Some are viviparous, such as man, the
horse, the seal, and all other animals that are hair-coated, and, of
marine animals, the cetaceans, as the dolphin, and the so-called
Selachia. (Of these latter animals, some have a tubular air-passage
and no gills, as the dolphin and the whale: the dolphin with the
air-passage going through its back, the whale with the air-passage
in its forehead; others have uncovered gills, as the Selachia, the
sharks and rays.)
What we term an egg is a certain completed result of conception
out of which the animal that is to be develops, and in such a way that
in respect to its primitive germ it comes from part only of the egg,
while the rest serves for food as the germ develops. A 'grub' on the
other hand is a thing out of which in its entirety the animal in its
entirety develops, by differentiation and growth of the embryo.
Of viviparous animals, some hatch eggs in their own interior,
as creatures of the shark kind; others engender in their interior a
live foetus, as man and the horse. When the result of conception is
perfected, with some animals a living creature is brought forth,
with others an egg is brought to light, with others a grub.
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