NUCLEOPLASMIC RELATIONS IN ARCELLA 69 



just before division occurs. Conditions may be somewhat sim- 

 ilar in Arcella, and accordingly measurements were made of 

 specimens of both lines at various times during the day, so that 

 an average size might be obtained. 



One very great advantage possessed by Arcella over the other 

 protozoa thus far studied with a view to the solution of nucleo 

 cytoplasmic problems is the fact that its nuclei are of the sup- 

 posedly primitive type, having all their chromatin clumped to- 



B 



Fig. 44 Arcella dentata. Outlines of the chromatin masses within the nu- 

 clei of living specimens. In A the pairs represent the chromatin masses from 

 single specimens from the larger line (150.2ba) ; these were selected to show the 

 range of variation. In B are similar pairs from the smaller line (58eg.). X 900. 



gether in a compact mass in the center. It is thus easy to meas- 

 ure the chromatin mass separated out from the other nuclear 

 constituents. This chromatin mass is spherical or nearly so, and 

 is distinctly visible in the living animal. Camera-lucida draw- 

 ings of the nuclei of living specimens were made; a no. 10 ocular 

 and a 3-mm. water-immersion lens were used for this purpose. 

 This combination was found to give a magnification of 900 di- 

 ameters. A series of these drawings is reproduced in figure 44, 

 so as to show the various sizes of the chromatin masses within 



