What Carry On film has Kenneth Williams giving students a lecture?

Saw this on one of those clip shows a year back.
Kenneth Williams plays a teacher/lecturer in what I assume was a
university or college. He's supposed to be narrating to a projector
reel about stone age archetecture, but unbeknownst to him, it's
actually a film of an exotic dancer, which the students watch with
open jaws.

No idea what film it's from, or if it's even from one of the films in
the first place.