Dr. Murai Éva szerk.: Parasitologia Hungarica 21. (Budapest, 1988)

of organisms possible on the basis of their observable traits. At the present state of amphistome investigations, the holomorphological (macro- and histomorphological and semaphoront traits), ecological (intermediate and definitive hosts) and distributional data offer usable characters in the analysis of phyletic relationships. Whatever kind of characters are taken into account, the most valuable ones seem to be those which 1) show an altering series of character states within the taxon, 2) show alterations of character states related with one another, 3) are not adaptive in nature. In this context and at the level of the present taxonomic analysis (subfamilial level), the greatest confidence was attributed to the structure of the reproductive system, the excretory system, the type of cercariae, the structure of the pharynx and^he habitat of the adults. The reproductive system is regarded to be one of the most conservative ones because the programme of propagation (which is, among others, the prerequisite of the existance of a given species) requires a definitive structure of its own. Thus, it is subject to variability to a lesser extent than that of the somatic ones and reflects phylogenetic relationship more reliably than the others do. The excretory system is also characterized by its own conservative nature. At subfamilial level the position of its pore in relation to that of Laurer's canal and the position of the excretory bladder were taken into account. In the early stage of the study, the cercariae were differentiated on the basis of their pigmentation (Cercaria pigmentata Pagenstecher, 1857; Cercaria pigmentata Sonsino, 1892). Later, the presence or absence of the pharyngeal appendages were used. Recently, JAIN (1972) pointed out the diagnostic value of the existence of the cross-connection between the main descending excretory trunks. In 1930 WILLEY described Cercaria poconensis, characterized by the branching of the main excretory ducts. The writer regards it to be a new type, and he named it "Cercaria intermedia", due to the intermediate position of the structure of the main excretory ducts. Accordingly, three types of cercariae can be distinguished in Paramphistomata viz. I. Cercaria diplocotylea, II. Cercaria intermedia. III. Cercaria pigmentata. There is well-defined correlation between the structure of the cercariae and the structure of the adults' reproductive organs. The structure of the pharynx is of variable appearance. The pharynx consists of the pharyngeal body itself and the appendages attached to it when they are present. There are well recognizable concordances among the development of the pharyngeal body, the appendages and the habitat of the flukes (consistency of the gut content). Accordingly, the structure of the pharynx can appear to be an adaptive character state in nature and it has lower taxonomic value in the phylogenetic analysis, whereas it is a very valuable character for traditional taxonomic purposes. Amphistomes are inhabitants of the alimentary tract or the organs connected with it (liver, lung). Their occurrence in the intestines or even lower parts of the digestive tube is characteristic for the amphistomes of lower vertebrates (with a few exceptations) and it is one of the plesiomorphic ecological traits. The aim of the analysis of character states, listed above, is to distinguish between the characters of general significance (plesiomorphic) and those of special significance (apomorphic) which is the first step to establish a phyletic relationship. Combining all traits at hand in such a manner, the cladograms and classification schemes, based on these weighted characters, will prove to be the best representatives of the phyletic relationships. Two character states offer possibility for dichotomy within the suborder Paramphistomata. One of them is the presence or absence of the cirrus pouch and the other is the position of the excretory pore and the opening of Laurer's canal. The present writer prefers the former trait because this feature is rather in concordance with the type of cercariae, habitat of the flukes and, furthermore, it produces a more symmetrical dichotomy. This trait des-