During surgery for a benign cyst on the kidney, the surgeon notes that the patient’s right kidney has two ureters and two renal pelves. This malformation is

E. The ureteric bud seems to be preprogrammed to undergo repeated divisions. These divisions normally begin on contact with the metanephric blastema. If the ureteric bud undergoes division prematurely, duplication of the ureter and renal pelvis occurs. In some circumstances, two separate kidneys may form.