The present investigation has shown that combined treatment with dexamethasone and prednisolone or with hydrocortisone and dexamethasone enhances the susceptibility of albino rats to Paragonimus miyazakii, presumably by suppressing the host’s immune responses. In the rats given these combined treatments, the size and egg production of worms were markedly increased. Use of dexamethasone or prednisolone alone had relatively little influence on the growth and maturity of P. miyazakii. In serological analysis and agar double diffusion, considerable differences were recognized between the gamma-globulin fractions and antigen-antibody systems (Precipitin bands) of the treated groups and the untreated group. The mechanism of action of these immunosuppressants in this system remains obscure.

An in vitro larval precipitate test using second-stage Toxocara canis larvae and an indirect fluorescent antibody (IFA) test employing cuticles of T. canis larvae as antigen were evaluated using antisera produced in pigs experimentally infected with T. canis, T. cati, Ascaris suum, Toxascaris leonina and Parascaris equorum. The former test was both specific and sensitive and is suggested as a reliable and simple method of detecting Toxocara antibodies in pigs. The latter test was considered unsuitable because of cross-reactions that occurred when sera from pigs infected with other ascarids were tested. An IFA test for Ascaris antibodies, employing cuticles of A. suum larvae as antigen, is described. The degree of specificity of this test suggests that it may be of value in the detection of antibodies to Ascaris in pigs under natural conditions.

Brood capsules were obtained from freshly collected cysts of equine and ovine strains of Echinococcus granulosus. Protoscoleces were freed from brood capsules either by mechanical disruption or pepsin-HCl digestion. Preparations of protoscoleces studied included: mechanically released protoscoleces without further treatment, or incubated either in HCl pH 2·0 or in evaginating solution (containing Na taurocholate) for 24 h; pepsin-HCl released protoscoleces without further treatment or incubated in evaginating solution for 24 h or 7 days. Half of each preparation of ovine protoscoleces was fixed in absolute methanol.

All fresh preparations of protoscoleces lysed rapidly when incubated in normal human serum. Studies with a fluorescein isothiocyanate (FITC) labelled sheep anti-human C3 antiserum revealed the presence of C3 on the surface of lysing protoscoleces. Antibody could not be detected on the surface of any of the preparations of fresh or methanol-fixed protoscoleces using direct or indirect fluorescent antibody tests suggesting that the classical pathway of complement activation was not involved in the lytic process. Strong evidence for lysis by the alternate pathway of complement activation was the lysis of protoscoleces which had been treated with pepsin-HCl and lysis of protoscoleces in guinea-pig serum deficient in C4 component of complement.

Cyst wall, brood capsules and evaginated protoscoleces of E. granulosus (ovine and equine) and E. multilocularis were fixed in 10% formol-saline embedded in paraffin and cut at 8 μm. Specific rabbit antisera to antigen 5 and antigen B of hydatid cyst fluid were used with immunoperoxidase methods to localise the antigens in the histological sections.

Antigen 5 was found in all parasites and was associated with cells of the subtegumental area of the protoscolex, the brood capsule wall and the germinal membrane. The labelled antigen appeared as distinct granules in all areas. It is suggested that antigen 5 may be synthesised in all of these sites and that a source of the antigen in cyst fluid may be the germinal and brood capsule membranes. The laminated membranes of E. granulosus (ovine and equine) were, except for the superficial layers, free from antigen 5.

Antigen B was present in all parasites. It was distributed diffusely throughout the laminated membrane, germinal membrane and brood capsule wall. There were areas of densely labelled antigen B on the surface of the distal cytoplasm of the protoscolex tegument and the surface of calcareous corpuscles. The distribution of antigen B in relation to PAS positive meterial and possible complement activating substances is discussed.

The laminated membrane of E. granulosus was apparently more permeable to antigen B than to antigen 5. It is suggested that differences in the diffusion of these antigens through the laminated membranes of hydatid cysts in the same or different host species may account for variable serological responses during infection.

Notocotylus tadornae n.sp. is described from the New Zealand paradise shelduck Tadorna variegata (Gmelin), and Notocotylus gippyensis (Beverley-Burton, 1958), is recorded from three waterfowl species in New Zealand. The life histories of both species are shown to involve an hydrobiid snail Potamopyrgus antipodarum, as intermediate host. The taxonomic affiliations of N. tadornae and N. gippyensis are discussed.

From original observations and from data in the literature, a key to cercariae of British strigeoids for which life-cycles are known has been compiled. The value of various characters of systematic importance is discussed.

Oxyhaemoglobins of six digenetic trematodes,—Srivastavaia indica, Gastrothylax crumenifer, Gigantocotyle explanatum, Fasciolopsis buski, Gastrodiscoides hominis, Isoparorchis hypselobagri, and of their 3 vertebrate hosts, Bubalus, bubalis, Sus scrofa, Wallago attu, were subjected to alkali denaturation at a pH of 12·4. All oxyhaemoglobins from trematodes and their hosts differ from each other in the rate and extent of alkali denaturation which may be explained due to variations in the amino acid sequences of a particular haem protein in addition to other factors.

From the known species occurring in crocodilians, the genus Dujardinascaris is redefined and found to be a homogenous group of species, with dujardini Travassos, 1920 as the type species. The following new species are described and added to the genus: gedoelsti, puylaerti, waltoni, mawsonae and taylorae. The following species are excluded from the genus: vandenbrandeni, australiensis, tasmani, alata and antipini. The distribution of the species in Dujardinascaris is as follows: in African crocodiles—dujardini, madagascariensis, gedoelsti, and puylaerti; in South American caimans—longispicula, paulista, and chabaudi (possibly a synonym of paulista); in North American alligator–waltoni; in Crocodylus acutus—helicina; in the Indian gavial—woodlandi; in crocodiles in Papua New Guinea and Australia—mawsonae and taylorae.

These species are differentiated mainly by the relative length of the spicules and the form of the guber naculum in the males and by the relative length of the vagina and the form of the vulva in the females.

The genus Sulcascaris is upheld and redefined. Sulcascaris sulcata from Chelonia mydas and Caretta caretta is redescribed, from Rudolphi's type material and material from the Mediterranean and Western Pacific, demonstrating that the excretory pore opens between the subventral lips and that the excretory cell is bilateral, comprising a short filamentar right component and a more capacious ribbon-like left component containing the nucleus. The phylogenetic significance of this form of excretory system occurring in an ascaridoid of a marine reptile is discussed. It is concluded from comparative studies, based on measurements, sections and electron scanning micrographs, that fourth stage larvae of S. sulcata collected from the stomach of turtles are identical with fourth stage ascaridoid larvae found in the adductor muscle of scallops (Amusium balloti and Chlamys sp.) and that turtles become infected with this species by eating bivalves. Adult S. sulcata were obtained from tank-reared C. caretta fed with encapsulated larvae from scallops.