The aircraft entered the circuit in preparation for a practice single engine landing. The gear was selected down, however neither pilot checked that the gear-down light illuminated. The aircraft was landed with the gear retracted and the pilots reported that they then noticed that the gear motor circuit breaker had popped. The circuit breaker had probably popped during the previous retraction cycle. During the approach the pilot under instruction was concentrating on handling the asymmetric situation, while the instructor was closely monitoring the airspeed and the handling techniques being employed. During the landing flare the gear up warning horn operated, but its sound was masked by the louder tone of the stall warning.
