they colour the saliva. If these results do not follow it is a sign that the passages of the body, through which the residue is secreted, are clogged and closed. For the region about the eyes is, of all the head, the most [15] seminal part; a proof of this is that it alone is visibly changed in sexual intercourse, and those who indulge too much in this are seen to have their eyes sunken in. The reason is that the nature of the semen is similar to that of the brain, for the material of it is watery (the heat being acquired later). And the seminal discharges are from the region of the diaphragm, for the first principle of nature is there, so that the [20] movements from the pudenda are communicated to the chest, and the smells from the chest are all perceived through the respiration.
8 · In men, then, and in other kinds, as said before, such deficiency occurs sporadically, but the whole of the mule kind is sterile. The reason has not been [25] rightly given by Empedocles and Democritus, of whom the former expresses himself obscurely, the latter more intelligibly. For they offer a single demonstration for all animals which unite against their affinities. Democritus says that the genital passages of mules are spoilt in the mother’s uterus because the animals from the [30] first are not produced from parents of the same kind. But we find that though this is so with other animals they are none the less able to generate; yet, if this were the reason for their sterility, all others that unite in this manner ought to be sterile. Empedocles assigns as his reason that the mixture of the seeds becomes dense, each of the two seminal fluids out of which it is made being soft, for the hollows in each [747b1] fit into the densities of the other, and in such cases a hard substance is formed out of soft ones, like bronze mingled with tin. Now he does not give the correct reason in the case of bronze and tin—we have spoken of them in the Problems—nor, to take [5] general ground, does he take his principles from the intelligible. For how do the hollows and solids fit into one another to make the mixing, e.g. in the case of wine and water? This saying is quite beyond us; for how we are to understand the hollows of the wine and water is too far beyond our perception. Again, when, as a matter of [10] fact, horse is born of horse, ass of ass, and mule of horse and ass (it does not matter which is the male and which the female), why in the last case does there result something so dense that the offspring is sterile, whereas the offspring of male and female horse, male and female ass, is not sterile? And yet the generative fluid of the [15] male and female horse is soft. But both sexes of the horse cross with both sexes of the ass, and the offspring of both crosses are sterile, according to Empedocles, because from both is produced something dense, the seeds being soft. If so, the offspring of stallion and mare ought also to be sterile. If one of them alone united [20] with the ass, it might be said that the cause of the mule’s being unable to generate was the unlikeness of that one to the generative fluid of the ass; but, as it is, whatever be the character of that generative fluid with which it unites in the ass, such it is also in the animal of its own kind. Then, again, the demonstration is intended to apply to both male and female mules alike, but the male alone does generate at seven years of age, it is said, whereas the female is entirely sterile, and [25] even she is so only because she does not complete the development of the embryo, for a female mule has been known to conceive.
Perhaps an abstract proof might appear to be more plausible than those already given; I call it abstract because the more general it is the further is it removed from the appropriate principles. It runs somewhat as follows. From male [30] and female of the same species there are born in course of nature male and female of the same species as the parents, e.g. male and female puppies from male and female dog. From parents of different species is born a young one different in species; thus if a dog is different from a lion, the offspring of male dog and lioness or of lion and [748a1] bitch will be different from both parents. If this is so, then since mules are produced of both sexes and are not different in species from one another, and a mule is born of horse and ass and these are different in species from mules, it is impossible that anything should be produced from mules. For another kind cannot be, because the [5] product of male and female of the same species is also of the same species, and a mule cannot be, because that is the product of horse and ass which are different in form, and it was laid down that from parents different in form is born a different animal. Now this theory is too general and empty. For all theories not based on the appropriate principles are empty; they only appear to be connected with the facts [10] without being so really. As geometrical arguments must start from geometrical principles, so it is with the others; that which is empty may seem to be something, but is really nothing. Now the basis of this particular theory is not true, for many animals produced from different species are fertile, as was said before. So we must not inquire into questions of natural science in this fashion any more than any other questions; we shall be more likely to find the reason by considering the facts [15] peculiar to the two kinds concerned, horse and ass. In the first place, each of them, if mated with its own kind, bears only one young one; secondly, the females are not always able to conceive from the male (that is why breeders put the horse to the [20] mare again at intervals). Indeed, the mare is deficient in menstrual flow, discharging less than any other quadruped, and the she-ass does not admit the impregnation, but ejects the semen with her urine, which is why men follow flogging her after intercourse. Again the ass is an animal of cold nature, and so is not wont to [25] be produced in wintry regions because it cannot bear cold, as in Scythia and the neighbouring country and among the Celts beyond Iberia, for this country also is cold. For this cause they do not put the jackasses to the females at the equinox, as they do with horses, but about the summer solstice, in order that the ass-foals may be born in a warm season, for the mothers bear at the same season as that in which [30] they are impregnated, the period of gestation in both horse and ass being one year. The animal, then, being, as has been said, of such a cold nature, its semen also must be cold. A proof of this is that if a horse mount a female already impregnated by an ass he does not destroy the impregnation of the ass, but if the ass be the second to mount her he does destroy that of the horse because of the coldness of his own [748b1] semen. When, therefore, they unite with each other, the generative elements are preserved by the heat of the one of them, that contributed by the horse being the hotter; for in the ass both the semen and the material are cold, and those of the horse are hotter. Now when either hot is added to cold or cold to hot so as to mix, the [5] result is that the embryo itself arising from these is preserved and thus these animals are fertile when crossed with one another, but the animal produced by them is no longer fertile but unable to produce perfect offspring.
And in general each of these animals naturally tends towards sterility. The ass has all the disadvantages already mentioned, and if it should not begin to generate [10] after the first shedding of teeth, it no longer generates at all; so near is the constitution of the ass to being sterile. The horse is much the same; it tends naturally towards sterility, and to make it entirely so it is only necessary that its generative secretion should become colder; now this is what happens to it when mixed with the corresponding secretion of the ass. The ass in like manner comes [15] very near generating a sterile animal when mated with its own species. Thus when the difficulty of a cross contrary to nature is added to the difficulty they have in producing a single young one when united with their own species, the result of the cross, being still more sterile and contrary to nature, will need nothing further to make it sterile, but will be so of necessity.
We find also that the bodies of mules grow large because the matter which is [20] secreted in other animals to form the menstrual flow is diverted to growth. But since the period of gestation in such animals is a year, the mule must not only conceive but must also nourish the embryo till birth, and this is impossible if there is no menstrual discharge. But there is none in the mule; the useless part of the nutriment is discharged with the excretion from the bladder—this is why male mules do not [25] sniff at the pudenda of the females, as do the other solid-hoofed animals, but only at the excretion itself—and the rest of the nutriment is used up to increase the size of the body. Hence it is sometimes possible for the female to conceive, as has been known to happen before now, but it is impossible for her to complete the process of [30] nourishing the embryo and bringing it to birth.
The male, again, may sometimes generate, both because the male sex is naturally hotter than the female and because it does not contribute any material substance to the mixture. The result in such cases is a ginnus, that is to say, a [749a1] deformed mule; for ginni are produced also from the crossing of horse and ass when the embryo is diseased in the uterus. The ginnus is in fact like the so-called metachoera in swine, for a metachoerum also is a pig deformed in the uterus; this may happen to any pig. The origin of human dwarfs is similar, for these also have their parts and their whole development deformed during gestation, and resemble [5] ginni and metachoera.
1 · We have now spoken about the sterility of mules, and about those [10] animals which are viviparous both externally and within themselves. The generation of the oviparous sanguinea is to a certain extent similar to that of the animals that walk, and all may be embraced in the same general statement; but in other respects there are differences in them both as compared with each other and with those that walk. All alike are generated from sexual union, the male emitting semen [15] into the female. But among the ovipara birds produce a perfect hard-shelled egg, unless it be injured by disease, and the eggs of birds are all two-coloured. The Selachian fishes, as has been often said already, are oviparous internally but [20] produce the young alive, the egg changing previously from one part of the uterus to another; and their egg is soft-shelled and of one colour. One of this class alone does not produce the young from the egg within itself, the so-called fishing-frog; the reason of which must be stated later. All other oviparous fishes produce an egg of [25] one colour, but this is imperfect, for its growth is completed outside the mother’s body by the same cause as are those eggs which are perfected within.
Concerning the uterus, what differences there are among them and for what reasons, has been stated previously. For in some of the viviparous creatures it is high [30] up near the hypozoma, in others low down by the pudenda; the former in the Selachia, the latter in animals both internally and externally viviparous, such as man and horse and the rest; in the ovipara it is sometimes low, as in the oviparous fish, and sometimes high, as in birds.
Some embryos are formed in birds spontaneously, which are called wind-eggs [749b1] and ‘zephyria’ by some; these occur in birds which are not given to flight nor rapine but which produce many young, for these birds have much residual matter, whereas in the birds of prey such secretion is diverted to the wings and feathers, while the [5] body is small and dry and hot; and the menstrual secretion and the semen are residues. Since then both the wings and the semen are made from residual matter, nature cannot afford to spend much upon both. And for this same reason the birds [10] of prey are neither given to treading much nor to laying many eggs, as are the heavy birds and those flying birds whose bodies are bulky, as the pigeon and so forth. For such residual matter is secreted largely in the heavy birds not given to flying, such [15] as fowls, partridges, and so on, and that is why their males tread often and their females produce much material. Of such birds some lay many eggs at a time and some lay often; for instance, the fowl, the partridge, and the Libyan ostrich lay many eggs, while the pigeon family do not lay many but lay often. For these are [20] between the birds of prey and the heavy ones; they are flyers like the former, but have bulky bodies like the latter; hence, because they are flyers and the residue is diverted that way, they lay few eggs, but they lay often because of their having bulky bodies and their stomachs being hot and very active in concoction, and [25] because moreover they can easily procure their food, whereas the birds of prey do so with difficulty.
Small birds also tread often and are very fertile, as are sometimes small plants, for what causes bodily growth in others turns in them to a seminal residuum. Hence the Adrianic fowls lay most eggs, for because of the smallness of their bodies the [30] nutriment is used up in producing young. And low-bred birds are more fertile than high-bred ones; for their bodies are more fluid and bulkier, whereas those of the latter are leaner and drier, since a high-bred spirit is found rather in such bodies as the latter. Moreover the thinness and weakness of the legs contribute to making the [750a1] former class of birds naturally inclined to tread and to be fertile, as we find also in the human species; for the nourishment which otherwise goes to the legs is turned in such into a seminal secretion, what nature takes from the one place being added at the other. Birds of prey, on the contrary, have a strong walk and their legs are thick [5] owing to their habits, so that for all these reasons they neither tread nor lay much. The kestrel is the most fertile; for this is nearly the only bird of prey which drinks, and its moisture, both innate and acquired, along with its heat is favourable to [10] generative products. Even this bird does not lay very many eggs, but four at the outside.