Answer to Parasite Case of the Week 587: Balantioides (formerly Balantidium, Neobalantidium) coli. Note the characteristic circumferential cilia and large "kidney bean" shaped macronucleus:
I have a pdf of the 1931 French manuscript (with my own translation) if anyone is interested in it. I should note that my French is very rusty, so there may be some errors! Just send me a message at firstname.lastname@example.org if you would like a copy.
I'd also encourage you to read all of the interesting comments from this case. There are a lot of great pearls in there.