trophozoite of Balantidium coli with large kidney-shaped macronucleus and cystostome positioned to the left.  This is the only ciliate, parasitic to humans.  400x
trophozoite of B. coli. Note the cilia, macronucleus with micronucleus seen in upper portion of indent of the macronucleus and the cytostome to the left. The symptoms of this infection are similar to amoebiasis.  The infective stage is the cyst.  400x