This thesis considers normal fission to consist of at least 2 operations: equal division of all genes, and formation of a cell-plate in such a manner that each daughter cell receives an equal section of each maternal gene. It is unnecessary to this thesis to consider whether the genes are in a nucleus, or are arranged along chromosomes or comparable bodies. It is assumed that as long as this type of division continues, the organisms will remain uniform. Variation, it is suggested, may result from irregularities in cell division. This may take the form of failure of 1 or more genes to divide, or failure of the cell-plate to segregate the segments of a divided gene to the daughter cells. Several examples are cited to illustrate the manner in which observed variations may be explained on the basis of this hypothesis.