Entamoeba histolytica

This trichrome-stained photomicrograph depicts a binucleated cyst of the amoebic parasite, Entamoeba histolytica. In bright-field microscopy, E. histolytica cysts are spherical and usually measure 12 to 15 µm (range may be 10 to 20 µm). A mature cyst has 4 nuclei, while an immature cyst may contain only 1 to 3 nuclei. Peripheral chromatin is fine, uniform, and evenly distributed. Elongated, chromatoid bodies with bluntly rounded ends may sometimes be found. Glycogen can be diffuse or absent in mature cysts while clumped in immature cysts. Image courtesy CDC/Dr. Mae Melvin, 1977. (Photo by Smith Collection/Gado/Getty Images).