[Light and electron microscope studies on two types of giant schizonts (globidial schizonts) in the abomasum of sheep (author's transl)].

25 sheep were investigated for globidial schizont infection in the abomasum. Two types of giant schizonts, which had a diameter of about 250 mum up to 500 mum, were observed. Each type was found to contain morphologically different parasites. In type 1 the parasites were ovoid with a length of about 4 mum and had 24 subpellicular microtubules, whereas in type 2 the parasites were spindle-shaped, measured about 6 mum in length and had only 22 subpellicular microtubules. Both types of parasites, however, were characterized by a 1.5-2 mum large vacuole, which was always situated anterior to the nucleus. Thus the parasites observed here differed from the fine structure of the merozoites of the Eimeria and Sarcocystis species. At the earliest stage observed in the development of the parasites the schizont cytoplasm was subdivided into many spheroidal blastophores, which were still present in old stages. The interior of the blastophores is filled with many nuclei resulting from repeated divisions, whereby they pass through three different shapes. Independently from the nuclear divisions the anlagen of the daughter cells appeared within the blastophores. First these anlagen consist of a conoid and a concentric ring of short microtubules (22 or 24). Up to 8 anlagen were seen close to each other. As development proceeds, the blastophore membrane is elevated into a cone-shaped projection which later elongated into a finger-like bud. This bud, the developing parasite, contained the primordia of the rhoptries, the newly formed inner membranes of the pellicle and a nucleus. In a late stage of development the parasites were completely formed except for an attachment of their posterior ends to the remains of the blastophore. Thus nuclear divisions and daughter cell formation are two different phases in the species studied here, whereas in the endodyogeny of sarcosphoridia these both processes are closely connected. In light microscopy the globidial schizonts from the abomasum of sheep seemed to be covered by a thick, two-layered cyst wall. By means of electron microscopy it was shown, that the inner layer is identical with the host-cell cytoplasm enclosing utricle-like a giant parasitophorous vacuole. The outer surface of the host cell had numerous, up to 14 mum long microvilli. These microvilli and numerous macrophages scattered between formed evidently the outer layer seen in light microscopy. The host cell itself was filled with numerous bundles of fibrillar origin, long rows of vacuoles and mitochondria and made a very dense impression. The inner surface of the host cell formed numerous intravacuolar tubules of about 50 nm in diameter and about 4 mum in length. Summarizing it was found that the globidial schizonts differed clearly from the cysts of sarcosporidia. The thickness of the limiting system, however, may probably retain the parasites longer than usual in the genus Eimeria. Finally these globidial schizonts from the abomasum of sheep were compared to those from the small intestine.