hours. Since the embryo needs air, the shell is
riddled (especially at the blunt end) with some
10,000 pores that add up to a hole about 2 mm
in diameter.
Germ-Side Up: Primordial Yolk
Have you ever noticed that when you crack
open a raw egg, the germ cell — the
pinhead-sized white disc that carries the
hen’s DNA — usually comes to the top of
the yolk? It does so because the channel of
primordial white yolk below it is less
dense than the yellow yolk — so the egg
cell’s side of the yolk is lighter, and rises.
In the intact egg, the chalazae allow the
germ cell to return to the top whenever the
hen rearranges her eggs.
That persistent bit of uncoagulated yolk
at the center of a hard-cooked egg is
primordial white yolk, especially rich in
iron, which the hen deposits in its eggs
when they’re barely a quarter-inch/6 mm