52 



ROBERT W. HEGNER 



Family ap. 69 was started on June 29th with a specimen col- 

 lected at Cold Spring Harbor. Its nine members all possessed 6 

 nuclei and ranged in diameter from 32 to 36 units with a mean 

 diameter of 34.22 units. This family thus differs from both 

 famil}^ ap. 5 and from families ap. 38 and ap. 39, its members 

 being somewhat larger than those of family ap. 5 in comparison 

 to the number of nuclei present, and very much larger in this 

 respect than the members of families ap. 38 and ap. 39. These 

 data make more certain the conclusion reached as the result of 



msBeter of shell 



Fig. 36 Arcella polypora. Family ap. 34. Curves for the variations in di- 

 ameter in groups of specimens arranged according to nuclear number; plotted 

 from table 21. The ordinates are numbers of specimens; the abscissae are 

 diameters, and the numbers at the tops of the curves indicate the number of nuclei 

 in the corresponding groups of specimens. 



earlier observations, that different families differ with regard to 

 nuclear number and diameter. 



5. Family ap. 34. Comparison of nuclear number and dia- 

 meter, with family ap. 5. Family ap. 34 was chosen for extended 

 observations, and records were made of 355 specimens. The 

 distribution of the diameters of 302 of these is shown in table 21 

 and also the correlation between nuclear number and diameter 

 within the family. The nuclei could not be counted with cer- 

 tainty in fifty-three of the specimens, and hence these are not 

 included in the table. Figure 36 shows by means of curves the 

 differences in diameter of the groups in family ap. 34 arranged 



