Showing papers in "Parasitology in 1968"

The feeding processes of the cattle tick Boophilus microplus (Canestrini): Part II. The sequence of host-tissue changes

Abstract: 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.

Quantitative studies on the kinetics of establishment and expulsion of intestinal nematode populations in susceptible and immune hosts. Nippostrongylus brasiliensis in the rat.

Abstract: 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.

Death of schistosome cercariae during penetration of the skin. II. Penetration of mammalian skin by Schistosoma mansoni.

Abstract: 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.

The development of Theileria parva in the salivary glands of the tick, Rhipicephalus appendiculatus.

Abstract: Sections of salivary glands from the tick R. appendiculatus have been studied to obtain data on the incidence and development of Theileria parva during feeding. Adult ticks previously fed as nymphs on infected cattle were allowed to attach to rabbits after different periods following moulting and removed for dissection after different periods of attachment. The maximum number of parasites was present from the 3rd to the 5th days of attachment when 30·5–42 % of salivary glands were infected. A small number of undeveloped parasites was observed in the salivary glands of unfed ticks. The parasites were classified by their appearance into young, intermediate and mature forms and it was shown that the greatest numbers of mature forms were present on the 4th and 5th days of attachment. It was concluded that with this strain of ticks, reared and infected under the described conditions, the most suitable time for the recovery of the infective forms of T. parva would be the 4th day of feeding. Acknowledgements are due to the technical staff who contributed to this work, but especially to Mrs D. Backhurst who supervised the processing of the many sections, to Mr B. Wood who prepared the photomicrographs and to Mr K. P. Bailey who maintained the colony of infected R. appendiculatus . This work was carried out during the assignment of one of us (L.P.J.) by the Food and Agricultural Organization of the United Nations to the East African Veterinary Research Organization.

Notes on Ascaris and Toxascaris, with a definition of Baylisascaris gen.nov.

Abstract: 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)

A new species of Angiostrongylus in an Australian rat, Rattus fuscipes.

Abstract: A survey of lungworm infection in rats in Queensland has shown that 23% of Rattus norvegicus, 6·5% of R. rattus 4·5% of R. fuscipes and 0% of Melomys cervinipes were infected with lungworms. Detailed examination of the lungworms revealed that there are two distinct species; one is Angiostrongylus cantonensis which was found to occur in R. norvegicus and R. rattus, the other is a new species, namely, A. mackerrasae, which was found in R. fuscipes in an area of rainforest near Brisbane. Some R. norvegicus in Brisbane also harboured A. mackerrasae. The two species were distinguished by the length of the spicules, relative length and appearance of the postero-lateral ray in the male, the presence of a minute projection at the tip of the tail in the female, length of the vagina and the distance between anus and vulva. The first-stage larvae of the two species were found to be identical. As this species has been found to be the only lungworm in R. fuscipes which is an indigenous Australian rat, it is suggested that A. mackerrasae may have originated in the Australian region.I wish to express my sincere gratitude to Professor J. F. A. Sprent and Dr L. R. Ash for their advice and encouragement during this study. Special thanks are also due to Miss M. Cremin for her assistance and to Mr H. Lavery for providing specimens from North Queensland. This work was supported by a grant from the U.S. Department of Health, Education and Welfare No. A 107023–02.

The development of the adhesive organs of some diplectanid, tetraonchid and dactylogyrid gill parasites (Monogenea)

Abstract: 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 host-finding behaviour of the hen flea, Ceratophyllus gallinae (Schrank) (Siphonaptera)

Abstract: 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.

Ixodes pacificus Cooley and Kohls, 1943: Its life-history and occurrence

Abstract: 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.

The hatching mechanism of the egg of Fasciola hepatica L.

Abstract: 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.

On the bionomics of Crepidostomum metoecus (Braun, 1900) and Crepidostomum farionis (Müller, 1784) (Trematoda: Allocreadiidae)

Abstract: The life-cycles of the two species of Crepidostomum occurring in a stream in North Wales are investigated. Both species share the same arthropod and definitive hosts, viz. Gammarus pulex and Salmo trutta, respectively, but have different molluscan hosts, viz.: Lymnaea peregra for C. metoecus and Pisidium casertanum for C. farionis.C. metoecus and C. farionis have annual cycles, hence periodicity of occurrence in their hosts. In C. metoecus the dynamics of occurrence in the three hosts are correlated. The inverse relationship in G. pulex and S. trutta as well as the existence of a time-lag of 3–4 months between the establishment of this worm in G. pulex and in S. trutta are discussed.Neither premunition nor age-resistance occurs in the parasitization of S. trutta and G. pulex by C. metoecus. The increase in the rate and degree of infestation with the age and length of fish, except in the oldest and longest group, is shown to be due to trophic factors.C. metoecus is more abundant and widely distributed in the stream than C. farionis. This fact is associated with the occurrence of their molluscan hosts.Experimental observations were made on the stages in the life-history of C. metoecus, including the mode of emergence of the cercaria, invasion of shrimps and encystment, as well as development of the metacercariae in G. pulex.More cercariae are shed by day and at higher temperatures, and they live for about 5 days at 8 °C. The metacercaria undergoes considerable development before becoming infective. C. metoecus does extensive damage to L. peregra, has no observed ill-effect on trout, and apparently affects the life-span of shrimps adversely only in cases of very heavy infestations.The non-parasitization of Cottus gobio by the two flukes is probably due to the prevailing ecological factors.My thanks are due to Professor H. B. N. Hynes and Dr J. C. Chubb for many helpful criticisms at all stages of this study; to Miss Joan Venn for helping with the sampling programme; and the Commonwealth Scholarship Commission in the United Kingdom for financial support.

The histopathology of Fasciola hepatica infections in sheep

Abstract: 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.

The pathogenic effects of Eimeria praecox and E. acervulina in the chicken.

Abstract: Eimeria praecox produced less effect on body-weight gain and food consumption than E. acervulina. No deaths occurred and no weight loss followed infection with doses of oocysts up to 10. However, there was a depression of body-weight gain in birds infected with both species and changes in the permeability of the intestine were noted from as early as 3½ h after infection. This suggests that increased intestinal permeability is not the major factor in the greater pathogenicity of E. acervulina compared with E. praecox. Eimeria acervulina produced considerably greater effects on the host as evidenced by mortality, body weight gain and food consumption.I wish to thank Mr B. J. Millard and Mr M. Shirley for technical assistance and Dr B. M. Freeman for help with the statistics in Table 2.

Radioactive studies on the feeding of larvae, nymphs, and adults of the cattle tick, Boophilus microplus (Canestrini).

Abstract: 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.

Membrane (contact) digestion in the three species of tapeworm Hymenolepis diminuta, Hymenolepis microstoma and Moniezia expansa.

Abstract: The presence of living tapeworm increases the rate of hydrolysis of starch by α-amylase in vitro. This effect indicates that ‘membrane digestion’ may be one function of the tegument of tapeworms. The effect varies with the surface area and region of the tapeworm. Fixed tapeworm pieces do not enhance starch hydrolysis. The results may provide evidence both for and against the current explanations of membrane digestion. Some possible mechanisms involved in membrane digestion in tapeworms are considered. The importance of membrane digestion in the physiology of gut parasites and the possibility of its wide occurrence are discussed.We wish to thank Dr J. Llewellyn for his criticism and advice during the preparation of this manuscript and for providing rats and mice infected with Hymenolepis. We also thank Dr R. A. Thornhill for examining some tapeworm tissue under the electron microscope; also Mr A. Wilson of the Meat Inspection Department of the Birmingham Meat Market for his unfailing co-operation.

Passive protection with cells or antiserum against Nippostrongylus brasiliensis in the rat

Abstract: Rats can be passively protected against N. brasiliensis either with antiserum or with cells. Only some pools of antiserum (15 of 48 pools) and a few batches of cells (three of 11 batches) were protective.Protective activity was found in serum taken after one infection as frequently as after several infections and gave the same degree of protection. This suggests that second and subsequent infections do not stimulate an anamnestic increase in protective antibodies in the circulation.Serum and cells taken from the same rats were unrelated in their protective capacity; sometimes serum protected when the cells were ineffective and the reverse also occurred.Cells transferred from the spleen, peritoneal cavity or mesenteric lymph nodes were capable of initiating reagin formation, irrespective of their ability to protect against N. brasiliensis.When protection was achieved with transferred cells, the parasite life-cycle was shortened by only 1–2 days.We have found no evidence that a delayed mechanism of the homograft type is concerned in immunity to N. brasiliensis in the rat.We thank Miss W. D. Griffiths and Mr A. J. Edwards for their willing assistance. The statistical analysis was kindly done for us by Miss M. V. Mussett of the Statistics Department at our Institute.

A fine structural study on the merozoite of Eimeria tenella with special reference to the conoid apparatus

Abstract: The ultrastructure of the merozoite of Eimeria tenella has been studied by means of electron microscopy. The first-generation merozoite is approximately 3·4 μm in length, and 1·2 μm in width, while the second-generation merozoite is approximately 10·5 μm in length and 1·5 μm in width.The cell wall of the merozoite consists of a double membrane, but at the anterior extremity the existence of a fluted collar gives the appearance of two narrow double membranes separated by a zone of less electron-dense material. Twenty-four surface fibrils are distributed around the periphery; they extend along the entire length of the organism and lie beneath the double limiting membrane.The anterior end of the merozoite is distinguished by a conoid apparatus which includes several components. A bulbiform outer annulus is invested by a fluted collar, and itself encloses an extrusible papilla. Two osmiophilic fibrils, the paired organelles, arise within the extrusible papilla and extend longitudinally into the cytoplasm. Twenty-four smaller fibrils, or toxonemes, also arise within the conoid and pass back into the main body of the organism.The cytoplasm of the merozoite includes mitochondria, glycogen, dense elliptical granules and endoplasmic reticulum, together with a definite Golgi complex. A nucleus is located in the posterior third of the organism and is enclosed by a perforated double membrane. At the posterior extremity the double membrane which bounds the organism is broken by a pore 700 A in diameter.Our sincere thanks are due to Mr P. Richmond for technical assistance, and we are grateful to the Central Veterinary Research Laboratory, Weybridge, for supplying the strain of Eimeria tenella.

Death of schistosome cercariae during penetration of the skin: I. Penetration of bird skin by Austrobilharzia terrigalensis

Abstract: 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.

The larval development of Merizocotyle sp., a monocotylid monogenean from the nasal fossae of Raia undulata

Abstract: 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.

Neurosecretory granules in the infective stage of Haemonchus contortus.

Abstract: Large numbers of electron-dense bodies, 700–1900 A 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.

Vitamin requirements of the Coccidia of the chicken.

Abstract: 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.