182 PROTOZOA 



lines of evidence. These independent evidences of evolutionary 

 relationship will be discussed later. Figure 1 anticipates that dis- 

 cussion by diagramming the inferred relationship of the six va- 

 rieties that have been studied serologically: varieties 1, 2, 3, 4, 

 8, and 9. The serologic results are summarized in Beale ( 1954 ) , 

 except for the subsequent publications by Finger (1956; 1957a, 

 b) on variety 2; by Melechen (1955) on variety 3; by Austin et 



Fig. 1. Inferred evolutionary relationships of varieties 1, 2, 3, 4, 8, and 

 9 of Paramecium aurelia, the only varieties that have been studied serolog- 

 ically. 



al. (1956), Margolin (1956a,b), and Skaar (1956) on variety 4; 

 and by Pringle (1956) on variety 9; and unpublished work of 

 Preer on variety 2 and Sonneborn and associates on varieties 4 

 and 8. 



The most closely related varieties are 4 and 8 and their sero- 

 type systems show the greatest resemblance. For the most part, 

 each serotype found in one variety is matched by a serologically 

 recognizable corresponding serotype in the other variety; but a 

 few serotypes have thus far been found only in one or only in 

 the other variety. Further, the corresponding serotypes are sel- 

 dom if ever serologically identical although they commonly cross- 

 react. The cross reactions are usually weaker than those involv- 

 ing corresponding serotypes of different strains of the same 

 variety. 



The differences between these two varieties and variety 2 are 

 much more marked. Several serotypes (A, C, E, F, G, and II) 

 have been recognized in variety 2 which correspond to serotypes 

 ol varieties 4 and 8, but they show marked differences in specific- 

 it}. There are, moreover, some general resemblances in the sys- 

 tem ol serotypes, which, as will appear, distinguish these three 



