{101}[Illustration: FIG. 34.—Life-history of _Coccidium schubergi_. _a_, Penetration of epithelium-cell of host by sporozoite; _b-d_, stages of multiple cell-formation in naked state (schizogony); _e_, _f_, formation of oogamete; _g_, conjugation; _h-j_, formation of sperms (_s_); _k_, development of zygote (fertilised ovum) to form four spores; _l_, formation of two zoospores (or sickle germs) in each spore. (From Calkins's _Protozoa_, after Schaudinn.)] In some cases the oogametes are at first oblong, like ordinary merozoites, and round off in the gut. The microgametocyte, or spermatogone, has the same character, but is smaller; it applies itself like a cap to one pole of the oogamete, which has rounded off; it then divides into four sperms, whose cytoplasm is not sharply separated; one of these then separates from the common mass, enters the oogamete, and so conjugation is effected, with an oosperm as its result. This latter mode of conjugation is that of _Adelea ovata_ and _Coccidium lacazei_: the former is probably the more primitive and the commoner. The sperms {102}of Coccidiidae, when free, usually possess two long flagella, either both anterior, or a very long one in front and a short one behind, both turned backwards. The genus _Coccidium_ affects many animals, and one species in particular, _C. cuniculi_ Rivolta, attacks the liver of young rabbits,[108] giving rise to the disease "coccidiosis." _Coccidium_ may also produce a sort of dysentery in cattle on the Alpine pastures of Switzerland; and cases of human coccidiosis are by no means unknown. _Coccidium_-like bodies have been demonstrated in the human disease, "molluscum contagiosum," and the "oriental sore" of Asia; similar bodies have also been recorded in smallpox and vaccinia, malignant tumours and even syphilis, but their nature is not certainly known; some of these are now referred to Flagellata (see p. 121). Closely allied to the Coccidiidae are the HAEMOSPORIDAE, dwellers in the blood of various cold-blooded Vertebrates,[109] and entering the corpuscles as sporozoites or merozoites to attain the full size, when they divide by schizogony; they are freed like those of the next family by the breaking up of the corpuscle. The merozoites were described by Gaule (1879) as "vermicles" ("Würmchen"), and regarded by him as peculiar segregation-products of the blood; though Lankester had described the same species in the Frog's blood as early as 1871, with a full recognition of its true character. His name, _Drepanidium_, has had to give way, having been appropriated to another animal, and has been aptly replaced by that of _Lankesterella_. The sexual process of _Karyolysus_ has been found to take place in a Tick, that of _Haemogregarina_ in a Leech, thus presenting a close analogy to the next group, which only differs in its less definite form in the active state, and in the lack of a cell-wall during brood-formation.