The "Fits" come from the Lewis Carroll poem The Hunting of the Snark. Carroll was 42 when he wrote it and Lewis makes references to the number 42 in several of his works including The Hunting of the Snark and Alice in Wonderland.

Series 2 episodes were originally titled, again, Fit The First through to Fifth. Since the series' revival with 2004's Teriary Phase, they - and the 1978 Christmas special - have been retrospectively re-titled Fit The Seventh through to Twelfth.