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.)