Abstract
1. The vegetative forms of amebae may be developed in vitro from the cysts. 2. The cysts of Entamoeba tetragena and Entamoeba coli each produce only a single vegetative individual. It has not been observed in vitro that a number of daughter amebae, corresponding to the number of nuclei present in the cyst, emerge from the mother cyst, as claimed by Casagrandi and Barbagallo, Schaudinn, and a number of other investigators. 3. The daughter nuclei in the cystic stage correspond to the gamete nuclei of other protozoa. The syngamic nuclear union in the case of these two amebae does not take place in the tetranuclear stage of the cyst, as claimed by Schaudinn and Wenyon, but during reproduction. 4. The process of autogamy of both amebae is not restricted to two nuclei; it may involve more than two, which unite to form a syncaryon. In the case of all other protozoa, autogamy is restricted to two nuclei. 5. In order to distinguish the two types of autogamy, one has been termed simple autogamy and the other polynuclear autogamy. The latter may again be classified according to the number of nuclei involved, as trinuclear and tetranuclear autogamy. 6. The majority of cysts treated for 5 minutes in a 2 per cent solution of hydrochloric acid survives. 7. It was possible to demonstrate in vitro the developmental cycle of Entamoeba tetragena. 8. No evidence of heterogamy has been observed in vitro in Entamoeba tetragena or Entamoeba coli. 9. The vegetative form of Entamoeba tetragena, at a certain stage of its life cycle in vitro, shortly after its formation, has not only one or two, but may have as many as three or four nuclei.