Erosion of the uterine epithelium is initiated when the cells at the tips of the chorionic villi stimulate the maternal cells to become (1). The (1) cells then become (2) and are desquamated, together with some sub-epithelial (3). This erosion of the uterine epithelium also causes some damage to the maternal (4). The resulting hemorrhage adds blood cells to the mass of cellular debris that is beginning to form; however, most of the blood accumulates on the borders of the Chorion frondosum (i.e. between the Chorion frondosum and Chorion laeve). This accumulation forms two bands of clotted blood, which are referred to as (5). Together with the secretions of the uterine glands, the mass of cellular debris is absorbed as (6) by the cells at the tips of the chorionic villi.