370 University of California Publications in Zoology [Vol. 18 



the middle of that organelle. A careful study has shown that the 

 so-called solution band in E. patella at least is not homogeneous, but 

 that it is granular, indicating a very compact massing of the granules 

 at one region and a subsequent passing of them out over the light 

 staining reconstruction plane to the more diffusely arranged reorgan- 

 ized parts of the macronucleus. This contraction reminds one of the 

 synizesis which was designated by McClung (1905) as occurring in 

 orthopteran germ cells. However, we are not willing to admit that 

 this contraction in Euplotes is an artifact (Whiting 1917, and Hance, 

 1917), as some of McClung 's students have recently suggested for 

 orthopteran cells, since it appears after use of all the killing fluids 

 and stains employed by us. 



The second contraction is that of the nucleus as a whole, which 

 follows the first contraction and immediately precedes the constriction 

 of the organism. This was described in an earlier paragraph and its 

 significance will be discussed later. 



It seems very doubtful that the term solution plane, as used by 

 Griffin (1910) is in any way the proper term to use in denoting the 

 condensed band appearing across the nucleus. As was pointed out in 

 the paragraph above, this band is not homogeneous but granular. True, 

 a change does take place and the chromatin grains coming out of this 

 band may not be the same as those going into it, but observational 

 evidence fails to show that the chromatin is in solution, but rather to 

 show that the granules in that region have become crowded into a 

 compact mass and that they pass over the reorganization plane not as 

 precipitated granules, but as granules which have undergone some sort 

 of physical and possibly chemical reorganization. 



For these macronuclear phenomena we would propose the terms 

 ''contraction phase" to indicate the contraction of the nucleus as a 

 whole, while in place of the terms reconstruction bands as given by 

 Griffin (1910) we would suggest "reorganization bands," indicating 

 a purely physical reorganization of the nuclear material through a 

 contraction of the chromatin, rather than a solution of the chromatin 

 in the karyolymph. 



What reason can be assigned to such a behavior of the macro- 

 nucleus? This is a difficult question to answer satisfactorily. Such a 

 phenomenon is not peculiar to Euplotes but has been observed in other 

 forms. Calkins (1911) describes a distinct reorganization of the 

 macronucleus at the time of division in Uronychia. Here the changes 

 are not quite similar to those occurring in Euplotes, but the reorgan- 



