There are two sources of stem cells in animals: embryonic stem cells and adult stem cells.Embryonic stem cells are present in the early stages of embryo development and are totipotent.After about seven days a mass of cells called the blastocyst is formed.The cells of the blastocyst are pluripotent.Embryonic stem cells remain pluripotent in the fetus until birth.Adult stem cells are present throughout life from birth. They are found in certain areas such as the bone marrow and are multipotent.Adult stem cells can be triggered by scientist to become pluripotent.Stem cells can be harvested from the umbilical cords of newborn babies.