Inheritance of Atypical Form in Paramecium aurelia.

Abstract

In all of the lines of a pedigree culture of Paramecium aurelia, which had been derived from an animal isolated from the Woodruff culture, in approximately the 12,000th generation, and bred on beef extract in the usual way, there appeared animals showing a “lump” on the peristomal side of the posterior end. 1 During the next week similarly atypical animals appeared in a hay infusion mass culture, which had been seeded with animals from the above lines three months prior to the appearance of the “mutation”, and also in the lines of a second pedigree culture derived from an animal isolated from this mass culture.

These atypical animals appeared healthy and active and when isolated each gave rise to two daughter cells showing the lump. As a rule the lump was visible in both daughter cells before division was complete, although in a few cases, it was not apparent until several hours afterward. Furthermore the lumps showed considerable variation in size. With such variations, however, the character persisted in all of the lines, none of them ever again showing a perfectly typical animal.

In the course of time the vitality of the animals became slightly lowered, and at the end of 25 days some of the lines died, having attained from 16 to 24 generations. The remaining lines are still in pedigree, having retained the lump for 30 generations, or 2 months. In the latter lines at least one definite period of endomixis has occurred without any apparent effect on the new character.

In brief, a new character has arisen, in a manner unknown, almost simultaneously in a number of different though related lines and has been inherited, so far, through 30 generations, involving one endomictic period.