318 GRIFFIN. 



disappear in the usual manner, leaving tlie reconstruction planes joined; 

 the new chromatin reticula advance toward the center from both sides, 

 unite, and leave no trace of the plane of junction. 



A division of the chromatin substance by one, two, or three planes is 

 not an uncommon character of the meganuclei of the Infusoria. Biitschli 

 mentions the presence of "KernspaUen" in Euplotes, Aspidisca, Dysteria, 

 Ifassula, Strombidium, Spirochona, and Stylonychia, and in the families 

 Chlamydodonta, Holophryiua, Trachelina, and Tintinnoina. The re- 

 construction bands of Euplotes were long ago observed by Stein (1859), 

 but they do not seem to have received any attention from other authors. 



The clefts {KernspaUen) in the meganuclei of Stylonychia have been 

 the classical examples of this kind of structure, all other similar ap- 

 pearances apparently having been interpreted as being the same. Judging 

 from the accoimt given by Biitschli, the KernspaUen of Stylonychia are 

 structures entirely different from the reconstinictiou bands of Euplotes. 

 They appear in the nuclei of Stylonychia shortly after division, disap- 

 pearing as the next division begins, and usually lie a little in front of the 

 middle of the anterior nucleus and behind the middle of the posterior one. 

 If we agree that the two meganuclei of Stylonychia represent not separate 

 bodies, but a stage of precocious division of a single meganucleus, the 

 position of the "KernspaUen" reminds us of the appearance of the 

 reconstruction bands of Euplotes first at the opposite ends of the nucleus. 

 Beyond this, there is no apparent resemblance either in structure or 

 history. I do not Itnow of any work on the "KernspaUen" of other in- 

 fusoria sufheiently detailed to permit a comparison to be drawn with the 

 reconstruction bands of Euplotes. 



Balbiani, in 1895, suggested that the unstained substance in the 

 "KernspaUen" of Stylonychia may be composed of a mass of achromatic 

 material, or archoplasm. No substantiation of this suggestion has yet 

 appeared, nor do the observations of nuclear division in Stylonychia in- 

 dicate that the "KernspaUen" exercise any directive influence upon the 

 process. 



Whether the reconstruction bands of Euplotes are of the same nature 

 as the "KernspaUen" of Stylonychia or not, it is certain that they are not 

 composed of arclioplasmic substance, but are regions where a solution, 

 change, and reconstruction of the chromatin occurs. The elimination of 

 superfluous cliromatin fi-om the nucleus has been observed to occur in 

 numerous Protozoa, and in some Metazoa. Many different means exist 

 for the accomplishment of this object. In some cases granules of 

 chromatin pass bodily through the nuclear membrane into the cytoplasm, 

 where they may remain indefinitely and perform some useful function or 

 may be rapidly altered into unrecognizable substances. In others, the 

 useless chromatin is extruded from the chromosomes, but dissolved within 

 the nucleus. Elimination regularly occurs before either division or con- 

 jugation, evidently as a part of the preparation for these processes. 



