Cells capable of transferring immunity to Trichinella spiralis, i.e. of accelerating adult worm expulsion, were present in the mesenteric lymph nodes of mice infected for 4, 6 or 8 days, but not in mice infected for only 2 days. The time-course of worm expulsion in mice infected on the day of transfer was similar in recipients of day 8 cells, expulsion becoming marked only when the recipients had been infected for at least 6 days. Transfer of cells 4 or 6 days after infection did not result in an accelerated worm expulsion; transfer 1 or 2 weeks before infection did not enhance the level of immunity in recipient mice. In contrast to the results obtained with mesenteric lymph node cells (MLNC) no immunity was trsnsferred when recipients were given spleen cells taken from donors infected for 8 days. It is suggested that MLNC do not cause worm expulsion directly, but cooperate with another component of the host's defence mechanism. Accelerated expulsion in recipients of cells was accompanied by a premature decline in fecundity of female worms. Evidence is presented to show that worm expulsion and impaired reproduction may represent independent aspects of the immune response to T. spiralis.

When mice were irradiated immediately before infection with Trichinella spiralis there was a profound and long-lasting interference with their ability to expel adult worms from the intestine. Irradiation given after the fifth day of infection was progressively less effective in this respect. The ability to expel worms was not restored when mesenteric lymph node cells (MLNC) were transferred (a) on the day of infection in mice irradiated one day previously, or (b) on day 7 of an infection in mice irradiated on day 6, even though the MLNC transferred immunity to intact recipients. Transfer of bone marrow (BM) alone was also without effect. However, worm explusion was restored if, following irradiation and injection of BM, 10 days were allowed for BM differentiation before transfer of MLNC. This restoration was effective even after lethal levels of irradiation and was clearly dependent upon a donor-derived BM component cooperating with, or responding to, the activity of the transferred MLNC. The possibility that the BM component is non-lymphoid in nature is discussed.

The development and growth of Haemonchus contortus was studied in the stomach of the laboratory rabbit. Less than 1% of the ensheathed infective larvae givrn to rabbits become established, whereas after exsheathment in vitro under physiological conditions, 20–30% of the larvae administered developed to nthe 4th stage. Following doses of up to 10000 larvae, nearly all worms were lost from the 16th to the 21st day after infection, but after doses of 50000 larvae considerable numbers of 4th-stage larvae were recovered 25 days after infection. No adult worms were recovered and no eggs were found in the faeces. Infection was accompanied by inflammation, haemorrhage, disruption and flattening of the mucus secreting cells and by mononuclear infiltration. No cellular reactions in the immediate vicinity of the nematodes in the mucosa or changes in the pH of the stomach contents were observed.

Unlike in other acanthocephalans, the overian balls of Centrorhynchus corvi are complex and are composed of 24–30 ovarian ball units. Each ovarian ball unit consists of three structural and functional units – the oogonial syncytium, developing oogenetic cells and the supporting syncytium – complementary to the ovarian balls of other acanthocephalans. Three metamorphic stages of the nuclei in the oogonial syncytium are described, depending on the nuclear morphology, chromatin structure and appearance of the nucleolus. Third-stage nuclei bulge out at the periphery of the oogonial syncytium and are surrounded by its cytoplasm and a thin membrane. Ultimately these are separated from the oogonial syncytium to from oogonia containing small amounts of cytoplasmic components derived from the oogonial syncytium. Nuclei of the young oogonia, oognia at the budding stage, and 3rd-stage nuclei of the oogonial syncytium all possess nucleoli and are similar also in their nuclear dimensions and cytochemical affinities. Nuclear resemblances, and cytoplasmic similarities of the oogonia and oogonial syncytium with regard to the presence of lipids, RNA and proteins support the concept of the origin of oogonia from the oogonial syncytium.

The free oogonia divide mitotically in the cellular zone where they undergo a single mitotic division and the resulting oocytes enter the prophase of meiosis. I. The meiotic primary oocytes in contrast to the permeiotic primary oocytes of other acanthoscephalans enter the growth phase which is closely accompanied by the accumulation of various ooplasmic components such as basophilic yolk nucleus which is composed of RNA, proteins, lipoproteins and phospholipids. Histochemical features of the oogonial and supporting syncytium are described.

Photoleter anterouterus Fischthal & Nasir, 1974, from Pelecanus occidentalis Linnaeus and Pelecanus erythrorhynchos Gmelin from Florida, USA and the ventrogenital complexes of Photoleter gastrophilus (Kossack, 1910) from Delphinus delphis Linnaeus from Queensland, Australia and of Phocitrema fusiforme Goto & Ozaki, 1930 from Alopex lagopus (Linnaeus) and Phoca vitulina Linnaeus from Alaska are redescribed. The genus Photoleter Odhner, 1914 is emended and compared with Phocitrema Goto & Ozaki, 1930 and both genera are compared with members of, and as a result transferred from the family Opisthorchiidae Looss, 1899 to, the subfamily Centrocestinae Looss, 1899, family Heterophyidae Odhner, 1914.

A coccidium belonging to the family Adeleidae was discovered in the mid-gut cells of Tipula paludosa. A new genus Rasajeyna and a new species nannyla are established because this pathogen differs from previously described coccidia. A diagnosis of R. nannyla is given.

The endogenous phase of R. nannyla is restricted to larvae. The oocysts, which are the external phase of the parasite, are swallowed by the leatherjackets and excyst in the anterior mid-gut. The sporozoites, 36·5 µm (± 5·4 µm, 95% confidence limits) long, 15·7 µm (± 1·8 µm, 95% confidence limits) wide, each containing a refractile body, enter the anterior mid-gut cells where the 1st schizogony occurs. The refractile bodies are retained during the early nuclear divisions. The sausage-shaped merozoites, 28·2 µm (± 4·3 µm, 95% confidence limits) long, 7·1 µm (± 0·9 µm, 95% confidence limits) wide, with posterior nuclei exhibit three distinct types of movement. (a) An active flexion of the body which is thought to occur during the intracellular phase. (b) A flicking action by both ends of the body. This is thought to occur during the free phase. (c) A spiralling motion which is thought to aid the entry of the merozoite into the cells.

The nucles of the intracellular merozoite divides several times, forming a multinucleate body. The merozoites of the 2nd schizogony form in groups at the poles of the schizont. The merozites are indistinguishable from each other until after a period of growth has ensued, when they are differentiated as macro- and microgametocytes. The pear-shaped macrogamete 44·3 µm (± 4·5 µm, 95% confidence limits) long, 21·6 µm (± 3·2 µm, 95% confidence limits) wide, which contains a crescent-shaped structure in the nucleus. The microgametocyte grows to 40·3 µm (± 2·7 µm, 95% confidence limits) long, 16·7 µm (± 1·5 µm, 95% confidence limits) wide and then attaches itself lengthwise to the macrogamete. A membrane is then secreted around both partners. Nuclear division produces 4 microgametes, one of which fertilizes the female. The 1st and 2nd oocyst membranes are deposited before cytoplasmic shrinkage and meiosis. The zygote is 44·6 µm (± 4·2 µm, 95% confidence limits) long and 33·7 µm (± 4·1 µm, 95% confidence limits ) wide. Cytoplasmic condensation around the nuclei forms the sporoblasts which mature into sporocysts each containing 1 sporozoite. The zygote may be expelled from the larvae at any juncture after fertilization.

Previous studies using radioactive miracidia have shown that a number of non-host snails and bivalves, interposed as ‘decoys’ in linear test channels, may interfere with the capacity of Fasciola hepatica miracidia to infect Lymnaea truncatula. Applying similar experimental principles, the role of several other potential interferents have been analysed in the present study. Daphnia pulex (Cladocera) and larvae of Corethra sp. (Diptera) exercised significant interfering effects by protecting ‘target’ snails from infection. Evidence suggested that this effect was a result of their normal predatory behaviour. Other organisms including Herpobdella testacea and Helobdella stagnalis (Hirudinea), Acellus aquaticus (Isopoda), Planaria lugubris (Turbellaria) and L. Truncatula egg clusters failed to interfere with miracidial host-finding. Nor did P. lugubris and L. truncatula ‘conditioned water’ interfere with the capacity of the miracidia to infect their host snail.

A Babesia-free batch of laboratory reared Boophilus decoloratus ticks was infected with a Kenyan strain of Babesia bigemina by feeding them on a steer infected by inoculation of a blood stabilate. The engorged female ticks showed developing stages of B. bigemina in their haemolymph and subsequently their progeny transmitted the parasite to a susceptible splenectomized steer.

Attempts were made to produce stabilates from pre-fed larvae and nymphs derived from infected batches of B. decoloratus. Only the stabilates derived from the nymphs pre-fed either on cattle or rabbits produced B. bigemina infection when inoculated intravenously into susceptible cattle.

An initial observation converning the failure of [3H]thymidine at high specific activity to be incorporated into the DNA of Crithidia fasciculata for more than a brief intitial period has been correlated with the presence at high specific activity in the organism of thymidine phosphorylase activity with an equilibrium in the direction of catabolism. This enzyme degrades thymidine to thymine which is not utilized by the organism. The enzyme has also been shown to be present in a number of other trypanosomatids, including the culture forms of Trypanosoma cruzi, where the specific activity was nearly as high as that in C. fasciculata.

Evidence is presented that in C. fasciculata, the culture forms of T. cruzi and possibly other species of trypanosomatid, the thymidine phosphorylase, together with a thymidylate phosphatase, forms a catabolic pathway which degrades thymine nucleotides to thymine, which is then excreated. About 60% of the thymine nucleotides made by organisms appear to be matabolized through the pathway, suggesting that their synthesis is not subject to completely effective regulatory control.