RoboTuna II taken apart for inspection. This 2.4- metre-long robot is propelled by motors that flex its body. Monitoring of the robot as it swims in a water tank, allows research to be conducted on the physics of underwater propulsion. The robot is modelled on the bluefin tuna, which, over 160 million years, has evolved into a highly efficient swimmer. Photographed at the Massachusetts Institute of Technology, Cambridge, USA.