The adult stage and nymph 2 of Hoplopleura johnsonae sp.nov. and the nymphal stages of H. captiosa Johnson are described. The morphology of Hoplopleura nymphs and the infraspecific variations of H. captiosa Johnson are discussed, and a key to the seven species of Hoplopleura Enderlein known in Thailand is also presented.

I am grateful to Dr K. C. Emerson, Arlington, Virginia, and Dr Zofia Wegner, Gdansk-Wrzeszcz, Poland, for the loan of materials on which this work was based. I am also indebted to Dr Phyllis T. Johnson, University of California at Irvine, and Dr Edwin F. Cook, University of Minnesota, for their suggestions as to this species complex and reading the manuscript.

The commencement and duration of haemolysis and the length of time the erythrocytes remain intact in engorged virgin and fertilized females and in male Ornithodoros savignyi were investigated by means of red cell antigens.

There were no differences between fertilized and unfertilized females, haemolytic tests were possible in both groups up to 120 h after engorgement.

In the male group haemolytic tests were possible only up to 24 h after engorgement.

In both female groups inhibition of the in vitro haemolysis could be observed until the fifth day, after feeding on a calf with erythrocyte mosaicism, indicating the loss or masking of antigens due to the damage of cell walls.

The authors wish to thank Dr G. Theiler for her interest and advice during this work.

Ten-month-old Blackface sheep double vaccinated with X-irradiated larvae of H. contortus were shown to be highly resistent to individual challenge with 50000 larvae. Compared to unvaccinated sheep, the percentage reductions in the numbers of worms established 6, 9, 12 and 16 days after challenge were 83, 90, 99 and 100 respectively. The immune response was directed against the 3rd and 4th larval stages.

The author wishes to express his thanks to his colleagues at the Wellcome Laboratories for Experimental Parasitology for their co-operation and help during the period of this experiment.

This work was supported by a grant from Allen and Hanburys Ltd., Ware, England.

The method of attachment of the cattle tick Boophilus microplus (Canestrini) has been investigated on cattle of different breeds and susceptibility to infestation.

Despite their differing sizes, the larval, nymphal and adult mouthparts penetrate to a similar depth towards the base of the Malpighian layer. Penetration may occur within 5 min of the arrival of the tick on the host.

Attachment is accomplished by the secretion of a cement substance in which the mouthparts are embedded and which adheres firmly to the hosts skin.

The cement consists of two main components: a cortex of carbohydrate-containing protein, stabilized by quinone tanning and disulphide linkages, and an internum which is lipoprotein in nature.

The start of the secretion of cement and the initial cutting of the host tissues by the chelicerae occur simultaneously. Final rapid engorgement of each stage is preceded by a secondary secretion of cement into a fluid-filled cavity which forms directly beneath the mouthparts and provides additional support.

It is concluded that attachment is an entirely mechanical process by an inert cement which does not provoke the development of host-parasite factors inimical to the tick.

It is with much pleasure that we acknowledge generous financial support by the Australian Cattle and Beef Research Committee which has made possible this project.

An examination with light and electron microscopes has been made of the cell type which is considered by some authors to be a sporozoan parasite, Rhabdospora thelohani, and by others to be a tissue cell of fishes and amphibians.

The cell type was found in the minnow Phoxinus phoxinus in many tissue sites, including olfactory and pharygneal epithelia, kidney, eyes and brain. In some specimens it could not be found in any tissue.

The cell has a thick fibrous wall, a basal nucleus, an apical mitochondrial zone, a Golgi body, and from 8 to 50 characteristic refractile rodlets.

The rodlets give a negative reaction to the Feulgen test for nuclear material, but are positive to the periodic acid–Schiff stain, a test for polysaccharide. Glycogen does not appear to be present in the rodlets.

Under certain circumstances the rods rupture the cell wall and may protrude in the apical region of the cell.

The structures described are discussed with the evidence for and against a parasitic interpretation of the cell. It is concluded that Rhabdospora is a protozoan parasite, whose exact functional and taxonomic status is as yet unknown.

I am grateful to Professor G. E. H. Foxon and to Professor P. C. C. Garnham for their encouragement, advice, and helpful criticism of the manuscript. I am further indebted to the National Spastics Society for the use of the electron microscope housed in Guy&s Hospital Medical School, and to Mr I. D. Bradbrook for his assistance with the histological techniques.

In the present experiment the response of sheep to a single infection with Haemonchus contortus at graded doses, and their responses to two subsequent infections with 3000 infective larvae, were studied. The response of the sheep was investigated by estimation of faecal worm egg counts on alternate days throughout the course of the experiment and by following the development of the parasite by differential worm counts performed on animals slaughtered at crucial times.

Initial infections were established with graded doses of 500–2700 infective larvae. The proportion of infective larvae which became established at each dose, development of the worm burden and fecundity per adult worm were similar for each dose.

Following first challenge infection with 3000 infective larvae there were no effects which could be related to the previous level of infection. Whereas there was no difference in egg production per female worm, a small but consistent increase in the number of retarded larvae was observed in the previously infected animals (6% of the burden was in the 4th larval stage at day 56) compared with the previously uninfected control animals (2% in the 4th stage at day 56).

Following a second challenge with 3000 infective larvae an increase in the number of retarded larvae was again observed, and, in addition, egg production per female worm was reduced compared with egg production in previously uninfected sheep given a similar challenge infection.

The results of the initial infections suggest that control of the growth and development of H. contortus infection by factors independent of an active host response does not occur in worm burdens established from doses as high as 2700 infective larvae.

A comparison has been made of the attenuating effect on N. brasiliensis larvae of X-rays (HVL, 8 mm Al) and γ-rays from 60Co over the range 10–80 kr. In the dose range where attenuation was manifested as a decrease in total worm burden the γ-rays had an RBE (relative biological effect) of 0-7 relative to the X-rays as unity.

Because of the enhancement of infectivity occurring at low radiation doses, attenuation in this region is better assessed in terms of alteration to the sex-ratio of the parasite rather than effect on total population.

This work was supported by grants from the Agricultural Research Council and the Horse Race Betting Levy Board, and was carried out during the tenure by one of the authors (T. Kassai) of a British Council exchange scholarship.

Thanks are due to Dr T. Martin Young and Mr J. S. Orr of the Radiotherapy Department, Western Infirmary, Glasgow, for access to radiation sources and helpful advice.

Investigations on the host specificity of plerocercoids of Schistocephalus solidus were carried out using the technique of surgically transferring plerocercoids from the body cavity of Gasterosteus aculeatus to various other fish. Plerocercoids survived in all cases when transferred from G. aculeatus to other G. aculeatus; when tranferred to Pungitius pungitius the worms survived for long periods but failed to grow. Plerocercoids transferred to Coitus gobio, Nemacheilus barbatula, Phoxinus phoxinus, Salmo trutta, Coregonus clupeoides, Perca fluviatilis, Rutilus rutilus and Esox lucius always died within 2–10 days after being transferred. Electron-microscopic examinations of the tegument of plerocercoids transferred to new hosts showed: in G. aculeatus normal appearance throughout the experiment; in P. pungitius degeneration of the microtrichs after 6 days; and in S. trutta complete destruction of the tegument in 7 days.

Plerocercoids of the genus Diphyllobothrium survived the transfer from Gasterosteus aculeatus to Salmo trutta and continued to grow in their new host.

Infection of fish with S. solidus by feeding infected copepods and by aspetic injection of procercoids into the body cavity of the fish were also tried. Gasterosteus aculeatus became infected using both these methods but it was not possible to infect Pungitius pungitius.

The response of sheep given six sensitizing infections each of 3000 infective larvae of H. contortus at fortnightly intervals to a challenge infection of 3000 infective larvae has been studied. While a large proportion of the challenge infection (ca. 3000 parasites) persisted to termination of the experiment on day 141 in sheep (group 3) in which the challenge was superimposed upon the sensitizing infections, only a mean of 437 worms, including both 4th-stage larvae and adults, was recorded at this time in another group (group 5) in which the sensitizing infections were terminated by anthelmintic treatment on day 90, i.e. 8 days before challenge. The proportion of the total worm burdens of the challenge infections arrested at the 4th larval stage was increased for both groups (25% for group 3 and 18% for group 5) by comparison with unsensitized control groups (4% for group 6 and 2% for group 7).

As the effect of immunological control was expressed more vigorously in the group (group 5) in which the sensitizing infections were terminated before challenge it seems likely that recovery of immunological competence occurred in these animals following removal of the sensitizing infections. This conclusion suggests that, owing to the persistence of the sensitizing infections and therefore exposure of the immune mechanism to continuous antigenic insult, the animals which received the superimposed challenge infection had entered a phase of immunological exhaustion during the challenge period.

The free-living phase of the life-cycle of Nematodirus helvetianus was studied out of doors on grass plots and the effects of temperature and humidity on the free-living stages were studied in the laboratory. The results of these observations are discussed in relation to the bionomics of N. battus and N. filicollis, and tentative deductions made regarding the epidemiology of N. helvetianus infection.

I wish to thank Mr J. Bailey for technical assistance.

One of a large number of Lymnaea peregra (Mull.) from a pond near Glasgow was found to be infested with Cercaria diplostomi gasterostei.

C. d. gastrostei has been found to penetrate Gasterosteus aculeatus and develop into a diplostomulum in the retina of the eyes.

Large numbers of G. aculeatus from the pond have been found with Diplostomulum gasterostei occurring in the retina.

Infested heads of fish were fed to domestic ducklings and pigeons, and adult stages of a worm considered to be a new species and named D. gasterostei were obtained.

Morphological details of the cercaria, diplostomulum and the adult worm are described.

The author wishes to thank Dr C. A. Hopkins for reading and criticising the manuscript, Dr D. A. Erasmus and Dr G. Rees for valuable suggestions. My thanks are due also to the technical staff of the Department who assisted me in the collection of snails and fishes, and to Mr Francis Deen who did the sectioning of the specimens. This work was in part supported by a grant from Shell Oil Company (London).

The bladder of the cysticerci, the larvae of cestodes, is a transitory embryonic organ; its morphology is related to its mode of development and the localization of the parasite in its intermediate host. The bladder makes possible the adaptation of the cysticercus to unusual conditions of its development. A certain degree of analogy between the trophoblast of the mammalian embryo and the bladder of the cysticerci adapted to the development in the tissues of mammals can be drawn.

Among over 700 Australian birds dissected, Geopetitia spp. were found in three. These are described as new species, as follows: G. streperae from Strepera melanoptera, G. chibiae (female only) from Chibia bracteata, and G. falco (female only) from Falco longipennis.

Types of the new species will be deposited in the South Australian Museum. Paratype material of G. streperae will be in the Helminthological Collection of the Zoology Department of the University of Adelaide.

The three birds from which the Geopetitia spp. were taken were collected by ornithologists of the South Australian Museum, to whom I am most grateful.

Plasmodium vinckei infections, which usually kill mice within 7 days, can be terminated in the majority of cases by a single injection of chloroquine phosphate equivalent to 10 mg/100 g body weight. After such drug treatment the parasites disappear from the blood for 6–11 days, after which a recrudescence with a low peak occurs. Most animals overcome this second parasitaemia and the parasites finally disappear completely. After recovery, mice exhibit an immune response to a challenge infection and, after a short period of parasitaemia during which a low peak is reached, the animals recover completely. This immunity, once acquired, apparently persists for the lifetime of the host. The establishment of the immune state depends on the period of patent parasitaemia during the primary infection and the longer this period the greater is the chance of a solid immunity developing. Immunity may be exhibited by mice treated with chloroquine as early as the 3rd day of infection. Killed parasites have no immunizing effect. Mice splenectomized before infection are capable of an immune response, and mice splenectomized after radical cure are also able to overcome a challenge infection. In both these cases more than one injection of chloroquine is required. The immunity produced in mice is that of the true sterile type, equivalent to that produced against P. berghei in rats, and is species-specific, conferring no resistance to infection with P. berghei. P. vinckei infections in mice provide a useful immunological model for laboratory studies. The immune response is predictable and easy to induce, and this parasite is therefore superior to P. berghei for immunological studies. Attention is drawn to the fact that in P. vinckei the infection is brought under control by the immune response and not by the antimalarial drug; therefore this ought to be taken into consideration in the assessment of drug trials.

An experimental study of hatching in the oxyurid nematode Aspiculuris tetraptera indicates that the major factors in the initiation of hatching are the pH and temperature of the environment and that the process is aerobic. Carbon dioxide and reducing agents do not appear to be as important factors in the hatching of eggs of this nematode as they are in the hatching of eggs of ascarids. It is suggested that the physiology of hatching in ascarids is not necessarily the typical nematode pattern.

My grateful thanks are due to Dr P. Tate, Director of the Molteno Institute, and to Dr D. L. Lee for their encouragement and very helpful discussions on various aspects of this study.

It has been shown that the 5th or adult stage of Trichinella spiralis stimulates strong immunity in mice. This was shown using a transfer technique and irradiated worms. A comparison between the immunity produced by a normal infection and one which has been irradiated is made and explanations offered to explain the fact that less immunity is stimulated by irradiated larvae.

I would like to express my gratitude to H.M. Treasury and to the Agricultural Research Council for financial support during the time that this work was conducted. I would also like to thank Professor W.I.B. Beveridge, within whose department this work was conducted, for the facilities provided. I would also like to record my gratitude to Dr W. C. Campbell for the many stimulating discussions we have had on the subject of Trichinella.

The body wall of the daughter sporocyst of Cercaria bucephalopsis haimaena Lacaze-Duthiers, 1854, is shown by the electron-microscope to consist of an external syncytial tegument, lying on a basement membrane, and an internal cellular subtegument, which surrounds a body cavity containing developing cercariae.

The syncytial tegument has areas of dense cytoplasm alternating with sparse reticulate cytoplasm. The dense cytoplasm contains nuclei, a few mitochondria and secretory products which probably include a neutral mucopolysaccharide. This may be the precursor of the acid mucopolysaccharide in the sparse reticulate cytoplasm and on the surface of the daughter sporocyst.

Nutrients are probably absorbed through the outer plasma membrane of the tegument, pass through the sparse reticulate cytoplasm in the middle region of the tegument, the inner plasma membrane and basement membrane into the subtegument.

The ultrastructure of the tegument of adult and larval Digenea are compared.

We would like to thank Dr Gwendolen Rees for allowing us to examine the electron-micrographs of Parorchis acanthus. We are also grateful to Professor E. W. Knight-Jones for the provision of excellent working facilities and to the Science Research Council, for a grant to one of us (E.A.B.) which made the work possible.

Partly developed strobila of Echinococcus granulosus from a 28–38 days infection in a dog have been brought to maturity by culturing in both liquid and diphasic media.

Surface-sterilization of the worms from dogs was achieved by use of antibiotics. Maturation was most successful in a diphasic system consisting of Parker 199+10% inactivated bovine serum over a solid base of coagulated bovine serum and a gas phase of 8% O2+5% CO2 in N2.

In the most successful results in diphasic media, a 28-day-old strobila reached maturity after a further 14 days in vitro culture, and a 35-day-old strobila matured after 6 days culture.

Ova produced in vitro showed activity but were not tested for infectivity. Abnormalities developed in some cultures, especially in monophasic media.

This work was supported by the Australian Wool Board, the World Health Organization and U.S. Public Health Service Research Grant no. E 4707–03.