Erythrocytic development of P cynomolgi in monkey and human hosts. Giemsa-stained thin films of P cynomolgi in (A) monkey (M mulatta) normocytes and (B) human reticulocytes matured ex vivo over a period of 42 hours. The parasite was staged into the following categories: tiny ring (0-6 hours after invasion), small ring (6-12 hours after invasion), large rings (12-18 hours after invasion), early trophozoites (18-24 hours after invasion), late trophozoites (24-30 hours after invasion), early schizonts (30-36 hours after invasion), and mature schizonts (36-42 hours after invasion). Scale bar = 10 μm.