300 



GAEY N. CALKINS 



subsequent paper. It is not present in young cells after divi- 

 sion, nor during conjugation, and disappears at an early stage 

 of the division activities. 



The two portions of each macronucleus, separated by the 

 nuclear cleft, are apparently different in chromatin make-up, 



Fig. 4 Early stage of division. The macronuclei have lost, or are losing, the 

 nuclear cleft and the distal chromatin; the five micronuclei are in mitosis; the 

 new adoral zone forms anteriorly to the center of the body. X 800. 



Fig. 5 Division stage with fragmented macronucleus preparatory to fusion. 

 X 800. 



Fig. 6 Fusion of the macronuclei. Four micronuclei in mitosis. X 800. 



one portion being less dense than the other. At an early stage 

 in division the chromatin granules of the less dense portion, con- 

 centrate into a single granule in each nucleus (fig. 4). Later, 

 these granules are cast off, and are absorbed in the cytoplasm 

 (fig. 5). This differentiation may be accompanied by further 



