The Complete Works of Aristotle One and Two

The cuckoo, though not a bird of prey, lays few eggs, because it is of a cold nature, as is shown by the cowardice of the bird, whereas a generative animal should be hot and moist. That it is cowardly is plain, for it is pursued by all the birds and lays eggs in the nests of others. [15]

The pigeon family are in the habit of laying two for the most part, for they neither lay one (no bird does except the cuckoo, and even that sometimes lays two) nor yet many, but they frequently produce two, or three at the most, generally two, for these numbers lie between one and many. [20]

It is plain from the facts that with the birds that lay many eggs the nutriment is diverted to the semen. For most trees, if they bear too much fruit, wither away after the crop when nutriment is not reserved for themselves, and this seems to be what happens to annuals, as leguminous plants, corn, and the like. For they consume all [25] their nutriment to make seed, their kind being prolific. And some fowls after laying too much, so as even to lay two eggs in a day, have died after this. For both the birds and the plants become as it were purged, and this condition is an excess of secretion [30] of residual matter. A similar condition is the cause of the later sterility of the lioness, for at the first birth she produces five or six, then in the next year four, and again three cubs, then the next number down to one, then none at all, showing that the residue is being used up and the semen is failing along with the advance of years.

We have now stated in which birds wind-eggs are found, and also what sort of [750b1] birds lay many eggs or few, and for what reasons. And wind-eggs, as said before, come into being because while seminal material exists in the female, birds have no menstrual discharge like viviparous sanguinea (for they occur in all these latter, [5] more in some, less in others, and in some only enough in quantity just to mark the class). The same applies to fish as to birds, and so in them too is found an embryonic formation without impregnation, but it is less obvious because their nature is [10] colder. The secretion corresponding to the menstrual fluid of vivipara is formed in birds at the appropriate season for the discharge of residue, and, because the region near the hypozoma is hot, it is perfected so far as size is concerned, but in birds and fishes alike it is imperfect for generation without the seminal fluid of the male; the [15] cause of this has been previously given. Wind-eggs are not formed in the flying birds, for the same reason as prevents their laying many eggs; for the residual matter in birds of prey is small, and they need the male to give an impulse for the [20] discharge of it. The wind-eggs are produced in greater numbers than the impregnated but smaller in size for one and the same reason; they are smaller in size because they are imperfect, and because they are smaller in size they are more in number. They are less pleasant for food because they are less concocted, for in all foods the concocted is more agreeable. It has been sufficiently observed, then, that [25] neither birds’ nor fishes’ eggs are perfected for generation without the males. As for embryos being formed in fish also (though in a less degree) without the males, the fact has been observed especially in river fish, for some are seen to have eggs from [30] the first, as has been written in the Histories1 concerning them. And generally speaking in the case of birds even the impregnated eggs are not wont for the most part to attain their full growth unless the hen be trodden continually. The reason of [751a1] this is that just as with women intercourse with men draws down the secretion (for the uterus being heated attracts the moisture and the passages are opened), so this happens also with birds; the residual matter corresponding to the menstrual fluid advances a little at a time, and is not discharged externally, because its amount is [5] small and the uterus is high up by the hypozoma, but trickles together into the uterus itself. For as the embryo of the vivipara grows by means of the umbilical cord, so the egg grows through this matter flowing to it through the uterus. For when once the hens have been trodden, they all continue to have eggs almost [10] without intermission, though very small ones. Hence some are wont to speak of wind-eggs as not coming into being independently but as mere relics from a previous impregnation. But this is a false view, for sufficient observations have been made of their arising without impregnation in chickens and goslings. Also the female partridges which are taken out to act as decoys, whether they have ever been [15] impregnated or not, immediately on smelling the male and hearing his call, become filled with eggs in the latter case and lay them in the former. The reason why this happens is the same as in men and quadrupeds, for if their bodies chance to be in rut they emit semen at the mere sight of the female or at a slight touch. And such birds [20] are of a lascivious and fertile nature, so that the impulse they need is but small when they are in this excited condition, and the secreting activity takes place quickly in them, wind-eggs forming in the unimpregnated and the eggs in those which have been impregnated growing and reaching perfection swiftly.

[25] Among creatures that lay eggs externally birds produce their egg perfect, fish imperfect, but the eggs of the latter complete their growth outside as has been said before. The reason is that the fish kind is very fertile; now it is impossible for many eggs to reach completion within the mother and therefore they lay them outside. [30] They are quickly discharged, for the uterus of externally oviparous fishes is near the generative passage. While the eggs of birds are two-coloured, those of all fish are one-coloured. The cause of the double colour may be seen from considering the power of each of the two parts, the white and the yolk. For the matter of the egg is secreted from the blood [(no bloodless animal lays eggs)]2 and that the blood is the [751b1] material of the body has been often said already. The one part, then, of the egg is nearer the form of the animal coming into being, that is the hot part; the more earthy part gives the substance of the body and is further removed. Hence in all two-coloured eggs the animal receives the first principle of generation from the [5] white (for the vital principle is in that which is hot), but the nutriment from the yolk. Now in animals of a hotter nature the part from which the first principle arises is separated off from the part from which comes the nutriment, the one being white [10] and the other yellow, and the white and pure is always more than the yellow and earthy; but in the moister and less hot the yolk is more in quantity and more fluid. This is what we find in lake birds, for they are of a moister nature and are colder than the land birds, so that the so-called yolk in the eggs of such birds is large and less yellow because the white is less separated off from it. But when we come to the [15] ovipara which are both of a cold nature and also moister (such is the fish kind), we find the white not separated at all because of the small size of the eggs and the quantity of the cold and earthy matter; therefore all fish eggs are of one colour, and white compared with yellow, yellow compared with white. Even the wind-eggs of [20] birds have this distinction of colour, for they contain that out of which will come each of the two parts, alike that whence arises the principle of life and that whence comes the nutriment; only both these are imperfect and need the influence of the male in addition; for wind-eggs become fertile if impregnated by the male within a certain period. The difference in colour, however, is not due to any difference of sex, [25] as if the white came from the male, the yolk from the female; both on the contrary come from the female, but the one is cold, the other hot. In all cases then where the hot part is considerable it is separated off, but where it is little it cannot be so; hence the eggs of such animals, as has been said, are of one colour. The semen of the male [30] only sets them; and therefore at first the egg in birds appears white and small, but as it advances it is all yellow as more of the sanguineous material is continually mixed with it; finally as the hot part is separated the white takes up a position all round it and equally distributed on all sides, as when a liquid boils; for the white is naturally [752a1] liquid and contains in itself the vital heat; therefore it is separated off all round, but the yellow and earthy part is inside. And if we enclose many eggs together in a bladder or something of the kind and boil them over a fire so as not to make the [5] movement of the heat quicker than the separation of the white and yolk in the eggs, then the same process takes place in the whole mass of the eggs as in a single egg, all the yellow part coming into the middle and the white surrounding it.

We have thus stated why some eggs are of one colour and others of two. [10]

2 · The principle of the male is separated off in eggs at the point where the egg is attached to the uterus, and the reason why two-coloured eggs are unsymmetrical, and not perfectly round but sharper at one end, is that the part of the white in which is contained this principle must differ from the rest. Therefore the egg is harder at this point than below, for it is necessary to shelter and protect this [15] principle. And this is why the sharp end of the egg comes out of the hen later than the blunt end; for the part attached to the uterus comes out later, and the egg is attached at the point where is the said principle, and the principle is in the sharp end. The same is the case also in the seeds of plants; the principle of the seed is attached sometimes to the twig, sometimes to the husk, sometimes to the pericarp. [20] This is plain in the leguminous plants, for where the two cotyledons of beans and of similar seeds are united, there is the seed attached to the parent plant, and there is the principle of the seed.

A difficulty may be raised about the growth of the egg; how is it derived from the uterus? For if animals derive their nutriment through the umbilical cord, [25] through what do eggs derive it? They do not, like grubs, acquire their growth by their own means. If there is anything by which they are attached to the uterus, what becomes of this when the egg is perfected? It does not come out with the egg as the [30] cord does with animals; for when its egg is perfected the shell forms all round it. This problem is rightly raised, but it is not observed that the shell is at first only a soft membrane, and that it is only after the egg is perfected that it becomes hard and brittle; this is so nicely adjusted that it is still soft when it comes out (for otherwise it would cause pain in laying), but no sooner has it come out than it is fixed hard by cooling, the moisture quickly evaporating because there is but little of [752b1] it, and the earthy part remaining. Now at first a certain part of this membrane at the sharp end of eggs resembles an umbilical cord, and projects like a pipe from them while they are still small. It is plainly visible in small aborted eggs, for if the bird be drenched with water or suddenly chilled in any other way and cast out the [5] egg too soon, it appears still sanguineous and with a small tail like an umbilical cord running through it. As the egg becomes larger this is more twisted round and becomes smaller, and when the egg is perfected this end is the sharp end. Under this is the inner membrane which separates the white and the yolk from this. When the [10] egg is perfected, the whole of it is set free, and naturally the umbilical cord does not appear, for it is now the extreme end of the egg itself.

The egg is discharged in the opposite way from the young of vivipara; the latter are born head-first, the part where is the first principle leading, but the egg is discharged as it were feet first; the reason of this being what has been stated, that [15] the egg is attached at the point where is the first principle.

The young bird is produced out of the egg by the mother’s incubating and aiding the concoction, the creature developing out of part of the egg, and receiving growth and completion from the remaining part. For nature not only places the [20] material of the creature in the egg but also the nourishment sufficient for its growth; for since the mother bird cannot perfect her young within herself she produces the nourishment in the egg along with it. Whereas the nourishment, what is called milk, is produced for the young of vivipara in another part, in the breasts, nature does this for birds in the egg. The opposite, however, is the case to what [25] people think and what is asserted by Alcmaeon of Croton. For it is not the white that is the milk, but the yolk, for it is this that is the nourishment of the chick, whereas they think it is the white because of the similarity of colour.

The chick then, as has been said, comes into being by the incubation of the [30] mother; yet if the temperature of the season is favourable, or if the place in which the eggs happen to lie is warm, the eggs get concocted, both those of birds and those of oviparous quadrupeds. For these all lay their eggs upon the ground, where they are concocted by the heat in the earth. Such oviparous quadrupeds as do visit their eggs and incubate do so rather for the sake of protecting them.

[753a1] The eggs of these quadrupeds are formed in the same way as those of birds, for they are hard-shelled and two-coloured, and they are formed near the hypozoma as are those of birds, and in all other respects resemble them both internally and externally, so that the inquiry into their causes is the same for all. But whereas the [5] eggs of quadrupeds are hatched out by the mere heat of the weather owing to their strength, those of birds are more exposed to destruction and need the mother-bird. Nature seems to wish to implant in animals a 3 sense of care for their young: in the inferior animals this lasts only to the moment of giving birth; in others it continues till they are perfect; in all that are more intelligent, during the bringing up of the [10] young also. In those which have the greatest portion in intelligence we find familiarity and love shown also towards the young when perfected, as with men and some quadrupeds; with birds we find it till they have produced and brought up their young, and therefore if the hens do not incubate after laying they get into worse [15] condition, as if deprived of something natural to them.

The young is perfected within the egg more quickly in warm weather, the season aiding in the work, for concoction is the work of heat. For the earth aids in the concoction by its heat, and the brooding hen does the same, for she infuses the [20] heat that is within her. And it is in the hot season, as we should expect, that the eggs are more apt to be spoilt and the so-called ‘uria’ are produced; for just as wines turn sour in the heats from the sediment getting stirred up (for this is the cause of their being spoilt), so is it with the yolk in eggs, for the sediment and yolk are the earthy [25] part in each case, and that is why the wine becomes turbid when the sediment mixes with it, and the like applies to the eggs that are spoiling because of the yolk. It is reasonable then that such should be the case with the birds that lay many eggs, for it is not easy to give the fitting amount of heat to all, but (while some have too little) others have too much and this makes them turbid, as it were by putrefaction. But [30] this happens none the less with the birds of prey though they lay few eggs, for often one of the two becomes rotten, and the third practically always, for being of a hot nature they make the moisture in the eggs to overboil so to say. For the nature of the white is opposed to that of the yolk; the yolk congeals in frosts but liquefies on [753b1] heating, and therefore it liquefies on concoction in the earth or by reason of incubation, and becoming liquid serves as nutriment for the developing chick. If exposed to heat and roasted it does not become hard, because though earthy in nature it is only so in the same way as wax is; accordingly on heating too much the [5] eggs become watery and rotten, †if they be not from a liquid residue.†4 The white on the contrary is not congealed by frost but rather liquefies (the reason of which has been stated before), but on exposure to heat becomes solid. Therefore being concocted in the development of the chick it is thickened. For it is from this that the [10] young is formed (whereas the yolk turns to nutriment) and it is from this that the parts derive their growth as they are formed one after another. This is why the white and the yolk are separated by membranes, as being different in nature. The precise details of the relation of the parts to one another both at the beginning of generation [15] and as the animals are forming, and also the details of the membranes and umbilical cords, must be learnt from what has been written in the Histories;5 for the present investigation it is sufficient to understand this much clearly, that, when the heart has been first formed and the great blood-vessel has been marked off from it, two umbilical cords run from the vessel, the one to the membrane which encloses the [20] yolk, the other to the membrane resembling a chorion which surrounds the whole embryo; this latter runs round the membrane of the shell. Through the one of these the embryo receives the nutriment from the yolk, and the yolk becomes larger, for it [25] becomes more liquid by heating. This is because the nourishment, being of a material character, must become liquid, just as it is with plants, and at first this embryo, whether in an egg or in the mother’s uterus, lives the life of a plant, for it receives its first growth and nourishment by being attached to something else.

[30] The second umbilical cord runs to the surrounding chorion. For we must understand that, in the case of animals developed in eggs, they have the same relation to the yolk as the embryo of the vivipara has to the mother so long as it is within the mother (for since the nourishment of the embryo of the ovipara is not completed within the mother, the embryo takes part of it away from her); and their relation to the outermost membrane, the sanguineous one, is like that of the viviparous embryo to the uterus. At the same time the egg-shell surrounds both the [754a1] yolk and the chorion analogous to the uterus, just as if it should be put round both the embryo itself and the whole of the mother. This is so because the embryo must [5] be in the uterus and attached to the mother. Now in the vivipara the uterus is within the mother, but in the ovipara it is the other way about, as if one should say that the mother was in the uterus, for that which comes from the mother, the nutriment, is the yolk. The reason is that the process of nourishment is not completed within the mother.

[10] As the creature grows the umbilicus running to the chorion collapses first, because it is here that the young is to come out; what is left of the yolk, and the umbilical cord running to the yolk, collapse later. For the young must have nourishment as soon as it is hatched; it is not nursed by the mother and cannot immediately procure its nourishment for itself; therefore the yolk enters within it [15] along with its umbilicus and the flesh grows round it.

This then is the manner in which animals produced from perfect eggs are hatched in all those, whether birds or quadrupeds, which lay eggs with a hard shell. These details are plainer in the larger creatures; in the smaller they are obscure [20] because of the smallness of the masses concerned.

3 · The class of fishes is also oviparous. Those among them which have the uterus low down lay an imperfect egg for the reason previously given, but the so-called Selachia produce a perfect egg within themselves but are externally [25] viviparous except one which they call the fishing-frog; this alone lays a perfect egg externally. The reason is the nature of its body, for its head is many times as large as the rest of the body and is spiny and very rough. This is also why it does not receive its young again within itself nor produce them alive to begin with, for as the size and [30] roughness of the head prevents their entering so it would prevent their exit. And while the egg of the Selachia is soft-shelled (for they cannot harden and dry its circumference, being colder than birds), the egg of the fishing-frog alone is solid and firm to protect it outside, but those of the rest are of a moist and soft nature, for [754b1] they are sheltered within and by the body of the mother.

The young are produced from the egg in the same way both with those externally perfected (the fishing-frogs) and those internally, and the process in these eggs is partly similar to, partly different from that in birds’ eggs. In the first place they have not the second umbilicus which runs to the chorion under the [5] surrounding shell. The reason of this is that they have not the surrounding shell, for it is no use to them since the mother shelters them, and the shell is a protection to the laid eggs against external injury. Secondly, the process in these also begins on the surface of the egg but not where it is attached to the uterus; for birds are [10] developed from the sharp end and that is where the egg was attached. The reason is that the egg of birds is separated from the uterus, but in most though not all Selachia the egg is still attached to the uterus when perfect. While the young develops upon the surface the egg is consumed by it just as in birds and the other [15] animals detached from the uterus, and at last the umbilicus of the now perfect fish is left attached to the uterus. The like is the case with all those whose eggs are detached from the uterus, for in some of them the egg is so detached when it is perfect.

The question may be raised why the development of birds and fishes differs in [20] this respect. The reason is that in birds the white and yolk are separate, but fish eggs are one-coloured, the corresponding matter being completely mixed, so that there is nothing to stop the first principle being at the opposite end, for the egg is of the same nature both at the point of attachment and at the opposite end, and it is easy to draw [25] the nourishment from the uterus by passages running from this principle. This is plain in the eggs which are not detached, for in some of the Selachia the egg is not detached from the uterus, but is still connected with it as it comes downwards with a view to the production of the young alive; in these the young fish when perfected is [30] still connected by the umbilicus to the uterus when the egg has been consumed. From this it is clear that previously also, while the egg was still round the young, the passages ran to the uterus. This happens as we have said in the smooth dogfish.

In these respects and for the reasons given, the development of fishes differs from that of birds, but otherwise it takes place in the same way. For they have the one umbilicus in like manner as that of birds connecting with the yolk—only in [755a1] these fishes it connects with the whole egg (for it is not divided into white and yolk but all one-coloured)—and get their nourishment from this, and as it is being consumed the flesh in like manner encroaches upon and grows round it. [5]

Such is the process of development in those fish that produce a perfect egg within themselves but are externally viviparous.

4 · Most of the other fish are externally oviparous, all laying an imperfect egg except the fishing-frog; the reason for this exception has been previously stated, and the reason also why the others lay imperfect eggs. In these also the development [10] from the egg runs on the same lines as that of the Selachian and internally oviparous fishes, except that the growth is quick and from small beginnings and the outside of the egg is harder. The growth of the egg is like that of a grub, for those animals which produce grubs give birth to a small thing at first and this grows by itself and [15] not through any attachment to the parent. The reason is similar to that of the growth of yeast, for yeast also grows great from a small beginning as the more solid part liquefies and the liquid is aerated. This is effected in animals by the nature of [20] the vital heat, in yeasts by the heat of the juice commingled with them. The eggs then grow of necessity through this cause (for they have in them a yeasty residue), but also for the sake of what is better; for it is impossible for them to attain their [25] whole growth in the uterus because these animals have so many eggs. Therefore they are very small when set free and grow quickly, small because the uterus is narrow for the multitude of the eggs, and growing quickly that the race may not perish, as it would if much of the time required for the whole development were [30] spent in this growth; even as it is most of those laid are destroyed. Hence the class of fish is prolific, for nature makes up for the destruction by numbers. Some fish actually burst because of the size of the eggs, as the fish called the pipe-fish—for its eggs are large instead of numerous, what nature has taken away in number being [35] added in size.

So much for the growth of such eggs and its reason.

[755b1] 5 · A proof that these fish also are oviparous is the fact that even viviparous fish, such as the Selachia, are first internally oviparous, for it is plain that the whole class of fishes is oviparous. Where, however, both sexes exist and the eggs are [5] produced in consequence of impregnation, the eggs do not arrive at completion unless the male sprinkle his milt upon them. Some erroneously assert that all fish are female except in the Selachian fishes, for they think that the females of fish differ from what are supposed to be males only in the same way as in those plants [10] where the one bears fruit but the other is fruitless, as olive and oleaster, fig and caprifig. They think the like applies to fish except the Selachia; for they do not dispute the sexes in these. And yet there is no difference in the males of Selachian fishes and those belonging to the oviparous class in respect of the organs for the [15] milt, and semen can be seen oozing out of males of both classes at the right season. The female also has a uterus. But if the whole class were females and some of them unproductive, then not only should those which lay eggs have a uterus but also the others, only the uterus of the latter should be different from that of the former. But, [20] as it is, some of them have organs for milt and others have a uterus, and this distinction obtains in all except two, the erythrinus and the channa, some of them having the milt organs, others a uterus. The difficulty which drives some thinkers to this conclusion is easily solved if we look at the facts. They say quite correctly that [25] no animal which copulates produces many young, for of all those that generate from themselves perfect animals or perfect eggs none is prolific on the same scale as the oviparous fishes, for the number of eggs in these is enormous. But they had overlooked the fact that fish-eggs differ from those of birds in one circumstance. [30] Birds and all oviparous quadrupeds, and any of the Selachia that are oviparous, produce a perfect egg, and it does not increase outside of them, whereas the eggs of fish are imperfect and do so complete their growth. Moreover the same thing applies to cephalopods also and crustacea, yet these animals are actually seen [35] copulating, for their union lasts a long time, and it is plain in these cases that the one is male and the other has a uterus. Finally, it would be strange if this distinction did [756a1] not exist in the whole class, just as male and female in all the vivipara. The cause of the ignorance of those who make this statement is that the differences in the copulation and generation of various animals are of all kinds and not obvious, and so, basing their study on a few cases, they think the same must hold good in all cases. [5]

So also those who assert that conception in female fishes is caused by their swallowing the semen have not observed certain points when they say this. For the males have their milt and the females their eggs at about the same time of year, and the nearer the female is to laying the more abundant and the more liquid is the milt [10] formed in the male. And just as the increase of the milt in the male and of the egg in the female takes place at the same time, so is it also with their emission, for neither do the females lay all their eggs together, but gradually, nor do the males emit all the milt at once. All these facts are in accordance with reason. For just as the class [15] of birds in some cases has eggs without impregnation, but few and seldom, impregnation being generally required, so we find the same thing, though to a less degree, in fish. But in both classes these spontaneous eggs are infertile unless the male, in those kinds where the male exists, shed his fluid upon them. Now in birds [20] this must take place while the eggs are still within the mother, because they are perfect when discharged, but in fish, because the eggs are imperfect and complete their growth outside the mother in all cases, those outside are preserved by the sprinkling of the milt over them, even if nothing fertile comes into being inside by way of impregnation, and here it is that the milt of the males is used up. Therefore it [25] comes down the ducts and diminishes in quantity at the same time as this happens to the eggs of the females, for the males always attend them, shedding their milt upon the eggs as they are laid. Thus then they are male and female, and all of them copulate (unless in any kind the distinction of sex does not exist), and without the semen of the male no such animal comes into being. [30]

What contributes to their error is also the fact that the union of such fishes is brief, so that it is not observed even by many of the fishermen, for none of them ever watches anything of the sort for the sake of knowledge. Nevertheless their copulation has been seen, for fish (when the tail part does not prevent it)6 copulate like the dolphins by throwing themselves alongside of one another. But the dolphins [756b1] take longer to get free again, whereas such fishes do so quickly. Hence, not seeing this, but seeing the swallowing of the milt and the eggs, even the fishermen repeat [5] the same simple tale, so much noised abroad, as does Herodotus the story-teller,7 as if fish were conceived by the mother’s swallowing the milt—not considering that this is impossible. For the passage which enters by way of the mouth runs to the intestines, not to the uterus, and what goes into the intestines must be turned into [10] nutriment, for it is concocted; the uterus, however, is plainly full of eggs, and from whence did they enter it?

Much deceived also are those who make a foolish statement about the trochus and the hyena. Many say that the hyena, and Herodorus of Heraclea says that the [5] trochus, has two pudenda, those of the male and of the female, and that the trochus impregnates itself but the hyena mounts and is mounted in alternate years. This is untrue, for the hyena has been seen to have only one pudendum, there being no lack of opportunity for observation in some districts, but hyenas have under the tail a line [10] like the pudendum of the female. Both male and female have such a mark, but the males are taken more frequently; this casual observation has given rise to this opinion. But enough has been said of this.

7 · Touching the generation of fish, the question may be raised, why it is that [15] in the selachia neither the females are seen discharging their eggs nor the males their milt, whereas in the non-viviparous fishes this is seen in both sexes. The reason is that the whole selachian class do not produce much semen, and further the females have their uterus near the hypozoma. For the males and females of the one [20] class of fish differ from the males and females of the other class in like manner, for the selachia are less productive of semen. But in the oviparous fish, as the females lay their eggs on account of their number, so do the males shed their milt on account of its abundance. For they have more milt than just what is required for copulation, [25] as nature prefers to expend the milt in helping to perfect the eggs, when the female has deposited them, rather than in forming them at first. For as has been said both further back and in our recent discussions, the eggs of birds are perfected internally but those of fish externally. The latter, indeed, resemble in a way those animals [30] which produce a grub; for the product discharged by them is still more imperfect. It is the male that brings about the perfection of the egg both of birds and of fishes, only in the former internally, as they are perfected internally, and in the latter externally, because the egg is imperfect when deposited; but the result is the same in both cases.

[757b1] In birds the wind-eggs become fertile, and those previously impregnated by one kind of male change their nature to that of the later impregnator. And if the eggs be behindhand in growth, then, if the same cock treads the hen again after leaving off treading for a time,8 he causes them to increase quickly, not, however, at [5] any period whatever, but if the treading take place before the egg changes so far that the white begins to separate from the yolk. But in the eggs of fishes no such limit of time has been laid down, but the males shed their milt quickly upon them to preserve them. The reason is that these eggs are not two-coloured, and hence there is no such limit of time fixed with them as with those of birds. This fact is what we [10] should expect, for by the time that the white and yolk are separated off from one another, the bird’s egg already contains the principle that comes from the male parent (for the male contributes this).

Wind-eggs, then, participate in generation so far as is possible for them. That they should be perfected into an animal is impossible, for an animal requires [15] sense-perception; but the nutritive faculty of the soul is possessed by females as well as males, and indeed by all living things, as has been often said; and that is why the egg itself is perfect only as the embryo of a plant, but imperfect as that of an animal. If, then, there had been no male sex in the class of birds, the egg would have been [20] produced as it is in some fishes, if indeed there is any kind of fish of such a nature as to generate without a male; but it has been said of them before that this has not yet been satisfactorily observed. But as it is both sexes exist in all birds, so that, considered as a plant, the egg is perfect (and that is why it does not change again after impregnation); but in so far as it is not a plant it is not perfect, nor does [25] anything else result from it; for neither has it come into being simply like a real plant nor from copulation like an animal. Eggs, however, produced from copulation but already separated into white and yolk take after the first impregnator; for they already contain both principles. [30]

8 · The young are produced in the same way also by the cephalopoda, e.g. cuttlefish and the like, and by the crustacea, e.g. crayfish and their kindred, for these also lay eggs in consequence of copulation, and the male has often been seen uniting with the female. Therefore those who say that all fish are female and lay [758a1] eggs without copulation are plainly speaking unscientifically from this point of view also. For it is a wonderful thing to suppose that the former animals lay eggs in consequence of copulation and that fish do not; if again they were unaware of this, it is a sign of ignorance. The union of all these creatures lasts a considerable time, as in insects, and naturally so, for they are bloodless and therefore of a cold nature. [5]

In the cuttlefish and calamaries the eggs appear to be two, because the uterus is divided and appears double, but that of the octopus appears to be single. The reason is that the shape of the uterus in the octopus is round in form and spherical, the cleavage being obscure when it is filled with eggs. The uterus of the crayfish is [10] also bifid. All these animals also lay an imperfect egg for the same reason as fishes. In the crayfish and their like the females produce their eggs so as to keep them attached to themselves, which is why the side-flaps of the females are larger than [15] those of the males, to protect the eggs; the cephalopoda lay them away from themselves. The males of the cephalopoda sprinkle their milt over the females, as the male fish do over the eggs, and it becomes a continuous and glutinous mass, but in the crayfish and their like nothing of the sort has been seen or can be naturally expected, for the egg is under the female and is hard-shelled. Both these eggs and [20] those of the cephalopoda grow after deposition like those of fishes.

The cuttlefish while developing is attached to the egg by its front part, for here alone is it possible, because this animal alone has its front and back part pointing in the same direction. For the position and attitude of the young while developing you [25] must look at the Histories.9

9 · We have now spoken of the generation of other animals, those that walk, fly, and swim; it remains to speak of insects and testacea according to the plan laid down. Let us begin with the insects. It was observed previously that some of these [30] are generated by copulation, others spontaneously, and besides this that they produce a grub, and why this is so. For pretty much all creatures seem in a certain way to produce a grub first, since the most imperfect embryo is of such a nature; and in all animals, even the viviparous and those that lay a perfect egg, the first [35] embryo grows in size while still undifferentiated into parts; now such is the nature of the grub. After this stage some of the ovipara produce the egg in a perfect [758b1] condition, others in an imperfect, but it is perfected outside as has been often stated of fish. With animals internally viviparous the embryo becomes egg-like in a certain sense after its original formation, for the liquid is contained in a fine membrane, just [5] as if we should take away the shell of the egg, and that is why they call the abortion of an embryo at that stage an ‘efflux’.

Those insects which generate at all generate a grub, and those which come into being spontaneously and not from copulation do so at first from a formation of this nature. For we must put down caterpillars also and the product of spiders as a sort [10] of grub. And yet some even of these and many of the others may be thought to resemble eggs because of their round shape, but we must not judge by shapes nor yet by softness and hardness (for what is produced by some is hard), but by the fact that the whole of them is changed into the body of the creature and the animal is not [15] developed from a part of them. All these products that are of the nature of a grub, after progressing and acquiring their full size, become a sort of egg, for the husk about them hardens and they are motionless during this period. This is plain in the grub of bees and wasps and in caterpillars. The reason of this is that their nature, [20] because of its imperfection, oviposits as it were before the right time, as if the grub, while still growing in size, were a soft egg. Similar to this is also what happens with all other insects which come into being without copulation in wool and other such materials and in water. For all of them after the grub-stage become immovable and [25] their integument dries round them, and after this the latter bursts and there comes forth as from an egg an animal perfected in its third stage, and of these the winged sort are more numerous than those which walk.

Another point is quite natural, which may be wondered at by many. Caterpillars at first take nourishment, but after this stage do so no longer, but what is called [30] by some the chrysalis is motionless. The same applies to the grub of wasps and bees …10 after this comes into being the so-called pupa, which has nothing of the kind. For an egg is also of such a nature that when it has reached perfection it grows no more in size, but at first it grows and receives nourishment until it is differentiated [35] and becomes a perfect egg. Sometimes the grub contains in itself the material from which, as it feeds, a residue is produced11—e.g. the grubs of bees and wasps; [759a1] sometimes it gets its nourishment from outside itself, as caterpillars and some others.

It has thus been stated why such animals go through a threefold development and for what reason they become immovable again after moving. And some of them come into being by copulation, like birds and vivipara and most fishes, others [5] spontaneously, like some plants.

10 · There is much difficulty about the generation of bees. If it is really true that in the case of some fishes there is such a method of generation that they produce eggs without copulation, this may well happen also with bees, to judge from [10] appearances. For they must either bring the young brood from elsewhere, as some say, and if so the young must either be spontaneously generated or produced by some other animal, or they must generate them themselves, or they must bring some and generate others, for this also is maintained by some, who say that they bring the [15] young of the drones only. Again, if they generate them it must be either with or without copulation; if the former, then either each kind must generate its own kind, or some one kind must generate the others, or one kind must unite with another for the purpose (I mean for instance that bees may be generated from the union of bees, drones from that of drones, and kings from that of kings, or that all the others may [20] be generated from one, as from what are called kings and leaders, or from the union of drones and bees, for some say that the former are male, the latter female, while others say that the bees are male and the drones female). But all these views are impossible if we reason first upon the facts peculiar to bees and secondly upon those [25] which apply more generally to other animals also.

For if they do not generate the young but bring them from elsewhere, then bees ought to come into being also, if the bees did not carry them off, in the places from which the old bees carry the seeds. For why, if new bees come into existence when the seeds are transported, should they not do so if the seeds are left there? They [30] ought to do so just as much, whether the seeds are spontaneously generated in the flowers or whether some animal generates them. And if the seeds were of some other animal, then that animal ought to be produced from them instead of bees. Again, that they should collect honey is reasonable, for it is their food, but it is strange that they should collect the young if they are neither their own offspring nor [35] food. With what object should they do so? for all animals that trouble themselves about the young labour for what appears to be their own offspring.

[759b1] But, again, it is also unreasonable to suppose that the bees are female and the drones male, for nature does not give weapons for fighting to any female, and while the drones are stingless all the bees have a sting. Nor is the opposite view [5] reasonable, that the bees are male and the drones female, for no males are in the habit of working for their offspring, but as it is the bees do this. And generally, since the brood of the drones is found coming into being among them even if there is no mature drone present, but that of the bees is not so found without the presence of [10] the kings (which is why some say that the young of the drones alone is brought in from outside), it is plain that they are not produced from copulation, either of bee with bee or drone with drone or of bees with drones. (That they should import the brood of the drones alone is impossible for the reasons already given, and besides it is unreasonable that a similar state of things should not prevail with all the three [15] kinds alike.) Then, again, it is also impossible that the bees themselves should be some of them male and some female, for in all kinds of animals the two sexes differ. Besides they would in that case generate their own kind, but as it is their brood is not found to come into being if the leaders are not among them, as men say. And an [20] argument against both theories, that the young are generated by union of the bees with one another or with the drones, separately or with one another, is this: none of them has ever yet been seen copulating, whereas this would have often happened if the sexes had existed in them. It remains then, if they are generated by copulation at [25] all, that the kings shall unite to generate them. But the drones are found to come into being even if no leaders are present, and it is not possible that the bees should either import their brood or themselves generate them by copulation. It remains then, as appears to be the case in certain fishes, that the bees should generate the drones without copulation, being indeed female in respect of generative power, but [30] containing in themselves both sexes as plants do. Hence also they have the instrument for fighting, for we ought not to call that female in which the male sex is not separated. But if this is found to be the case with drones, if they come into being [35] without copulation, then it is necessary that the same account should be given of the bees and the kings and that they also should be generated without copulation. Now if the brood of the bees had been found to come into being among them without the [760a1] presence of the kings, it would necessarily follow that the bees also are produced from bees themselves without copulation, but as it is, since those occupied with the tendance of these creatures deny this, it remains that the kings must generate both their own kind and the bees.

As bees are a peculiar and extraordinary kind of animal so also their [5] generation appears to be peculiar. That bees should generate without copulation is a thing which may be paralleled in other animals, but that what they generate should not be of the same kind is peculiar to them, for the erythrinus generates an [10] erythrinus and the channa a channa. The reason is that bees themselves are not generated like flies and similar creatures, but from a kind different indeed but akin to them, for they are produced from the leaders. Hence in a sort of way their generation is analogous. For the leaders resemble the drones in size and the bees in possessing a sting; so the bees are like them in this respect, and the drones are like [15] them in size. For there must needs be some overlapping unless the same kind is always to be produced from each; but this is impossible, for at that rate the whole class would consist of leaders. The bees, then, are assimilated to them in their power of generation, the drones in size; [if the latter had had a sting also, they would have [20] been leaders, but as it is this much of the difficulty remains, for the leaders are like both kinds at once, like the bees in possessing a sting, like the drones in size].12

But the leaders also must be generated from something. Since it is neither from the bees nor from the drones, it must be from their own kind. The cells of the kings [25] are produced last and are not many in number.

Thus what happens is this: the leaders generate their own kind but also another kind, that of the bees; the bees again generate another kind, the drones, but do not [30] also generate their own kind—this has been denied them. And since what is according to nature is always in due order, therefore it is necessary that it should be denied to the drones even to generate another kind than themselves. This is just what we find happening, for though the drones are themselves generated, they generate nothing else, but the process reaches its limit in the third stage. And so beautifully is this arranged by nature that the three kinds always continue in [760b1] existence and none of them fails, though they do not all generate.

Another fact is also natural, that in fine seasons much honey is collected and many drones are produced, but in rainy seasons a large brood of ordinary bees. For the wet causes more residual matter to be formed in the bodies of the leaders, the [5] fine weather in that of the bees, for being smaller in size they need the fine weather more than the kings do. It is right also that the kings, being as it were made with a view to producing young, should remain within, freed from the labour of procuring necessaries, and also that they should be of a considerable size, their bodies being, as it were, constituted with a view to bearing young, and that the drones should be [10] idle as having no weapon to fight for their food and because of the slowness of their bodies. But the bees are intermediate between the two other kinds, for this is useful for their work, and they are workers as having to support not only their young but also their fathers. And it agrees with our views that the bees attend upon their kings [15] because they are their offspring (for if nothing of the sort had been the case the facts about their leadership would be unreasonable), and that, while they suffer the kings to do no work as being their parents, they punish the drones as their children, for it is nobler to punish one’s children and those who have no work to perform. The fact [20] that the leaders being few generate the bees in large numbers seems to be similar to what obtains in the generation of lions, which at first produce five, afterwards a smaller number each time, at last one and thereafter none. So the leaders at first produce a number of workers, afterwards a few of their own kind; thus the brood of [25] the latter is smaller in number than that of the former, but where nature has taken away from them in number she has made it up again in size.

Such appears to be the truth about the generation of bees, judging from theory [30] and from what are believed to be the facts about them; the facts, however, have not yet been sufficiently grasped; if ever they are, then credit must be given rather to observation than to theories, and to theories only if what they affirm agrees with the observed facts.

A further indication that bees are produced without copulation is the fact that the brood appears small in the cells of the comb, whereas, whenever insects are [761a1] generated by copulation, the parents remain united for a long time but produce quickly something of the nature of a grub and of a considerable size.13

Concerning the generation of animals akin to them, as hornets and wasps, the facts in all cases are similar to a certain extent, but are devoid of the extraordinary [5] features which characterize bees; this we should expect, for they have nothing divine about them as the bees have. For the so-called ‘mothers’ generate the young and mould the first part of the combs, but they generate by copulation with one another, for their union has often been observed. As for all the differences of each of [10] these kinds from one another and from bees, they must be investigated with the aid of the illustrations to the Histories.

11 · Having spoken of the generation of all insects, we must now speak of the testacea. Here also the facts of generation are partly like and partly unlike those in [15] the other classes. And this is what might be expected. For compared with animals they resemble plants, compared with plants they resemble animals, so that in a sense they appear to come into being from semen, but in another sense not so, and in one way they are spontaneously generated but in another from their own kind, or some of them in the latter way, others in the former. Because their nature answers [20] to that of plants, therefore few or no kinds of testacea come into being on land, e.g. the snails and any others, few as they are, that resemble them; but in the sea and similar waters there are many of all kinds of forms. But the class of plants has but [25] few and one may say practically no representatives in the sea and such places, all such growing on the land. For plants and testacea are analogous; and in proportion as liquid has more life-supporting power than solid, water than earth, so much does the nature of testacea differ from that of plants, since the object of testacea is to be [30] in such a relation to water as plants are to earth, as if plants were, so to say, land-shell fish, shell-fish water-plants.

For such a reason also the testacea in the water vary more in form than those on the land. For the nature of liquid is more plastic than that of earth and yet not much less material, and this is especially true of the inhabitants of the sea, for fresh [761b1] water, though sweet and nutritious, is cold and less material. That is why animals having no blood and not of a hot nature are not produced in lakes nor in the fresher among brackish waters, but only exceptionally; but it is in estuaries and at the [5] mouths of rivers that they come into being, as testacea and cephalopoda and crustacea, all these being bloodless and of a cold nature. For they seek at the same time the warmth of the sun and food; now the sea is not only water but much more material than fresh water and hot in its nature; it has a share in all the parts of the [10] universe, water and air and earth, so that it also has a share in all living things which are produced in connexion with each of these elements.14 Plants may be assigned to land, the aquatic animals to water, the land animals to air, but variations of quantity and distance make a great and wonderful difference. The fourth class must [15] not be sought in these regions, though there certainly ought to be some animal corresponding to the element of fire, for this is counted in as the fourth of the elementary bodies. But the form which fire assumes never appears to be peculiar to it, but it always exists in some other of the elements, for that which is ignited appears to be either air or smoke or earth. Such a kind of animal must be sought in [20] the moon, for this appears to participate in the element removed in the third degree from earth. The discussion of these things, however, belongs to another subject.

To return to testacea, some of them are formed spontaneously, some emit a sort of generative substance from themselves, but these also often come into being [25] from a spontaneous formation. To understand this we must grasp the different methods of generation in plants; some of these are produced from seed, some from slips, planted out, some by budding off alongside, as the class of onions. In the last way are produced mussels, for smaller ones are always growing off alongside the [30] original, but the trumpet-shells, the purple-fish, and those which are said to ‘honeycomb’ emit masses of a liquid slime as if originated by something of a seminal nature. We must not, however, consider that anything of the sort is real semen, but that these creatures participate in the resemblance to plants in the manner stated above. Hence when once one such creature has been produced, then is produced a number of them. For all these creatures are liable to be even spontaneously [762a1] generated, and so to be formed still more plentifully in proportion if some are already existing. For it is natural that each should have some superfluous residue attached to it from the original, and from this buds off each of the creatures growing alongside of it. Again, since the nutriment and its residue possess a like power, it is [5] likely that the product of those testacea which ‘honeycomb’ should resemble the original formation, and so it is natural that a new animal of the same kind should come into being from this also.

All those which do not bud off or ‘honeycomb’ are spontaneously generated. Now all things formed in this way, whether in earth or water, manifestly come into [10] being in connexion with putrefaction and an admixture of rain-water. For as the sweet is separated off into the matter which is forming, the residue of the mixture takes such a form. Nothing comes into being by putrefying, but by concocting; putrefaction and the thing putrefied is only a residue of that which is concocted. For [15] nothing comes into being out of the whole of anything, any more than in the products of art; if it did art would have nothing to do, but as it is in the one case art removes the useless material, in the other nature does so. Animals and plants come into being in earth and in liquid because there is water in earth, and air in water, [20] and in all air is vital heat, so that in a sense all things are full of soul. Therefore living things form quickly whenever this air and vital heat are enclosed in anything. When they are so enclosed, the corporeal liquids being heated, there arises as it [25] were a frothy bubble. Whether what is forming is to be more or less honourable in kind depends on the embracing of the vital principle; this again depends on the medium in which the generation takes place and the material which is included. Now in the sea the earthy matter is present in large quantities, and consequently the testaceous animals are formed from a concretion of this kind, the earthy matter [30] hardening round them and solidifying in the same manner as bones and horns (for these cannot be melted by fire), and the body which contains the life being included within it.

The class of snails is the only class of such creatures that has been seen uniting, but it has never yet been sufficiently observed whether their generation is the result of the union or not.

It may be asked, if we wish to follow the right line of investigation, what it is in [762b1] such animals the formation of which corresponds to the material principle. For in the females this is a residual secretion of the animal, potentially such as that from which it came, by imparting motion to which the principle derived from the male perfects the animal. But here what must be said to correspond to this, and whence [5] comes or what is the moving principle which corresponds to the male? We must understand that even in animals which generate it is from the incoming nourishment that the heat in the animal makes the residue, the beginning of the conception, by secretion and concoction. The like is the case also in plants, except that in these [10] (and also in some animals) there is no further need of the male principle, because they have it mingled with the female principle within themselves, whereas the residual secretion in most animals does need it. The nourishment again of some is earth and water, of others a combination of these, so that what the heat in animals produces from their nutriment, the heat of the warm season in the environment puts [15] together and combines by concoction out of the sea-water and the earth. And the portion of the vital principle which is either included along with it or separated off in the air makes an embryo and puts motion into it. Now in plants which are spontaneously generated the method of formation is uniform; they arise from a part [20] of something, and while some of it is the starting-point of the plant, some is the first nourishment of the young shoots. Other animals are produced in the form of a grub, not only those bloodless animals which are not generated from parents but even some sanguinea, as a kind of mullet and some other river fishes and also the eel kind. [25] For all of these, though they have but little blood by nature, are nevertheless sanguinea, and have a heart with blood in it as the origin of the parts; and the so-called ‘entrails of earth’, in which comes into being the body of the eel, have the nature of a grub.

Hence one might suppose, in connexion with the origin of men and quadrupeds, [30] that, if ever they were really ‘earth-born’ as some say, they came into being in one of two ways; that either it was by the formation of a grub at first or else it was out of eggs. For either they must have had in themselves the nutriment for growth (and such a conception is a grub) or they must have got it from elsewhere, and that either from the mother or from part of the conception. If then the former is impossible (I mean that nourishment should flow to them from the earth as it does in animals from the mother), then they must have got it from some part of the conception, and [763a1] such generation we say is from an egg.

It is plain then that, if there really was any such beginning of the generation of all animals, it is reasonable to suppose it to have been one of these two. But it is less reasonable to suppose that it was from eggs, for we do not see such generation [5] occurring with any animal, but we do see the other both in the sanguinea above mentioned and in the bloodless animals. Such are some of the insects and such are the testacea which we are discussing; for they do not develop out of a part of something (as do animals from eggs), and they grow like a grub. For the grub grows [10] towards the upper part and the first principle, since in the lower part is the nourishment for the upper. And this resembles the development of animals from eggs, except that these latter consume the whole egg, whereas in the grub, when the upper part has grown by taking up into itself part of the substance in the lower part, the lower part is then differentiated out of the rest. The reason is that in later life [15] also the nourishment is absorbed by all animals in the part below the hypozoma.

That the grub grows in this way is plain in the case of bees and the like, for at first the lower part is large in them and the upper is smaller. The details of growth in the testacea are similar. This is plain in the whorls of the spiral-shelled creatures, [20] for always as the animal grows the whorls become larger towards the front and what is called the head of the creature.

We have now pretty well described the manner of the development of these and the other spontaneously generated animals. That all the testacea are formed [25] spontaneously is clear from such facts as these. They come into being on the side of boats when the frothy mud putrefies. In many places where previously nothing of the kind existed, the so-called lagoon-oysters, a kind of testacea, have come into [30] being when the spot turned muddy through want of water; thus when a naval armament cast anchor at Rhodes a number of clay vessels were thrown out into the sea, and after some time, when mud had collected round them, oysters used to be found in them. Here is another proof that such animals do not emit any generative substance from themselves; when certain Chians carried some live oysters over from [763b1] Pyrrha in Lesbos and placed them in narrow straits of the sea where tides clash, they became no more numerous as time passed, but increased greatly in size. The so-called eggs contribute nothing to generation but are only a sign of good [5] condition, like fat in the sanguinea, and therefore the oysters are savoury eating at these periods. A proof that this substance is not really eggs is the fact that such ‘eggs’ are always found in some testacea, as in pinnae, trumpet-shells, and purple-fish; only they are sometimes larger and sometimes smaller; in others, as scallops, mussels, and the so-called lagoon-oysters, they are not always present but [10] only in the spring; as the season advances they dwindle and at last disappear altogether; the reason being that the spring is favourable to their being in good condition. In others again, as the ascidians, nothing of the sort is visible. (The details concerning these last, and the places in which they come into being, must be [15] learnt from the History.)

BOOK IV

[20] 1 · We have thus spoken of the generation of animals both generally and separately in all the different classes. But, since male and female are distinct in the most perfect of them, and since we say that the sexes are first principles of all living things whether animals or plants, only in some of them the sexes are separated and [25] in others not, therefore we must speak first of the origin of the sexes in the latter. For while the animal is still imperfect in its kind the distinction is already made between male and female.

It is disputed, however, whether the embryo is male or female, as the case may be, even before the distinction is plain to our senses, and further whether it is thus [30] differentiated within the mother or even earlier. It is said by some, as by Anaxagoras and other of the physicists, that this antithesis exists from the beginning in the seeds; for the seed, they say, comes from the male while the female [764a1] only provides the place, and the male is from the right, the female from the left, and so also that the male embryo is in the right of the uterus, the female in the left. Others, as Empedocles, say that the differentiation takes place in the uterus; for he says that if the uterus is hot what enters it becomes male, if cold, female, the cause [5] of the heat or cold being the flow of the menstrual fluids, according as it is colder or hotter, older or more recent. Democritus of Abdera also says that the differentiation of sex takes place within the mother; that however it is not because of heat and cold that one embryo becomes female and another male, but that it depends on the [10] question which parent it is whose semen prevails,—not the whole of the semen, but that which has come from the part by which male and female differ from one another. This is a better theory, for certainly Empedocles has made a rather lighthearted assumption in thinking that the difference between them is due only to cold and heat, when he saw that there was a great difference in the whole of the [15] sexual parts, the difference in fact between the male pudenda and the uterus. For suppose two animals already moulded in embryo, the one having all the parts of the female, the other those of the male; suppose them then to be put into the uterus as into an oven, the former when the oven is hot, the latter when it is cold; then on the view of Empedocles that which has no uterus will be female and that which has will [20] be male. But this is impossible. Thus the theory of Democritus would be the better of the two, at least as far as this goes, for he seeks for the difference in this development and tries to set it forth; whether he does so well or not is another question.

Again, if heat and cold were the cause of the difference of the parts, this ought to have been stated by those who maintain the view of Empedocles; for to explain [25] the origin of male and female is practically the same thing as to explain this, which is the manifest difference between them. And it is no small matter, starting from temperature as a principle, to collect the cause of the origin of these parts, as if it were a necessary consequence for this part which they call the uterus to be formed [30] in the embryo under the influence of cold but not under that of heat. The same applies also to the parts which serve for intercourse, since these also differ in the way stated previously.

Moreover male and female twins are often found together in the same part of the uterus; this we have observed sufficiently by dissection in all the vivipara, both [35] land animals and fish. Now if Empedocles had not seen this it was only natural for him to fall into error in assigning this cause of his; but if he had seen it it is strange [764b1] that he should still think the heat or cold of the uterus to be the cause, since on his theory both these twins would have become either male or female, but as it is we do not see this to be the fact.

Again he says that the parts of the embryo are sundered, some being in the male and some in the female parent, which is why they desire intercourse with one [5] another. If so it is necessary that the substance of these parts too should be separated from one another and that a union should take place—but not on account of cooling or heating. But perhaps it would be superfluous to discuss thoroughly such a cause 1 as this for its whole character seems to be fanciful. If, however, the [10] facts about semen are such as we have actually stated, if it does not come from the whole of the body of the male parent and if the secretion of the male does not give any material at all to the embryo, then we must make a stand against both Empedocles and Democritus and any one else who argues on the same lines. For then it is not possible that the body of the seed should exist sundered, part in the [15] female parent and part in the male, as Empedocles says in the words: ‘But the nature of the limbs hath been sundered, part in the man’s . . . ’;2 nor yet that the whole is drawn off from each parent and the combination of the two becomes male or female according as one part prevails over another. [20]

And, to take a more general view, though it is better to say that the one part makes it female by prevailing through some superiority than to assign nothing but heat as the cause without any reflection, yet, as the form of the pudendum also differs, we need an explanation of the fact that both these parts go along with each other. If it is because they are near each other, then each of the other parts also [25] ought to go with them, for one of the prevailing parts is always near another; thus the offspring would be not only female or male but also like its mother or father respectively.

Besides, it is absurd to suppose that these parts should come into being as something isolated, without the body as a whole having changed along with them. Take first and foremost the blood-vessels, round which the whole mass of the flesh lies as round a frame-work. It is not reasonable that these should become of a [30] certain quality because of the uterus, but rather that the uterus should do so on account of them. For though it is true that each is a receptacle of blood of some kind, still the system of the vessels is prior to the other; the moving principle must always be prior to that which it moves, and it is because it is itself of a certain [35] quality that it is the cause of the development. The difference, then, of these parts as compared with each other in the two sexes is a result; not this but something else must be held to be the first principle and the cause, even if no semen is secreted by [765a1] either male or female, but the embryo is formed in any way you please.

The same argument as that with which we meet Empedocles and Democritus [5] will serve against those who say that the male comes from the right and the female from the left. If the male contributes no material, there can be nothing in this view. If, as they say, he does contribute something of the sort, we must confront them in the same way as we did the theory of Empedocles, which accounts for the difference [10] between male and female by the heat and cold of the uterus. They make the same mistake as he does, when they account for the difference by their ‘right and left’, though they see that the sexes differ actually by the whole of the sexual parts; for what reason then is the body of the uterus to exist in those embryos which come [15] from the left and not in those from the right? For if an embryo has come from the left but has not acquired this part, it will be a female without a uterus—or maybe a male with one. Besides, as has been said before, a female embryo has been observed in the right part of the uterus, a male in the left, or again both at once in the same [20] part, and this not only once but several times. [Or the male in the right part, the female in the left; and no less both are formed in the right part.]3

Some again, persuaded of the truth of a view resembling that of these philosophers, say that if a man copulates with the right or left testis tied up the [25] result is male or female offspring respectively; so at least Leophanes asserted. And some say that the same happens in the case of those who have one or other testis excised, not speaking truth but vaticinating what will happen from probabilities and jumping at the conclusion that it is so before seeing that it proves to be so. Moreover, they know not that these parts of animals contribute nothing to the [30] production of one sex rather than the other; a proof of this is that many animals in which the distinction of sex exists, and which produce both male and female offspring, nevertheless have no testes, as the footless animals; I mean the classes of fish and of serpents.

[35] To suppose, then, either that heat and cold are the causes of male and female, or that the different sexes come from the right and left, is not altogether [765b1] unreasonable in itself; for the right of the body is hotter than the left, and the concocted semen is hotter than the unconcocted; again, the thickened is concocted, and the more thickened is more fertile. Yet to put it in this way is to seek for the [5] cause from too remote a starting-point; we must draw near the primary causes in so far as it is possible for us.

We have, then, previously spoken elsewhere of both the body as a whole and its parts, explaining what each part is and for what reason it exists. But the male and female are distinguished by a certain capacity and incapacity. (For the male is that [10] which can concoct and form and discharge a semen carrying with it the principle of form—by ‘principle’ I do not mean a material principle out of which comes into being an offspring resembling the parent, but I mean the first moving cause, whether it have power to act as such in the thing itself or in something else—but the [15] female is that which receives semen, but cannot form it or discharge it.) And all concoction works by means of heat. Therefore the males of animals must needs be hotter than the females. For it is by reason of cold and incapacity that the female is more abundant in blood in certain parts of her anatomy, and this abundance is an evidence of the exact opposite of what some suppose, thinking that the female is hotter than the male for this reason, i.e. the discharge of menstrual fluids. It is true [20] that blood is hot, and that which has more of it is hotter. But they assume that this discharge occurs through excess of blood and of heat, as if it were possible for everything to be equally blood if only it be liquid and sanguineous in colour, and as if it might not become less in quantity but purer in quality in those who assimilate [25] nourishment properly. In fact they look upon this residual discharge in the same light as that of the intestines, when they think that a greater amount of it is a sign of a hotter nature, whereas the truth is just the opposite. For consider the production of fruit; the nutriment in its first stage is abundant, but the useful product derived from it is small, indeed the final result is nothing at all compared to the quantity in [30] the first stage. So is it with the body; the various parts receive and work up the nutriment, from the whole of which the final result is quite small. This is blood in some animals, in some its analogue. Now since the one sex is able and the other is [35] unable to reduce the residual secretion to a pure form, and every capacity has a certain corresponding organ, whether the faculty produces the desired results in a lower degree or in a higher degree, and since the two sexes correspond in this [766a1] manner (the terms ‘able’ and ‘unable’ being used in more senses than one)— therefore it is necessary that both female and male should have organs. Accordingly the one has the uterus, the other the male organs.

Again, nature gives both the faculty and the organ to each individual at the [5] same time, for it is better so. Hence each region comes into being along with the secretions and the faculties, as e.g. the faculty of sight is not perfected without the eye, nor the eye without the faculty of sight; and so too the intestine and bladder come into being along with the faculty of forming the residues. And since that from which an organ comes into being and that by which it is increased are the same (i.e. [10] the nutriment), each of the parts will be made out of such a material and such residual matter as it is able to receive. In the second place, again, it is formed, as we say, in a certain sense, out of its opposite. Thirdly, we must understand besides this that, if it is true that when a thing perishes it becomes the opposite of what it was, it is necessary also that what is not under the sway of that which made it must change [15] into its opposite. After these premisses it will perhaps be now clearer for what reason one embryo becomes female and another male. For when the first principle does not bear sway and cannot concoct the nourishment through lack of heat nor bring it into its proper form, but is defeated in this respect, then must the material [20] change into its opposite. Now the female is opposite to the male, and that in so far as the one is female and the other male. And since it differs in its faculty, its organ also is different, so that the embryo changes into this state. And as one part of first-rate importance changes, the whole system of the animal differs greatly in form along with it. This may be seen in the case of eunuchs, who, though mutilated in one part [25] alone, depart so much from their original appearance and approximate closely to the female form. The reason of this is that some of the parts are principles, and when a principle is moved many of the parts that go along with it must change with it.

[30] If then the male is a principle and a cause, and the male is such in virtue of a certain capacity and the female is such in virtue of an incapacity, and if the definition of the capacity and of the incapacity is ability or inability to concoct the nourishment in its ultimate stage, this being called blood in the sanguinea and the analogue of blood in the other animals, and if the cause of this capacity is in the first principle and in the part which contains the principle of natural heat—therefore a [766b1] heart must be formed in the sanguinea (and the resulting animal will be either male or female), and in the other kinds which possess the sexes must be formed that which is analogous to the heart.

This, then, is the first principle and cause of male and female, and this is the part of the body in which it resides. But the animal becomes definitely female or [5] male by the time when it possesses also the parts by which the female differs from the male, for it is not in virtue of any part you please that it is male or female, any more than it is able to see or hear by possessing any part you please.

To recapitulate, we say that the semen has been laid down to be the ultimate residue of the nutriment. By ultimate I mean that which is carried to every part of [10] the body, and this is also the reason why the offspring is like the parent. For it makes no difference whether we say that the semen comes from all the parts or goes to all of them, but the latter is the better. But the semen of the male differs in that it contains a principle within itself of such a kind as to set up movements also in the embryo and to concoct thoroughly the ultimate nourishment, whereas the secretion [15] of the female contains material alone. If, then, the male element prevails it draws the female element into itself, but if it is prevailed over it changes into the opposite or is destroyed. But the female is opposite to the male, and is female because of its inability to concoct and of the coldness of the sanguineous nutriment. And nature assigns to each of the residues the part fitted to receive it. But the semen is a residue, [20] and this in the hotter animals with blood, i.e. the males, is moderate in quantity, which is why the recipient parts of this residue in males are only passages. But the females, owing to inability to concoct, have a great quantity of blood, for it cannot be worked up into semen. Therefore they must also have a part to receive this, and this part must be unlike the passages of the male and of a considerable size. This is [25] why the uterus is of such a nature, this being the part by which the female differs from the male.

2 · We have thus stated for what reason the one becomes female and the other male. Observed facts confirm what we have said. For more females are produced by the young and by those verging on old age than by those in the prime of [30] life; in the former the heat is not yet perfect, in the latter it is failing. And those of a moister and more feminine state of body are more wont to beget females, and a liquid semen causes this more than a thicker; now all these characteristics come of deficiency in natural heat.

Again, more males are born if copulation takes place when north than when south winds are blowing; for animals’ bodies are more liquid when the wind is in the [35] south, so that they produce more residue—and more residue is harder to concoct; hence the semen of the males is more liquid, and so is the discharge of the menstrual fluids in women.

Also the fact that menstruation occurs in the course of nature rather when the [767a1] month is waning is due to the same causes. For this time of the month is colder and moister because of the waning and failure of the moon; as the sun makes winter and summer in the year as a whole, so does the moon in the month. This is not due to the [5] turning of the moon, but it grows warmer as the light increases and colder as it wanes.

The shepherds also say that it not only makes a difference in the production of males and females if copulation takes place during northern or southerly winds, but [10] even if the animals while copulating look towards the south or north; so small a thing will sometimes turn the scale and cause cold or heat, and these again influence generation.

The male and female, then, are distinguished generally, as compared with one another in connexion with the production of male and female offspring, for the causes stated. However, they also need a certain correspondence with one another; [15] for all things that come into being as products of art or of nature exist in virtue of a certain ratio. Now if the hot preponderates too much it dries up the liquid; if it is very deficient it does not solidify it; for the product we need the due mean between the extremes. Otherwise it will be as in cooking; too much fire burns the meat, too [20] little does not cook it, and in either case the process is a failure. So also there is need of due proportion in the mixture of the male and female elements. And for this cause it often happens to many of both sexes that they do not generate with one another, but if divorced and remarried to others do generate; and these oppositions [25] show themselves sometimes in youth, sometimes in advanced age, alike as concerns fertility or infertility, and as concerns generation of male or female offspring.

One country also differs from another in these respects, and one water from another, for the same reasons. For the nourishment and the condition of the body [30] are of such or such a kind because of the tempering of the surrounding air and of the food entering the body, especially the water; for men consume more of this than of anything else, and this enters as nourishment into all food, even solids. Hence hard waters cause infertility, and cold waters the birth of females. [35]

3 · The same causes must be held responsible for the facts that some children resemble their parents, while others do not (some being like the father and others like the mother, both in the body as a whole and in each part); and that they [767b1] resemble their parents more than remoter ancestors, and resemble those ancestors more than any chance individual; and that males rather resemble their fathers, females their mothers; and that some, though resembling none of their relations, yet do at any rate resemble a human being, but others are not even like a human being [5] but a monstrosity. For even he who does not resemble his parents is already in a certain sense a monstrosity; for in these cases nature has in a way departed from the type. The first departure indeed is that the offspring should become female instead of male; this, however, is a natural necessity. (For the class of animals divided into [10] sexes must be preserved, and as it is possible for the male sometimes not to prevail over the female, either through youth or age or some other such cause, it is necessary that animals should produce female young.) And the monstrosity, though not necessary in regard of a final cause and an end, yet is necessary accidentally. As [15] for the origin of it, we must look at it in this way. If the generative residue in the menstrual fluids is properly concocted, the movement imparted by the male will make the form of the embryo in the likeness of itself. (Whether we say that it is the semen or this movement that makes each of the parts grow, makes no difference; nor again whether we say that it makes them grow or forms them from the [20] beginning, for the formula of the movement is the same in either case.) Thus if this movement prevail, it will make the embryo male and not female, like the father and not like the mother; if it prevail not, the embryo is deficient in that faculty in which it has not prevailed. By ‘each faculty’ I mean this. That which generates is not only [25] male but also a certain sort of male, e.g. Coriscus or Socrates, and it is not only Coriscus but also a man. In this way some of the characteristics of the father are more near to him, others more remote from him considered simply as a parent and not in reference to his accidental qualities (as for instance if the parent is a scholar or the neighbour of some particular person). Now the peculiar and individual has [30] always more force in generation. Coriscus is both a man and an animal, but his manhood is nearer to what is peculiar to him than is his animal-hood. In generation both the individual and the class are operative, but the individual is the more so of [35] the two, for this is the substance. And the offspring is produced indeed of a certain quality, but also as a certain ‘this’, and this latter is the substance. Therefore it is from the forces of all such things that the movements come which exist in the semen; potentially from remoter ancestors but in a higher degree from whatever [768a1] individual is nearer (and by the individual I mean e.g. Coriscus or Socrates). Now since everything changes not into anything haphazard but into its opposite, therefore also that which is not prevailed over in generation must change and become the opposite, in respect of that particular force in which the generative and [5] moving element has not prevailed. If then it has not prevailed in so far as it is male, the offspring becomes female; if in so far as it is Coriscus or Socrates, the offspring does not resemble the father but the mother. For as father and mother are opposed in general, so also the individual father is opposed to the individual mother. The like applies also to the forces that come next in order, for the offspring always changes [10] rather into the likeness of the nearer ancestor, both in the paternal and in the maternal line.

Some of the movements exist actually, others potentially; actually, those of the father and the general type, as man and animal; potentially, those of the female and [15] the remoter ancestors. Now if it lose its own nature, it changes to its opposites, but the movements which form the embryo relapse into those nearly connected with them; for instance, if the movement of the male parent relapses, it changes by a very slight difference into that of his father, and in the next instance into that of his grandfather; and in this way in the female line too the movement of the female [20] parent changes into that of her mother, and, if not into this, then into that of her grandmother; and similarly also with the more remote ancestors.

Naturally then it is most likely that the characteristics of male and of the father will go together, whether they prevail or are prevailed over. For the difference between them is small so that there is no difficulty in both concurring, for Socrates is an individual man with certain characteristics. Hence for the most part the male offspring resemble the father, and the female the mother. For the loss of [25] both characters takes place at once, and the change is into the two opposites; now female is opposed to male, and mother to father.

But if the movement coming from the male principle prevails while that coming from Socrates does not, or vice versa, then the result is that male children [30] are produced resembling the mother and female children resembling the father.

If again the movements relapse, then if the male character remains but the movement coming from the individual Socrates relapses into that of the father of Socrates, the result will be a male child resembling its grandfather or some other of its more remote ancestors in the male line on the same principle. If the male principle be prevailed over, the child will be female and resembling most probably its mother, but, if the movement coming from the mother also relapses, it will [35] resemble its mother’s mother or the resemblance will be to some other of its more remote ancestors in the female line on the same principle.

The same applies also to the separate parts, for often some of these take after [768b1] the father, and others after the mother, and yet others after some of the remoter ancestors. For, as has been often said already, some of the movements which form the parts exist actually and others potentially. We must grasp certain general principles, not only that just mentioned (that some of the movements exist [5] potentially and others actually), but also two others, that if a character be prevailed over it changes into its opposite, and, if it relapse it is resolved into the movement next allied to it—if less, into that which is near, if more, into that which is further removed. Finally, the movements are so confused together that there is no [10] resemblance to any of the family or kindred, but the only character that remains is that common to all, i.e. being a man. The reason for this is that this accompanies all the individual characteristics; man is universal, while Socrates, the father, and the mother, whoever she may be, are individuals.

The reason why the movements relapse is this. The agent is itself acted upon by [15] that on which it acts; thus that which cuts is blunted by that which is cut by it, that which heats is cooled by that which is heated by it, and in general the moving cause (except in the case of the first cause of all) does itself receive some motion in return; e.g. what pushes is itself in a way pushed again and what crushes is itself crushed [20] again. Sometimes it is altogether more acted upon than acting, so that what is heating or cooling something else is itself cooled or heated, sometimes having produced no effect, sometimes less than it has itself received. (This question has been treated in the special discussion of action and reaction, where it is laid down in what classes of things action and reaction exist.) Now that which is acted on escapes [25] and is not mastered, either through deficiency of power in the concocting and moving agent or because what should be concocted and formed into distinct parts is too cold and in too great quantity. Thus the moving agent, mastering it in one part but not in another, makes the embryo in formation to be multiform, as happens with [30] athletes because they eat so much. For owing to the quantity of their food their nature is not able to master it in such a way that their form grows proportionately and remains symmetrical; therefore their limbs develop irregularly, sometimes indeed almost so much that no one of them resembles what it was before. Similar to this is also the disease known as satyriasis, in which the face appears like that of [35] some other creature—a satyr—owing to a quantity of unconcocted humour being diverted into parts of the face.

[769a1] We have thus discussed the cause of all these phenomena, why female and male offspring are produced, why some are similar to their parents, female to female and male to male, and others the other way about, females being similar to the father and males to the mother, and in general why some are like their ancestors [5] while others are like none of them, and all this as concerns both the body as a whole and each of the parts separately. Different accounts,4 however, have been given by some of the natural scientists as to why children are like or unlike their parents. They give two versions of the reason. Some say that the child is more like that parent of the two from whom comes more semen, this applying equally both to the [10] body as a whole and to the separate parts, on the assumption that semen comes from every part; if an equal part comes from each, then, they say, the child is like neither. But if this is false, if semen does not come off from the whole body, it is clear that [15] the reason assigned cannot be the cause of likeness and unlikeness. Moreover, they are hard put to it to explain how it is that a female child can be like the father and a male like the mother. For those who assign the same cause of sex as Empedocles or Democritus say what is on other grounds impossible, and those who say that it is determined by the greater or smaller amount of semen coming from the male or [20] female parent, and that this is why one child is male and another female, cannot show how the female is to resemble the father and the male the mother, for it is impossible that more should come from both at once. Again, for what reason is a child generally like its ancestors, even the more remote? None of the semen has [25] come from them at any rate.

But those who account for the similarity in the manner which remains to be discussed, explain this point better, as well as the others. For there are some who say that the semen, though one, is as it were a seed-aggregate of many elements; just as, [30] if one should mix many juices in one liquid and then take some from it, it would be possible to take, not an equal quantity always from each juice, but sometimes more of one and sometimes more of another, sometimes some of one and none at all of another, so they say it is with the generative fluid, which is a mixture of many [35] elements, for the offspring resembles that parent from which it has derived most. Though this theory is obscure and in many ways fictitious, it aims at what is better expressed by saying that what is called the seed-aggregate exists potentially, not [769b1] actually; it cannot exist actually, but it can do so potentially. But if we assign only one sort of cause, it is not easy to explain all the phenomena—the distinction of sex, [5] why the female is often like the father and the male like the mother, and again the resemblance to remoter ancestors, and further the reason why the offspring is sometimes unlike any of these but still a human being, but sometimes, proceeding further on these lines, appears finally to be not even a human being but only some kind of animal, what is called a monstrosity. [10]

For, following what has been said, it remains to give the reason for such monsters. If the movements relapse and the material is not controlled, at last there remains what is most universal, that is to say the animal. Then people say that the child has the head of a ram or a bull, and so on with other animals, as that a calf has [15] the head of a child or a sheep that of an ox. All these monsters result from the causes stated above, but they are none of the things they are said to be; there is only some similarity, such as may arise even where there is no defect of growth. Hence often jesters compare someone who is not beautiful to a goat breathing fire, or again to a ram butting, and a certain physiognomist reduced all faces to those of two or three [20] animals, and his arguments often prevailed on people.

That, however, it is impossible for such a monstrosity to come into existence— I mean one animal in another—is shown by the great difference in the period of gestation between man, sheep, dog, and ox, it being impossible for each to be developed except in its proper time. [25]

This is the description of some of the monsters talked about; others are such because certain parts of their form are multiplied so that they are born with many feet or many heads.

The account of the cause of monstrosities is very close and similar in a way to that of the deformed; for monstrosity is actually a kind of deformity. [30]

4 · Democritus said that monstrosities arose because two emissions of seminal fluid fall into the uterus: the earlier one is operative and is not ejected, and the later also enters the uterus, so that the parts of the embryo grow together and get confused with one another. But in birds, he says, since copulation always takes place quickly, both the eggs and their colour cross one another. But if it is the fact, as it manifestly is, that several young are produced from one emission of semen and [770a1] a single act of intercourse, it is better not to desert the short road to go a long way about, for in such cases it is absolutely necessary that this should occur when the semen is not separated but all enters the female at once.

If, then, we must attribute the cause to the semen of the male, this will be the [5] way we shall have to state it, but in general we must rather suppose that the cause lies in the material and in the embryo as it is forming. Hence also such monstrosities appear very rarely in animals producing only one young one, more frequently in those producing many, most of all in birds and among birds in the common fowl. For [10] this bird produces many young, not only because it lays often like the pigeon family, but also because it has many embryos at once and copulates all the year round. Therefore it produces many double eggs, for the embryos grow together because they are near one another, as often happens with many fruits. In such double eggs, [15] when the yolks are separated by the membrane, two separate chickens are produced with nothing abnormal about them; when the yolks are continuous, with no division between them, the chickens produced are monstrous, having one body and head but [20] four legs and four wings; this is because the upper parts are formed earlier from the white, their nourishment being drawn from the yolk, whereas the lower part comes into being later and its nourishment is one and indivisible.

A snake has also been observed with two heads for the same reason, this class [25] also being oviparous and producing many young. Monstrosities, however, are rarer among them owing to the shape of the uterus, for by reason of its length the numerous eggs are set in a line.

Nothing of the kind occurs with bees and wasps, because their brood is in separate cells.

[30] But in the fowl the opposite is the case, whereby it is plain that we must hold the cause of such phenomena to lie in the material. So, too, monstrosities are commoner in other animals if they produce many young. Hence they are less common in man, for he produces for the most part only one young one and that perfect; even in man monstrosities occur more often in regions where the women [35] give birth to more than one at a time, as in Egypt. And they are commoner in sheep and goats, since they produce more young. Still more does this apply to the fissipeds, [770b1] for such animals produce many young and imperfect, as the dog, the young of these creatures being generally blind. Why this happens and why they produce many young must be stated later, but in them nature has made an advance towards the production of monstrosities in that what they generate, being imperfect, is so far unlike the parent; now monstrosities also belong to the class of things unlike the [5] parent. Therefore this accident also often invades animals of such a nature. So, too, it is in these that the so-called ‘metachoera’ are most frequent, and the condition of these also is in a way monstrous, since both deficiency and excess are monstrous. For the monstrosity belongs to the class of things contrary to nature, not any and [10] every kind of nature, but nature taken as what holds for the most part; nothing can happen contrary to nature considered as eternal and necessary, but only in those cases where things generally happen in a certain way but may also happen in another way. In fact, even in the case of monstrosities, whenever things occur contrary indeed to the established order but still always in a certain way and not at [15] random, the result seems to be less of a monstrosity because even that which is contrary to nature is in a certain sense according to nature, whenever, that is, the formal nature has not mastered the material nature. Therefore they do not call such things monstrosities any more than in the other cases where a phenomenon occurs [20] habitually, as in fruits; for instance, there is a vine which some call ‘smoky’; if this bear black grapes they do not judge it a monstrosity because it is in the habit of doing this very often. The reason is that it is in its nature intermediate between white and black; thus the change is not a large one nor, so to say, contrary to nature; at least, it is not a change into another nature. But in animals producing many [25] young these things occur because the numerous embryos hinder one another from becoming perfect and interfere with the generative motions.

A difficulty may be raised concerning the production of many young and the multiplication of the parts and concerning the production of few young or only one [30] and the deficiency of the parts. Sometimes animals are born with too many toes, sometimes with one alone, and so on with the other parts, for they may be multiplied or they may be mutilated. Again, they may have the generative parts doubled, the one being male, the other female; this is known in men and especially in goats. For what are called ‘tragaenae’ are such because they have both male and female [35] generative parts; there is a case also of a goat being born with a horn upon its leg. Changes and deficiencies and multiplications are found also in the internal parts, [771a1] animals either not possessing some at all, or possessing them in a mutilated condition, or too numerous or in the wrong place. No animal, indeed, has ever been born without a heart, but they are born without a spleen or with two spleens or with one kidney; there is no case again of total absence of the liver, but there are cases of [5] its being incomplete. And all these phenomena have been seen in animals perfect and alive. Animals also which naturally have a gall-bladder are found without one; others are found to have more than one. Cases are known, too, of the organs changing places, the liver being on the left, the spleen on the right. These phenomena have been observed, as stated above, in animals whose growth is [10] perfected; at the time of birth great confusion of every kind has been found. Those which only depart a little from nature commonly live; not so those which depart further, when the unnatural condition is in the parts which are sovereign over life.

The question then about all these cases is this. Are we to suppose that a single cause is responsible for the production of a single young one and for the deficiency [15] of the parts, and also for the production of many young and the multiplication of parts, or not?

In the first place it seems only reasonable to wonder why some animals produce many young, others only one. For it is the largest animals that produce one, e.g. the elephant, camel, horse, and the other solid-hoofed ungulates; of these some are larger than all other animals, while the others are of a remarkable size. But the [20] dog, the wolf, and practically all the fissipeds produce many, even the small members of the class, as the mouse family. The cloven-footed animals again produce few, except the pig, which belongs to those that produce many. Now we should expect the large animals to be able to generate more young and to produce [25] more semen. But precisely what we wonder at is the reason for not wondering; it is just because of their size that they do not produce many young, for the nutriment is expended in such animals upon increasing the body. But in the smaller animals nature takes away from the size and adds the excess to the seminal secretion. [30] Moreover, more semen must be used in generation by the larger animal, and little by the smaller. Therefore many small ones may be produced together, but it is hard for many large ones to be so, and to those intermediate in size nature has assigned the intermediate number. We have formerly given the reason why some animals are large, some smaller, and some between the two. Some produce one young, some few, [771b1] some many: for the most part, the solid-hoofed produce one, the cloven-footed few, the fissipeds many. (The reason of this is that, generally speaking, their sizes correspond to this difference.) It is not so, however, in all cases; for it is the largeness [5] and smallness of the body that is cause of few or many young being born, not the fact that the kind of animal has one, two, or many toes. A proof of this is that the elephant is the largest of animals and yet is many-toed, and the camel, the next [10] largest, is cloven-footed. And not only in animals that walk but also in those that fly or swim the large ones produce few, the small many, for the same reason. In like manner also it is not the largest plants that bear most fruit.

We have explained then why some animals naturally produce many young, [15] some but few, and some only one; in the difficulty now stated we may rather be surprised with reason at those which produce many, since such animals are often seen to conceive from a single copulation. Whether the semen of the male contributes to the material of the embryo by itself becoming a part of it and mixing [20] with the semen of the female, or whether, as we say, it does not act in this way but brings together and fashions the material within the female and the generative secretion as the fig-juice does the liquid substance of milk, what is the reason why it does not form a single animal of considerable size? For certainly in the parallel case [25] the fig-juice is not separated if it has to curdle a large quantity of milk, but the more the milk and the more the fig-juice put into it, so much the greater is the curdled mass. Now it is no use to say that the several regions of the uterus attract the semen and therefore more young than one are formed, because the regions are many and [30] the cotyledons are more than one. For two embryos are often formed in the same region of the uterus, and they may be seen lying in a row in animals that produce many, when the uterus is filled with the embryos. (This is plain from the dissections.) Rather the truth is this. As animals complete their growth there are certain limits to their size, both upwards and downwards, beyond which they cannot [35] go, but it is in the space between these limits that they exceed or fall short of one another in size, and it is within these limits that one man (or any other animal) is [772a1] larger or smaller than another. So also the generative material from which each animal is formed is not without a quantitative limit in both directions, nor can it be formed from any quantity you please. Whenever, then, an animal, for the cause [5] assigned, discharges more of the secretion than is needed for beginning a single animal, it is not possible that only one should be formed out of all this, but a number limited by the appropriate size in each case; nor will the semen of the male, or the power residing in the semen, form anything either more or less than what is [10] according to nature. In like manner, if the male emits more semen than is necessary, or more powers in different parts of the semen as it is divided, however much it is it will not make anything greater; on the contrary it will dry up the material and destroy it. So fire also does not continue to make water hotter in proportion as it is itself increased, but there is a fixed limit to the heat of which water is capable; if [15] that is once reached and the fire is then increased, the water no longer gets hotter but rather evaporates and at last disappears and is dried up. Now since it appears that the secretion of the female and that from the male need to stand in some proportionate relation to one another (I mean in animals of which the male emits semen), what happens in those that produce many young is this: from the very first [20] the semen emitted by the male has power, being divided, to form several embryos, and the material contributed by the female is so much that several can be formed out of it. (The parallel of curdling milk, which we spoke of before, is no longer in point here, for what is formed by the heat of the semen is not only of a certain quantity but also of a certain quality, whereas with fig-juice and rennet quantity alone is concerned.) This then is just the reason why in such animals the embryos [25] formed are numerous and do not all unite into one whole; it is because an embryo is not formed out of any quantity you please, but whether there is too much or too little, in either case there will be no result, for there is a limit set alike to the power of the heat which acts and to the material so acted upon.

On the same principle many embryos are not formed, though the secretion is [30] much, in the large animals which produce only one young one, for in them also both the material and that which works upon it are of a certain quantity. So they do not secrete such material in too great quantity for the reason previously stated, and what they do secrete is naturally just enough for one embryo alone to be formed from it. If ever too much is secreted, then twins are born. Hence such cases seem [35] rather to be monstrous because they are contrary to the general and customary rule.

Man belongs to all three classes, for he produces one only and sometimes many [772b1] or few, though naturally he almost always produces one. Because of the moisture and heat of his body he may produce many (for semen is naturally fluid and hot), but because of his size he produces few or one. On account of this it results that in [5] man alone among animals the period of gestation is irregular; whereas the period is fixed in the rest, there are several periods in man, for children are born at seven months and at ten months and at the times between, for even those of eight months do live though less often than the rest. The reason may be gathered from what has [10] just been said, and the question has been discussed in the Problems. Let this explanation suffice for these points.

The reason why the parts may be multiplied contrary to nature is the same as the cause of the birth of twins. For the reason exists already in the embryo, whenever more material gathers than is required by the nature of the part. The [15] result is then that either one of its parts is larger than the others, as a finger or hand or foot or any of the other extremities or limbs; or again if the embryo is cleft there may come into being more than one, as eddies do in rivers; as the water in these is carried along with a certain motion, if it dash against anything two systems come [20] into being out of one, each retaining the same motion; the same thing happens also with the embryos. They generally are attached near one another, but sometimes at a distance because of the movement taking place in the embryo, and especially because of the excess of material returning to that place whence it was taken away while retaining the form of that part whence it arose as a superfluity. [25]

In certain cases we find a double set of generative organs [one male and the other female].5 When such duplication occurs the one is always functional but not the other, because it is always insufficiently supplied with nourishment as being contrary to nature; it is attached like a tumour (for such growths also receive nourishment though they are a later development than the body proper and [30] contrary to nature). If the formative power prevails, both are similar; if it is altogether vanquished, both are similar; but if it prevail here and be vanquished there, then the one is female and the other male. (For whether we consider the reason why the whole animal is male or female, or why the parts are so, makes no difference.)

[35] When we meet with deficiency in such parts, e.g. an extremity or one of the other limbs, we must assume the same cause as when the embryo is altogether aborted (abortion of embryos happens frequently).

[773a1] Outgrowths differ from the production of many young in the manner stated before; monsters differ from these in that most of them are due to embryos growing together. Some however are also of the following kind, when the monstrosity affects [5] greater and more sovereign parts, as for instance some monsters have two spleens or more than two kidneys. Further, the parts may migrate, the movements being diverted and the material changing its place. We must decide whether the monstrous animal is one or is composed of several grown together by considering the vital principle; thus, if the heart is a part of such a kind then that which has one [10] heart will be one animal, the multiplied parts being mere outgrowths, but those which have more than one heart will be two animals grown together through their embryos having been confused.

It also often happens even in many animals that do not seem to be defective and whose growth is now complete, that some of their passages may have grown [15] together or others may have been diverted from the normal course. Thus in some women before now the os uteri has remained closed, so that when the time for menstruation has arrived pain has attacked them, till either the passage has burst open of its own accord or the physicians have removed the impediment; some such cases have ended in death if the rupture has been made too violently or if it has been [20] impossible to make it at all. In some boys, on the other hand, the end of the penis has not coincided with the end of the passage where the urine is voided, but the passage has ended below, so that they crouch sitting to void it, and if the testes are drawn up they appear from a distance to have both male and female generative organs. The [25] passage of the solid food also has been closed before now in sheep and some other animals; there was a cow in Perinthus which passed fine matter, as if it were sifted, through the bladder, and when the anus was cut open it quickly closed up again nor could they succeed in keeping it open.

[30] We have now spoken of the production of few and many young, and of the outgrowth of superfluous parts and also of monstrosities.

5 · Superfoetation does not occur at all in some animals but does in others; of the former some are able to bring the later formed embryo to birth, while others can only do so sometimes. The reason why it does not occur in some is that they produce [773b1] only one young one, for it is not found in solid-hoofed animals and those larger than these, as owing to their size the secretion is all used up for the one embryo. For all these have large bodies, and when an animal is large its foetus is large in proportion, [5] e.g. the foetus of the elephant is as big as a calf. But superfoetation occurs in those which produce many young because the production of more than one at a birth is itself a sort of superfoetation, one being added to another. Of these all that are large, as man, bring to birth the later embryo, if the second impregnation takes [10] place soon after the first, for such an event has been observed before now. The reason is that given above, for even in a single act of intercourse the semen discharged is more than enough for one embryo, and this being divided causes more than one child to be born, the one of which is later than the other. But when the embryo has already grown to some size and it so happens that copulation occurs again, superfoetation sometimes takes place, but rarely, since the uterus generally closes in women during the period of gestation. If this ever happens (for this also has [15] occurred) the mother cannot bring the second embryo to perfection, but it is cast out in a state like what are called abortions. For just as, in those animals that bear only one, all the secretion of the female is converted to the first formed embryo because of its size, so it is here also; the only difference is that in the former case this happens [20] at once, in the latter when the foetus has attained to some size, for then they are in the same state as those that bear only one. In like manner—since man naturally would produce many young, and since the size of the uterus and the quantity of the female secretion are both greater than is necessary for one embryo, only not so much so as to bring to birth a second—therefore women and mares are the only [25] animals which admit the male during gestation, the former for the reason stated, and mares both because of the barrenness of their nature and because their uterus is of superfluous size, too large for one but too small to allow a second embryo to be brought to perfection by superfoetation. And the mare is naturally inclined to sexual intercourse because she is in the same case as the barren among women; these latter are barren because they have no monthly discharge (which corresponds [30] to the act of intercourse in males) and mares have exceedingly little. And in all the vivipara the barren females are so inclined, because they resemble the males when the semen has collected in the testes but is not being got rid of. For the discharge of the menstrual fluids is in females an emission of semen, they being unconcocted [774a1] semen as has been said before. Hence it is that those women also who are incontinent in regard to such intercourse cease from their passion for it when they have borne many children, for, the seminal secretion being then drained off, they no [5] longer desire this intercourse. And among birds the hens are less disposed that way than the cocks, because the uterus of the hen-bird is up near the hypozoma; but with the cock-birds it is the other way, for their testes are drawn up within them so that, if any kind of such birds has much semen naturally, it is always in need of this [10] intercourse. In females then it encourages copulation to have the uterus low down, but in males to have the testes drawn up.

It has been now stated why superfoetation is not found in some animals at all, why it is found in others which sometimes bring the later embryos to birth and sometimes not, and why some such animals are inclined to sexual intercourse while [15] others are not.

Some of those animals in which superfoetation occurs can bring the embryos to birth even if a long time elapses between the two impregnations, if their kind is abundant in semen, if their body is not of a large size, and if they bear many young. For because they bear many their uterus is spacious, because they are abundant in [20] semen the generative discharge is copious, and because the body is not large but the discharge is in greater measure than is required for the nourishment wanted for the embryo, therefore they can not only form animals but also bring them to birth later [25] on. Further, the uterus in such animals does not close up because there is a quantity of the residual discharge left over. This has happened before now even in women, for in some of them the discharge continues during all the time of pregnancy. In women, however, this is contrary to nature, so that the embryo suffers, but in such [30] animals it is according to nature, for their body is so formed from the beginning, as with hares. For superfoetation occurs in these animals, since they are not large and they bear many young (for they have many toes and the many-toed animals bear many), and they abound in semen. This is shown by their hairiness, for the quantity [35] of their hair is excessive, these animals alone having hair under the feet and within the jaws. Now hairiness is a sign of abundance of residual matter, wherefore among [774b1] men also the hairy are given to sexual intercourse and have much semen rather than the smooth. In the hare it often happens that some of the embryos are imperfect while others of its young are produced perfect.

[5] 6 · Some of the vivipara produce their young imperfect, others perfect; the one-hoofed and cloven-footed perfect, most of the many-toed imperfect. The reason for this is that the one-hoofed produce one young one, and the cloven-footed either one or two generally speaking; now it is easy to bring the few to perfection. All the [10] many-toed animals that bear their young imperfect give birth to many. Hence, though they are able to nourish the embryos while newly formed, their bodies are unable to complete the process when the embryos have grown and acquired some size. So they produce them imperfect, like those animals which generate a grub; for some of them when born are scarcely brought into form at all, as the fox, bear, and [15] lion, and some of the rest in like manner; and nearly all of them are blind, as not only the animals mentioned but also the dog, wolf, and jackal. The pig alone produces both many and perfect young, and thus here alone we find any overlapping; it produces many as do the many-toed animals, but is cloven-footed or solid-hoofed (for there certainly are solid-hoofed swine). They bear, then, many [20] young because the nutriment which would otherwise go to increase their size is diverted to the generative secretion (for considered as a solid-hoofed animal the pig is not a large one), and also it is more often cloven-hoofed, striving as it were with the nature of the solid-hoofed animals. For this reason it produces sometimes only one, sometimes two, but generally many, and brings them to perfection before birth [25] because of the good condition of its body, being like a rich soil which has sufficient and abundant nutriment for plants.

The young of some birds also are hatched imperfect and blind; this applies to all small birds which lay many eggs, as crows, jays, sparrows, swallows, and to all those which lay few eggs without producing abundant nourishment along with the [30] young, as ring-doves, turtle-doves, and pigeons. Hence if the eyes of swallows while still young be put out they recover their sight again, for the birds are still developing, not yet developed, when the injury is inflicted, so that the eyes grow and sprout afresh. And in general the production of young before they are perfect is [35] owing to inability to continue nourishing them, and they are born imperfect because they are born too soon. This is plain also with seven-months children, for since they [775a1] are not perfected it often happens that even the passages, e.g. of the ears and nostrils, are not yet opened in some of them at birth, but only open later as they are growing, and many such infants survive.

In man males are more often born defective than females, but in the other animals this is not the case. The reason is that in man the male is much superior to [5] the female in natural heat, and so the male foetus moves about more than the female, and on account of moving is more liable to injury, for what is young is easily injured since it is weak. For this same reason also the female foetus is not perfected equally with the male in women (but they are so in the other animals, for in them [10] the female is not later in developing than the male). For while within the mother the female takes longer in developing, but after birth everything is perfected more quickly in females than in males; I mean, for instance, puberty, the prime of life, and old age. For females are weaker and colder in nature, and we must look upon the female character as being a sort of natural deficiency. Accordingly while it is [15] within the mother it develops slowly because of its coldness (for development is concoction, and it is heat that concocts, and what is hotter is easily concocted); but after birth it quickly arrives at maturity and old age on account of its weakness, for all inferior things come sooner to their perfection, and as this is true of works of art [20] so it is of what is formed by nature. For the reason just given also twins are less likely to survive in man if one be male and one female, but this is not at all so in the other animals; for in man it is contrary to nature that they should run an equal course, as their development does not take place in equal periods; but the male must [25] needs be too late or the female too early; in the other animals, however, it is not contrary to nature. A difference is also found between man and the other animals in respect of gestation, for animals are in better bodily condition most of the time, whereas in most women gestation is attended with discomfort. Their way of life is [30] partly responsible for this, for being sedentary they are full of more residual matter; among nations where the women live a laborious life gestation is not equally conspicuous and those who are accustomed to work bear children easily both there and elsewhere; for work consumes the residual matter, but those who are sedentary [35] have a great deal of it in them because not only is there no monthly discharge during pregnancy but also they do not work; therefore their travail is painful. But work exercises them so that they can hold their breath, upon which depends the ease or [775b1] difficulty of child-birth. These circumstances then, as we have said, contribute to cause the difference between women and the other animals in this state, but the most important thing is this: in some animals the discharge is small, and in some not [5] visible at all, but in women it is greater than in any other animal, so that when this discharge ceases owing to pregnancy they are troubled (for if they are not pregnant they are afflicted with ailments whenever the discharges do not occur); and they are more troubled as a rule at the beginning of pregnancy, for the embryo is able indeed [10] to stop the discharges but is too small at first to consume any quantity of the secretion: later on it takes up some of it and so alleviates the mother. In the other animals, on the contrary, the residual matter is but small and so corresponds with the growth of the foetus, and as the secretions which hinder nourishment are being [15] consumed by the foetus the mother is in better bodily condition than usual. The same holds good also with aquatic animals and birds. If it ever happens that the body of the mother is no longer in good condition when the foetus is now becoming [20] large, the reason is that its growth needs more nourishment than the residual matter supplies. (In some few women it happens that the body is in a better state during pregnancy; these are women in whose body the residual matter is small so that it is all used up along with the nourishment that goes to the foetus.)

[25] 7 · We must also speak of what is known as a ‘mole’, which occurs rarely in women but still is found sometimes during pregnancy. For they produce what is called a mole; it has happened before now to a woman, after she had had intercourse with her husband and supposed she had conceived, that at first the size of her belly [30] increased and everything else happened accordingly, but yet when the time for birth came on, she neither bore a child nor was her size reduced, but she continued thus for three or four years until dysentery came on, endangering her life, and she produced a lump of flesh which is called a mole. Moreover this condition may continue till old age and death. Such masses when expelled from the body become [35] so hard that they can hardly be cut through even by iron. Concerning the cause of this phenomenon we have spoken in the Problems; the same thing happens to the [776a1] embryo in the womb as to meats half cooked in roasting, and it is not due to heat, as some say, but rather to the weakness of the heat. (For their nature seems to be weak and unable to perfect or to put the last touches to the process of generation. Hence it [5] is that the mole remains in them till old age or at any rate for a long time, for in its nature it is neither perfect nor altogether a foreign body.) It is want of concoction that is the reason of its hardness, for half-cooking is also a sort of want of concoction.

A difficulty is raised as to why this does not occur in other animals, unless indeed it has entirely escaped observation. We must suppose the reason to be that [10] woman alone among animals is subject to troubles of the uterus, and alone has a superfluous amount of menstrual fluids and is unable to concoct them; when, then, the embryo has been formed of a liquid hard to concoct, then comes the so-called mole into being, and this happens naturally in women alone or at any rate more than in other animals.

[15] 8 · Milk is formed in the females of all internally viviparous animals, becoming useful for the time of birth. For nature has made it for the sake of the nourishment of animals after birth, so that it neither fails at this time at all nor yet is at all superfluous; this is just what we find happening, unless anything chance [20] contrary to nature. In the other animals the period of gestation does not vary, and so the milk is concocted in time to suit the moment, but in man, since there are several times of birth, it must be ready at the first of these; hence in women the milk is useless before the seventh month and only then becomes useful. That it is only [25] concocted at the last stages is what we should expect to happen also as being due to a necessary cause. For at first such residual matter when secreted is used up for the development of the embryo; now the nutritious part in all things is the sweetest and the most concocted, and thus when all such elements are removed what remains must become of necessity bitter and ill-flavoured. As the embryo is perfecting, the [30] residual matter left over increases in quantity because the part consumed by the embryo is less; it is also sweeter since the easily concocted part is less drawn away from it. For it is no longer expended on moulding the embryo but only on slightly increasing its growth, the embryo being now as it were stationary because it has reached perfection (for in a sense there is a perfection even of an embryo). [776b1] Therefore it comes forth from the mother and changes its mode of development, as now possessing what belongs to it; and no longer takes that which does not belong to it; and it is at this season that the milk becomes useful.

The milk collects in the upper part of the body and the breasts because of the original plan of the organism. For the part above the hypozoma is the part that [5] controls life, while that below is concerned with nourishment and residual matter, in order that all animals which move about may contain within themselves nourishment enough to make them independent when they move from one place to another. From this upper part also is produced the generative secretion for the reason mentioned in the opening of our discussion. But both the secretion of the male and [10] the menses of the female are of a sanguineous nature, and the first principle of this blood and of the blood-vessels is the heart, and the heart is in this part of the body. Therefore it is here that the change of such a secretion must first become plain. This is why the voice changes in both sexes when they begin to bear seed (for the first [15] principle of the voice resides there, and is itself changed when its moving cause changes). At the same time the parts about the breasts are raised visibly even in males but still more in females, for the region of the breasts becomes empty and spongy in them because so much material is drained away below. This is so also in [20] those animals which have the breasts low down.

This change in the voice and the parts about the breasts is plain even in other creatures to those who have experience of each kind of animal, but is most remarkable in man. The reason is that in man the production of secretion is greatest [25] in both sexes in proportion to their size as compared with other animals. [I mean menstruation in women and the emission of semen in men.]6 When, therefore, the embryo no longer takes up the secretion in question but yet prevents its being discharged from the mother, it is necessary that all the residual matter should [30] collect in all those empty parts which are set upon the same passages. And such is the position of the breasts in each kind of animals for both causes; it is so both for the sake of what is best and of necessity.

It is here, then, that the nourishment in animals is now formed and becomes concocted. As for the cause of concoction, we may take that already given, or we may take the opposite, for it is a reasonable view also that the embryo being larger [777a1] takes more nourishment, so that less is left over about this time, and the less is concocted more quickly.

That milk has the same nature as the secretion from which each animal is formed is plain, and has been stated previously. For the material which nourishes is [5] the same as that from which nature forms the animal in generation. Now this is the sanguineous liquid in the sanguinea, and milk is blood concocted (not corrupted; Empedocles either mistook the fact or made a bad metaphor when he wrote that [10] milk ‘on the tenth day of the eighth month comes into being, a white pus’,7 for putrefaction and concoction are opposite things, and pus is a kind of putrefaction but milk is concocted). While women are suckling children menstruation does not occur according to nature, nor do they conceive; if they do conceive, the milk dries [15] up. This is because the nature of the milk and of the menses is the same, and nature cannot be so productive as to supply both at once; if the secretion is diverted in the one direction it must needs cease in the other, unless some violence is done contrary to the general rule. But this is as much as to say that it is contrary to nature, for in [20] all cases where it is not impossible for things to be otherwise than they generally are but where they may so happen, still what is the general rule is what is according to nature.

The time also at which the young animal is born has been well arranged. For when the nourishment coming through the umbilical cord is no longer sufficient for the foetus because of its size, then at the same time the milk becomes useful for the coming nourishment and the blood-vessels round which the so-called umbilical cord [25] lies as a coat collapse as the nourishment is no longer passing through it; for these reasons it is at that time also that the young animal enters into the world.

9 · The natural birth of all animals is head-foremost, because the parts above the umbilical cord are larger than those below. The body then, being suspended [30] from the cord as in a balance, inclines towards the heavy end, and the larger parts are the heavier.

10 · The period of gestation is, as a matter of fact, determined generally in each animal in proportion to the length of its life. For it is reasonable that the development of the long-lived animals should take a longer time. Yet this is not the cause of it, but the correspondence holds for the most part; for though the larger and [777b1] more perfect sanguinea do live a long time, yet the larger are not all longer-lived. Man lives a longer time than any animal of which we have any credible experience except the elephant, and yet the human kind is smaller than that of the bushy-tailed [5] animals and many others. The real cause of long life in any animal is its being tempered in a manner resembling the environing air, along with certain other circumstances of its nature, of which we will speak later; but the cause of the time of gestation is the size of the offspring. For it is not easy for large masses to arrive at [10] their perfection in a small time, whether they be animals or, one may say, anything else whatever. That is why horses and animals akin to them, though living a shorter time than man, yet carry their young longer; for the time in the former is a year, but in the latter ten months at the outside. For the same reason also the time is long in [15] elephants; they carry their young two years on account of their excessive size.

We find, as we might expect, that in all animals the time of gestation and development and the length of life aim naturally at being measured periods. By a period I mean, e.g., a day and night, a month, a year, and the times measured by these, and also the periods of the moon, that is to say, the full moon and her [20] disappearance and the halves of the times between these, for it is by these that the moon’s orbit fits in with that of the sun, the month being a period common to both.

The moon is a first principle because of its connexion with the sun and its participation in its light, being as it were a second smaller sun, and therefore she [25] contributes to all generation and development. For heat and cold varying within certain limits make things to come into being and after this to perish, and it is the motions of the sun and moon that fix the limit both of the beginning and of the end [30] of these processes. Just as we see the sea and all bodies of water settling and changing according to the movement or rest of the winds, and the air and winds again according to the course of the sun and moon, so also the things which grow out of these or are in these must follow suit. For it is reasonable that the periods of the [778a1] less important should follow those of the more important. For in a sense a wind, too, has a life and birth and death.

As for the revolutions of the sun and moon, they may perhaps depend on other principles.

It is the aim, then, of nature to count the coming into being and the end of [5] animals by the numbers of these higher periods, but nature does not bring this to pass accurately because matter cannot be easily brought under rule and because there are many principles which hinder generation and decay from being according to nature, and often cause things to fall out contrary to nature.

We have now spoken of the nourishment of animals within the mother and of [10] their birth into the world, both of each kind separately and of all in common.

BOOK V

1 · We must now investigate the qualities by which the parts of animals differ. I mean such qualities of the parts as blueness and blackness of the eyes, height and depth of pitch in the voice, and differences in colour and in hair or [20] feathers. Some such qualities are found to characterize the whole of a kind of animals sometimes, while in other kinds they occur at random, as is especially the case in man. Further, in connexion with the changes in the time of life, all animals are alike in some points, but are opposed in others as in the case of the voice and the colour of the hair, for some do not grow grey visibly in old age, while man is subject [25] to this more than any other animal. And some of these affections appear immediately after birth, while others become plain as age advances or in old age.

Now we must no longer suppose that the cause of these and all such phenomena is the same. For whenever things are not the product of nature in [30] general nor yet characteristic of each separate kind, then none of these things is such as it is or is so developed for the sake of anything. The eye for instance exists for a final cause, but it is not blue for a final cause unless this condition be characteristic of the kind of animal. In fact in some cases this condition has no connexion with the account of the animal’s essence, but we must refer the causes to [778b1] the material and the motive principle on the view that these things come into being by necessity. For, as was said originally in the outset of our discussion, when we are dealing with definite and ordered products of nature, we must not say that each is of a certain quality because it becomes so, rather that they become so and so because [5] they are so and so, for the process of becoming attends upon being and is for the sake of being, not vice versa.

Past students of nature, however, took the opposite view. The reason for this is that they did not see that the causes were numerous, but only saw the material and efficient and did not distinguish even these, while they made no inquiry at all into [10] the formal and final causes.

Everything then exists for a final cause, and all those things which are included in the definition of each animal, or which either are for the sake of some end or are ends in themselves, come into being both through this cause and the rest. But when we come to those things which come into being without falling under the heads just [15] mentioned, their cause must be sought in the movement or process of coming into being, on the view that the differences which mark them arise in the actual formation of the animal. An eye, for instance, the animal must have of necessity (for an animal is supposed to be of such a sort), but it will have an eye of a particular kind of necessity in another sense, not the sense mentioned just above, because it is its nature to act or be acted on in this or that way.

[20] These distinctions being drawn let us speak of what comes next in order. As soon then as the offspring of all animals are born, especially those born imperfect, they are in the habit of sleeping, because they continue sleeping also within the mother when they first acquire sensation. But there is a difficulty about the earliest period of development, whether the state of wakefulness exists in animals first, or [25] that of sleep. Since they plainly wake up more as they grow older, it is reasonable to suppose that the opposite state, that of sleep, exists in the first stages of development. Moreover the change from not being to being must pass through the intermediate condition, and sleep seems to be in its nature such a condition, being as [30] it were a boundary between living and not living, and the sleeper being neither altogether non-existent nor yet existent. For life most of all appertains to wakefulness, on account of sensation. But on the other hand, if it is necessary that the animal should have sensation and if it is then first an animal when it has acquired sensation, we ought to consider the original condition to be not sleep but only something resembling sleep, such a condition as we find also in plants, for indeed at [779a1] this time animals do actually live the life of a plant. But it is impossible that plants should sleep, for there is no sleep which cannot be broken, and the condition in plants which is analogous to sleep cannot be broken.

It is necessary then for the animal to sleep most of the time because the growth [5] and the weight lie on the upper part of the body (and we have stated elsewhere that such is the cause of sleep). But nevertheless they are found to wake even in the womb (this is clear in dissections and in the ovipara), and then they immediately fall into a sleep again. This is why after birth also they spend most of their time in [10] sleep.

When awake infants do not laugh, but while asleep they both laugh and cry. For animals have sensations even while asleep, not only what are called dreams but also others besides dreams, as those persons who arise while sleeping and do many [15] things without dreaming. For there are some who get up while sleeping and walk about seeing just like those who are awake; these have perception of what is happening, and though they are not awake, yet this perception is not like a dream. So infants presumably have sense-perception and live in their sleep owing to [20] previous habit, being as it were without knowledge of the waking state. As time goes on and their growth is transferred to the lower part of the body, they now wake up more and spend most of their time in that condition. Children continue asleep at first more than other animals, for they are born in a more imperfect condition than other animals that are produced in a perfect state, and their growth has taken place [25] more in the upper part of the body.

The eyes of all children are bluish immediately after birth; later on they change to the colour which is to be theirs permanently. But in the case of other animals this is not visible. The reason for this is that the eyes of other animals are more apt to have only one colour; e.g. cattle are dark-eyed, the eye of all sheep is [30] pale, of others again the whole kind is blue or grey-eyed, and some are yellow as the majority of goats themselves, whereas the eyes of men happen to be of many colours, for they are blue or grey or dark in some cases and yellow in others. Hence, [779b1] as the individuals in other kinds of animals do not differ from one another in the colour, so neither do they differ from themselves, for they are not of a nature to have more than one colour. Of the other animals the horse has the greatest variety of colour in the eye, for some of them actually have eyes of different colour; this [5] phenomenon is not to be seen in any of the other animals, except in some men.

Why then is it that there is no visible change in the other animals if we compare their condition when newly born with their condition at a more advanced age, but that there is such a change in children? We must consider just this to be a sufficient cause, that the part concerned has only one colour in the former but several colours in the latter. And the reason why the eyes of infants are bluish and [10] have no other colour is that the parts are weaker in the newly born and blueness is a sort of weakness.

We must also gain a general notion about the difference in eyes, for what reason some are blue, some grey, some yellow and some dark. To suppose that the [15] blue are fiery, as Empedocles says, while the dark have more water than fire in them, and that this is why the former, the blue, have not keen sight by day, viz. owing to deficiency of water in their composition, and the latter are in like condition by night, viz. owing to deficiency of fire—this is not well said if indeed we are to assume sight to be connected with water, not fire, in all cases. Moreover it is [20] possible to render another account of the cause of the colours, but if indeed the fact is as was stated before in the treatise on the senses, and still earlier than that in the investigations concerning soul 1—if this sense organ is composed of water and if we were right in saying for what reason it is composed of water and not of air or [25] fire—then we must assume the water to be the cause of the colours mentioned. For some eyes have too much liquid to be adapted to the movement, others have too little, others the due amount. Those eyes therefore in which there is much liquid are [30] dark because much liquid is not transparent, those which have little are blue; (so we find in the sea that the transparent part of it appears light blue, the less transparent watery, and the unfathomable water is dark or deep-blue on account of its depth). When we come to the eyes between these, they differ only in degree.

We must suppose the same cause also to be responsible for the fact that blue [780a1] eyes are not keen-sighted by day nor dark eyes by night. Blue eyes, because there is little liquid in them, are too much moved by the light and by visible objects in respect of their liquidity as well as their transparency, but sight is the movement of this part in so far as it is transparent, not in so far as it is liquid. Dark eyes are less [5] moved because of the quantity of liquid in them. For the nocturnal light is weak; at the same time also liquid is in general hard to move in the night. But if the eye is to see, it must neither not be moved at all nor yet more than in so far as it is transparent, for the stronger movement drives out the weaker. Hence it is that on [10] changing from strong colours, or on going out of the sun into the dark, men cannot see, for the motion already existing in the eye, being strong, stops that from outside, and in general neither a strong nor a weak sight can see bright things because the liquid is acted upon and moved too much.

The same thing is shown also by the morbid affections of each kind of sight. [15] Cataract attacks the blue-eyed more, but what is called night-blindness the dark-eyed. Now cataract is a sort of dryness of the eyes and therefore it is found more in the aged, for this part also like the rest of the body gets dry towards old age; [20] but night-blindness is an excess of liquidity and so is found more in the younger, for their brain is more liquid.

The sight of the eye which is intermediate between too much and too little liquid is the best, for it has neither too little so as to be disturbed and hinder the movement of the colours, nor too much so as to cause difficulty of movement.

[25] Not only the above-mentioned facts are causes of seeing keenly or the reverse, but also the nature of the skin upon what is called the pupil. This ought to be transparent, and it is necessary that the transparent should be thin and white and even, thin that the movement coming from without may pass straight through it, [30] even that it may not cast a shadow by wrinkling (for this also is a reason why old men have not keen sight, the skin of the eye like the rest of the skin wrinkling and becoming thicker in old age), and white because black is not transparent, for that is just what is meant by ‘black’, what is not shone through, and that is why lanterns [780b1] cannot give light if they be made of black skin. It is for these reasons then that the sight is not keen in old age nor in the diseases in question, but it is because of the small amount of liquid that the eyes of children appear blue at first.

And the reason why men especially and horses occasionally have eyes of different colours is the same as the reason why man alone grows grey and the horse is the only other animal whose hairs whiten visibly in old age. For greyness is a [5] weakness of the fluid in the brain and a lack of concoction, and so is blueness of the eyes; excess of thinness or of thickness produces the same effect, according as this liquidity is too little or too much. Whenever then nature cannot make the eyes correspond exactly, either by concocting or by not concocting the liquid in both, but [10] concocts the one and not the other, then the result is differently coloured eyes.

The cause of some animals being keen-sighted and others not so is not simple but double. For things are called keen in two ways (and this is the case in like manner with hearing and smelling). In one sense keen sight means the power of [15] seeing at a distance, in another it means the power of distinguishing as accurately as possible the objects seen. These two faculties do not occur together in the same individual. For the same person, if he shade his eyes with his hand or look through a tube, does not distinguish the differences of colour either more or less in any way, [20] but he will see further; in fact, men in pits or wells sometimes see the stars. Therefore if any animal’s brows project far over the eye, but if the liquid in the pupil is not pure nor suited to the movement coming from external objects and if the skin over the surface is not thin, this animal will not distinguish accurately the [25] differences of the colours but it will be able to see from a long distance (just as it can from a short one)2 better than those in which the liquid and the covering membrane are pure but which have no brows projecting over the eyes. For the cause of seeing keenly in the sense of distinguishing the differences is in the eye itself; as on a clean [30] garment even small stains are visible, so also in a pure sight even small movements are plain and cause sensation. But it is the position of the eyes that is the cause of seeing things far off and of the movements coming to the eyes from distant objects. [35] For animals with prominent eyes do not see well at a distance, whereas those which have their eyes lying deep in the head can see things at a distance because the [781a1] movement is not dispersed in space but comes straight to the eye. For it makes no difference whether we say, as some do, that seeing is caused by the sight going forth from the eye—on that view, if there is nothing projecting over the eyes, the sight must be scattered and so less of it will fall on the objects of vision and things at a [5] distance will not be seen so well—or whether we say that seeing is due to the movement coming from the objects; for the sight also must see, in a manner resembling the movement. Things at a distance, then, would be seen best if there were, so to say, a continuous tube straight from the sight to its object, for the movement from the object would not then be dissipated; but, if that is impossible, [10] still the further the tube extends the more accurately must distant objects be seen.

Let these, then, be given as the causes of the difference in eyes.

2 · It is the same also with hearing and smell; to hear and smell accurately mean in one sense to perceive as precisely as possible all the distinctions of the [15] objects of perception, in another sense to hear and smell far off. As with sight, so here the sense-organ is the cause of distinguishing well the distinctions, if both that [20] organ itself and the membrane round it be pure. For the passages of all the sense-organs, as has been said in the treatise on sensation, run to the heart, or to its analogue in creatures that have no heart. The passage of the hearing, then, since this sense-organ is of air, ends at the place where the innate breath causes in some [25] animals the pulsation and in others respiration;3 and that is why we are able to understand what is said and repeat what we have heard, for as4 was the movement which entered through the sense-organ, such again is the movement which is caused by means of the voice, being as it were of one and the same stamp, so that a man can [30] say what he has heard. And we hear less well during a yawn or expiration than during inspiration, because the starting-point of the sense-organ of hearing is set upon the part concerned with breathing and is shaken and moved as the organ moves the breath, for while setting the breath in motion it is moved itself. The same thing happens in wet weather or a damp climate.5 … And the ears seemed to be [781b1] filled with air because their starting-point is near the region of breathing.6

Accuracy then in judging the differences of sounds and smells depends on the purity of the sense-organ and of the membrane lying upon its surface, for then all [5] the movements become clear in such cases, as in the case of sight.7 Perception and non-perception at a distance also depend on the same things as with sight. For those animals can perceive at a distance which have channels, so to say, running through the parts concerned and projecting far in front of the sense-organs. Therefore all [10] animals whose nostrils are long, as the Laconian hounds, are keen-scented, for the sense-organ being above them, the movements from a distance are not dissipated but go straight to the mark, just as with those who shadow the eyes with the hand.

Similar is the case of animals whose ears are long and project far like the eaves [15] of a house, as in some quadrupeds, with the internal spiral passage long; these also catch the movement from afar and pass it on to the sense-organ.

In respect of sense-perception at a distance, man is, one may say, the worst of all animals in proportion to his size, but in respect of judging the differences he is [20] the best of all. The reason is that the sense-organ is pure and least earthy and material, and he is by nature the thinnest-skinned of all animals for his size.

The workmanship of nature is admirable also in the seal, for though a viviparous quadruped it has no ears but only passages for hearing. This is because [25] its life is passed in the water; now the ear is a part added to the passages to preserve the movement of the air at a distance; therefore an ear is no use to it but would even bring about the contrary result by receiving a mass of water into itself.

We have thus spoken of sight, hearing, and smell.

[30] 3 · As for hair, men differ in this themselves at different ages, and also from all other kinds of animals that have hair. These are almost all which are internally viviparous, for even when the covering of such animals is spiny it must be considered as a kind of hair, as in the hedgehog and any other such animal among the vivipara. Hairs differ in respect of hardness and softness, length and shortness, straightness [782a1] and curliness, quantity and scantiness, and in addition to these qualities, in their colours, whiteness and blackness and the intermediate shades. They differ also in [5] some of these respects according to age, as they are young or growing old. This is especially plain in man; the hair gets thicker as time goes on, and some go bald on the front of the head; children indeed do not go bald, nor do women, but men do so [10] by the time their age is advancing. Human beings also go grey on the head as they grow old, but this is not visible in practically any other animal, though more so in the horse than others. Men go bald on the front of the head, but turn grey first [15] on the temples; no one goes bald on these or on the back of the head. Some such affections occur in a corresponding manner also in animals which have not hair but something analogous to it, as the feathers of birds and scales in the class of fish.

For what purpose nature has made hair for animals has been previously stated [20] in the work dealing with the causes of the parts of animals; it is the business of the present inquiry to show under what circumstances and for what necessary causes each particular kind of hair occurs. The principal cause then of thickness and thinness is the skin, for this is thick in some animals and thin in others, rare in some [25] and dense in others. The different quality of the included moisture is also a helping cause, for in some animals this is greasy and in others watery. For generally speaking the skin is of an earthy nature; being on the surface of the body it becomes [30] solid and earthy as the moisture evaporates. Now the hairs on their analogue are not formed out of the flesh but out of the skin, the moisture evaporating and exhaling in them, and therefore thick hairs arise from a thick skin and thin from a thin. If then the skin is rarer and thicker, the hairs are thick because of the quantity of earthy matter and the size of the pores, but if it is denser they are thin because of the [782b1] narrowness of the pores. Further, if the moisture be watery it dries up quickly and the hairs do not gain in size, but if it be greasy the opposite happens, for the greasy is not easily dried up. Therefore the thicker-skinned animals are as a general rule [5] thicker-haired; however, the thickest-skinned are not more so than other thick-skinned ones, for the causes mentioned, as is shown by the class of swine compared to that of oxen and to the elephant and many others. And for the same reason also the hairs of the head in man are thickest, for this part of his skin is thickest and lies [10] over most moisture and besides is very rare.

The cause of the hairs being long depends on the evaporating moisture not being easily dried. Of this there are two causes, quantity and quality; if the liquid is much it does not dry up easily nor if it is greasy. And for this reason the hairs of the [15] head are longest in man, for the brain, being fluid and cold, supplies great abundance of moisture.

The hairs become straight or curly on account of the vapour arising in them. If it be smoke-like, it is hot and dry and so makes the hair curly, for it is twisted as [20] being carried with a double motion, the earthy part tending downwards and the hot upwards. Thus, being easily bent, it is twisted owing to its weakness, and this is what is meant by curliness in hair. It is possible then that this is the cause, but it is also possible that, owing to its having but little moisture and much earthy matter in it, it [25] is dried by the surrounding air and so coiled up together. For what is straight becomes bent, if the moisture in it is evaporated, and runs together as a hair does when burning upon the fire; curliness will then be a contraction owing to deficiency of moisture caused by the heat of the environment. A sign of this is the fact that [30] curly hair is harder than straight, for the dry is hard. And animals with much moisture are straight-haired; for in these hairs the moisture advances as a stream, not in drops. For this reason the Scythians on the Black Sea and the Thracians are straight-haired, for both they themselves and the environing air are moist, whereas [783a1] the Aethiopians and men in hot countries are curly-haired, for their brains and the surrounding air are dry.

Some, however, of the thick-skinned animals are fine-haired for the cause previously stated, for the finer the pores are the finer must the hairs be. Hence the [5] class of sheep have such hairs (for wool is a multitude of hairs).

There are some animals whose hair is soft and yet less fine, as is the case with the class of hares compared with that of sheep; in such animals the hair is on the surface of the skin, and so is not long but in much the same state as the scrapings [10] from linen, for these also are not long but are soft and do not admit of weaving.

The condition of sheep in cold climates is opposite to that of man; the hair of the Scythians is soft but that of Sarmatian sheep is hard. The reason for this is the [15] same as it is also in all wild animals. The cold hardens and solidifies them by drying them, for as the heat is pressed out the moisture evaporates, and both hair and skin become earthy and hard. In wild animals then their open-air life is the cause, in the others the nature of their location. A proof of this is also what happens in the [20] sea-urchins which are used as a remedy in stranguries. For these, too, though small themselves, have large and hard spines because the sea in which they live is cold on account of its depth (for they are found in sixty fathoms and even more). The spines [25] are large because the growth of the body is diverted to them, since having little heat in them they do not concoct their nutriment and so have much residual matter and it is from this that spines, hairs, and such things are formed; they are hard and petrified through the congealing effect of the cold. In the same way also plants are [30] found to be harder, more earthy, and stony, if the region in which they grow looks to the north than if it looks to the south, and those in windy places than those in sheltered, for they are all more chilled and their moisture evaporates.

Hardening, then, comes of both heat and cold, for both cause the moisture to [35] evaporate, heat per se and cold per accidens (since the moisture goes out of things along with the heat, there being no moisture without heat), but whereas cold not [783b1] only hardens but also condenses, heat makes a substance rarer.

For the same reason, as animals grow older, the hairs become harder in those which have hairs, and the feathers and scales in the feathered and scaly kinds. For [5] their skins become harder and thicker as they get older, for they are dried up, and old age, as the word implies,8 is earthy because the heat fails and the moisture along with it.

Men go bald visibly more than any other animal, but still such a state is something general, for among plants also some are evergreens while others are [10] deciduous, and birds which hibernate shed their feathers. Similar to this is the condition of baldness in those human beings to whom it is incident. For leaves are shed by all plants, from one part of the plant at a time, and so are feathers and hairs [15] by those animals that have them; it is when they are all shed together that the condition is described by the terms mentioned, for it is called ‘going bald’ and ‘the fall of the leaf’ and ‘moulting’. The cause of the condition is deficiency of hot moisture, such moisture being especially the greasy and hence greasy plants are more evergreen. (However, we must elsewhere state the cause of this—for other [20] causes also contribute to it.) It is in winter that this happens to plants (for the change from summer to winter is more important to them than the time of life), and to those animals which hibernate (for these, too, are by nature less hot and moist than man); in men it is the seasons of life that correspond to summer and winter. [25] Hence no one goes bald before the time of sexual intercourse, and at that time it is in those naturally inclined to such intercourse that baldness appears, for the brain is naturally the coldest part of the body and sexual intercourse makes men cold, being a loss of pure natural heat. Thus we should expect the brain to feel the effect of it [30] first, for a little cause turns the scale where the thing concerned is weak and in poor condition. Thus if we reckon up these points, that the brain itself has but little heat, and further that the skin round it must needs have still less, and again that the hair must have still less than the skin inasmuch as it is the furthest removed from the brain, we should reasonably expect baldness to come about this age upon those who [35] have much semen. And it is for the same reason that the front part of the head alone goes bald in man and that he is the only animal to do so; the front part goes bald [784a1] because the brain is there, and man is the only animal to go bald because his brain is much the largest and the moistest. Women do not go bald because their nature is like that of children, both alike being incapable of producing seminal secretion. [5] Eunuchs do not become bald, because they change into the female condition. And as to the hair that comes later in life, eunuchs either do not grow it at all, or lose it if they happen to have it, with the exception of the pubic hair; for women also grow that though they have not the other, and this mutilation is a change from the male to [10] the female condition.

The reason why the hair does not grow again in cases of baldness, although both hibernating animals recover their feathers or hair and trees that have shed their leaves grow leaves again, is this. The seasons of the year are the turning-points of their lives so that when these seasons change they change with them by growing [15] and losing feathers, hairs, or leaves respectively. But the winter and summer, spring and autumn of man are defined by his age, so that, since his ages do not return, neither do the conditions caused by them return, although the cause is similar. [20]

We have now spoken pretty much of all the other conditions of hair.

4 · But as to their colour, it is the nature of the skin that is the cause of this in other animals (and also of their being unicoloured or varicoloured); but in man it is not the cause, except of the hair going grey through disease (not through old age), [25] for in what is called leprosy the hairs become white; on the contrary, if the hairs are white because of old age, the whiteness does not derive from the skin. The reason is that the hairs grow out of skin; if, then, the skin is diseased and white the hair [30] becomes diseased with it, and the disease of hair is greyness. But the greyness of hair which is due to age results from weakness and deficiency of heat. For as the body declines in vigour we tend to be cold at every time of life, and especially in old age,9 this age being cold and dry. We must remember that the nutriment coming to each part of the body is concocted by the heat appropriate to the part; if the heat is [784b1] inadequate the part perishes, and deformity or disease results. (We shall speak more in detail of causes in the treatise on growth and nutrition.) Whenever, then, the hair in man has naturally little heat and too much moisture enters it, its own [5] proper heat is unable to concoct the moisture and so it is decayed by the heat in the environing air. All decay is caused by heat—not the innate heat, as has been stated elsewhere. And as there is a decay of water, of earth, and all such material bodies, so [10] there is also of the earthy vapour, for instance what is called mould (for mould is a decay of earthy vapour). Thus also the liquid nutriment in the hair decays because it is not concocted, and what is called greyness results. It is white because mould also, practically alone among decayed things, is white. The reason for this is that it has [15] much air in it, all earthy vapour being equivalent to thick air. For mould is, as it were, the antithesis of hoar-frost; if the ascending vapour be frozen it becomes hoar-frost, if it be decayed, mould. Hence both are on the surface of things, for vapour is superficial. And so the comic poets make a good metaphor in jest when [20] they call grey hairs ‘mould of old age’ and ‘hoar-frost’. For the one is generically the same as greyness, the other specifically; hoar-frost generically (for both are a vapour), mould specifically (for both are a form of decay). A proof that this is so is this: grey hairs have often grown on men in consequence of disease, and later on [25] dark hairs instead of them after restoration to health. The reason is that in sickness the whole body is deficient in natural heat and so the parts besides, even the very small ones, participate in this weakness; and again, much residual matter is formed in the body and all its parts, so that the incapacity in the flesh to concoct the [30] nutriment causes the grey hairs. But when men have recovered health and strength again they change, becoming as it were young again instead of old; in consequence the states change also. Indeed, we may rightly call disease an acquired old age, old age a natural disease; at any rate, some diseases produce the same effects as old age.

Men go grey on the temples first, because the back of the head is empty of [785a1] moisture owing to its containing no brain, and the fontanelle has a great deal of moisture, a large quantity not being liable to decay; the hair on the temples, however, has neither so little that it can concoct it nor so much that it cannot decay, [5] for this region of the head being between the two extremes is exempt from both states. The cause of greyness in man has now been stated.

5 · The reason why this change does not take place visibly on account of age in other animals is the same as that already given in the case of baldness; their brain is small and less fluid than in man, so that the heat required for concoction does not [10] altogether fail. Among them it is most clear in horses of all animals that we know, because the bone about the brain is thinner in them than in others in proportion to their size. A sign of this is that a blow on this spot is fatal to them—thus Homer also [15] has said: ‘where the first hairs grow on the skull of horses, and a wound is most fatal’.10 As then the moisture easily flows to these hairs because of the thinness of the bone, whilst the heat fails on account of age, they go grey. The reddish hairs go grey sooner than the black, redness also being a sort of weakness of hair and all [20] weak things ageing sooner.

It is said that cranes become darker as they grow old. The reason for this would be that their feathers are naturally finer than others and as they grow old the moisture in the feathers is too much to decay easily.

Greyness comes about by some sort of decay, and is not, as some think, a [25] withering. A sign is the fact that hair protected by hats or other coverings goes grey sooner (for the winds prevent decay and the protection keeps off the winds), and the fact that it is aided by anointing with a mixture of oil and water. For, though water [30] cools things, the oil mingled with it prevents the hair from drying quickly, water being easily dried up. That the process is not a withering, that the hair does not whiten as grass does by withering, is shown by the fact that some hairs grow grey from the first, whereas nothing springs up in a withered state. Many hairs also whiten at the tip, for there is least heat in the extremities and thinnest parts.

When the hairs of other animals are white, this is caused by nature, not by any [785b1] affection. The cause of the colours in other animals is the skin; if they are white, the skin is white, if they are dark it is dark, if they are piebald in consequence of a mixture of the hairs, it is found to be white in the one part and dark in the other. But [5] in man the skin is in no way the cause, for even white-skinned men have very dark hair. The reason is that man has the thinnest skin of all animals in proportion to his size and therefore it has not strength to change the hairs; on the contrary the skin itself changes its colour through its weakness and is darkened by sun and wind, [10] while the hairs do not change along with it at all. But in the other animals the skin, owing to its thickness, has the influence belonging to the soil in which a thing grows: that is why the hairs change according to the skin but the skin does not change at all in consequence of the winds and the sun. [15]

6 · Of animals some are uni-coloured (I mean by this term those of which the kind as a whole has one colour, as all lions are tawny; and this condition exists also in birds, fish, and the other classes of animals alike); others though many-coloured are yet whole-coloured (I mean those whose body as a whole has the same colour, as [20] a bull is white as a whole or dark as a whole); others are vari-coloured. This last term is used in two ways; sometimes the whole kind is vari-coloured, as leopards and peacocks, and some fish, e.g. the so-called ‘thrattai’; sometimes the kind as a whole is not so, but such individuals are found in it, as with cattle and goats and, among [25] birds, pigeons; the same applies also to other kinds of birds. The whole-coloured change much more than the uniformly coloured, both into the simple colour of another individual of the same kind (as dark changing into white and vice versa) and into both colours mingled. This is because it is a natural characteristic of the [30] kind as a whole not to have one colour only, the kind being easily moved in both directions so that the colours both change more into one another and are more varied. The opposite holds with the uniformly coloured; they do not change except by an affection, and that rarely; but still they do so change, for before now white [35] individuals have been observed among partridges, ravens, sparrows, and bears. This happens when the course of development is perverted, for what is small is easily [786a1] spoilt and easily moved, and what is developing is small, the beginning of all such things being on a small scale.

Change is especially found in those animals of which by nature the individual is whole-coloured but the kind many-coloured. This is owing to the water which [5] they drink, for hot waters make the hair white, cold makes it dark, an effect found also in plants. The reason is that the hot have more air than water in them, and the air shining through causes whiteness, as also in froth. As, then, skins which are white by reason of some affection differ from those white by nature, so also in the [10] hair the whiteness due to disease or age differs from that due to nature in that the cause is different; the latter are whitened by the natural heat, the former by the external heat. Whiteness is caused in all things by the vaporous air imprisoned in them. Hence also in all animals not uniformly coloured all the part under the belly is [15] whiter. For practically all white animals are both hotter and better flavoured for the same reason; the concoction of their nutriment makes them well-flavoured, and heat causes the concoction. The same cause holds for those animals which are uniformly-coloured, but either dark or white; heat and cold are the causes of the [20] nature of the skin and hair, each of the parts having its own special heat.

The tongue also varies in the simply coloured as compared with the varicoloured animals, and again in the simply coloured which differ from one another, as white and dark. The reason is that assigned before, that the skins of the vari-coloured are vari-coloured, and the skins of the white-haired and dark-haired [25] are white and dark in each case. Now we must conceive of the tongue as one of the external parts, not taking into account the fact that it is covered by the mouth but looking on it as we do on the hand or foot; thus since the skin of the vari-coloured animals is not uniformly coloured, this is the cause of the skin on the tongue being also vari-coloured.

[30] Some birds and some wild quadrupeds change their colour according to the seasons of the year. The reason is that, as men change according to their age, so the same thing happens to them according to the season; for this makes a greater difference to them than the change of age.

The more omnivorous animals are more vari-coloured to speak generally, and [786b1] this is what might be expected; thus bees are more uniformly coloured than hornets and wasps. For if the food is responsible for the change, we should expect varied food to increase the variety in the movements and in the residual matter of the food, from which come into being hairs and feathers and skins.

[5] So much for colours and hairs.

7 · As to the voice, it is deep in some animals, high in others, in others again well-pitched and in due proportion between both extremes. Again, in some it is loud, in others small, and it differs in smoothness and roughness, flexibility and [10] inflexibility. We must inquire then into the causes of each of these distinctions.

We must suppose then that the same cause is responsible for high and deep voices as for the change which they undergo in passing from youth to age. The voice is higher in all other animals when younger, but in cattle that of calves is deeper. We [15] find the same thing also in the male and female sexes; in the other kinds of animals the voice of the female is higher than that of the male (this being especially plain in man, for nature has given this faculty to him in the highest degree because he alone [20] of animals makes use of speech and the voice is the material of speech), but in cattle the opposite obtains, for the voice of cows is deeper than that of bulls.

Now the purpose for which animals have a voice, and what is voice and sound generally, has been stated partly in the treatise on sensation, partly in that on the [25] soul. But since lowness of voice depends on the movement being slow and its highness on its being quick, there is a difficulty in knowing whether it is that which moves or that which is moved that is the cause of the slowness or quickness. For some say that what is much is moved slowly, what is little quickly, and that this is the cause of some animals having a deep and others a high voice. Up to a certain [30] point this is well said (for it seems to be rightly said in a general way that the depth depends on a certain amount of the air put in motion), but not altogether, for if this were true it would not be easy to speak both soft and deep at once, nor again both loud and high. Again, the depth seems to belong to the nobler nature, and in songs the deep note is better than the high-pitched ones, the better lying in superiority, [787a1] and depth of tone being a sort of superiority. But then depth and height in the voice are different from loudness and softness, and some high-voiced animals are loud-voiced, and in like manner some soft-voiced ones are deep-voiced, and the same applies to the tones lying between these extremes. And by what else can we [5] define these (I mean loudness and softness of voice) except by the large and small amount of the air put in motion? If then height and depth are to be decided in accordance with the distinction postulated, the result will be that the same animals will be deep- and loud-voiced, and the same will be high- and soft-voiced; but this is [10] false.

The reason of the difficulty is that the words ‘great’ and ‘small’, ‘much’ and ‘little’ are used sometimes absolutely, sometimes relatively to one another. Whether an animal has a great voice depends on the air which is moved being much absolutely, whether it has a small voice depends on its being little absolutely; but whether they have a deep or high voice depends on their being thus differentiated in [15] relation to one another. For if that which is moved surpasses the strength of that which moves it, what is moved must go slowly; if the opposite, quickly. The strong, then, on account of their strength, sometimes move much air and make the movement slow, sometimes, having complete command over it, make the movement swift. On the same principle the weak either move too much air for their strength [20] and so make the movement slow, or if they make it swift move but little because of their weakness.

These, then, are the reasons of these contrarieties, that neither are all young animals high-voiced nor all deep-voiced, nor are all the older, nor yet are the two [25] sexes thus opposed, and again that not only the sick speak in a high voice but also those in good bodily condition, and, further, that as men verge on old age they become higher-voiced, though this age is opposite to that of youth.

Most young animals, then, and most females set but little air in motion because of their want of power, and are consequently high-voiced, for a little air is [30] carried along quickly, and in the voice what is quick is high. But in calves and cows, in the one case because of their age, in the other because of their female nature, the part by which they set the air in motion is not strong; at the same time they set a [787b1] great quantity in motion and so are deep-voiced; for that which is borne along slowly is heavy, and much air is borne along slowly. And these animals set much in movement whereas the others set but little, because the vessel through which the breath is first borne has in them a large opening and necessarily sets much air in [5] motion, whereas in the rest the air is better dispensed. As their age advances this part which moves the air gains more strength in each animal, so that they change into the opposite condition, the high-voiced becoming deeper-voiced than they were, and the deep-voiced higher-voiced, which is why bulls have a higher voice than [10] calves and cows. Now the strength of all animals is in their sinews, and so those in the prime of life are stronger, the young being weaker in the joints and sinews; moreover, in the young they are not yet tense, and in those now growing old the tension relaxes; hence both these ages are weak and powerless for movement. And [15] bulls are particularly sinewy, even their hearts, and therefore that part by which they set the air in motion is in a tense state, like a sinewy string stretched tight. (That the heart of bulls is of such a nature is shown by the fact that a bone is actually found in some of them, and bones seek the nature of sinew.)

[20] All animals when castrated change to the female character, and utter a voice like that of the females because the sinewy strength in the principle of the voice is relaxed. This relaxation is just as if one should stretch a string and make it taut by hanging some weight on to it, as women do who weave at the loom, for they stretch [25] the warp by attaching stone weights to it. For in this way are the testes attached to the seminal passages, and these again to the blood-vessel which takes its origin in the heart near the organ which sets the voice in motion. Hence as the seminal [30] passages change towards the age at which they are now able to secrete the semen, this part also changes along with them. As this changes, the voice too changes, more indeed in males, but the same thing happens in females too, only not so plainly, the [788a1] result being what some call ‘bleating’ when the voice is uneven. After this it settles into a deep or high voice of the succeeding time of life. If the testes are removed the tension of the passages relaxes, as when the weight is taken off the string or the [5] warp; as this relaxes, the principle which moves the voice is loosened in the same proportion. This, then, is the reason why the voice and the form generally change to the female character in castrated animals; it is because the principle is relaxed upon [10] which depends the tension of the body; not that, as some suppose, the testes are themselves a knot of many principles, but small changes are the causes of great ones, not per se but when it happens that a principle changes with them. For the principles, though small in size, are great in potency; this, indeed, is what is meant by a principle, that it is itself the cause of many things without anything else being [15] higher than it.

The heat or cold also of their habitat contributes to make some animals of such a character as to be deep-voiced, and others high-voiced. For hot breath being thick causes depth, cold breath being thin the opposite. This is clear also in pipe-playing, [20] for if the breath of the performer is hotter, that is to say if it is expelled as by a groan, the note is deeper.

The cause of roughness and smoothness in the voice, and of all similar inequality, is that the part or organ through which the voice is conveyed is rough or [25] smooth or generally even or uneven. This is plain when there is any moisture about the trachea or when it is roughened by any affection, for then the voice also becomes uneven.

Flexibility and inflexibility depend on the softness or hardness of the organ, for what is soft can be regulated and assume any form, while what is hard cannot; thus [30] the soft organ can utter a loud or a small note, and accordingly a high or a deep one, since it easily regulates the breath, becoming itself easily great or small. But hardness cannot be regulated.

Let this be enough on all those points concerning the voice which have not been previously discussed in the treatise on sensation and in that on the soul. [788b1]

8 · With regard to the teeth it has been stated previously that they do not exist for a single purpose nor for the same purpose in all animals, but in some for nutrition, in others also for fighting and for vocal speech. We must, however, [5] consider it not alien to the discussion of generation to inquire into the reason why the front teeth are formed first and the grinders later, and why the latter are not shed but the former are shed and grow again.

Democritus has spoken of these questions but not well, for he assigns the cause [10] too generally without investigating the facts in all cases. He says that the early teeth are shed because they are formed in animals too early, for it is when animals are practically in their prime that they grow according to nature, and suckling is the cause he assigns for their being found too early. Yet the pig also suckles but does not [15] shed his teeth, and, further, all the saw-toothed animals suckle, but some of them do not shed any teeth except the canines, e.g. lions. This mistake, then, was due to his speaking generally without examining what happens in all cases; but this is what we ought to do, for any one who makes any general statement must speak of all the particular cases.

Now we assume, basing our assumption upon what we see, that nature never [20] fails nor does anything in vain so far as is possible in each case. And it is necessary, if an animal is to obtain food after the time of taking milk is over, that it should have instruments for the treatment of the food. If, then, as Democritus says, this [25] happened about the time of reaching maturity, nature would fail in something possible for her to do. And, besides, the operation of nature would be contrary to nature, for what is done by violence is contrary to nature, and it is by violence that he says the formation of the first teeth is brought about. That this view then is not true is plain from these and other similar considerations.

[30] Now these teeth are developed before the flat teeth, in the first place because their function is earlier (for dividing comes before crushing, and the flat teeth are for crushing, the others for dividing), in the second place because the smaller is naturally developed quicker than the larger, even if both start together, and these [789a1] teeth are smaller in size than the grinders, because the bone of the jaw is flat in that part but narrow towards the mouth. From the greater part, therefore, must flow more nutriment to form the teeth, and from the narrower part less.

The act of sucking in itself contributes nothing to the formation of the teeth, but the heat of the milk makes them appear more quickly. A proof of this is that [5] even in suckling animals those young which enjoy hotter milk grow their teeth quicker, heat being conducive to growth.

They are shed, after they have been formed, partly because it is better so (for what is sharp is soon blunted, so that a fresh relay is needed for the work, whereas [10] the flat teeth cannot be blunted but are only smoothed in time by wearing down), partly from necessity because, while the roots of the grinders are fixed where the jaw is flat and the bone strong, those of the front teeth are in a thin part, so that they are weak and easily moved. They grow again because they are shed while the bone is [15] still growing and the animal is still young enough to grow teeth. A proof of this is that even the flat teeth grow for a long time, the last of them cutting the gum at about twenty years of age; indeed in some cases the last teeth have been grown in quite old age. This is because there is much nutriment in the broad part of the [789b1] bones, whereas the front part being thin soon reaches perfection and no residual matter is found in it, the nutriment being consumed in its own growth.

Democritus, however, neglecting the final cause, reduces to necessity all the operations of nature. Now they are necessary, it is true, but yet they are for a final [5] cause and for the sake of what is best in each case. Thus nothing prevents the teeth from being formed and being shed in this way; but it is not on account of these causes but on account of the end; these are causes in the sense of being the moving and efficient instruments and the material. So it is reasonable that nature should perform most of her operations using breath as an instrument, for as some [10] instruments serve many uses in the arts, e.g. the hammer and anvil in the smith’s art, so does breath in things formed by nature. But to say that necessity is the cause is much as if we should think that the water has been drawn off from a dropsical patient on account of the lancet alone, not on account of health, for the sake of [15] which the lancet made the incision.

We have thus spoken of teeth, saying why some are shed and grow again, and others not, and generally for what cause they are formed. And we have spoken of the other affections of the parts which are found to occur not for any final end but of [20] necessity and on account of the motive cause.