When Space Shuttle Atlantis docks with the Mir space station later this week, it will deliver 64 desert beetles that may help scientists understand how space flight changes the body's internal clock. Two "beetle kits" will be flown in, each with 32 "beetle activity monitors" that will allow investigators to track beetle movement. Scientists want to determine if the "circadian" timing system shows evidence of adaptation during long-term exposure to altered gravitational fields. They also hope to learn whether exposure to altered gravitational fields changes the system's sensitivity to light. "The circadian timing system influences almost all physiological and behavioral functions," says co-investigator Tana M. Hoban-Higgins, an assistant researcher at UC Davis. "Research on this simple biological system also should suggest future experiments to increase our understanding of issues relating to biomedical problems of space flight." The internal body clock coordinates an organism's physiology and behavior, including sleep/wake, body temperature and hormone cycles, with the external 24-hour day. Photographs are available at http://ccf.arc.nasa.gov/dx. Also available is video footage. .