40 



ROBERT W. HEGNER 



larger than 24 units. After several generations it became 

 necessary to raise the upper limit in the low line from 24 to 25 

 and then to 26 units, because of the small number of specimens 

 ■produced with a diameter less than 25 units. An attempt was 

 made to count the nuclei of the specimens obtained during this 

 period, and in a large proportion of the cases this was accom- 



Fig. 32 Arcella polypora. Family ap. 5. Pedigree of part of the specimens 

 obtained during the first period. The variations in diameter are large. 



plished. The data obtained are presented in tables 13 and 14. 

 As indicated in table 13, the mean difference in diameter between 

 the high and low lines was 4.75 units. This difference is very 

 much greater than it w^as possible to obtain with A. dentata 

 during a longer period with many more specimens and a larger 

 number of generations. 



