NUCLEOPLASMIC RELATIONS IN ARCELLA 



43 



During this time the specimens were separated into classes 

 according to the number of nuclei they possessed, and both 

 the largest and the smallest members were saved in each class, 

 all others being discarded. Here, as usual, past performance 

 was used as a basis for selection. Table 15 shows the results 

 obtained. The specimens fell into four classes with 3, 4, 5, and 

 6 nuclei, respectively. The range of variation in diameter was 



TABLE 15 



Arcella polypora. Family ap. 5. Correlation table for nuclear number and diame- 

 ter of the shell in 263 specimens. These were obtained during a period of twenty- 

 four days when the largest arid smallest specimens imder each nuclear number 

 were selected. The unit of measurement is 4.3 ix. Coefficient of correlation, 

 0.752 ± 0.018 



about the same for those with 3 and 4 nuclei, and exactly the 

 same for those with 5 and 6 nuclei. The mean diameter, how- 

 ever, increased steadily from that of 25.12 units in the 3-nu- 

 cleated class to 29.35 units in the 6-nucleated class. The coeffi- 

 cient of correlation between nuclear number and diameter is 

 large and, of course, would have been much greater if selec- 

 tion had not been practiced. Figure 33 shows by means of 

 curves the differences in diameter of the groups in family ap. 5 

 arranged according to nuclear number. 



5. Changes in nuclear number and their results. The changes 

 in nuclear number during this period were of two principal 



