A successful attempt was made to induce immunological tolerance to N. brasiliensis in laboratory rats by exposing them to larval infections before the age of immunological maturity.

The adult capacity of rats to eliminate a primary infection in 3 weeks and to acquire resistance to reinfection was developed by 5 weeks of age. On the other hand, primary infections of 250–660 larvae, originating before 4 weeks of age, survived in 61 of 83 rats up to 10 weeks. These rats were not resistant to challenge at 5 or 7 weeks of age, nor did the challenge infection undergo immune elimination. Such tolerance was evident even in rats whose primary worm burden was chemically abbreviated prior to challenge.

It was not always possible to distinguish between tolerant and immune animals on the basis of egg output patterns. Suppression of egg output occurred even in tolerant rats harbouring relatively stable female populations.

For immunological experiments on N. brasiliensis infection in rats, the determination of a ‘take ratio’ is advocated: (20 day take/10 day take) × 100. This ratio eliminates the error inherent in variability of takes and renders comparable the results of different experiments.

The work was carried out in 1965 during tenure by one of us (T.K.) of an Exchange Scholarship under the British–Hungarian Cultural Agreement. Supervision by Professor W. Mulligan and the co-operation of colleagues in the Wellcome Laboratories are gratefully acknowledged.

The growth and development of Dipylidium caninum, Hymenolepis citelli, H. diminuta, H. microstoma, and H. nana were examined in Ctenocephalides felis, and the Hymenolepis species further examined in the reference host Tribolium confusum. This is the first recorded infection of C. felis with these four species of Hymenolepis and also of a flea with H. citelli.

Growth and development of the four species of Hymenolepis were comparable in C. felis and T. confusum. Observations relative to scolex formation indicated that perhaps only one basic sequence occurs in the genus Hymenolepis.

Growth and metamorphosis of the flea host had no important effects upon Hymenolepis development. However, presumably owing to greater crowding in C. felis than in T. confusum, an increased amount of retarded development was noted in cestodes from fleas. In contrast, the growth and metamorphosis of the flea host did affect the development of D. caninum. Little growth occurred in larval fleas but with the onset of pupation an increased growth rate was initiated, the cestode reaching almost its maximum size prior to the emergence of the adult flea. Cysticercoid differentiation and maturation mostly occurred within the adult.

A survey was made of the helminth fauna of 657 herring gulls (474 ‘adults’ and 183 chicks) in northern Caernarvonshire and Anglesey during the period July 1962 to November 1964. A total of 31 species of helminths were identified (10 species of Trematoda, 11 of Cestoda and 10 of Nematoda), including 1 new species, four new host records and three new British records. Two species of Mallophaga were identified from the birds. In three cases (Gymnophallus deliciosus, Paricterotaenia porosa and Capillaria contorta) a significant difference was found in the burden carried by male and female birds. ‘Adult’ birds were generally found to be more heavily infected with helminths than the chicks, with the exception of the nematode Cyathostoma lari, which was found more frequently in the chicks. A new intermediate host for Capillaria contorta was noted, namely Eiseniella tetraedra.

Three species of Trematoda, two of Cestoda, and two of Nematoda were found to be cyclic (seasonal) in their time of appearance. Tetrabothrius spp. appeared most frequently in winter, whilst Anomotaenia larina was found only during the summer months. C. lari showed a primary peak of appearance in summer, with a secondary peak in winter. Capillaria contorta appeared in high numbers throughout the year.

The distribution of helminths within the birds was also examined. Gymnophallus deliciosus was generally found in the gall bladder, whilst Parorchis acanthus was found only in the rectum. Intestinal trematodes were normally found in the mid-third of the small intestine (e.g. Spelotrema excellens, Himasthla elongata). In the case of C. lingua, however, peak numbers were found in the duodenum, whilst Brachylaemus fuscatus was found most frequently in the posterior third of the small intestine. Cestodes appeared most frequently in the anterior or posterior thirds of the small intestine (e.g. Tetrabothrius spp., Anomotaenia micracantha). Hymenolepis cirrosa showed two peaks of infection along the length of the small intestine, a small one in the anterior third, a much larger one in the posterior third. Attempts were made to correlate the helminth burden found with the food eaten by the birds and the availability of intermediate hosts.

I should like to thank Mr J. Hobart and Dr I. V. Herbert for all the help that they have given me in the preparation of this manuscript, and also the bodies that gave me permission to shoot birds on their land, particularly the Nature Conservancy. Finally, I would like to thank the S.R.C. for the grant that made this work possible.

The acquired immunity of twenty-eight splenectomized and twenty-three intact cattle following primary inoculation with either of two strains (the Y and the R strain) of Babesia bigemina was investigated. Some of these animals were carriers, while others had ceased to be infected. Observations were made on the response of splenectomized animals challenged up to four times with the original infecting (homologous) strain and finally with the heterologous strain.

In the splenectomized animals, a total of sixty-three homologous challenges produced parasitaemias in only twenty-seven instances, and these were generally delayed and of lower intensity than in control animals. Fifteen negative transmission tests performed shortly after thirty-two challenges showed that it was difficult to re-establish the homologous strain in some animals that had achieved self-cure. Substantial homologous immunity had developed within 16 weeks of the primary infection in animals which were no longer carrying B. bigemina.

All twenty-one splenectomized animals subjected to heterologous challenge developed well-marked parasitaemias. Nine of these had been highly immune to homologous challenge 2 weeks earlier. Eight of the twenty-one were carriers at the time of challenge and these showed much lower parasitaemias than the self-cured animals which almost invariably were acutely affected.

Challenges of twenty-three intact steers confirmed that the two strains differed immunologically. Six of twelve challenged homologously failed to show detectable parasitaemia, whereas all eleven challenged heterologously developed parasitaemias.

The tissue stages and the erythrocytic stages of a malarial parasite infecting a flying squirrel of Darjeeling (Petaurista magnificus) are described. It is shown that this parasite cannot be accommodated in the existing genera of the malarial parasites of mammals (Plasmodium, Hepatocystis and Nycteria). A new genus, Rayella, is proposed to receive this parasite, which is named Rayella rayi (synonym: Plasmodium sp., Ray, 1949; Hepatocystis rayi, Tokura & Wu, 1961). The tissue stages of the parasite are represented by the groups of small schizonts in the form of cystic bodies, which occur in association with the smaller blood-vessels of the liver.

The author is grateful to Professor P. C. C. Garnham of the London School of Hygiene and Tropical Medicine, London, for his interest and valuable advice. The author wishes to record his special thanks to Professor H. N. Ray who kindly placed the relevant literature and his slides and drawings at the disposal of the author. Professor Ray's unpublished drawings of the erythrocytic stages of the malarial parasite of the flying squirrel (Petaurista inornatus) are reproduced here with his special permission.

The wall of the trunk, that of the praesoma, and the lemnisci of Acanthocephalus ranae have been studied by electron microscopy. Striations visible in sections of the body wall under the light microscope do not correspond with the ‘striped layer’ revealed by the electron microscope.

A new region, the ‘canal layer’, has been described. This contains canals running into the body wall from cuticular pores.

Structurally the wall of the trunk and that of the praesoma are similar. The lemnisci resemble the ‘inner layer’ of the praesoma wall. However, it is suggested that the wall of the trunk differs physiologically from that of the praesoma, and from the lemnisci. The possible roles of the wall of the praesoma and the lemnisci in fat excretion or uptake have been discussed.

The body wall of A. ranae has been compared with that of the other acantho-cephalans studied with the electron microscope.

Grateful acknowledgement is made to D.S.I.R. (now S.R.C.) for a research grant to the Department of Zoology for the purchase of a Huxley ultramicrotome, a vacuum coating unit, and an AEI EM 6 electron microscope.

I am grateful to Dr D. A. Erasmus for reading and criticizing the manuscript, and to Mr T. Davies for valuable technical assistance.

Sepedon h. hispanica was collected in freshwater marshes in southern Spain and reared through its entire life-cycle in the laboratory.

Larvae of this species differ from those of the twenty-one other reared species of Sepedon in not normally invading water, feeding as parasitoids throughout the first half of larval life (that is, permitting their food snails to live for several days), and in restricting their diet to the genus Succinea during that time.

Each newly hatched larva of S. h. hispanica crawls between the mantle and foot of a living Succinea elegans, S. pfeifferi or S. putris and remains there while developing into or completely through the second larval instar.

After the death of the first food snail the larva becomes predatory and loses its host specificity. Then it attacks a wide range of pulmonate snails, kills each victim quickly, and destroys a series of individuals belonging to species of Succinea, Lymnaea and Physa.

Adults of S. ruficeps and S. scapularis were reared from larvae and pupae collected in Ethiopia.

The larvae of both African species are aquatic predators which kill and consume various pulmonate snails unselectively. They are equivalent ecologically to all other larvae of Sepedon previously described.

The egg, three larval instars, and puparium of S. h. hispanica, and the mature larvae and puparia of S. ruficeps and S. scapularis, are described and figured.

A key is presented to immature stages of the Palaearctic species of Sepedon.

We wish to thank Dr W. C. Frohne, Alaska Methodist University, Anchorage, Alaska for collecting and rearing Sepedon ruficeps and S. scapularis. Dr E. Morales Agacino, Instituto Espanol de Entomologia, Madrid; Dr M. Mendizabol, Dr J. Verdejo and D. J. Paris Lopez, Instituto de Acclimatacion, Almeria; and Professor Dr I. Docavo Alberti and Dr B. Llopis Minguez, University of Valencia, aided during the senior author's field-work in Spain. We thank Dr J. Verbeke, Institut royal des Sciences naturelles de Belgique, for determinations and distributional data; Mr L. W. Stratton, Harpenden, England, and Dr H. J. Walter, Dayton, Ohio, Museum of Natural History, for determinations of Gastropoda; and Mrs L. Lyneborg, Zoological Museum, Copenhagen, for Fig. 25.

Adelphocystis aeikineta, a new species of monocystid gregarine, is found in the coelom of the earthworm Keffia variabilis in which the trophozoites occur in large numbers in permanently associated pairs. They are large, measuring 750–1500, μm in length, and exhibit continual peristaltic motion. The ectosarc of the trophozoite is markedly striated and there is no evidence of any anterior differentiation. The gametocytes are rounded and the presumed bipolar sporocysts measure 12–14·5 μm in length. Some associated pairs occur in groups enclosed in a membrane and there is evidence that gametocytes may form under these conditions. A. aeikineta is placed in the subfamily Zygocystinae and separated from Zygocystis on its elongate shape. The site of infection of this gregarine, and others recently described, suggests that the morphological basis on which the family Monocystidae is divided into subfamilies and genera is inadequate and a sounder classification should take into account these sites of infection.

The material on which this paper is based was collected while I was in receipt of a Wellcome Trust Travelling Grant, and I wish to thank the Trust for this support. It is also a pleasure to thank Mr R. W. Sims of the British Museum (Natural History) who identified the earthworms, Dr Keith Vickerman who helped me to collect them and Mr R. B. Freeman who advised me on the nomenclature.

After infection with the nematode Trichuris muris 70–75% of mice of the Schofield strain developed an immunity to the parasite and eliminated the worms between the 16th and 19th days after infection. In these mice the acquired immunity persisted for at least 3 months and prevented the establishment of subsequent infections.

In 25–30% of the mice immunity was not produced and infections developed into mature worms. These non-resistant mice remained susceptible to further infection.

The development and action of the immune response were suppressed completely by the administration of cortisone acetate.

The ecology of the tick Ixodes trianguliceps Bir. is described from material collected at two localities in Wytham Estate near Oxford. The hosts examined were bank voles, Clethrionomys glareolus Schr., field voles, Microtus agrestis (L.), and field mice, Apodemus sylvaticus (L.).

The seasonal distribution of the tick is biannual, with spring and autumnal peaks as found in Ixodes ricinus (L.). Larvae occur throughout the year but principally in spring and autumn. Nymphs are found only from late spring until the autumn, and adults principally in the spring with a small peak in autumn.

Larvae and nymphs of I. trianguliceps were more abundant on male than on female bank voles, but there was no significant difference in the infestation of males and females by adult ticks. Similarly there was no significant difference in the infestation of adult and juvenile bank voles.

Larvae and nymphs occur principally on the ears, but the adult ticks are found mainly on the neck or body, although the ears were not excluded from infestation.

The seasonal distribution and life-history is discussed with reference to similar studies made in the Soviet Union and in Poland. Male ticks were found in copula on the host, and both males and nymphs were collected from the nests of voles.

A tentative summary of the life-history of I. trianguliceps is given based on known facts for the hedgehog tick, Ixodes hexagonus Leach, which has a similar seasonal occurrence.

We wish to thank Professor Don Arthur for identification of much of the tick material, especially in the early stages of this study, and for useful criticism of the draft manuscript. The work was carried out while one of us (M.J.C.) was a research student in the Hope Department of Entomology, Oxford, and the other (C.H.S.W.) a research student at the Bureau of Animal Population, Oxford. For facilities in both departments we wish to express our gratitude.

The development and survival of the eggs and larvae of T. colubriformis was studied by spreading the daily faecal output of an infected sheep for 1 or 2 weeks on grass plots 6 ft square. The observations were carried out for 3 years and broadly similar results were obtained in each year. Eggs placed on the ground from November to February failed to develop. A large proportion of the eggs placed on the ground in March disintegrate but those which develop do so slowly. Infective larvae are not produced for 8–12 weeks and they are relatively short lived. As conditions become more favourable development becomes more rapid, taking 8 weeks in April 6 weeks in May and only 1 week in June, July and August. A larger proportion of the eggs develop into infective larvae and their time of survival increases. On most plots larvae did not die out until the following April. The prolonged period of snow during the winter of 1962–63 tended to preserve larvae rather than kill them. The relevance of these results to the control of trichostrongylosis is discussed and it is concluded that it would be impossible under British conditions to devise a system of rotational grazing which would satisfactorily control trichostrongylosis and at the same time ensure economic utilization of the herbage.

We are grateful to Mr C. R. Phillips and Mr T. Doy for technical assistance during the course of this investigation.

A marked difference in the rate and extent of growth of the third-stage larvae of Amplicaecum robertsi was observed in the liver of indigenous Australian rats, as compared with non-indigenous rats. This difference was not correlated with the number of larvae recovered. The suggestion is made that the greater growth in indigenous rodents might be due to the availability or accessibility of a growth factor in the former group, or a manifestation of ‘adaptation tolerance’, an immunological unresponsiveness arising from adaptation in a geographically isolated host-parasite association. Observations on incidence of natural infection supported the hypothesis in relation to Rattus assimilis but not to Melomys cervinipes.

Thanks are due to Dr C. Dobson for help with the presentation of results.

The growth rate of Schistocephalus solidus was measured in culture at 4°, 7°, 12°, 17°, 23°, 27°, 30°, 33°, 35° and 40 °C. Between 7° and 23 °C the rate of growth increased nearly exponentially, with a Q10 of 3·6. Between 23° and 27 °C growth rate was maximal; above 27 °C, after 8 days in culture, weight increase was shown only by worms which were too small to mature. Even in these worms the weight increase was very small and was probably due to partial maturation which occurs from 30 °C upwards. The larger the plerocercoid and the higher the temperature up to 40 °C the bigger the percentage weight loss, due to earlier maturation.

Incubation of plerocercoids for 4 days at 35 °C, although inducing maturation and suppressing somatic growth, did not destroy the ability of the worm to grow when returned to 23 °C.

Two hypotheses to explain the pattern of morphogenesis in Schistocephalus plerocercoids and adults are propounded; the evidence favours the existence of two enzyme systems, one controlling somatic growth with peak efficiency near 23 °C and the other controlling maturation with peak efficiency near 40 °C.

The authors gratefully acknowledge financial support for this work from Shell International Petroleum Company Limited. It is also a pleasure to thank Miss Patricia Grant for technical help.

Resistance to E. necatrix induced by complete life-cycle infections was transferable from duodenum to caeca and vice versa.

Complete life-cycle infections with E. tenella protected against subsequent attempts to infect with 2nd-generation merozoites. A similar experiment using E. necatrix showed a partial effect.

E. necatrix gametogony-only infections did not protect against subsequent gametogony-only infections and did not protect against schizogony in the duodenum. They did suppress oocyst production resulting from entire life-cycle infections.

Satisfactory oocyst production from the intra-caecal inoculation of second generation E. necatrix merozoites was not obtained.

Repeated oral infections with E. tenella or E. necatrix reduced subsequent cross-infections with E. necatrix or E. tenella respectively by approximately half. Both schizogony and gametogony stages were affected.

A similar result was obtained with E. tenella oocyst inoculation when previous infections were initiated by the intra-caecal injection of E. necatrix sporozoites.

Oocyst production from the oral administration of E. tenella oocysts to birds previously infected with gametogony stages only of E. necatrix was much reduced but the schizogony stages of the challenge infection were not appreciably affected. Previous repeated caecal inoculation of E. necatrix merozoites did not reduce oocyst production from subsequent inoculations of E. tenella merozoites or of E. necatrix merozoites.

Thanks are due to Mr P. L. Long for his interest and advice. The excellent technical assistance of Mr Brian Millard and other members of the Parasitology Department is also gratefully acknowledged.

The oncomiracidium of the monogenean skin parasite Entobdella soleae finds its flatfish host, Solea solea, by chemoreception. The free-swimming larva responds to a specific substance secreted by the skin of the common sole, attaches itself to this skin and immediately sheds its ciliated epidermal cells. Larvae respond in the same way to agar jelly which has been in contact with the skin of S. solea.

The oncomiracidia attach to S. solea skin in preference to that of other soleid fishes (Buglossidium luteum and Solea variegata), pleuronectid fishes (Limanda limanda, Pleuronectes platessa) and elasmobranch flatfishes (Raia spp.).

Larvae respond strongly to isolated epidermis from Solea solea but show no response to the fish's cornea, indicating that the attractive substance is produced by the mucus cells in the fish's epidermis.

The larvae attach with equal readiness to skin from the upper and lower surfaces of S. solea. Thus the preponderance of young parasites on the upper surfaces of soles is due not to a preference for the upper skin but to the fact that the lower skin is in contact with the substratum and cannot be reached by the larvae.

These results led to speculations on the way in which host specificity evolved in the Monogenea.

I am indebted to Mr J. E. Green of the Plymouth Laboratory for setting up a tank containing infected soles and for maintaining the tank and feeding the fishes for many months.

I am also grateful to the Directors and Staff of the Plymouth Laboratory and the Fisheries Laboratory, Lowestoft, for hospitality and assistance. I am particularly grateful to Mr J. Riley of the Lowestoft Laboratory for providing various flatfishes.