30 



ROBERT W. HEGNER 



the descendants of the smaller piece (155b) were at first smaller 

 and possessed fewer spines than those of the larger piece (155a), 

 but after several generations they became similar in these char- 

 acters. The formation of empty shells and nuclear doubling 

 occurred as in the other lines studied, and the specimens after 

 becoming binucleate, soon regained the mean condition of 

 the line from which the original progenitor of the line was taken. 

 Figure 29 shows stages from one original quarter of specimen 

 155 to the attainment of the normal binucleate condition. 

 The line was discontinued when specimens with 11 and 12 



i(X55a) 



18-29(2) 

 (155) 



8-19(1)' 



7-18(1)' 



.7-18 E 



9-22(2): 



8-19 E 



.10-25(2) ^10-27(2) 



^9-25(2) -11-25(2) 



• 8-23(2) 11-26(2 ) 10-27(2 ) 



,7-18(1) 7-18(1): 



.7-18 E 



,7-16(1)' 



i(155T>), 



9-21(2) 10-23 (3 gan.) 12-28 



^ 8-17 (1 ) 7-18 (1 ) 9-19 (1 ) 



_^9-17 E 

 -16(1) — -7-16(1) 7-19(1) 9-19(1): 



-10-23 (4 g5n.) 10-29 



Fig. 28 Arcella dentata. Pedigree of part of specimens in line 155 



spines and with diameters of from 27 to 29 units began to 

 appear. Table 8 contains the data as regards spine number 

 and diameter in the members of the line. It is thus evident 

 that one nucleus and less than one-fourth of the normal amount 



TABLE 8 



Arcella dentata. Family 155. Table showing variations in, spine number and 

 in diavieter of the uninucleates, binucleates, and empty shells belonging to family 

 155. The unit of measurement is 4-3 n 



