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PROTOZOOLOGY 



Table 6. — Groups, varieties and mating types in Paramecium 

 aurelia (Sonneborn) 



indicates that conjugation does not occur; numbers show the 



maximum percentage of conjugant-pairs formed; Inc. 



indicates incomplete mating reaction 



In P. bursaria, Jennings (1938, 1939) found three varieties. Va- 

 rieties 1 and 3 contain 4 mating types each, while variety 2, eight 

 mating types. Jennings and Opitz (1944) further found variety 4 

 (Russian), composed of tw r o mating types and variety 5 under which 

 several Russian clones were placed. Chen (1946a) added variety 6 

 (originating in Europe) containing four mating types. Thus in this 

 species of Paramecium, there are now six varieties, containing 23 

 mating types (Table 7), and mating reaction occurs even among 

 enucleate fragments of animals of different mating types of the same 

 variety (Tartar and Chen, 1941). In Euplotes patella, Kimball (1939) 

 observed six mating types which he designated as type I to type VI 

 (Table 8). 



Though the members of a clone are of the same mating type and 

 therefore do not conjugate, a clone may undergo at very long inter- 

 vals (some 2000 culture days), "self -differentiation" into tw r o mating 

 types which then conjugate (Jennings, 1941). Furthermore, Jennings 



