Paramecium bursaria is known to include 6 varieties (Jennings, '39; Jennings and Opitz, '44; Chen, '46a). Members of any one of these 6 varieties do not, as a rule, mate with members of any of the other varieties. I n each variety animals of diverse mating types conjugate readily; animals of the same mating type do not conjugate. Varieties I, 11, and I11 have been found in the United States. Variety I is known to contain 4 mating types designated A, B, C, and D ; Variety 11, 8 mating types, designated E, F, G, H, J, I<, L, and M ; Variety 111, 4 mating types, designated N, 0, P, and Q. Varieties IV and V were found in Russia. Variety IV is known to have two mating types, designated R and S. Only one mating type (mating type T) has so far been found in Variety V. Further collections from Russia will probably yield other mating types in this variety. Variety VI, found in Czechoslovakia, England and Ireland, is known to contain 4 mating types designated U, V, W, and X. Thus, there are now known in this species of Paramecium 6 varieties containing 23 mating types.
While in China, from December 1946 to July 1947, the writer made a study of mating types of Paramecium bursaria found in China in order to ascertain whether or not the Chinese animals belong to any of the above 6 varieties. It was found * Part of this work was carried out in the Institute of Zoology, Academia Sinica,