COCCIDIOSIS 129 
gins to grow in size at the expense of the host cell. This is known as 
the trophozoite stage (fig. 13 D). 
(b) Asexual multiplication or schizogony. When fully developed 
the trophozoite has a diameter of 10 to 12 microns. In preparation 
for propagation. the nucleus divides into a number of daughter nuclei 
which arrange themselves in a zone at the periphery. This consti- 
tutes the schizont stage and represents the beginning of asexual mul- 
tiplication or schizogony (fig. 18 E). ach nucleus becomes sur- 
rounded with protoplasm and assumes a long narrow form with 
pointed ends. The length ranges from 6 to 10 microns (fig. 138 F G). 
These bodies, known as merozoites, differ from sporozoites in that 
their nuclei contain a small particle of chromatin, the karyosome. 
From 8 to 20 merozoites are formed from 1 schizont. On separation 
from one another (fig. 18 H), the merozoites work their way into 
other cells, lining the intestinal tract and may repeat the process 
of development just outlined, or differentiation into sexual forms 
may take place within the newly invaded cells. This process is 
termed gametogony. 
(c) Sexual reproduction or gametogony. Two forms of the or- 
ganism are now produced, the macrogametocyte or female mother 
cell (fig. 18 I J) and the microgametocyte or male mother cell (fig. 
13 IJ). Both forms are oval in shape, the former being somewhat 
larger and more granular than the latter. Also the former gives 
rise to only one daughter cell or macrogamete (fig. 13 K) while 
the latter produces a large number of minute, biflagellate, actively 
motile male cells or microgametes (fig. 13 K). The macrogametes 
are from 11.8 to 17.5 microns in length and 6 to 11 microns in 
breadth, in sections. The microgametes are 3 to 4 microns in length, 
in sections. 
(d) Fertilization. Fertilization takes place through the entrance 
of the microgamete or male cell into the structure of the female 
cell or macrogamete at the thin spot at one end known as the mi- 
cropyle (fig. 13 L). After the entrance of the male cell the macro- 
gamete secretes protoplasm which plugs the opening and prevents 
the entrance of other microgametes. On union of the nuclei of the 
two gametes, a zygote is formed which proceeds to spore formation or 
sporogony (fig. 13 MN). 
(e) Sporogony. The zygote is surrounded by a tough double con- 
toured membrane which is extremely resistant. This stage is known 
as the egg stage, or odcyst. The contents are at first granular and 
grayish in appearance (fig. 13 N). Later the granular material is 
