320 GRIFFIN. 



There is a large field for research in the comparative morphology and 

 physiology of the meganuclei of the Infusoria, and for a long time to 

 come general conclusions can not safely be drawn regarding them, their 

 activities, and relationships. However, these observations on the mega- 

 nucleus of Euplotes indicate that the meganucleus is more of an active 

 and less of a passive agent in the cell life than many zoologists seem to 

 believe. The very fact that the chromatin of the meganucleus is recon- 

 structed in a manner which must include an elimination of passive 

 (vegetative) chromatin, such as occurs in niiclei of the ordinary type, 

 indicates that the meganucleus is not only an aggregation of such spher- 

 ules of vegetative or nutritive chromatin, but includes in addition most 

 other properties of the ordinary cell-nucleus. 



The fonn of the nucleus is not altered during the first half of the 

 period of chromatin reconstruction, but as the reconstruction bands 

 approach the center of the nucleus the phase of concentration so universal 

 in meganuclei of this shape is entered upon. Both ends become shorter 

 and thicker, at the same time losing any small irregularities of contour. 

 The more nearly the reconstruction bands approach each other, the more 

 marked becomes the shortening of the limbs of tlie nucleus. The central 

 portion, that is, the part lying between the reconstruction bands, is not 

 usually affected. Figures 14 (Plate V) and 18 (Plate VI) 'show that 

 this region has increased in thickness, which is not the case in figures 

 8, 10, and 13 (Plate V). As the ends of the nucleus become shorter 

 and thicker, the threads of cliromatin are also changed in the same 

 manner, so that the chromatin becomes condensed. Chromatin conden- 

 sation always follows, never precedes, the reconstruction phase. There- 

 fore, the center of a nucleus in which the reconstruction planes are 

 close to each other often presents a marked contrast to the greatly con- 

 centrated ends. Unless the stain is carefully extracted the condensed 

 portions of a nucleus appear unif oi'mly stained, as if the chromatin net- 

 work had been welded into a homogeneous mass. It is certain that the 

 reticulum does not disappear at any stage, even that of greatest concen- 

 tration, but in the last stages it is often impossible to distinguish the 

 threads. Figure 23 (Plate VI) shows the appearance of a poorly 

 extracted nucleus in the concentration pliase, in which a reticulum is 

 visible in only two places. After the reconstruction of the chromatin is 

 complete, the concentration proceeds veij rapidly, until the nucleus be- 

 comes a short, thick rod, varying somewhat in form, which lies in the 

 region formerly occupied by the center of the horseshoe-shaped nucleus. 

 The process of concentration is evidently one of contraction of both ends 

 of the nucleus toward the center, for the latter portion of the nucleus 

 does not move from its place. 



"Bei dieser Concentrirung gegliederter Kerne muss die Membran wohl eine 

 wesentliche Eolle spielen, da wii- wissen, dass die Verbindungsfiidehen haiifig 

 nur von ihr gebildet zii sein seheinen." (Biitschli, Protozoa, p. 1524.) 



