THE PHYSIOLOGY OF FERTILIZATION IN CILIATES 295 



variety. Less perfect "fits" resulting in weaker linkages and less strong 

 mating reactions should, and in most cases do, occur in intervarietal 

 combinations of plus and minus mating types. 



In P. cctudatinn an even larger number of sexually isolated varie- 

 ties has been reported. Gilman (1950) has described eleven varieties 

 and has tested these against the four Japanese varieties found by 

 Hiwatashi (1949a). Two of the latter failed to conjugate with any 

 of Gilman's cultures (Gilman, 1950) and are therefore distinct varie- 

 ties. This gives a total of thirteen varieties with twenty-five mating 

 types (only one mating type has so far been found in variety 10). 

 Aside from these Y. T. Chen (1944) has described four Chinese varie- 

 ties. These have not been tested against the American or Japanese 

 varieties and may include additional varieties. 



Although mating generally occurs only between the two types in 

 a variety, Gilman (1949) does report seven intervarietal reactions. 

 One of these links varieties 3 and 6; the remaining six reactions link 

 varieties 2, 8, 9, and 10 in such fashion that two general types appear 

 (the reaction between types XVIII and XX is so irregular that the 

 writer suspects an error). Gilman's (1949) data are summarized in 

 Table II, and the similarity to the situation in P. aiirelia is apparent. 

 As in the latter species the mating reactions between types within a 



TABLE II 



Intervarietal Mating Reactions in Paramecium caudatum 



Varieties which give no intervarietal reactions are not included in this table. 

 Type XIX, variety 10, has not yet been discovered. 



