 Today, we know that some of these observations are related to the (maternal) inheritance of organelles residing in the cytoplasm, such as the mitochondria and chloroplasts, organelles which carry their own DNA. This however does not encompass all the mechanisms which underlie cytoplasmatic inheritance. Paradigmatic work on cytoplasmatic inheritance done by Sonneborn, Beale, Nanney, and their colleagues in the 1950s and 1960s, was concerned with patterns of inheritance in unicellular organisms, and in particular the protist genus Paramecium. It was suggested that the self-sustaining regulatory loops that maintain gene activity or inactivity in a cell would persist through cell division, provided the non-DNA components of the system (many of which reside in the cytoplasm in eukaryotic microogranisms) were shared among daughter cells. In this way, alternative regulatory phenotypic states would be inherited. Among the properties whose inheritance was studied were mating-type variations, serotype variations, and the structural or “surface inheritance” of ciliary structures. Remarkably, microsurgical changes to the ciliary structures on the surface of Paramecium cells are inherited by offspring. The stability of induced characters once the stimulus was removed (called “cellular memory”) and the number of generations characters were maintained varied widely. However, the results indicated that long-term stability and heritability need not be the result of changes to the DNA sequence (Nanney 1958).