1916] Wilson: On the Life-Histori/ of a Soil Amoeba 259 



extruded oliromatiu lies at the opposite side (pi. 21, figs. 69, 74). The 

 karyosome resumes its central position and the peripheral chromatin 

 flattens out on the nuclear membrane. 



The chromatin from the periphery of the nucleus is gradually given 

 off into the cytoplasm, for soon after its flattening out chromidia begin 

 to appear (pi. 21, fig. 75) and these increase in size and number as the 

 amount and staining capacity of the peripheral chromatin decreases 

 (pi. 21, fig. 78). The latter finally all disappears and mononucleate 

 cysts are found with numerous darkly stained spheroidal chromidia of 

 variable size and no peripheral chromatin in the nucleus (pi. 21. 

 fig. 81). 



The chromatin is evidently diffused out into the cytoplasm, for the 

 stain of the cyst is much deeper in the region of the nucleus than it is 

 at the periphery, a condition which is not found in old cysts. This 

 diffused chromatin collects in clumps at first near the nucleus (pi. 21, 

 figs. 75, 78) and later extends to the region further out in the cytoplasm 

 (pi. 21. fig. 81), forming chromidia in slightly irregular spheres of 

 dift'erent sizes. Though at first small, these spheres are later nearly 

 equal in size to the karyosome. 



In the older cysts the chromidia are large and few in number, 

 sometimes as few as six, and they finally all disappear in about three 

 days after eneystment. None have ever been found e.jected into the 

 region between the amoeba and the cyst wall, as Dobell (1914) has 

 figured for some in Amoeba laccrtae, though the fact that in the older 

 cysts they are found nearer the periphery of the cytoplasm than in the 

 younger ones, might be considered to indicate that fate (pi. 21, figs. 

 78, 81). The evidence, however, seems to me to indicate that the 

 chromidia are digested or absorbed. 



A complete series has not been found in binucleate forms, but from 

 the stages found the process of chromatin extrusion in these is like that 

 in the mononucleate cyst (pi. 21, figs. 77, 80). 



Another point which should be mentioned here is that while amoebas 

 may ordinarily be induced to come out of a cyst, never has an amoeba 

 been induced to do so in which there were chromidia which can be 

 seen in the living cysts, but these same amoebas will come out after 

 the chromidia have disappeared. 



(b) Chromtdia in Other Amoeb.\s 

 Process of chromidial formation somewhat similar to that given 

 above have been described by investigators in other species of Amoeba. 



