60 ROBERT W. HEGNER 



h. Selection within the family for specimens large and small 

 in diameter was immediately effective and two lines were ob- 

 tained showing a mean difference in diameter of 4.75 units of 4.3 n 

 each. 



c. Changes in nuclear number occurred before and during the 

 selection period, and all of the members of the low line were 

 found to possess 4 nuclei, whereas those of the high line con- 

 tained 5 or 6 nuclei. 



d. Selection of the largest and smallest specimens within 

 groups of members containing certain numbers of nuclei indicate 

 the range of the diameters of specimens with each nuclear num- 

 ber. The correlation betw^een nuclear number and diameter is 

 very marked (.752 d= .018) and the mean diameter increases as 

 the number of nuclei increases. 



e. Changes in nuclear number occurred at irregular intervals 

 arid consisted usually of an increase or decrease of one nucleus. 

 In several cases the number of nuclei doubled from 3 to 6. 

 Changes in nuclear number were accompanied by changes in 

 diameter, and in every case an increase in the number of nuclei 

 led to an increase in diameter, and a decrease to a decrease in 

 diameter. 



/. The range in nuclear number was from 3 to 7, but speci- 

 mens wdth 1 and 2 nuclei were obtained by bisecting specimens 

 with 3 or 4 nuclei. Usually the parental condition was soon re- 

 gained by the descendants of these pieces, but enough uninucleate 

 and binucleate progeny were reared to prove that in these speci- 

 mens, as well as in those with a greater number of nuclei, the 

 diameter is closely correlated with nuclear number. No empty 

 shells were formed at the time of a numerical increase in the 

 nuclei. 



6. Comparisons of the nuclear number and diameter of speci- 

 mens in different families resulted as follows : 



a. Among twenty-five families there were some whose members 

 possessed few nuclei but were of large diameter and others whose 

 members possessed a larger number of nuclei but were smaller 

 in diameter. 



