The pathogenicity and pathology of Ascaridia galli infections of poultry were studied using repeated doses of varying numbers of eggs. No significant effect due to infection was seen on p.c.v. and Hb. values of infected chickens. Haemo concentration occurred parallel with sporadic diarrhoea, which follows high levels of repeated dosing. This phenomenon complicated the interpretation of blood protein values. A/G ratios were, however, worked out and analysed. No significant differences were noticed between the groups and it was concluded that under the levels of inoculation employed during the study there were no significant effects of A. galli infections on blood protein values as well as p.c.v. and Hb.values of infected chickens.

Symptomatic developments, macroscopic lesions and pathological changes of intestinal tissues due to infection were followed up in detail. They were most severe in chickens on the least nutritive diet and sustaining the highest levels of repeated doses. Pathogenicity of larval and adult parasites was described. The presence of large numbers of adult parasites was associated with intestinal obstruction in host. This was seen mostly in chickens on low nutrition and sustaining either low or high levels of repeated inoculation, and very rarely also in chickens under high plane of nutrition but sustaining repeated inoculation of small numbers of eggs. Cellular infiltration as a result of infection was found to be extremely rare.It was present as fibroblasts and only in association with dead larvae.

The author is indebted to the Department of Technical Cooperation, under whose Fellowship the study was carried out; the Department of Zoology, Edinburgh University, for facilities provided; the Ministry of Agriculture, Fisheries and Food; Lasswode Poultry Research Laboratories, for the free supply of chickens used here; Dr J. A. Campbell of Edinburgh University for his keen interest, encouragement and advice throughout this work; and finally to G. Obiwelozor for reproducing the photographs from the original manuscript.

The covering layer of Amphibdella flavolineata has been found to be a syncytial cytoplasmic epidermis bearing scattered microvilli and connecting with parenchymally situated ‘cell’ bodies or cytons by means of conspicuous, microtubulelined cell processes. There was no evidence from a comparison of the covering epidermis of the juvenile blood living form and that of the gill living adult that this layer in the juvenile was especially modified for life in the host blood system.The epidermis of adult and juvenile worms was found to be remarkably similar, the main difference being that that of the adult was slightly thicker and bears longer microvilli. Apart from some lamellate bodies of doubtful significance, the inclusions found in the epidermis of adult and juvenile forms were also very similar.The outer epidermis of the juvenile monogenean was found to be quite different from that of Schistosoma mansoni in that it is not permeated by incursive channels and contains many more mitochondria than the epidermis of the digenean. The epidermal cell bodies of Amphibdella tend to have electron-lucent areas especially in the ‘ apical cell’ regions leading to the cell processes that connect with the outer layer. Electron-dense granules secreted by the epidermal cells accumulate in these ‘clear’ regions before being transferred to the outer layer. There is some slight evidence that these electron-lucent regions may have contained glycogen. The epidermal ‘cell’ bodies of the juvenile tend to be multinucleate, whilst those of the adult are usually uninucleate.

Thanks are due to the Director and staff of the Marine Biological Laboratory, Plymouth for providing accommodation and material. The assistance of Mr George Best of the Plymouth Laboratory and Mr Harry Edge of King's College London Botany Department, who maintain the microscopes used in this work, is especially appreciated.

Observations on the egg-content of 78 counted populations of Metastrongylus apri showed that there was a positive correlation between population size and mean egg-content per female. In bilateral infections within one host, a significant tendency was shown for the larger of the two populations to outstrip the smaller in mean egg-content per female. There was no correlation between sex-ratio and mean egg-content. It is suggested that the effect of the host's defences against individual parasites is mitigated when large numbers of parasites are present.

A positive correlation was found between the sex-ratios of populations in left and right lungs, and there was a significant predilection of M. apri for the right lung.

I am indebted to Dr S. Peto, Microbiological Research Establishment, Porton, Wilts, for statistical advice, and to T. Wall and Sons Ltd., Atlas Road, London, N.W. 10, for access to abattoir material.

The nematode, Heterotylenehus autumnalis, generally failed to develop successfully in Musca domestica L., Orthellia caesarion (Meigen) and Ravinia l'herminieri(Robineau-Desvoidy). Failure is attributed mainly to host resistance in the form of haemocytic encapsulation of the small gamogenetic female nematode. In a few instances, the nematode was able to complete development successfully in housefly and Orthellia, but was not capable of leaving the host. These few instances of development in the unnatural, experimental hosts are attributed in part to general ’weakening’ of the host by superparasitism. In many cases superparasitism resulted in the death of the fly larvae or pupae.

Tracheolar proliferation was usually associated with the encapsulated nematodes and there was evidence that many of them were expelled from the host during pupation. We also observed nematodes with cephalic caps of dark material, presumably melanin, and some that were tightly girdled with this material. A host reaction, apparently never before reported for a parasitized insect, was the darkening (presumably melanization) of the larval anal organ.

The authors would like to express their appreciation to Dr A. J. Nappi, Biology Department, State University of New York, Oswego, New York, and Dr G. 0. Poinar, Jr., Department of Entomology and Parasitology, University of California, Berkeley, California, for reading an early draft of the manuscript and offering critical comments. The senior author would like to express his deep appreciation to Dr W. R. Nickle, Nematology Investigations, Crops Research Division, Agr. Res. Serv., USDA, Beltsville, Maryland, and to Dr H. Welch, Zoology Department, University of Manitoba, Winnipeg, Canada, for their help and encouragement during the course of this study. This study was supported in part by a grant from the University of Connecticut Research Foundation.

Reinfection of the insects Tenebrio molitor and Schistocerca gregaria by the Eugregarines Gregaria polymorpha and G. garnhami respectively is not caused by the retention of the gametocyst and the release of sporocysts inside the gut. The gametocyst has to pass out from the insect gut, dehisce, and the sporocysts have to be ingested in order for reinfection to occur. Thus it is possible to stop reinfection by preventing the host from ingesting sporocysts. The development of spore ducts on the gametocyst of G. garnhami is inhibited if the gametocysts are prevented from leaving the hindgut of the locusts.

I would like to thank Professor L. H. Finlayson for his advice for many helpful discussions.

The distribution and fine structure of gland cells in the miracidium of Fasciola hepatica is described. There is a large flask-shaped, multinucleate, apical gland lying ventrally in the anterior. On each side of this are pairs of uninucleate accessory gland cells. Both apical gland and accessory gland cells communicate with the tip of the apical papilla. A third group of vesiculated gland cells opens by ducts at the base of the apical papilla. The miracidium is covered with a surface mucous coat and this appears to be directly extruded from the underlying ciliated epithelial cells. The findings are discussed with relevance to attachment to, and penetration of, the snail intermediate host.

The population dynamics of Ascaridia galli infections of poultry was studied under repeated doses of 10, 100 and 1000 eggs. Daily doses were continued for 6 weeks only. At low dose rates patency is noted by the fifth week. At higher dose rates there is an accumulation of larvae whose development has been arrested at a precise developmental stage, i.e. the third larval stage. Sporadic development of some of these larvae to adults occurs later. Arguments are produced to show that this inhibition of larval development is a resistance and not a density-dependent phenomenon. The epidemiological significance of this inhibition is discussed. This resistance phenomenon is shown to occur in single infection experiments where 1000 eggs were used. This gives rise to the development of a worm population of two facies. The whole finding is suggested to be related in some way to the phenomenon of ‘tissue phase’, which is accepted as a normal life-cycle behaviour of this parasite. A brief review of previous work on this is given and it is postulated that the ‘tissue phase’ phenomenon is not an obligatory part of the normal life-cycle of the parasite but represents a reaction to factors of resistance inherent in chickens and controlled to a large extent by a complex dynamic interplay of dose size and the chickens.

I wish to thank the Department of Technical Co-operation and the Federal Government of Nigeria for financing this project, Dr Boulton of the Poultry Research Centre, Edinburgh, for advice on nutrition, and the Department of Zoology, especially Dr J. A. Campbell, University of Edinburgh, for facilities and advice on the work. I am greatly indebted to the Ministry of Agriculture, Fisheries and Food, Poultry Research Laboratories, Lasswade, for the free supply of chickens used in this work.

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.

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.

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.

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.

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.

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.

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.

After 24 h desiccation at 28–29 °C and approximately 50 % relative humidity about 70 % of B. microplus larvae drank sufficient solution containing 1·5 mCi of 32P per ml for their movements on the host to be followed with a portable G-M counter. Reduced viability of the labelled ticks could not be detected when they were kept for 24 h on the host and either allowed to feed or prevented from doing so. When feeding was continued for 72 h or when larvae were incubated for 3–4 weeks, adverse effects were found, the severity of which could not be directly related to the amount of 32P label. Desiccation, handling of larvae and exposure to radiation in the drinking solution may have contributed to their reduced viability.

Since resistance to the tick is manifest within the first 24 h after infestation labelled larvae could be used to compare development on different hosts during this time. Even after feeding for 72 h, larvae were more adversely affected by host resistance than by labelling damage.

We would like to thank Mr C. A. Schuntner for helpful advice and Mrs J.Galligan for technical assistance. The financial support of the Australian Meat Research Committee is gratefully acknowledged. Messrs D. Hancox and S. R.Henderson assisted with some of the experiments.

The genitalia of the Pupipara are markedly modified from those of other higher Cyclorrhapha and the nomenclature used is mainly descriptive and controversial; different terminologies have been used by the various authors.