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