In the darkness of the deep ocean, some animals create their own light. Among these is the Hawaiian bobtail squid Euprymna scolopes, which forms a partnership with the luminous bacterium Vibrio fischeri. The squid houses colonies of these bacteria in special light organs, and it can control the brightness and direction of their illuminations. But these organs do much more than produce light - they detect it too. The organs generate nervous signals when they sense light and they're loaded with proteins responsible for detecting it. The light organs are effectively an extra set of primitive eyes, each equipped with its own "iris" and "lens". The squid comes equipped with a pair of living, 'seeing' flashlights.