What is a placenta? (And why does it matter?)

credit: www.birthingfromwithin.com

Norman Ford's book When Did I Begin? is a treasure trove of information about fetal development, plus some very interesting reflections on how the biological facts bear on whether each of us was once a zygote or once a fetus. This is a matter of pure metaphysical interest but also with possible ethical implications.  Ford offers several reasons to doubt that