GENERAL CONSIDERATIONS 23 



macronucleus. A small granule in the center of the cleft represents the 

 first of the reorganized nuclear material. As the cleft pushes across the 

 diameter of the nucleus, the central reorganized chromatin increases in 

 amount. Two separate "reorganization bands" result when the wedge- 

 shaped cleft reaches the opposite side of the macronucleus. These bands 

 then move in opposite directions, traversing the entire macronucleus and 

 disappearing at the two ends. The increasing zone of staining chromatin 

 granules, is quite different in appearance and in staining capacity from 

 the chromatin in parts of the nucleus which have not been traversed 



Figure 6. Aspidisca lynceus. Origin and further history of the reorganization bands. 

 (After Summers, 1935). 



by the bands. After disappearance of the bands at the ends, the nucleus 

 condenses to form the typical division macronucleus of Aspidisca. Here 

 again, therefore, there has been a physical change in the chromatin and a 

 change that is brought about through activity of substances which form 

 the nuclear cleft. 



A similar process takes place in the genus Euplotes, the reorganization 

 bands of which have been studied by numerous investigators. Griffin 

 (1910) was the first to describe them fully as "reconstruction bands," 

 but by later writers, beginning with Yocom (1918), they have been 

 known as "reorganization bands." In Euplotes the bands begin one at 

 each end of the macronucleus and proceed toward the middle, where 

 they meet and disappear. There is no unanimity of opinion as to what 

 takes place during this passage of the bands, but all agree that some re- 

 organization of the chromatin occurs. Griffin [loc. cit.) expressed the 

 opinion that all of the chromatin is disolved and later re-formed without 

 the erstwhile impurities. Yocom [loc. cit.), on the other hand, holds that 



