Interaction between the ureteric bud and the metanephrogenic blastema is essential for the development of the kidneys. This interaction leads to the division of the ureteric bud and to the formation of the ampullae. Blastemal caps further develop in the region of the ampullae, which in turn give rise to nephrogenic vesicles. The vesicles differentiate in the same sequence as the mesonephros: initially pear-shaped, connecting to the ampulla through the secretory tubule, becoming S-shaped, developing into the glomerular capsule. The connection of a nephron to a terminal ampulla leads to a new division of the ampulla.