About the twentieth day, if you open the egg and touch the
chick, it moves inside and chirps; and it is already coming to be
covered with down, when, after the twentieth day is ast, the chick
begins to break the shell. The head is situated over the right leg
close to the flank, and the wing is placed over the head; and about
this time is plain to be seen the membrane resembling an after-birth
that comes next after the outermost membrane of the shell, into
which membrane the one of the navel-strings was described as leading
(and, by the way, the chick in its entirety is now within it), and
so also is the other membrane resembling an after-birth, namely that
surrounding the yolk, into which the second navel-string was described
as leading; and both of them were described as being connected with
the heart and the big vein. At this conjuncture the navel-string
that leads to the outer afterbirth collapses and becomes detached from
the chick, and the membrane that leads into the yolk is fastened on to
the thin gut of the creature, and by this time a considerable amount
of the yolk is inside the chick and a yellow sediment is in its
stomach. About this time it discharges residuum in the direction of
the outer after-birth, and has residuum inside its stomach; and the
outer residuum is white (and there comes a white substance inside). By
and by the yolk, diminishing gradually in size, at length becomes
entirely used up and comprehended within the chick (so that, ten
days after hatching, if you cut open the chick, a small remnant of the
yolk is still left in connexion with the gut), but it is detached from
the navel, and there is nothing in the interval between, but it has
been used up entirely.