INHERITED VARIATION ARISING DURING VEGETATIVE REPRODUCTION IN PARAMECIUM AURELIA

¹ From the Zoölogical Laboratory of the Johns Hopkins University and the Marine Biological Laboratory, Woods Hole, Mass.

The clone of Paramecium aurelia studied in this investigation produces branches which differ from the original clone in many respects. They are larger, have a different form, reproduce at a greater rate, and are less resistant to unfavorable conditions than the original type. These branches consistently manifest their diverse characteristics and none has ever been known to revert to the original type in any of the cases which were studied. No rule or regularity was found in the production of the altered lines except that when a line became altered, lines which were separated from it by only one or two fissions usually became altered at the same time or nearly the same time. Unlike diverse clones, these diverse races of the same clone give after conjugation populations which are on the whole very similar. The unaltered type gave after conjugation only a very small proportion (4 per cent) of lines which were similar in size, form and fission rate to the parent clone.

From these observations and experimental results the conclusion is drawn that the variation is produced by mutations of one member of the four or five heterozygous pairs of genes which are necessary to produce the normal type of this clone.