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On The Generation Of Animals   

in all the parts of the 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. 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 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 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

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 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
produced mussels, for smaller ones are always growing off alongside
the original, but the whelks, the purple-fish, and those which are
said to 'spawn' 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 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 likely that the product of those
testacea which 'spawn' 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 'spawn' are spontaneously
generated. Now all things formed in this way, whether in earth or
water, manifestly come into 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 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, 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
were a frothy bubble. Whether what is forming is to be more or less
honourable in kind depends on the embracing of the psychical
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 hardening round them and solidifying in the same
manner as bones and horns (for these cannot be melted by fire),

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