The placenta (Latin for cake, from Greek plakoenta, accusative of plakoeis - πλακοείς, "flat", referencing its appearance in humans) is an ephemeral organ present in placental vertebrates, such as eutherial mammals and sharks during gestation (pregnancy). Protherial (egg-laying) and metatherial (marsupial) mammals don't produce a placenta. The placenta develops from the same sperm and egg cells that form the fetus, and functions as a foeto… (More on Placenta)