NUCLEOPLASMIC RELATIONS IN ARCELLA 



63 



The uninucleate offspring was provided with only a small amount 

 of cytoplasm and died after a few days. In this case, evidently, 

 something interfered with normal fission and the nuclei were 

 unequally distributed, three remaining within the parent and 

 only one being contributed to the offspring. The latter died, 

 probably because of the small amount of cytoplasm it possessed. 

 The parent with 3 nuclei may then have become binucleate 

 again during the next fission, if only one of the nuclei divided 

 and the four thus obtained were equally distributed between it 

 and its next offspring. 



TABLE 27 



Arcella discoides. Table giving the distribution of diameters in seven families. 

 The unit of measurement is 4.3 ii 



iVnother case worthy of mention is that of the appearance of 

 a large but temporary variation. This also occurred in family 

 3. The pedigree (fig. 41) shows how a sudden large decrease in 

 diameter from 29 to 26 and then to 25 units was followed by a 

 rapid increase from 25 to 29 and then to 30 units, which was 

 near the normal family dimensions. 



A thu'd irregularity was noted in family ad. 10. A diameter 

 much less than normal of several nearly related specimens was 

 due to a crease in the shell which was passed on for one genera- 

 tion, and then disappeared, the full size of the specimens being 

 regained. All of these specimens possessed the normal number 

 of nuclei — 2. The following series of figures gives the diameters 

 in units of the immediate offspring of five successive generations, 

 and the letter c indicates which specimens were creased. 

 32 - 29 - 28c - 26c - 30 - 31 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 30, NO. 1 



