GENERAL CONSIDERATIONS 



21 



Figure 4. Urolep- 

 tus halseyi Calk. 

 X-bodies, chromatin 

 elimination, and nu- 

 clear cleft, in prep- 

 aration for division 

 of the macronude- 

 us. (After Calkins, 

 1930.) 



method, leaving vacuoles in the nuclear substance. 

 Toward the beginning of the following period of 

 division, these X-granules, as they were called, be- 

 come larger and more numerous, and collect, form- 

 ing a disc which extends across the nucleus nearer 

 one end than the other. This disc stains with acid 

 dyes and is entirely dissolved by the Feulgen hy- 

 drolysis. It forms the familiar Kernspalt of the 

 ciliate macronucleus and its substance appears to 

 act as a catalyst, for the smaller portion of the 

 nucleus between the disc and the nearer end of 

 the nucleus separates from the larger moiety (Figs. 

 3A, 3B; Fig. 4), and eight of these large frag- 

 ments now unite in the cytoplasm to form a single 

 division nucleus, while the eight smaller fragments, 

 with their contained X-bodies and chromatin, are 

 resorbed in the cell. 



Here, then, is evidence of metabolic activity and 

 change leading to the phenomena of cell divi- 

 sion. 



Reorganization of the Macronucleus and 

 Other Derived Structures in Ciliata 



Analogous processes of chromatin elimination, 

 which numerous observers have referred to as evi- 

 dence of "nuclear purification," occur in different 

 ways in other ciliates. Kidder (1933) described a 

 core of modified chromatin accumulating in the 

 center of the macronucleus of Conchophthirus (Kid- 

 deria) mytili ( Fig. 5 ) . This core condenses into a 

 small deeply staining ball which, upon division of 

 macronucleus, remains for a time in the connecting 

 strand of the daughter nuclei, but ultimately dis- 

 appears in the cytoplasm. A similar protrusion, 

 referred to only incidentally by Rossolimo and 



