By means of serial sections of experimentally infected Eisenia foetida with Metastrongylus spp. The distribution of larvae within the host has been determined. The exact position in the host intestine at which larvae penetrate has been shown to be the crop. The preferred site for localization and development of the parasite has further been shown to be the lamellar sinuses of the calciferous glands, although larvae were recovered from the dorsal blood vessel, hearts and perienteric blood sinuses. The way in which larvae pass from the gut to their definitive positions in the host has been discussed and it is supposted that this is determined by the configuration of the blood system rather than by a predilection for an environment low in free carbon dioxide. The pathology of infection and the distribution of alkaline and acid phosphatases, lipases, non-specific esterases RNA, DNA and haemaglobin have been described. The distribution of phosphatases in the gut is suggested to be concerned in the uptake of nutrients. The presence of an active zone of enzyme activity in the subcuticular regions of the parasite has been shown and the significance of this discussed. The parasite has been shown to feed directly on host blood.

A simple apparatus for the collection of helminth eggs from faeces by means of a gas-circulated saturated salt solution is described. Nearly all the Nematodirus spp. eggs in both bovine and ovine faeces were recovered and shown to be viable.

The IgM levels in rabbits infected with Trypanosoma gambiense are raised. Agglutinating antibody has been found in the IgM immunoglobulin fraction of sera obtained from these infected rabbits. Agglutinating antibody was first found in the IgM fraction and later in the infection appeared in both the IgM and IgG fractions. Precipitating antibody to blood trypanosome antigens was found solely in the IgG fraction.

On the basis of the data presented here a working hypothesis is developed to explain the raised IgM immunoglobulin levels found in the sera of rabbits and humans infected with T. gambiense.

Total lipid from adult male and adult paired Schistosoma mansoni has been fractionated by thin-layer chromatography. Phospholipid, free sterol, and triglyceride were major components of both mixtures. A remarkably small amount of sterol ester was found in adult flukes considering the prevalence of this compound in mouse blood. Free fatty acids were found to be a minor component. Cholesterol was the major free sterol present.

The technical assistance of Mrs Katye Ross Summerlin is gratefully acknowledged.

When egg-masses of Lucilia illustris, taken from carcasses, were mounted on the body of living vertebrates (Clarius batrachus, Bufo melanostictus, Rana tigrina, Hemidactylus fluviviridis, Columba livia and Suncus murinus), the larvae hatched in the majority of cases under normal conditions of room temperature, and entered into the body of the experimental hosts, ultimately killing them. It appeared that the larvae fed on the brain first before turning their attention to other soft tissues of the hosts. The specimens fed on living tissue had a shorter period of development than those bred on dead animals and the period of development was shortest when the host was a living warm-blooded animal.

Thanks are due to Mr H. Oldroyd of the British Museum of Natural History, London, for kindly identifying the fly. The authors also wish to thank Dr T. N. Ghosh of the Calcutta School of Tropical Medicine, who helped with literature; and Dr S. K. Das Gupta, of the Darjeeling Government College, who helped with suggestions at the time of preparing the manuscript.

The aim of the present contribution has been to draw attention to the technique of covariance analysis in the study of factors influencing the oviposition of ixodid ticks.

The example given as an illustration shows the high degree of sensitivity of the technique and its effectiveness in removing the bias due to the sample differences in the mean female weights of different treatment groups. This bias has not been removed in any published work on egg-production studies of ticks, so preventing precise comparisons of different conditions to be made.

My thanks are due to Dr D. E. Moorhouse for helpful advice and to the Australian Meat Research Committee for generous financial support. The cooperation and assistance of Mr W. J. Roulston and his staff of the Division of Entomology, C.S.I.R.O. is gratefully acknowledged.

The behaviour of the sand martin flea Ceratophyllus styx jordani Smit was studied in relation to its ecology.

The cocooned resting imago in the host's old nest is the main over-wintering stage. Mechanical disturbance of the cocoons by the exploratory habits of the newly returned sand martins elicits emergence of the imagines in spring. The seasonal rise in temperature is not, by itself, important in causing emergence, as it does not become effective until many weeks after the martins have returned, by which time undisturbed fleas are likely to have died inside their cocoons.

When the imagines break out of their cocoons they are negatively photo-tactic, but become positively phototactic within 24 h. This response takes them outwards along the martin's disused burrow until the increasing intensity of light reduces their activity so that they aggregate on the lower lip of the entrance. Positive phototaxis prevents them dispersing downwards from the entrance.

Periodically the fleas bury themselves in sand; this response may function for water conservation. The proportion buried is greatest at night.

The sand martin's habit of hovering close to a succession of entrances renders it accessible to the fleas, whose main host-finding response is an outward jump from the burrow entrance. This jump is released by a sudden decrease in light intensity and is directed towards dark objects. Vibration and air currents do not release jumping.

Dispersal from aggregations in disused burrows may occur by transport on the host, or by spontaneous horizontal emigration along the cliff face, or by falling after an unsuccessful host-finding jump. Fleas which have fallen become negatively geotactic and positively anemotactic. Fleas wandering on the cliff face visually detect burrow entrances up to 30 cm away, and turn towards them. Preference for moister sand and, possibly, a negative phototactic response, may induce the fleas to remain in newly found burrows.

Small aggregations of fleas also occur at the entrances of burrows currently in use by martins. Fleas circulate between the entrance and nest chamber of these burrows, until the martin begins to incubate its eggs. The entrance aggregation then disappears and fleas accumulate in the nest chamber. There is some interchange of fleas between infested burrows in the martin's pre-incubation period.

The general pattern of behaviour resembles that of C. gallinae. Behavioural differences between the two species are related to the ecology of their hosts. C. styx is adapted to dispersal and host finding in its host's breeding site, whereas C. gallinae is adapted to reach foraging birds. This difference partly accounts for the narrow host specificity of C. styx and the wide host range of C. gallinae.

My grateful thanks are due to Chris. Mead and Giles Pepler for information on sand martins' behaviour and migratory arrival. I would also like to thank Brian Little, who introduced me to several colonies in the Tyne Valley. The valuable advice of the Hon. Miriam Rothschild and Dr E. T. Burtt is especially acknowledged.

Ultrastructural observations on the intestine of Metastrongylus sp. have shown that it is composed of a single layer of epithelial cells each with a basally placed nucleus and resting on a basement layer. The basal plasma membrane of each cell is highly infolded and at the cell apex the lateral plasma membranes of adjacent cells are thickened to form a terminal bar.

The brush border consists of numerous microvilli which possess dilated tips. The tips contain a granular material and the evidence obtained suggests that they are released into the lumen indicating a form of micro-apocrine secretion. Golgi complexes, glycogen, lipid droplets and granular endoplasmic reticulum are present in the intestinal cells. The Golgi complexes are associated with the production of an electron dense body. Other inclusions are cytolysome-like in their structure. The discharge of lamellar bodies into the intestinal lumen is described and the role of the intestine in secretion, absorption, and excretion is discussed.

The authors wish to acknowledge the co-operation and facilities provided by Professor J. Brough in the Department of Zoology and Mr J. H. M. Hughes (Veterinary Officer) for allowing unrestricted access to infected material at the Roath abattoir, Cardiff. Grateful acknowledgement is also expressed for the financial support given to one of us (T. J.) by the Pig Industry Development Authority. Any views expressed in this paper are not necessarily those of the Authority.

The authors also wish to express their appreciation of the excellent technical assistance provided by Mr T. W. Davies.

The infective larvae of S. ratti were non-feeding and none of a wide variety of possible substrates had any effect on the respiratory rate of intact worms. Sodium succinate increased the oxygen uptake of larval homogenates.

The cytochrome chain inhibitors, sodium cyanide, sodium azide and urethane all reversibly inhibited the respiration of the infective larvae. The inhibition caused by carbon monoxide was photo-reversible and 2,4-dinitrophenol inhibited respiration rather than stimulated it. Methylene blue increased the oxygen uptake of homogenates, but had no effect on the intact larva. Iodoacetamide and sodium arsenite irreversibly inhibited respiration, whilst sodium fluoride, sodium pyrophosphate and sodium malonate were without effect on the intact larvae.

This work was carried out during the tenure of a Medical Research Council Scholarship.

Babesia rodhaini remains in the blood of most rats from 2 to 12 months after the acute primary parasitaemia has subsided. By analogy with some trypanosome and malaria infections it is suggested that piroplasms may have the capacity for antigenic variation, thus allowing the parasite to survive in the host for so long albeit as a chronic infection. A population of B. rodhaini was isolated which was considerably less sensitive in passive transfer experiments to two pools of serum from recovered rats than the normal passage population.

I thank Dr S. F. Barnett for his advice during the work and Dr F. Hawking and my colleagues at Mill Hill for criticizing the manuscript. This work was carried out during the tenure of an Agricultural Research Council Studentship.

Sera pooled from rats which were immune to Babesia rodhaini infection had demonstrable protective activity against the piroplasm in non-immune rats. When inoculated with parasites or close to the time of infection, antiserum caused a delay in the onset of patency but did not usually affect the course and severity of the patent parasitaemia in young rats. There were more survivors when antiserum was given in a series of small doses over a period rather than a single large inoculum at the time of infection. Serum from rats previously reinfected several times, when injected into infected rats during the early stages of patency, was followed by a rapid fall in parasite numbers. A severe secondary parasitaemia eventually ensued in these animals.

I would like to thank Dr S. F. Barnett for his advice during the work and Dr F. Hawking and my colleagues at Mill Hill for criticizing the manuscript. This work was carried out during the tenure of an Agricultural Research Council Studentship.

At present our knowledge of the host-parasite relationships of the Schistosomatidae and their snail intermediate hosts is meagre. Because this knowledge is necessary in the search for effective therapeutic and control measures it would be useful to find an in vitro procedure facilitating continuous progenesis of schistosomes without the use of a snail host.

The ultrastructure and development of the body wall of Polymorphus minutus is described during the acanthella stages in the intermediate host Gammarus pulex.

The cortex of the early acanthella is simple in structure, consisting of a syncytium containing giant nuclei, mitochondria, Golgi bodies, endoplasmic reticulum and a few lipid bodies. The cuticle is penetrated by pores which open into vesicles in a vesicular region.

The cortex gives rise to the body wall, neck and lemnisci of the adult, and may be considered as divided initially into two and later three functionally different regions: an outer absorptive region, an inner storage region and a layer between which develops to provide firm, resistant skeletal protection.

Absorption is facilitated by the increase in surface area due to the pores which penetrate the surface. This region is functional throughout development and the pores increase in number, possibly by division, as the animal grows. Beneath the pores a pore canal layer develops towards the end of the late acanthella stage.

During development supporting fibres are deposited throughout the cortex. Beneath the vesicular layer a concentration of mitochondria, Golgi bodies and endoplasmic reticulum deposit the fibres of the felt layer. In the anterior meta-soma no felt layer is found, but the body spines originate from this region.

The inner region of the cortex, or radial layer, contains the giant nuclei, which are arranged in the early acanthella in 5 rings of 4, 6, 5 or 6, 6 and 5 nuclei respectively. During development they produce dendritic process and finally fragment. They are considered here to be concerned with the formation of the felt layer and lemnisci rather than the ‘lacunar channels’. The inner cortical region becomes ensely packed with lipid bodies, and it is suggested that these may be responsible, owing to fixation artifact, for the so-called ‘lacunar channels’ previously described in these regions, the extensive cavities seen in some light microscope preparations being filled with a fluid lipid rather than an aqueous solution.

The lemnisci are similar in appearance to the cortex except for regions of concentrated endoplasmic reticulum.

The mitochondria in the cortex of the acanthella appear to be aerobic rather than anaerobic, as they possess many cristae and are larger than the mitochondria of the adults.

My thanks are due to Dr D. W. T. Crompton for advice and encouragement, and to Dr D. H. Northcote and Dr F. B. P. Wooding for time on the Phillips Electron Microscope 100. This work was carried out during the tenure of an S.R.C. studentship.

Camallanus marinus sp.nov. is described from eleven specimens recovered from a variety of marine fishes. It is the only species in Camallanus s.s. with a single spicule. Spinitectus palawanensis sp.nov. is described from two males and one female found in a scombrid fish. It is characterized by having 12–17 rings of 60–65 spines, a spicule ratio of 5:1, and ten pairs of caudal papillae. Cucullanus lutjani, sp.nov. is described from two specimens from lutjanid fishes. It is distinct in lacking a preanal sucker, in possessing a gubernaculum and eight pairs of cloacal papillae.Oceanicucullanus padfica gen. et sp.nov. is described from two specimens found in cyprinid fish. It is most similar to Indocucullanus, differing from it in the absence of a gubernaculum, and in possessing three pairs of teeth in the radii of the oesophagus. Philometra (Philometra) lateolabracis Yamaguti, 1935; Terranova sp.; and Procamallanus spp. are reported for the first time in the Philippines.

We wish to thank Dr D. S. Rabor, Silliman University, Damageute, Negros Oriental, Republic of the Philippines, for general support in field activities, and Dr Loren Wood, Curator of Fishes, and Dr Robert F. Inger, Curator of Reptiles, Chicago Museum of Natural History, for identification of hosts. Acknowledgement is also made to Dr Betty June Myers for technical assistance and advice in handling materials.

Cotugnia columbae sp.nov. from the domestic pigeon is described and compared with other species of the genus. The tapeworm measures 108–130 mm in length and 2·236 mm in maximum breadth. The rostellum bears 200 hooks, 7·7–10·6 μm. long arranged in two rows. Testes number 105–130 and the cirrus pouch measures 0·354–0·376 x 0·054–0·065 mm.

We are grateful to Dr C. M. Singh, Director, Indian Veterinary Research Institute, and to Dr H. D. Srivastava, erstwhile Assistant Director and Head of the Division of Parasitology, for their interest in these studies and for the provision of the necesssary facilities.

Histomoniasis was transmitted to poults inoculated orally with recently harvested whole intact male worms in three trials (4/5, 5/6, 2/4), but not with female worms (0/5, 0/9, 0/3). When triturated male worms were given in two trials, the rate of transmission was reduced (3/5, 0/10). Triturated female worms given orally produced histomoniasis in 1/9 poults. These results suggest that further unknown steps may be involved in histomonad transmission by heterakid worms.

This study was partially supported by NSF Grant GB-5227.

The amount of [14C]methionine in the stomach, anterior and posterior intestine wall and lumen, blood and caecum of a rat, and in the anterior and posterior parts of the tapeworm Hymenolepis diminuta in the intestine, was measured at intervals from 10 min to 10 h after feeding a meal of 2 g glucose and 37.5 mg methionine by stomach tube.

Nearly all the meal left the stomach within 5 h; the amount entering the tapeworm depended on the position of the worm. That part lying in the anterior half of the intestine was subjected to a rapid influx reaching a maximum concentration of at least 8 mM within 1–3 h after the meal was administered. The level in the worm then dropped to about 20 % of the peak level, although the stomach was still emptying and the level of methionine in the intestine wall was still rising. This was a stable state, and equal to the concentration in the posterior part of the worm which was reached 2 h after the rat was fed.

The reason why the anterior part of the worm should show a big influx and efflux is discussed and related to changes in concentration of methionine in the lumen. The lack of such a flux into and out of the worm further down the intestine is related to the host's homeostatic control of amino acid balance in the intestine.

The results prove that dietary imbalance of amino acids affect the amino acid pool in a tapeworm for about 3 h, if it lies in the anterior of the gut. A dietary regime is suggested which should produce a prolonged effect and thereby retard growth of the worm.

The weights of the parts of the worms found in the anterior and posterior half of the small intestine revealed an unexpected phenomenon; the majority of the tapeworm, by weight, lies in the anterior of the intestine for about 4 h following a meal, but in the posterior of the intestine after the stomach has emptied.

It is a great pleasure to thank Miss Gillian Moore and Miss Patricia Grant for technical assistance, and Shell International Petroleum Company, London, for financial support.

A study on transfer of drug resistance between species of malaria parasites was carried out in mixed infections of P. berghei and P. vinckei. The biological characters which served as contrasting markers for separation of the two species were the inability of the ‘old’ blood-passaged strain of P. vinckei to develop in suitable mosquito vectors and its failure to produce parasitaemia in the adult golden hamster. Facility of sporogonic development and cyclical transmission and a pronounced virulence for the adult hamster marked the N.K. 65 strain of P. berghei.

Development of a maximal and stable resistance to 200 mg/kg pyrimethamine in the P. vinckei strain was achieved by a gradual increase in drug level in successive blood transfers.

Mixed, simultaneous infections of pyrimethamine-resistant P. vinckei and sensitive P. berghei were experimentally induced in white mice. Subinoculations of the mixed infection at the height of parasitaemia was carried out in adult hamsters. Suppression of the P. vinckei infection in the hamster by innate resistance and the reappearance of P. berghei in the blood was noted. Tests with the maximal concentration of pyrimethamine (200 mg/kg) showed the acquisition of drug resistance in some of the P. berghei infected hamsters. Persistence of the acquired resistance was demonstrated following fifteen successive blood transfers in the absence of drug pressure and after five cyclical transmissions.

Parallel control experiments with pyrimethamine-sensitive P. vinckei and P. berghei in mixed infections failed to reveal any enhancement in drug resistance. No spontaneous drug-resistant mutant was found in the sensitive P. berghei after exposure to a single course of treatment with the drug, and persistence of parasites in some treated animals was considered as individual variations in host reactions to the drug. This resistance never persisted after blood transfer or cyclical transmission. No loss in drug resistance had been found following transfer of the resistant R strain from mouse to hamster. A marked difference in the course of the plasmodial infection and in the length of survival of mice inoculated with the drug-resistant P. berghei was noted following treatment with pyrimethamine in various concentrations. It is suggested that these differences represent a selective action of the drug on a heterogenic P. berghei population, consisting of drug-resistant and drug-sensitive parasites in the blood of the host.

Injection of sonified material from pyrimethamine-resistant P. vinckei and P. berghei into mice inoculated with a drug-sensitive P. berghei failed to induce enhancement of resistance to the drug.

The phenomenon of drug-resistance transfer observed under experimental conditions in rodent malaria is viewed in the light of similar phenomena in micro-organisms.

We gratefully acknowledge the assistance rendered by Mr Jerold Sklarsh.

This paper is Contribution no. N 408 from the Army Research Programme on Malaria. The work was carried out under the sponsorship of the Commission on Malaria, Armed Forces Epidemiological Board, and supported in part by the United States Office of the Surgeon General, Department of the Army.

The nephridial system of M. expansa has been studied using light and electron microscopy, and a number of histochemical techniques have been used on sections of the worm. The organization of the nephridial system and the fine structure of the flame cells and the nephridial ducts are described. Pores, which connect the nephridial lumen to the intercellular space of the connective tissue, exist at the junction of a flame cell and a nephridial duct. These pores may be considered nephrostomes and the system therefore is not protonephridial as defined by Hyman (1951).

The epithelium lining the nephridial ducts has a structure which suggests that it is metabolically active. It is postulated that the beating of the cilia of the flame cells draws fluid into the ducts via the nephrostomes, with absorption and/or secretion of solutes being carried out by the epithelial cells of the duct walls. The function of the nephridial system is discussed.

I am grateful to Professor James Brough for the provision of research facilities at the Department of Zoology, University College, Cardiff, andtoDrD. A. Erasmus for much helpful advice during the course of the work. I wish to thank Professors W. Peters and T. Wilson for critically reading the manuscript and Miss M. Williams and Mr T. Davies for expert technical assistance.

I also wish to thank the Veterinary Inspector and his staff at the Roath Abattoir, Cardiff, for their kind co-operation and assistance in obtaining material.

The work was carried out under the tenure of an S.R.C. research scholarship.

The fine structure of the flame cells, tubules and excretory pore of the miracidium of Fasciola hepatica are described. The tubules are formed from the flattened surfaces of cells rolled round and joined at their tips by a desmosome. Vesicles are present in the wall of the tubule, possibly indicating secretory activity. Clubshaped microvilli are present only in the terminal region near the excretory pore. Possible functions of the system are discussed.