326 



THE BIOLOGY OF STENTOR 



Conjugation in S. coeruleus, largely following the 

 account of Mulsow, 191 3. 



1. Stentors attach by areas just below membranellar bands, 

 maintaining a separating partition or fusing to some degree. 



2. Old macronuclear nodes break apart, become spherical, and 

 may show honeycomb structure. (These organelles are omitted 

 from subsequent drawings up to stage 11.) The 50-70 micro- 

 nuclei are near the macronuclear nodes. 



3. Micronuclei separate freely in the cytoplasm, all enlarging 



and stain less intensely. 



4. Up to 10 micronuclei in both cells degenerate. Others 

 divide mitotically but not simultaneously, giving about 60 nuclei 

 in each. These are probably not maturation but "multiplicative" 

 divisions. Stages in mitosis are shown below: 



a: homogeneous, swollen micronucleus. 



b: parachute stage, with chromatin at one end, single 



spindle pole at the other. 

 c: chromatin pulling toward equator (by traction fibers?). 



Degeneration may occur after this phase. 

 d: equatorial ring of chromatin. 

 e: development of second spindle pole, spindle fibers 



pointing toward centrioles. 

 /.• polar cones flatten as nucleus becomes cylindrical; no 



fibers found between chromosomes, approximately 80 



in number. 



