24 



ROBERT W. HEGNER 



Experiment 2, line 158alb. Progenitor: First offspring (uninu- 

 cleate) of the nucleated piece of uninucleate specimen 158a; spines, 9; 

 diameter, 24 units. 



Descendants: Sixty-four uninucleates were recorded; these belonged 

 to sixteen generations and were produced during a period of nearly 

 two months (January 15 to March 4, 1918). No empty shells were 

 formed and no binucleate specimens occurred during this period, but 

 no doubt they would have appeared if the line had been kept longer. 

 The following table gives the mean diameters and spine numbers of 

 the sixty-four offspring arranged according to generations. 



These data show in a very striking manner the gradual increase in 

 diameter and spine number during the first three or four generations, 

 and the attainment in later generations of a mean diameter and a mean 

 spine number characteristic of the uninucleates of family 150. Since 

 the nucleus is the same after the operation as before, we must attribute 

 the small size of the progeny of the first generation to limitations due 

 to the small amount of cytoplasm present. Apparently the nucleus 

 is capable of reacting with a certain amount of cytoplasm, and when, 

 after three or four generations the maximum quantity of cytoplasm has 

 been formed, equilibrium is attained and no further increase takes 

 place. The quantity of cytoplasm may in turn be dependent upon the 

 capacity of the shell. 



Experiment 3, line 161a. Progenitor: Uninucleate specimen from 

 third generation of line 158a, spines, 9; diameter, 25 units (fig. 21, B). 



Descendants: 



Uninucleates. 

 Empty shells 

 Binucleates. . 



NUMBER 

 OF SPECIMENS 



8 



4 



14 



MEAN SPINE 

 NUMBER 



10.13 

 10.25 

 13.14 



MEAN 



DIAMETER 



25.50 

 26.75 

 29.93 



The process of empty shell formation and nuclear doubling, and the 

 gradual increase of uninucleates and binucleates to a condition charac- 

 teristic of the original line, 150, occurred as in line 158a. 



