The observations described here were made partly on cultured human amnion cells (AV3/INO clone cell line) and partly on mouse embryo cells transformed into neoplastic cells in vitro by SV40 virus (ER-SV40 cells). The procedures designed by us for cell cloning and for adaptation to monodisperse suspension cultures are described. The cell cycle of AV3/INO cells was studied by pulse-labeling with tritiated thymidine. An interesting phenomenon, a very peculiar and probably significant intracell formation is described. Intracells are classified as either spurious, i.e. cells incorporated into another cell by phagocytosis, or genuine, formed within the mother cell by a gemmation process of the endoplasmic reticulum, with subsequent organization of a nucleolus and nucleus. The gemmule may be formed in two ways, which are termed prevacuolar or disjunctive, and postvacuolar. The DNA of the nucleus of intracells could originate either from the nucleus or from the mitochondria of the mother cell.