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On The Generation Of Animals   

for the earthy matter does not come to the surface in their eggs any
more than in themselves. This is why they lay eggs in themselves,
for if the egg were laid externally it would be destroyed, having no

Animals that are cold and rather dry than moist also lay eggs, but
the egg is imperfect; at the same time, because they are of an
earthy nature and the egg they produce is imperfect, therefore it
has a hard integument that it may be preserved by the protection of
the shell-like covering. Hence fishes, because they are scaly, and
crustacea, because they are of an earthy nature, lay eggs with a
hard integument.

The cephalopods, having themselves bodies of a sticky nature,
preserve in the same way the imperfect eggs they lay, for they deposit
a quantity of sticky material about the embryo. All insects produce
a scolex. Now all the insects are bloodless, wherefore all creatures
that produce a scolex from themselves are so. But we cannot say simply
that all bloodless animals produce a scolex, for the classes overlap
one another, (1) the insects, (2) the animals that produce a scolex,
(3) those that lay their egg imperfect, as the scaly fishes, the
crustacea, and the cephalopoda. I say that these form a gradation, for
the eggs of these latter resemble a scolex, in that they increase
after oviposition, and the scolex of insects again as it develops
resembles an egg; how so we shall explain later.

We must observe how rightly Nature orders generation in regular
gradation. The more perfect and hotter animals produce their young
perfect in respect of quality (in respect of quantity this is so with
no animal, for the young always increase in size after birth), and
these generate living animals within themselves from the first. The
second class do not generate perfect animals within themselves from
the first (for they are only viviparous after first laying eggs),
but still they are externally viviparous. The third class do not
produce a perfect animal, but an egg, and this egg is perfect. Those
whose nature is still colder than these produce an egg, but an
imperfect one, which is perfected outside the body, as the class of
scaly fishes, the crustacea, and the cephalopods. The fifth and
coldest class does not even lay an egg from itself; but so far as
the young ever attain to this condition at all, it is outside the body
of the parent, as has been said already. For insects produce a
scolex first; the scolex after developing becomes egg-like (for the
so-called chrysalis or pupa is equivalent to an egg); then from
this it is that a perfect animal comes into being, reaching the end of
its development in the second change.

Some animals then, as said before, do not come into being from
semen, but all the sanguinea do so which are generated by
copulation, the male emitting semen into the female when this has
entered into her the young are formed and assume their peculiar
character, some within the animals themselves when they are
viviparous, others in eggs.

There is a considerable difficulty in understanding how the plant is
formed out of the seed or any animal out of the semen. Everything that
comes into being or is made must (1) be made out of something, (2)
be made by the agency of something, and (3) must become something. Now
that out of which it is made is the material; this some animals have
in its first form within themselves, taking it from the female parent,
as all those which are not born alive but produced as a scolex or an
egg; others receive it from the mother for a long time by sucking,
as the young of all those which are not only externally but also
internally viviparous. Such, then, is the material out of which things
come into being, but we now are inquiring not out of what the parts of

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