Observations on the movement of fluids in the vicinity of the mouthparts of actively feeding female Dermacentor andersoni were made with the aid of trans-illuminated live-hamster pouch host-tissue. Following tick attachment and the invasion of ‘attaching cement’ into the outer skin layers, there appeared a progressive release of host blood as the tick settled into a feeding pattern. Short periods of sucking, each followed by an immediate ejaculation of saliva, became lengthened as feeding progressed, as did the resting intervals between sucking. Other movements brought about by the tick included a ‘toying’ of the tissue fluid, a rapid vibration of the same, and a distinct regurgitation of host-blood material. A sudden haemorrhage usually appeared at the feeding site about 2½ h after attachment of partially fed ticks.

Speculations are made concerning the part played by the release of tick saliva and tick water loss, its probable relationship to host paralysis, and its apparent role in tick nourishment.

Young rabbits were infected by mouth with sporulated Eimeria stiedae oocysts and killed at 1, 3, 5, 8, 12, 16, 24, 30, 48, 54, 72, 84, and 96 h after infection. Sporozoites were found in the lamina propria of the duodenum between 5 and 8 h after infection. Sporozoites were present in the mesenteric lymph nodes, both free and within lymphatic monocytes at between 12 and 84 h after infection. No sporozoites were observed in duodenal portal blood. These observations provide morphological evidence compatible with a lymphatic route of migration between duodenum and mesenteric lymph nodes, probably within lymphatic monocytes. The route to the bile duct epithelium is discussed and a subsequent migration in the portal blood suggested.

I wish to express my gratitude to Dr D. F. Kelly of the School of Veterinary Medicine, Cambridge, for his guidance and constructive criticism, and to Dr Elaine Rose of the Houghton Poultry Research Station, St Ives, for her invaluable advice on technical problems and for donating the oocysts for the study. I should also like to thank Dr E. A. Pierce of the Department of Animal Physiology, Babraham, and Mr P. Long of Houghton for their advice.

This study was carried out as a Research Project during the Natural Sciences Tripos, Part II Pathology course 1965, in the Department of Pathology, Cambridge.

Echinoparyphium hydromyos sp.nov. with forty-five collar spines is described from the Australian water rat, Hydromys chrysogaster Geoffr.

The cercaria occurs naturally in Plananisus isingi (Cotton & Godfrey), and all stages in the life-history have been demonstrated experimentally.

Encystation occurs in the kidneys of tadpoles.

The adult is most closely related to Echinoparyphium recurvatum (Linstow). It differs from this in its greater number of eggs and in its life-history. E. recurvatum occurs predominantly in birds, and is rarely found naturally in mammals. E. hydromyos has been found only in a mammal.

Cercaria echinoparyphii hydromyos is compared with C. clelandae Johnston and Angel; it differs from the latter in the ‘compound’ nature of the excretory granules. The adult of C. clelandae has not been demonstrated in spite of a number of experiments to determine it.

Type material has been deposited in the South Australian Museum.

I wish to acknowledge the help given by my colleague, Patricia M. Thomas, in field work and in other ways, and by Mr Ian Smith, of this department, in the experimental work on life-history studies.

A new species of coccidium E. duodenalis sp.nov., has been described, from the pheasant. It is characterized by the subspherical shape of the oocyst, the lack of polar granules and the presence of large sporocystic residual bodies. Endogenous stages are found in the epithelial cells lining the villi, and occur chiefly in the duodenum and upper intestine. Second-generation merozoites form gametocytes and/or third-generation schizonts. The prepatent period is 5 days.

E. duodenalis is moderately pathogenic, doses of 50 000 oocysts causing a 30% mortality and a significant weight loss in the survivors. Treatment with a range of sulphonamides in the drinking water was successful as was preventive treatment with Sulphaquinoxaline mixed with the food.

Acknowledgements are due to Mr S. F. M. Davies for initiating this programme and carrying out a number of the animal inoculations, to Dr Helen Hein for help and advice in the design of the experiments and to Dr L. P. Joyner for advice in the preparation of the manuscript. The author also wishes to thank Miss C. N. Hebert for the statistical analysis of weight gains and Mr M. A. Peirce, Mr G. L. Choon, Miss J. Saddington and Miss M. Blore for technical assistance.

The egg shell of Fasciola was investigated by electron microscopy and found to consist of a fine reticulum of fibrils. No evidence for concentric lamellae was discovered.

The amino acids of the shell were identified using chromatography and it was suggested that the original protein was of a simple fibrous type. An unidentified spot was thought to represent a hydrolysis product of the cross-linkage. The effect of sodium hypochlorite on the shell, was also studied.

The ‘vitelline membrane’ of the fully developed egg was found to consist of a layer of peri-vitelline material beneath which were two closely opposed unit membranes. The origin of these layers was discussed.

The permeability of the shell and vitelline membrane was studied using simple physical techniques and radiotracers. The shell was found to be freely permeable to small molecules. The vitelline membrane complex was thought to represent the main barrier to permeability but an uptake of phosphate ions amounting to 8% of total phosphate, was recorded. This may have been more apparent than real as most of the activity was probably associated with egg shells rather than contents.

I would like to thank Professor O. W. Richards in whose department this work was carried out, Dr F. Call for supervision of the work and Professor B. G. Peters for his many helpful criticisms. Lastly, I am indebted to Miss M. Morris without whose expert assistance the electron microscope studies would not have been possible.

A group of thirty-nine Merino-Border Leicester cross-bred lambs were given six sensitizing doses each of 3000 infective Haemonchus contortus larvae. Previous studies showed that this treatment produced a state of immunological exhaustion (Dineen & Wagland, 1966a). In the present study the regeneration of the immunological response was followed by challenging the sensitized animals and previously uninfected control animals with 3000 infective larvae at 2, 4, 8 and 16 weeks after termination of the sensitizing infections with an anthelmintic. Faecal egg counts were carried out on infected animals twice weekly throughout the course of the experiment, and differential worm counts were performed on groups of animals slaughtered 48 days after challenge.

The results show that maximum regeneration of the immune response occurred when periods of 4 and 8 weeks were permitted to elapse between removal of the sensitizing infections and challenge. At 16 weeks the response of the sensitized animals to challenge infection was not significantly different from that of the control animals.

In contrast to results recorded in the previous communication, a high mortality (49%) occurred among the sheep during sensitization. In the earlier experiment the sensitizing infections were given at fortnightly intervals whereas they were given at weekly intervals in the present experiment.

Interpretation of the study is based upon the threshold behaviour of immunological responsiveness in parasite immunity, the occurrence of an immunological latent period and the relationship of this period to the developmental rate of the parasite, the susceptibility of the 4th larval stage to immunological attack, and the immunological privilege of the adult worm. These phenomena have been described in previous communications in the present series.

We are greatly indebted to Mr Emil Teleki and Misses Helen Giller and Lindy Stothart for their excellent technical assistance.

The effects of parasitism by the daughter sporocyst of Cercaria bucephalopsis haimaena Lacaze-Duthiers, 1854, on the digestive cells of Cardium edule L. was investigated by comparing histochemically stained cells in healthy and parasitized animals. Two effects were apparent: (a) the branches of the daughter sporocysts compress the walls of the digestive gland ducts and tubules, and cut off the more distal tubule cells from their food supply, inducing starvation autolysis, (b) in digestive tubule cells not so cut off, glucose, glycogen, glycoproteins, phospholipid and proteolipid food storage globules and acid mucopolysaccharide are reduced. Neutral lipids, fatty acids, alkaline phosphatase, acid phosphatase and non-specific esterase are increased and there is also a compensatory increase in the number of food vacuoles. In the visceral haemocoel, in the neighbourhood of the parasite, glucose, fatty acids, neutral lipids and acid mucopolysaccharide are increased and glycogen reduced.

We are grateful to Professor E. W. Knight-Jones, for helpful comments and good working facilities, and to the Science Research Council, for the grant of a research studentships to one of us (E.A.B.).

The distribution of carbohydrates, lipids and enzymes in the daughter sporocyst and contained cercariae of Cercaria bucephalopsis haimaena Lacaze-Duthiers, 1854, is mapped and used as an indication of metabolism. It is concluded that host glucose, glycogen, fatty acids and neutral lipids are absorbed and pass through the syncytial tegument into the cellular sub-tegument. They are then either metabolized or passed into the body cavity and contained cercariae. Glucose seems to be either converted into glycogen and glycoproteins or metabolized anaerobically. The end products of anaerobic respiration are fatty acids and neutral lipids. These pass into the excretory system, which flushes them into the body cavity of the daughter sporocyst, from where they enter the body of the developing cercariae. In the cercariae they are deposited, together with host lipids, possibly as less toxic higher fatty acids or other stored lipids. The stored glycogen and lipids in the cercariae are probably utilized aerobically during the free-living existence. The transport of nutrients and excretory products across the cell membranes may be aided by alkaline phosphatase and esterase activity, as is the metabolism of carbohydrates and lipids. Acid mucopolysaccharide precursors appear to be synthesized in the dense cytoplasm of the mid-tegument of the daughter sporocyst and secreted into the host's visceral haemocoel. Acid phosphatase and esterase found in this region may be involved in the synthesis and also in the breakdown of complex incoming nutrients.

We are grateful to Professor E. W. Knight-Jones for laboratory facilities and to the Science Research Council for a grant to one of us (E. A. B.) which made the work possible.

The cyst wall of Parorchis acanthus Nicoll, consists of an outer wall of three layers and an inner wall of two layers. The outer wall is hemispherical, complete, attached to the substratum and extends as a flange around the margin. The composition of its three layers differ dorsally and ventrally. Dorsally the layers are: (1) acid mucopolysaccharide and neutral mucopolysaccharide, (2) protein and lipoprotein, (3) acid mucopolysaccharide, neutral mucopolysaccharide and glyco-protein. Ventrally the layers are: (1) acid mucopolysaccharide, protein and lipoprotein, (2) acid mucopolysaccharide. The middle layer in both is secreted by the ventral granular cystogenous glands and the outer and inner layers, dorsally and ventrally, by the dorsal and ventral agranular cystogenous glands respectively.

The inner cyst wall is oval in surface view. It consists of two layers, both of neutral mucopolysaccharide, the outer giving a more pronounced reaction. Both are secreted by the dorsal granular cystogenous glands. The ventral wall is strengthened by a secretion from the plug-forming gland cells and consists of neutral mucopolysaccharide. All the layers of the cyst wall show the same histochemical reactions as the glands which secrete them.

Studies on the fine structure of the cercaria have revealed mammalian-type synapses in the neuropile of the central nervous system, rind cells around the ganglia, an elaborate arrangement of muscles in the wall of the oral sucker, the flame cell structure and the structure of the granules contributing to the formation of the cyst wall.

Some factors controlling differentiation of the protoscoleces of Echinococcus into strobilate or cystic stages, in vitro, have been identified. Development in a strobilate direction requires (a) evagination of the scolex, (b) contact of the evaginated scolex with a suitable nutritive substrate. These conditions are satisfied by treating fresh protoscoleces with pepsin and by evaginating them with trypsin + pancreatin + dog bile and subsequently culturing in diphasic media.

The most satisfactory diphasic system so far developed consisted of a base of bovine serum (coagulated by heating) with a liquid phase of Parker 199 medium +20% hydatid fluid and a gas phase of 8% O2+5% CO2 in N2. In this diphasic system, protoscoleces have been cultured to the 3-proglottid strobilate stage with the anlagen of the male and female genitalia formed: the first proglottid appeared after 30 days culture in vitro compared with 16 days in vivo; three proglottids were formed after 60 days. Development in vitro stopped just short of mature egg-producing worms.

That an intimate contact of a ‘placental’ nature takes place between the parasite and the solid proteinaceous base is shown by the fact that strobilization never took place in cultures lacking bases or in those in which the serum base was separated from the protoscoleces by a cellulose membrane. Cytological and ultra-structure studies of an evaginated protoscolex revealed that fully developed microtriches were present only in the rostellar region and not in the post-sucker region. It is concluded that it is this anterior region which makes initial contact with the nutritive substrate—a contact which appears to provide the ‘strobilization stimulus’. It is not known if the ‘strobilization stimulus’ is stimulatory (i.e. nervous) or nutritive or both. Contact with a non-nutritive base (i.e. agar) does not induce strobilization.

In any one sample of protoscoleces, after a high initial evagination, only about 30–40% finally remained evaginated and continued to show sucker activity. The degree of evagination appears to be characteristic for any sample of protoscoleces and may be related to the source of the hydatid cysts. It may prove to be a genetically determined character.

Evaginated protoscoleces became inactive under certain conditions and the degree of activity seems to be related to stimulatory and nutritive factors. The activity of evaginated protoscoleces was used as a criterion for assessing the effectiveness of a culture medium or condition. Evaginated protoscoleces which lost their activity developed small posterior bladders as did the majority of unevaginated protoscoleces. In both cases, posterior bladders enlarged and secreted a PAS-positive layer which formed the laminated membrane of a miniature hydatid cyst.

The well-known appearance of vesicular forms in cultures appears to be related to unfavourable culture conditions in vitro, such as a low or high pH or a low or high O2 tension.

It is pointed out that since the morphogenesis of Echinococcus protoscoleces can now be controlled to a considerable extent in vitro and since the contents of any one cyst have the same genotype, this organism provides exceptionally interesting material for studies on morphogenesis.

Acknowledgement is made to the Australian Wool Board, the National Institutes of Health, U.S. Public Health Services Grant No. AI-04707–03 and the World Health Organizati on for generous financial assistance in support of this work.

The skilful technical assistance of Mr A. B. Howkins and Mrs Mary Barton is also acknowledged.

The first full account of the life-cycle of an Eimeria sp. from the pheasant is given. The strain, isolated from pheasant chicks by single oocyst inoculation is identified as E. phasiani. It is shown that there are three distinct asexual stages prior to the onset of the sexual stage.

I should like to express my sincere gratitude to Dr E. U. Canning for her supervision and helpful advice, and to Professor O. W. Richards, F.R.S., for permission to work at the Imperial College Field Station. I am also grateful to Mr T. H. Blank, of the Eley Game Advisory Service, Fordingbridge, Hants, who gave day-old pheasant chicks for this study.

The work was financed by a scholarship from the Agricultural Research Council.

Eimeria phasiani was shown to be pathogenic to young pheasant poults. Doses of 100000 or more oocysts proved fatal to birds up to 3 weeks old. Lesser doses produced losses in the live-weight gain of the host.

Two separate strains of E. phasiani were completely susceptible to 0·006% (w/w) Sulphaquinoxaline, but less so to 0·006% (w/w) Amprolium and 0·0125% (w/w) Zoalene.

I should like to express my sincere gratitude to Dr E. U. Canning for her supervision and helpful advice, and to Professor O. W. Richards, F.R.S., for permission to work at the Imperial College Field Station. I am also grateful to Mr T. H. Blank, of the Eley Game Advisory Service, Fordingbridge, Hants, who gave day-old pheasant chicks for this study.

The work was financed by a scholarship from the Agricultural Research Council.

Acanthocotylid (monogenean) parasites inhabit the skin of rays, and the lack of cilia on the infective larvae of these parasites may be an adaptation to the host's bottom-living habits.

Freshly hatched larvae must remain on the sea-bottom until a ray settles on top of them, when the larvae then have the opportunity to attach themselves to the host's ventral surface. Acanthocotyle lobianchi, which infects Raia montagui and R. clavata at Plymouth, becomes sexually mature on the host's ventral surface and rarely wanders from it, but A. elegans, which is found on R. clavata only, migrates to the dorsal surface of the host before reaching sexual maturity.

The larvae of acanthocotylids use their haptoral hooklets to attach themselves to the host's epidermis, but as the parasites increase in size the load on these hooks becomes acute. This load is relieved not as in other monogeneans by the development of hamuli but by the transformation of the posterior third of the larval body into an accessory ‘pseudohaptor’.

I am obliged to the Director and Staff of the Plymouth Laboratory for laboratory facilities and to Mr J. E. Green for his interest and help on many occasions.

The capsule, which surrounds the acanthocephalan parasite Moniliformis dubius in its intermediate host, the cockroach, Periplaneta americana, has been studied in the electron microscope. Some observations were also made with the light microscope.

The capsule surrounding the developing parasite (acanthella) taken from the haemocoel of its host consists largely of closely packed vesicles, which are empty of electron-dense contents.

The vesicles arise from the surface membrane of the insect's haemocytes, which surround the parasite. Long tubular protrusions arise from the haemocyte's surface and, on separating, swell to form rounded vesicles.

The capsule, which surrounds the later resting stage (cystacanth), has apparently been stretched by the growth of the parasite after haemocytic activity has declined. An amorphous, electron–dense component is also evident at this stage.

We are grateful to Mrs A. Baker and Miss R. Jantunen for their technical assistance and to Dr A. C. S. Crossley for his comments on the work.

Experimentally infected female mice and naturally infected female jackrabbits are more susceptible to infection with Taenia multiceps than males. It appears that cortisone has the greatest effect in altering rates in mice when injected between days 1 and 14 following exposure of mice. Cortisone elevates infection rates in male mice but not in females. Cortisone does, however, alter the distribution pattern in a similar manner in both sexes. The biology of coenuriasis in rabbits and mice is discussed and compared.

I wish to thank Dr J. R. Egerton of the Merck Institute, Rahway, New Jersey, for supplying cortisone used in this study. I also thank Dr Robert Sullivan and Dr Ralph Amen for their criticisms and suggestions in the preparation of this manuscript.

Endolimax blattae, a small amoeba living in the cockroach hind gut, was cultivated in vitro for the first time.

Growth and encystment took place in diphasic serum-saline media with or without the addition of starch.

E. blattae grew well at 25 and 37°C. At the latter temperature the flagellates and Blastocystis which contaminated recently isolated strains were eliminated.

More amoebae and cysts were produced in cultures supplied with starch than in those without starch, and there seemed to be a relationship between depletion of starch and onset of encystment.

The results are discussed with reference to conditions in the natural environment.

I wish to express my thanks to Professor H. P. Moon, in whose department this work was carried out, for his help and advice, to my supervisor Dr Marjorie G. Guthrie for her advice, encouragement and constructive criticism, and to Dr Ann Bishop, F.R.S., and Dr Elspeth W. McConnachie for their invaluable advice on in vitro cultivation.

Some morphological characteristics of Cephalochlamys namaquensis from Xenopus muelleri collected at Kajansi, Kampala, are described.

Specimens of cestodes from other localities in Africa are compared with those from Kajansi in order to assess the reliability of the characters of the proposed genus Pseudocephalochlamys Yamaguti, 1959. Reasons are given for rejecting the genus.

The embryonated, non-operculate egg capsules hatch at once in water. The ciliated coracidium is eaten by cyclopid copepods and the oncosphere rapidly penetrates through the mid-gut wall into the haemocoel. The procercoid develops a cercomer which moves actively during development and which retains the six hooks of the oncosphere. The procercoid develops the scolex, osmoregulatory canals and calcareous corpuscles typical of the adult while within the copepod. It is enclosed within a membrane. The procercoid is infective to Xenopus toads 20 days after being ingested by the copepod. No other intermediate host has been found.

Thermocyclops infrequens Kiefer is the intermediate host at Kajansi, Kampala. The maximum number of C. namaquensis recovered from one toad was 103; usually there are between 1 and 6 per toad. Between 22% and 100% of Xenopus muelleri and X. laevis from different localities are infected with C. namaquensis.

I wish to express by thanks to the Fisheries Officers and fishermen of Kajansi Fish Farm who have willingly caught Xenopus for me whenever required, and also to the many other people who have assisted me in getting specimens with which to work.

I am also indebted to Mr L. Rugema who prepared most of the histological preparations, to Dr J. Green, Westfield College, London, who kindly identified Thermocyclops infrequens, and to Dr G. Rees, University College of Wales, Aberystwyth, who gave me many useful comments during the course of this work.

A research grant from Makerere University College contributed towards the cost of obtaining specimens.