The replication of metagons and mu particles from Paramecium in another cell—Didinium

1. The maintenance of mu particles and metagons from Paramecium aurelia (stock 540, syngen 1) in another ciliate protozoan Didinium nasutum has been shown to occur. 2. It has been shown that mu particles could not be supported in Didinium without metagons. One particular strain of Didinium has, however, never been able to support mu even when metagons were present. 3. The continued production of metagons in Didinium was shown to take place even when the Didinium was fed on killer Paramecium of genotype m1m1m2m2. 4. After destruction of the metagons in Didinium by ribonuclease there was no subsequent reappearance of metagon activity. 5. Metagons and mu particles were eliminated from Didinium during encystment. 6. It is considered that the increase of metagons in Didinium is due to self-replication. In Paramecium the metagons replicate only slowly or not at all. 7. It is concluded that the metagon is a gene product in Paramecium which takes on at least one other property, replication, when introduced into Didinium.