The distribution of glycogen has been studied in P. minutus by means of histochemical methods. The strongest staining for glycogen was detected in the proboscis, the radial layer of the body wall and the non-contractile parts of the muscles.

Histochemical methods have also been used to study the localization of the activity of ten oxidoreductase enzymes. The enzymes are situated in the mitochondria of P. minutus, the distribution of which corresponds closely with that of glycogen.

I am grateful to Dr P. Tate for helpful discussions, and to Drs D. L. Lee and F. P. B. Wooding for criticizing the manuscript. Thanks are also due to Mr D. Barnard for technical assistance.

The rate of development of sterile 2nd-instar beet eelworm (Heterodera schachtii Schm.) larvae to the adult stage on excised sterile roots of sugar beet (Beta vulgaris L.) was studied.

Culture methods were as previously described (Moriarty, 1964). Sterile excised sugar-beet roots were placed on White's medium gelled with 0·75 % agar, inoculated with about 0·1 ml of an aqueous suspension containing several hundred sterile 2nd-instar eelworm larvae, and kept at 25 ± 0·5 °C. After 24 h the roots were transferred to liquid White's medium. Two roots were stained in acid fuchsin lactophenol (Goodey, 1963) every 24 h, for 19 days. Later, the length of main root axis and total length of laterals were measured, the number of laterals counted, the eelworms dissected out and the larval instars identified (Raski, 1950).

When roots were removed for staining, the liquid medium was examined for eelworms. Only adult males were ever found, and these are included in the counts in Table 1.

The rate of development of larvae varied greatly, about half did not develop beyond the 2nd instar (Table 1) and from the fifth day onwards some atrophied. One root in which many adults developed was kept 41 days before killing and staining: there were still some 2nd-instar larval cuticles, devoid of contents except for the buccal stylet, and presumably dead. The average number of all instars found per root did not decline during the 19 days of observations: therefore few of the atrophying larvae could have been missed. The percentage of larvae that entered the roots was variable and small.

The cuticle of adults of Nippostrongylus brasiliensis has been described using histological, histochemical and ultrastructural techniques.

The cuticle has the following layers: an outer triple-layered membrane; a single cortical layer; a fluid-filled layer which is traversed by numerous collagen fibrils; struts which support the fourteen longitudinal ridges of the cuticle and which are suspended by collagen fibrils in the fluid-filled layer; two fibre layers, each layer apparently containing three layers of fibres; and a basement lamella.

The fluid-filled layer contains haemoglobin and esterase.

The muscles of the body wall are attached to either the basement lamella or to the fibre layers of the cuticle.

The mitochondria of the hypodermis are of normal appearance.

The longitudinal ridges of the cuticle appear to abrade the microvilli of the intestinal cells of the host.

Possible functions of the cuticle are discussed.

I wish to thank Dr P. Tate, in whose department this work was done, for helpful suggestions and criticism at all stages of this work, and Mr A. Page for technical assistance. I also wish to thank Professor Boyd for permission to use the electron microscope in the Department of Anatomy.

Immunity to N. brasiliensis in rats is stimulated primarily by the adult worms. An initial infection consisting solely of adult worms terminated at the same time as an infection consisting of all the parasitic stages.

Immunity is not stage specific. Immunity stimulated by adult worms acts not only on adult stages inhibiting their reproduction but also inhibits the development to maturity of larvae in a challenge infection.

Rats infected solely with female adult worms, whether egg producing or sterile, are more resistant to reinfection than rats infected with male worms only.

Immunity stimulated by a single normal infection lasts a long time but it does not depend on the persistence of adult worms in the intestine of the rats.

This work was done during the tenure of a Commonwealth Scholarship awarded by the Association of Commonwealth Universities.

Acquired resistance to some nematode parasites can be suppressed by daily administration of cortisone acetate to the host. Cortisone treatment completely suppressed previously acquired resistance of mice to Trichinella spiralis (Coker, 1956) and suppressed, at least partially, the acquisition of resistance to T. spiralis by rats during initial infection (Markell & Lewis, 1957).

A previous report (Weinstein, 1955) suggested cortisone acetate treatment was less effective in the suppression of acquired resistance of rats to Nippostrongylus brasiliensis. Weinstein showed that daily treatment with 2 mg cortisone acetate throughout five immunizing infections and continued during the challenge infection increased the number of worms in the intestine and had a marked effect on the cellular response in the skin and lungs. However, there was no significant effect when daily cortisone treatment commenced only on the fifth day before the challenge infection. This result suggested that acquisition of immunity to N. brasiliensis was partially overcome by cortisone treatment, but the same level of drug treatment had no effect on immunity already acquired.

In the experiments reported here, previously acquired resistance to N. brasiliensis was suppressed completely and the initiation of immunity stopped, either completely or at a very early stage, by treatment with the cortisone derivatives prednisolone or betamethasone. The complete suspension of all manifestations of acquired resistance obtained by treatment with these drugs was used to investigate the fate of larvae migrating in an immune host.

The rats and strain of parasite, and the methods of handling them, have been described previously (Ogilvie, 1965).

Female mice survived longer than male mice when infected with 400 eggs but not when infected with 100 eggs of Amplicaecum robertsi.

The larvae grew to greater lengths in young than in older mice; smaller worm burdens were also found in the older animals.

The growth of the larva was associated with the total worm burden of the host. As the worm burdens, of 40-day-old female mice, increased up to 281 individuals the length of the larvae attained after 14 days decreased; when the larval population increased above this number the lengths of the worms also increased.

These crowding effects are discussed in relation to competition for nutrients, immunological suppression of larval growth and to the ability of large larval populations to swamp the resistance mechanisms of the host. It is suggested that the increased growth of the larvae in large populations is due to their ability to break down the liver of the infected host more efficiently than small populations. However, this eventually leads to the deaths of the host through total liver breakdown.

This work was done during the tenure of a Senior Research Fellowship from the Wool Research Board of Australia. My best thanks are due to Mr J. James for his assistance with the statistics, to Professor J. F. A. Sprent for his help and advice and to Mr C. Wilkinson for his assistance.

When rats infected with Moniliformis dubius were dosed orally with labelled sodium phosphate considerable quantities of 32P were found to have been absorbed by the gut-mucosa of the rats and the tissues of the parasites. When the rats were dosed intraperitoneally considerable quantities of 32P were found in the gut-mucosa of the rats but only small quantities in the tissues of the parasites. Similar results were obtained when the experiment was repeated using labelled L-leucine 14C in place of the phosphate and estimating 14C in place of 32P.

The available evidence indicates that M. dubius depends for some of its food-requirements on the contents of the gut of its host rather than on the tissues of its host.

Preliminary experiments showed that the rate of uptake of L-leucine 14C by M. dubius in vitro was decreased if one of the following amino acids were present: DL-valine, DL-serine or DL-methionine.

The author wishes to thank the Department of Biochemistry of the University of Adelaide for the assistance given to him with the experiments on the estimation of 14C.

Two groups of sheep born and raised worm-free were dosed with 3000 infective Haemonchus contortus larvae. Group 1 were each given a single dose of infective larvae on day 0 while the group 3 animals were dosed with 100 infective larvae per day for 30 consecutive days. The results of faecal worm-egg counts performed on alternative days, and of differential worm counts carried out on animals slaughtered at crucial times during the course of infection, showed that retardation of development at the 4th larval stage occurred in the group 3 infections and was the major effect of control of the parasitic burden. There was no evidence that egg production per female was affected.

Three animals of the nineteen infected in group 1 died during the course of the experiment owing to the pathogenic effects of the worm burden. Deaths did not occur among the animals of group 3. This finding was correlated with the observation that haematocrit levels were consistently lower among the animals of group 1 than among those of group 3.

The results are interpreted in terms of the theory of threshold behaviour of the immunological response to parasitic infection.

We are greatly indebted to Dr D. F. Stewart for his interest and constructive criticism during the course of these studies, and to Mr E. Teleki and Misses Helen Giller and Lindy Stothart for their valuable technical assistance.

The study involved observations of only the macroscopically visible forms (immature and mature adults) of the parasite Labiostrongylus longispicularis (Wood) in the stomachs of Red Kangaroos, Megaleia rufa (Desmarest).

The large size of the worm (females 30–60 mm long and males 25–40 mm) facilitated the study.

The life-cycle of the species is not yet known but some information is given on the hatching of eggs, survival of larvae, and the results of experimental infections of rabbits.

Reproducing adult worms were found in samples of kangaroos from two geographically widely separated areas only during the period March–August, namely autumn and winter in Australia. During this period immature macroscopically visible forms were absent or present only in very small numbers. The size of the immature adults increased gradually from August onwards.

The proportion of female worms in the samples averaged 71% in those containing immature forms and 74% in samples containing only mature worms.

The relationship between weight and length of worms at different stages of development was determined. Male and female worms differed both in size and rate of growth.

The level of infection with immature and reproducing adult worms was correlated with the length of tibia of the host. Kangaroos approximately 18 months old with tibia approximately 400 mm long were infected on average with 3000 immature or 150 mature worms, while kangaroos with tibia 480 mm long carried on average twenty immature or three mature worms.

The reduction in the mean level of infection with increasing age (tibia length) was found to be statistically greater for immature than for mature worms.

Seasonal variations in the relation between the length and weight of the worms and the age of the host were demonstrated and a possible connexion with physiological changes within the parasite was suggested.

The age of the host had the strongest negative effect upon the growth rate of the worms at the time when marked increase in the weight of worms, particularly females, took place.

Thanks are due to Mr G. A. McIntyre of the Division of Mathematical Statistics, C.S.I.R.O., Dr J. D. Dunsmore and Mr B. V. Fennessy of the Division of Wildlife Research, Mr P. I. Sommerville of the Division of Animal Health, McMaster Laboratory, C.S.I.R.O., and Dr W. L. Nicholas of the Australian National University, Canberra, for reading and criticizing the manuscript. Messrs E. R. Hesterman and C. Kogon of the Division of Wildlife Research provided valuable technical assistance.

Observations are described on Polymorphus minutus in its final and intermediate hosts from a wildfowl reserve in Kent. The appearance of the parasite in the reserve followed the alteration of the course of the River Darent, an operation which created a suitable habitat for the intermediate host, Gammarus pulex.

The parasite has been found to occupy the same region of the intestine in the Mallard as in domestic ducks, but it occupies a more anterior region in the Tufted Duck. Worms of varying age have been shown to be present in natural infections of wildfowl.

P. minutus and a cestode, Dicranotaenia coronula, appear to compete for attachment sites in the intestine of Mallard. This competition may be a factor which causes the attachment zone of P. minutus to be extended anteriorly.

The presence of the parasite in the reserve appears to be causing the population of G. pulex to decrease.

It is suggested from the observations made on the birds of the reserve, from the results of infecting domestic ducks and from a consideration of the list of final hosts of the parasite, that there exist strains of P. minutus, adapted to development in different species of birds.

We wish to thank Dr P. Tate for helpful discussions, and Dr I. C. Williams, Department of Zoology, University of Hull, for the identification of the cestodes and criticism of the manuscript. Thanks are also due to Drs J. M. and D. L. Harrison, Mr G. Wallis and Mr A. Meikle for assistance with the population studies and the collection of some of the material.

The Oxyuridae parasitic in Primates have a restricted host range with, in the wild, one species of parasite characteristic of one genus of host (Inglis, 1961). Under such conditions one would expect the hosts and their parasites to show parallel evolutionary trends. While this is not established in detail there is a broad correlation between the trends that can be established in the morphology of the parasites and the phylogenies of the hosts (Inglis, 1965).

Recently some parasites were reported which suggested that the Hapalidae could be considered primitive monkeys of the superfamily Ceboidea rather than specialized (Inglis & Dunn, 1964), but it was then stressed that, because few parasite records were available, the suggestion must be tentative. However, two further samples of pin-worms from Hapalidae have now become available which also support this suggestion. One sample is from Oedipomidas oedipus (reported by Menschel & Stroh (1963) as Enterobius minutus) and the other is from Callimico goeldii. Both samples represent new species which are described below.

The specimens from C. goeldii are particularly interesting because they represent a species which is clearly con-generic with those from the Hapalidae that have been studied. This suggests that Callimico should be referred to the family Hapalidae rather than to the family Cebidae or even, as is suggested by some authors, to a distinct family Callimiconidae.

Both the new species are referable to the genus Trypanoxyuris and the opportunity is taken to publish an illustration of the lateral view of the male tail of Trypanoxyuris callithricis (Fig. 1).

Rhabdostyla elongata sp.nov. is described and figured. This peritrich was found as an epibiont on Lernaea barnimiana, a copepod parasitic on the Nile Perch, Lates niloticus in Lake Albert.

Epistylis articulata Fromentel is recorded as an epibiont of Dolops and Argulus, which parasitize a wide range of fish in Lake Albert.

My thanks are due to Mr M. J. Holden who identified the fish as they were removed from the nets, and to Dr G. Fryer, who identified Lernaea barnimiana and has helped with the literature. I am also grateful for a grant from the Leverhulme Trust which made possible the collection of this material.

The distribution of two stages of the nematode Labiostrongylus longispicularis (Wood) in thirty-eight stomachs of the Red Kangaroo, Megaleia rufa (Desmarest) has been analysed statistically.

A quadratic regression was used where y = log of mean worm densities of stomach sections + 1 and x = numerical values of the mid-positions of the sections. The analysis revealed significant maxima in the proximity of the cardiac region. The maxima in stomachs with relatively large numbers of worms were found to be further away from the pylorus than in the stomachs with small numbers of worms. The mean maximum densities were about fifty worms per 100 g of stomach content in highly infected animals and about eight in low infections. It is suggested that freshly chewed food or saliva may be a factor regulating the distribution of worms.

The parasite was absent from the stomach's pyloric region where the pH is low.

Sex and size of the worm were independent of its position in the stomach.

The average number of eggs per adult female in the different stomach sections roughly corresponded to the density of worms in these sections, but the sample material was inadequate to show that this relationship was statistically significant.

The mean number of fertilized eggs per female worm was 3300.

Thanks are due to Professor E. J. Williams of the University of Melbourne and Mr B. V. Fennessy of the Division of Wildlife Research, C.S.I.R.O., for reading and criticizing the manuscript, and to Messrs E. R. Hesterman and C. Kogon for technical assistance.

The body wall of Polymorphus minutus has been studied with the electron microscope and the structure of the various layers has been described.

The layers are the same in number as those seen with the light microscope, and pores have been found which penetrate the cuticle. Thus, the structure of the surface layers is such as would facilitate the absorption of nutrients.

It has been found that the cuticle and striped layer extend over the trunk spines, a feature which increases the area of the absorptive surface of the parasite.

The structure of the striped layer of the praesoma supports the theory that the praesoma body wall and lemnisci are involved in the absorption of fat.

Mitochondria have been detected in the felt and radial layers of the body wall and in the circular and longitudinal muscles.

The body wall of this acanthocephalan worm is entirely different from the body wall of trematodes, cestodes and parasitic nematodes.

We are grateful to Dr P. Tate for helpful discussions, Dr R. J. Skaer for criticism of the manuscript and to Professor J. D. Boyd for permission to use the electron microscope in the Department of Anatomy. Thanks are also due to Mr A. J. Page for technical assistance.

The specific composition of the parasitic helminth fauna of wild ruminants in Britain has not been examined for 30 years, and the series of surveys to be described were undertaken to provide data on this aspect of helminth epidemiology. With the increase in interest in conservation of wild stock, and especially ruminants, in recent years, information on the epidemiology of their helminth infections is an essential adjunct to any schemes for their protection and husbandry.

The common roe deer, Capreolus capreolus capreolus, is distributed throughout Europe and Asia, the other subspecies, G. c. pygargus, the Siberian roe, G. c. bedfordi, the Manchurian roe, and C. c. melanotis, the Szechwan roe, being limited in range. It is indigenous to Britain, and over the centuries its populations have undergone great numerical fluctuations. Though at one time nearly extinct in England except in the counties on the Scottish marches it appears at present to be in a period of resurgence, and the range is extending from dense foci in the south and south-east to join the northern population. It has always been numerous in mainland Scotland and a few of the Western Isles, but is extinct in Wales and Ireland (Whitehead, 1964). The roe is the smallest of our indigenous deer and differs from the others in its breeding habits, not forming herds, but grouping as family units of buck, doe and offspring. On the mainland of Europe, however, herding does take place, and a limited migration has even been observed in Russian roe (Flerov, 1952). Its habitat is essentially woodland, but it grazes open areas to some extent and, not-withstanding its timid character, lives in close proximity to man in agricultural and even in urban areas.

The free-living larval stages of Bunostomum trigonocephalum are better adapted to low temperatures than high temperatures. Most survived at 10°C.

In tap water, 1st-stage larvae survived for 11 days at 0°C, 17 days at 5°C, 20 days at 10°C, 15 days at 15°C, 18 days at 20°C, 15 days at 25°C, 9 days at 30°C, 7 days at 34°C, 4 days at 35°C, 16 h at 40°C, 40 min at 45°C and 20 min at 50°C.

In tap water infective larvae survived for 40 days at 0°C, 70 days at 5°C, 100 days at 10 and 15°C. 65 days at 20°C, 48 days at 25°C, 38 days at 30°C, 14 days at 34°C, 6 days at 35°C, 5 days at 40°C, 3 h at 45°C and 105 min at 50°C.

In tap water at room temperature infective larvae survived for 26 days in January, 20 days in February, 21 days in March, 13 days in April, 10 days in May, 6 days in June, 9 days in July and August, 11 days in September, 12 days in October, 14 days in November and 17 days in December.

I thank Professor M. B. Lal for his interest and for providing laboratory facilities in the Department of Zoology, University of Lucknow; Dr Premvati for guidance; and the Scientific Research Committee, U.P., India, for financial help.

Cells of six isolates of Trypanosoma lewisi from the United States, England, Puerto Rico, Costa Rica, and Singapore were matched against antiserum to the ‘L’ isolate in microagglutinin chambers. Antisera were prepared in Sprague-Dawley rats. Serum protein determinations were made by the biuret reaction; electrophoretic fractionations of serum proteins were done with a semi-closed horizontal system (Evans & Stirewalt, 1947) at 4°C for 24 h, 120 V, and 8 mA with paper strips. Electrolyte was veronal buffer, pH 8·6 and μ 0·058. Agglutinin absorptions were carried out using inactivated anti-‘L’ sera.

Total protein (mg/ml) values were higher in all infected animals (60 vs. 54). Albumin values (%) were higher in controls (47 vs. 40);α-1 fractions were essentially unchanged (15%) as were α-2 values (6%). β Fractions were elevated in infected groups (21 vs. 17%), as were the γ globulins (19 vs. 12%).

Three protocols employing agglutinin reactions were completed. In two protocols 3+ agglutinin end-points were obtained with four isolates using 1·45–1·47 μg of immune γ globulin. Two of the isolates (Puerto Rico and Singapore) required 10 times this amount of immune globulin for the same end-point. In two other tests all isolates gave reaction end-points that required greater quantities (by a factor of ca. 500) of immune γ globulin than obtained in the first two tests, and there was further evidence that the Costa Rican isolate was quantitatively different from the others. These facts are interpreted to mean that all six geographic isolates show close qualitative relationships to each other, but that the relationships for the Puerto Rican, Singapore and Costa Rican isolates are quantitatively different. Agglutinins could not be absorbed from immune serum by any of the cells.

Periodicity of occurrence in the final host has been observed in only a few of the known Acanthocephala of fish (Van Cleave, 1916; Steinstrasser, 1936; Komarova, 1950; Shulman & Shulman-Albova, 1953). The periodicity appears to be due to the simultaneous operation of a complex of physiological, developmental and ecological factors.

In the present investigation a detailed study has been made of both the occurrence and the developmental cycle of Echinorhynchus truttae in its hosts in a small trout stream, Afon Terrig, in North Wales. An attempt has also been made to ascertain to what extent some of the various and varying ecological and physiological factors influenced the incidence, degree of parasitization and the development of the worm in nature.

Samples of the intermediate host, Gammarus pulex pulex L., and the final host the brown trout, Salmo trutta L., were taken monthly at three points or stations where the stream was readily accessible. Station I was at Rhydtalog as far upstream as practicable. Station III was at the opposite end of the stream near Caegwydd and station II was about mid-way between the other two sampling points. To ensure that each host sample was examined in as fresh a condition as possible, autopsy of the intermediate host was completed before the definitive host was taken.

Within the first week of each month from November 1961 to January 1963, shrimps were taken from over a stretch of about 30 m at each station.