Sensory systems are characterized by developmental periods during which they are susceptible to environmental modifications, in particular to sensory deprivation. The experiment, XENOPUS, on Soyuz in 2008 was the fourth space flight experiment since 1993 to explore whether tail and vestibular development of Xenopus laevis has a gravity-related critical period. During this flight, tadpoles were used that had developed either the early hindlimb (stage 47) or forelimb bud (stage 50) at launch of the spacecraft. The results revealed (1) no impact of microgravity on the development of the roll-induced vestibuloocular reflex (rVOR) in both stages and (2) a stage-related sensitivity of tail development to microgravity exposure. These results were combined and compared with observations from space flights on other orbital platforms. The combined data revealed (1) a narrow gravity-related critical period for rVOR development close to the period of the first appearance of the reflex and (2) a longer one for tail development lasting from the early tail bud to the early forelimb bud stage. J. Exp. Zool. 315:505–511, 2011. © 2011 Wiley Periodicals, Inc.