The embryo begins developing very rapidly, and by 22 days the heart begins to beat. By the end of the third week the backbone, spinal column and nervous system are developing. Kidneys, the liver and the digestive tract are already taking shape. By the end of the first month the embryo is ten thousand times larger than at the blastocyst stage. At this stage of development the head of the embryo is almost one half of his or her total size.
Brain tissues grow rapidly, dividing and becoming a miniature brain that is distinctly human.
Fingers and feet are beginning to develop. Facial features, including ears, nose, lips and tongue, form with clarity during this month. Eyes form and darken when pigment is produced around day 35. Eyelids cover the eyes and will soon form a protective seal, reopening during the seventh month. Near the end of the month the skeleton changes from cartilage to bone.