Studies with both the light and electron microscope on the bladder wall of Cysticercus longicollis have revealed details of its structure and shown that it contains structures comparable with those of adult cestodes. The structure of the everted scolex of the fully developed cysticercus has also been studied. Development of the scolex and rostellum has been briefly considered and is similar to that of C. fasciolaris and C. pisiformis. The importance of the tegument in both bladder wall and scolex is emphasised.

The rostellar hooks appear first as small cones to which a base is added after some growth has occurred. Mature and immature hooks probably contain keratin. Results of histochemical tests on this and other parts of the cysticercus have been given.

Thanks are due to Dr L. G. Goodwin, Director of the Nuffield Institute of Comparative Medicine, London Zoo, for allowing the author to use the EM 6 B and photographic facilities. Dr J. Mahon of Imperial College, London, kindly read the script, gave advice on it and provided photomicrographic facilities. The author is grateful to the Principal and Governors of West Ham College of Technology for general and financial support of the project.

The host–parasite relationships of several notoedrid and teinocoptid mites of two Malaysian bats, Cheiromeles torquatus (the hairless bat) and Cynopterus brachyotis (the common fruit bat), were studied.

C. torquatus is parasitized by five species of Notoedres (family Sarcoptidae)—N. alexfaini, N. longisetosus, N. elongatus, N. rajamanickami and N. cheiromeles. Two, N. alexfaini and N. longisetosus, are responsible for generalized mange, which affects mainly the trunk. The three remaining species produce small, discrete lesions, each having a distinctive morphology and polarity.

Notoedres elongatus causes papilliform swellings, usually over the bony parts of the wing. It inhabits deep burrows in the swellings, which consist largely of hyper-plastic connective tissue heavily infiltrated with round cells. The lesions produced by N. rajamanickami resemble those of N. elongatus, except that they are located on the head in the neighbourhood of the vibrissae and are not elevated. N. cheiromeles dwells in cupules in the stratum corneum on various parts of the body, including the wings. These cupules are formed as a result of an intense hyper-keratosis in the immediate vicinity of the mites.

The reaction of the skin of Cynopterus brachyotis to the teinocoptid mite, Teino-coptes asiaticus (family Teinocoptidae), expresses itself chiefly as an extensive acanthosis. There is little or no thickening of the stratum corneum except on the lips of the epidermal cupule in which the anterior end of the mite rests. The dermis underlying the mite undergoes moderate fibroblastic proliferation.

We would like to thank Mr Lim Boo Liat of the Institute for Medical Research, Kuala Lumpur, and Mr Eric Alfred of the National Museum, Singapore, who very kindly allowed us to examine material from their collections. Mr Lim also assisted in other ways and proved to be a genial and helpful host when we visited his laboratory at the IMR. We are also most grateful to Professor John Harrison, who so generously provided us with space in his department.

A new flagellate, Proteromonas hemidactyli sp.nov., is described from the large intestine of the lizard, Hemidactylus brooki, in Hyderabad, India. It is characterized by a long, slender and fusiform body, two similar but subequal flagella, a kidney-shaped sub-blepharoplastic body, a ribbon-like paranuclear body and a vesicular nucleus. A parabasal body is absent.

I am extremely grateful to Dr S. S. Qadri, Reader in Zoology, Osmania University, Hyderabad for his guidance and advice during the course of this work. I am thankful to Dr S. Mehdi Ali, Professor of Zoology, Marathwada University, and Dr S. N. Singh, Professor of Zoology, Osmania University, for providing me with laboratory and library facilities. Thanks are also due to the Council of Scientific and Industrial Research, New Delhi, for the award of a fellowship.

The presence of living tapeworm increases the rate of hydrolysis of starch by α-amylase in vitro. This effect indicates that ‘membrane digestion’ may be one function of the tegument of tapeworms. The effect varies with the surface area and region of the tapeworm. Fixed tapeworm pieces do not enhance starch hydrolysis. The results may provide evidence both for and against the current explanations of membrane digestion. Some possible mechanisms involved in membrane digestion in tapeworms are considered. The importance of membrane digestion in the physiology of gut parasites and the possibility of its wide occurrence are discussed.

We wish to thank Dr J. Llewellyn for his criticism and advice during the preparation of this manuscript and for providing rats and mice infected with Hymenolepis. We also thank Dr R. A. Thornhill for examining some tapeworm tissue under the electron microscope; also Mr A. Wilson of the Meat Inspection Department of the Birmingham Meat Market for his unfailing co-operation.

Superinfection of naturally infected puppies with large numbers of Toxocara canis eggs induced a self-cure reaction. There was a sharp fall in Toxocara egg output following superinfection in most of the puppies. In most, but not all the puppies, the existing worm burden was eliminated. Eliminated worms were full of fertile eggs, but, in the puppies in which egg production fell sharply without expulsion of the worm burden, egg production by the naturally acquired worms was suppressed only transiently.

Antibody production, measured by the complement-fixation test, was directly related to resistance to superinfection but not to self-cure.

Acquired resistance reduced the pathogenic effects of superinfection, and prevented development of the parasite beyond the second stage.

It is a pleasure to thank Professor P. Seneviratna, University of Ceylon, for his constructive criticisms of the manuscript and the facilities provided.

The writer thanks Mr W. G. Senaratne for technical assistance and typing of the manuscript.

This work was carried out with a special research grant from the University of Ceylon.

The ultrastructure of the merozoite of Eimeria tenella has been studied by means of electron microscopy. The first-generation merozoite is approximately 3·4 μm in length, and 1·2 μm in width, while the second-generation merozoite is approximately 10·5 μm in length and 1·5 μm in width.

The cell wall of the merozoite consists of a double membrane, but at the anterior extremity the existence of a fluted collar gives the appearance of two narrow double membranes separated by a zone of less electron-dense material. Twenty-four surface fibrils are distributed around the periphery; they extend along the entire length of the organism and lie beneath the double limiting membrane.

The anterior end of the merozoite is distinguished by a conoid apparatus which includes several components. A bulbiform outer annulus is invested by a fluted collar, and itself encloses an extrusible papilla. Two osmiophilic fibrils, the paired organelles, arise within the extrusible papilla and extend longitudinally into the cytoplasm. Twenty-four smaller fibrils, or toxonemes, also arise within the conoid and pass back into the main body of the organism.

The cytoplasm of the merozoite includes mitochondria, glycogen, dense elliptical granules and endoplasmic reticulum, together with a definite Golgi complex. A nucleus is located in the posterior third of the organism and is enclosed by a perforated double membrane. At the posterior extremity the double membrane which bounds the organism is broken by a pore 700 A in diameter.

Our sincere thanks are due to Mr P. Richmond for technical assistance, and we are grateful to the Central Veterinary Research Laboratory, Weybridge, for supplying the strain of Eimeria tenella.

Echinoparyphium serratum sp.nov., with 37 collar spines, is described from experimentally infected ducklings and chickens. It appears to be most closely related to E. aconiatum but differs from it in having smaller eggs, fewer tegument spines, almost confluent vitellaria in the post-testicular region, and the inner margin of the ventral sucker is serrated. The natural host is unknown but thought to be a bird.

Bile composition may account for the markedly different recovery percentages of adult worms from the two experimental hosts.

Miracidia hatch between 9 and 11 days at 22 °C. Experimental infections of snails with miracidia have not been obtained.

Rediae occur naturally in Isidorella brazieri Smith, and free-swimming cercariae encyst in the pericardium of the same species of snail.

This latter part of the life-cycle is based on strong circumstantial evidence. A few cysts were occasionally found in the pericardium of Lenameria sp. but the enclosed metacercariae were dead.

The cercaria can be distinguished from Cercaria echinata, the cercaria of E. aconiatum, and C. equispinosa in having cystogenous gland cells containing granular material only, and the inner margin of the ventral sucker serrated.

I would like to record my sincere thanks to Professor J. D. Smyth for his advice, and comments on the manuscript.

Seventy-five per cent of Echinoparyphium serratum metacercariae excysted within 10 min in a trypsin/sodium cholate solution after successive pretreatments with pepsin and sodium dithionite. Excystment appears to be an active process as the cyst wall is unaffected by the treatment except in the vicinity of the ‘escape aperture’.

Optimum development to sexual maturity in vivo required 72 h and was divided into six easily recognized stages against which development in vitro could be judged. These were undifferentiated (excysted metacercariae), cell multiplication, organogeny, gametogeny, vitellogenesis and oviposition. Migration of the juveniles from the lower regions of the intestine to the duodenum in the first few hours after infection was noted.

Cultures were prepared from excysted metacercariae and a variety of media were used. The beneficial effects of shaking cultures were apparent. No development took place in media containing saline, Parker 199 medium, homologous and heterologous sera, chicken embryo extract, albumen and glucose, either alone or in various combinations, although, relative to saline or Parker 199 medium controls, survival times were increased in some and decreased in others. Survival in some media above pH 7 was longer than below pH 7. Serum substrates in culture vessels, and the presence of additional glucose, did not increase longevity.

Development to organogeny was achieved using a yolk/albumen/saline or 199 medium, and addition of yeast extract to this favoured the later stages of development up to and including vitellogenesis. In general only a small percentage of juveniles in each culture reached vitellogenesis, and the amount of egg-shell protein formed and the size of the worms was always less than in vivo. Furthermore, development in vitro was much more prolonged than in vivo. Variability in development in vitro may be due to failure of the excystment procedure to satisfy completely the physiological ‘triggers’ which are probably necessary for normal development.

In some specimens vitellogenesis was reached without production of sperm. In others, production of eggs was thought to be inhibited by either a general deterioration of the juveniles or premature ‘tanning’ of the egg-shell protein, as significant amounts of egg-shell protein, sperm, and apparently normal ova were present.

The results of culturing E. serratum are compared briefly with those of D. phoxini.

I should like to record my sincere thanks to Professor J. D. Smyth for his advice and comments on the manuscript.

Five strains of Entamoeba histolytica isolated from man and capable of growth at room temperature were tested for virulence by inoculation into the caeca of young rats. The results showed all strains to have a low infectivity and none produced caecal ulceration. Ten laboratory strains of E. histolytica were examined for growth at 25 °C, but none were established at this low temperature.

The presence of three types of cystogenous gland cells, designated as protein, mucopolysaccharide, and mucoprotein cells, in P. gralli cercariae has been demonstrated.

The protein cells are PAS-negative but positive for tyrosine-, histidine-, and arginine-containing proteins. No tryptophane is detectable in this type of cell. The mucopolysaccharide cells are positive for acid mucopolysaccharides and are gamma-metachromatic. The mucoprotein cells are PAS-positive and diastaseresistant.

The mechanism of metacercarial cyst formation is described. The fully formed cyst consists of three walls designated inner, middle and outer walls. The outer wall is subdivided into a basal and a peripheral layer.

Histochemical studies on the cyst walls have shown that the outer and middle walls are PAS-negative but the inner wall is PAS-positive and diastase-resistant. All the walls include proteins but differ in their amino acid contents.

By comparing the chemical composition of the cyst walls with that of the three types of cystogenous gland cells, it is evident that each cyst wall is formed from the secretions of two or more types of cells. The outer and middle walls appear to be formed from the secretions of both protein and mucopolysaccharide cells, and the inner wall from protein, mucopolysaccharide, and mucoprotein cells.

This research was supported in part by a grant from the American Cancer Society.

Results of the present study indicate that a wide range in coenurus fluid glucose concentration occurs among larvae of Taenia multiceps. Further, a definite correlation exists between bladder size and glucose concentration in the coenurus fluid; larger bladders have greater glucose concentration per unit volume of coenurus fluid. Based on analyses of bladder fluid glucose following alloxan induced hyper-glycaemia, an abrogation of the established size-coenurus fluid glucose concentration occurred. A diabetic state did not alter glycogen concentration in the tissues or lactic acid levels in the fluids of the same coenuri. The functional significance of bladder fluid glucose in maintaining tissue glycogen at constant levels is briefly discussed.

I wish to acknowledge Dr George Lauff, Director, W. K. Kellogg, Biological Station, for constructive criticism of the manuscript and for providing facilities and equipment during the summers of 1966 and 1967.

This paper describes the quantitative aspects of establishment and expulsion of Nippostrongylus brasiliensis in the normal and immune rat. It is proposed that this helminth infection may be described in terms of four phases. These are: (1) loss phase 1 (LP1). A proportion of the infecting dose of larvae is immobilized or destroyed before or during the course of migration via the lungs to the intestine. (2) The plateau phase. The worm number remains static in the predilection site. (3) Loss phase 2 (LP2). This is analogous to the self-cure reaction and during this worms are expelled from the host by an immunological mechanism. The onset of the expulsion is sudden and the process is exponential. It continues at a steady rate until a threshold is reached. (4) Threshold phase. A small residual population of worms is not expelled and survives for a fairly prolonged period.

The pattern is maintained in immune animals undergoing second or third infections but there are quantitative differences. With increasing number of infections LP1 becomes greater, the plateau phase is shortened and the expulsion rate of LP 2 increases. It is suggested that the rate coefficient of this phase is an accurate measure of the immune status of the animal. The threshold phase is of a similar order in first, second and third infections. These results are discussed with regard to their significance as a measure of the immune status of the host, their implication regarding the mechanism of helminth expulsion and their relevance to other helminth infections.

The authors wish to thank the Agricultural Research Council and Allen and Hanburys Ltd. for the financial support which made this work possible. During this period Ellen E. Jarrett held a Horserace Betting Levy Board Scholarship.

The development of the free-living infective larvae of a homogonic strain Strongyloides ratti is described.

The larvae develop only between 15 and 34 °C. Transfer experiments show the temperature block to be in the preparation for the second moult.

Within the temperature range 15–34 °C, increasing the temperature speeds up the rate of development of all the larval stages equally, the Q10 for development being 2·5.

The maximum percentage development occurs at 20 °C. The percentage development is highest in faeces–peat culture (95% development at 20 °C), whilst the percentage development in charcoal and vermiculite cultures is about the same (75% development at 20 °C.).

Larvae grown on charcoal cultures are larger than those grown on vermiculite, which are larger than those grown on peat. No significant difference was found in the length:oesophagus and length:width ratios or in the variability of larvae grown at different temperatures or on different culture media.

Different worm densities in the cultures of from 2000 to 10000 larvae per g of culture did not affect either the size of the infective larve or the percentage development.

The optimum temperature for survival is 15 °C. Worms grown at 20 °C lived longer than worms grown at any other temperature. There was no evidence of temperature adaptation by the larvae.

The infective larvae are positively thermotactic, and show maximum activity at 37 °C.

I should like to thank my supervisor, Dr Tate, for his advice and encouragement. The work was carried out during the tenure of a Medical Research Council Scholarship.

A method of breeding and maintaining L. natalensis cultures in the laboratory is described.

The infection of snails with F. gigantica miracidia and the collection of metacercariae is discussed. The mean number of metacercariae arising from cercariae produced by each snail was 652·6, over a period of 8·2 days.

It is shown that after 3 months storage F. gigantica metacercariae are still viable when excysted in vitro by using artificial pepsin and trypsin enzymes.

The author wishes to express his thanks to Dr G. M. Urquhart of the Wellcome Laboratories for Experimental Parasitology, University of Glasgow, Veterinary Hospital, Bearsden Road, Bearsden, Glasgow, who has read through this paper and made the necessary corrections.

Large numbers of electron-dense bodies, 700–1900 Å in diameter, usually seen each with its own limiting membrane, were found in axons of the ventral nerve of infective juveniles of H. contortus. Axons containing these granules merged, without limiting membranes, with a ‘light’, diffusely granular region, about 1·5–2 μm3. The ‘light’ area also merged without boundaries with the underlying cuticle which was different from the surrounding cuticle. This modified cuticle, of which the anterior border lies about 1·3 μm from the posterior edge of the excretory pore, extends slightly beyond the ‘light’ area. Otherwise it is a useful topographical marker for the extent of the ‘light’ area.

It is considered that the ‘light’ region has a special role in the physiology of the cuticle.

I wish to thank Mrs M. Ross for expert technical assistance and Mr R. I. Sommerville for valuable advice. This work was supported by a U.S. Public Health Service Grant, AI 04093–05. The use of the Siemens electron microscope was made possible by a grant from the Australian Research Grants Committee. Financial help from Parke, Davis and Co. (Australia) is also gratefully acknowledged.

Experiments were performed to determine at what phase or phases of its parasitic development Boophilus microplus becomes infected with Babesia bigemina. Problems due to Boophilus microplus being a one-host tick were overcome by artificially transferring ticks from one host to a second just prior to a moult. In several experiments, a babesiacide was used to eliminate parasites so that the exposure of ticks to infection could be restricted to one phase of their development. Further information was obtained by correlating the presence or absence of patent parasitaemia in the bovine with the presence or absence of infection in ticks which fed on it.

It was found that ticks were susceptible to infection for approximately the last day of their parasitic life. Infection at other times, that is, during larval, nymphal and the major part of the adult stages was not usual. Four of five attempts to infect larvae and all five attempts to infect nymphs were negative.

Infection of ticks always resulted when a patent parasitaemia coincided with the last day of parasitic life. Ticks were infected in all thirteen instances when these conditions existed but in only seven of eighteen instances when the animal was a carrier but was not showing parasitaemia.

Stage-to-stage transmission did not occur, although suitable conditions for this existed on nine occasions.

The cellular and syncytial components of the mature uterine bell of the palaeacanthocephalan, Polymorphus minutus are described, and compared with previous accounts of the histology of uterine bells. Each uterine bell always contains 17 separately distinguishable nuclei. This situation provides a good illustration of the phenomenon of organ eutely, common in Acanthocephala. The luminal spaces of the bell are described and their relevance to the translocation of eggs discussed.

I should like to thank Dr D. W. T. Crompton for his help and encouragement during the course of this work and Dr P. Tate for the provision of facilities. The work was carried out during the tenure of an S.R.C. Research Studentship.

A method for rearing blowfly larvae giving good synchronization of growth is described. Electron microscope studies showed that the lateral lamellae of the pharyngeal ridges each have a swelling at the tip, and that the lamellae from adjacent ridges are interdigitated in a regularly alternate pattern. Formation of the ridges in the second-instar larva begins 8 h before the moult when the four rows of partially syncytial epidermal cells lying beneath the floor of the pharynx begin to form nine dorsal projections. These lengthen and gradually take up the form of the ridges, the fine divisions which are the lateral lamellae being the last feature to develop. After a two-layered epicuticle has been formed the cytoplasm rapidly withdraws from the ridges leaving them, and the new floor of the pharynx, strengthened by a network of fibres. At the moult a further zonse of cuticle, showing parallel striations, is added to the base of the ridges. The lateral lamellae are epicuticular structures. The importance of the intracellular formation of cuticle is discussed.

I should like to thank Dr P. Tate under whose supervision this work was carried out for helpful advice, and wish to acknowledge financial support from the Agricultural Research Council in the form of a Postgraduate Studentship.

Eimeria praecox produced less effect on body-weight gain and food consumption than E. acervulina. No deaths occurred and no weight loss followed infection with doses of oocysts up to 10. However, there was a depression of body-weight gain in birds infected with both species and changes in the permeability of the intestine were noted from as early as 3½ h after infection. This suggests that increased intestinal permeability is not the major factor in the greater pathogenicity of E. acervulina compared with E. praecox. Eimeria acervulina produced considerably greater effects on the host as evidenced by mortality, body weight gain and food consumption.

I wish to thank Mr B. J. Millard and Mr M. Shirley for technical assistance and Dr B. M. Freeman for help with the statistics in Table 2.

The adult and two nymphal stages of Hoplopleura kitti sp.nov. from Rattus berdmorei Blyth, and the adult stage of Polyplax pricei sp.nov. from Rattus niveiventer Hodgson are described and illustrated.

I thank Dr K. C. Emerson, 2704 N. Kensington Street, Arlington, Virginia 22207 for making these specimens available to me for this study. I am grateful to Dr Edwin F. Cook of the University of Minnesota for reading the manuscript.