258 Vniversitij of California Puhlicationx in Zoology [Vol.16 



6. Chromatin Extrusion 

 Chromidia have been found in trophozoites, in flagellates, and in 

 iudividnals during the period prior to, and during the early phases of 

 encystment. In all eases chromidia formation is at the expense of the 

 karyosome, and there is always heavy peripheral chromatin on the 

 nuclear membrane during chromidia! formation. The formation in the 

 trophozoite, which has already been described, has to do with the 

 formation of exogenous buds. That found in the flagellate stage would 

 probably have been cut off in exogenon.s buds had the individuals not 

 been transformed into flagellates. Chromidia found coincidently with 

 cyst formation, the details of which are given below, differ from the 

 above in early proc&ss of production, in size and in fate. 



(a) Chromidiai, Formation in Cysts 



Tlie process of the formation of chromidia in cysts seems to be a 

 normal one, because it ha.s been found in every encysting culture 

 regardless of whether or not the culture came from an individual 

 recently isolated from the soil, or from one from a culture which had 

 been kept under laboratory conditions for more than a year. It does 

 not appear to be a pathological phenomenon. It is begun in an amoeba 

 while it is still moving about or after it has rounded up to encyst. 

 It is initiated in the karyosome and ends in the formation of large 

 spheroidal, sometimes irregular, chromidia which later disappear 

 Throughout the process stainable lines may or may not be found extend- 

 ing from the nuclear membrane into the karyosome. 



The first indication of the process is an enlargement of the karyo- 

 some as well as an increase in the entire nuclear volume (pi. 21, fig. 

 67 ) . The karyosome has darkly stained granules at the periphery, then 

 a lightly stained region, in the center of which is a darkly .stained 

 spherical mass, a condition which differs from that of the enlarged 

 karyosome of mitosis as well as from that prior to chromidiai forma- 

 tion as seen in budding individuals. Fusion takes place among the 

 granules at the surface of the karyosome so that they become larger 

 and more deeply stained (pi. 21, fig. 68). After this stage is reached 

 the central sphere, the expurged karyosome, begins to move out of its 

 globe of peripheral chromatin (pi. 21, fig. 70). It breaks through one 

 side (pi. 21, fig. 71) and the peripheral globe takes on the appearance 

 of a cup (pi. 21, fig. 76). The process of separation continues (pi. 21, 

 figs. 72, 73) and is evidently completed with force, for the large dark 

 karyosome is found pressed against the nuclear membrane, while the 



