The ultrastructure of Entamoeba histolytica.

The ultrastructure of the trophozoite of Entamoeba histolytica cultivated in vitro on artificial media is described from electron-microscope studies made by the authors and from other published accounts. The authors point out that the description does not present a complete picture of the trophozoite of this species of amoeba since no detailed studies of the dysenteric form in infected host organs have yet been made and that nothing is known about the ultrastructure of cysts and the process of cyst formation, maturation and germination.The cytoplasm is confined by a 3-layered cytoplasmic membrane and contains many different organelles: subpellicular dark bodies, ribosomes, helical aggregates of ribosomes, osmiophilic lipoid granules, short dark tubular bodies of unknown origin and function, food vacuoles and some very small vacuoles thought to be lysosomes. Neither mitochondria nor a Golgi apparatus could be found. In the nucleus, the chromatin material is accumulated around the periphery and the nucleolus is centrally situated. The nuclear envelope is a double-layered membrane with numerous pores. Some groups of button-like particles were seen within the nucleus and it is thought that they are probably symbiotic virus-like particles.Some comparisons are made with the ultrastructure of other amoebae, both parasitic and free-living, and some further lines of study are suggested.