And this resembles the development of
animals from eggs, except that these latter consume the whole egg,
whereas in the scolex, 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
also the nourishment is absorbed by all animals in the part below
the hypozoma.
That the scolex 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 turbinata, 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 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 limnostrea, a kind of oyster, have come into
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
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.
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