First indications for gland cells, belonging to the adhesive organ, appear about 7 days after hatching (Fig. 7). Columnar cells originate between the epithelial cells adjacent to the basement membrane, initially containing a roundish nucleus surrounded by rough endoplasmic reticulum. Rapidly the columnar cells extend towards the epithelial surface. Secretory granules, delivered by the endoplasmic reticulum in the cell base, migrate towards the apical cell pole where they accumulate. Thereby the granules apparently track along microtubules (Fig. 7B) by overcoming a still remaining central bottleneck. The columnar cells, always occurring in clusters in the mature adhesive organ, likewise develop simultaneously with the other cells of the cluster. However, the columnar cells are not yet separated from each other by intermediate epithelial cells but have still direct contact with the other columnar cells in the cluster.