Dr. Holló Ferenc szerk.: Parasitologia Hungarica 3. (Budapest, 1970)
The sporozoites force themselves through the narrow micropyle with visible effort and they may sometimes fail. The sporozoites of E.tenella are elongate cylindrical bodies, tapering toward one end. They have a distinct apical ring (RYLEY, 1969, and others) from which 24 fibrils extend posteriorly beneath the bilamellar membrane. At the apical end there is also a conoid consisting of spirally wound tubes which very likely plays some role during penetration into the host cell. The nucleus of the sporozoite is centrally located and there is a larger homogenous paranuclear body behind it. This structure also occurs in the sporocysts of other Eimeriae often with an additional smaller prenuclear body. In light micrographs, these structures can be visualized by various staining methods but, naturally, their ultrastructure remains to be identified electronmicroscopically . Excystation of the sporozoites and their penetration into the intestinal epithelial cells introduces schizogony, the first - asexual - stage of endogenous 'development. Up to now it was generally accepted that sporozoites invaded directly the epithelial cells where they rounded up and developed to schizonts each within a pale parasitophorous vacuole. VAN DOORNINCK and BECKER (1957) showed that the sporozoites of E.necatrix first entered the lamina propria via transport by macrophages and passed only in a second step into the lining epithelium of the 1IEBERKÜHN crypts. Sometimes the sporozoites are phagocytized by the macrophages. The macrophage-transport of E.tenella sporozoites was described by PATTIL10 (1957), C HAUE Y and BURNS (1959) and others. The occurrence of sporozoites in fibrocytes and macrophages was noted also by us and these findings have been confirmed by SCH01TYSECK (1953), and SCHOITYSECK et al. (1969). According to TYZZER's (1929) studies, the sporozoites of E.te nella may settle not only in the coecum, but also in the mucous epithelium of the intestinal segments adjacent anteriorly and
