(14) 



cent papers of Ewing (1914, 1914a, 1916^, for example) this 

 precaution has been neglected. 



My first cultures of Centropyxis aculeata began in 

 October, 1914, with the isolation of fifty individuals from 

 a pipetteful of aebris taken from a mat of Oedogonium 

 growing on a lotus stem in the Komev/ood pond , Baltimore . 

 About twenty of these lines died out during the first month, 

 wwhile I was learning the best culture methods. At the end 

 of this time the thirty remaining lines all seemed to be 

 distinct from each other. To keep the cult^ores within 

 manageable bounds, only the four largest clones were con- 

 tinued for two m.onths more. In considering inheritance 

 v.'ithin a population, then, the population consists only of 

 these four clones, numbers 9, 30, 41 and 43, containing in 

 all 1049 individuals. 



It was evident, from the very first, that at least two 

 distinct strains existed in my material. A glance at Table 

 I or Figure 4 shows clearly that line 30 differs most deci- 

 dedly fromi the other three lines. Their small size, rapid 

 fission rate and high spine number differentiate individuals 

 of this line from the others at first sight. 



The other three lines resemble each other more closely. 

 The differences betv/een them are more minute. Line 43 is 

 the most clearly distinct of the three. Its higher fission 

 rate alone would suffice to separate it from the others, and 

 its distinctness is further shown by the slightly smaller 

 size and lower spine number uf its members. 



The other two lines, 9 and 41, are closely allied. The 

 most striking difference between them lies in the higher 



