154 



On the Genetics of the Ciliate Protozoa 



distinctive characters of 6 such " pure lines " of cnudatum. and 5 of 

 aurelia are fully set forth by Jennings and Hargitt (1910). 



64. The nature of these pure lines will be instantly envisaged in 

 the accompanying diagram (Fig. 4). We here see (upper line) outlines 



X340 



of individuals of mean size belonging to eight different races of Para- 

 mecium, drawn to the same scale. The differences in size are remarkable 

 — the actual mean length of the largest race (L., caudatum) reaching 

 230 /ti, of the smallest (i, aurelia) only 90^. 



65. Within each race the individuals may differ considerably from 

 one another in size — as a result of growth, nutrition, and external 

 conditions. This is shown diagrammatically in Fig. 4 (lower line), 

 which depicts the relative dimensions of 10 individuals belonging to 



