When sporozoites of E. necatrix or E. brunetti are injected into the caeca of coccidia-free chickens they penetrate the caecal epithelium and initiate life-cycles which are similar to those developing in the usual sites in the small intestine. Viable oocysts of E. necatrix are produced which can be sporulated and, when given to coccidia-free chickens, produce characteristic infections in the small intestine. Possible implications of this investigation are discussed.

A fourfold enhancement of resistance to diamino-diphenylsulphone has been produced over a period of 15 months in strain A of P. gallinaceum by subjecting the strain, maintained in a state of patent infection, to increasing doses of the drug.

The DDS-resistant strain was cross-resistant to the minimum effective dose of sulphadiazine and slightly resistant to twice this dose, but it showed only a slight enhancement of resistance to pyrimethamine and proguanil.

The antimalarial action of DDS was antagonized by p–A.B. in the ratio of 100 to 1. DDS, in the minimum effective dose, was antagonized completely by folic acid if given in equal doses, but not by smaller doses of the antagonist; the antagonism was not competitive.

The relationship of cross-resistance between p–A.B.-inhibited sulphonamides and proguanil and pyrimethamine is discussed.

Stream net samples in the Esk estuary reveal the infection, in winter, of the Gammarus zaddachi zaddachi Spooner, 1947 (Crustacea, Amphipoda) population alone with the plerocercoids of Diplocotyle sp. (Eucestoda, Spathebethriidea). Large plerocercoids are found in both sexes of the gammarids but the parasitized females are significantly larger than the non-infected ones and their fertility may be reduced.

I wish to express my thanks to Professor I. Chester-Jones of the University of Sheffield Department of Zoology in whose laboratories this work was carried out, and to Dr F. Segrove (of the same Department) for advice and constructive criticism.

A number of experiments was carried out on Polycercus lumbrici to induce evagination of the cysticercoid in vitro. The results indicate that in nature the containing cyst is ruptured by pressure and abrasion in the gizzard of the bird host and that evagination is induced mainly by the action of gastric juice followed by pancreatic juice, heat assisting the process by exciting vigorous movements in the larvae. By a process of elimination it has been shown that the effective agents are the pepsin in the gastric juice and pancreatin in the pancreatic juice. The latter probably causes contraction of the muscles of the wall of the caudal vesicle which forces out the scolex.

The development of Archigetes limnodrili in species of Limnodrilus is described. There is no free-living larva and eggs are ingested by the tubificids. Growth and development is completed within the body cavity of the annelid, and egg liberation is accomplished by release of the parasite and decay of its body.

Breeding of A. limnodrili takes place throughout the year. In the localities investigated there was no evidence that a fish host was required in the life-cycle. Progenesis was the only type of development encountered in Britain.

A. limnodrili exhibits an unusual degree of host specificity, being found only in species of Limnodrilus. It is suggested that this is due to differences in the composition of the coelom or intestine of Limnodrilus compared to other genera.

The degree of infection in all localities is very low, and shows no regular seasonal variation. There is no similarity in the seasonal changes in different localities.

The relationship between the host and parasite is a stable one, and there is little mutual damage. Factors contributing to this stability are discussed.

The development of A. limnodrili is compared with that of other species of Archigetes, and the life-history discussed with particular reference to the phenomenon of progenesis.

I wish to thank Professor R. J. Pumphrey in whose Department this work was carried out, and Dr J. C. Chubb for his constant advice and criticism. I also wish to thank Dr K. H. Mann and the University of Reading for provision of specimens and permitting me the use of their facilities. The work was carried out during the tenure of a Nature Conservancy Research Studentship.

Recent experimental work has indicated that species of Archigetes are capable of infecting and maturing in fishes in addition to tubificids.

The genus Archigetes is re-defined on the basis of morphological and biological characters, with particular emphasis on recent life history studies. All species capable of neotenic development have been re-united in a single genus.

A description of all species of Archigetes together with a key for their identification are included. New synonomies are discussed.

The relationship of Archigetes to other genera of the family is briefly considered, and it is concluded that it forms the terminal stage in a series showing the attainment of neotenic development.

I wish to thank Professor R. J. Pumphrey in whose Department the work was carried out, and Dr J. C. Chubb for advice and help in the preparation of this manuscript. I am also grateful to Professor K. Berg and Dr R. L. Calentine for the loan of specimens. The work was carried out during the tenure of a Nature Conservancy Research Studentship.

The dry weight and nitrogen content of Hymenolepis diminuta were studied after a period of 15 days‘ growth in rats receiving different diets. The special diets were fed during the last 7 days of this period, that is, while the major part of growth is occurring but before shedding proglottids.

Replacement of all the protein (casein) of the diet by carbohydrate resulted in greater development of the worm. However, replacement of casein by fat had no effect on worm development, indicating that removal of protein is not a significant factor, whereas addition of carbohydrate is effective.

Since exchange of casein by the nutritionally incomplete protein zein did not affect worm development significantly, protein quality appears not to be a factor in growth of H. diminuta.

The addition of tryptophan and lysine to the meal containing zein, in order to raise its nutritional value to that of casein, did not influence the growth of the parasite. However, the feeding of the same amounts of these two amino acids at times other than those of giving zein depressed the growth of the parasite. This was not due to type of protein (zein) fed in the rest of the diet, since a similar phenomenon occurs when casein is the dietary protein, or when a protein-free diet rich in carbohydrate is given. Addition of these amino acids, singly, either to diets containing protein or deficient in protein, had significant actions on worm growth, which was sometimes stimulated and in other circumstances reduced.

The nitrogen balance of the host was unaffected by the worm burden.

We are deeply indebted to Dr C. A. Hopkins for providing facilities, for infection of rats with the cestode, and for his helpful advice. Miss M. Cowan provided skilled technical assistance during the feeding of the animals and analysis of the host and parasite tissues. One of us (D.F.M.) gratefully acknowledges the Award of a Commonwealth Bursary from the Royal Society and the Nuffield Foundation.

The tegument of Proteocephalus pollanicoli is organized at two levels. The external level is a syncytial layer of protoplasm composed of vesicles in a granular matrix. The surface of this level has microvillus-like structure, microtriches, with sharp electron dense tips and less dense bases. Pinocytotic vesicles, large vacuoles, and evaginations occur at the surface of the external level, whereas mitochondria and lipid droplets tend to be concentrated basally. The basal plasma membrane has in some places small invaginations and at others large evaginations forming protoplasmic tubes which connect the external and internal levels.

The internal level is composed of individual areas of dense, granular protoplasm, each of which has a nucleus. These areas, or cuticular cells, contain lipid droplets, mitochondria, short lengths of agranular endoplasmic reticulum and phospholipid bodies. Two cuticular cells lying close together may be joined by a protoplasmic bridge and thereby form a limited syncytium.

The morphology of the tegument of this proteocephalid is compared with that of the cyclophyllidean species and the function of the tegument in parasitic helminths is discussed.

I should like to acknowledge the technical assistance of Mr W. Ferguson and Mr A. Lyness. My thanks are also due to the Wellcome Trust for a grant to purchase the Akashi Transcope and ancillary equipment.

Leptocotyle minor is a monogenean parasite specialized for living on the denticlecovered skin of the dogfish Scyliorhinus canicula. Each adult parasite attaches itself to the outer surface of a single denticle. Small postlarvae are found on the inner surfaces of the denticles. The denticles have hard enamel on both inner and outer exposed surfaces. Haptoral hooks, such as are present in other monogenean oncomiracidia, would be unable to penetrate this hard surface and are absent in postlarval and adult parasites which attach themselves by cement. The oncomiracidium possesses six haptoral spicules which may be homologues of the marginal hooks of other monogeneans, but these spicules disappear early in postoncomiracidial development.

Adult parasites feed on the host's epidermis which lies between the denticles. The position of small postlarvae on the inner surfaces of the denticles enables them to reach the epidermis for feeding purposes. Growth then permits young parasites to migrate away from the epidermis on to the outer surfaces of the denticles.

Adult parasites move from one denticle to another in a leech-like manner, and copulation occurs between parasites which meet as a result of these movements.

I am grateful to the Director and Staff of the Plymouth Laboratory for their hospitality and particularly to Mr J. E. Green for his interest and co-operation.

A short account of the biology and life-cycle of Diplostomum spathaceum is given.

The morphology of the forebody is described in some detail. The lappets are well developed and function as organs of attachment as well as being reservoirs for the secretion from the forebody gland cells. The adhesive organ is variable in form and the muscles facilitating the movements are described in detail. Pressure changes in the excretory system are thought to assist in evaginating the adhesive organ.

The histochemical tests gave the following results. The phosphatases present in the adhesive organ and the forebody gland cells are of the acid variety, the alkaline phosphatase is only present in the cuticle, traces of it occur in the lappets and forebody gland cells. No leucine aminopeptidase activity was observed. The esterase present is either a pseudocholinesterase or a non-specific B-esterase. The presence of RNA is confined to areas of enzyme formation.

The in vitro studies confirmed the absence of alkaline phosphatase and the presence of acid phosphatase and esterase in the forebody. They also showed a secretion of acid phosphatase and esterase to the exterior of the parasite.

Diplostomum spathaceum has very little effect on the host mucosa, but some lysis of the host tissues in contact with the forebody and especially the lappets, is observed. The response of the host to the parasite is likewise very small.

The source of nutrients for D. spathaceum is believed to be the contents of the host alimentary tract, host mucus secretions and to a small extent disintegrated host tissues.

I am very grateful to Dr D. A. Erasmus for advice and encouragement during this study and to Professor J. Brough for his interest and for provision of excellent working facilities. The work was conducted during the tenure of a Rotary Foundation Scholarship for International Understanding and a grant from Nylands Nation (Helsingfors, Finland).

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.

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.

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 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.

After penetrating through the body wall into the haemocoel of Bradysia paupera, the fertilized female of Tipius sciarae increased in size and slowly expelled the enlarging uterine cells through the vulva.

Within 7 days of penetration, the females were mature and began laying eggs into the haemocoel of the host. The eggs hatched in 3 days and, within 2 weeks, the host–s body was swarming with juvenile nematodes. The juveniles moulted three times in the body cavity of the host and 4th-stage forms emerged through ruptures in the intestine or body wall (in larval hosts) or were deposited on the surface of the soil (by adult female flies). They then moulted to adult forms while remaining ensheathed in their last juvenile cuticle, mated, and the fertilized infective females were ready to enter a new host.

Most parasitized fly larvae died before reaching the pupal stage but some emerged as adults, still carrying the nematodes within them. All parasitized adult flies were sterile. Infested larvae had smaller fat bodies and adult histoblasts than normal larvae and took twice as long to develop.

Preliminary tests suggested that this nematode may be useful in controlling sciarid gnats in glasshouses.

T. sciarae (Bovien) and T. gibbosus (Leuckart) were compared.

This work was done at Rothamsted Experimental Station, Harpenden, Herts, England, while the author held a postdoctoral grant from the National Institutes of Health, Bethesda, Maryland. I thank Mr F. G. W. Jones for a place in the Nematology Department, Dr Audrey Shepherd for supplying the New Blue R stain, Dr J. B. Goodey for advice, and Dr K. Lindhardt, Denmark, for the loaning of the late Dr Bovien–s slides of T. sciarae.

Three species of the genus Neoaplectana, nematodes from insects, when grown axenically, could be differentiated consistently by morphological, cultivational and serological criteria.

All three species were cultivated for consecutive generations on solid media such as a rabbit kidney slice at the bottom of an enriched agar slant. In axenic cultures with various liquid media, including some which were chemically defined, the ensheathed larvae of N. glaseri matured and produced offspring which in turn developed and reproduced; N. dutkii (‘DD-136’) larvae matured, but a new generation did not develop; the majority of N. carpocapsae larvae survived but did not mature. Living N. glaseri, used as a source of antigens to detect homologous antibodies, gave fewer cross-reactions than preparations of sonicated and frozen worms, and fewer false negative reactions than used cultivation media.

Morphological differences between the three species in cultures are described.

This work was done at The Rockefeller Institute in the department of Dr William Trager, with the technical assistance of June I. Schloemer and, subsequently, Kristin L. Schmidtchen. Preliminary morphological descriptions were made in association with M. B. H. Chitwood of the U.S. Department of Agriculture's Beltsville Parasitological Laboratory in Maryland. The author and work were supported by grants from the U.S. National Institutes of Health, 5-K3-AI-9522 and AI-04842.

Trichonema larvae are affected by light of visible wavelengths and there is a klinokinetic response to light intensity, the smallest rates of turning occurring in light of about 300 ft-c, and the rate of turning increasing with increased intensity (900 ft-c). In dim light the vertical migration of larval nematodes would be greatest, which explains in part the large recoveries from grass at dawn and dusk.

I thank Professor O. W. Richards, F.R.S., for permission to work at the Imperial College Field Station, and Professor B. G. Peters for help and advice. The work was financed by the Department of Scientific and Industrial Research.

Pumping of the pharynx of Panagrellus has been shown to be a complex process involving three stages: the uptake of a number of globules by the corpus, the passage of the aggregate globule through the isthmus, and expulsion of the globule into the intestine by a number of pumps of the posterior bulb. It is suggested that Aplectana pumps in a similar manner to Panagrellus but at a faster rate. The pharynx of Rhabditis operated in two stages, involving the uptake of food first by the anterior half of the organ, and the subsequent passage of the ingested material through the isthmus and posterior bulb.

The pumping action of the posterior bulb suggests that the corrugated valves have a primarily valvular function. Regurgitation of intestinal contents through the pharynx is prevented by the internal pressure of the animals tending to force the walls of the organ together, and by the action of series of valves found throughout the lengths of the pharynges.

I should like to thank Professor J. E. Harris and Dr H. D. Crofton for their help during the course of this work, which was carried out during the tenure of a Postgraduate Studentship awarded by the Agricultural Research Council.

Ixodes arvicolae Warburton was collected at 2-monthly intervals from January 1961 to August 1962 on a total of 226 Apodemus sylvaticus and 264 Crocidura suaveolens cassiteridum in the Scilly Isles. Twenty-one adult females (out of a total forty-two ticks) were found on Apodemus and one adult female (out of a total 106 ticks) on Crocidura. No adult males were found. Ticks were collected from the hosts throughout the year, but in Crocidura there was a suggestion of greater frequency for larvae during the summer. I. arvicolae was also found on Mus musculus in the Scilly Isles and on Microtus agrestis in Cornwall.

We wish to thank Professor D. R. Arthur of King's College, University of London, for identification of the ticks involved in this study, and Dr Alec Milne of the University of Newcastle upon Tyne for helpful criticism of the manuscript.