The format of the show's entire run was a series of cliff-hanger adventure serials. Each of the Doctor's adventures would be told across several half-hour episodes, with a cliff-hanger ending each one. Each "season" of the show would be broken into several stories, taking usually 4 to 6 episodes to play out - on-screen, each individual episode would begin with the title of the story ("The Android Invasion", to name one), followed by the story's author, then what episode the story the audience was watching ("Part One", for example). This method of titling wasn't established until late in the third season; prior to that, every episode was given its own unique title. Because of this, there are no 'official' story titles to the earliest adventures, though semi-official ones have been consistently used on DVDs, books, etc.
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