The worm described in the present paper was obtained from the stomach of the common cat-fish, Clarias batrachus Bl. from Nagpur, C.P., India. Only 5 out of the 22 individuals examined harboured this parasite and as many as eight were obtained from a single individual. With the exception of two specimens, they were preserved in glycerol and were not subsequently used. The remaining two specimens were flattened out between glass slides and fixed in Mann's fluid.

In the course of my previous work on the structure of the head and mouth parts of the Streblidae (1929), I encountered some difficulty in identifying the different species of the genus Raymondia. A careful examination of the specimens in the collection of the British Museum and of my own specimens showed that the descriptions and figures given by the authors who studied these insects in the dried condition are not quite adequate. In dried specimens of these minute flies it is often impossible to distinguish clearly the chaetotaxy of the head and the thorax and the characters present in the wings, which are generally interlocked. Moreover, the parts of the male genitalia lying in the abdomen are absolutely inaccessible. When examined in the cleared specimens the genitalia of the different species have been found to possess distinctive characters.

The intensity of Plasmodium berghei infections decreases as the age of the rat host increases. The nature of this ‘age immunity’ was investigated. No experimental support was found for innate resistance involving either serum non-antibody factors or changes in the erythrocytes that inhibit parasites in older rats. A cross reacting immune response active against P. berghei was not found. Evidence is presented which shows that rats less than 7 weeks old lack at least part of the functional immunological apparatus by which older rats produce a protective immune response. It is suggested that the defect might involve T lymphocytes.

The cestode, Hymenolepis diminuta, and the acanthocephalan, Moniliformis dubius, were found, by Chandler (1939) and Burlingame & Chandler (1941) respectively, to undergo an anterior migration in the intestine of rats after the establishment of the infection. More recently, these results have been confirmed by Holmes (1961, 1962) who stated that it is not unlikely that the worms select optimum sites along one or more of the many gradients known or postulated to exist along the length of the small intestine.

Many complex life cycle parasites exhibit seasonal transmission between hosts. Expression of parasite traits related to transmission, such as the manipulation of host phenotype, may peak in seasons when transmission is optimal. The acanthocephalan Acanthocephalus lucii is primarily transmitted to its fish definitive host in spring. We assessed whether the parasitic alteration of 2 traits (hiding behaviour and coloration) in the isopod intermediate host was more pronounced at this time of year. Refuge use by infected isopods was lower, relative to uninfected isopods, in spring than in summer or fall. Infected isopods had darker abdomens than uninfected isopods, but this difference did not vary between seasons. The level of host alteration was unaffected by exposing isopods to different light and temperature regimes. In a group of infected isopods kept at 4°C, refuge use decreased from November to May, indicating that reduced hiding in spring develops during winter. Keeping isopods at 16°C instead of 4°C resulted in higher mortality but not accelerated changes in host behaviour. Our results suggest that changes in host and/or parasite age, not environmental conditions, underlie the seasonal alteration of host behaviour, but further work is necessary to determine if this is an adaptive parasite strategy to be transmitted in a particular season.

Although oocyst morphology was always considered as a reliable parameter for coccidian species discrimination we describe strain variation of turkey coccidia, Eimeria adenoeides, which remarkably exceeds the variation observed in any other Eimeria species. Two strains have been isolated – the first strain maintains the typical oocyst morphology attributed to this species – large and ellipsoidal – while the second strain has small and ovoid oocysts, never described before for this species. Other biological parameters including pathogenicity were found to be similar. Cross-protection between these 2 strains in 2 immunization and challenge experiments was confirmed. Sequencing and analysis of 18S and ITS1 ribosomal DNA revealed a close relationship according to 18S and a relatively distant relationship according to ITS1. Analysis of 18S and ITS1 sequences from commercial turkey coccidiosis vaccines Immucox®-T and Coccivac®-T revealed that each vaccine contains a different strain of E. adenoeides and that these strains have 18S and ITS1 sequences homologous to the sequences of the strains we have isolated and described. These findings show that diagnostics of turkey coccidia according to oocyst morphology have to be carried out with caution or abolished entirely. Novel PCR-based molecular tools will be necessary for fast and reliable species discrimination.

In order to investigate the molecular taxonomy within Trypanosoma cruzi, the ribosomal small subunit (18S) gene was amplified by polymerase chain reaction (PCR) from a selection of 21 stocks and 3 outgroup taxa. Amplification products were digested with 10 restriction enzymes; restriction fragments were separated by polyacrylamide gel electrophoresis and profiles were visualized by silver staining. Upon analysis of such riboprint profiles, an estimate of pairwise phenetic distance between stocks of T. cruzi was calculated. Upon principal coordinate analysis of this data matrix, a tendency towards a bi-polar grouping of stocks was observed. These 2 groups were predominantly either zymodeme 1 stocks or zymodeme 2 stocks. The position of zymodeme 3 stocks remained intermediate between the 2 groups but did not form a coherent group by themselves. It would therefore appear premature to warrant division of T. cruzi into 2 discrete taxa or subspecies until the relationships of further zymodeme 3 stocks are elucidated.

The lice which infest man belong to the order Anoplura Leach 1817, containing two sub-orders, (i) Siphunculata Meinert 1891 and (ii) Mallophaga Nitzsch 1818. The family Pediculidae Leach is included in the Siphunculata1. Owing to the confusion which still persists in the literature regarding the nomenclature and systematic position of the two sub-orders of Anoplura, it appears expedient to review the evidence upon which the statement contained in the preceding paragraph is based.

Despite some years of enquiry, the mechanism that leads to intra-erythrocytic death of malarial parasites during the host's response to infection has not been elucidated. We report here that serum from mice undergoing a successful immune response to Plasmodium chabaudi does not inhibit Plasmodium falciparum unless the Pl. chabaudi is virulent enough to rise to at least 50% parasitaemia and to cause illness. This appears to be true of the 556 KA and DS strains of Pl chabaudi, and also other murine malaria parasites. In mice infected with Pl. chabaudi 556 KA inhibitory activity coincided with the presence of TNF in their serum. Exogenous TNF generated inhibitory activity in the serum of mice only if the animals were pretreated with Proprionobacterium acnes, implying a role for activated macrophages downstream from TNF in this process. The difference in inhibitory activity against Pl. falciparum in serum from mice infected with Pl. chabaudi of more or less virulence may be one of degree. Alternatively two distinct mechanisms may operate, the second coming into operation only in ill mice, with higher parasite burdens.

Male and female schistosomes are generally assumed to form stable monogamous pairs for the whole span of their long existence in the mammalian host. Recent evidence from mixed infections has shown that Schistosoma mansoni males can displace S. intercalatum males from their homologous partners, but no information exists about the existence of similar phenomena within a single schistosome species. Here, we determine whether male S. mansoni can displace males of the same species from pre-formed pairs in vivo. The availability of clear-cut genetic markers of drug resistance in schistosomes was exploited to show that hycanthone sensitive S. mansoni males can displace homospecific hycanthone resistant males from pre-formed pairs and vice versa. The frequency of changes is dependent on the magnitude of the excess single males competing with paired worms. The possible mechanics and the biological significance of mate changing are discussed.

The in vivo activity of two cyclosporins, cyclosporin A (CsA) and a non-immunosuppressive derivative of dihydrocylosporin A (DHCsA-d) against three tapeworms, Hymenolepis microstoma, H. diminuta and Mesocestoides corti, has been assessed. CsA reversibly reduced the dry weight of H. microstoma in the mouse, briefly delayed oviposition and had a statistically significant effect on worm numbers recovered. Oral and subcutaneous treatments of both CsA and DHCsA-d were effective in reducing worm weight; juvenile worms were most susceptible but worms of all ages responded to drug by a dramatic reduction in weight from which they recovered. Multiple courses of CsA were no more active than single courses of treatment but dose response suggested that a threshold level of drug was necessary to evoke activity. By contrast, H. diminuta in the rat was completely unaffected by CsA but no explanation for the differences in drug response by these two closely related helminths is forthcoming. Mesocestoides corti responded reversibly to CsA in the mouse by a reduction in asexual proliferation of both liver and peritoneal cavity tetrathyridia. The data presented argue in favour of a range of anti-parasitic activities by cyclosporins but the details of the various putative modes of action remain to be defined.

The coccidian dealt with in this paper is a parasite of the blood, fat bodies and connective tissue of Tribolium ferrugineum. W. A. Riley and L. Krogh were the first and perhaps the only ones who noticed stages of this parasite, when studying the histology of the larvae of this beetle. They found the pupae and adults uninfected, but in the course of the present work some of them were heavily infected, though only a small number could be examined.

The results are described of a study of the distribution of the antigens in F. hepatica at various stages of development, and in the liver and spleen of experimentally infected rats using globulins labelled with fluorescein isothiocyanate, from rats and sheep infected with F. hepatica.

Possible uses of this technique in aiding the diagnosis of fascioliasis are indicated.

I wish to thank Dr A. W. J. Broome for a supply of the metacercariae of F. hepatica, and Dr J. S. S. Lowe who kindly isolated and labelled the globulins with fluorescein isothiocyanate. Miss Enid Eccleston gave valuable technical assistance.

Oncospheral agglutination given by sera immunized with Hymenolepisnana eggs is described as a new way of assessing H. nana infection. All sera of mice which possessed acquired protective immunity against reinfection by H. nana eggs had the potency to induce oncospheral agglutination in vitro. Only oncospheres, which had been hatched, agglutinated, no agglutination occurred in sera from uninfected mice. Oncospheral agglutination was carried out by mixing 0·1 ml of serial two-fold dilutions of serum and 0·1 ml of Hanks' balanced salt solution containing about 600 hatched oncospheres. Titre of agglutinins was indicated as a reciprocal of the final dilution capable of giving agglutination clusters made of three or more oncospheres. Agglutinins developed within 14 days after a primary infection with 500 shell-free eggs. There was no rapid increase of agglutinins within 4 days following a secondary infection. The titre increase coincided with the increase in dosages of eggs. Agglutinins were thought to be immunoglobulins, because the potency of the serum to agglutinate oncospheres was extinguished after absorption of globulins with rabbit anti-mouse globulin serum.

Agglutinins were produced in rabbits by intravenous injections of shell-free eggs. The titres of the rabbit sera were much higher than those of mouse sera.

This account is based upon the study of forty monogenetic trematodes belonging to the genus Calicotyle Diesing, 1850, found in the following hosts, locality and habitats:

Polyclonal antisera raised against Plasmodium knowlesi reacted with (1) NADP-specific glutamate dehydrogenase (GLDH) of P. knowlesi, (2) GLDH of P. falciparum and (3) GLDH of Proteus spp. The antisera did not react with NAD(P) GLDH from bovine liver. Polyclonal antisera raised against the GLDH of Proteus spp. cross-reacted with GLDH from P. falciparum. Monoclonal antibodies (McAbs) obtained from mice immunized with Proteus GLDH were either specific for the bacterial enzyme or cross-reacted with P. falciparum GLDH. The selected McAbs did not react with GLDI-1 from P. knowlesi, P. chabaudi or P. berghei. The GLDH of P. falciparum was shown to be a cytosolic protein (by FAT) with a subunit molecular weight of approximately 49000 Da (by immunoprecipitation) having a pre dominantly hexameric form (by sucrose density gradient). Implications of the conserved sequences of GLDHs and other enzymes are discussed.

The functional organization of the tail musculature of two species of cercariae has been studied by examination of serial sections in the light and transmission electron microscopes. A three-dimensional reconstruction of the tail has been established. The fine structure of the muscle cells has been investigated and the complexity of organization is related to the requirement for a fast contracting system in the cercarial tail.

The tegument of adult Schistosoma mekongi has been studied by both scanning and transmission electron microscopy. The gross surface topography of the parasite resembles that of S. japonicum, in that branched ridges, microvilli and sensory papillae predominate; such characteristics distinguish these two species from the non-oriental schistosomes. A unique feature of S. mekongi, however, is the numerous pleomorphic protruberances which are concentrated particularly on the middle three-fourths of the body surface. Transmission electron microscopy has revealed that these protruberances enclose bundles of microfilaments which appear to insert into the tegumental outer membrane. The microfilaments are suggested to have a supportive or stabilizing function, and may compensate for the absence of more typical crystalline spines. The tegumental outer membrane is typically heptalaminate in section, while the basal membrane infoldings are surrounded by concentrations of mitochondria. Three types of tegumental inclusion bodies have been recognized. Discoid bodies and membraneous bodies are morphologically identical to those described in all other schistosome species, except that the latter inclusions have been seen connected to each other and to the tegumental outer membrane by unique channels lined with trilaminate membrane. The third inclusion takes the form of spherical, lucent vesicles containing membrane fragments; these may represent the remains of spent membraneous bodies.

This study used light and electron microscopy to provide observations and morphometric details of the life-cycle of the gymnophallids (Trematoda, Digenea), Parvatrema margaritense (Ching, 1982) n. comb., the parthenogenetic metacercariae (‘germinal sacs’) of which were previously described by Ching (1982) as Cercaria margaritensis. The research was instigated by the discovery, on the Barents Sea coast, of a high prevalence of gymnophallid sporocysts and cercariae in the bivalve Turtonia minuta and an equivalent presence of distinctive gymnophallid metacercariae in the gastropod Margarites helicinus. Experiments and data obtained from naturally infected M. helicinus demonstrated that cercariae released from the bivalves invaded the gastropods to give rise to the metacercariae. Two generations (M1 and M2) of these parthenogenetic metacercariae were formed in the extrapallial cavities of their bivalve hosts and they, in turn, gave rise to a third generation (M3) which was shown to infect marine ducks such as the eider (Somateria mollissima). As only small numbers of cercariae are released from T. minuta, it was concluded that the inclusion of parthenogenetic metacercariae in the life-cycle is particularly significant. It allows each cercaria that infects M. helicinus to give rise to over 2000 invasive metacercariae. Evidence suggests that the parthenogenetic metacercariae are commensal rather that parasitic in the pallial cavities of their hosts. Implications of this for theories of early digenean evolution are discussed.

The development of the epidermis of the oncomiracidium larva of Entobdella soleae was studied in embryos dissected from the egg and processed for electron microscopy. At first (7- to 8-day embryos at 15 °C) the embryo is covered with a nucleated primary epidermis of flattened cells which are closely associated with the viteUine cells and may take up nutrients from them. This layer is either replaced by or develops into the secondary epidermis which consists of ciliated cellular regions joined by an apparently syncytial interciliary cytoplasmic layer. Both ciliated cells and interciliary cytoplasm are at first nucleated but later both lose their nuclei. There may be a turnover of ciliated epidermal cells at the surface of young embryos. Between days 16–20 a discontinuous presumptive adult epidermis appears beneath the ciliated cells which has connexions to cell bodies lying in the parenchyma. This layer, apparently fuses with the syncytial (?) interciliary regions which have by this time lost their nuclei. After shedding of the ciliated cells, the presumptive adult epidermis spreads out to form a continuous syncytial covering to the post-larva. The ciliated epidermal cells apparently lose their nuclei between days 20 and hatching. This may be associated with the ‘programmed life’ of the ciliated cells. Details of the food reserves and morphology of the ciliated cells are discussed in connexion with the energetics of these cells.