Five species of acephaline gregarine parasites – Apolocystis pilosa Meier from Lumbricus castaneus, L. festivus, L. rubellus and L. terrestris, Monocystis arcuata Boldt from L. castaneus, Nematocystis gracilis Berlin (= N. anguillula var. gracilis) from L. castaneus and L. rubellus, Zygocystis cometa Stein from Allolobophora caliginosa and Z. eiseniae Loubatieres from Eisenia foetida – identified during the present work are new to the British record.

The characteristics of two other monocystids, N. lumbricoides Hesse and N. lumbricoides var. pilosa Meier are identical apart from the presence of short ectoplasmic hairs on the latter trophozoite's body. Since the presence of ectoplasmic hairs which are projections on the trophozoite's body is often utilized in gregarine speciation, the hairy and the hairless monocystids should be described separately.

Berlin (1924) identified N. anguillula var. gracilis from the seminal vesicles of Lumbricus terrestris, L. rubellus and L. castaneus. This trophozoite should have been described as a separate species, N. gracilis Berlin and not as a variety of a totally different species originally described by Hesse (1909) from a host, Pheretima rodericensis, a megascolecid oligochaete, not found in Europe.

The writer wishes to express his sincere appreciation to Dr Anne Terry for her advice and useful suggestions, and to Mr D. Etherington, the head of department, for his encouragements throughout this research period.

Attempts were made to infect Stomoxys calcitrans, Lucilia sericata and Musca domestica with embryonated eggs of Toxocara canis and Toxascaris leonina. Only Musca domestica was successfully infected with Toxocara canis eggs.

Six Beagle pups were given anthelmintic treatment and infected flies were then fed to five of them. The five pups were examined at varying intervals, the sixth being used as a control. Four of the experimentally infected pups showed evidence post-mortem of having become infected with Toxocara canis by the ingestion of Musca domestica. Larvae of Toxocara canis were recovered from several tissues. Immature and adult forms were recovered from the intestinal contents. The results suggest that flies of Musca domestica are not only a source of infection to the dog, but that they may be of importance in the spread of toxocariasis in man.

I would like to thank Professor A. O. Betts and Dr W. P. Beresford-Jones for their encouragement and helpful criticism and also Mr G. Yeoman and Mr B. C. Warren of Beecham Research Laboratories, Wheathampstead, for their assistance and for the supply of flies. I am also very grateful to Mr and Mrs D. Appleton, Carmarthenshire, Wales for their co-operation in treating and supplying the beagle pups.

Erythrocytes of Tropidurus torquatus (Sauria, Iguanidae) infected with Plasmodium (Sauramoeba) tropiduri show acid phosphatase activity in Golgi vesicles, multivesicular bodies, secondary lysosomes and autophagic vacuoles. The functional relations between these structures and exocytotic activity is discussed.

The authors express their gratitude to: Professor A. G. E. Pearse for his helpful criticism of the work and during the preparation of the revised manuscript; to Professor P. C. C. Garnham for his advice and for his provision of facilities. We are also indebted to Mr Ian McLure for his help in translating the original Spanish into English.

Histological, histochemical and ultrastructural methods have been used to study gut structure and digestive physiology in the parasitic nematodes Rhabdias bufonis (Schrank, 1788) and R. sphaerocephala (Goodey, 1924). Both species are parasitic in the lungs of their amphibian hosts and feed entirely upon blood drawn from the lung capillaries.

Three gland cells are present in the oesophagus, one in each sector. The two subventral ducts open, by way of ampullae, into the lumen of the oesophagus about a quarter of its length from the anterior end. The dorsal gland opens similarly into the base of the buccal capsule. It is suggested that the glands produce a B-esterase, in an histochemically inactive form in situ, which is responsible for haemolysis and the bulk of extracellular digestion. Only one cell type is present in the intestine and this is entirely absorptive in function.

The major part of haemoglobin digestion is extracellular, partly by a process of contact digestion involving the B-esterase and acid phosphatase which are present in association with the microvilli. Haematin results from this process and is precipitated in the gut lumen. A smaller proportion of haemoglobin is taken up by the gut cells and is broken down intracellularly by lysosomes, originating in Golgi in the basal gastrodermis. These show endopeptidase activity and later acid phosphatase in some of the bodies of the lysosomal sequence and only at the light microscope level. The iron-containing pigment haemosiderin resulting from digestion is retained in the lysosome residues and forms the pigment granules in the gastrodermis. The products of extracellular digestion absorbed by the gastrodermis are synthetized into lipid by a lipase, probably produced by GER.

This investigation was supported in part by Research Grant AI 06295 of the United States Public Health Service. The final manuscript was prepared during the tenure of a Postdoctoral Fellowship from the British Egg Marketing Board. I wish to extend my gratitude to Dr J. B. Jennings for advice and encouragement throughout this work.

Histological, histochemical and ultrastructural methods have been used to study gut structure and digestive physiology in Cosmocerca ornata (Dujardin, 1845). The nematode is parasitic in the small intestine and rectum of Rana temporaria, and feeds solely upon the gut contents of the host, primarily bacteria and cellular debris rather than fluid material.

Only a small buccal capsule is present and no host tissue is ingested. Rigid channels at the tips of the oesophageal radii and a spiral arrangement of the corpus lumen are probably concerned in expressing any fluid in the food while retaining the particulate matter. The latter is then shredded by three large valvular flaps projecting into the lumen of the posterior oesophageal bulb. One gland is present in each sector of the bulb. There is some evidence that two secretions are produced in each subventral sector, an electron-dense one posteriorly which is released into the lumen below the valve flaps, and an electron-lucid one synthesized more anteriorly which is released in the anterior region of the bulb. Only one secretion is produced in the dorsal gland, similar to that in the anterior subventral sector, and which is poured into the lumen of the posterior corpus. The intestine is not differentiated into distinct regions and contains no gland cells. A prominent striated border of microvilli is present, varying from 25 μm in the foregut to 0·5 μm in the hindgut. They have a prominent core composed of minute fibrils and an outer glycocalyx covering.

Digestion is entirely extracellular, bacteria and cellular debris in the ingesta being broken down by a C-esterase present in the oesophageal gland secretions. It is completed by a process of contact digestion with the same enzyme adsorbed on to the glycocalyx. Acid phosphatase, also produced by the oesophageal glands and present on the microvilli, may be concerned in the absorption of the resultant digestion products and any simple solutes in the food made available by host extracellular enzymes. GER and free ribosomes present in the distal regions of the gastrodermis are probably concerned in the assimilation of the absorbed materials into glycogen which is stored in large quantities in the gastrodermis.

This investigation was supported in part by Research Grant AI 06295 of the United States Public Health Service. The final manuscript was prepared during the tenure of a Postdoctoral Fellowship from the British Egg Marketing Board.

The habitat of patients with L. minor infection in Trinidad, Tobago and Surinam is described. Three species of Lagochilascaris are redescribed and compared. A new species from Felis concolor is described and a synopsis, with a key to the genus is provided.

The development of L. minor is described from eggs and larval stages obtained from neck lesions of patients. The developmental pattern through third- and fourth-stage larvae was found to conform closely to that of other ascaridoid species, but the tail of the second-stage larva showed a unique conformation.

The earliest stage of development found in human lesions was the third stage, the smallest larva being 1·8 mm in length. The third moult was observed at about 5 mm and the fourth moult at 8 mm. Adult worms were observed with a minimum length of 5 mm in the male and 6 mm in the female. Eggs were present in some females of 8 mm length.

The observations are discussed in relation to previous concepts concerning the affinities, host specificity and evolution of this group of nematodes.

The writer takes pleasure in acknowledging the considerable help he received in this work from several colleagues and friends: Professor J. J. C. Buckley for sending specimens of L. minor and L. buckleyi from the Department of Helminthology, London School of Hygiene and Tropical Medicine; Drs A. G. Chabaud and Marie-Claude Durette from the Museum national d'Histoire naturelle, Paris for sending specimens of L. major; Dr P. Araujo from the Universidade de São Paulo, Faculdade de Farm´cia e Bioquímica for sending specimens of L. minor; Dr J. F. Teixeira de Freitas of the Instituto Oswaldo Cruz, Rio de Janeiro for sending specimens of L. turgida; Drs M. D. Little and P. C. Beaver from the Department of Tropical Medicine, Tulane University New Orleans, for sending specimens of L. minor and notes on their observations relating to L. minor. Grateful acknowledgement is also due to Dr O. H. Siung of the Ministry of Health, Port of Spain, Trinidad, and Dr Cox, Chief Medical Officer, Tobago, Dr A. H. Jonkers and his colleagues at the Trinidad Regional Virus Laboratory, and to His Excellency Dr B. F. J. Oostburg, Minister of Health of Surinam, for their considerable help and co-operation which enabled the writer to observe patients and examine specimens in Trinidad and Surinam. The able technical assistance of Miss Mary Cremin, Mrs A. McKeown and Mrs A. Green is gratefully acknowledged. Financial assistance for this study was provided under grants from the Australian Research Grants Committee, the U.S. Dept. of Health, Education and Welfare no. A. 107023–02, and the University of Queensland Research Grant.

The spermiogenesis and spermatozoan morphology of the palaeacanthocephalan, P. minutus were studied by a variety of electron microscopical methods.

Spermiogenesis occurs in syncytial clusters of spermatids exhibiting synchronous development. The outstanding events of the spermiogenic process are an enormous elongation of the spermatid nucleus and the eventual breakdown of the spermatid nuclear envelope.

The mature spermatozoon is a filiform cell about 60 μm long and motile by propagated undulations. It consists of two parallel elongate components, the single flagellum and the spermatozoan body. The former has a 9 + 2 tubule organization and the latter contains glycogen granules and membrane-bound dense inclusions as well as a region of condensed chromatin of nuclear origin. No mitochondria appear to be present.

In the University of Cambridge I should like to thank Professor H. Goodwin for the provision of electron microscope facilities and Mr B. Chapman for teaching me to use them. At King's College, London I am indebted to Professor D. R. Arthur and Professor F. R. Whatley for facilities and Mr H. Edge for excellent technical assistance. The work reported in this paper was initiated during the tenure of an S.R.C. Research Studentship and completed whilst in receipt of a Research Fellowship from the Nuffield Foundation.

A dihydrofolate reductase has been isolated from free-parasite preparations of the primate malarial parasite, Plasmodium knowlesi. Its properties are similar to those reported for the enzyme from the rodent malarial parasite, P. berghei, even though the base compositions of the DNA of these two species are quite different. The Kms for substrate and cofactor are 3 × 10−6M and 1 × 10−6M respectively and the molecular weight is ˜ 200000. Concentrations of pyrimethamine and trimethoprim as low as 1 × 10−9M and 3 × 10−8M respectively are sufficient to cause 50% inhibition of enzyme activity. The sensitivity to inhibition by pyrimethamine and trimethoprim of growth of cultures of P. knowlesi has also been investigated. Preliminary experiments showed that it was only the schizont stage that was susceptible to the action of the drugs and that in their presence, normal nuclear divisions and segmentation did not occur and subsequently, no reinvasion of fresh red cells took place. The minimum concentrations of drug required to produce these effects were 10−9M for pyrimethamine and 10−7M for trimethoprim. Thus, there is a close correlation between the concentrations of pyrimethamine and trimethoprim required to inhibit the dihydrofolate reductase in a cell-free system and the growth of the parasite in vitro. Pyrimethamine (10−9M) did not, however, affect the incorporation of radioactive precursors into DNA, RNA or protein of schizont stage parasites until after morphological damage could be seen and reinvasion was complete in control cultures. The time courses of incorporation of [14C]algal protein hydrolysate into protein in the presence (10−9M) or absence of pyrimethamine are the same as those described recently with immune serum. The possibility is thus raised as to whether pyrimethamine and immune serum act in the same way.

One of us (P.I.T.) received financial assistance from the World Health Organization. We thank Dr F. Hawking for many helpful discussions, Miss Jane Dunnett and Mr T. Scott-Finnigan for technical assistance and Dr O. D. Standen for samples of pyrimethamine and trimethoprim.

A dilution medium for the cultivation in vitro of the erythrocytic stages of P. knowlesi has been simplified to contain the following: a balanced salt solution, glucose, isoleucine, methionine, adenosine, p-aminobenzoic acid, biotin and calcium pantothenate. The medium, in the presence of plasma gave better results than the Harvard medium for the growth of P. knowlesi during one asexual cycle and also allowed the subculture of the parasites through three asexual cycles before a reduction in the number of parasites was observed.

We should like to thank Dr F. Hawking and Dr K. N. Brown for their advice and Mr T. J. Scott-Finnigan for technical assistance. One of us (P.I.T.) received financial assistance from the World Health Organization.

Histological, histochemical and ultrastructural methods have been used to study the gut structure and digestive physiology in the parasitic nematode Cyathostomalari E. Banchard, 1849. The nematode is parasitic in the orbito-nasal sinuses of its host and feeds exclusively upon blood.

Three gland cells are present in the oesophagus, one in each sector. The two subventral gland ducts open into the lumen of the oesophagus at the level of the nerve ring, and the dorsal gland duct into the base of the buccal capsule. It is suggested that the latter gland may produce an anticoagulin, histolytic and/or haemolytic secretions, histochemically-inactive in situ. The intestine is syncytial, with no differentiation into secretory components, and its distal surface is provided with a prominent brush border of long microvilli.

A non-specific esterase, thought to originate in the oesophageal gland secretions, causes haemolysis of ingested erythrocytes. The major part of haemoglobin digestion is extracellular, partly by a process of contact digestion on the microvilli, initiated by the esterase, and the protein is then further broken down by an exopeptidase of the ‘leucine aminopeptidase’ type, and the products absorbed into the gastrodermis possibly with the aid of an acid phosphatase present on or in the microvilli. An insoluble iron-containing compound, which is not haematin, results from breakdown of the prosthetic group. A smaller proportion of haemoglobin is taken up by the gastrodermis and digested intracellularly by the action of lysosomal hydrolases. An endopeptidase and an acid phosphatase are present in the gastrodermis, possibly in sacs of GER which are suggested to be primary lysosomes and which fuse with the endocytosed heterophagosomes. The insoluble pigment haematin results from digestion within the heterolysosomes, and this gives rise to the iron-containing gastrodermal pigment granules. The products of extracellular digestion are absorbed by the gastrodermis where they are synthetized into lipid by a lipase, which probably resides in whorls of GER.

This investigation was supported in part by Research Grant AI 06295 of the United States Public Health Service. The final manuscript was prepared during the tenure of a Postdoctoral Fellowship from the British Egg Marketing Board. I wish to extend my gratitude to Dr J. B. Jennings for advice and encouragement throughout this work.

The distribution of Tetrahymena limacis in its natural host Deroceras reticulatum, and the tissue responses to infection are described. Contrary to previous observations, T. limacis occurred throughout the tissues and organs of its host; the organisms were especially numerous in the kidney, the mantle shield, and in grossly visible papules on the external epithelium. Aspirates from such papules yielded numerous ciliates.

T. limacis elicited a considerable pathologic response and appeared to contribute to an increase in morbidity and mortality among slugs. Tissue responses were focal (fibrotic encapsulation of isolated organisms) and diffuse (necrosis, mechanical tissue destruction, and metaplasia). Efforts to establish infection in seven species of molluscs other than D. reticulatum were unsuccessful.

An extramolluscan cyst stage of T. limacis is reported for the first time. Both resting and reproductive cysts were observed. Since free-swimming trophozoites of T. limacis are not long lived, the organism is more likely an obligate rather than a facultative parasite of molluscs. Observations also suggest that slugs are infected via the respiratory pore rather than orally.

It is a pleasure to acknowledge the aid and counsel given by Dr J. O. Corliss in identifying the ciliate and to Miss Lorin DuBois for technical assistance.

The immune reaction of the mouse to the cestode, Hymenolepis microstoma, has been investigated. The mouse can carry a worm burden of up to 500 mg wet wt and there is no evidence either of rejection of the parasite by the mouse or a slowing down of growth rate of the mouse as a result of the parasite.

The nature of the antibody response has been investigated with regard to the type of antibody, onset of production, and titre.

The nature of the antibody is discussed together with the fact that there is no rejection of the parasite. The possibility that a cellular immune response might be necessary for rejection is also discussed.

I should like to express my thanks to Dr T. S. C. Orr of Fisons Research Laboratories, Loughborough, for many helpful comments and suggestions during the course of this work.

My thanks are due also to Professor C. A. Hopkins who put the facilities of the Wellcome Laboratory at my disposal at all times. My thanks, too, to Miss Gillian Moore whose technical assistance was invaluable.

The work was in part supported by a Grant from Fisons Ltd.

The hatching of Hymenolepis diminuta eggs and penetration of the emergent hexacanths in adult and larval Tenebrio molitor beetles had been described. Hatching was shown to be a two-stage process involving rupture of the eggshell by the insect's mandibles and digestion of the remaining egg-layers in the midgut lumen. Penetration of hatched embryos was examined by histological methods that demonstrated the rate of migration and the route taken by hexacanths entering the haemocoel of adult beetles. Differences in the arrangement of the midgut tissues in adult and larval T. molitor were detected and shown to account for the failure of hexacanths to complete migration in the larvae. The role of the embryonic hooks and penetration gland secretions during hatching and penetration has also been discussed.

I should like to thank Professor T. R. E. Southwood for providing generous research facilities, Dr June Mahon for her advice and encouragement, and in particular, Dr W. Mordue for his continuous interest and many useful criticisms. This work was conducted during the tenure of a Science Research Council Studentship at Imperial College of Science and Technology, London, S.W. 7.

The effects of P. burrili adults on the chicken host are outlined. There was no evidence that infections of up to 20 flukes caused marked pathological changes in the nictitating membrane to which flukes attach in an intimate 'placental' manner by the ventral sucker.

The food material of adult flukes is largely lacrimal secretion; it appears that blood can be excluded from the diet since the caecal contents are colourless and haemoglobin was not detected histochemically. Little material was detected in the caeca by the histochemical techniques used. The presence of a mucus coat around flukes was noted and it is suspected that materials of nutritional significance may be conserved in this coat for long periods. Glucose was demonstrated in the parenchyma surrounding the uterus. It is suggested that this might indicate either (a) polysaccharide degradation in this region; (b) polysaccharide synthesis; or (c) a site of accumulation of glucose which enters through the tegument and caeca. The presence of greatest activity in the uterine region may be indicative of nutritional dependence of the developing miracidium on the parent fluke.

The gastrodermis of the caeca is regular, consisting of flattened cells with a very prominent PAS positive, striated border of microvilli. The cytoplasm of the cells contains appreciable amounts of RNA. Protease, acid phosphatase and possibly esterase have been demonstrated in the gastrodermis.

Possible esterase activity occurs in the ventral sucker, alkaline phosphatase is present in the lining of the excretory ducts, and acid phosphatase has also been demonstrated in the pharynx, both suckers, and subcuticular region.

Ferritin was ingested by flukes in vivo and this enabled the digestion cycle to be followed. Flukes ingested little or no ferritin in vitro. Digestion was completed within 13 h and appeared to take place in close association with the striated border rather than in the lumen. The possibilities are that (a) material is digested intracellularly within the microvilli; (b) membrane (contact) digestion takes place; (c) extracellular digestion, in close association with the striated border, takes place. These processes are not necessarily mutually exclusive.

I should like to thank Professor J. D. Smyth for his helpful advice. This study was carried out during the tenure of an Australian National University Research Scholarship.

The intraperitoneal inoculation of chickens with 100–170 mg of Statolon, an artificial interferon inducer in mammals, induced the production of a virus interference factor in the serum. Chickens, 3 and 5 weeks old given 40–170 mg Statolon i.p. produced significantly fewer oocysts after infection with E. maxima than untreated chickens.

Only three serum samples (from a large number examined) taken from chickens 1, 4 or 6 days after E. tenella infection or 6 h and 6 days after E. maxima infection showed slight but significant antiviral effects.

The kinetics of low-level repeated infections of Nippostrongylus brasiliensis in the laboratory rat were studied.

The administration of five infective larvae each weekday to the rats produced an infection which was cumulative over 16 weeks and which did not produce an acute host immune response.

The repeated administration of 50 larvae/weekday produced a primary immune response after 14 days. This caused partial worm expulsion and the suppression of egg output but the resistance of these rats to reinfection was not as pronounced as that seen in classical laboratory infections where heavier but less frequent larval exposures are used. The secondary worms that established in these rats did not elicit an acute host immune response even when the worm burden was as high as 756 worms.

It is suggested that the kinetics of this type of infection more closely approximate those found under natural conditions than do those of a ‘classical’ laboratory infection.

We wish to thank Misses G. Merchant, L. Cleaver and J. Cobb for able technical assistance, and Dr B. M. Ogilvie (National Institute for Medical Research, Mill Hill, London) for her helpful comments and discussions.

Demodex carolliae, a parasite of the bat Carollia perspicillata, is described for all stages of its life cycle. The sequences and adaptive features of this life cycle are detailed. Some information is presented on the population structure and the pathogenicity of this species.

This research was supported in part by Grant W83–1 to Dr F. Lukoschus from the Netherlands Foundation for the Advancement of Tropical Research (WOTRO).

Cestodes collected from birds of El Recreo, Zelaya, Nicaragua are reported. Sacciuterina mathevossiani sp.nov. from Rhamphocaenus rufiventris is the only species in the genus with 32 rostellar hooks, each 22–24 μm long, and with 5–9 testes. Angularella beema (Clerc, 1906) Strand, 1928, from Iridoprocne albilinea, is partially redescribed. Also reported are Dilepis undula (Schrank, 1788) Weinland, 1858, from Turdus grayi; Anomotaenia mutabilis (Rudolphi, 1819) Baer et Bona, 1960, from Florida caerulea; Ophiovalipora lintoni (Olsen, 1937) Coil, 1950, from Butorides viriscens; Hymenolepsis pellucida Fuhrmann, 1906, from Ramphocelus paserinii and Gymnostinops montezuma; and Raillietina (R). maplestonei Southwell, 1930, from Amazona autumnalis. All are new records for Nicaragua.

Thanks are expressed to Dr Thomas R. Howell, University of California who, assisted by Mr John Zeiger, collected and identified the hosts. The collecting of birds was supported in part by a grant to Dr Howell from the University of California Association in Tropical Biogeography. Gratitude is also expressed to Dr W. H. Coil, University of Kansas, who examined some of the specimens and offered helpful suggestions, and to Miss Dorothy B. Segal, Beltsville Parasitological Laboratory, for checking the records on Angularella.

1. Trichonema spp. infective larvae once stimulated move in darkness, dim and bright visible light and ultra-violet light. There was no significant difference between the distances moved in these photic conditions.

2. Movement patterns were variable but certain shapes of tracks, rates of reversal and reversing types were typical of certain light conditions.

3. The rate of reversing was dependent on light conditions and was random in direction.

4. Sensory adaptation was suggested in visible light, but not in ultra-violet at 366 μm.

5. Movement analyses in flashing light suggested that pulsating stimuli at intervals of 100 ms or less were required for sensory input approximating to physiologically continuous stimulation.

6. Larvae showed an idiosyncrasy in their tracks, repeated tracking with the same individual giving less varied tracks than with different larvae.

The author is indebted to Mr J. M. Smith for his painstaking efforts in preparing the tracks and his willing and skilful assistance throughout.

Twenty-one sheep were killed after having been kept for varying times on a pasture contaminated with Haemonchus contortus. The proportions of linguiform A to linguiform B phenotypes were estimated for the H. contortus populations of each sheep. They gave further evidence that the linguiform B phenotype gradually replaces the linguiform A phenotype during the summer. Given the genetic basis of the phenotype it is pointed out that this seasonal change would appear to be inconsistent with any theory stating that essentially only one generation of worms is involved in the yearly outbreaks of disease.