Dr. Murai Éva szerk.: Parasitologia Hungarica 20. (Budapest, 1987)

The other structures of labella, the pseudotracheae (Fig, 10) were also studied. The pseudotracheae touch the surface where the fly is sucking from, from the filtering to the intermediate positions of the labella (see Fig. 31). The pseudotracheae of the three Musca species are not much different in their structure and since they are rather small (ca. 10 jam), they are insignificant in differentiation of these species. The pseudotracheae are open (or closed) channels running from the periphery to the entrance of the food-channel and they play a role both in filtering (differentiating) the food particles and in the transport of food (Fig. 25). The fine structure of these channels was described by GRAHAM-SMITH (1930) based on studies by traditional light microscopy. His observations can be complemented by SEM micrographs in some details. Our Figs 33-34 compare their schematic structure based on light microscopy and on SEM micrographs. Their annular structure is also discernible on SEM pictures (Fig. 25) but fish-tail ends and wish-bone ends are hardly distinguishable (Figs 33, 34). In fact, one fish-tail end and laterally directed twig of its neighbouring two wish-bone ends are joint into such a chitinous plate which turns laterally and slightly ventrally (Figs 26-271 These latter ventrally directed chitinous plates have one process each towards their two neighbouring plates and they are articularly connected (Fig. 28). These same chitinous plates are continued into the membrane covering the haemocoel of the labella. This fact becomes important when the haemocoel is filled up with haemolympha: the membrane is raised and these chitinous plates tighten the fissures of the pseudotracheal rows (Figs 33, 34, 28, 29). An efflux of the haemocoel results in the opening of the pseudotracheal rows through a reverse mechanism (Fig. 26). This latter process has been surveyed by SEM micrographs only and no more documentative data were searched for. For the harmful effect on the surface (epithelium) caused by the secretophagous flies, nothing but any movement of the pseudotracheal rows is to be considered. The significance of these movements is proved by those minor injuries (abrasions) which are seen on projecting points of a tissue-culture caused by a sucking of a house fly (Fig. 30) (for details see MEDVECZKY et al., 198 8, KOVÁCS SZ. et al. , in print). DISCUSSION The morphology of the mouthparts of three species of Musca was studied from the point of view of a better knowledge of those structures which enable the flies to injure the animal epithelia while sucking. The importance of this point of view is underlined by the fact that flies frequently vomit. This way the microbial pathogens sucked in other places (a diseased animal, etc. ) will be scarified into the host animal through epithelial microlesions caused by the sucking and biting of the flies (e. g. MEDVECZKY et al., 1988). The secretophagous flies which have traditionally been regarded as passive carriers, this way are active causative agents ensuring the establishment of infections through their "bites". Our present work is aimed at surveying the morphological aspects of this intricate process. Originally, the hypopharynx and the labrum of the haustellum and the chitinous structures of the labella seem to be the objectives to be considered. In the haustellum, the labrum and the hypopharynx are acute structures, borne on a firm base and forming the food-channel. Their apices (below and above the food-channel) reach the level of the lamellae of the labella. In the sucking position when the lamellae of the labella are reclinate (and the prestomal teeth are directed laterally), the apex of the labrum-hypopharynx can reach the surface where the fly is sucking from, and may cause injuries on the animal epithelia. We cannot exclude this as a real possibility, though our trials to detect the nature of the microlesions did not prove any lesion as a result of this kind of function of the labrum-hypopharynx. Possibly, studies of other kind can exclude the importance of this function. The prestomal teeth are the sharpest chitinous structures on the labella even at first glance (Fig. 9-10). The main features of the prestomal teeth of the different species of Musca have been described by light microscopic studies. In the present study schematic drawings of these teeth were made based on SEM micrographs, emphasizing their main contours in order to present a basis for differentiating these species in the proper position of the mouth-