Sheep infected with Oesophagostomum columbianum showed anorexia, loss of weight, diarrhoea and macroscopically obvious oedema and inflammation of the alimentary tract. Arthus-like lesions caused by the larvae developed particularly in the large intestine.

The gross immunological responses of the sheep were associated with antibodies in greater titre within the mucus of the gut than in the serum. Acquired immunity was manifest through an antibody-antigen reaction which was localized mostly in the large intestine and which involved proliferation of the lymphoid tissue of the gut and an increased synthesis of protein. Lower titres of antibody in serum than in mucus may indicate leakage of antibody away from the gut. The direct effects of antibody were established by the respiratory inhibition of the 3rd-stage larvae. The presence of antibody was associated with particularly high concentrations of β globulin after first and β and γ globulins after second infection. Specific antibody was demonstrated in these protein fractions by blockage of electrophoretic movement by larval antigen in the buffer.

The antibody-antigen reaction may act as a trigger which releases the nonspecific effects of excess mucus production and oedema which causes mechanical dislodgement of the infection. The natural and specific respiratory inhibitory effects of mucus on the worm would facilitate this dislodgement process.

The greatest cellular reactions occurred where there was an active infection. Usually these reactions were associated with oedema, hyperaemia and an increase in the size of the mesenteric lymph nodes.

Observations on the movement of fluids in the vicinity of the mouthparts of actively feeding female Dermacentor andersoni were made with the aid of trans-illuminated live-hamster pouch host-tissue. Following tick attachment and the invasion of ‘attaching cement’ into the outer skin layers, there appeared a progressive release of host blood as the tick settled into a feeding pattern. Short periods of sucking, each followed by an immediate ejaculation of saliva, became lengthened as feeding progressed, as did the resting intervals between sucking. Other movements brought about by the tick included a ‘toying’ of the tissue fluid, a rapid vibration of the same, and a distinct regurgitation of host-blood material. A sudden haemorrhage usually appeared at the feeding site about 2½ h after attachment of partially fed ticks.

Speculations are made concerning the part played by the release of tick saliva and tick water loss, its probable relationship to host paralysis, and its apparent role in tick nourishment.

The germ-cell cycle and method of reproduction in the daughter sporocysts of the bucephalid Cercaria bucephalopsis haimeana (Lacaze-Duthiers, 1854) and the gymnophallid Cercaria dichotoma Lebour, 1911 (non Müller) from the edible cockle, Cardium edule L., have been investigated by the examination of stained sections. A review is given of the principal interpretative theories which attempt to explain the nature of the reproduction and the homology of the germinal sacs of the Digenea. It is suggested that the life-cycle includes a cyclic alternation of homologous generations. Of these, the miracidium/mother-sporocyst and the daughter germinal-sac generations usually reproduce by apomictic parthenogenesis but polyembryony may also occur secondarily in some species.

We are very grateful to Dr Gwendolen Rees and Professor E. W. Knight-Jones for considerable help with the manuscript.

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.

Young rabbits were infected by mouth with sporulated Eimeria stiedae oocysts and killed at 1, 3, 5, 8, 12, 16, 24, 30, 48, 54, 72, 84, and 96 h after infection. Sporozoites were found in the lamina propria of the duodenum between 5 and 8 h after infection. Sporozoites were present in the mesenteric lymph nodes, both free and within lymphatic monocytes at between 12 and 84 h after infection. No sporozoites were observed in duodenal portal blood. These observations provide morphological evidence compatible with a lymphatic route of migration between duodenum and mesenteric lymph nodes, probably within lymphatic monocytes. The route to the bile duct epithelium is discussed and a subsequent migration in the portal blood suggested.

I wish to express my gratitude to Dr D. F. Kelly of the School of Veterinary Medicine, Cambridge, for his guidance and constructive criticism, and to Dr Elaine Rose of the Houghton Poultry Research Station, St Ives, for her invaluable advice on technical problems and for donating the oocysts for the study. I should also like to thank Dr E. A. Pierce of the Department of Animal Physiology, Babraham, and Mr P. Long of Houghton for their advice.

This study was carried out as a Research Project during the Natural Sciences Tripos, Part II Pathology course 1965, in the Department of Pathology, Cambridge.

The structural relationship between cells of the parenchyma and those of the alimentary and excretory systems, and tegument are described.

Junctional complexes are formed in areas of close cell apposition. They occur laterally on invaginations of parenchymal processes which are embedded in the epithelial cells of the alimentary and excretory systems, and on flat plaques between parenchymal cells and the tegument.

The ultrastructure of the complexes has been resolved and a three-dimensional interpretation is put forward. It is suggested that the complex is a type of desmosome.

The findings reported here add support to the suggestion made in a previous paper that the parenchyma may function as a transport system in this fluke.

We wish to acknowledge grants from the Wellcome Trust and the S.R.C. for the purchase of an Akashi TRS 50 and an A.E.I. EM 6B electron-microscope respectively. This research and that reported in a previous paper were carried out while one of us (S.S.E.G.) was in receipt of a Training Studentship Grant from the Wellcome Trust.

We also wish to thank Mr W. Ferguson and Mr A. Lyness for photographic and technical assistance.

A new coccidium Caryospora demansiae sp.nov. is described from the Australian snake Demansia psammophis (Elapidae). This is the first report of this genus from Australia. A host check-list of the genus Caryospora is given and the characters of the known species are tabulated.

I would like to thank Mr O. Kelly and Mr J. Winter of the Zoology Department, University of Queensland, for help with supplying the snakes and to Dr H. M. D. Hoyte of the Parasitology Department, University of Queensland, for his careful reading of the manuscript.

Additional ultrastructural features of the tegument of Fasciola hepatica, after glutaraldehyde fixation and high resolution, have been observed.

Two distinct types of tegumental cells are shown to be present, the type 1 cell having been previously described. Details of the fine structure of the nucleus, mitochondria, endoplasmic reticulum and Golgi complex of the type 2 cell are given. The type 2 cell is characterized by biconcave secretory bodies derived from the Golgi complex and the latter is intimately related to the granular endoplasmic reticulum, from which it is derived by blebbing. The type 2 cells are connected by protoplasmic tubes to the same surface syncytium as type 1 cells.

These new findings of the structure of the tegument of Fasciola are compared with previous reports on the ultrastructure of the tegument in other flukes.

I should like to express my sincere thanks to the following: the Wellcome Trust and S.R.C. for grants to purchase an Akashi TRS 50 and an A.E.I. E.M. 6B electron microscope respectively; the Royal Society for a personal grant to purchase a Reichert Ultramicrotome and a vacuum coating unit.

My thanks are also due to Mr W. Ferguson for photographic skill and to Mr A. Lyness for technical assistance and microscope maintenance, and my Research Associate, Mrs S. S. E. Dermott, for expert electron-microscopy.

Three new species of Isospora from Australian lizards are described, viz. Isospora amphiboluri from Amphibolurus barbatus (Agamidae), I. egerniae from Egernia whitii (Scincidae), and I. ablephari from Ablepharus boutonii (Scincidae) and Heteronota bineoi (Gekkonidae). A further Isospora sp. is mentioned from Phyllurus cornutus (Gekkonidae). A table of comparative data of lacertilian Isospora is given, and also a host check-list.

I would like to thank Miss J. Arnold of the Department of Zoology, University of Western Australia, for her identification of many of the lizards, and Miss S. Curtis for her drawings. Finally I wish to thank Dr H. M. D. Hoyte, Department of Parasitology, University of Queensland, for his interest, and helpful criticism of the manuscript.

Echinoparyphium hydromyos sp.nov. with forty-five collar spines is described from the Australian water rat, Hydromys chrysogaster Geoffr.

The cercaria occurs naturally in Plananisus isingi (Cotton & Godfrey), and all stages in the life-history have been demonstrated experimentally.

Encystation occurs in the kidneys of tadpoles.

The adult is most closely related to Echinoparyphium recurvatum (Linstow). It differs from this in its greater number of eggs and in its life-history. E. recurvatum occurs predominantly in birds, and is rarely found naturally in mammals. E. hydromyos has been found only in a mammal.

Cercaria echinoparyphii hydromyos is compared with C. clelandae Johnston and Angel; it differs from the latter in the ‘compound’ nature of the excretory granules. The adult of C. clelandae has not been demonstrated in spite of a number of experiments to determine it.

Type material has been deposited in the South Australian Museum.

I wish to acknowledge the help given by my colleague, Patricia M. Thomas, in field work and in other ways, and by Mr Ian Smith, of this department, in the experimental work on life-history studies.

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.

Five new species of Eimeria are described, viz. E. ablephari from Ablepharus boutonii (Scincidae), E. egerniae from Egernia whitii (Scincidae), E. gehyrae from Gehyra variegata (Gekkonidae), E. lampropholidus from Lampropholis guichenoti and E. leiolopismatis from Leiolopisma challengeri. The characters of these species and the other coccidia from lizards are tabulated and a host check-list is given. Gall bladder parasitism is discussed as is the significance of complete sporogony occurring within the host's body. Some ideas concerning the possible events occurring in the evolution of the Haemosporina are presented.

I wish to thank Miss J. Arnold of the Zoology Department, University of Western Australia, for her identification of many of the lizards and Miss S. Curtis for her drawings. Finally I wish to thank Dr H. M. D. Hoyte, Department of Parasitology, University of Queensland, for his interest and helpful criticism of the manuscript.

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.

Both histological and histochemical studies have been made of the food, mode of feeding, gut cell structure and digestive sequences in a selected number of digenetic trematodes.

The species investigated range from gut-dwelling trematodes feeding on the superficial epithelial tissues and associated mucoid secretions of the host to those forms living within the respiratory and circulatory system and feeding exclusively on blood.

The mode of feeding is suctorial, brought about by the muscular pharynx and normal attachment process of the oral sucker. In one case there is evidence that this purely mechanical process is supplemented with enzymic secretions produced by the trematode which have a histolytic effect upon host tissues.

On the basis of gut cell structure the species investigated are divided into those with cells and associated microvilli that vary in size and appearance so that the gastrodermal border is irregular in outline, and those with a gastrodermis comprising regular cuboidal or columnar cells bearing microvilli organized into a striated border. There is evidence to suggest that this difference in gut cell structure reflects differences in digestion. In all cases, gland cells are absent from the gastrodermis which is capable of both secretory and absorptive functions.

Digestion is predominantly an extracellular process, but the exact sequence varies according to the nature of the food ingested and different degrees of adaptation are shown by the trematodes to the blood-feeding habit. The tissue-feeding species show less modification.

I wish to thank Dr J. B. Jennings for helpful discussion and advice throughout the course of this work. The study was undertaken during the tenure of a Studentship from the Department of Scientific and Industrial Research.

A new species of coccidium E. duodenalis sp.nov., has been described, from the pheasant. It is characterized by the subspherical shape of the oocyst, the lack of polar granules and the presence of large sporocystic residual bodies. Endogenous stages are found in the epithelial cells lining the villi, and occur chiefly in the duodenum and upper intestine. Second-generation merozoites form gametocytes and/or third-generation schizonts. The prepatent period is 5 days.

E. duodenalis is moderately pathogenic, doses of 50 000 oocysts causing a 30% mortality and a significant weight loss in the survivors. Treatment with a range of sulphonamides in the drinking water was successful as was preventive treatment with Sulphaquinoxaline mixed with the food.

Acknowledgements are due to Mr S. F. M. Davies for initiating this programme and carrying out a number of the animal inoculations, to Dr Helen Hein for help and advice in the design of the experiments and to Dr L. P. Joyner for advice in the preparation of the manuscript. The author also wishes to thank Miss C. N. Hebert for the statistical analysis of weight gains and Mr M. A. Peirce, Mr G. L. Choon, Miss J. Saddington and Miss M. Blore for technical assistance.

The ultrastructure of the intra-erythrocytic stage of a haemogregarine in the gecko, Gehyra variegata, has been studied and numerous points of similarity to Plasmodium, Toxoplasma, Sarcocystis, Lankesterella, Eimeria and the M-organism were found. The protozoon was invested by a triple-layered pellicle, and possessed at least two micropyles. A conoid and apical rings were observed at the anterior end. Other cell constituents included nucleus, microtubules, endoplasmic reticulum, mitochondria, toxonemes and a variety of vacuoles. Loosely surrounding the parasite was an unusual convoluted membrane, which in appropriate planes of section, displayed corrugations on both surfaces. It was not clear whether this membranous structure should be regarded as an integral part of the protozoon or as an external coat which could be discarded upon emergence from the host red cell. Within its external sheath, the parasite lay in a periparasitic vacuole which was limited by a conventional unit membrane from the host red cell cytoplasm. The parasite did not exhibit any evidence of pinocytosis or phagocytosis.

Our sincere thanks are due to Dr E. H. Mercer, Professor J. D. Smyth and Dr M. J. Mackerras for advice. Miss N. Carroll gave technical assistance.

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.

Cercaria patialensis Soparkar, 1924, emerging from the snail Melanoides tuberculatus (Müller) has been encountered at Waltair. The cercariae begin to emerge from the snail at dusk and continue to do so during the period of darkness.

Stages resembling the adult but without the development of eggs have been encountered in nature on the fresh water fishes Panchax panchax (Ham. & Buch.) and Esomus danricus (Bleeker). These stages have also been raised experimentally by exposing P. panchax, E. danricus and fingerlings of Catla catla Ham. & Buch. to the cercariae.

The cercaria is referable to the genus Transversotrema Witenberg, 1944.

It is suggested that there may not be a metacercarial stage in the life-cycle of Transversotrema spp.

The egg shell of Fasciola was investigated by electron microscopy and found to consist of a fine reticulum of fibrils. No evidence for concentric lamellae was discovered.

The amino acids of the shell were identified using chromatography and it was suggested that the original protein was of a simple fibrous type. An unidentified spot was thought to represent a hydrolysis product of the cross-linkage. The effect of sodium hypochlorite on the shell, was also studied.

The ‘vitelline membrane’ of the fully developed egg was found to consist of a layer of peri-vitelline material beneath which were two closely opposed unit membranes. The origin of these layers was discussed.

The permeability of the shell and vitelline membrane was studied using simple physical techniques and radiotracers. The shell was found to be freely permeable to small molecules. The vitelline membrane complex was thought to represent the main barrier to permeability but an uptake of phosphate ions amounting to 8% of total phosphate, was recorded. This may have been more apparent than real as most of the activity was probably associated with egg shells rather than contents.

I would like to thank Professor O. W. Richards in whose department this work was carried out, Dr F. Call for supervision of the work and Professor B. G. Peters for his many helpful criticisms. Lastly, I am indebted to Miss M. Morris without whose expert assistance the electron microscope studies would not have been possible.