458 
The Philippine Journal of Science 
1921 
it desirable to figure a number of these cysts (Plate 3, 
figs. 1 to 12) . The oocysts also show considerable variation in 
outline, from those that are virtually oval to those that resemble 
a bottle or elongated flask — a shape that is more or less charac- 
teristic of the species. This variation is shown in the plates 
that accompany this article. 
The oocyst, itself, is a delicate, transparent, double-contoured 
affair with a perfectly smooth surface. Some writers have 
described a delicate membrane lying within the cysts and a 
structure at the constricted end that has been interpreted as 
the micropyle. I have not been able to convince myself of the 
presence of either of these in the cysts I have studied; but I 
have been compelled to make my studies at this time with 
achromatic objectives, and it may be that my failure to demon- 
strate them has been due to lack of proper optical equipment. 
Noc(l2) suggests that the bottle-neck appearance of the cysts 
may be due to the pressure of the elongated sporocysts as they 
rotate within the oocyst. I think this interpretation is incor- 
rect, for one frequently finds undeveloped cysts which show 
the constriction at one end (vide the plate accompanying 
Dobell’s article). (3) 
I regret I cannot give adequate treatment of the dimensions 
of these cysts at the present time. Recently, the cross hair on 
my filar micrometer became broken, and such measurements as 
I have made have been made with an ordinary ocular micro- 
meter and a stage micrometer in whose accuracy I have not great 
confidence. I am giving measurements of nine oocysts selected 
at random, and they are shown in Table 1. 
Table 1. — Measurements of nine oocysts of Isospora hominis. 
Length. 
Breadth. 
U 
u, 
33.2 
13.6 
36.4 
13.6 
39.0 
14.5 
35.8 
15.8 
39.1 
12.7 
37.3 
18.2 
38.2 
19.1 
39.1 
19.4 
40.0 
17.6 
These measurements were made with a Ramsden micrometer 
ocular at a magnification of about 715 diameters. 
Nearly all of the measurements shown in Table 1 will be seen 
to exceed the dimensions reported by other workers. Dobell (3) 
