ltiplication of the
parasites, the latter begin to make preparations for the exogenous
cycle, inaugurated by gametogony. When conjugation has taken place and
sporogony is begun, the danger to the host is at an end. So that, if the
acute stage of the disease is once successfully passed, the regenerative
capacity of the epithelium may be able to restore something like
equilibrium to the deranged metabolism in time to prevent collapse.

Morphology and life-history.

_Coccidium schubergi_, parasitic in the intestine of a centipede
(_Lithobius forficatus_), may be taken as an example of a Coccidian
life-history (see Schaudinn, 1900): some of the more important
variations exhibited by other forms will be noted afterwards. The
trophozoite, or actively-growing parasite, is an oval or rounded body
(fig. 3, I.). The general cytoplasm shows no differentiation into
ectoplasm and endoplasm; it is uniformly alveolar in character. The
nucleus is relatively large, and possesses a distinct membrane and a
well-marked reticulum in which are embedded grains of chromatin. Its
most conspicuous feature is the large deeply-staining karyosome, which
consists of the greater part of the chromatin of the nucleus intimately
bound up with a plastinoid basis. When fully grown, the trophozoite (now
a schizont) undergoes schizogony. Its nucleus divides successively to
form a number of nuclei, which travel to the periphery, and there become
more or less regularly disposed (fig. 3, II. and III.). The protoplasm
in the neighbourhood of each next grows out, as a projecting bud,
carrying the nucleus with it. In this manner are formed a number of
club-shaped bodies, the merozoites, which are at length set free from
the parent-body (IV.), leaving a certain amount of residual cytoplasm
behind. By the rupture of the disorganized host-cell,[2] the
fully-formed merozoites are liberated into the intestinal lumen, and
seek out fresh epithelial cells. Each is more or less sickle-shaped, and
capable of active movements. Once inside a new host-cell, the merozoite
grows to a schizont again.

After this course has been repeated several times, gametogony sets in,
the trophozoites growing more slowly and becoming the parent-cells of
the sexual elements (gametocytes), either male individuals
(microgametocytes) or female ones (megagametocytes). A microgametocyte
(fig. 3, VI. [mars]) is characterized by its dense but finely reticular
or alveolar cytoplasm, very differ