In a recent paper ('13) we have shown that there is biparental inheritance of the rate of fission in Paramecium-the two lines of progeny descended from a pair of conjugants being more alike in their rates of fission than would be the case if their parents had not conjugated. The present paper examines the question whether there is likewise biparental inheritance in size as a result of conjugation.
The material for this examination was derived from the extensive Experiment 16, described in our previous paper. I n this experiment 482 lines of propagation, derived from the two members, a and b, of 241 pairs, were cultivated side by side, under uniform conditions, for forty-seven days. In addition to the main slide cultures, employed for the study of the rate of fission, there was kept a small mass culture of each line. Thesemass cultures were likewise kept under uniform conditions; they furnished for measurement large numbers of specimens of each line.
On April 17, 1913, twenty-five days after conjugation, and nineteen days after the mass cuftures were set in progress, a considerable number of specimens from each line were killed in Worcester's fluid and preserved for measurement. Later, 2687 of these specimens were measured. Those .measured belonged to 86 diverse lines, derived from 43 diverse pairs of conjugants; thus on the average a trifle above 31 specimens were measured from each of the 86 lines. The numbers measured varied, however, from 16 to 66 for given lines (table 3).
It would of course have been of interest if descendants from a larger number of pairs could have been included, but the details of conducting so large an experiment as this one, concerned mainly with the study of the rate of fission, are so laborious that we did 193