The muscular saucer-shaped haptor of the monogenean parasite Entobdella soleae is attached to the skin of its host Solea solea by means of a suction pressure generated within the sea-water-filled cavity enclosed between the cup-shaped haptor and the skin of the fish. The suction pressure is produced by the action of a pair of extrinsic muscles which are situated in the body of the parasite. Each extrinsic muscle communicates with the haptor by means of a long tendon which passes through a fair-lead in a prop-like accessory sclerite and is inserted on the end of a girder-like anterior hamulus embedded in the roof of the concavity of the haptor. The pull exerted by the muscles lifts the girders and the roof of the suction cup in which they are embedded relative to the props, thereby producing a suction pressure.

An electron microscope was used to investigate the ultrastructure of the tendon, which was found to consist largely of unbranched banded fibrils which differed from the collagen fibrils of vertebrate tendon in their diameter and periodicity.

I would like to express my thanks to Dr J. Llewellyn for suggesting the problem and for much helpful discussion. I am also grateful to Dr M. P. Osborne for tuition on the cutting of sections for electron microscopy. The work was conducted during the tenure of a Fishery Research Training Grant from the Development Commission.

Uninfected erythrocytes of Rana boyli, in the presence of glucose, utilized 214μ1. O2/hr./108 cells. Cells infected with Haemogregarina boyli increased oxygen consumption approximately 12% for a 10% rate of infection. Alkaline phosphatase and zymohexase, but not acid phosphatase, urease, lipase or peroxidase, were demonstrated in the parasites by cytochemical means.

The studies presented in this paper describe the effects of control exerted by the immunological response of the host (sheep) on the developmental stages and fecundity of the parasite Nematodirus spathiger. Thirty Merino lambs, maintained worm-free, were randomly divided among three treatment groups each containing ten animals. The group 1 lambs were each given a single dose of 50,000 infective larvae, the group 2 animals were given a single dose of 130,000 infective larvae, and the group 3 animals were given twenty-five consecutive daily doses of 2000 infective larvae. Group fecundity was estimated by performing worm egg counts on daily faecal samples and development of the parasite burden was followed by carrying out differential worm counts on animals slaughtered at crucial stages during the infections. Total fecundity was greatest in group 1 and least in group 3 with group 2 intermediate. An inverse relationship between total fecundity and percentage retardation of development (percentage of 4th-stage larvae in the total worm burden) was demonstrated between the three treatment groups.

The results of the studies also show that control of the parasitic infection is mediated about threshold levels of immunological responsiveness and is expressed by (1) elimination at the infective (L3) stage, (2) retardation of development at the L4 stage, (3) reduction in egg production of the adult female, (4) elimination of adult worms, and (5) discrimination against the female in both the degree of retardation in the L4 stage and the extent of elimination in the adult stage.

Great variation in response was observed between individuals within treatment groups. The source of variation is attributed to differences in degree of antigenic disparity of the parasite with individual members of the heterozygous host population in which antigenic characters are not uniformly segregated.

The concept of ‘fitness’ of the parasitic species was introduced into the discussion to provide a rational interpretation of the results.

We are indebted to Dr S. S. Y. Young, Division of Animal Genetics, C.S.I.R.O., for advice and assistance with the statistical analyses, which were performed by Mrs M. Tonkin, and to Dr D. F. Stewart for his constructive criticism of the manuscript. Careful technical assistance was given by Mr E. Teleki and Misses Helen Giller and Berenice Merchant.

Cytamoeba bacterifera from urodeles (Batrachoseps attenuatus, Aneides lugubris, A. flavipunctatus and Dicamptodon ensatus) show a thin peripheral ring of DNA and a less definite, heterogeneous central portion after Feulgen treatment; toluidine blue reveals a similar configuration. Exposure to DNA-ase and RNA-ase, followed by toluidine blue and Feulgen treatment, substantiates the localization of DNA; RNA is present in small quantity and restricted to the periphery of the parasite.

Mitochondria (2–5μ long rod-shaped, central bodies) can be detected with Janus Green B, and osmium tetroxide yields a dark central mass of rods and granules as well as peripheral granules; Sudan Black IV is without action. Zymohexase and acid phosphatase can be detected by cytochemical means, but peroxidase, lipase, urease and alkaline phosphatase were not noted.

From the evidence presented, C. bacterifera is considered a living entity and is tentatively relegated to the Piroplasmida.

The writer would like to express his appreciation to Dr R. S. Bray of the American Foundation for Tropical Medicine, Harbel, Liberia, for his counsel and suggestions.

A modification of the controlled test is described. This is designed to assess the value of a drug against immature as well as against the adult stages of the gastrointestinal nematodes of sheep. The use of faecal egg-count data in the assessment of anthelmintic activity is compared with the critical and controlled tests and the comparative value of all three types of test is discussed.

Entobdella diadema produces spermatophores from a pair of follicular glands lying one on each side of the body alongside the main nerve cord, and the secretion of these glands is stored in a two-chambered reservoir within the cirrus-sac.

The vagina is made up of two regions, a wide distal part to receive, accommodate and digest the spermatophores, and a proximal narrow part connected through the vitelline reservoir with the oviduct.

E. diadema Monticelli, 1901, is shown to be distinct from E. bumpusii Linton, 1900, and has been recorded from two new hosts, Dasyatis pastinaca at Plymouth, and Myliobatis aquila at Naples.

We wish to thank the directors and staffs at the Plymouth Marine Laboratory and at the Stazione Zoologica, Naples, for providing excellent facilities for the above studies to be carried out. The work was assisted by a grant to one of us (J. L.) from the Trustees of the Browne Fund, to whom grateful acknowledgement is made.

A simple but efficient apparatus for harvesting nematodes migrating from their insect hosts is described. Infected host larvae are supported, in contact with water, on a nematode-permeable diaphragm resting in the mouth of a large funnel. A battery of funnels can be connected in series and their water-level maintained by a common constant-level device.

Haematoloechus (Haematoloechus) exoterorchis sp.nov. and H. (H.) micrurus sp.nov. have been found in the lungs of Rana occipitalis (Gunther) in South Ghana.

62·5% of the frogs were infested with one or other or with both species.

The two species occupy different positions in the lungs of the host. H. (H.) exoterorchis is cylindrical and is wedged, anterior end foremost, into the alveoli. H. (H.) micrurus is flattened and remains free in the central lumen of the lung.

In the former case the wall of the alveolus, containing the worm, becomes stretched to a thin membrane.

The morphology of both species is described with reference to their different habitats.

A brief discussion of the genus is included.

I am most grateful to the University of Ghana and to the staff of the Zoology Department at Legon for the facilities which they placed at my disposal and without which the work could not have been done.

Lobochona insularum sp.nov., a collar ciliate (Chonotrichida), an ectocommensal on the pleopodal bristles of a gribble from Hawaii, is described. L. insularum differs from the previously described chonotrichidan ectocommensals of the gribbles, L. limnoriae on Limnoria lignorum and Lobochona prorates on Limnoria tripunctata, in the outlines of the body and of the marginal lappets of the collar.

This work was supported by a grant from the National Science Foundation. Various facilities were made available by the Allan Hancock Foundation of the University of Southern California.

Acknowledgement is given to Dr Bayard H. McConnaughey, who discovered the organism and prepared the slides.

1. The distribution of glycogen and lipids in three oxyuroids (Aspiculuris tetraptera, Enterobius vermicularis and Syphacia obvelata) is described and found to be similar to that in ascarids and other oxyuroids.

2. Evidence is presented for the presence of both polysaccharides (possibly glycogen) and lipids in the cuticle.

3. It is suggested that the chitinous layer of the egg-shell of A. tetraptera contains phospholipids in association with proteins.

4. The distribution of phospholipids is described and it is suggested that their role is mainly structural.

I am grateful to Dr P. Tate for advice and encouragement and to Dr D. L. Lee for much useful discussion and advice.

The large and small forms of Tylenchorhynchus macrurus are distinguished as separate species. The large form becomes T. icarus and differs from the small form, T. macrurus in the greater number of annules on the female tail, longer stylet and slimmer body. The oxygen consumption of both species is similar when assessed in terms of body surface area. Soil samples from the field indicated that (a) greatest concentrations of T. icarus occurred at about 5 cm. depth, (b) few occurred below 24 cm., the depth of the top soil, and (c) numbers of T. icarus in the top 5 cm. of soil decreased during dry periods and increased after rain. T. icarus migrates to the wet end of a moisture gradient and has maximum mobility in soil at a moisture content corresponding to field capacity and at 20° C. T. icarus survived osmotic pressure equivalent to 1 m urea for 4 days. Their oxygen consumption increased with increasing osmotic pressure but in 1 m urea there was a decline which was even more pronounced in 2 m urea. Of a population of T. icarus 35% survived for 32 weeks in soil with plants. In damp sand at 10° C, oxygen consumption was steady for 32 weeks but after 48 weeks the nematodes were dead. It is suggested that the free-living stages of plant parasitic nematodes have similar migratory habits.

In three series of infections 32 mice were given metacercarial cysts of Fasciola hepatica X-irradiated at 3 Kr.: 8 mice received 20 cysts each and 10 mice 40 cysts each. In serial kills 9–24 days after infection 127 young flukes were recovered, 10 + 49 entire and 39 + 29 in serial sections of infected liver. These flukes were stunted and inhibited in their development. During a period of 8–22 days the length and breadth of the flukes increased from 0·53 mm. x 0·27 mm. to 1·12 mm. x 0·37 mm., whereas the mean length and breadth of normal flukes 22 days old is 3·4 mm. x 1·9 mm. The intestines of the flukes have about 10–14 lateral diverticula or sacculations but not normal branches during this period. In the sections of 12– to 29–day infections 16 dead flukes were observed in various stages of disintegration but flukes deemed alive at the time of fixation were noted in all stages from 8 days onwards, although some of them were injured by inflammatory processes set up in the liver. Injury is caused by massive infiltrations into the inner substance of the cuticle of band-type neutrophil leucocytes, which raise the epicuticle in extensive blister-like formations, but the basal portion of the cuticle (lamina vitrea) remains more or less intact. The cuticular sheets ultimately fragment, apparently as a result of chemical action, and leucocytes which had infiltrated into the cuticle rejoin the aggregate of similar cells inside the burrow. How the leucocytes effect an entry into the cuticle is not clear, but it is more probably by chemical than by physical means. When the epicuticle has been destroyed the fluke is in a dying condition. Few leucocytes penetrate into the parenchyma, suggesting that the lamina vitrea is relatively resistant to these cells and that death is due to chemical action following widespread but superficial damage to the cuticle.

The remaining 14 mice which received 40 X-irradiated cysts each were challenged 22 days later with 10 or 5 normal cysts. This procedure was followed by serial kills at intervals during the period 8–53 days after infection. Three almost mature flukes were recovered at 32 days and one mature fluke at 39 days. The mature fluke was of unusually small size (6·4 mm. x 4·3 mm.), but it had shed many viable eggs into the bile duct and gall bladder. The numbers of flukes of the challenge infections did not differ significantly from those of normal controls: 62 flukes in groups of 1–8 per mouse provided means of 4·4 flukes per mouse and 55·4 flukes per 100 cysts. In similar experimental infections of mice (which, however, received 2 doses of cysts X-irradiated at 4 Kr.) Hughes (1963) recovered 39 flukes in groups of 1–7 per mouse, providing means of 3·5 flukes per mouse and 35·3 flukes per 100 cysts. In his control experiments, which also serve as the writer's controls, 10 mice received 10 normal cysts each and in 22– to 29–day infections 34 flukes were recovered in groups of 3–5 per mouse, providing means of 4·25 flukes per mouse and 42·5 flukes per 100 cysts. There is therefore no evidence of immunity in terms of either delayed maturation or reduced fluke burdens. At all stages of infection flukes of the challenge infection bear comparison with flukes of single normal infections, except for an apparent diminution of growth (which requires confirmation) about 3–4 weeks after infection. This accords with generally accepted opinion that any small degree of immunity which is acquired by the hosts of liver flukes is almost undemonstrable. Further experiments with reduced periods between infections with X-irradiated cysts and a challenge infection may be profitable and are in progress but it is suggested that in such experiments nutritional effects may arise as a result of modification of the hepatic tissue on which young flukes feed by leucocytic infiltrations of the inflammatory reaction which is normally directed towards the repair of damage caused by the flukes.

My former pupil Denys H. Hughes, of the Parasitology Group, Allen and Hanburys (Ware), kindly set up the experimental mice to my specifications and I am deeply grateful to him for this kindness and consideration and for the respect he has shown for my wishes. Mice and cysts—X-irradiated as required— were supplied by Allen and Hanburys, for which my thanks are also proffered.

My personal technician, Mr John Wells, has attended to my technical needs constantly. In addition to making numerous series of excellent sections and whole mounts, he undertook the task of measuring several dimensions of more than 100 flukes. His patience and perseverance in the face of continual requests for more and more, good and still better materials has been commendable and I am glad to express my gratitude to him. I am grateful also to Mr R. D. Reed of this Department, who prepared the photomicrographs for Pls. 1–4 of this paper, sometimes when under the pressure of other duties.

Large numbers of Plagiorchis (M.) megalorchis Rees, 1952, were found in the small intestine of dying pheasant chicks in Peeblesshire, Scotland. This is the first record of this trematode in pheasants. In one chick one specimen of Brachylaemus fuscatus (Rud, 1819) was found, which is a new host record in this country. Unusual virulence of these trematodes in pheasants and turkeys is noted, showing lack of adaptation to these hosts. In addition to chironomids and midge, culicine larvae were infected with cercariae from naturally infected Lymnaea pereger. It is proposed to consider P. laricola Skrjabin as described and illustrated by Chertkova (1953) to be Plagiorchis bikhovskayae n.nom.

The author wishes to express his thanks to R. H. Duff, M.R.C.V.S., of the Ministry of Agriculture, Veterinary Laboratory, Lasswade, for placing the first pheasant chicks at his disposal, and to A. Howe, the gamekeeper at Holylee, for his information and willing help.

1. Four trematodes, Gastrothylax crumenifer, Cotylophoron cotylophorum, Paramphistomum explanatum and Fasciola gigantica have been used for quantitative analysis of their inorganic constituents.

2. Calcium, magnesium and phosphorus content have been determined.

3. All the four trematodes contain large amounts of phosphorus (0·61–1·05%); but the amounts of calcium (0·025–0·045%) and magnesium (0·029–0·065 %) are small.

1. A method of trapping small mammals has been described and Apodemus sylvaticus, Clethrionomys glareolus, Microtus agrestis and Sorex araneus were captured. The method of trapping has been discussed.

2. A survey of the endoparasites found in the four host species has been produced. The two more common hosts and four of their parasites have been chosen for more detailed study.

3. The infection levels of the parasites in the two hosts have been calculated and compared with other published data.

This work was carried out during the tenure of a Department of Scientific and Industrial Research Studentship. My thanks are due to Dr H. D. Crofton for his very helpful supervision and criticism and to Professor J. E. Harris, F.R.S., in whose department this work was done, for the facilities provided.

Data on 279 species of trematodes of birds and mammals are analysed in tables, to show the molluscan orders and families that act as first intermediate hosts of various trematode families.

Host-specificity is highly developed in the first larvae of trematodes and it is suggested that, as a consequence of this, certain species, genera and families of molluscs harbour a greater variety of trematodes than others. The families Lymnaeidae, Physidae, Planorbidae, Hydrobiidae and Thiaridae are by far the most important first-intermediate hosts of the trematodes of birds and mammals whose life cycles are known; each family acting as host of not less than twenty-four species and eight families of trematodes.

This paper is published with the approval of the Director General of Health, Canberra, A.C.T.

From 24 May to 4 July 1961 about 12,000 roach, Rutilus rutilus (L.), died in a lake at Brynmill Park, Swansea, South Wales. Even this high figure may be an underestimate of the actual mortality rate as it is based entirely on extractions of dead fish from the surface waters by members of the Brynmill and District Angling Club, who used landing nets from the shore only, although at fairly regular intervals. The daily counts of dead roach are represented on a histogram (Text-fig. 1). It is also of interest that in the early summer of 1961 large numbers of roach succumbed in other regions of the British Isles; about 30,000 died in the River Trent, Derbyshire, and 3000 in the lake in St James's Park, London. Newspaper reports in both localities attributed the cause to a deficiency of oxygen. For the outbreak in South Wales, however, similar reports suggested that ‘white spot disease’ caused by the ciliated protozoan Ichthyophthirius was responsible for the mortality.