Nine hundred and five brown trout were collected from the River Teify, West Wales, over a period of 12 months and their helminth infestations are considered in relation to the age and sex of the host and season.

Only one statistically significant difference could be detected between levels of infestation in male and female trout of 1 and 2 years of age.

When trout of 3 years of age and over were spawning or recovering from the effects of spawning there is a tendency for sexually mature females to be more heavily infested with some parasites than the males. During the season of growth and maturation of the gonads this trend was reversed or became less marked. In the case of fish that were not spent or spawning the statistically significant differences showed the males to be more heavily infested than the females.

The possible reasons for these variations are discussed with particular reference to the roles of ‘physiological’ and ‘behavioural’ or ecological resistance'.

1. A detailed description, with illustrations, is given, of the sequences in development and maturation of the genitalia in Tetrabothrius erostris. This is the first such account of any member of the new order Tetrabothridea.

2. The effect of the very marked protandry on the form of the remainder of the genitalia is discussed.

3. Attention is drawn to the unusual ovary which produces sclerotin and which it is proposed to call a ‘calycal-ovarium’.

4. Comparison is made of the embryophore with that of the Cyclophyllidea. There is a suggestion that the embryophore may be formed of sclerotin in T. erostris.

5. Par-uterine vesicles have been described for the first time in any member of the Tetrabothridea. These vesicles arise from the uterine primordium and have previously been confused with testes.

6. The complex affinities of the order Tetrabothridea are discussed and some support arises for the creation of this new order.

One diphyllidean and five tetraphyllidean cestodes from Australian elasmobranchs are described and figured. Echinobothrium heroniensis sp.nov., from Himantura granulata (Macleay, 1883) possesses two groups each of 42 apical hooks, eight rows each of 25 hooks on the cephalic peduncle and ten testes in each proglottid. In Anthobothrium sexorchidum sp.nov. from T. lymna (Forskal, 1775) there are only six testes and the bothridium is irregularly divided into a number of shallow areolae while in Rhinebothrium himanturi sp.nov. from Himantura granulata there are 22 proglottids, 52 loculi and 19–20 testes. Comments are made on the taxonomy of Rhinebothrium sp., Spiniloculus mavensis and Yorkeria parva. The value of some helminths, especially cestodes from elasmobranchs, as an aid to the study of the taxonomy, biology and zoogeography of their hosts is briefly discussed with reference to some previous papers on this topic. Previous work on the cestodes of Australasian marine fishes is summarized briefly.

1. The distribution of acid and alkaline phosphatases in the hepatopancreatic cells of the molluscan host of Echinoparyphium sp. and in the redia and cercaria of this trematode has been studied.

2. There is a heavier concentration of acid phosphatase in the hepatopancreas of infected snails than in uninfected snails.

3. No acid phosphatase is present in the bodies of the rediae or cercariae but this enzyme is present in the contents of the redial caeca.

4. Alkaline phosphatase activity is greater in the hepatopancreas of infected snails than in uninfected snails.

5. Alkaline phosphatase is present in the tissues of the rediae and the cercariae, especially in the fully developed cercariae.

6. It is suspected that the increase in acid and alkaline phosphatases in Helisoma trivolvis infected with Echinoparyphium redia is correlated with the breakdown of glycogen by the parasite.

This research was made possible by Grants E-3443, E-3443C1, and AI 3443–03 from the Institute of Allergy and Infectious Diseases, National Institutes of Health, U.S. Public Health Service. The author is grateful to Mr Randall W. Snyder, Jr., School of Medicine, The University of Virginia, for technical assistance.

Observations are reported on the fluctuations in populations of gastro-intestinal nematode parasites in 68 calves on two dairy farms in Fiji based on fortnightly faecal worm egg counts over a 3-year period. On one of the farms the calves began to graze soon after birth; on the other farm they were reared indoors until they were weaned at 6 months of age.

The important species were Cooperia spp., Bunostomum phlebotomum, Haemonchus placei, H. similis and Oesophagostomum radiatum. Only small numbers of Trichostrongylus spp., Mecistocirrus digitatus and Neoascaris vitulorum were present.

Potentially pathogenic worm burdens were only found in young cattle, mostly between 2 and 15 months of age. Faecal egg counts for each parasite species rose independently to a peak and then declined to low levels. For most species there was a close relationship between the time at which the peak faecal egg count occurred and the age of calves on the same farm, irrespective of the season in which the calves began to graze. This is considered to be due to the high rainfall and constant high temperatures throughout the year resulting in at least minimal favourable conditions for the development and survival of the pre-parasitic stages of all species in all months of the year. It is concluded that the succession of species which occurred must be strongly influenced by intrinsic factors in the life-history of each parasite.

Tere were differences in the levels of peak egg counts between groups of calves which began to graze in different seasons but almost all parasite species examined were affected equally. The lowest levels were recorded in calves which were first exposed continuously to infection at the beginning of the dry season and the highest levels in those exposed at the beginning of the wet season.

Protection of calves from parasite infection, by indoor rearing until weaning at 6 months of age, did not confer any striking advantage as the acquisition of potentially pathogenic worm burdens was merely delayed.

The results are discussed in the light of recent theoretical concepts regarding the immunological control of helminth parasite infection.

I am indebted to Mr A. E. Harness of Wainivesi for permitting observations to be made on his dairy farm, to Deo Raj Singh and Ram Kumar for technical assistance, and to Dr D. F. Stewart and Dr J. K. Dineen of the McMaster Laboratory for their criticism of the manuscript. My thanks are due to Miss Suzanne Dodd and Mr I. T. Roper of the McMaster Laboratory for the preparation of the figures. The permission of the Director of Agriculture, Fiji, to publish this paper is gratefully acknowledged.

1. The different lipid fractions in Gastrothylax crumenifer after starvation for 8–10 hr. have been estimated.

2. The percentages of different fractions in the total ether extract were found to be: acetone-insoluble material 16, unsaponifiable matter 25, saturated fatty acids 5, unsaturated fatty acids 20, glycerol 2 and unidentified lipids 32.

3. The above percentages of lipid fractions have been compared with the corresponding data for different parasites obtained by other workers.

1. The exrectory system of Anoplocephala perfoliata has been re-described and shown to consist of a dorsal ‘network’ system of vessels to which the flame cells are connected and a ventral pair of longitudinal vessels linked only by a transverse vessel in each proglottid.

2. The two excretory systems unite only in the apical ramifying vessels of the scolex.

3. Alkaline phosphatase activity was demonstrated in the cuticular microvilli, the subcuticular region and in the excretory vessels.

4. Non-specific esterase, insensitive to 10−4m E 600, was located in the lappets and embryonated eggs and esterases, inhibited by 10−4m E600, in parts of the cuticle and subcuticular region and parenchyma.

5. Cholinesterases were found in the nervous system and in the reproductive ducts.

6. Aminopeptidase was found in the neck region, in the undifferentiated proglottids, the active testes and ovaries, the male reproductive ducts and in the region of high metabolic activity in the fringe of the proglottid.

The structure of the spores of Encephalitozoon cuniculi Levaditi, Nicolau & Schoen, 1923, shows that it belongs to the Order Microsporidia Balbiani, 1882 and that the genus Encephalitozoon is a synonym for the older Nosema Nägeli, 1857. Therefore, the species of Microsporidia described from mammals are now: Nosema cuniculi (Levaditi, Nicolau & Schoen, 1923), Nosema rabiei (Manouelian & Viala, 1924) and Nosema chagasi (Torres, 1927). Another microsporidian in mammals is Thelohania apodemi (Doby, Jeannes & Rault, 1963).

The perch was the principal host for the plerocercoid of Triaenophorus nodulosus in Llyn Tegid.

Three stages of plerocercoid development were recognized: non-encapsuled developing plerocercoids, encapsuled but living mature plerocercoids, and dead encapsuled degenerate plerocercoids.

The stomach contents of the perch were analysed and planktonic crustaceans were found to be a significant part of the food from May to December. No change in diet in relation to length was found.

The period of occurrence of developing plerocercoids in the perch livers was March to June. This in relation to other evidence was shown to indicate the period of infection of the perch by the procercoids.

The three stages of plerocercoid development recognized were found to occur simultaneously in a few perch, and thus may represent infections acquired over three successive seasons.

There was no seasonal periodicity of occurrence of the plerocercoids in the perch.

All the perch examined were more or less equally infected by plerocercoids. There was no tendency for older, longer perch to be more heavily infected.

One to five capsules, normally containing one plerocercoid each, occurred in the livers of the infected perch.

For the perch examined there was a dynamic equilibrium between establishment of procercoids from the copepod host, and loss of plerocercoids by degeneration within the perch.

The mature plerocercoids form the reservoir of infection for the definitive host of T. nodulosus, the pike.

A method is described by which viable sporozoites of the sheep parasite, Eimeria arloingi, may be obtained in sterile solution and free of any extraneous vegetable matter. Faeces are washed through metal sieves and the oocysts separated by a gravity floatation technique. The oocysts are sterilized and floated free of any remaining faecal debris in a solution of sodium hypochlorite. Sporulation is induced by constant aeration in water. Excystation is effected by incubating firstly under an atmosphere of carbon dioxide and secondly in a solution of trypsin and sheep bile.

I wish to thank Professor H. R. Carne for encouragement and advice, and Mr R. F. Jones for skilful technical assistance.

A method is described for obtaining sterile second-instar larvae of beet eelworm, Heterodera schachtii Schm., and culturing them to the adult stage on sterile excised roots of sugar beet, Beta vulgaris L. It was shown that beet eelworm is a primary pathogen, for sound uninjured radicles were invaded by larvae, and normal development of adult males and females followed. No females were fertilized, and no eggs were produced, which suggested that parthenogenesis cannot occur. Eelworm development stimulated the production of lateral roots. More adult females developed on radicles inoculated 24 hr. after excision than on radicles inoculated 72 hr. after excision, which may be related to the occurrence of maximum root extension during the first few days after excision. It is suggested that there are two parts in root tissue reactions: a thickening of cell walls as a wound reaction to mechanical injury, and formation of a syncytium in response to a chemical stimulus from the eelworm.

I thank my wife for assistance with this work, which was financed by the Sugar Beet Research and Education Committee.

In the intestine of freshwater fishes, two morphologically different types of diplomastigine flagellates have so far been found to exist: Hexamita salmonis (Moore, 1920) specific for fishes, and Spironucleus elegans Lavier, 1936, identical with the flagellate from amphibia.

The identity of the Spironucleus from fishes and amphibia has been demonstrated by infecting Pterophyllum scalare with flagellates from newts per os, per rectum and with contaminated food.

A redescription of motile stages of both Hexamita salmonis and Spironucleus elegans is presented, together with a list of existing findings of fish diplomastigines, and a brief discussion.

The naturally oviposited egg of Dasymetra conferta is fully embryonated and it hatches only after it is ingested by the snail host, Physa spp.

Hatching appears to be in response to some stimulus supplied by the living snail. The stimulus causes the larva to exercise a characteristic series of body movements and to liberate a granular sustance (hatching enzyme) from the larger pair of its cephalic glands. This enzyme reacts with the vitelline fluid to create pressure within the egg capsule, and with the cementum of the operculum, so that it may be lifted away. The larva's escape from the shell, therefore, is due to a combination of pressure and body movements.

The hatched larva has a membranous body wall, supporting six epidermal plates, an apical papilla, two penetration glands and a central matrix (the presumptive brood mass).

It lives for about an hour within the snail and during this time there is a reorganization of the central matrix which terminates in the formation of an 8-nucleated syncytial brood mass.

The miracidial ‘case’, consisting of the body wall and the epidermal plates, ultimately ruptures to liberate the brood mass. Once the brood mass is free it penetrates through the gut wall in an incredibly short time.

1. Examination of dividing trophozoites of E. invadens revealed that the peripheral granules did not contribute directly to the formation of chromosomes. Material for the chromosomes seemed to be derived from the karyosome and the perikaryosomal particles. No centrioles and spindle mechanism were noticed.

2. The nucleus showed Feulgen-positive material at all stages; in the interphase the reaction was faint because of the poor staining of the karyosome and widely dispersed perikaryosomal particles. The intensity of the staining reaction increased with the onset of division and continued so till late anaphase.

3. Nuclear division in the cyst was found to be different from that of the trophozoites and involved the formation of a typical spindle.

4. Karyosomes of the nuclei of the uni-, bi-, tetra-nucleate cysts were all positive to Feulgen staining.

5. Observations on amoebae undergoing cytokinesis showed that the process of division supports the amoeboid movement theory of cleavage put forward by Chalkley (1935, 1951).

Thanks are due to Dr P. Tate for constant guidance and encouragement during the course of this work and to Dr E. W. McConnachie for kindly giving the cultures and for critically reading through the manuscript. The work was carried out during the tenure of a Royal Society and Nuffield Foundation Commonwealth Bursary.

Within recent years, problems of host-parasite relationships have been receiving increasing attention from parasitologists. This is particularly true in the study of the cestodes Echinococcus spp., where predilection for different hosts—when considered with the morphology of the adult and the growth and development of the larva—seemed sufficiently significant to lead to the establishment of the two species, E. granulosus and E. multilocularis. Much experimental and field work has been carried out on a variety of vertebrate hosts and a number of new, naturally infected and laboratory hosts have been reported. A survey of intermediate and definitive hosts has been undertaken in this laboratory as part of a study to investigate whether factors of morphological, physiological or biochemical origin were concerned in host specificity. These data, together with some genetical considerations, form the basis of the present paper.

1. Pipunculus semifumosus (Kowarz) is an internal parasite of a number of common British Delphacidae. The life cycle and immature stages of the parasite are described.

2. The external and internal effects of parasitism on the delphacid host are described. Reductions in size and genital aberrations are related to the stage at which the host is attacked, and are most marked in female delphacids.

Ciné film and direct observation showed that microphagous, plant and animal nematodes have the same basic wave pattern when moving. Their speed is linearly related to the product of their length and wave frequency during unrestricted movement in deep water. The speed, wave pattern and frequency of the plant nematode Ditylenchus dipsaci and the animal nematode Trichostrongylus colubriformis changed in a similar way in response to changes in water film thickness on the surface of agar of different concentrations. T. colubriformis like D. dipsaci were most mobile in a sand-water medium at a suction corresponding to the stage when most of the water has drained from the pores. The optimum temperature for activity of T. colubriformis and D. dipsaci was about 20° C. and both survived desiccation at 50% relative humidity and 24° C. for 32 days. T. colubriformis was attracted to and aggregated around grass roots (Phleum pratense). The results suggest that the free-living stages of microphagous, plant parasitic and animal parasitic nematodes move similarly and that nematodes can be divided arbitrarily into three groups: (1) those active enough to swim in deep water; (2) those able to swim in thick water films, escape from the soil and ascend plants above ground level; and (3) those too inactive to swim, the crawlers, which are largely confined to the soil. The habitat of free-living stages of nematodes, irrespective of their host or feeding habits, is probably related to their propulsive power.

We thank Dr D. Poynter for supplying the animal parasites used.

The incidence and prevalence of coccidia have been studied in populations of free-living red kangaroos, Megaleia rufa, and grey kangaroos, Macropus canguru, in four geographically distinct areas in Australia.

Two new species of Eimeria—E. wilcanniensis and E. toganmainensis—are described from M. rufa, and five—E. cunnamullensis, E. gungahlinensis, E. purchasei, E. kogoni, and E. hestermani—from M. canguru.

The incidence of coccidia ranged from 6 to 14% in populations of M. rufa and from 26 to 70% in M. canguru. The susceptibility of the animals to coccidia was analysed in relation to the tibia length. Red kangaroos with tibia approximately 360 mm. long and corresponding to an age of about 12 months were found to be most susceptible. No clinical cases of coccidiosis were seen in the field.

Special thanks are due to the owners or managers of the properties on which the kangaroos were sampled; to members of the staff of the Regional Pastoral Laboratory ‘Gilruth Plains’ for their assistance in sampling, and to Messrs E. R. Hesterman, C. Kogon, and D. Purchase, who assisted in the field and the laboratory. Three species of Eimeria have been named after them in acknowledgement of their work. Messrs B. V. Fennessy and J. H. Calaby of this Division kindly read the manuscript.

I wish to thank Dr G. B. Sharman for his permission to work with captive kangaroos in Canberra, and Mr E. Slater who took the photographs.

1. The mode of attachment of Echinococcus granulosus to the dog intestine was examined.

2. In an attached worm, the scolex was found to penetrate deeply into the crypts of Lieberkühn, with the rostellum fully extended, the hooks penetrating the epithelium lightly and each sucker holding a ‘plug’ of mucous cells in its cavity.

3. The expansion of the rostellar tip was aided by a muscular disk, the rostellar pad, which probably assists attachment by forcing the hooks outwards.

4. The epithelium in the region of the suckers showed eosinophilic reactions which may indicate a mild host reaction.

5. The existence of a small group of spindle-shaped secretory cells which form a rostellar gland, lying immediately anterior to the rostellar pad, is reported. This gland was found to be the source of secretion droplets seen to be released in vitro from the scolex region.

6. The secretion droplets were found to be exceptionally labile and not preserved in the rostellar gland cells by routine fixation methods. Prolonged fixation (5–12 months) in formol (7% formaldehyde) gave excellent preservation but globules were fairly well preserved after 3 months fixation. Fixation in Baker's formol-calcium for 2 weeks followed by controlled chromation was also found to retain the secretion reasonably well but not as adequately as the prolonged fixation.

7. The secretion was found to be negative to the PAS, bromo-phenol blue (with Hg), and ninhydrin-Schiff reactions. The areas adjacent to the globules gave a protein reaction and the periphery of the globules appeared dark by phase contrast microscopy.

8. The secretion was weakly positive to performic acid-Schiff and gave strong reactions with Sudan Black after controlled chromation, both in frozen and wax sections. These results suggest that the secretion may be a liproprotein or a lipid-protein coacervate but it is recognized that confirmation by biochemical methods is desirable.

9. The possible immunological implications of these results are discussed.

This work was supported by the Australian Wool Research Committee and the U.S. Public Health Service Grant No. E. 4707–02. The technical assistance of Mrs A. L. Warrener and Mr A. B. Howkins is gratefully acknowledged.