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S. E. M. study of the dorsal anterior one third of male Schistosoma bovis and of the anterior ventral border of the gynaecophoric duct. S. bovis was previously described as possessing spineless tubercles. This is so in specimens obtained from experimentally infected rodents, but in cattle, on the contrary, when conditions are favourable, teguments have spiny tubercles. Two morphological types have been observed: the first in Bos taurus from Sardinia, the second in domestic (Bos indicus) and wild (Hippotragus equinus and Damaliscus korrigum) bovids from Senegal, Tchad and Centrafrican Republic.

The cercaria was shed by an Anisus rotundatus experimentally infected with a parasite of Bos taurus in Vendée (France). This Trematode was identified as Paramphistomum cervi. The snail natural host is unknown. The chaetotaxy of the cercaria differs from that of other European species of Paramphistomum and particularly from P. leydeni and P. daubneyi both species which occur in Vendée. The morphology of the adult precludes any relationship with P. ichikawai also present in Vendée. Therefore it very likely represents a species which was synonymised with P. cervi or a new species.

A survaey of Corsican Molluscs, in October 1980, confirms the extension of Potamopyrgus jenkinsi. However two types of biotopes could be distinguished. In the first Potamopyrgus is very abundant and Isidora truncata (= Bulinus truncatus) was not found. In the second type Potamopyrgus are less numerous and coexist with Bulinids. That the colonization by Potamopyrgus is relatively ancient leads us to believe that the second type does not correspond to a preliminary stage of contamination, but rather reflects a stage of equilibrium.

The "miracidial chaetotaxic index" of a human strain of Schistosoma mansoni from West-Africa displays an abrupt decrease following three first transmissions Biomphalaria pfeifferi, white mouse. Then it increases gradually up to a new balance. The value of the index permits to estimate the human or murine characteristic of the natural infections in Guadeloupe. According to stations the index of miracidia issued from rats is widely different. Stations where both rat and man are infected show strong differences from a station where infection seems exclusively murine (Grand-Etang). Results agree with these concerning cercariae. Possibility of intervention of murine strains infecting man in Guadeloupe and apt to cause an especially severe bilharziasis is called up.

The cercarial index defined by Bayssade-Dufour (1977) differs according to the hosts in which Schistosoma mansoni is cycled. This index is close to 1 in African human strains, 1.3 in Carribbean human strains, and 1.6 in strains kept for a number of years in rodents. The first epidemiological and experimental results supported the argument that the transmission of intestinal bilharzia in the mountainous refuge of infection at Grand-Etang, Guadeloup, is maintained exclusively by murine rodents. New epidemiological and experimental data lead us to believe that the black rat of Guadeloup is an inadequate host for S. mansoni, incapable of maintaining the parasite beyond a few cycles.

Cercarial chaetotaxy of Haplorchis taichui (Haplorchiinae, Heterophyidae) is described and compared to that of ten other Opisthorchioidea: three belonging to the Acanthostomidae (Acanthostominae), one to the Opisthorchiidae (Opisthorchiinae) and six to the Heterophyidae (among these, two Centrocestinae, two Apophallinae, one Euryhelminthinae and one Haplorchiinae). Cercarial chaetotaxy allow us to distinguish the considered species and genera, but does not support division of the Opisthorchioidea into families as these have been defined based on morphology of adults; it suggests that the Heterophyidae is heterogenous; it allows us to recognize the Opisthorchioidea characterized by a loss of hexaradial symmetry on the first cephalic cycle of sensillae and by the presence of two to five pairs of sensillae on a tail with proximal excretory apertures.

Cercarial chaetotaxy of Gastrodiscus aegyptiacus (Paramphistomoidea), parasite of the Horse, is described. Cercariae were shed by experimentally infected Bulinus forskalii. This description is the first one of a Gastrodiscidae. The cercarial chaetotaxy of the Gastrodiscidae is quite different from those of Paramphistomoidea and Diplodiscidae.

Paramphistomum microbothrium and P daubneyi are two sibling-species. The value of morphological criteria which have been used to distinguish the adults is not accepted by all authors. On the contrary, criteria based upon larval stages, except miracidia, permit an easy diagnosis. P. microbothrium parasitizes Bulinids, the rediae have a long intestine, germ-balls are inequal in size, cercariae are long-tailed and possess numerous lateral somatic bristles: about 9 by a half-body and numerous caudal bristles: about 17 pairs. P. daubneyi parasitizes Lymneids, the rediae have a short intestine, germ-balls are of equal size, cercariae are short-tailed and posses few lateral somatic bristles (about 4 by a half-body) and relatively few caudal bristles: about 6 pairs. In addition to the cercaviae, argentophilic structures of miracidia and rediae of P. daubneyi are described.

The "cercarian chaetotaxic index" from the human strain of Schistosoma mansoni from West Africa is conspicuously modified during the third transmission Biomphalaria pfeifferi-white mouse only. This might be the explanation why Planorbs collected in Guadeloupe discharge slightly different cercariae whether they come from stations where the infestation is predominantly from human origin or from stations where the infestation is predominantly from murine origin. On the contrary, the "Grand Etang" station is significatively different from all the others and seems to be exclusively murine transmitted.

The life cycle of a senegalese strain of Fasciola gigantica was carried out in France from adults recovered in the liver of naturally infected cattle (Bos taurus). Laboratory-reared Lymnaea natalensis experimentally infected shed numerous cercariae. Metacercariae were used for successful infection of sheep. In the miracidium, variations are observed in the disposition of the medio-ventral epithelial cell of the second tier. The distribution of the superficial argentophilic structures is similar to that of the miracidium of F. hepatica. The chaetotaxy of the cercaria is very closely related to that of the cercaria of a strain of F. gigantica from Madagascar shed by Lymnaea hovarum but it differs clearly from that of the cercaria of F. hepatica. The encystment of a great number of cercariae (25 %) on the surface of water suggests that this is an important factor in the extension of the foci of contamination, and therefore increases greatly the risks of infection not only for animal but also for man. It is possible that human fascioliasis caused by F. gigantica is a disease, the importance of which is under-estimated.

Integumentary argentophilic structures in miracidium and cercaria of Schistosoma japonicum, chinese strain, are described in detail. - Miracidium. The pattern of organites between the first and second tier and between the second and third tier in miracidia of S. japonicum is identical to that in miracidia of S. incognitum, but differs from that seen in miradicia of other species of Schistosoma. - Cercaria. Chaetotaxy differs from that reported in a previous study but, in our opinion, these differences concern the interpretation of the authors and not the structure of the cercaria. S. japonicum is clearly distinguished from other species In the genus by the reduced number of sensory receptors on the tail.

The life cycle of Paramphistomum leydeni Näsmark, 1937, is carried out in the laboratory. Adults were obtained from the rumen of a naturally infected Bos taurus in Czechoslovakia. Laboratory-reared Planorbis planorbis experimentally infected shed the first cercariae two months after exposure to miracidia. Argentophilic structures in miracidia and cercariae are described. In miracidia, these structures are similar to those previously described from species of Paramphistomum: P. togolense, P. phillerouxi, P. daubneyi, P. microbothrium. They differ, however, from those of Calicophoron calicophorum. In cercariae, argentophilic structures have some features in common with those of the species of Paramphistomum mentioned above, especially at the levels CII and AM V, but the very peculiar acetabular chaetotaxy allows us to distinguish P. leydeni from these species. Thus, each species can easily be differentiated from the related species; moreover the genus Paramphistomum as characterized by Näsmark (1937) appears to be justified.

A description is given of cercarial chaetotaxy of two Centrocestinae (Heterophyidae, Opisthorchioidea) from Malaysia: Centrocestus formosanus and Centrocestus sp.--Comparison with cercarial chaetotaxy of taxonomically related groups indicates that 1. The chaetotaxy of the Centrocestinae agrees with that of other Opisthorchioidea, 2. There is an important difference between chaetotaxy of Centrocestinae and other Heterophyidae which suggest that the family is heterogeneous.

Integumentary argentophilic structures of the miracidium and cercaria are described and with those of F. gigantica compared. In the miracidia, the pattern of the organites of the terebratorium and the arrangement of the papillae between the first and second tier of epidermal plates are similar for the two species. However, the disposition of the medio-ventral plate of the second tier allows the miracidia of the two related species to be distinguished statistically. In the cercariae, the chaetotaxy differs between F. hepatica and F. gigantica in two cephalic regions and on the tail (presence of UD papillae in F. hepatica, absence in F. gigantica). The chaetotaxy of a daughter-redia of F. hepatica is also described. There is an important concentration of papillae around the buccal aperture, whereas at the pharyngeal and post pharyngeal levels, papillae are more spaced on the side supposed to be ventral, and scarce on the side considered dorsal.

Superficial argentophilic structures of the miracidium and cercaria of Paramphistomum phillerouxi Dinnik, 1961, are descrifed in detail. Concerning the miracidium they are similar to those of the miracidia of some species belonging to the genus. On the other hand the chaetotaxy of the cercaria is different from that of the cercaria of P. togolense (Alberet et coll., 1978) and therefore this appears to constitute a good criterium for the taxonomy of this group.

Though it is presently admitted that Schistosoma intercalatum is a well individualized species, detailed studies of superficial argentophilic structures of the miracidium and chaetotaxy of the cercaria do not allow these larval stages to be distinguished from those of S. bovis. Therefore this emphasizes the close relationship between the two parasites.

Mature worms were obtained from a sheep experimentally infested with metacercariae issued from cercariae emitted by naturally infested snails: Bulinus (Bulinus) forskalli collected near Lomé (Togo). Miracidia were used for infection of these laboratory-reared snails which gave numerous cercariae. Larval stages are studied. Morphological and histological characters of the adult and the very peculiar shape of the sporocyst distinguish this trematode from the other known species of the genus. The superficial argentophilic structures of the miracidium and cercaria are described in detail because, to our point, they constitute the best criteria for the taxonomy of this group.

The study of the teguments of male Schistosoma intercalatum with SEM shows two different morphological types: a) Type Cameroon (Edea) (consistent with the previous studies by Kuntz et al.). b) Type Zaïre (Kisangani) similar to type Gabon (Libreville).

The comparative study of the excretory system provides new data on the number of flame cells of two cercariae of Diplodiscus from Poland and Togo but does not allow to distinguish them. On the other hand, the comparison of the superficial sensory apparatus shows significant differences. The cercariae from Togo differ from these of Poland by a much lower number of all the cephalic papillae and papillae of cycle Cv, a higher number of acetabular papillae, and the presence of 9 to 12 pairs of dorsal papillae in the median part of the tail. Therefore the African Diplodicus is not D. subclavatus. We identify it as D. fischthalicus.