42 



ROBERT W. HEGNER 



changes in size took place during this period, but later work 

 proved this explanation to be correct. The correlation between 

 the parents and offspring during this period is very striking 

 (table 14). 



TABLE 13 



Arcella polypora. Family ap. 5. First selection period. Table giving the mean 

 diameter of the shell and the number of nuclei possessed by the specimens in the 

 high line (ap. 5a) and low line {ap. 5b). The unit of measurement is 4-3 n 



NUMBER 



WITH 

 6 NTJCtEI 



High (ap. 5a) . 

 Low (ap. 5b). 



65 



1 The number of nuclei could not be determined with certainty in a few of 

 the specimens. 



TABLE 14 



Arcella polypora. Family ap. 5. Correlation table for diameter of the shell in 

 parents and progeny during a period of eight days when selection for specimens 

 with large and small diameters was practiced. Coefficient of correlation, 0.742 



± 0.258 



Jf.. Results of selection for large and small diameters within 

 groups with the same number of nuclei. Period 3. On May 19 

 a new selection period of twenty-four days was inaugurated. 



