THE NUCLEI OF UROLEPTUS MOBILIS 



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a subsequent publication in connection with its appearance after 

 encystment, after conjugation, and during regeneration. 



In connection with the history of the macronucleus as given 

 above, I find it difficult to interpret Engelmann's statement that 

 the number of these nuclei, in his species, is constantly six. 

 Such a condition might arise if two of the nuclei produced by the 

 second division, should divide again; or it might arise if two of 



Figs. 13, 14, and 15 Division of the macronucleus and beginning cell division. 

 X 800. 



the eight nuclei formed by the third division should degenerate. 

 A third possibility seems more probable, viz., that Engelmann 

 was mistaken. 



B. The micronuclei 



The history of the micronuclei during cell division is much 

 less clear than that of the macronuclei. This is due mainly to 

 the fact that the number is not constant; some cells have six, 



