Abstract
Dysentery amebae may live for 72 hours in vitro. The transition of the large vegetative forms into the cyst may be observed in vitro. The large vegetative ameba always passes into an intermediate stage before assuming the small vegetative form. The atypical forms are dysentery amebas with abnormal nuclei and cytoplasm. When circumstances are unfavorable encystment takes place. Under favorable conditions, on the other hand, they may again change into typical forms. The majority of the "degenerative" forms of Hartmann cannot be so classed. According to our observation, they represent forms which have been described here. Hartmann's Entamoeba histolytica is really a typical transitional form of Entamoeba tetragena. The origin and significance of the central vacuole have been elucidated. Nuclear division of the dysentery ameba proceeds in three ways. The typical forms divide on the whole mitotically, and the atypical a mitotically or in a primitively mitotic manner.