Bypass holes for rotor cooling

In a multi-stage turbine wherein at least one turbine wheel (12) supports a row of buckets (14) for rotation, and wherein the turbine wheel (12) is located axially between first and second annular fixed arrays of nozzles (36, 38), a cooling air circuit for purging a wheelspace between the turbine wheel (12) and the second fixed annular array of nozzles (38) comprising a flowpath through a shank portion (50) of one or more buckets (14) connecting a wheel space between the turbine wheel (12) and the first fixed annular array of nozzles (36) with the wheel space between the turbine wheel (12) and the second fixed annular array of nozzles (38).