Birds of the pigeon kind, such as the ringdove and the
turtle-dove, lay two eggs at a time; that is to say, they do so as a
general rule, and they never lay more than three. The pigeon, as has
been said, lays at all seasons; the ring-dove and the turtle-dove
lay in the springtime, and they never lay more than twice in the
same season. The hen-bird lays the second pair of eggs when the
first pair happens to have been destroyed, for many of the hen-pigeons
destroy the first brood. The hen-pigeon, as has been said,
occasionally lays three eggs, but it never rears more than two chicks,
and sometimes rears only one; and the odd one is always a wind-egg.

Very few birds propagate within their first year. All birds,
after once they have begun laying, keep on having eggs, though in
the case of some birds it is difficult to detect the fact from the
minute size of the creature.

During the period above referred to the chick
sleeps, wakes up, makes a move and looks up and Chirps; and the
heart and the navel together palpitate as though the creature were
respiring. So much as to generation from the egg in the case of birds.

Birds lay some eggs that are unfruitful, even eggs that are
the result of copulation, and no life comes from such eggs by
incubation; and this phenomenon is observed especially with pigeons.

Twin eggs have two yolks. In some twin eggs a thin partition
of white intervenes to prevent the yolks mixing with each other, but
some twin eggs are unprovided with such partition, and the yokes run
into one another. There are some hens that lay nothing but twin
eggs, and in their case the phenomenon regarding the yolks has been
observed. For instance, a hen has been known to lay eighteen eggs, and
to hatch twins out of them all, except those that were wind-eggs;
the rest were fertile (though, by the way, one of the twins is
always bigger than the other), but the eighteenth was abnormal or
monstrous.

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.

The disposition of the several constituent parts is as
follows. First and outermost comes the membrane of the egg, not that
of the shell, but underneath it. Inside this membrane is a white
liquid; then comes the chick, and a membrane round about it,
separating it off so as to keep the chick free from the liquid; next
after the chick comes the yolk, into which one of the two veins was
described as leading, the other one leading into the enveloping
white substance. (A membrane with a liquid resembling serum envelops
the entire structure. Then comes another membrane right round the
embryo, as has been described, separating it off against the liquid.
Underneath this comes the yolk, enveloped in another membrane (into
which yolk proceeds the navel-string that leads from the heart and the
big vein), so as to keep the embryo free of both liquids.)

3


When the egg is now ten days old the chick and all its parts are
distinctly visible. The head is still larger than the rest of its
body, and the eyes larger than the head, but still devoid of vision.
The eyes, if removed about this time, are found to be larger than
beans, and black; if the cuticle be peeled off them there is a white
and cold liquid inside, quite glittering in the sunlight, but there is
no hard substance whatsoever. Such is the condition of the head and
eyes. At this time also the larger internal organs are visible, as
also the stomach and the arrangement of the viscera; and veins that
seem to proceed from the heart are now close to the navel. From the
navel there stretch a pair of veins; one towards the membrane that
envelops the yolk (and, by the way, the yolk is now liquid, or more so
than is normal), and the other towards that membrane which envelops
collectively the membrane wherein the chick lies, the membrane of
the yolk, and the intervening liquid. (For, as the chick grows, little
by little one part of the yolk goes upward, and another part downward,
and the white liquid is between them; and the white of the egg is
underneath the lower part of the yolk, as it was at the outset.) On
the tenth day the white is at the extreme outer surface, reduced in
amount, glutinous, firm in substance, and sallow in colour.