The Nature and Inheritance of Mating Types in Euplotes Patella.

N A previous paper (KIMBALL 1939b), the occurrence of six mating I types in the ciliate protozoan Euplotes patella was reported. These have since been designated by the Roman numerals I to VI. Considerable information which has now been gained about the inheritance and nature of the action of the mating types in this organism will be set forth in the present paper. The investigations presented here may be divided into three main parts: (I) the method of inheritance of the mating types as determined by appropriate crosses, (2) evidence on the nature of the action of the mating type in bringing about conjugation, (3) an analysis of the exceptional conjugation, which, as pointed out by KIMBALL (1939b), is not infrequent in this species. The results of these investigations indicate that the mating types in Euplotes patella are basically dependent upon a relatively simple genetic mechanism. However, the exceptions, which are not uncommon, indicate that there are secondary complications, but these are not thoroughly understood. The inheritance of mating types appears rather different from that found by SONNEBORN (1939) for Paramecium aurelia and by JENNINGS (1941) for P. bursaria.