A comparative study was made of defined regions of the alimentary tract of third-stage larvae of T. colubriformis and H. placei. The general organization of the tract was similar in both nematodes. The mouth, buccal cavity and oesophagus were lined with cuticle. Muscle cells, apical cells and gland cells were present in the oesophagus. In both species the gland cells contained secretory granules of similar morphology. The lumen of the intestine was ill-defined and apparently nonfunctional. Dense bodies observed in the intestinal cells differed in the two species.

We are grateful to Dr D. W. Brocklesby for his help and advice. We would also like to thank Dr D. L. Lee and Dr W. G. MacMillan for helpful discussions.

Quantitative chromatographic analysis of the free amino acids of the head–foot muscle of uninfected and infected Littorina littorea indicates that there is specific variation in the physiological effects of parasitism. The total concentration of free amino acids in the host head–foot muscle showed an increase of 10·9% with infections of Cryptocotyle lingua rediae, a decrease of 12·7% with infections of Himasthla leptosoma rediae and a decrease of 57·5% with infections of Cercaria emasculans sporocysts. These effects probably depend on three main factors namely, the nature, size and mobility of the larvae of the three species concerned and the influence of these factors in determining the extent of any damage to the hepatopancreas of the host.

The larvae of C. lingua are probably less affected by the changes they induce in the free amino acid pool of the host than the larvae of H. leptosoma and Cercaria emasculans which induce changes equivalent to starvation.

This work was conducted during the tenure of a Science Research Council Studentship. I would like to thank Professor B. John and Mr A. R. Hockley for their helpful advice and criticism.

Acetylcholinesterase activity, measured per unit wet weight, is relatively low in the eggs and infective larvae of N. brasiliensis. It increases rapidly during the parasitic phase, especially in the late 3rd- and early 4th-larval stages. Activity in normal adults is extremely high (× 15 egg activity) and this is doubled again in immune-damaged adults. Possible functions of N. brasiliensis acetylcholinesterase are discussed.

It is a pleasure to acknowledge the technical assistance of Miss Anne Cronin and Miss Beryl Crooks.

A new trematode, Burnellus trichofurcatus, is described from South Australia from the freshwater catfish, Tandanus tandanus. It appears to have affinities with Monodhelmis Dollfus, 1937 and Mehratrema Srivastava, 1939, but is probably most closely related to Tandanicola Johnston, 1927 (Fellodistomatidae: Tandanicolinae). It is assigned to the Fellodistomatidae Nicoll, 1909, as emended by Cable (1953). Cercaria trichofurcata Johnston & Angel, 1940 is shown to be the larval stage. The cyst stage is omitted from the life cycle, with infection of the catfish occurring directly, probably by mouth. Further comments on developmental stages are given. The sporocyst is not branched, as described by Johnston & Angel (1940). The miracidium of Tandanicola bancrofti is reported, and the life history of this species is discussed. The genus is named for Dr R. H. Burnell in recognition of his help, over a number of years, in collecting animals used in these life history studies.

I would also like to acknowledge information and help given me by Dr J. C. Pearson, of the University of Queensland, and information on fish given me by Mr C. J. M. Glover, of the South Australian Museum.

Microspines 0·05 μm long and 0·002 μm in diameter at the base have been demonstrated on the egg shells of S. japonicum. They are protrusions of the shell but are structured into inner and outer layers of differing electron density.

Spines observed on the shell of S. haematobium can be flexed by contact with host cell membranes. Firm, perhaps binding, contact is suggested. The spine length serves to define a space between the shell wall and the host cell membrane which could represent the primary interface of host parasitic contact.

The host-specificity of monocystids was investigated experimentally by infesting infection-free Dendrobaena subrubicunda f. typica with sporocysts of Apolocystis megagranulata and A. lavernensis normally found in Dendrobaena subrubicunda and Allolobophora longa respectively. An attempt to infect worms raised free from infection with sporocysts of Monocystis agilis normally harboured by Lumbricus spp. was unsuccessful. Eighteen of the thirty identified monocystids were found to be monobiotic (species-specific), eleven were oligobiotic (genus-specific) and only one was polybiotic (family-specific).

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 the research period.

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.

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.

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 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.

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.

Scanning electron-micrographs have shown the covering of microvilli on the surface of the redia of Parorchis acanthus. In the contracted state the elongated microvilli with bulbous extremities seen in the surface grooves may be the result of compression. The surface of the epidermis of the cercaria is smooth on a large area of the ventral surface and lattice-like with microvilli, laterally, anteriorly, dorsally and on the tail. The spines on the body can be withdrawn into sheaths by the contraction of muscle fibres inserted into the basement lamina below each spine.

I would like to express my sincere gratitude to Dr I. ap Gwynn of this department for preparing the scanning electron-micrographs and the School of Engineering Science, University of North Wales, Bangor for the use of their stereoscan. I should also like to thank Mr M. C. Bibby for technical assistance and Professor E. G. Gray and Dr W. Sinclair for assistance with the transmission electron-micrographs.

The cercaria of Parorchis acanthus swims by a series of spasmodic ventral flexions of the body moving with the dorsal surface of the body foremost. The wave of contraction continues along the tail which therefore moves dorso-ventrally. Creeping movements precede cyst formation. The structure of the tail is admirably suited to swimming movements and to rapid shortening and lengthening. The wall is provided with circular and longitudinal muscles and abundant mitochondria. The centre of the tail contains fluid in which is a network of large myoblasts the processes of which overlap and probably slide over one another during the tail movements. Glands opening into the terminal tail invagination secrete an adhesive substance consisting of mucoprotein and glycoprotein which together with the vesicular secretion around the aperture enables the tail tip to attach itself to the substratum.

I would like to express my sincere thanks to Dr I. ap Gwynn of this department for invaluable help in the preparation of the electron-micrographs and Mr R. A. Moore and Mr M. C. Bibby for technical assistance.