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Summary Morphological events leading to cyst formation in a cyst-bearing Leptomonas sp. isolated from the hemipteran Oncopeltus varicolor were monitored by light and electron microscopy. In LIT cultures, cyst-bearing flagellates appear at the end of the lag phase and from then on the number of detached mature cysts increases steadily. The cysts develop at the point of the flagellum-cell body junction from the parental flagellate. Plasma-membranes of flagellate and cysts remain connected while they remain attached. Immature cysts present microtubules and a large tubular mitochondrion. Mature cysts are dense, ovalshaped, with few distinguishable organelles, such as a modified nucleus, a rudimentary flagellar pocket and a network of fibrils possibly of kinetoplast origin. During excystation, cysts gradually regain the missing organelles and morphological features of active promasti-gotes. Even cysts, with a very dense and distinct chromatin, retain the ability to undergo cell division in culture.

SUMMARYTwo domestic guinea-pigs (Cavia porcellus), bought in Pinheiros, São Paulo State, Brazil, were taken by their owners a farm in the rural district of Capão Bonito, close to the Atlantic Forest, São Paulo, where they both developed tumour-like and ulcerating lesions on the ears. The causative agent was identified as Leishmania (L.) enriettii, based on biological characters and isoenzyme profiles. Sources of the parasite in wild mammals, and the possible sandfly vector species discussed.

The course of experimental oral infection of Musca domestica with Herpetomonas samuelpessoai and two new isolates from houseflies was followed for up to 40 days using optical and electron microscopy. The fly's rectum was found to be the preferential site of colonization by flagellates, mainly at places near papillar insertions but not on the papillae themselves. Midgut infection was transient, and infection of the crop did not last longer than 1 week. Promastigotes were the predominant colonizing forms and could be seen either free in the gut lumen or attached via hemidesmosomes to the rectum wall. Adherent flagellates exhibited flagellar projections and surface membrane blebs. Many flagellates displayed longitudinal body foldings yielding star-like images in cross sections. Opisthomastigotes could be seen in small numbers as free swimmers, mainly in the rectum.

Summary Electron microscopy of thin sections and detergent extracted preparations of certain trypanosomatids of the genus Phytomonas revealed the unusual presence in some flagellates of an intracytoplasmic flagellum which appears as a naked axoneme encircling the nucleus before emerging at the anterior end of the cell. Another feature of these atypical flagellates is the absence of the flagellar pocket normally present in trypanosomatids at the emergence of the flagellum.

The Brindley's glands of Panstrongylus megistus were studied under the antomic, histologic and ultrastructural point of view. These glands located in the insect's methatorax are paired and have an opening near the third parir of the feet. Beside this aperture, ther are evaporation areas. Shape, sixe and aspect of the gland vary according to the feeding status. The glands are composed by a tubular part corresponding to the duct and a sack-like portion corrsponding to the secretory part. By electron microscopy we observed that the basal part of the epithelium has many interdigitations associated with mitochondria. On the apical surface where epicuticular foldings are located an electonlucent space is often seen. The glands are composed of the following elements: 1) superficial epithelial cells, located just below the apical surface foldings; 2) secretory cells; which are long and have an intracellular canalicule which changes according to the functional state of the cell; 3) a collecting duct to the secretory cells and covered with an epicuticle, reaching up to the gland's lumen; and 4) cells around the duct.

SummaryThe interaction between mouse peritoneal macrophages and ‘Y’ strain Trypanosoma cruzi bloodstream forms was studied at optical and electron microscopical levels. The method of marking lysosomes with Thorotrast, either before or after infection of cell monolayers with parasites, revealed that secondary lysosomes fused with phagosomes shortly after trypanosome interiorization. In spite of this, 24 h later most parasites were no longer in a vacuole but lay free within the host cell cytoplasm, multiplying actively. At this time, and up to shortly before 96 h when parasites escaped to the external milieu, most parasitized cells were not lethally injured, as revealed by the Trypan blue dye-exclusion test. Only when parasites were released into the external medium was this situation reversed and infected macrophages took up the dye.

The initial interaction between infective forms of Trypanosoma cruzi and host cells in vivo was studied at the ultrastructural level. In order to follow these events, T. cruzi bloodstream forms were inoculated into the cheek-pouch of hamsters—a peculiar region devoid of lymphatic vessels. This region was chosen as injection site because, unlike other regions, trypanosomes remained there and multiplied locally up to 15 days after inoculation. Parasites were detected initially outside cells or inside neutrophils. Only after the first week following inoculation were developing and multiplying trypanosomes seen inside macrophages or other resident cells. Parasites persisted until 15–20 days after inoculation, but by about the 28th day they were no longer seen.

SYNOPSIS. An electron microscope study was made of the “cyst-like bodies” (CLBs) previously described in cultures of Trypanosoma conorhini. It is again suggested that CLBs are a process of reproduction which involves fusion of epimastigotes, repeated divisions of DNA-containing organelles and organization of daughter epimastigotes that, after being completely formed, may be found free within the large central “vacuole” of the CLB. This “vacuole,” it is now evident, results from the fused and muchdilated flagellar reservoirs of parent epimastigotes. Our interpretation of the CLBs and their possible genetic significance are discussed.