All improvements made in accordance with the provisions of this act may be made by the township supervisors of such township by contract, to be let by the township supervisors to the lowest and best bidder after three weeks publication in at least two newspapers published in the county in which such township is located, or such improvements may be made partly by the township and partly by contract, to be let only after advertisement as hereinbefore provided. All the work of making said improvement may be done by the township.