In humans, the metanephros (ault kidney) begins as an aggregate of mesenchymal stem cells that are detectable by the fifth gestational week as two small areas in the intermediate mesoderm close to the pelvic aorta. It is approximately at this time that the nephric duct produces a finger-like projection called the ureteric bud that has, or will soon invade, the aggregate of cells known as the metanephric mesenchyme.