After takeoff the pilot raised the landing gear. Doing so in this aircraft involved selecting the undercarriage lever to the UP position then manually operating a ratchet handle. A short while later the pilot noticed that the selector lever on the undercarriage ratchet handle had become disconnected and had fallen beneath the floor of the aircraft where it was no longer accessible in flight. He was now unable to lower the landing gear. The pilot flew for a while to reduce fuel and then carried out a ‘wheels up’ landing on the grass strip. He was unhurt and vacated the aircraft normally. There was no fire.