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Addendum 



Material that appeared too late for the manuscript includes new informa- 

 tion on sexuality in Tetrahymeva from the Nanney-Elliott group, a detailed 

 study of the role of irradiations in the mating rhythmicity of Paravieciuni 

 bursaria (Ehret, 1953), and a comprehensive review of the cell surface in rela- 

 tion to metazoan fertilization (Runnstrom, 1952). 



Elliott and Hayes (1953) found three interbreeding mating types in Tetra- 

 hymeria pyriforniis material collected at Woods Hole. From the Fi, Fo, F^, and 

 back cross progeny obtained by mating two of these (Type I, stock WH-6 x 

 type II, stock WH-14) Nanney and Caughey (1953) isolated a total of seven 

 pure mating types. These seven types form an interbreeding system; any one 

 of the types will conjugate with the remaining six types. These workers empha- 

 size that the first sign of a sexual reaction (pairing) does not occur for at least 

 90 minutes after mixing complementary types. Immediate agglutinative mating 



