70 



ROBERT W. HEGNER 



the two lines studied, and also to indicate the differences in di- 

 ameter of the chromatin masses between the two lines. 



The diameters of the drawings were measured in units of 0.25 

 mm. Table 29 gives the distribution of the diameters thus ob- 

 tained. The range of variations was in line 150.2ba. from 36 to 

 56 units, with a mean diameter of 47.82 units; and that in line 

 58eg. was from 24 to 41 units with a mean diameter of 35.66 units. 

 There was thus a difference of 12.16 units between the mean di- 

 ameters of the chromatin masses in the two lines. These data 

 prove conclusively that the diameters of the chromatin masses 

 within these two lines were different and that the chromatin 



TABLE 29 



Arcella dentata. Table showing the distribution oj the diameters of the two chro- 

 matin masses in forty specimens each of lines 150.2ba and 58eg. The chromatin 

 masses within the living animals were drawn with a camera lucida magnified 

 900 diameters, and the diameters of these drawings were there recorded in units 

 of 0.25 mm. 



masses in the smaller line were much smaller than those in the 

 larger line. 



Another fact brought out by these measurements is that the 

 two chromatin masses in any specimen are often exactly equal 

 in size and usually almost of the same size. The differences in 

 diameter between members of the pairs of chromatin masses in 

 the specimens are tabulated in table 30. In line 150.2ba. the 

 m.embers of twelve pairs were equal in size and those of the other 

 twenty-eight pairs differed from each other in diameter from 1 to 

 4 units, the average difference for the forty pairs being 1.5 units. 

 In line 58eg, the members of seventeen pairs were equal in size 

 and those of the other twenty-three pairs also differed from each 

 other from 1 to 4 units in diameter, the mean difference being 

 0.98 unit. 



