Ultrastructure of daughter sporocysts and cercariae of Schistosoma japonicum were studied 2 and 4 months after infection of Oncomelania hupensis hupensis. The body walls of daughter sporocysts are similar at all infectious stages. They consist of an external syncytial tegument on a basement membrane, and an internal cellular subtegument surrounding a body cavity containing developing cercariae. The cercariae embryos develop 2 months after infection from germinal balls in the brood chamber of the daughter sporocyst. They are at first enveloped by a primitive epithelium rising from the daughter sporocyst. Four months after infection, the cercariae were almost fully developed and the primitive epithelium had degenerated. The body wall of the cercaria consists of a thin tegument covered by a surface coat of fibrous material and connected to the subtegumental cells by cytoplasmic processes. The matrix of the tegument contains numerous dense bodies, vacuoles, and spines. Two types of sensory structures - uniciliated and multiciliated - are found at the anterior tip of the cercaria. There are five pairs of penetration gland cells of two distinct types differentiated by the morphology of secretory granules. Flame cells are found in both daughter sporocysts and in cercariae. The cilia of the flame cells are characterized by the typical 9 and 2 cilium pattern.

Summary Besnoitia besnoiti merozoites obtained from cysts in naturally infected bovines and passaged in Vero‐cells were multiplied in cultures of Vero‐ and CRFK‐monolayers. Their development was studied for 7 days p. i. by light and electron microscopy. As early as 24 h p. i. intracellularly situated single parasites were found; 48 h p. i. up to 10 merozoites of Besnoitia were seen in a single parasitophorous vacuole. Irregularly arranged clusters of up to 32 zoites on the 3rd day p. i. changed into regularly formed rosettes of Besnoitia. After the 4th day p. i. the extracellular forms predominated. During asexual multiplication of the parasites plaque formations could be observed 4—5 days p. i. as a cytopathogenic effect, followed 6—7 days p. i. by complete destruction of the monolayers. The predominant type of multiplication with Besnoitia is endodyogeny, which starts by the spherical mother cells developing two merozoite‐anlagen. Forming the daughter cell pellicle, the nucleus of the mother cell shrinks to a large extent and finally divides, the thicker posterior merozoite pole being left open. The young daughter cells remain connected with this pole by a common residual body until the final division takes place. A special form of endodyogeny is the rosette‐formation resulting from several endodyogenies without any separation of the young merozoites from the mother cell. The not yet fully differentiated merozoites of a rosette situated in a parasitophorous vacuole thus induce a mass multiplication of finally well‐developed merozoites of Besnoitia besnoiti. Zusammenfassung Die Ultrastruktur der asexuellen Vermehrung von Besnoitia besnoiti (MAROTEL, 1912) in Vero‐ und CRFK‐Zellkulturen Aus Zysten natürlich infizierter Rinder gewonnene, in Vero‐Zellen passagierte Besnoitia besnoiti‐Merozoiten wurden in Vero‐ und CRFK‐Zellkulturen vermehrt. Ihre Entwicklung konnte 7 Tage lang licht‐ und elektronenmikroskopisch untersucht werden. 24 Std. p. i. traten vereinzelt intrazellulär liegende Parasiten, 48 Std. p.i. bis zu 10 Besnoitia‐Merozoiten in einer gemeinsamen parasitophoren Vakuole auf. Bis zu 32 unregelmäßig zu Haufen angeordnete Zoiten am 3.Tg. p.i. wechselten mit regelmäßig geformten Besnoitia‐Rosetten ab. Nach dem 4.Tg. p.i. traten überwiegend extrazelluläre Parasiten auf. Als zytopathischer Effekt konnte 4—5 Tg. p. i. Plaquebildung, 6—7 Tg. p. i. komplette Zellzerstörung beobachtet werden. Die Endodyo genie stellt den Haupttyp der ungeschlechtlichen Vermehrung von Besnoitia dar, wobei in jeder Mutterzelle zwei Merozoitenanlagen gebildet werden. Von hier aus entwickelt sich die Tochterzellpellikula und gleichzeitig vergrößert und teilt sich der Mutterzellkern. Die jungen Tochterzellen bleiben mit ihrem offenen, verdickten hinteren Pol mit einem gemeinsamen Restkörper bis zur endgültigen Teilung verbunden. Eine besondere Form der Endodyogenie ist die Rosettenbildung, die eine Folge von mehreren Endodyogenien ohne Abtrennung der Merozoiten von der Mutterzelle darstellt. Die noch nicht ausdifferenzierten, als Roset...

Bank voles (Clethrionomys glareolus) were infected by stomach tube with Frenkelia sporocysts from the faeces of buzzards (Buteo buteo). The voles were sacrificed at regular intervals and their livers examined electronmicroscopically. Seven days p.i. developmental stages of Frenkelia could be detected in liver parenchymal cells. The youngest schizonts detected are enveloped by a pellicle consisting of two membranes. This pellicle, which is in direct contact with the host cell mitochondria, shows marked invaginations which increase with the development of the schizont. A parasitophorous vacuole is not detectable. In developing schizonts numerous sections through nuclei with nucleic spindles and merozoite anlagen (dome-shaped) structures) are visible. It is not clear whether there are several nuclei or a section through one large and lobed nucleus. Within the merozoite anlagen the conoid and the subpellicular microtubules are formed first. By the prolongation of the dome-shaped structures towards the posterior pole, the nucleus and the other newly formed cell organelles are incorporated into the forming merozoite. The posterior pole of the merozoite still remains open at this stage of development. With increasing differentiation the merozoites become lancet-shaped, their apical poles bing always directed towards the periphery of the schizont. The outer membrane of the pellicle of the schizont forms the outer part of the pellicle of the merozoites by invaginating around them. At this stage of development the inner membrane of the pellicle of the schizont is no longer detectable. Thus the typical pellicle of the motile stages of sporozoaonsisting of three membranes is formed. In the centre of the merozoites which lie freely in the liver cell a residual body is present. The host cell reacts against the parasites by forming a thick border of mitochondria and distinct endoplasmic reticulum.

Scanning and transmission electron microscopical investigations revealed that Genés organ in unfed and ovipositing females of Dermacentor reticulatus is formed as a double-sac-structure consisting of an outer epithelial and an inner cuticular sac. In ovipositing ticks the latter emerges through the camerostomal aperture to the exterior. Genés organ in unfed ticks consists of a corpus, two posterior horns and a pair of undeveloped glands at each side, which differentiate in ovipositing ticks to compound, branched tubular glands with a main efferent duct for each gland opening into the lumen between the epithelial and the cuticular sac. Genés organ of egg-laying females corresponds basically in morphology and structural organization to that of unfed ticks. Compared with unfed ticks, however, in ovipositing ticks the corpus and horns are longer and broader, the glands are fully developed and the cuticular sac is evertable. The epithelial sac as the outermost part of Genés organ is continuous with the hypodermis of the basis capituli and the scutum, arises at the camerostomal aperture, forms the corpus and the two blind-ending horns, passes into the epithelium of the main excretory ducts of the glands and envelops the cuticular sac. The cuticular sac passes into the cuticle of the basis capituli and the scutum, arises at the camerostomal aperture, is folded, expands into the horn tips and consists inwards of a smooth epicuticula and outwards of a fibrous endocuticula. Muscles originating from the scutum pass caudomedially through the epithelial sac and are inserted into the cuticular sac. The entire surface of the maximally everted cuticular sac is covered with an amorphous mass. In cleaned samples, ledge-like structures appear on the lateral surface. These ledges turn into balloon-like structures which extend over the medial and dorsal surface. The entire surface including the balloon-like structures and the ledges are provided with numerous cribrate pits.

The fine structure of trophozoites and especially of merozoites of Babesia herpailuri is described before and after treatment with Imidocarb (Wellcome). The mostly piriform to oval merozoites possess an outer membrane and a supporting membrane below. The intratorium consists of a polar ring, rhoptries micronemes and the sperical body which lies beside the big nucleus and next to mitochondria. The endoplasmic reticulum and invaginations are not clearly formed. The cellular changes of Babesia herpailuri, observed one hour after drug treatment in trophozoites and six hours later in merozoites, concern the form and function of the parasite: widening of the subpellicular endoplasmic reticulum and of the perinuclear space; sporadic dilatation of the endoplasmic reticulum of the merozoites (9 fig.). Damaged membranes, dissolution of the cellular membrane, disintegration of the nuclei as are known effects of the Berenil treatment to Babesia herpailuri, are not noted results after the Imidocarb treatment. The original membrane systems of trophozoites as well as of merozoites, remain unaffected by the drug as long as investigations were carried on (24 h). The satisfying prophylactic effect of Imidocarb as well as the insignificant cellular damages on merozoites may be due to the small feeding of hemoglobin.