FERTILIZATION 637 



differentiated, they divide at every subsequent body division, as in 

 Euplotes patella. 



The macronuclei grow to their normal size and are distributed by 

 body fissions to the daughter and granddaughter cells, if more than the 

 vegetative number are formed, as in Paramecium. Thus the ordinary 

 vegetative form is reestablished. 



During their development, the young macronuclei undergo some 

 striking and significant changes. Several investigators have reported 

 marked enlargement of the macronuclear Anlagen in ciliates, since the 

 early description of the "ball-of-yarn" stage in Nyctotherus cordiformis 

 by Stein (1867). 



Calkins (1930) showed that the macronuclear Anlage of Uroleptus 

 halseyi at first contains no chromatin, if chromatin be defined as a 

 nucleic acid containing substance. As the young macronucleus grows, 

 minute chromatin granules are formed within the matrix and grow in 

 size and number until the nucleus is filled with large, intensely staining 

 chromatin granules. Subsequent divisions of this "placenta" and of the 

 cell body restore the normal vegetative nuclear complex. 



A number of other ciliates show enlargement of the placenta to a size 

 greater than that of the ordinary condition, after which shrinkage, or 

 condensation, reduces it to its vegetative size. According to MacDougall 

 (1925), the young Anlage of Chilodonella uncinata stains very faintly 

 at first, but more intensely later. The enlargement continues until the 

 young macronucleus nearly fills the cell. 



In Euplotes patella (Turner, 1930), as in Uroleptus, the early macro- 

 nuclear Anlage contains little, if any, demonstrable chromatin. After 

 several hours of growth, a fine chromatin reticulum develops and is 

 transformed into a broken spireme. The chromatin spireme enlarges 

 with the nucleus and resembles the "ball of yarn" in Nyctotherus cor- 

 diformis, as pictures by Stein (1867) and Wichterman (1937), except 

 that the spireme is more tortuous. Earlier stages resemble those of 

 Metopus sigmoides as drawn by Noland (1927), and of Paraclevelandia 

 simplex (Kidder, 1938) in cystic reorganization. The spireme finally 

 becomes shorter and very much thicker, as chromatin granules are 

 formed along its periphery. At this stage a fine thread is discernible run- 

 ning through the center of the spireme. The granules become scattered 

 throughout the macronuclear Anlage as the structure of the spireme 



