Human beings undergo amazing development in the 9 months of prenatal development. These images show an embryo at 30 days (about the size of a poppy seed), an embryo at 8 to 9 weeks (about the size of an olive), and a fetus at 5 months (about the size of a pomegranate).

CLAUDE EDELMANN/SCIENCE SOURCE and BIOPHOTO ASSOCIATES/SCIENCE SOURCE and JAMES STEVENSON/SCIENCE SOURCE