The tegument of Haplometra cylindracea is protoplasmic. It is organized on two levels, a surface syncytium (‘cuticle’ of the light microscopists) and tegumental cells which lie among the parenchymal cells below the muscle layers. The surface syncytium and tegumental cells are joined together by protoplasmic, tube-like, processes.

The surface syncytium is covered apically and basally by a unit plasma membrane. It contains mitochondria, vacuoles, lipid bodies, spines with a crystalline structure and dense secretory bodies. This syncytium lies on a basement membrane and a thick, fibrous, interstitial layer. The connecting protoplasmic processes, which originate from the base of the syncytium, are vacuolated and have few inclusions but, as they approach the tegumental cells, they become progressively filled with cytoplasm, cell inclusions and dense bodies.

The tegumental cells consist of individual areas of nucleated protoplasm, usually lying in groups. These cells contain dense secretory bodies, mitochondria, a few lipid droplets, crystalline inclusions, and Golgi complexes. The Golgi complexes and granular endoplasmic reticulum are jointly involved in the production of a dense, probably proteinaceous, secretory body. Some qualitative regional differences in tegumental ultrastructure are described.

The tegument of Haplometra is compared with that of other species so far described and like them must be considered both a protective and a secretory epithelium.

I should like to express my sincere thanks to the following: The Wellcome Trust and Science Research Council for grants to purchase an Akashi TRS 50 and and A.E.I. EM6B electron microscope respectively; the Royal Society for a personal grant to purchase a Reichert Ultramicrotome and a vacuum coating unit; the Wellcome Trust for a grant to employ a Research Associate.

A collection of copepods from marine fishes, mainly elasmobranchs from South India was examined. Nine species are described of which six are new, one belonging to a new genus. The species described are Caligus dasyaticus Rangnekar, C. lepeophtheropsis sp.nov. Pseudopetalus dussumieri (Rangnekar), Dissonus sp., Nesippus vespa Kirtisinghe, Kroyeria minuta sp.nov., Eudactylina lancifera sp. nov., E. alata sp.nov., and Eudactylinopsis curvatus gen.nov., sp.nov.

The dry weight, nitrogen content, and total carbohydrate content of Hymenolepis diminuta were studied after a period of 15 days growth in rats, maintained on different diets. The special diets were fed during the last 7 days of this period.

Using equal iso-molecular quantities, seven amino acids, representing the different classes of neutral amino acids, acidic amino acids and basic amino acids, have been screened for their effect on worm growth when added as free dietary supplement to the different diets. All of them, to a greater or lesser extent, had significant effects on worm growth.

The award of a research grant by the Standing Advisory Committee for Medical Research in the British Caribbean is gratefully acknowledged. I am also indebted to Professors J. C. Waterlow and C. von Holt for the loan of equipment in order to carry out the carbohydrate and nitrogen determinations, to Professor I. M. Good-body for his continued interest and support, and to the Rippel Foundation for research facilities.

Larvae of Taenia crassiceps have been shown to absorb L-valine and L-methionine by a process of active transport. Uptake is maximal at about 43 °C and a pH of about neutrality, and concentration against a gradient has been demonstrated. In advanced larvae, the absorption mechanism has been shown to be specific for neutral aliphatic amino acids, with an uncharged amino group in the α-position. Competitive inhibitions of uptake have been demonstrated in the presence of other amino acids.

Comparison has been made with a mechanism present in Hymenolepis diminuta for the uptake of neutral amino acids, demonstrated by Read et al. (1963), and the absorption of L-methionine by the two species has been compared in detail.

The uptake of valine and methionine by the two types of larvae has been compared in detail: the presence of two types of sites for the uptake of these aminoacids has been suggested.

The absorption of the L-isomers of glutamic acid, proline, serine, glycine and leucine has been demonstrated in advanced larvae. Separate mechanisms for the uptake of acidic amino acids, basic amino acids and neutral aromatic amino acids have been suggested.

Thanks are due to Professor G. Chapman, in whose department this work was carried out, and to Miss E. Clarry for her willing assistance. We would also like to thank Dr G. Ayrey, of the Queen Elizabeth College Isotope Unit, for his valuable help, especially in the development of a technique for the simultaneous counting of 14C and 3H. The work was supported by a research grant from the Wellcome Trustees, to whom we are most grateful.

The monogenean Diplozoon paradoxum occurs on Abramis brama, Gobio gobio, Phoxinus phoxinus and Rutilus rutilus in northern England. In any one area, the infection is present in some waters but absent in others and predominates in rivers rather than in ponds or reservoirs.

D. paradoxum is randomly distributed on the gills, sides of the gill apparatus, hemibranchs and surfaces of primary lamellae of G. gobio, P. phoxinus and R. rutilus (except for P. phoxinus where inner hemibranchs carry more worms), but prevails on median sectors of the gills of these hosts. In A. brama the parasite is more numerous on certain gills, on the right side of the gill apparatus, and on the inner hemibranchs, but is randomly disposed on primary lamellar surfaces and along the gills. Except on G. gobio attachment is predominantly to two primary lamellae rather than one. This may reduce dislodging effects of the gill ventilating current by leaving portions of the lamellar surfaces unoccupied and allowing unimpeded flow in these regions.

This work was conducted during tenure of a Science Research Council Research Studentship. Research facilities in the Department of Zoology, University of Leeds, were kindly provided by Professor J. M. Dodd. Other facilities in the Biological Station, St John's, Newfoundland, were provided by the Director, Dr W. Templeman. Statistical advice offered by Dr E. Broadhead, Department of Zoology, and Professor C. L. Oakley, Department of Bacteriology, both of the University of Leeds, is gratefully acknowledged. I am indebted to Dr R. Wynne Owen, Department of Zoology, for constant advice and encouragement and for critical reading of the manuscript.

Inglisonema typos, gen.nov., sp.nov., is described from Pitta versicolor Swainson, from Queensland. The new genus is distinguished by the presence of three teeth in a small buccal capsule, simple oesophagus, precloacal sucker with chitinous ring in the male, and unequal spicules. It is placed in the superfamily Seuratoidea; a new subfamily, Inglisonematinae, is proposed for it, differing from all others in the superfamily in the presence of unequal spicules.

Cylicospirura heydoni (Baylis) is redescribed, from what is assumed to be paratype material (Queensland) and from Dasyurus quoll (Tasmania) and Dasyurops maculatus (N.S. Wales). Cyathospirura dasyuridis, sp.nov., is described from the same host spp., from N.S.W. and Tasmania.

Some specimens and some intact nodules were sent by Mr Green of Queen's Museum, Launceston, Tasmania. Skinned animals were given to me for dissection by Mr Peter Aitken, Curator of Mammals, at the South Australian Museum. To both of these collectors I am most grateful.

Types of the new species will be deposited in the South Australian Museum.

The hatching mechanism of the liver fluke egg was investigated and a new interpretation put forward. Light stimulates the miracidium and, when fully activated, the miracidium is responsible for altering the permeability of the membrane on the internal concave surface of the viscous cushion. Prior to expansion the cushion (a fibrillar mucoprotein complex) is in a dehydrated or semihydrated state. The change in permeability of the enclosing membrane allows the fluid egg contents to permeate into the cushion. The fibrillar matrix becomes hydrated and an increase in volume occurs. This compresses the miracidium and sacs and an internal pressure is set up which gradually increases until the operculum finally ruptures and flies back violently. The cushion and miracidium are then expelled by the hypertonicity of the egg contents.

I would like to thank Professor O. W. Richards, in whose department this work was carried out, also Dr F. Call and Professor B. G. Peters for their many helpful criticisms. I am also grateful to Miss Mary Morris for assistance with the electron microscopy.

Studies on immunological response of rabbits to Toxocara canis infection have been reported. It was observed that rabbits previously infected by two sublethal doses of 1200 infective ova each, with a 14-day interval between the two doses, acquired strong immunity to the effects of reinfestation induced by a large dose of infective ova, i.e. 100000. Post-mortem studies indicate that immunity is mainly directed against the migration of larvae to the lungs. The animals which resisted the effects of reinfestation showed an enhanced antibody response as shown by complement-fixation and agar-diffusion precipitin tests.

The precipitin reaction in the sera of animals infected by oral and subcutaneous routes respectively was studied with three preparations of antigen, namely, saline extracts, boiled saline extracts of adult worms, and saline extracts of infective ova. It was observed that the extract of adult worms was deficient in a minimum of three antigenic components present in the extract of infective ova.

It is a pleasure to thank Professor C. A. McGaughey for the facilities given for this study, Professor P. Seneviratna for his constructive criticism, and Messrs W. G. Senaratne and K. G. Karunaratne for technical assistance and the photo graphy respectively.

Acanthobothrium quadripartitum sp.nov., from the intestine of Raja naevus in the North Sea and English Channel is described and figured. In adult morphology it resembles A. brevissime Linton, 1908, more closely than any other known species of the genus. A. quadripartitum is one of the smallest known tapeworms and occurs in numbers of up to 13000 in one intestine. Preliminary observations indicate that it has little damaging effect on the epithelial cells of the host's mucosa.

I am indebted to Professor V. C. Wynne-Edwards for providing excellent research facilities and to the Director and Staff, in particular Dr B. B. Rae, Dr Z. Kabata and Mr Stuart Pirie, Marine Laboratory, Aberdeen, for laboratory space and material.

A large percentage of the cercariae of Schistosoma mansoni die while penetrating the abdominal skin of rats or mice but relatively few cercariae die in the skin of hamsters.

Comparison of hamsters and mice infected from the same pool of cercariae showed that the higher percentage of cercariae recovered as adult worms from hamsters than from mice was due to the lower percentage of cercariae which died during penetration of hamster skin.

In similar comparisons of rats with mice the lower percentage of adult worms recovered from rats was not entirely accounted for by the higher percentage of cercariae which died in rat skin. Losses of schistosomula at later stages of development are apparently higher in rats than in mice.

Cercariae die within 10 min after beginning to penetrate the skin of mice. At this stage the cercariae, which are now termed schistosomula, are attempting to penetrate the Malpighian layer of the epidermis. Five minutes later many schistosomula have entered the dermis.

The cause of death of cercariae has not been determined. It is not related to the development of sensitivity to water which accompanies the transition from cercaria to schistosomulum. Sensitivity to water appears much sooner after penetration in some cercariae than in others; even after 30 min in the skin some cercariae can tolerate a return to water.

In rats, hyper-immunized by a series of infections with cercariae through the abdominal skin, the percentage of challenging cercariae which die in the abdominal skin shows a slight increase over controls. No further mortality of schistosomula occurs during the next 24 h.

Age resistance to infection with S. mansoni could not be demonstrated in comparisons of young mice (1 month) with old mice (1 year) of the Parkes and CBA strain.

We should like to thank Dr F. Hawking for performing the skin biopsies on the dogs and Mrs P. Clark and Miss J. Marsh for their excellent technical assistance.

Experimental infections of lambs with Fasciola hepatica are described. The growth rate of the parasite, time of entry to the bile ducts, and time of patency are recorded and a preferential migration of the parasite in the liver parenchyma noted. The gross and histological lesions produced in the liver from 1 to 40 weeks after infection are described and compared with previous observations in cattle.

The parenchymal migration of the parasite is shown to consist of two phases, a free migrating phase up to the 6th week, and a localized phase after the 6th week prior to entry into the bile ducts. Hepatic cell regeneration is observed and hepatic fibrosis is minimal. The localized phase of migration is associated with a unique peripheral palisade of giant cells in the fluke tracts and with the formation of pseudofollicular aggregation of lymphocytes. The presence of flukes in the bile ducts produces fibrosis of the duct walls. The walls, however, remain pliable and expanded to accommodate the parasites and calcification was never observed.

For normal development of the parasites, Eimeria acervulina and E. tenella in the chicken, dietary thiamine, riboflavin, biotin, nicotinic acid and folic acid are required. E. acervulina required thiamine for second schizogony and sporulation; riboflavin for first schizogony and possibly gametogony, biotin for the development of the sporozoites/trophozoites and for gametogony, and nicotinic acid for schizogony and gametogony. E. tenella required thiamine and riboflavin for gametogony; biotin for first schizogony; and nicotinic acid for second schizogony.

The adhesive organs of diplectanid, tetraonchid and dactylogyrid monogeneans develop in very similar ways indicating that all these gill parasites are closely related to each other. The oncomiracidia make initial contact with the general body skin or the lining of the buccal cavity to which they attach themselves by 14 or 16 ventrally orientated marginal hooklets. The growing parasites then find their way to the gills which call for a different kind of adhesive apparatus. In order to anchor itself between two of the host's secondary gill lamellae, two pairs of the parasite's marginal hooklets migrate to the dorsal surface of the haptor and two of the four developing hamuli rotate so that they also point dorsally.

In diplectanids the hamuli are assisted by accessory friction pads (squamodiscs) which develop on the surface of the body anterior to the hooks.

In dactylogyrids the ventral hamuli do not develop and are represented in the adult only by small spicules. In contrast the marginal hooklets grow during larval development and become important adult attachment organs, together with the dorsal hamuli.

Adults of Tetraonchus monenteron feed on the epidermis covering the gills.

I am most grateful to the Director and Staff of the Laboratory of the Marine Biological Association at Plymouth and particularly to Mr J. E. Green for help and hospitality. I would also like to express my thanks to the East Suffolk and Norfolk River Authority and particularly to the Fishery Superintendent, Mr E. Q. Bitton, and to Mr D. Leary, for supplying me with freshwater fishes.

The original description of Ixodes tatei was given by Arthur (1959) and based on three females taken from a rock partridge of unknown species and from a fox (Vulpes sp. ?) in Jarmo, Chemchemal Valley, Kirkuk (type locality) and the Zagros Mountains, Erbil, both in north-eastern Iraq. The material, on which the following account is based, consisted of two females, one gorged nymph, one slightly fed nymph and two fully gorged larvae. They were collected from the head of Alectoris graeca, which was shot about 20 km south of Jerusalem on 17 December 1966 and sent to me by Professor O. Theodor of the Hebrew University. One female, one nymph and one larva have been deposited in the Hebrew University, Hadassah Medical School, and one female, one nymph and one larva are retained in my collection. The holotype female is deposited in the Chicago Natural History Museum, Cat. no. 84472.

The species described in this paper were found in Bithynia tentaculata from the Wentloog level, near Cardiff, South Wales. The larval stages of Psilotrema oligoon are redescribed and the taxonomy of the adults discussed. C. frondicola sp.nov. is a psilostome cercaria which has the probable flame-cell formula 2 [4 + 4 + 4 + 4 + 3 + 3] = 44. It emerges at night or during early morning, is positively phototactic and will not normally encyst on anything but vegetation. C. granocutis sp.nov. is also a psilostome cercaria; it is very small and has the probable flame-cell formula 2 [3 + 3 + 3 + 3 + 3] = 30. It emerges during the afternoon and will encyst freely on a variety of substrata.

I thank Professor J. Brough of the Zoology Department, Cardiff, for the facilities provided, Dr D. A. Erasmus for supervising and encouraging this work and Dr S. M. Willmott, Director of the Commonwealth Bureau of Helminthology, for providing library facilities. This study was carried out during the tenure of a D.S.I.R. research studentship.

The family Ascarididae, as defined by Hartwich (1957) and emended by Osche (1958), comprises species in the genera Ascaris, Toxascaris, Parascaris and Lagochilascaris, all occurring in terrestrial mammals. Other ascaridoids of terrestrial mammals occur in Crossophoridae and Toxocaridae, the latter including Toxocara and Neoascaris (see Hartwich, 1957; Sprent, 1957; Osche, 1958).

The seagull, a natural host of Austrobilharzia terrigalensis, was infected with cercariae through a small area of breast skin; 40% of the schistosomula recovered from the skin shortly afterwards were dead. In budgerigar skin 29% of the schistosomula were dead, but mortality in the skin of ducklings was much higher (85%). The budgerigar is a useful laboratory host for this schistosome, but ducklings are completely resistant to experimental infection mainly because of the barrier effect of the skin.

Rapid recovery of schistosomula from budgerigar skin established that the majority of deaths occurred during the first 15 min after application of cercariae. In sections of skin fixed after 10 min nearly all the schistosomula were in the epidermis between the narrow stratum corneum and the living cells of the Malpighian layer. In seagull and budgerigar skin most schistosomula succeeded in crossing the Malpighian layer in the next 5 min, but in ducklings nearly all schistosomula completely failed to penetrate this layer.

In vitro experiments in which cercariae were allowed to penetrate through several layers of dead epidermis, isolated from dried budgerigar skin, into balanced saline, showed that schistosomula are not killed by host cells or a soluble toxic substance. The possibility that the epidermis contains an insoluble toxic substance could not be excluded.

The proportion of schistosomula which died during penetration of dead epidermis was related to the number of layers in the barrier, suggesting that schistosomula may die owing to exhaustion caused by the intense activity of penetration.

About 30% of the glycogen reserves of cercariae were utilized during penetration of budgerigar skin. In dead schistosomula the glycogen reserve had been reduced by 80%, but the significance of this observation is uncertain because much of the glycogen may have been autolysed after death of the schistosomula. Exposure of cercariae to glucose before penetration did not affect the proportion which died in the skin.

Schistosomula adapt to the osmotic pressure in the skin, which is one-third that of sea water, and 30 min after penetration they are rapidly killed if returned to sea water. This process of adaptation is not related to mortality of schistosomula during penetration of the skin.

We wish to acknowledge the expert technical assistance of Mrs J. Morgan. This investigation was supported in part by research grant AI-04707 from the National Institute of Allergy and Infectious Diseases, United States Public Health Service.

Chick embryos have been infected with sporozoites of Eimeria tenella, but not with E. brunetti, and died from coccidiosis 5 days after infection.

Chick embryos can be protected from death due to coccidiosis by some but not all drugs which give a therapeutic response in chickens. The system is therefore not satisfactory as a screening tool, but may have applications in studies on the nature of drug activity.

Studies based on the mixed antiglobulin reaction have shown that γ-globulin is adsorbed from normal human sera by the cuticle of parasitic nematodes. Using antiglobulins specific for IgA, IgM and IgG, it was possible to demonstrate uptake to titres of 4, 64 and 128, respectively. Adsorption continued for at least 24 h, and the responsible immunoglobulins could be absorbed from the sera by nematode preparations.

A comparison of normal human sera with sera from cases of ascariasis and visceral larva migrans revealed that there was no significant difference between the titre of anti-cuticular immunoglobulins in normal sera or sera from helmin-thiases. It is suggested that these immunoglobulins adsorbed by the nematode cuticle represent cross-reacting, naturally occurring antibodies.

I am sincerely grateful to Professor R. R. A. Coombs, F.R.S., for his help, advice and encouragement, and to Mr M. J. Eburne for splendid technical assistance.