sporozoite bent on itself; d, the
spore has split along its outer coat or epispore, but the sporozoite
is still enclosed in the endospore; e, the sporozoite, freed from the
endospore, is emerging; f, the sporozoite has straightened itself out
and is freed from its envelopes. (From Wasielewski, after A.
Schneider.)]

Comparing the life-cycle of other Coccidia with that just described, a
greater or less degree of modification is frequently met with. In the
process of schizogony two orders of division sometimes occur; the
parent-schizont first divides up into a varying number of rounded
daughter-schizonts (schizontocytes), each of which gives rise, in the
usual manner, to a cluster of merozoites,[3] which thus constitute a
second order of cells. Siedlecki (1902) has found this to be the case in
_Caryotropha mesnilii_ (fig. 4), and Woodcock (1904) has shown that it
is most probably really the same process which Smith and Johnson (1902)
mistook for sporogony when originally describing their Coccidian of the
mouse, _Klossiella_. In _Caryotropha_, a perfectly similar state of
affairs is seen in the formation of microgametes from the
microgametocyte; this is additionally interesting as showing that this
process is neither more nor less than male schizogony.

Coming to the sexual generation, considerable variation is met with as
regards the period in the life-history when sexual differentiation first
makes its appearance. Sexuality may become evident at the very beginning
of schizogony, as, e.g. in _Adelea ovata_ (Siedlecki, 1899), where the
first-formed schizonts (those developed from the sporozoites) are
differentiated into male and female (micro-and mega-schizonts) (see
Plate II., fig. 5). Correspondingly, the merozoites, to which they give
rise, are also different (micro-and mega-merozoites). In one or two
cases sexuality appears even earlier in the cycle, and has thus been
carried still farther back.

The Coccidia, as a whole, have not developed the phenomenon of
association of the sexual individuals prior to gamete-formation which is
so characteristic of Gregarines. Their method of endeavouring to secure
successful sporulation, and thus the survival of the species, has been
rather by the extreme specialization of the sexual process. In place of
many female elements, which the primitive or ancestral forms may be
assumed to have had,[4] there is always, save possibly for one
exception,[5] only a single relativ