Two weeks after conception, the developing individual enters the embryonic period, which lasts from week 2 through week 8, and he or she is now called an embryo.
As an embryo develops through an intricate, preprogrammed process of cell division, it grows 10,000 tunes larger by 4 weeks of age, attaining a length of about one-fifth of an inch. At this point it has developed a rudimentary beating heart, a brain, an intestinal tract and a number of other organs. Although all these organs are at a primitive stage of development, they are clearly recognizable. Moreover, by week 8, the embryo is about an inch long, and has discernible arms and legs and a face.