250 C. CLIFFORD DOBELL. 
with the movements of the animal, and with the change of 
position of the food masses lying in the cytoplasm. The con- 
dition figured is brought about by the pressure upon the 
nucleus as it is being forced into the pseudopodium, which is 
being thrust out. This may be repeatedly seen in living 
creatures. The nucleus itself is not really amoeboid, but 
undergoes passive distortion. 
Encystment.—I have experienced great difficulty in 
finding any stages in this animal other than those just 
described. For a long time I could find no indications of 
encystment, in spite of trying all the means I could think of 
to bring it about. When I did discover the cysts, however, 
I came upon them in immense numbers, so that I was able to 
follow the process of encysting in great detail. All encyst- 
ing forms were found in December, January and February 
(cf. the case of the flagellates), but this is perhaps merely a 
coincidence. 
Before encysting, Entamoeba undergoes certain changes 
in its nucleus. ‘I'he chromatin at the periphery increases in 
amount and is then gradually extruded' into the cytoplasm, 
where it lies in irregular masses (fig. 60). These masses 
gradually increase in size by the chromatin granules running 
together (figs. 61, 64, etc.) The process continues until 
quite a large quantity of chromatin is lying free in the cyto- 
plasm. At about the same time the nucleus develops a 
karyosome at its centre. The karyosome always has the 
structure (seen in figs. 60, 61, 64) of a little heap of loosely 
packed granules. Fine filaments connecting it with the peri- 
phery can usually be distinguished (cf. fig. 60, etc.) The 
amoeba now slowly rounds itself off, and a large vacuole 
appears in the cytoplasm (fig. 61) When it has reached this 
stage the organism secretes a delicate cyst membrane (figs. 
63, 64). In the living animal these cysts have a very 
characteristic and striking appearance, with their large 
nucleus, refractive chromatin masses, and big vacuole (fig. 63). 
1 T have not been able to watch this in the living animal. The state- 
ment is based upon a study of fixed and stained material. 
