1918] Yocum: The Neuromotor Apparatus of Euplotes Patella 369 



of migration of the bands there is little change in the size of the 

 nucleus (pi. 15, fig. 14). However, as the two bands approach each 

 other the whole nucleus shortens and thickens, the granules are 

 crowded close together and it seems that there is more or less of a 

 coalescence of the granular elements, for many granules can be seen 

 which are equal in size to three, or four or more of the original 

 granules. As the bands come nearer together the nucleus becomes 

 more contracted until the greatest period of concentration occurs at 

 about the time that the body begins to constrict (pi. 16, fig. 18). At 

 the period of greatest concentration the granular structure of the 

 nucleus has become almost obliterated, and the nucleus has an almost 

 homogeneous structure. In specimens which are very much destained 

 the contracted nucleus is seen to be made up of large chromatin masses 

 very much crowded together. 



As the body begins to constrict the nucleus again elongates. The 

 granules are very irregular in size and shape, and appear as though 

 they were being pulled by considerable force, for many of the large 

 granules are much elongated and look something like chromosomes 

 (pi. 16, fig. 19). However, there is no evidence that chromosomes do 

 form, for the macronucleus divides amitotically with no indication 

 that the chromatin granules are divided in any way comparable to the 

 division of chromosomes. As the constriction of the animal continues 

 the macronucleus elongates and becomes narrow in the region of the 

 constriction of the body until finally it is completely severed (pi. 16, 

 fig. 21). 



While it is impossible to distinguish the position of the two fused 

 reorganization bands at the time of greatest contraction, it seems that 

 their plane of fusion must be the plane of division of the macronucleus, 

 for the nucleus divides into two approximately equal parts. 



Before the nucleus has completely divided, it has begun to bend in 

 what is to be the anterior daughter organism and also just posterior 

 to the plane of constriction. When divided the nuclei are each shaped 

 somewhat as an inverted letter L, with the base of the letter extending 

 across the anterior end of the animal and the long arm along the left 

 side (pi. 16, fig. 21). Associated with the daughter macronuclei are 

 the daughter micronuclei, which lie near the angle of the L. 



Such a contraction of the chromatin material at once reminds one 

 of the contraction stages occurring in metazoan germ cells. The first 

 contraction, that occurring in the reorganization bands, is a progressive 

 contraction, and begins at the end of the nucleus and migrates toward 



