Under favorable conditions amebas divide by binary fission (splitting) to produce two daughter amebas, the nucleus dividing by mitosis. When an ameba is divided artificially, the portion containing the nucleus forms a new cell membrane and continues as a whole animal, while the other portion lives only as long as its present food supply lasts, ultimately dying, since it cannot ingest food or reproduce. If conditions are unfavorable, e.g., in the absence of food and water, amebas secrete a firm protective covering and encyst until conditions are again favorable to active division.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.