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Description de 3 nouvelles especes Neodiplostomum fastigatum, N. pitangi et Uvulifer weberi n.sp.

A combination of histochemical and electron microscope techniques have demonstrated, in Cyathocotyle bushiensis, alkaline phosphatase activity in the matrix of the tegument, in the distal and basal plasma membranes of the tegument, in the wall of the ducts extending from the adhesive organ gland cells and in the wall of the adhesive organ microvilli. Acid phosphatase activity was much stronger and was present in the tegument matrix and in the granular component of the secretion from the adhesive organ gland cells. Strong acid phosphatase activity was also present in the cisternae of the endoplasmic reticulum of the adhesive organ gland cells.I am greatly indebted to Professor Brough for the excellent facilities available within this department. I also wish to thank Professor J. Sinclair (Department of Mining) for electron microscope facilities extended to me in the early stages of this investigation, and to Mr W. Henderson, Mr T. Davies and Miss M. Williams for their invaluable assistance. The purchase of the Huxley ultramicrotome, coating unit and an AEI EM 6 electron microscope was made possible by a grant from the Science Research Council.

The life-cycle of many strigeoid trematodes contains encysted metacercariae as disseminating and infective stages. The cyst wall may vary in form from a thin bag-like structure loosely covering the metacercaria (as in Posthodiplostonmm) to a thick layer, closely investing the parasite and forming a cyst of fixed outline. The cyst wall enclosing the metacercaria of Cyathocotyle is of this thick, rigid type. Extensive histochemical studies have been carried out on the cyst wall of Posthodiplostonmm (Hunter and Hunter, 1940; Bogitsh, 19G2), but the characteristics of the other types of strigeid cyst wall are as yet undefined.

Eighteen species of metacercariae of the order Strigeatoidea (Trematoda, Digenea) are described from tropical and subtropical freshwater fishes of Argentina. Sixteen of them belong to the superfamily Strigeoidea and two to Clinostomatoidea. Ten are new species, five belong to previously known trematode species, and three are not specifically named.On the basis of the morphology of these metacercariae, probable life cycles and host–parasite relations are discussed. A general conclusion is drawn that the South American trematodes are more primitive than their counterparts from other continents.Different groups of fish hosts are recognized, each with a different history of association with their present environment. Originally marine fishes adapted to life in fresh water with the aid of increased endocrine activity, primarily thyroid activity. The high levels of endocrine secretions affected the parasites of these fishes, causing metacercariae to develop neotenically. The hosts which were originally freshwater appear to exert less influence on their parasites. Their metacercariae have a more or less normal course of development.Attention is drawn to the evolution in behaviour of strigeoid metacercariae. Primitive species infect less protected sites in the host. With progressive evolution, increasingly more protected sites are selected by the parasite. The evolution culminates in infection of the lens of the eye, which offers the best protection to the parasite against destructive influences of the environment.It is suggested that the metacercariae are guided to their selected infection site by an "engram," or a specific memory, developed and fixed in the course of many generations. New research into parasite behaviour is urged.

Autopsies on 144 bullheads (Ictalurus melas and I. nebulosus) from North Dakota and Minnesota revealed a high incidence of diplostomulum-infected lenses. The majority of these lenses possessed dorsally situated cysts. The incidence and intensity of infection varied from one collection area to another, but the cysts typically housed more flukes than the lenses. Anatomical and histological comparisons between normal and parasitized eyes indicate that the cyst results from a herniation of the lens near the point of attachment of the dorsal ligament. The pressure required for this protrusion appears to come from the parasites, the hyperplastic lens epithelium, and the reactivity of the lens substance to the parasites. Cyst production, its effects, and its relationship to host age and worm burdens are discussed. The occurrence of strigeoid metacercariae in the lenses and optic chambers of fishes was first reported by von Nordmann (1832). Since then similar cases of parasitism have been recorded from many species of fish, presumably involving many species of flukes. An appreciation of their ubiquitous distribution can be gained from the synopsis of larval strigeoids by Hoffman (1960), and from various fish parasite surveys. Despite these numerous reports there appear to be only two accounts of such flukes being associated with abnormal growths on the fish lens. LaRue, Butler, and Berkhout (1926) reported the localization of diplostomulum metacercariae "in small knobs or projections from the lens" of Ictalurus nebulosus taken in Michigan. More recently in Britain Erasmus (1958) noted a rarely occurring "tumor-like" growth on the lenses of Received for publication 8 June 1964. * From a thesis submitted to the University of Minnesota in partial fulfillment of the requirements for the degree of Doctor of Philosophy. This work was supported in part by the following: National Science Foundation Fellowship for Teaching Assistants, 1962; National Institutes of Health Predoctoral Fellowship GPM-14,398-R1; and the American Cancer Society Institutional Research Grant IN-13D to the University of Minnesota. t Present address: Department of Biology, University of North Dakota, Grand Forks, North Dakota. Leuciscus idus which had been infected experimentally with Cercaria X Taylor and Baylis, 1930. The present study was undertaken when black bullheads, Ictalurus melas (Rafinesque), were found to possess a high incidence of protrusions on their lenses parasitized by diplostomulum metacercariae. The purposes of this paper are to report the incidence and intensity of infection, and to describe the pathological conditions seen in naturally infected bullheads. MATERIALS AND METHODS From 1957 to 1964 autopsies were conducted on 141 I. melas and 3 I. nebulosus collected from North Dakota and Minnesota. Localities, incidence of infection and cysts, and average worm burdens for I. melas are presented in Table I. The limited information for I. nebulosus is not included in tabular form, although all three specimens were infected. Until dissected all fish were held in large tanks supplied with running well water and compressed air. A daily feeding of uncooked oatmeal seemed to provide an adequate diet. The fish were killed by inserting a scalpel into their brains. The eyes were removed with iridectomy scissors and placed in 0.6% saline. By using fine forceps, dissecting needles, and microscalpel, the eye could be opened without damaging the lens or its cyst. The darker dorsal portion of the iris was used as a guide in orienting the excised eye prior to opening it. By using a dissecting microscope it was relatively easy to count the flukes within the freshly excised lens. Most of the cysts were too opaque to show all the worms, hence these structures were teased