The 55th episode of Gene Roddenberry’s science fiction series Star Trek premieres on NBC, guest starring Robert Lansing and Teri Garr. An oddball episode concerning itself heavily with its time-traveling guest star, Assignment: Earth is actually a sneaky “pilot” for a potential Star Trek spinoff – and Gene Roddenberry’s hedge against unemployment, as he has every reason to believe, at the end of Star Trek’s second season, that his series is about to be cancelled.

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The 110th and final episode of Irwin Allen’s adventure series Voyage To The Bottom Of The Sea airs on ABC, starring Richard Basehart and David Hedison. Barry Atwater guest stars.
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The Australian Broadcasting Corporation premieres the first episode of the science fiction series Vega 4, starring John Fassen (a veteran of ABC’s first genre series, The Stranger). This series is a follow-up to the 1966 series The Interpretaris.
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ABC premieres the first episode of the Filmation animated series Fantastic Voyage, based on the
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ABC premieres the first episode of Irwin Allen’s sci-fi series Land Of The Giants, starring Gary Conway, Don Matheson, Deanna Lund, and Don Marshall.