A cycloguanil-resistant strain of Plasmodium gallinaceum was produced relatively rapidly by passage through chicks treated with low but effective doses of the drug, the dose being increased as resistance developed.

The strain was cross-resistant to proguanil but not to pyrimethamine or chloroquine.

A strain highly resistant to proguanil was resistant to cycloguanil but only slightly resistant to pyrimethamine.

A strain highly resistant to pyrimethamine was resistant to proguanil and cycloguanil.

Passage for 20 months through birds treated with doses of cycloguanil which suppressed infection for relatively long periods failed to change the sensitivity of the strain to this drug or to proguanil. Although the relatively large dose did not eradicate the infection in any of the birds, subinoculations demonstrated that parasites were absent from the blood for a period in some of the birds, though infections finally developed.

I am indebted to Parke Davis and Company for the supply of cycloguanil, to Imperial Chemical Industries Ltd. for the proguanil hydrochloride and chloroquine phosphate and to Burroughs Wellcome and Company for the pyrimethamine base.

Biochemical studies on the phosphatase systems of Gastrothylax crumenifer have been made. The maximum activity of the phosphatase enzyme was found to be at 5 pH. The action of magnesium and fluoride ions on the acid phosphatase activity shows that both act as inhibitors. The day-to-day variation in the phosphatase activity of the samples, as measured by block differences, was found to be significant at different pH levels. The heat denatured extract showed low and fairly constant acid phosphatase activity.

Fasciola tragelaphi sp.nov. from the bile ducts of a Tragelaphus spekei shot in the Chobe swamps of Rhodesia differs from other species of the genus in its very large size (10.2–12.0 cm long in fixed and mounted specimens), in the shape of its body and in the distribution and arrangement of the reproductive organs. The testes lie almost entirely in the posterior half of the body, well away from the female genitalia, which lie mostly in the anterior third of the worm. The ovary is always bilateral, and the coiled uterus runs in a straight line between the caeca to the genital atrium. A prepharyngeal pouch found in this species is compared with that found in other members of the genus Fasciola and in related genera.

We gratefully acknowledge the help given during the preparation of this paper by the staff of the Bureau, particularly Mr G. Dimmock for technical assistance. We would also like to thank Mr S. Prudhoe for reading the manuscript and offering useful advice, Mr B. Bracegirdle for producing the photograph of the whole worm reproduced in the Plate, fig. 1 and to Bechuanaland Hunters Ltd., particularly I. M. Henderson, for obtaining further specimens for examination.

One of a large number of Lymnaea peregra (Mull.) from a pond near Glasgow was found to be infested with Cercaria diplostomi gasterostei.

C. d. gastrostei has been found to penetrate Gasterosteus aculeatus and develop into a diplostomulum in the retina of the eyes.

Large numbers of G. aculeatus from the pond have been found with Diplostomulum gasterostei occurring in the retina.

Infested heads of fish were fed to domestic ducklings and pigeons, and adult stages of a worm considered to be a new species and named D. gasterostei were obtained.

Morphological details of the cercaria, diplostomulum and the adult worm are described.

The author wishes to thank Dr C. A. Hopkins for reading and criticising the manuscript, Dr D. A. Erasmus and Dr G. Rees for valuable suggestions. My thanks are due also to the technical staff of the Department who assisted me in the collection of snails and fishes, and to Mr Francis Deen who did the sectioning of the specimens. This work was in part supported by a grant from Shell Oil Company (London).

The bladder of the cysticerci, the larvae of cestodes, is a transitory embryonic organ; its morphology is related to its mode of development and the localization of the parasite in its intermediate host. The bladder makes possible the adaptation of the cysticercus to unusual conditions of its development. A certain degree of analogy between the trophoblast of the mammalian embryo and the bladder of the cysticerci adapted to the development in the tissues of mammals can be drawn.

Six different histochemical techniques were employed to study the sites of deposition of glycogen, other carbohydrates, and carbohydrate complexes in uninfected Crassostrea virginica and those parasitized by the larvae of the trematode Bucephalus sp. The carbohydrate and carbohydrate complexes occurring in the parasites were also studied.

In uninfected oysters, glycogen is stored in the digestive diverticula, in Leydig cells located between the diverticula in the digestive gland, in the matrices of the palps, mantle, and gills, in walls of blood vessels, and in ova. There is a marked reduction of stored glycogen at these sites in infected oysters. In addition, the glycogen-storing diverticular cells and the interdiverticular Leydig cells are ruptured and/or lysed and the enclosed glycogen is expelled to the exterior.

Glycogen is found in the sporocysts; however, very little if any is present in cells comprising young germ balls. It is only after the elongate germ balls commence differentiating into cercariae that glycogen appears in their bodies.

In uninfected oysters, glucose deposits are present in the same Leydig cells in which stored glycogen is found. Glucose is believed to be the hexose from which the stored glycogen is synthesized. In infected oysters, the reduction of glucose in Leydig cells is almost complete.

There are histochemically demonstrable amounts of glucose in the blood vessels and sinuses of infected oysters while such is not the case in uninfected ones. This phenomenon is explained by the destruction of the sites of glycogen synthesis and storage in infected oysters, thus bringing about hyperglycaemia resulting from the accumulation of glucose taken in from the exterior.

The presence of glucose deposits adhering to the gill surfaces of infected oysters may represent the direct absorption of glucose from the environment and contribute to the hyperglycaemic conditions.

The absorption of glucose by sporocysts is suggested by the finding of this hexose adhering to the exterior and in the wall of certain sporocysts.

Gamma metachromatic globules are present in the digestive diverticula of uninfected oysters. Their number is increased in infected oysters. In addition, the connective tissue layers abutting the base of the epithelial lining of the stomach and intestine and the fibres at the base of the surface epithelium of the gills of uninfected and infected oysters are metachromatic. Metachromasia at these sites is believed to be due to acid mucopolysaccharides.

Acid mucopolysaccharides are present in certain cells intermingled among the ciliated epithelial lining of the gastric and intestinal walls and in secretory cells along the surface of the mantle, gills and palps. The histochemical reactions at these sites remain unaltered in infected oysters.

Only older sporocysts include acid mucopolysaccharides in the walls.

In older germ balls, acid mucopolysaccharides are present in the small somatic cells situated on the surface, beneath the enveloping membrane. These are believed to be cuticle-secreting cells.

In developing cercariae, acid mucopolysaccharides are found in the cuticle and certain parenchymal cells.

There is an increase in the number of ‘brown cells’ in infected oysters. The smallest and largest do not include acid mucopolysaccharides but those that measure between 0·006 and 0·012 mm are partially or totally positive for acid mucopolysaccharide. Slight metachromasia and sphingomyelins also are associated with certain ‘brown cells’ found in the digestive glands of infected oysters.

Large ‘brown cells’ in the intertubular spaces in the digestive glands of both uninfected and infected oysters have been observed to undergo division.

The histological anatomy of the male reproductive tract as well as the cytochemistry of the cells of different regions of the male tract in Aspiculuris tetraptera are described.

It is shown that there are at least three different regions of the vas deferens, each of which releases one or more substances into the lumen of the male system and thus contributes to the composition of the semen. The histochemical nature of these secretions is given and it is suggested that the secretions of the distal vas deferens are oxytocic.

My thanks are due to Professor J. D. Smyth of the Australian National University, Canberra, for the gift of RNA-ase (L. Light and Co.) and some other histochemical reagents, to Dr T. R. R. Mann, C.B.E., F.R.S., and Dr D. L. Lee, for helpful discussions during the course of this study and for reading the draft manuscript.

The distribution of Trichostrongylus colubriformis in the intestine of the non-immune guinea-pig is described. At day 10 of the primary infection the majority of larvae were found in the anterior half of the small intestine with progressively smaller numbers in all parts of the gut posterior to this. However, soon after day 10 a migration of the worm population took place so that by day 15, before there had been a reduction in the total present, the majority of worms were found in the posterior small intestine. Thereafter the posterior movement continued, but while the numbers in the large intestine increased the movement then coincided with the beginning of the expulsion of the worms.

By the irradiation of guinea-pigs prior to infection the posterior migration was prevented, indicating that the latter was the result of a host response.

The independent migration of two generations of parasites was noted and two possible explanations are put forward.

This work was carried out during the tenure of a Research Training Scholarship awarded by the Animal Health Trust.

The author would like to thank Professor W. I. B. Beveridge in whose Department this work was carried out, and also Mr King of the Department of Radio-therapeutics, University of Cambridge, who irradiated the guinea-pigs used in Expt. 3.

A bladder fluke from the toad Bombina variegata is described and erected as a new species under the name of Gorgoderina alobata sp.nov. A comparison is made between this trematode and G. carli Baer, 1930, from India. It is also compared with the other two previously described European species, G. vitelliloba (Olsson, 1876) and G. skrjabini Pigulevsky, 1953.

A series of line drawings of the unsporulated and sporulated oocysts of the species of Eimeria found in cattle and sheep in Britain has been compiled.

The incidence of the different species in faecal samples from animals, of which only a minority were known to be suffering from enteritis or diarrhoea, has been recorded. Samples from sheep frequently contained five or six different species among which those that are believed to be pathogenic (E. arloingi, E. crandallis, E. ninaekohlyakimovae) were the most common.

The samples from cattle most frequently contained two or three species. E. bovis and E. zuerni, which are associated with acute disease, were the most common.

The brush border of the intestinal cells of the infective larva of Trichinella spiralis is shown to consist of microvilli. It is suggested that large vesicular complexes in association with Golgi complexes may be responsible for the production of the mucopolysaccharide or mucoprotein filling the lumen of the intestine. Indirect evidence of a latent intranuclear virus infection is presented. The cuticle lining the hind gut, although continuous with the external cuticle, is not similar in structure.

I would like to thank Dr D. L. Lee for instruction in all aspects of this work, Professor Boyd for the use of the Anatomy Department electron microscope and the Agricultural Research Council for financial support.

Among over 700 Australian birds dissected, Geopetitia spp. were found in three. These are described as new species, as follows: G. streperae from Strepera melanoptera, G. chibiae (female only) from Chibia bracteata, and G. falco (female only) from Falco longipennis.

Types of the new species will be deposited in the South Australian Museum. Paratype material of G. streperae will be in the Helminthological Collection of the Zoology Department of the University of Adelaide.

The three birds from which the Geopetitia spp. were taken were collected by ornithologists of the South Australian Museum, to whom I am most grateful.

Lecithaster musteli sp.nov. from the five-bearded rockling, Onos mustelus (L.), at Mumbles Head, Swansea, is described and compared with other species of the genus.

The genus Lecithaster Lühe, 1901 is reviewed. An emended definition of the genus is given with keys, diagnostic features, and brief notes of the nine recognized species. L. gibbosus (Rud.) Lühe, 1901 is briefly redescribed.

L. intermedius Szidat, 1954 is considered to be a synonym of L. gibbosus (Rud.) Lühe, 1901.

I am deeply indebted to Dr B. L. James for his advice and indispensable assistance throughout the work and the preparation of this paper. I am also grateful to Professor E. W. Knight-Jones for his interest and for providing the working facilities, and to Mr S. Prudhoe, British Museum (Natural History), for his advice, for allowing me to examine slides of L. gibbosus and for the use of the library.

The cuticle of the third-stage larva of Nippostrongylus brasiliensis consists of seven layers: an outer triple-layered membrane, a double-layered outer cortex, an inner cortex, a matrix layer, a striated layer and two fibril layers. In each ‘annule’ two fibres run transversely around the nematode and lie between the inner cortex and the matrix layer. There is no basement lamella.

The hypodermis is a thin layer between the muscles and the cuticle, but expands to form the dorsal, ventral and lateral cords. The nerves lie between the plasma membrane of the hypodermis and the basement membrane or between the plasma membrane of the hypodermis and the sarcolemma of the muscles. The muscle cells are typical of those described previously for nematodes. The ‘myofibrils’ are apparently similar to those of Ascaris.

An excretory canal is present in each lateral cord and is enclosed by the basement membrane but is not embedded in the hypodermal tissue. Numerous small vesicles appear to move across the wall of the excretory canal and open into the central lumen.

I am grateful to Dr P. Tate, Dr R. W. Horne and Dr K. A. Wright for helpful discussions, to Professor C. P. Read and Dr A. Enders for the use of facilities at Rice University, Houston, Texas and to Professor J. D. Boyd for permission to use the electron microscope in the Department of Anatomy. Thanks are also due to Mr A. J. Page for technical assistance.

The genitalia of Diplectanum aequans (Wagener) Diesing are described and a functional interpretation is postulated.

Spermatophores are produced from a pair of diffuse glands lying laterally amidst the vitellaria. The secretion from these glands is stored in an anterior reservoir, across the centre of which is a viscous disk which delineates two internal chambers.

Each spermatophore has an elongated stalk and an ovoid head and is considered to be moulded in a muscular bulb and in the penis, prior to extrusion through the penis.

The penis is composed of two concentric tubes and it has a slight hook at its distal end. The vagina has a glandular base and muscular lips. Its internal cast corresponds to the shape of the penis tip.

Copulation in D. aequans is described.

The occurrence and biological significance of spermatophore production in animals are discussed.

I would like to acknowledge the help given to me by the Director and Staff of the Marine Biological Association Laboratory and also by the Proprietors of Cook and Sons Ltd., of Salcombe, Devon. I am most grateful to Dr J. Llewellyn for much helpful advice throughout the course of this study.

The work was conducted during the tenure of a D.S.I.R. Studentship and includes the results of special studies made possible by a grant from The Browne Fund of The Royal Society.

Plasmodium vinckei infections, which usually kill mice within 7 days, can be terminated in the majority of cases by a single injection of chloroquine phosphate equivalent to 10 mg/100 g body weight. After such drug treatment the parasites disappear from the blood for 6–11 days, after which a recrudescence with a low peak occurs. Most animals overcome this second parasitaemia and the parasites finally disappear completely. After recovery, mice exhibit an immune response to a challenge infection and, after a short period of parasitaemia during which a low peak is reached, the animals recover completely. This immunity, once acquired, apparently persists for the lifetime of the host. The establishment of the immune state depends on the period of patent parasitaemia during the primary infection and the longer this period the greater is the chance of a solid immunity developing. Immunity may be exhibited by mice treated with chloroquine as early as the 3rd day of infection. Killed parasites have no immunizing effect. Mice splenectomized before infection are capable of an immune response, and mice splenectomized after radical cure are also able to overcome a challenge infection. In both these cases more than one injection of chloroquine is required. The immunity produced in mice is that of the true sterile type, equivalent to that produced against P. berghei in rats, and is species-specific, conferring no resistance to infection with P. berghei. P. vinckei infections in mice provide a useful immunological model for laboratory studies. The immune response is predictable and easy to induce, and this parasite is therefore superior to P. berghei for immunological studies. Attention is drawn to the fact that in P. vinckei the infection is brought under control by the immune response and not by the antimalarial drug; therefore this ought to be taken into consideration in the assessment of drug trials.

By culturing Galleria mellonella, Neoaplectana sp. (DD-136) and Achromobacter nematophilus separately under axenic conditions in the laboratory, it was possible to study the relationship between the bacterium and nematode during nematode parasitism of the insect.

The infective-stage juveniles of the nematode were able to penetrate and kill the insect host without the presence of A. nematophilus or any other bacterium. However, without accompanying bacteria the nematode was unable to reproduce. Only when A. nematophilus or a possible replacement, such as Pseudomonas aeruginosa, was added to the blood did reproduction occur.

The relationship between A. nematophilus and the nematode is considered a mutualistic one, since the bacterium lives and is protected inside the intestine of the free-living stage of the nematode and is transported and released by the nematode to the haemolymph of a host insect. The nematode, in turn, is dependent on the bacterium for reproduction.

The pharyngeal pump of Ascaris has been shown to have a very high capacity. While the contraction rate of the organ is probably of the same order as those of complex pharynges, the volume of material ingested at each pump is relatively higher. It is suggested that the pharynx acts as a simple two-stage pump in which half the lumen is filled with food at any one time.

It has been suggested that the antagonism to the radial musculature of the pharynx resides in changes related to an increase in the diameter of the pharynx during the opening of its lumen. It is suggested that the closing of the lumen is facilitated by the increased tension in the outer coat of the pharynx and in the suspensory strands of the marginal tissues; and by the contraction of the radial musculature that is orientated towards the sides of the sectors of the pharynx, towards the marginal tissues.

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

For the tick Hyalomma anatolicum anatolicum, at constant temperature and humidity, the pattern of oviposition is constant, and consists of a peak period, usually after 2–3 days, followed by a gradual decline.

Oviposition proceeds more rapidly in constant darkness than in continuous light.

With increased temperature the oviposition period is decreased, but with increased humidity the period is extended.

The largest eggs are laid from 0 to 48 h after the peak of egg production, and no correlation has been observed between female size and egg size.

The number of eggs produced by a tick is directly proportional to its engorged weight, and since the engorged female weight is a direct reflexion of its unfed weight, the number of eggs laid is directly dependent on the size of the unfed female.

Guinea-pigs show partial immune response to adults of H. anatolicum anatolicum when the ticks are fed on them repeatedly. This minimizes the amount of nutrients imbibed and accordingly egg-laying potential is not realized.

The material on which this study was made was presented to us by Dr R. P. Chaudhuri, and we gratefully acknowledge his kindness.

An experimental study of hatching in the oxyurid nematode Aspiculuris tetraptera indicates that the major factors in the initiation of hatching are the pH and temperature of the environment and that the process is aerobic. Carbon dioxide and reducing agents do not appear to be as important factors in the hatching of eggs of this nematode as they are in the hatching of eggs of ascarids. It is suggested that the physiology of hatching in ascarids is not necessarily the typical nematode pattern.

My grateful thanks are due to Dr P. Tate, Director of the Molteno Institute, and to Dr D. L. Lee for their encouragement and very helpful discussions on various aspects of this study.