Clonal variation in paramecium. Heterogeneity within clones of identical serotypes.

Clones of genetically uniform paramecia differ in the extent to which they retain the antigenic type of a common ancestor. Some are faithful and are considered stable. Others are unstable. Apparently there are two kinds of "unstable" clones. One is composed of cells all of which tend to produce subclones with some cells which have transformed to new serotypes. Other "unstable" clones apparently are really composed of two or more kinds of cells, each of which tends to yield subclones which are made up almost exclusively of cells of one serotype, although some of these subclones are not of the original serotype. Support for the existence of such heterogeneous unstable clones is presented, and several possible mechanisms to account for their existence are discussed.