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  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 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 superfluous

  yeasty matter), but also for the sake of a final cause, for it is

  impossible for them to attain their whole growth in the uterus because

  these animals have so many eggs. Therefore are they 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 spent in this growth; even as it is most of those

  laid are destroyed before hatching. 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 'belone', for its eggs are large instead of numerous, what

  Nature has taken away in number being added in size.

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

  5

  A proof that these fish also are oviparous is the fact that even

  viviparous fish, such as the cartilaginous, are first internally

  oviparous, for hence it is plain that the whole class of fishes is

  oviparous. Where, however, both sexes exist and the eggs are

  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

  cartilaginous 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 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 cartilaginous, for they do not dispute the sexes in

  these. And yet there is no difference in the males of cartilaginous

  fishes and those belonging to the oviparous class in respect of the

  organs for the milt, and it is manifest that semen can be squeezed 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 (as with mules in the class of bushy-tailed animals),

  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, 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 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. Birds and all oviparous quadrupeds, and any of

  the cartilaginous fish 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 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 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, speculating on a small induction,

  they think the same must hold good in all cases.

  So also those who assert that conception in female fishes is

  caused by their swallowing the semen of the male 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 formed in the male. And just as the increase of the milt

  in the male and of the roe 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 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 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 they come into being by impregnation,

  and here it is that the milt of the males is used up. Therefore it

  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.

  What helps in the deception 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] copulate like

  the dolphins by throwing themselves alongside of one another. But

  the dolphins 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 the same simple tale,

  so much noised abroad, as Herodotus the storyteller, 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 nutriment, for it is concocted; the

  uterus, however, is plainly full of eggs, and from whence did they

  enter it?

  6

  A similar story is told also of the generation
of birds. For there

  are some who say that the raven and the ibis unite at the mouth, and

  among quadrupeds that the weasel brings forth its young by the

  mouth; so say Anaxagoras and some of the other physicists, speaking

  too superficially and without consideration. Concerning the birds,

  they are deceived by a false reasoning, because the copulation of

  ravens is seldom seen, but they are often seen uniting with one

  another with their beaks, as do all the birds of the raven family;

  this is plain with domesticated jackdaws. Birds of the pigeon kind

  do the same, but, because they also plainly copulate, therefore they

  have not had the same legend told of them. But the raven family is not

  amorous, for they are birds that produce few young, though this bird

  also has been seen copulating before now. It is a strange thing,

  however, that these theorists do not ask themselves how the semen

  enters the uterus through the intestine, which always concocts

  whatever comes into it, as the nutriment; and these birds have a

  uterus like others, and eggs are found them near the hypozoma. And the

  weasel has a uterus in like manner to the other quadrupeds; by what

  passage is the embryo to get from it to the mouth? But this opinion

  has arisen because the young of the weasel are very small like those

  of the other fissipeds, of which we shall speak later, and because

  they often carry the young about in their mouths.

  Much deceived also are those who make a foolish statement about

  the trochus and the hyena. Many say that the hyena, and Herodorus

  the Heracleot says that the 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 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 in the cartilaginous fish 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 cartilaginous class do not produce much semen, and further

  the females have their uterus near hypozoma. For the males and females

  of the one class of fish differ from the males and females of the

  other class in like manner, for the cartilaginous 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, 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 which produce a scolex, for the

  product discharged by them is still more imperfect than a fish's

  egg. 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.

  In birds the wind-eggs become fertile, and those previously

  impregnated by one kind of cock change their nature to that of the

  later cock. And if the eggs be behindhand in growth, then, if the same

  cock treads the hen again after leaving off treading for a time, he

  causes them to increase quickly, not, however, at any period

  whatever of their development, 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 should expect, for by the time that the white and

  yolk are separated off from one another, the birds egg already

  contains the principle that comes from the male parent.... for the

  male contributes to 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 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, wherefore 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 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, but in so far as

  it is not a plant it is not perfect, nor does 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 cock; for they already contain both principles, which is why

  they do not change again after the second impregnation.

  8

  The young are produced in the same way also by the cephalopoda, e.g.

  sepias and the like, and by the crustacea, e.g. carabi 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 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.

  In the sepias and calamaries or squids the eggs appear to be two,

  because the uterus is divided and appears double, but that of the

  poulps appears to be single. The reason is that the shape of the

  uterus in the poulp is round in form and spherical, the cleavage being

  obscure when it is filled with eggs. The uterus of the carabi is

  also bifid. All these animals also lay an imperfect egg for the same

  reason as fishes. In the carabi and their like the females produc
e

  their eggs so as to keep them attached to themselves, which is why the

  side-flaps of the females are larger than 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 sticky and

  glutinous mass, but in the carabi 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 those of the

  cephalopoda grow after deposition like those of fishes.

  The sepia 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 pointing in the same direction. For the position and attitude

  of the young while developing you must look at the Enquiries.

  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 are generated by copulation,

  others spontaneously, and besides this that they produce a scolex, and

  why this is so. For pretty much all creatures seem in a certain way to

  produce a scolex 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 embryo grows in size while still

  undifferentiated into parts; now such is the nature of the scolex.

  After this stage some of the ovipara produce the egg in a perfect

  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 as

  if we should take away the shell of the egg, wherefore they call the

  abortion of an embryo at that stage an 'efflux'.

  Those insects which generate at all generate a scolex, and those