The Legion of Space is a space opera science fiction series by American writer Jack Williamson. The story takes place in an era when humans have colonized the Solar System but dare not go farther, as the first extra-solar expedition to Barnard's Star failed and the survivors came back as babbling, grotesque, diseased madmen. They spoke of a gigantic planet, populated by ferocious animals and the single city left of the evil "Medusae". The Medusae bear a vague resemblance to jellyfish, but are actually elephant-sized, four-eyed, flying beings with hundreds of tentacles. The Medusae cannot speak, and communicate with one another via a microwave code. Source: Wikipedia (en)