Planet of the Spiders is the fifth and final serial of the 11th season of the British science fiction television series "Doctor Who", which was first broadcast in six weekly parts on BBC1 from 4 May to 8 June 1974. It was Jon Pertwee's last serial as the Third Doctor, the last regular appearance of Mike Yates, and marks the first, uncredited appearance of Tom Baker as the Fourth Doctor. This serial introduces the term "regenerate" to explain the Doctor's transformation into another appearance.