THE NUCLEI OF UROLEPTUS MOBILIS 



305 



In the vegetative stages the micronuclei are very minute 

 (1.6 M in diameter) and homogeneous in structure. They are 

 variously distributed in the cell, a typical distribution being 

 shown in figure 1. They lie, as a rule, close to the macronuclei, 

 but are never embedded in the latter. They undergo mitosis 



19 



21 



^< 



Figs. 19, 20, and 21 Cell division completed; four macronuclei present (fig. 

 19) which divide to form eight after daughter cells separate. The six micronu- 

 clei are reduced to four. X 800. 



which must be a slow process, for mitotic figures persist from 

 the beginning of segregation of the macronuclei until the ellip- 

 soidal nucleus is formed and ready to divide. Actual division 

 of all such mitotic nuclei does not occur, for there is no increase 

 in number at this period. 



On the contrary, the number actually, decreases until, when 

 the macronucleus is ready to divide, there are only two micro- 

 nuclei, and these are in mitosis (figs. 4 to 10). This decrease is 



