460 The Philippine Journal of Science 1921 
the periphery and a metabolic change of form, than by the ac- 
tual extrusion of the protoplasmic mass, as is the case in pseu- 
dopodia formation. 
I was able to follow the process of sporoblast formation in 
one cyst (Plate 1, figs. 5 to 10; Plate 2, fig. 1). The process 
of plastogamy, from the time of the appearance of the first signs 
of cleavage of the zygote, was forty minutes. Of course, there 
is no way of estimating the time of the entire process, for it 
is impossible to tell whether division of the nucleus occurs 
soon after zygosis or is deferred until just before division of the 
cell body occurs. 
The cyst in question was first seen by me at 10.40 a. m. 
The temperature of the laboratory at that time was 28° C., 
and it did not appreciably vary from that during the process. 
The material was mounted in physiological salt solution and 
sealed with vaseline. The zygote, at that time, showed a dis- 
tinct equatorial constriction (Plate 1, fig. 5). The cyst was 
sketched rapidly under the camera lucida. At 10.55 the cleft 
had become quite sharp (Plate 1, fig. 6). At this time the 
cell showed great protoplasmic activity. The outline of the 
cell was constantly changing and cyclosis was very marked. 
At 11.08 the outline of the dividing cell had lost its irreg- 
ularity and was becoming rounded (Plate 1, fig. 7). The 
cleft had distinctly deepened. The outer aspect of the cell was 
still more sharply defined and the cleft much deeper at 11.08 
(Plate 1, fig. 8), and at 11.17 the daughter cells 
were connected by a very slender strand only 
(Plate 1, fig. 9). At this stage, the posterior 
cell (lowermost in the figure) showed a slight 
transverse elongation, and at the same time a 
distinct movement of the two cells was ob- 
served. This was a slight to-and-fro rotation, 
as if the two cells were geared (text fig. 1); 
and when separation had become complete, at 
11.19, at which time the cells moved apart, this 
movement became more pronounced, and it 
Fic. 1. Oseillation of Continued until after 4 o’clock in the afternoon. 
sporoblasts | follow- At 11.30 o'clock, eleven minutes after sepa- 
Isospora hominis ration of the cells had taken place, the cells 
oP. were widely separated (Plate 1, fig. 10). The 
ectoplasmic layer began to show a tendency to stiffen, although 
it was still sufficiently plastic to allow for slight changes 
of external form. The general spherical shape was main- 
