Missing Link is a sequencer driven from a single motor. The motor drives a set of chains, each of which releases a hammer to play a single glockenspiel note via a special catchment link. Each successive chain has one link less then the last - hence the name - which results as phasing effect which generates mutating melodies and chords.
This video is not very good quality but shows the inner workings of the piece before the design was finalised. Various parts were glued to make it more durable.