A piroplasm was isolated from a wild-caught Psammomys obesus from the lower Jordan Valley. In wild-caught Psammomys the infection is submicroscopic or of very low intensity, but rises sharply following splenectomy. The animal from which the piroplasm was isolated died with a 44 % parasitaemia and haemoglobinuria, following splenectomy.

The piroplasm was transmissible to clean, laboratory-bred Psammomys, to hamsters and Meriones. It was not transmissible to, or gave rise only to transient infections in, adult mice, rats, Mastomys, Acomys and Arvicanthis. Suckling mice and rats showed low parasitaemias for a few days, although division forms of the parasite were observed.

No protective cross-immunity with Nuttallia danii was observed.

On the basis of its measurements, spectrum of infectivity to experimental animals and absence of cross-immunity with N. danii, the piroplasm of Psammomys is considered to be a new species.

The name Nuttallia meri, sp.nov. in memory of the late Prof. Gr. G. Mer, is proposed for this piroplasm of Psammomys obesus.

I should like to express my appreciation of the excellent technical assistance provided by Mrs Miriam Sarfatti and Mr A. Bortinger, and to thank Dr Y. Schlein for his help with some of the drawings. I am particularly indebted to Dr A. Hadani of the Kimron Veterinary Institute for providing me with Meriones and testing N. meri in his laboratory.

This study was supported by the Reubin Kunin and Samuel Lunenfeld Medical Research Foundation - to which grateful acknowledgement is made.

The ultrastructure and development of Histomonas meleagridis in the reproductive tract of male Heterakis gallinarum has been described. In the testis the protozoon is a relatively large amoeboid organism which lies between the epithelial cells of the testis and the spermatogonia, spermatocytes and spermatids. It is similar in appearance to the invasive stage which is found in the final host and like the invasive stage, it also feeds upon the host cells by phagocytosis. In the vas deferens the protozoon lies between the host cells, where it is much smaller than the stages in the testis but still amoeboid, and inside the cells of the vas deferens.Intracellular stages are much smaller than the other stages, are rounded in appearance and cause little or no damage to the host cell. They are similar to the stages found in oocytes of the female nematode. The possible role of the male nematode in the life cycle of the protozoon is discussed.

I wish to thank Mrs B. Fisher for technical assistance and Mr B. Carter for assistance with the photography.

The effect of continuing ingestion of eggs of A. galli on growth rates of chickens placed on different nutritional levels was studied under repeated doses of 10, 100 and 1000 infective eggs/day. With increasing amounts of protein in feed, there occurred significant weight differences between infected groups, the highest protein levels showing the longest duration in weight depression due to infection. On the other hand, assuming adequate nutrition of host, highest effects on growth rates were seen in chickens receiving daily doses of 1000 eggs daily and the lowest in chickens receiving 10 eggs daily.

The effect of repeated dose on growth rate is similar to the effect of single infections reported by previous workers except that the duration of the growth depression was much longer in the former due to pathogenic effects of inhibited larvae.

The author is indebted to the Department of Technical Cooperation, under whose Fellowship this study was carried out; to the Department of Zoology, Edinburgh University, where the work was done; to the Ministry of Agriculture, Fisheries and Food; Poultry Research Laboratories, Lasswade, for the free supply of chickens used here; and finally to Dr J. A. Campbell of Edinburgh University for his keen interest and advice throughout this work.

Two strains of T. congolense and two strains of T. vivax, resistant to normal therapeutic doses of trypanocidal drugs, were transmitted by G. morsitans and G. tachinoides through series of cattle in the absence of drugs to assess the transmissibility of the trypanosomes by tsetse flies and the stability of drug resistance in the organisms during cyclical development.

The characteristics of both strains of T. vivax and one strain of T. congolense were typical of the species, but the infectivity of the second strain of T. congolense for laboratory animals was abnormally low.

The transmissibility of the trypanosomes was assessed on the bases of the infection rates in tsetse flies used to transmit the strains and the periods required for the development of the trypanosomes in the flies and bovine hosts. The transmissibilities of both strains of T. vivax and the first strain of T. congolense were normal by comparison with data obtained by cyclically transmitting non-resistant trypanosomes of the same species, but the period required for the development of the second strain of T. congolense in tsetse flies was abnormally long.

There was no loss of drug resistance in any of the strains examined in the experiments. A strain of T. congolense retained resistance to diminazene aceturate at a dose rate of 7-0 mg/kg, homidium chloride at 2-0 mg/kg, quinapyramine sulphate at 4-4 mg/kg and isometamidium chloride at 0-5 mg/kg during a series of eight transmissions by tsetse flies in a period of 376 days.

Some species in Subuluridae, Thelaziidae and Ascaridiidae are discussed. Subulara helicospicula sp.nov. from malcohas and a bulbul from Borneo is described. It differs from other species in having long, unequal spicules which are helical throughout their distal half. Allodapa suctoria (Molin, 1860) Seurat, 1914, is reported from several species of birds from Taiwan, Borneo and Palawan. A. turnicis (Maplestone, 1931) Inglis, 1958, was found in the button quail, Turnix sustator on Palawan.

Thelazia digiticauda Schuurmans-Steckhoven, 1937, is redescribed from specimens recovered from the eyes of a ruddy kingfisher, Halcyon coromanda from Taiwan. Ceratospira inglisi sp.nov. from a cockatoo in Palawan and a pigeon in Borneo differs in spicule size from the three species so far described. Oxyspirura {Y.) mansoni (Cobbold, 1879) Skrjabin, 1931, was recovered from bamboo partridges, Bambusicola thoracica, from Taiwan, and Oxyspirura (0.) popawi Skrjabin, 1929, was found in the eyes of a swallow, Hirundo daurica in Taiwan.

Ascaridia columbae (Gmelin, 1790) Travassos, 1913, was common in a variety of pigeons in Borneo and Palawan, and A. subaequalis (Wehr, 1930) was found in the lesser coucal, Centropus bengalensis in Taiwan and in a common coucal, C. sinensis in Palawan.

Eperythrozoon mariboi sp.nov. is described from the red blood cells of splenectomized flying foxes (Pteropus macrotis epularius), from New Guinea. The parasite is polymorphic. The most common form is a fine line 5–8 μ long extending across the red blood cell. Marginal forms are also found. Multiple infections of the host cell also occur. In the initial infection ring forms were common, as well as other forms.

Parasitaemia was followed by anaemia, and the infections were characterised by repeated relapses at irregular intervals.

This work was supported by Grant No A1–08449 from the National Institutes of Health, United States Department of Health, Education and Welfare. I would like to thank Mr T. Ikupu and Mr T. Engendi, both of the University of Papua and New Guinea, for technical assistance; Mrs M. Cahill, also of the University of Papua and New Guinea for attempting to culture the organisms; Dr D. Weinman of Yale University, for confirming the identity of the parasites; Dr T. J. Dondero of the Hooper Foundation for translating some of the references into English; and Dr F. Colley also of the Hooper Foundation, for comments on the manuscript.

The analysis of some of the data in this paper was done while I was on study leave at the Institute for Medical Research, Kuala Lumpur, and I would like to thank its Director for the hospitality provided.

I would especially like to thank Mr Yap Loy Fong, Institute for Medical Research, Kuala Lumpur, for preparing Fig. 1.

Seven daily injections of betamethasone given early in the infection adversely affect the immune response of rats and mice to Babesia microti and B. rodhaini. Betamethasone given late in the infection, when the parasitaemias are declining, causes recrudescences. The effects of betamethasone are reversible and those animals which survive the primary parasitaemia recover even if further courses of drug treatment are given. Betamethasone causes recrudescences of parasitaemia in some voles and field mice harbouring subpatent infections. Attention is drawn to the possibility that the therapeutic use of corticosteroids may enhance piroplasm infections and that elevated corticosteroid levels, resulting from stress situations, may affect latent piroplasmosis in wild caught rodents.

Descriptions are given of the first and second-stage larvae of Strongylus edentatus, S. vulgaris, S. equinus and Trichonema nassatum and newly hatched larvae of Trichonema catinatum and Triodontophorus serratus. Information has been obtained on the growth of pre-infective larvae and on the structural changes which occur during the first ecdysis. Most of the species of newly hatched larvae studied can be differentiated on the basis of differences in appearance, dimensions and other morphological features. The advantages of differential diagnosis of horse strongylid infection using first-stage larvae rather than infective larvae are discussed.

My thanks are due to Dr H. D. Crofton for his constructive criticism and advice and to Professor H. E. Hinton, F.R.S. for the provision of laboratory facilities.This work would not have been possible without the willing co-operation of Mr L. J. Potter from whose slaughterhouse the parasites were collected. I am also indebted to the Horse Race Betting Levy Board for their financial assistance.

An account is given of the morphological characteristics of the larvae of Hyalomma anatolicum anatolicum and H. a. excavatum. Emphasis is placed on the importance of chaetotaxy in the identification of the larvae.

I am most grateful to Professor Don R. Arthur for reading the manuscript and for his most useful advice and encouragement. Also I wish to express my sincere thanks to Dr R. P. Chaudhuri, Dr C. M. Clifford, Dr V. Dhanda, Dr H. Hoogstraal and Profesor B. Feldman-Muhsam for supplying me with specimens.

The total lipids and the amount of neutral lipids of male and female N. brasiliensis, from 7-day and 15-day infections, have been studied quantitatively. There is an increase in total lipids from 10·9 ± 2 to 15·5 ± 2 % in females and an increase from 8·4 ± 1 to 14·6 ± 2 % in males. In both sexes there is a rise in cholesterol and trigylceride content and a fall in free fatty acid content. These changes are discussed with reference to the development of immunity of the host to this nematode.

I wish to thank Mrs B. Fisher, Mr A. W. Pearson and Mr N. Sykes for assistance during this work. These results form part of a programme of work supported by the A.R.C. while I was at the Molteno Institute, University of Cambridge, and continued at the Houghton Poultry Research Station. I wish to thank Dr P. Tate for accommodation at the Molteno Institute during the early part of this work.

This paper describes experiments to determine whether intestinal tissue mast cells and/or intestinal histamine are involved in the second, expulsive step of worm elimination. In neonatal rats, intestinal tissue contains only very little histamine and mature mast cells are encountered only sporadically. From birth to the adult age, there was a gradual rise in both intestinal mast cells and histamine.

During Nippostrongylus brasiliensis infection in the adult rat, the concentration of histamine in the small intestine was clearly lower than in uninfected controls.Especially low histamine values were found to occur on days 6–12 of a primary infection in the region where the main worm burden was located. Similarly, the number of tissue mast cells present in the epithelium of the jejunum was decreased in the same region and during the same period of time. From the observation that the bulk of the parasites are expelled at a time when histamme and mast cell levels are low, it was concluded that mast cells and their constituents were not an essential factor in the second step of worm elimination

This work was supported by the Schweizerische Nationalfonds zur Förderung der wissenschaftlichen Forschung (Grant 5200.3). The skilful technical assistance of Miss I. Beeger, Miss R. Keist and Miss M. Iseli is gratefully acknowledged. I thank Mr H. Berchtold, Biostatistisches Zentrum der Universität Zürich, for the statistical evaluation of the data.

1. It has been shown that the protein eggshell of Hymenolepis diminuta eggs was not significantly stabilized by sulphur or electrovalent linkages but was resistant to attack by proteolytic enzymes. Amino acid analysis demonstrated a marked preponderance of aromatic and heterocyclic acids and it has been suggested that these groups act as cross-linking agents in the shell protein.

2. The role of the lipid-containing subshell ‘membrane’ in protecting the enclosed embryo against fluctuations in pH and osmolarity in the external environment and infiltration of enzymes and toxic compounds has been demonstrated.

3. The cytoplasmic layer was shown to consist of a glucosamine-containing mucoprotein present in a dehydrated or semi-dehydrated state in the intact egg.In mechanically damaged eggs the cytoplasmic layer was rapidly dispersed by some proteolytic enzymes.

4. The embryophore enclosing the hexacanth embryo was composed of a sulphurrich protein that was weakened by some proteolytic enzymes and completely destroyed by others.

I should like to thank Professor T. R. E. Southwood, in whose department this work was carried out, and Dr June Mahon for her advice and encouragement.I am particularly grateful to Dr R. A. Wilson, Department of Biology, University of York, for the quantitative amino acid determinations on eggshell hydrolysates and for criticizing this manuscript. This research was conducted during the tenure of a Science Research Council Studentship and formed part of a thesis submitted for the Ph.D. degree, University of London.

Two behaviour patterns which could bring about clumping in N. brasiliensis, sexual attraction and thigmokinesis, were investigated. A T-tube choice-chamber to facilitate an in vitro study of sexual attraction is described. A method for studying aggregation is also outlined. Male N. brasiliensis were shown to be attracted to female worms, positive sexual attraction. Both sexes were shown to exhibit strong thigmokinetic responses, and possible functions of such behaviour are discussed.

I am grateful to Professors J. Brough and D. Bellamy for providing the facilities during the course of this study. I should also like to thank Dr E.. A. Hammond for his supervision, help and criticism throughout the project. This work was carried out during the tenure of a Scientific Research Council Studentship.

The uninfected digestive gland of Bithynia tentaculata consists of three main cell types: ‘absorptive’ cells, ‘thin’ cells and ‘secretory’ cells. With infection by sporocysts, rediae, or metacercaria, pressure effects caused a reduction in the lumen of the digestive gland tubules and this probably resulted in a starvation autolysis. Some tubules recovered from infection and in such cases there was a reduction in the height of the epithelium. A migration of the digestive gland nuclei was only evident in redial infections and this may have been due to the toxic effects of rediae. In addition, rediae directly ingested host digestive gland tissue.The digestive gland was reduced to about two-thirds of its normal size in all heavily infected snails. Secretory cells of the gland were more resistant to infection than were the absorptive or thin cells.

I am indebted to Dr F. R. Stranack for her supervision and guidance throughout this investigation, and to Dr G. Charles and Dr T. Jenkins for their continued help and advice. This study was carried out during the tenure of a Research Assistantship awarded by the Governors of Portsmouth Polytechnic.

A large proportion of Strongylus vulgaris, S. edentatus and Trichonema nassatum collected from the gut lumen of slaughtered horses during the winter did not contain eggs. The proportion of Trichonema catinatum without eggs declined to a low level during the winter and rose to relatively high levels during the summer, It has been concluded that worms without eggs are newly matured individuals and that seasonal variations in fecundity reflect similar fluctuations in the age distribution of the adult populations. These fluctuations are related to seasonal differences in the numbers of infective larvae ingested and to the length of parasitic development.Most Strongylus vulgaris, S. edentatus and Trichonema nassatum reach the adult stage during the winter and it has been suggested that an increase in worm numbers during this period is responsible for a rise in the faecal egg counts of horses in the spring. The observations on T. catinatum indicate that the level is maintained by the arrival of new individuals during the summer.

I wish to thank Dr H. D. Crofton for his constant advice and encouragement during this work and Professor H. E. Hinton, F.R.S., for the provision of laboratory facilities. I am indebted to Mr L. J. Potter for allowing me to collect the parasites from his slaughterhouse at Bishop Sutton, near Bristol. This work was carried out during a research studentship funded by the Horse Race Betting Levy Board.

1. The distribution of larvae within the dorsal longitudinal muscle fibre groups of A. aegypti infected with subperiodic B. malayi or B. pahangi and of M. uniformis infected with the former parasite was studied with the aid of serial sections.

2. In all experiments the top bundles of fibres contained fewer parasites than either the middle or lowest bundles, but whereas most parasites were concentrated in the middle bundles in A. aegypti there was no significant difference in M. uniformis between the bottom and middle fibre bundles. The lowermost fibre was not the most heavily parasitized of the dorsal longitudinal group.

3. Nothing is known of what determines whether or not a particular fibre becomes parasitized, but it was concluded that the distance between the fibre and the gut (from which the parasites emerge to travel to the muscle) is not the principal factor.

I am very much indebted to Mr Cheong Weng Hooi and his colleagues for collecting and processing mosquitoes in Kuala Lumpur and to Mrs J. Oliver who finished the processing in Liverpool. I am grateful also to Dr W. W. Macdonald for his advice and help in all stages of this work and to Miss M. A. Johnson who assisted with the care of the A. aegypti colony and prepared the diagrams for this paper.

The penetration barrier presented to the miracidium by the snail epithelium can be divided into three layers. The chemical composition and physical configuration of the outermost of these plays an important part in the initial attachment response of the miracidium. Attachment can be stimulated in the absence of the snail by pure chemicals in solution. However, the surface to which the miracidium attaches must have the correct physical configuration otherwise the miracidium is unable to form a stable attachment.

In vivo, the miracidial body begins to contract and relax following attachment to the snail. This coincides with the start of secretion by the apical gland and accessory gland cells. The snail's columnar epithelium is rapidly cytolysed so that 10 min after attachment the anterior of the miracidium has reached the underlying connective tissues.

As the miracidium penetrates the snail, its ciliated epithelial cells are shed in sequence from anterior to posterior. This shedding removes a protective barrier against osmosis which is probably the acid mucopolysaccharide present in the epithelial cells. The mechanism of shedding is not understood but involves the reversal of binding by the desmosomal mucosubstance which attaches the epithelial cells to surrounding intercellular ridges.

The miracidium metamorphoses into the sporocyst as it penetrates the snail, by forming a new body surface. The material for this is extruded from the vesiculated cells which lie beneath the musculature of the body wall. The process of surface formation coincides with cell shedding and moves backwards as cells are shed. At not more than 2·5 h after attachment the extruded cytoplasm forms a thin continuous layer over the surface of the organism. Contacts with underlying cells appear to have been broken and the cytoplasm is underlain by a thin fibrous basal lamella. In the first 24 h after penetration the surface of this syncytium becomes thrown into folds and metamorphosis into the sporocyst can be considered complete.

The chick embryo proved to be an eminently suitable medium for immunological studies on E. tenella infection, some of the difficulties encountered in the normal host, the hatched chicken, being circumvented.

Adoptive transfer of immunity to E. tenella infections in the chick embryo was obtained with antibodies and with cells from caecal tonsils. Protective factors (antibodies) were demonstrated in the serum of fowls which had been infected with E. tenella and in their progeny. Suspensions of caecal tosnil cells inoculated on to the CAM of developing chick embryos reduced the extent of subsequent infections with E. tenella and this was particularly marked when the cell donors had been immunized with E. tenella.

Serum globulin protected only when the donors were becoming immune, i.e. after the third inoculum of E. tenella oocysts. The experiment was not continued to the point at which the serum donors were ‘solidly immune’, when previous attempts to protect passively with serum have failed.

Maternally transmitted protection was demonstrated in embryos only at the time at which peak protection was afforded by serum globulin, but this is probably an unsatisfactory method of testing since antibodies are not present in allantoic fluid until late in incubation, when coccidial infections are already well established.Some reduction in the oocyst output of the progeny of immunized hens was found when these were challenged at 4 days of age.

The protection given by the inoculation of suspensions of cells from the caecal tonsils may have resulted from the production of antibodies by these cells or from their interaction with the parasite in some form of cell-mediated immune mechanism.

We are grateful to Mrs Patricia Hesketh, Mr Martin Shirley and Mr Ron Waters for technical assistance and to Mr Peter Townsend for care of the animals.

Active digenean larvae in Bithynia tentaculata were found to utilize both host carbohydrates and lipids, and these were incorporated into the bodies of developing cercariae. Although rediae obtain most of their nutrients by direct ingestion, a decrease in the glycogen and neutral fat content of intact digestive gland cells of snails infected with rediae suggests that these larvae may also absorb nutrients through their body walls, like sporocysts. In sporocyst infections, host glycogen is believed to be hydrolysed to glucose and other monosaccharides by the host's own enzymes, possibly phosphatases, which have been stimulated to greater activity by the parasites. These simple sugars, due to their small size, can then be absorbed through the sporocyst body wall. Similarly, host fats are probably degraded to fatty acids, possibly by a parasite-secreted lipase, prior to absorption by the parasites. Encysted metacercariae do not appear to feed, but they do have severe pressure effects which disrupt some of the digestive gland tubules. Such tubules show an increase in their neutral fat content and a decrease in phosphatase activity. Aminopeptidase enzymes secreted by active digenean larvae may be responsible for some lysis of host cells, and may also be involved in the breakdown of lymph proteins to amino acids.

I am indebted to Dr F. R. Stranack for her supervision and guidance throughout this investigation, and to Dr G. Charles and Dr T. Jenkins for their continued help and advice. This study was carried out during the tenure of a research assistantship awarded by the governors of Portsmouth Polytechnic.

1 Populations of Babesia rodhaini were isolated which were ‘putative’ variants of a reference population.

2. They were shown to have some antigenic dissimilarity to the reference population by comparing the response of rats immunized with irradiated parasites of the reference population, to challenge with either the reference population or with the variant populations. To the homologous challenge the immunized rats were strongly resistant. After a heterologous challenge, however, for the first 3 or 4 days the immunized rats showed no resistance but thereafter rapidly controlled the infection.

3. Five ‘variation’ populations were tested and all were shown to have some antigenic dissimilarity to the reference population. Two variant populations were compared and were not found to be identical with each other. There appeared, however, to be less dissimilarity between them and any one variant and the reference population.

Mrs J. Page and her successor Miss D. Leader, gave technical assistance. I thank my colleagues for helpful criticism of the manuscript.