As regards the shape of the womb, the reader is referred to my
treatise on Anatomy. The womb, however, is diverse in diverse
fishes, as for instance in the sharks as compared one with another
or as compared with the skate. That is to say, in some sharks the eggs
adhere in the middle of the womb round about the backbone, as has been
stated, and this is the case with the dog-fish; as the eggs grow
they shift their place; and since the womb is bifurcate and adheres to
the midriff, as in the rest of similar creatures, the eggs pass into
one or other of the two compartments. This womb and the womb of the
other sharks exhibit, as you go a little way off from the midriff,
something resembling white breasts, which never make their
appearance unless there be conception.

Dog-fish and skate have a kind of egg-shell, in the which is
found an egg-like liquid. The shape of the egg-shell resembles the
tongue of a bagpipe, and hair-like ducts are attached to the shell.
With the dog-fish which is called by some the 'dappled shark', the
young are born when the shell-formation breaks in pieces and falls
out; with the ray, after it has laid the egg the shell-formation
breaks up and the young move out. The spiny dog-fish has its close
to the midriff above the breast like formations; when the egg
descends, as soon as it gets detached the young is born. The mode of
generation is the same in the case of the fox-shark.