PARAMECIUM BURSARIA: LIFE HISTORY. I. IMMATURITY, MATURITY AND AGE

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Abstract
The life history of clones of P. bursaria shows successive periods: 1) a period of sexual immaturity, in which sexual reactions and conjugation do not ocur; 2) a transitional period in which weak sexual reactions occur in a few individuals; 3) maturity, in which sexual reactions are strongly marked and conjugation occurs readily; 4) a period of decline, ending in many (or all?) cases in death. The time of attainment of maturity depends on the cultural conditions. If the animals are well nourished and kept rapidly multiplying, maturity comes on early (in from a few weeks to 5 mo.); if they are subjected for some time to depressing conditions, maturity is delayed till the age of 10 to 14 mo. or more. The period of maturity lasts for several yrs. Mature clones usually react sexually strongly and form pairs; but in some clones the sexual reaction is not followed by conjugation. In the period of decline fission becomes slower, abnormalities appear, the cultures become scanty and ultimately die out. Clones have lived 9 yrs. in the laboratory before finally dying out. Conjugation may occur in the period of decline, but it then results in death of most or all of the ex-conjugants.