In an embryo, early in development, a urogenital ridge forms on each side of the abdomen. Along this ridge run the Wolffian and Müllerian ducts.
From the Wolffian ducts the lower part of the bladder develops in both sexes, but in males it also forms the epididymis, sperm tube (vas deferens) and sperm storage sac (seminal vesicle).
The Müllerian ducts are the female equivalent, but these degenerate in the male. It is named after Caspar Wolff who described the duct in 1759.