A five-year pedigreed race of Paramæcium without conjugation

The unicellular organisms afford a natural means of approach to the problem of fertilization, and the study of data, from a long series of careful experimental studies on these forms by various investigators, has pointed to the conclusion that the most important function of conjugation in the life history of the Protozoa is a satisfying of an inherent periodic physiological need of living matter, resulting in a renewal of the vigor of the cell. This “dynamic” view of fertilization has gradually assumed a commanding position, though it is neither contradictory nor confirmatory of the view that fertilization, resulting in amphimixis, is concerned in some way with the phenomenon of variation, or that it may be a process which enables certain forms to withstand changed environmental conditions.

The present paper briefly outlines the results which have been obtained to date from an intensive study of a pedigreed race of Paramacium aurelia with reference to the problem of protoplasmic senescence and the function of conjugation. I have previously published 1 the results obtained to September, 1910, and the reader is referred to earlier papers for further details of the culture and for a general discussion of the various phases of the work.

This culture was started on May I, 1907, with a “wild” Paramecium aurelia which was isolated from a laboratory aquarium. This individual was placed in about five drops of culture medium on a glass slide having a central ground concavity, and when the animal by division had formed four individuals, each of these was isolated on a separate slide to form the four lines, Ia, Ib, Ic, and Id, of this culture, Paramcecium I. The pedigreed culture has been maintained by a specimen isolated from each of these lines practically every day up to the present time, thus precluding the possibility of conjugation occurring and facilitating an accurate record of the number of generations attained.