||P.821 left column bottom paragraph: "Associated with the strong tissue polarity are clear migration pathways for cells, which can be studied in a variety of ways. In simple terms this is illustrated in figure 1 where cells marked in the crypt and studied at various times can be seen to move inexorably up the villus at a velocity of between one and two cell diameters per hour (Kaur & Potten 1986). Dolichos biflorus lectin staining in appropriate mice demonstrated that the cells move in straight vertical columns (Winton et al. 1988). The information shown in figure 1 indicates that cells produced by mitosis in the crypt live for only 2-3 days before they reach the tip of the villus from which they are extruded." See also Histology Text Atlas Book link paragraph directly above plate 13.4-"Autoradiographic studies indicate that the life span of a typical intestinal epithelial cell is only 3 to 4 days."