[Illustration: FIG. 1.--SECTION THROUGH RABBIT'S LIVER, INFECTED WITH
_COCCIDIUM CUNICULI_. (AFTER THOMA.)]
[Illustration: FIG. 2.--_KLOSSIA HELICINA_, FROM KIDNEY OF HELIX
HORTENSIS.
a, Portion of a section of the kidney showing normal epithelial cells
containing concretions (c), and enlarged epithelial cells containing
the parasite (k) in various stages; b, cyst of the _Klossia_
containing sporoblasts; c, cyst with ripe spores, each enclosing four
sporozoites and a patch of residual protoplasm. (From Wasielewski,
after Balbiani.)]
[Illustration: FIG. 3.--THE LIFE-CYCLE OF _COCCIDIUM SCHUBERGI_,
SCHAUD. (PAR. _LITHOBIUS FORFICATUS_). (FROM MINCHIN, AFTER
SCHAUDINN.)
I.-IV represents the schizogony, commencing with infection of an
epithelial cell by a sporozoite or merozoite. After stage IV the
development may start again at stage I, as indicated by the arrows; or
it may go on to the formation of gametocytes (V). V-VIII represents
the sexual generation. The line of development, hitherto single (I-IV)
becomes split into two lines--male (VI [mars], VII [mars], VIII
[mars]), and female (VI [venus], VII [venus], VIII [venus]),
culminating in the highly differentiated micro- and mega-gametes. By
conjugation these two lines are again united. IX, X, show the
formation of the zygote by fusion of the nuclei of the gametes. XI-XV,
sporogony. H.C, host-cell; N, its nucleus; mz, merozoite; szt,
schizont; ky, karyosome (or fragments of same); n.n, daughter-nuclei
of schizont; pl.gr, plastinoid grains; ooc, oocyst; n.zyg,
zygote-nucleus (segmentation-nucleus); sp.m, spore-membrane
(sporocyst); rp, residual protoplasm of oocyst ("reliquat kystal");
rp.sp, residual protoplasm of spore ("reliquat sporal"); sp.z,
sporozoite.]
[Illustration: FIG. 4.--PHASES OF _CARYOTROPHA MESNILII_, SIEDL. (PAR.
_POLYMNIA NEBULOSA_).
a, Young schizont in a cluster of spermatogonia; the host-cell
(represented granulated) and two of its neighbours are greatly
hypertrophied, with very large nuclei, and have fused into a single
mass containing the parasite (represented clear, with a thick
outline). The other spermatogonia are normal. b, Intracellular
schizont divided up into schizontocytes (c), each schizontocyte giving
rise to a cluster of merozoites arranged as a "corps en barillet";
spg, spermatogonia; h.c, host-cell; N, nucleus of host-cell or cells;
n, nucleus of parasite; szc, schizontocyte; mz, merozoites; r.b,
residual bodies of the schizontocytes. (From Minchin, after
Siedlecki.)]