I first thought The Sex Life of A Polyp was a legitimate documentary film, as did I'm sure everyone to whom I showed the 2007 National FIlm Registry's list, who wanted to find a movie on it to snicker about (just about everyone said "At last The Sex Life of A Polyp made the list!" or some such comment).
Well it turns out that this 1928 film is an eleven-minute Robert Benchley comedy short subject, of the very dry humor variety. It's now been posted on the Internet Archive and although the picture and sound quality leave much to be desired, you get the idea.
Link to short.
The film is also on a Kino DVD collection, but according to user comments on Amazon, the picture/sound quality is also under par for these rare shorts. Looks like a fun collection though.