Equal rites - a Discworld novel

The last thing the wizard Drum Billet did, before Death laid a bony hand on his shoulder, was to pass on his staff of power to the eighth son of an eighth son. Unfortunately for his colleagues in the chauvinistic (not to say misogynistic) world of magic, he failed to check on the new-born baby's sex...This is a third hilarious adventure by the author of "The Colour of Magic" and "The Light Fantastic."