Dr. Holló Ferenc szerk.: Parasitologia Hungarica 3. (Budapest, 1970)
Studies "by HORTON-SMITH and LONG (1965) threw a new light on the question of host specificity, but the new interpretation deduced from their findings does not contradict the previous ones. They noted that the sporozoites of E.necatrix and E.bru- netti , which normally settled in the small intestine, could also settle in the caecum in case they were injected directly into it. The sporozoites which penetrated the caecal epithelial cells started endogenic development as if they had had settled in the small intestine. The oocysts passed with the faeces were used with success for experimental infection of susceptible chickens. The parasitophorous vacuole formed by the cytoplasm around the penetrated parasite separates it from the host cell. Vacuole 'formation seems to be a result of the protective mechanism of the host cell, but it provides at the same time also certain protection for the developing parasite. The rounded-off sporozoites (trophozoites) give rise to merozoites by paramitosis (SCHOLTYSECK, 1953). The released merozoites invade further host cells. The number of merozoites may. vary from 2-3 to several hundreds. Second generation schizonts of the chicken coccidia E .tenella , E.necatrix and E.brunetti from each at least 100 merozoites. The latter stages represent a certain transition to giant schizonts - globidia - in which, several thousands (100 000) of merozoites may develop. Demonstration of schizonts of the above type in scrapings is of diagnostic value. The endogenous development of the Eimeriae of gallinaceous birds includes very likely more than one schizogonic generation. While TYZZER (1929) identified a single schizogonic generation of E.acervulina , WARREN and BALL (1967) found that there were at least three, and VETTEREIN G and DORAN (1966) described four of them. Four generations of schizonts were found also in the cycle of E.mivati (LONG and HORTON-SMITH, 1968). In most of the better known species, 3 schizogonic generations are usual.
