Results of the present study indicate that a wide range in coenurus fluid glucose concentration occurs among larvae of Taenia multiceps. Further, a definite correlation exists between bladder size and glucose concentration in the coenurus fluid; larger bladders have greater glucose concentration per unit volume of coenurus fluid. Based on analyses of bladder fluid glucose following alloxan induced hyper-glycaemia, an abrogation of the established size-coenurus fluid glucose concentration occurred. A diabetic state did not alter glycogen concentration in the tissues or lactic acid levels in the fluids of the same coenuri. The functional significance of bladder fluid glucose in maintaining tissue glycogen at constant levels is briefly discussed.

I wish to acknowledge Dr George Lauff, Director, W. K. Kellogg, Biological Station, for constructive criticism of the manuscript and for providing facilities and equipment during the summers of 1966 and 1967.

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.

When serotonin is injected intravenously into certain animals containing microfilariae it causes a sharp short rise in the microfilaria count in the blood, i.e. liberation of microfilariae from the lungs. This happens in the case of Dirofilaria immitis (in dog), D. repens (in dog), Loa loa (in drill), Edesonfilaria malayensis and another Dirofilaria-like microfilaria (in monkey), Monnigofilaria setariosa (in mongoose), and Dipetalonema gracile (in squirrel monkey); but not with Dip. witei (in gerbil) and Litomosoides carinii in cotton rats.

This action (upon D. immitis) is not inhibited by atropine. Administration of reserpine, harmine or harmaline to dogs did not exert any definite action on the microfilaria count of D. immitis. Serotonin had no obvious effect on the in vitro activity of microfilariae of L. loa or E. malayensis. Melatonin had no action in vivo upon any of the above microfilariae.

The action of serotonin upon microfilariae in vivo is similar to that of acetylcholine but it is not identical with it since the sensitivity of Dip. gracile and Dip. witei to the two compounds is different.

Apparently this action is not involved in the production of the 24 h periodicity shown by many microfilariae. It may depend upon disturbance of the normal neuromuscular mechanisms of the microfilariae by which they are retained in the small vessels of the lungs.

Macrolecithus papilliger sp.nov. from the stomach and intestine of Phoxinus phoxinus (L.) is described and its systematic position discussed. The life span in the fish, in captivity during January, is 5–6 weeks. The sequence of events in release of oocytes from the ovary and egg capsule formation has been observed in living specimens. Mature oocytes, in the ovary, are enclosed in groups of eight in a transparent membrane which ruptures, releasing them singly into the ovicapt. The egg capsule is formed in two stages: a transparent membrane is secreted, probably by Mehlis's gland, around the oocyte and vitelline cells in the ootype; later this is reinforced by vitelline globules released from the vitelline cells. These coalesce on the inner side of the membrane. The operculum is formed in the ootype. Histochemical tests support the observations.

I would like to express my gratitude to Mr S. Prudhoe, British Museum (Nat. Hist.), for helpful comments on this species and to Mr M. C. Bibby and Mrs M. Fisher for technical assistance.

The work was supported by a grant from the Science Research Council, for which I am most grateful.

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.

This paper describes the quantitative aspects of establishment and expulsion of Nippostrongylus brasiliensis in the normal and immune rat. It is proposed that this helminth infection may be described in terms of four phases. These are: (1) loss phase 1 (LP1). A proportion of the infecting dose of larvae is immobilized or destroyed before or during the course of migration via the lungs to the intestine. (2) The plateau phase. The worm number remains static in the predilection site. (3) Loss phase 2 (LP2). This is analogous to the self-cure reaction and during this worms are expelled from the host by an immunological mechanism. The onset of the expulsion is sudden and the process is exponential. It continues at a steady rate until a threshold is reached. (4) Threshold phase. A small residual population of worms is not expelled and survives for a fairly prolonged period.

The pattern is maintained in immune animals undergoing second or third infections but there are quantitative differences. With increasing number of infections LP1 becomes greater, the plateau phase is shortened and the expulsion rate of LP 2 increases. It is suggested that the rate coefficient of this phase is an accurate measure of the immune status of the animal. The threshold phase is of a similar order in first, second and third infections. These results are discussed with regard to their significance as a measure of the immune status of the host, their implication regarding the mechanism of helminth expulsion and their relevance to other helminth infections.

The authors wish to thank the Agricultural Research Council and Allen and Hanburys Ltd. for the financial support which made this work possible. During this period Ellen E. Jarrett held a Horserace Betting Levy Board Scholarship.

Field and laboratory observations on the nature and sequence of the host-finding responses of the hen flea Ceratophyllus gallinae are described. The imago over-winters within the cocoon. Tactile stimuli and a rise in temperature initiate emergence. Emigration from the nest is delayed for a few days by a negatively phototactic response, and begins when this becomes positive. The fleas are negatively geotactic and disperse upwards into the vegetation. Eventually they take up a characteristic posture, oriented towards the light. Jumping is elicited when the light intensity is suddenly reduced, and it is suggested that this enables the fleas to reach their avian host. Those fleas whose jump misses the host fall and form a secondary distribution on the ground. The readiness to jump rises during the first few days after cocoon emergence, then falls again, the rate of fall apparently being partly determined by water loss.

The author is much indebted to the Hon. Miriam Rothschild and Drs E. T. Burtt and M. J. Cotton for valuable advice, and to C. R. Brannigan for a critical discussion of the manuscript. The main part of the research was carried out during tenure of a post-graduate studentship provided by the Department of Scientific and Industrial Research.

Saline extracts of species of Ditylenchus and Heterodera initiated antibody production when inoculated separately into rabbits. On agar gel-diffusion plates these antisera gave a precipitate response against their homologous extracts and against extracts of some of the other nematode species. Up to four precipitation bands occurred, indicating the presence of at least four distinct antigens. Antisera to these extracts did not precipitate against extracts of the host plant or against the extracts of nematodes from other genera. None of the nematode extracts precipitated against normal serum. The precipitation response divided the Heterodera species tested into two groups, one containing H. schachtii, H. trifolii and H. rostochiensis and the other containing H. cruciferae, H. carotae and H. goettingiana with apparently no antigens common to both groups. The three species of Ditylenchus were serologically distinct, and it was not possible to interbreed D. myceliophagus and D. destructor. The extent of the postvulval sac was the most useful morphological character for separating D. myceliophagus from D. destructor. Only slight intraspecific serological differences were detected between five races (narcissus, oat, red clover, tulip and giant) of D. dipsaci and between the two pathotype populations (Colyton and Woburn) of H. rostochiensis. Precipitates occurred at the excretory pore of living larvae and adults of Ditylenchus species and at the vulval aperture of white females of Heterodera species placed in their homologous antisera.

We thank Dr A. J. Gibbs for much advice.

The development of the free-living infective larvae of a homogonic strain Strongyloides ratti is described.

The larvae develop only between 15 and 34 °C. Transfer experiments show the temperature block to be in the preparation for the second moult.

Within the temperature range 15–34 °C, increasing the temperature speeds up the rate of development of all the larval stages equally, the Q10 for development being 2·5.

The maximum percentage development occurs at 20 °C. The percentage development is highest in faeces–peat culture (95% development at 20 °C), whilst the percentage development in charcoal and vermiculite cultures is about the same (75% development at 20 °C.).

Larvae grown on charcoal cultures are larger than those grown on vermiculite, which are larger than those grown on peat. No significant difference was found in the length:oesophagus and length:width ratios or in the variability of larvae grown at different temperatures or on different culture media.

Different worm densities in the cultures of from 2000 to 10000 larvae per g of culture did not affect either the size of the infective larve or the percentage development.

The optimum temperature for survival is 15 °C. Worms grown at 20 °C lived longer than worms grown at any other temperature. There was no evidence of temperature adaptation by the larvae.

The infective larvae are positively thermotactic, and show maximum activity at 37 °C.

I should like to thank my supervisor, Dr Tate, for his advice and encouragement. The work was carried out during the tenure of a Medical Research Council Scholarship.

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 erythrocytes and plasma of a British and Brahman crossbred steer were labelled with 51Cr and 125I respectively. The radioactivity levels were subsequently maintained as constant as feasible by injecting the steers with calculated amounts of the appropriate labelled material on 3 consecutive days. The steers had previously been heavily infested with Boophilus microplus to ensure that all stages in the parasite's life-cycle would be present during the 4-day period, when the steers were being treated with isotopes.

Various stages of B. microplus larvae, nymphs and adults were collected and the uptake of red cells and plasma at each stage assessed by radioassay. In certain calculations, corrections were made for the uptake of blood fractions before the animals were made radioactive.

A relationship between the weight of the tick and its dietary intake was established. At all the stages of larval and nymphal feeding the plasma content of the diet was greater than that of the host blood. However, erythrocytes were detectable even in the earliest larval stages examined. Dropped fully engorged adult females contained more red cells per individual, and generally also more plasma, than engorged ticks removed from the host.

Fully engorged adult females took up as much as twice their own weight of blood components, but in none of the earlier stages did the tick concentrate its blood meal.

No obvious differences could be demonstrated statistically between the behaviour of the parasites on the two hosts. However, indications are that recently attached larvae took up more erythrocytes from the British animal.

We wish to thank Messrs A. K. Duffield, A. J. Short, B. Wilson, and Miss S. J. Shepherd, for skilful technical assistance.

The life-history of I. pacificus when fed on guinea-pigs under laboratory conditions is described. Feeding of the female proceeds for 10–11 days. Between 120 and 191 mg of concentrated food is found in the female's gut on detaching from this host, and this is directly related to the unfed body weight of the tick.

The egg-laying pattern, in general, shows an initial peak, after which the number of eggs tails off, the whole process lasting approximately 33–40 days. The number of eggs laid by females varies between 790 and 1300. The preoviposition period is about 11–16 days.

Larvae hatch in about 53–55 days, and their feeding time ranges from 4 to 9 days, although in the present experiments larvae emerging from early laid eggs took about 10 days to complete engorgements.

Moulting of larvae to nymphs at 90% R.H. took 37–38 days, and nymphs fed for 7–11 days, with most becoming replete on the ninth.

Very few females emerged from these nymphs, and those that did emerged in just over 30 days. The reasons for this are not clear. No diapause appeared to be necessary to complete the life-cycle, and with due allowance for hardening of the mouthparts the life-history of one generation was about 7 months. Females died within 3 or 4 months if hosts were not available.

From the literature and from hitherto unpublished records some 55 vertebrates have been implicated as hosts to I. pacificus; these hosts include a wide range of mammals, six species of birds and possibly nine species of lizards.

The species has been listed from British Columbia and from five western states of U.S.A. The need for more intensive ecological work on this species is emphasized.

We are indebted to Glen M. Kohls, J. D. Gregson and D. E. Johnstone for permission to use unpublished records from their respective institutions. One of us (D.R.A) is also indebted to the Wellcome Trustees for financial assistance to visit Canada during the preliminary stages of the work.

A method of breeding and maintaining L. natalensis cultures in the laboratory is described.

The infection of snails with F. gigantica miracidia and the collection of metacercariae is discussed. The mean number of metacercariae arising from cercariae produced by each snail was 652·6, over a period of 8·2 days.

It is shown that after 3 months storage F. gigantica metacercariae are still viable when excysted in vitro by using artificial pepsin and trypsin enzymes.

The author wishes to express his thanks to Dr G. M. Urquhart of the Wellcome Laboratories for Experimental Parasitology, University of Glasgow, Veterinary Hospital, Bearsden Road, Bearsden, Glasgow, who has read through this paper and made the necessary corrections.

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 early (0–18 h) migration of the larva of Ascaris suum in the white mouse was studied.

The eggs hatched in all gut regions posterior to the stomach, the time of maximal release being between 4 and 8 h after infection. The caecum was the site of maximum larval penetration.

Penetrating second-stage larvae produced demonstrable spreading factor reaction with Evan's Blue in the mucosa of the gut. Larvae were located in the venules and lymphatics of the caecum wall as well as in the ileo-colic and hepatic portal veins. Larvae were found in the liver after 9 h and in the lungs 12 h after infection. Larvae were not seen in the muscula externa of the gut and eggs were not found in any region of the body other than the gut lumen.

A similar pattern of larval distribution was seen in the gut wall of the rat and the guinea-pig.

I am greatly indebted to Dr D. A. Erasmus for his encouragement, advice and supervision during this investigation, and also for carrying out the experimental infections. I also wish to thank Professor J. Brough for the provision of excellent laboratory facilities. Many thanks are due to Mr J. H. M. Hughes (Veterinary Officer) and the meat inspectors at Roath Abattoir who provided me with infected material. I wish to acknowledge the financial support of the Pig Industry Development Authority and the Agricultural Research Council.

The growth and morphology of the excretory system of Stephanurus dentatus were investigated using both the light microscope and the electron microscope. In the 3rd-stage larva a branched tubular system extends from the posterior end of the excretory ampulla. The subventral glands are two elongated cells in the body cavity, and these do not appear to be attached to the tubular system.

The tubular and glandular portions of the excretory system are intimately associated with each other at the posterior end of the ampulla or sinus from the 4th-stage, but throughout their development they remain histologically distinctive. Moreover, the nuclei of each portion of the system are of two different types; those of the tubular system are similar to hypodermal nuclei, whereas the nuclei of the subventral glands are like the intestinal nuclei.

The lateral canals are extensions of the excretory sinus and lie embedded in the hypodermal tissue of the lateral chords. As the worm matures, the lateral canals increase in relative length, and the anterior branch of each lateral canal develops during the 4th stage.

Pink viscous fluid which passes from the excretory pore is identical in appearance with the fluid which is found in the lateral chords. It is suggested that the fluid in the lateral canals gains access to the excretory system by way of canaliculi in the wall of the lateral excretory canal.

I am most grateful to Professor J. F. A. Sprent for his interest and advice during this investigation, and to Mr J. J. Mines and Mr C. Boel for their able technical assistance. I gratefully acknowledge the financial support given for this study by the Australian Dairy Produce Board and the U.S. Department of Health, Education and Welfare (No. A 107023–02).

The oncomiracidium of Merizocotyle sp., a monocotylid monogenean from the nasal fossae of Raia undulata, has 14 marginal hooklets. It seems probable that these larvae swim directly into the nasal fossae or are carried through the nostrils by the olfactory water current without first attaching themselves to the body skin. The marginal hooklets are then supplemented by a pair of hamuli and by 23 suckers, arranged in two concentric rings. The suckers arise as pockets in the ventral surface of the haptor and develop successively in a postero-anterior direction, the inner ring reaching completion before the outer ring.

I would like to express my thanks to the Director, Professor R. Weill, and to the Staff of the Station Biologique at Arcachon in France. I am grateful to the Royal Society for a Pergamon Travel Award, which enabled me to visit Arcachon.

I would also like to thank Mrs Mary Hutchinson for assistance with histological work.

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 development of the feeding lesions of the ixodid tick Boophilus microplus was followed throughout the parasitic life-cycle on cattle of both Zebu and European breeds, using histological techniques.

The feeding lesion of this tick must be the result of an interaction between the tick and its host as it is neither the result of simple mechanical trauma, nor of lysis of the host tissues by salivary secretions of the tick alone, nor is it solely a result of an inflammatory response.

The histological evidence suggests that the diet of the tick in each instar changes as the lesion develops; first, tissue fluids are available, then tissue fluids along with leucocytes which have infiltrated the lesion, and finally these two components along with whole blood.

An early intense infiltration of eosinophils into the area of the mouthparts, typical of an immediate hypersensitive or anaphylactic response, was noted with European cattle on secondary and subsequent exposures to larvae. Hypersensitivity to tick infestation, which has been equated with resistance to infestation, was seen as an extreme of a normal spectrum of sensitization which results in an abnormal susceptibility.

The definitive lesion was similar with all hosts studied. It consisted of a cavity containing leucocytes, predominantly neutrophils, some lymphocytes and erythrocytes in an area of heavily infiltrated collagen.

It is concluded that this host-parasite relationship illustrates the concept of adaptation tolerance as proposed by Sprent (1962).

It is with much pleasure that we acknowledge the continued generous financial support by the Australian Meat Research Committee (formerly the Australian Cattle and Beef Research Committee), which has made possible this project.

Large numbers of electron-dense bodies, 700–1900 Å in diameter, usually seen each with its own limiting membrane, were found in axons of the ventral nerve of infective juveniles of H. contortus. Axons containing these granules merged, without limiting membranes, with a ‘light’, diffusely granular region, about 1·5–2 μm3. The ‘light’ area also merged without boundaries with the underlying cuticle which was different from the surrounding cuticle. This modified cuticle, of which the anterior border lies about 1·3 μm from the posterior edge of the excretory pore, extends slightly beyond the ‘light’ area. Otherwise it is a useful topographical marker for the extent of the ‘light’ area.

It is considered that the ‘light’ region has a special role in the physiology of the cuticle.

I wish to thank Mrs M. Ross for expert technical assistance and Mr R. I. Sommerville for valuable advice. This work was supported by a U.S. Public Health Service Grant, AI 04093–05. The use of the Siemens electron microscope was made possible by a grant from the Australian Research Grants Committee. Financial help from Parke, Davis and Co. (Australia) is also gratefully acknowledged.