Dr. Murai Éva szerk.: Parasitologia Hungarica 20. (Budapest, 1987)
labrum-hypopharynx out of the axis of the proboscis, i. e. out of the plates of the mentum (like a blade of a jack-knife). Nevertheless, this picture represents an artificial position in order to prove that the labrum and the hypopharynx together constitute a functional unit. If the labrum-hypopharynx complex is bent back to their original position, their apices terminate exactly between the lamellae of the labella (Figs 8-10). It can be supposed referring to these data that in the sucking position of the labella (see Fig. 31) the apex of the labrum and the hypopharynx (above and below the entrance of the food-channel) may touch and injure the surface where the fly is sucking from. However, we regard this as a morphological possibility only, which we did not manage to prove in direct trials. As for the labella (Fig. 10), the morphology and the function of the prestomal teeth and of the pseudotracheae were studied. The name "prestomal tooth" itself refers to some cutting and grinding function; indeed, they have a role in cutting up of food into proper pieces. This function can be deducted from the morphology and position of the prestomal teeth but morphology alone would leave questions open as for the way and expressivity of this function. In haematophagous species the labella is much reduced but prestomal teeth function as sharp cutting devices (McALPINE, 1981). The prestomal teeth of the three Musca species involved in our studies are rather different (Fig. 32). These teeth can precisely be characterized one by one but some common features are observable through the SEM micrographs. Schematic drawings of the prestomal teeth in lateral view were made on such a general impression. The prestomal tooth of the house fly (M. domestica) (Figs 11-12) has a thick base, narrowing in its "neck" and the crown of the tooth consists of a strong high, slightly indented main branch and of two weaker laterally directed side branches. Mean length of the teeth (based on SEM micrographs) is 65 to 70 jum, they are of 11- 15 urn at widest and 7. 5-8. 5 jum at their "neck". The prestomal tooth of the face fly (M. autumnalis ) (Figs 13-15) is longer, 75 to 85jum, slimmer than that of M. domestica. That tooth is 11-13 jum at widest and 3.7 to 5. 5 jum at its "neck". The base of the tooth is narrower than that of M. domestica, the two lateral branches of its crown are longer than the main branch and they are not indented. The main branch is indented and emerges from a concave emairgination between the lateral branches. The prestomal tooth of M. osiris (Figs 16-18) is 70 to 80 jum long, it is 15 to 20 jum at widest and ca. 5 jam wide at its "neck". The base of the tooth is narrow (like in M. autumnalis) , the three branches on its crown are nearly evenly high. The lateral branches are without indentation, the main branch is strongly indented. The main branch - since it is as strong as the lateral branches - does not emerge from an emargination between the lateral branches (in contrast to that of M. autumnalis). Comparing these sizes of teeth to the mean thickness of animal epithelia (i. e. 30-40 urn) we may conclude that such a tooth is capable of cutting through the whole epithelium. There are weighty arguments to support this morphological possibility when studying the fixation of these teeth. The teeth sit on a firm base on the discal sclerite. Their bases are connected to one another up to their neck by a chitinous plate and this way a one-sided row of teeth form a coherently moving -system. In addition, the teeth are connected one by one to the lamellae of labella through a chitinous plate (Figs 11-14, 16-18, 19-21). This latter chitinous plate is movable in harmony with the discal sclerite and these two connecting systems allow the vertical and also the horizontal movements of the prestomal teeth between the different positions (Fig. 31) and also those in a given position. All these movements are results of the changing pressure of the haemolympha and of the work of strings and muscles (WEST, 1951). Our trials with flies sucking ("biting") on living tissues furnish documentary proofs for these movements (Figs 22, 23). The mouthparts of the house fly are capable of biting out three epithelial cell-layers during the short period of a "bite". The heaps on the micrograph indicate the entrance of the food-channel, the breaks beside them are results of tearing of the prestomal teeth. An exact print of a prestomal tooth is well discernible on the surface of the epithelium (Fig. 23). These results are of another nature, and thus they are published elsewhere (MEDVECZKY et al., 1988, KOVÁCS-SZ. et al. , in print).
