This illustration of a composite photomicrograph reveals the ultrastructural details observed at two stages in the life cycle of the parasite, Entamoeba histolytica, stained with iodine is its cyst stage (lt), , and its Giemsa stain, trophozoite stage (cntr and rt). The cyst contained a chromatoid body and the four characteristic nuclei, each containing a single centrally located karyosome. Each E. histolytica trophozoite contained a single nucleus, within which was a single centrally located karyosome and peripherally located chromatin. Note the red blood cells ingested inside each of the trophozoites. CDC 1954