An attempt has been made to study the movements and feeding habits of juvenile forms of Fasciola hepatica as they pass through the wall of the host's intestines during the first 24 hr. of experimental infections in the mouse. Metacercarial cysts were fed to mice in large numbers (100–500) and the flukes were examined by means of sections during excystment and as free flukes and flukes making their way through various tissues. Excystment is regarded as essentially a feeding operation, the young fluke breaking through the fibrous inner cyst by the physical action of the ventral sucker in weakening the wall and the oral sucker in the actual breakthrough. Free forms were found in sections of infected intestines both in the lumen and lying between the villi, and penetrating forms were located inside the villi, in the submucosa and passing through the muscular layers and the serosa. A great deal of evidence was accumulated which indicates that the young fluke is able to break down epithelia, connective tissue and unstriped muscle fibrils and to feed upon the resultant products, thus proving itself to be a tissue feeder in the broadest sense of the term. The fluke's passage through the intestinal wall is by a devious route, tangential to the mucosa for some distance and then usually diagonally through the muscular layers, following the direction in which the circular muscle cells are oriented but cutting across the longitudinal muscle cells. This is probably due to the angle which the rim of the oral sucker makes with the longitudinal axis of the body, and it is a modification of the browsing habit which is seen when the feeding fluke lies on a plane surface. The tissue feeding proclivities of young flukes were also displayed in instances of penetration into lymph nodes and adipose tissue. These evidences support the opinion previously expressed by the writer that flukes migrating through the hepatic parenchyma, which are merely forms a little older and larger than the forms studied in the present researches, cannot be regarded as blood-feeders in the strict sense of the term but must also be regarded as tissue feeders. Attention is directed to the fact that very few digenetic trematodes have caecal outgrowths and that Fasciola and Fascioloides stand apart from all other genera in having dendritic outgrowths of the intestines. It is remarked also that the development of the ramifications of the intestines in Fasciola hepatica occurs during the first month, and largely during the second week, of juvenile life when the young flukes are eating their way through the hepatic parenchyma. During a few days the ramifications of the caeca develop to a greater extent than occurs during the entire lifespan of all other digenetic trematodes, with the exception of Fascioloides magna.

Strongyloides papillosus is found to be very common in the Lucknow area where 90% of the sheep are infected. The life-cycle is predominantly indirect, or heterogonic. The development of mature free-living adults takes place between 20° and 37° C., and 34° C. is the optimum temperature. At a temperature of 25° C., the percentage of free-living adults is 60–65 in summer (March to November) and practically 100 in winter (December to February). Immature females can develop at 40° C. in summer, but not in winter, under laboratory conditions.

Inhibition experiments in a hot oven incubator with varying percentages of humidity, and in a humidity chamber incubator with constant 100% humidity, maintained at temperatures varying from 40° to 50° C., show that in the humidity chamber incubator mature free-living adults develop at 34° C. after incubation for 12 hr. at 40° C., after 4 hr. at 42° C., after 2 hr. at 45° C. and after 15 min. at 50° C. The hot oven incubator allows mature free-living adults to develop at 34° C. after 8 hr. at 40° C., after 2 hr. at 42° C., after 1 hr. at 45° C. and after 15 min. at 50° C.

Histological investigations of the bile ducts of various hosts of F. hepatica during the early stages of infection, when the flukes are burrowing in the liver and have not yet reached the bile ducts, indicate that subtle changes are brought about, probably by chemical agencies and as a result of the inflammatory process, in the bile ducts of the hosts. The transitory appearance of minute cytoplasmic blebs at the free margins of the epithelial cells seems to inaugurate an intense hyperplasia of the epithelium with tubular ingrowths and adenomatous development of glandular tissue, and an associated fibrosis which produces a thick underlying layer of dense fibrous tissue. At the time of entry of the flukes into the biliary system the hyperplastic epithelium is intact, but soon the spines and suckers of the flukes abrade the superficial cells until this part of the duct is completely denuded. It is suggested that as a result of the inflammatory reaction, the fluke has been provided with a ‘pasture’ of hyperplastic epithelium and connective tissue on which it may continue to browse for considerable periods without necessarily affecting the host adversely. Tissue debris is found in the contents of the bile duct and similar homogenized materials occur in the caecal contents of the fluke. Previous researches have shown that the fluke will feed on various tissues, and it is suggested that this tissue-feeding habit persists during its life in the bile duct. These results agree with the findings of Müller (1923) but are at variance with the results obtained by other investigators, as is shown in discussion. The hyperplasia of the bile duct is not characteristic of fascioliasis, occurring also in clonorchiasis, opisthorchiasis and dicrocoeliasis, and in these and possibly other instances it is probably intimately connected with the nutrition of the flukes concerned.

The present paper is concerned with the description of six species of gregarines which are all parasites of British earthworms; they are: Apolocystis herculea (Bosanquet, 1894), A. lavernensis sp.nov., A. perfida sp.nov., A. rotaria sp.nov., A. spinosa sp.nov., A. villosa (Hesse, 1909) Cognetti, 1923. The observations upon which these descriptions are based form part of a larger survey of the monocystid fauna of several British earthworm species from the Cardiff area. The methods used are fully described in a previous paper (Rees, 1962).

1. An account is given of the intensity and incidence of infestation of the scorpaenid redfish, Sebastes marinus and S. mentella, by the parasitic copepods Peniculus clavatus, Sphyrion lumpi and Chondracanthopsis nodosus on three fishing grounds in the eastern North Atlantic, namely Iceland, Bear Island and the Barents Sea.

2. Peniculus clavatus was found to be a rare parasite on both species of redfish in the eastern North Atlantic. Adult female parasites were found during the months from September to February only; they were usually attached to the pelvic or dorsal fins of the host causing little damage.

3. Sphyrion lumpi was found to be a comparatively rare parasite on the deep-water Sebastes mentella throughout the eastern North Atlantic but it was found on S. marinus in the vicinity of Bear Island only. It seems justifiable to regard the Bear Island grounds as a centre of abundance of Sphyrion lumpi in the eastern North Atlantic. Adult female S. lumpi tended to infest medium-sized redfish more often than smaller or larger fish.

4. The infestation of Sebastes marinus and S. mentella by Chondracanthopsis nodosus has been examined in some detail and attention directed to the influence on infestation of the host species, geographical distribution, body length, age and sex of the host, and seasonal variations. The distribution of female C. nodosus within the gill chamber of the two species of redfish is described; it appears to be related to the need of the parasite to secure a protected and spatially limited habitat out of the mainstream of the ventilation current through the gill chamber.

5. The ecological relationships between Sebastes marinus and S. mentella and the three species of parasitic copepod are described together with the possibility of using these and other parasites as indicators of the host's mode of life. It is concluded that Chondracanthopsis nodosus and Sphyrion lumpi merit more detailed and extensive study as possible parasitological indicators of different stocks of redfish.

I wish to express my thanks to Messrs Jackson Mills Ltd., Fish Merchants and Curers, Hull, and to the Officer-in-Charge, D.S.I.R., Humber Laboratory, Hull, for their generous assistance in making redfish available for examination. I am also most grateful to Miss E. C. Howard, Librarian, Ministry of Agriculture, Fisheries and Food, Fisheries Laboratory, Lowestoft, for her invaluable assistance in providing certain otherwise unobtainable references in the literature.

During the early stages of infections of mice with Fasciola hepatica (6–11 days) the young flukes feed almost exclusively on hepatic cells which the oral sucker and the pharynx have broken down into a kind of homogenate containing Kupffer cells, invading leucocytes and some erythrocytes. As the flukes increase in size liver damage also increases in amount because of the larger burrows which are made. In some instances this does not adversely affect the host but in many infections excessive liver damage produces critical conditions which threaten the life of the host and its parasites. A comparison of the lesions produced in infections lasting 17–25 days with lesions produced after only 6–7 days has shown that the former, unlike the latter, are not due entirely to the feeding activities of the fluke. In short-term infections the inflammatory reaction produces the characteristic effects which are concerned with the healing of fluke tracts, but in older infections this reaction appears to be much more violent and tremendous leucocytic infiltrations break down apparently normal hepatic parenchyma and convert the terminal part of the burrow into a pool containing enormous numbers of invading leucocytes, broken hepatic cells and blood. These are the conditions which prevail at the onset of the critical period, when flukes have their growth inhibited as if by nutritional deficiencies. Some hosts are able to survive the critical period and nurture well-grown flukes for long periods, and may be able to obviate the critical conditions. It is suggested that the excessive damage which occurs in many instances during the critical period is not due to the feeding activities of the larger flukes but is a consequence of less restrained or even unrestrained inflammatory reactions which may lead to more serious pathogenic effects bordering on malignancy. This may be related to differences in the time spent by flukes in the hepatic parenchyma, early entry into the biliary system obviating these effects, late entry facilitating them.

1. In all species of the fusca group of tsetse flies (Glossina), except G. brevipalpis Newstead, a gelatinous structure, the genital fossa, is present at the anterior end of the uterus. On the surface of the genital fossa is a toughened structure known as the signum.

2. Probably chitin and certainly calcium are present in the substance of the signum of G. tabaniformis Westwood. An opaque concretion develops on the signum after the female has been fertilized. The concretions may be caused by a reaction between sperms or secretions from the male accessory glands and materials in the substance of the genital fossa; the possibility that the concretions are ‘mating scars’ produced by pressure of the harpes of the male on the signum is considered unlikely. Concretions are not present on the signa of all species.

3. A possible mechanism of fertilization in G. tabaniformis is discussed, and it is suggested that the signum may act as a protective shield for the anterior part of the uterus and common oviduct of the female from the harpes of the male which are inserted into the uterus during coitus. The views of Machado (1959) are discussed and it is agreed that the signum probably acts as a protective shield in all species in which it occurs and differences in the form of the signum between species may be related to differences in the form of the harpes of the male.

I wish to thank Dr J. Williamson for chromatography, Dr L. E. Stephen and Mr K. E. Broomfield for advice and assistance with the sectioning of the signa, Dr F. Peers for operating the Flame Photometer, Dr D. G. Godfrey for suggesting that the signa should be examined for calcium, and Mr W. Petana for taking the photomicrographs.

I am indebted to Dr K. C. Willett, Director of the West African Institute for Trypanosomiasis Research, for criticism of the manuscript.

1. Defence reactions to metazoan parasites have been reported in fourteen orders of insects. The observations are brought together and reviewed in the first part of the paper.

2. Examination of the various accounts that have been given shows that blood cells are always involved in insect defence reactions. They act by forming a cellular capsule, from which a connective-tissue envelope is usually developed, and in which melanin is often deposited.

3. The reaction of the epidermal cells at perforations made by parasites is of the nature of wound-healing, and plays no part in defence against metazoan parasites after they have entered the body.

4. Although several other tissues have been implicated, there is insufficient evidence to show that any of them make defence reactions, their response being limited to processes of regeneration.

5. It is concluded that the blood cells of insects are their only known agents of defence to internal metazoan parasites.

6. The principal groups of metazoan parasites infesting insects are considered in the third part of the paper, in order to see how the defence reactions made to them are related to their mode of attack and to the nature and consequences of their parasitism.

7. Most parasites elicit a defence reaction when they are in unusual hosts.

8. Some parasites, at certain stages of their life-history, are able to avoid eliciting a defence reaction in their usual hosts.

9. Some parasites elicit a defence reaction in their usual hosts but are able either to endure it in a dormant state or to resist it.

10. General problems of host specificity in relation to defence reactions are discussed. It is concluded that analysis of the stimuli that produce defence reactions has not yet gone far enough to explain the phenomena.

11. The effects of insect defence reactions on metazoan parasites range from no perceptible effect to destruction of the parasite.

12. The defence reactions of insects are influenced by the species, genetic strain, stage, instar, size, health and physiological state of the host; and by the species, genetic strain, physical and physiological activity, and health of the parasite. Environmental temperature and the presence of other parasites of the same or different species also have effects on the reactions.

13. A brief survey of defence reactions made by invertebrates other than insects shows that encapsulation has been reported in Annelida, Mollusca, Crustacea, Acarina, and larval echinoderms. So far as it goes, the survey does not reveal in these other groups any reaction to metazoan parasites of a kind radically different from the reactions observed in insects.

14. The historical development and present state of our knowledge of insect defence reactions is traced.

15. The reactions made by insects to innocuous parasites are of theoretical interest but of little consequence to the species concerned. It is their effect on potentially dangerous parasites that determines the value of defence reactions. Consideration of the evidence suggests that the protection afforded to insects by their defence reactions is greater than has been generally supposed.

16. The review makes apparent many gaps in our knowledge of the phenomena. A few of the outstanding problems are mentioned.

I am indebted to Mr R. T. Hughes of the Balfour Library for helping me to obtain journals not available in Cambridge; to Mr M. J. Ashby for the photography necessary in the preparation of the figures; and to Miss G. M. Edwards for her careful typing from my manuscript. The paper would not have been completed without the goodwill and assistance of two persons: Professor D. Keilin, F.R.S., encouraged me to continue and finish it when my effort flagged; my wife not only gave me positive help in many ways but also exercised great forbearance in allowing me to devote vacations and spare time to it.

Satchell (1947) described and keyed the larvae of 14 of the 19 British species of Psychoda, but this study did not include P. humeralis Mg., presumably because the author accorded generic rank to Philosepedon and Threticus which would put them outside his study of Psychoda sensu stricto. The larva of P. humeralis has been briefly described by Spärck (1920), but his figures are rather crude. A detailed treatment of the larval head is given by Anthon (1943). The present account is offered to facilitate identification of this species in the larval stage when used in conjunction with Satchell's comprehensive paper.

1. Different shapes and forms found in Toxoplasma gondii are associated with reproduction and growth. The functions of the toxoneme and the conoid are discussed.

2. A new structure, ‘lamella spiralis', is described in relation to the nucleus and the endoplasmic reticulum.

3. T. gondii reproduces either by dividing into two (binary fission) or by multiple division (schizogony), and by a type of endogenous budding. In the latter case small portions pinched off from the nucleus are rounded up to form several small organisms named ‘morulae'.

The author gratefully acknowledges the interest and valuable suggestions of Dr G. A. Gresham, M.D., who supervised this work; Dr J. M. Davis and Mr F. Allen, who were kind enough to read the manuscript critically, and Mr W. A. Mowlam for his technical help and advice on fixation techniques.

This work was carried out during the tenure of a research scholarship awarded by the United Kingdom Department of Technical Co-operation and the Eastern Nigerian Government.

Since its discovery in France by Mégnin (1878), Cheyletiella parasitivorax has been found in many countries—on rabbits (Oudemans, 1906; Pillars, 1925; Ford, 1944; Mykytowycz, 1957a; Womersley, 1941), on the dog (Humphreys, 1958), fox (Kuscher, 1940), cat (Niggli & Teuscher, 1959; Davies, 1941), man (Olsen & Roth, 1947) and even in phoretic association with fleas (Cooper, 1946). Hirst (1917) was the first to find the species in Britain and there have been several more recent records from this country.

The observations presented in this study indicate that the filose projections emerging from the apical or luminal surface of the epithelial cells lining the caeca of the trematodes Cleptodiscus kyphosi and C. reticulatus are sterocilia or microvilli. Their activity in the animal appears to be concerned with the absorption of substances from the lumen of the blindly ending caeca rather than with movement of material.

Acknowledgement is made that part of this work was carried out in the Department of Zoology and Anatomy of the University of Nebraska, Lincoln, Nebraska, and supported in part by a grant from the Nebraska Heart Association for 1959.

When Acridine Orange was dispersed in cod-liver oil, its characteristic green fluorescence remained unaltered following absorption of this mixture into the peripheral circulation from the intestine. This result implies that there was little or no change in the lipid or its suspensoid as a result of undergoing this physiological process. The selective combination of this dye in aqueous solution with the cytoplasmic components of specimens of Trypanosoma lewisi, also present in the blood smears with the droplets of the green-appearing oil, resulted in an alteration of fluorescence as indicated by the rose red appearance of these organisms.

The present findings on the absorption of lipid droplets, containing a fluorochrome, by trypanosomes occurring simultaneously in the circulation of rats confirm similar observations reported by Wotton & Halsey (1957). The possibility is suggested again that fats and oils may serve as pharmacological vehicles for orally administered trypanosomides for the elimination of trypanosomes.

Part of this study was carried out in the department of Zoology and Anatomy of the University of Nebraska, Lincoln, Nebraska, and was supported in part by a grant from the Nebraska Heart Association for 1959. We would like also to extend our appreciation to the Division of Laboratories of the Nebraska State Health Department of Lincoln, Nebraska, for the use of their ‘Fluorex’, ultraviolet illumination microscope unit.

Sulphaquinoxaline fed at 0·0125%, w/w, in the food principally affects the development of the second generation schizonts of Eimeria adenoeides in turkey poults. Amprolium, at the same concentration, acts on the first generation. Both drugs appear to exert some effect on gametogony. The activity of sulphaquinoxaline against this species is inhibited by p-aminobenzoic acid, and the activity of amprolium by thiamine.

We are grateful to Mrs B. M. Mitchell and Miss C. Hitchcock for technical assistance and to Mr A. D. Speed for the histological preparations.

In a survey on the worm parasites of cats in Calcutta, Chandler (1925) mentioned the common occurrence in dogs also of Echinochasmus perfoliatus (Ratz, 1908) which has also been listed by Bhalerao (1935) in cat, dog and man. According to Verma (1935), the dogs at Calcutta harboured three distinct flukes—a species of Echinochasmus, a heterophyid and a third species described by him under a new genus, Episthochasmus, as E. caninum. In a survey of the helminth parasites of pariah dogs examined at Calcutta, Mapleston & Bhaduri (1940) included Echinochasmus sp. amongst the six new records from India. Chatterji (1954) regarded Episthochasmus as a synonym of Episthmium Lühe, 1909 and Stephanoprora Odhner, 1911, Echinochasmus and Episthmium Lühe, 1909 as subgenera of Echinochasmus. A new species, based on two specimens collected from the intestine of pariah dog at Allahabad, was described as E. (Echinochasmus) canai. Relying on the character of the forward extension of vitelline follicles, Stephanoprora was to include forms with vitellaria extending to the posterior margins of anterior testis, Echinochasmus forms with vitelline follicles extending beyond the anterior testis but not anterior to the anterior margin of ventral sucker and Episthmium forms with follicles extending beyond the anterior margin of this sucker. Thus, Verma's species was named as E. (Episthmium) caninum.

1. Certain aspects of the general morphology of Polymorphus minutus are described together with a detailed description of the body wall.

2. An additional layer of the body wall, the epicuticle, has been demonstrated. It appears to consist of acid mucopolysaccharide and may have a function of protecting the parasite from the enzymes of its host.

3. A histochemical investigation has been made of the layers of the body wall and it is concluded that lipoprotein is one of the main structural components.

4. The distribution of the activity of the two enzymes, non-specific esterase and alkaline phosphatase, has been studied throughout the animal and the activity of a third enzyme, leucine aminopeptidase, has been detected in the body wall.

5. It is suggested that all the layers of the body wall, with the exception of the cuticle and epicuticle, are of metabolic importance. The striped layer may be connected with absorption and the felt and radial layers may be involved in the further metabolism of absorbed compounds.

6. The results obtained are used to formulate a possible structure of the surface of the parasite which would facilitate the absorption of nutrient substances through the body wall.

I am grateful to Dr P. Tate for advice and encouragement during this work, Dr R. J. Tatchell for helpful discussions, and Dr D. L. Lee for criticising the manuscript and Mr T. M. Warwick, Department of Zoology, University of Edinburgh for providing material.

The new species of Amblyomma described in this paper was collected and forwarded to the author for identification by Mr J. H. Calaby, Wildlife Section, C.S.I.R.O. This is the fourth species of the genus to be recorded from Western Australia, the others being A. australiense Neumann, A. albolimbatum Neumann, and A. triguttatum Koch (Roberts, 1953).

A n.gen. and n.sp. of a yeast-like micro-organism—Adlerocystis ornithodori—is described. This micro-organism is probably a symbiote of sperm cells of Ornithodoros tholozani. Another species, A. parkeri n.sp., is found in O. parkeri.

Adlerocystis sp. were also found in O. coriaceus, O. nicollei, O. erraticus, and O. savignyi.

The earliest stage of development of A. ornithodori was observed in the posterior lobe of the complex of accessory genital glands of the male, where it has the shape of a round cell. It is spindle-shaped when attached to the mature sperm in the spermatophore.

The development of A. ornithodori from a round cell to an elongated spindle-shaped organism, in vitro in the spermatophore, as well as in vitro, is described.

We wish to thank Dr W. Burgdorfer, the Rocky Mountain Laboratory, Mr R. Garcia, University of California, and Mr A. Avivi, the Israeli Institute of Biology, who provided ticks, as well as Mr E. B. Kennedy for taking the microphotographs and Mr N. Shultan from the Elyahu and Rosa Wunsch Electron Microscopy Laboratory for the electron micrograph, both from the Hebrew University Hadassah Medical School, Jerusalem.