The Xenopus experiment studies the development of cane toad tadpoles in spaceflight. After their stay in space, scientists will measure the effect of spaceflight exposure on the development of the tadpoles' sense of balance; this is controlled by the vestibular ocular system (inner ears and eyes). Xenopus is part of the BIO-4 mission which was launched into space with the Soyuz TMA-13 on 12 October 2008. The BIO missions provide flight opportunities for biology experiments requiring a short duration (less than 10 days) and limited on-orbit resources. They make use of the Russian Soyuz spacecraft for both launch and recovery of the experiment samples.