20 



ROBERT W. HEGNER 



were also larger and possessed more spines. This may be 

 brought out more clearly by comparing the means for lines 

 150.2a and 150.2b with those for the thirteen experimental 

 lines in this series as follows: 



In this table the greater mean diameter and mean spine 

 number of the empty shells and uninucleates in the microdis- 

 section series are quite striking. The binucleate specimens 

 belonged mostly to the first offspring after doubling, which 

 accounts for their smaller diameter and fewer spines. From 

 these data the following conclusions are reached. The large 

 amount of cytoplasm induces the immediate or very early for- 

 mation of an empty shell and the accompanying nuclear 

 doubling. It likewise is responsible for the greater diameter 

 and spine number of both the empty shells and of the uninu- 

 cleate specimens. These results are probably brought about 

 because of the inability of the single nucleus to control the 

 metabolism of such a large mass of cytoplasm. 



The full diameter and spine number characteristic of the 

 binucleate specimens belonging to family 150 were reached 

 by the second or third generations in these experimental lines. 

 The rapidity with which this normal condition was attained 

 was no doubt due also to the great initial amount of cj-toplasm 

 present. 



The pedigree of experiment 3 (fig. 19) is given as a sample of 

 what occurred in the remaining five of the thirteen experimental 

 lines, and the pedigree of experiment 4 is presented (fig. 20), 

 because several transitions from the binucleate condition to the 

 uninucleate condition appeared in this line. As in similar 

 cases cited previously, this condition was probably brought 

 about by the failure of the nuclei to divide at the time of fission, 

 and hence the parent and daughter each received a single nucleus. 



