So much for the conception and generation of birds.

It has been previously stated that fishes are not all oviparous.
Fishes of the cartilaginous genus are viviparous; the rest are
oviparous. And cartilaginous fishes are first oviparous internally and
subsequently viviparous; they rear the embryos internally, the
batrachus or fishing-frog being an exception.

Fishes also, as was above stated, are provided with wombs, and
wombs of diverse kinds. The oviparous genera have wombs bifurcate in
shape and low down in position; the cartilaginous genus have wombs
shaped like those of O birds. The womb, however, in the
cartilaginous fishes differs in this respect from the womb of birds,
that with some cartilaginous fishes the eggs do not settle close to
the diaphragm but middle-ways along the backbone, and as they grow
they shift their position.

The egg with all fishes is not of two colours within but is of
even hue; and the colour is nearer to white than to yellow, and that
both when the young is inside it and previously as well.