NUCLEOPLASMIC RELATIONS IN ARCELLA 67 



a correlation between size and nuclear number and that the 

 greater the number of nuclei, the larger the size. 



4. Shape as well as size is a character that is inherited within 

 families of Arcella vulgaris. 



6. THE RELATIONS BETWEEN CHROMATIN MASS AND CELL SIZE 



What the essential differences are between families ap. 5 and 

 ap. 34 of Arcella polypora is a problem that involves thestudj^of 

 the relation between chromatin mass and cell size, since the sug- 

 gestion presents itself at once that there may be a quantitative 

 difference in the amount of chromatin in the nuclei possessed 

 by members of the two families, but that the chromatin is qual- 

 itatively approximately alike. Before considering these two 

 families of A. polypora it will be instructive to examine the con- 

 ditions within two families of A. dentata. 



a. Chromatin mass and cell size within two families of Arcella 



dentata 



These two families had the following history before they were 

 used for the studies reported below. Line 150.2ba, which was 

 part of family 150, is fully described in the first part of this con- 

 tribution, having been used in the cutting experiments. The 

 original progenitor was collected at Baltimore on December 27, 

 1917, and when the experimental work upon its offspring was 

 discontinued a few specimens were kept in a Syracuse watch- 

 glass so that the line would not die out. These were examined 

 every day or two to see if any conjugation was taking place, 

 and about once each week six of the youngest specimens were 

 transferred to another watch-glass containing fresh food. No 

 conjugation was observed during the period when they were 

 thus being continued in mass culture. During the winter and 

 spring months this line produced a generation every two and one- 

 half days and there is no reason to suppose that this rate of repro- 

 duction changed after the mass-culture method was begun, hence 

 at the time the chromatin mass studies were begun the speci- 

 mens used represented about the 93rd generation. During the 



