DIVISION, NUCLEAR REORGANIZATION AND CONJUGATION IN 



ARCELLA VULGARIS. 



H. M. MACCUBDY. 



(Abstract.) 



The number of times a given individual, as recognized by sliell characters, 

 divides in pedigreed cultures was studied. A given individual produces a 

 limited number of daughter cells, and was not found to continue to divide 

 indefinitely, as has been maintained. The number of times a given individual 

 was found to divide varies from none up to twenty-seven, the highest number 

 found in a single case. 



The daughter cells, and in turn their offspring, behave in a similar way, 

 with the exceptions indicated. 



After a period of vegetative divisions in a line derived from one indi- 

 vidual, a period of "depression" occurs. This "depression" does not neces- 

 sarily occur in all of the offspring nor at the same time, but it usually does 

 occur in most of the offspring during a given period of time. Some of the 

 features marking this period are : Reduced activity, such as division, locomo- 

 tion, feeding; "punctate" shells, "empty" shells and uninucleate individuals. 

 Arcella vulgar-is typically has two vegetative nuclei. These features are not 

 necessarily accompaniments of "depression," and may sometimes be found in 

 unfavorable culture ; but they do occur in the best of cultural conditions at the 

 times of "depression." This is significant. 



Individuals may pass successfully through this period and enter upon a 

 new period of vegtative divisions or they may not do so. 



While some members of a line are "depressed," others were found to 

 undergo conjugation. 



After conjugation, the individuals after separation may differ markedly 

 in size from the parent line. It is believed these are "mutants." "Mutants" 

 may arise without an evident "depression" period. Jennings, 1917, found 

 what he regarded as mutations in Diffliigia corona. 



After conjugation, the individuals after separation usually proceed to 

 divide within one or two days. The exconjugants tend to produce the same 

 numbers of daughter cells at about the same rate. Ex-conjugants of Para- 

 moecia have been shown by Jennings to tend to have similar fission rates. 



In lines derived from a single individual, "depression" periods and con- 

 jugation have been found to occur at intervals of from four to six weeks in 

 most cases. This is for pedigreed cultures extending from the first of January, 

 1918, to the twenty-third of June, 1918, including many thousands of indi- 

 viduals. 



