74 ROBERT W. HEGNER 



The volumes of the two groups of chromatin masses are 

 approximately the same. 



A large amount of time and effort was devoted to an attempt 

 to rear young from the very large specimens of A. polypora col- 

 lected at Cold Spring Harbor (p. 57, table 25), but although 

 every care was taken only a few offspring were obtained. The 

 nuclei of these were not measured at the time, but later a wild 

 specimen was collected in which the nuclei could be seen very 

 clearly. There were 5 nuclei in this specimen; these had a mean 

 diameter of chromatin mass of 11.56 /x, and a mean volume of 

 chromatin mass of 808.86 cubic microns. The shell measured 

 202 ju in diameter. When these measurements are contrasted 

 with those given above for families ap. 5 and ap. 34, and when 

 figures 42, A, B, and C. are compared, it becomes evident that 

 the relation between the quantity of chromatin and the quantity 

 of cytoplasm is here similar to the relations established for 

 famiUes ap. 5 and ap. 34. 



c. The possible relation between the chromatin mass and the death 

 of certain specimens of Arcella dentata 



Among the lines obtained in family 58 of A. dentata during 

 selection experiments (Hegner, '19) was one labeled 58ed. The 

 members of this line were heritably different in size from the other 

 lines studied, being much smaller than any of the rest and pos- 

 sessing fewer spines. The line 58e. from which it was derived, 

 had a mean diameter of 27.05 units of 4.3 m each and a spine num- 

 ber of 10.99, whereas line 58ed. had a mean diameter of only 23.51 

 units and a mean spine number of 9.91. From this small line 

 58ed. there was obtained a line 58edb. containing extremely large 

 specimens. These had a mean diameter of 35.54 units and a 

 mean spine number of 17.54. However, in spite of the greatest 

 care, only a few of these large specimens were reared, and these 

 all died in the course of several weeks. 



Drawings of one chromatin mass in each of four specimens 

 belonging to this large line were made, and similar drawings of 

 chromatin masses in four specimens of the small parent line (fig. 



