R. T. Wells 
215 
Three or four days after insemination some of the amoebae generally 
become encysted. Encystment seems often to be immediately preceded 
by a remarkably active multiplication; this results in the formation of 
clumps of amoebae which may become massed together, giving the 
appearance of plasmodia. In the end each amoeba becomes rounded, 
the body shrinks, becomes more granular in appearance and acquires a 
thin envelope; this is at first single but later presents the characteristic 
appearance of double contour, the outer layer being wrinkled (figs, 12 
and 19). The original circular outline may be modified to become 
trihedral, polygonal or stellate, the nucleus becomes less distinct, the 
contractile vacuole ceases to open, until it becomes apparent that the 
youngest generation has reached the cystic stage from which its ancestors 
set out. In stained specimens many of the amoebae undergoing encyst¬ 
ment are seen to contain numerous internal buds (fig. 19). Not all 
the amoebae encyst about the same time; indeed, many are often found 
still motile in cultures more than a month old. 
(2) Amoeba of type (h). 
Attempts to obtain a culture the progeny of a single individual of 
this type did not succeed, but ultimately a culture originating from 
a number of small motile forms was obtained which in subculture was 
invariably found to yield cysts of the small type only. 
Germination of the cyst has not been directly observed in this strain; 
on six occasions a single cyst on fresh medium was kept under the oil- 
immersion lens for from 10 hours to three days without showing any 
signs of germination. Empty cyst shells have not been seen in un¬ 
stained specimens, but in stained films from the cultures they appear as 
rounded shrivelled bodies about 3-5 y in diameter (fig. 24). With 
surface of the agar.” He points out that amoebae grow below the surface of the agar, 
and that, in old cultures cysts may be focussed in various planes of the medium. 
I find that this is apparently a constant phenomenon in cultures of type (a). 
It is very difficult to interpret the active movements of these burrowing amoebae, as 
different points of their surface are at different levels, so that the whole body cannot be 
focussed at one time. Moreover, another amoeba might suddenly come into view in the 
field of the microscope having entered it from a higher or lower flow and thus give rise to 
an appearance of division on the part of the amoeba originally under observation. It seems 
at least probable that the activities of these lobulate bodies here described may he due to 
modified processes of fission and budding going on below the surface of the agar. The 
fact that these forms occur only below the surface accounts for their absence in fixed and 
stained films. \ 
