The thoracic skeleton and musculature of the Pupipara were studied and compared with the thorax of Musca and Glossina in order to identify the sclerites of the thorax of the Nycteribiidae. Comparative studies of the thorax and other features suggest that the Pupipara do not belong to the higher Calypterata. This comparison also supports the view which separates the Streblidae and the Nycteribiidae from the Hippoboscidae, and supplies evidence for reconsideration of the position of these two families among the Calyptera.

Gratitude is expressed to Professor O. Theodor of the Hebrew University, who supplied most of the Pupipara examined, to Professor R. Wenzel of the Field Museum of Natural History, Chicago, for species of American Streblidae and to Dr I. Paperna for the species of Glossina.

P. anoura was found in 55 % of pythons (M. spilotes variegatus) in Brisbane. Eggs contained first stage larvae after 8 days development; the first moult was completed by 10 days; the eggs were infective after 14 days. After ingestion by tadpoles, the larvae hatched from the eggs and migrated into the tissues but did not show any growth. In mice and rats the larvae migrated mainly to the liver, lungs and intestinal wall, where growth occurred to a length of 5–6 mm by 6 months after infection. The second moult was not observed, but the larvae were infective to pythons after 39–42 days development. From their structure it was assumed that after this time the larvae in mouse tissues were third-stage larvae.

Various species of Australian python, Morelia spilotes, Liasis amethistinus, L. fuscus and L. childreni, were experimentally infected with larvae of Polydelphis anoura by feeding nodules from the wall of the small intestine of experimentally infected mice and rats. The third moult occurred in the stomach within 14 days, moulting larvae at this stage measured between 3.5 and 7.0 mm long. Fourth-stage larvae occurred in all python species, the smallest being 4 mm. Growth and development of the fourth stage occurred at first in the oesophagus and stomach. Up to 2 months after infection, larvae had not grown more than 12 mm, yet they were clearly differentiated into males and females. In mouse-infected M. spilotes growth to 20 mm was reached by 154 days, but it was not until 183 days that adults were observed.

Comparison with adult specimens from P. reticulatus from Malaya confirmed the previous observation that Australian male specimens have relatively shorter spicules than male specimens from other geographical regions. Growth, development and location of larvae in mice, experimentally infected with eggs from Australian and Malayan specimens, appeared to be the same.

The fine structure and organization of the nervous system of the miracidium is described. The central ganglion consists of a mass of nerve fibres with peripherally situated cell bodies. Tracts of fibres run outward from the central mass to the muscles of the body wall and to specialized endings. The individual fibres contain several types of inclusions and synapses are common in the neuropile.

Excluding the eyespots, four kinds of specialized nerve endings are described. Two of these types terminate at the body surface and bear ‘cilia’. The other two terminate internally, one type within the body wall and the other type laterally, slightly anterior to the central ganglion. It is suggested that the function of three of the types of ending might be sensory, detecting chemical and mechanical stimuli, and the direction of gravity. The function of the fourth type of ending is problematical but might be secretory.

I am most grateful to Dr A. Robards for use of electron microscope facilities and to Mrs J. Denison for technical assistance.

The ultrastructure of the body wall of the third-stage larva of Haemonckus placei was studied. The cuticle was found to consist of eight layers: a thin outer layer, a membrane-bounded layer, an electron-dense layer, a thin irregular layer, an inner cortical layer, a matrix layer, a striated layer and a fibril layer. Interposed between the inner cortex and matrix were two transverse fibres.

The region between the fibril layers and the contractile part of the muscle cells was occupied by the hypodermis, which enlarged to form the dorsal, ventral and lateral cords. Within the cords lay hypodermal cells, nerves, crystalline inclusions and an excretory canal.

The sarcoplasmic part of the muscle cells was rich in glycogen and contained numerous mitochondria. Myofibrils of two types were present in the contractile part of the cell.

I am grateful to Dr D. W. Brocklesby for his help and advice and to Mr E. Harness for the production and supply of third-stage larvae. I would also like to thank Dr D. L. Lee and Mr W. G. MacMillan for helpful discussions.

Leucocytozoon sakharoffi of English rooks (Corvus f. frugilegus) underwent sporogony in female Simulium (Eusimulium) angustitarse, the cycle taking 3–4 days. Sporozoites from the salivary glands of S. angustitarse, both naturally and experimentally infected, gave rise to L. sakharoffi infections when injected to aparasitaemic rooks, with a minimum pre-patent period of 8 days.

I am very grateful to the following persons, for invaluable help in many ways: Mr C. Swan and Mr A. Ponchaud (Ministry of Agriculture, Fisheries and Food); Dr J. Ash, Mr N. A. Wood and Mr M. Holland (Game Research Association); Mr N. A. Hancock (Smith, Kline and French); Mr N. Biddlecombe (Breamore Estate); Dr L. Davies (Durham University); Professor D. S. Bertram, Mr E. J. Blackie, Miss L. Selden, Miss J. Freeman and Mr P. Mellor (London School of Hygiene and Tropical Medicine).

This work was generously supported by a grant from the Natural Environment Research Council.

The first marsupial demodicid, Demodex antechini, is described with notes on its life cycle, sexual dimorphism and pathology. This species is remarkably similar except for the marked sexual dimorphism, to demodicids of eutherian mammals. This suggests an early origin and a long evolutionary history of parallelism within the genus.

Our thanks to Patricia Woolley, Waite Agricultural Institute, Glen Osmond, Australia, for the specimens used in preparing this paper. We would also like to thank Clifford Desch for the photography and the drawings. The work reported here was supported in part by NSF Grant (GB-3516).

Fertilization phenomena has been observed in the malaria parasite of the Himalayan Flying Squirrel with blood showing heavy infection. The blood was obtained on the slide, put in the moist chamber, dried and stained. Two types of microgametes could be distinguished. One of these two types were found in various stages of the process of fertilization. More than one microgamete were often found to take part in fertilizing a single macrogamete. This is the first recorded case of polyspermy in malaria parasites.

Thanks are due to Mr Nandalal Pau for his help in preparing the Plate incorporated in this paper.

This investigation received financial support from the World Health Organization.

Some factors affecting the suceptibility of chick embryos to E. tenella infection have been examined. An incubation temperature of 41 °C was found to be more suitable for the development of the parasite than 38 or 39 °C. At the higher temperature development of schizonts was more rapid and mortality caused by the parasite occurred earlier and was substantially greater. Mortality, caused by E. tenella, was dose related and doses between 15000 and 45000 sporozoites produced 100 % mortality in embryos incubated at 41 °C.

There were differences in the susceptibility of three strains of W.L. embryos to E. tenella infection; ‘S’ strain W.L. embryos were more susceptible than either ‘C’ or ‘K’ strains. However, the susceptibility was not evident in hatched chickens of the ‘S’ strain.

Two laboratory strains of E. tenella (‘W’, ‘H’) were shown to produce different mortality levels in embryos; the ‘W’ strain was markedly more virulent, perhaps because schizonts of the 2nd generation matured more rapidly in both embryos and chickens inoculated with this strain of E. tenella.

I wish to thank Dr R. K. Cole of Cornell University for making three strains of W.L. embryos available to me for this work. I also wish to thank the Governing Body of the Houghton Poultry Research Station; the Agricultural Research Council and the Avian Diseases Department of Cornell University for making it possible for me to undertake a substantial part of this work at that University in 1968. Grateful thanks are due to Dr P. P. Levine, D. L'Amoreaux and M. S. Shirley for their help at various stages of the work.

Rabbits and mice, but not sheep, guinea-pigs or rats, were suitable hosts for secondary echinococcosis using protoscoleces obtained from Australian sheep. The host specificity is tentatively related to the phylogenetic relationship between the donor host and receptor host.

The development rate of hydatid cysts in mice is described in terms of increase in fresh weight, dry weight, and maximum cyst diameter. Fertile cysts were found after 8 months when the water content of the cysts had increased to more than 95 %. The diameter of fertile cysts up to 14 months ranged from 6 to 30 mm. By 14 months, the average fresh weight of cysts was greater than the body weight of the mice.

This work was carried out during the tenure of an Australian Wool Board Senior Postgraduate Scholarship, and forms part of a thesis to be presented for the degree of Doctor of Philosophy of the Australian National University.

I wish to thank my supervisor, Professor J. D. Smyth, for guidance and criticism.

A description is given of some features of the embryonic development, the structure of the oncomiracidium and the postlarval development of R. emarginata, a hexabothriid parasite on the gills of Raia clavata.

There are three phases in the larval development of the haptor of Rajonchocotyle: an oncomiracidial or marginal hook stage, a hamulus stage and a sucker stage. Neither the embryo nor the oncomiracidium ever possesses more than five pairs of marginal hooks and marginal hooks I (the posterior-most pair) are considered to be missing. The marginal hooks develop within distinct binucleate oncoblasts. During the early stages of post-oncomiracidial growth the secondary attachment organs of the haptor are formed and it is only after the completion of the development of the haptor that the reproductive organs begin to appear. Firstly, a pair of hamuli is acquired, followed by four pairs of suckers, which form in posterior-anterior succession at the site of marginal hooks III-VI. The first pair of suckers remains unarmed while the other three pairs acquire hooked sclerites and become the main functional attachment organs of the adult. As the first pair of suckers appears the posterior part of the haptor lengthens to form a caudal appendage. Hexabothriids are considered to show closer affinity to the 8-suckered chimaericolids and diclidophorids than to the 6-suckered polysto-matids, the unarmed suckers representing a simplification, by loss of the sclerite and reduction in sucker size, of an originally armed sucker.

I would like to express my thanks to Dr J. Llewellyn for his interest and for much helpful discussion.

Thanks are also due to the Director and Staff of the Marine Biological Association at Plymouth, in particular Mr J. E. Green for material and assistance, and to Dr A.j Brinkmann, of the Department of Zoology, University of Bergen, for supplying specimens of Squalonchocotyle borealis.