Three coccidian parasites were found in California Banded King Snakes, Lampropeltis getulus californiae: Isospora crotali, an intestinal Eimeria, and a haemogregarine. Schizogonous stages of the latter occurred predominantly in liver, and were remarkably similar to those described for other blood Coccidia.

Dr Charles E. Shaw of the San Diego Zoological Society identified the snakes, and Dr Gordon Ball, Professor of Zoology at the University of California, Los Angeles, kindly reviewed 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.

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.

It was found that antelopes in the Serengeti area, Tanzania, East Africa, are heavily infested with lung nematodes. Five species of the family Protostrongylidae, namely, Protostrongylus africanus sp.nov., P. etoshai Ortlepp, P. gazellae Yeh, Pneumostrongylus calcaratus Mönnig and P. cornigerus Ortlepp, as well as one species of the family Dictyocaulidae, Dictycaulus viviparus (Bloch), were recorded.

A detailed description of Protostrongylus africanus sp.nov., which is conspicuous for its gigantic size, is given, and the lesions caused by this lung nematode are described.

The distribution and incidence of lung nematodes in the various antelope species are discussed.

Echinoparyphium serratum sp.nov., with 37 collar spines, is described from experimentally infected ducklings and chickens. It appears to be most closely related to E. aconiatum but differs from it in having smaller eggs, fewer tegument spines, almost confluent vitellaria in the post-testicular region, and the inner margin of the ventral sucker is serrated. The natural host is unknown but thought to be a bird.

Bile composition may account for the markedly different recovery percentages of adult worms from the two experimental hosts.

Miracidia hatch between 9 and 11 days at 22 °C. Experimental infections of snails with miracidia have not been obtained.

Rediae occur naturally in Isidorella brazieri Smith, and free-swimming cercariae encyst in the pericardium of the same species of snail.

This latter part of the life-cycle is based on strong circumstantial evidence. A few cysts were occasionally found in the pericardium of Lenameria sp. but the enclosed metacercariae were dead.

The cercaria can be distinguished from Cercaria echinata, the cercaria of E. aconiatum, and C. equispinosa in having cystogenous gland cells containing granular material only, and the inner margin of the ventral sucker serrated.

I would like to record my sincere thanks to Professor J. D. Smyth for his advice, and comments on the manuscript.

An investigation was carried out to discover how the sporocysts of Cercaria doricha obtain nutrients from their host Turritella and how castration of the snail is brought about.

Histological studies of infected molluscan visceral humps showed no trace of toxic or mechanical damage by parasites. There appears to be an inverse relationship between the number of sporocysts and the amount of gonadial tissue.

Biochemical analyses of molluscan tissues indicated that parasitized snails were not depleted of amino acids or purines. The concentration of plasma protein was higher in parasitized snails and the concentration of free amino nitrogen in head–foot muscle showed an increase of 7%. Histochemical investigations indicated that sporocysts do not remove glycogen from the molluscan connective tissue which surrounds them. The sporocysts appear to lack copious secretions of proteinase.

The lack of conditions of starvation in parasitized specimens of Turritella, together with the great similarity of the free amino acid pools of sporocysts and molluscan gonad, suggests that the sporocysts obtain their food supply directly from the gonadial tubules. It is concluded that this is achieved by use of a placenta-like region of the sporocyst wall which is in contact with the gonadial tubule and which appears to be identical with the region of proliferation of the cercariae.

This paper formed part of a thesis for the degree of Doctor of Philosophy in the University of Reading. I wish to thank the Science Research Council and the University of Reading for financial awards, and Professor Alistair Graham for encouragement and guidance during the work.

Chevreuxia americana sp.nov. is described from the gizzard of the avocet, Recurvirostra americana, in Colorado. It is compared with the four previously described species in the genus.

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.

Small spines of maximum size 0.28 μm × 0.5 μm have been found all over the shells of the eggs of Schistosoma mansoni and S. haematobium. The small spines on S. haematobium eggs are less pointed than those on S. mansoni eggs. They consist of inner and outer parts made up of subunits, and they are continuous with the main part of the shell underneath. S. mansoni eggs still within the blood vessels of the gut have extracellular material between the spines and there is cell debris over them. The scanning electron microscope shows the increased surface area of the egg shell due to the small spines.

I wish to thank many people for their help with this work and in particular Dr F. Hawking, Dr S. R. Smithers and Mrs. L. Ebden.

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.

Seventy-five per cent of Echinoparyphium serratum metacercariae excysted within 10 min in a trypsin/sodium cholate solution after successive pretreatments with pepsin and sodium dithionite. Excystment appears to be an active process as the cyst wall is unaffected by the treatment except in the vicinity of the ‘escape aperture’.

Optimum development to sexual maturity in vivo required 72 h and was divided into six easily recognized stages against which development in vitro could be judged. These were undifferentiated (excysted metacercariae), cell multiplication, organogeny, gametogeny, vitellogenesis and oviposition. Migration of the juveniles from the lower regions of the intestine to the duodenum in the first few hours after infection was noted.

Cultures were prepared from excysted metacercariae and a variety of media were used. The beneficial effects of shaking cultures were apparent. No development took place in media containing saline, Parker 199 medium, homologous and heterologous sera, chicken embryo extract, albumen and glucose, either alone or in various combinations, although, relative to saline or Parker 199 medium controls, survival times were increased in some and decreased in others. Survival in some media above pH 7 was longer than below pH 7. Serum substrates in culture vessels, and the presence of additional glucose, did not increase longevity.

Development to organogeny was achieved using a yolk/albumen/saline or 199 medium, and addition of yeast extract to this favoured the later stages of development up to and including vitellogenesis. In general only a small percentage of juveniles in each culture reached vitellogenesis, and the amount of egg-shell protein formed and the size of the worms was always less than in vivo. Furthermore, development in vitro was much more prolonged than in vivo. Variability in development in vitro may be due to failure of the excystment procedure to satisfy completely the physiological ‘triggers’ which are probably necessary for normal development.

In some specimens vitellogenesis was reached without production of sperm. In others, production of eggs was thought to be inhibited by either a general deterioration of the juveniles or premature ‘tanning’ of the egg-shell protein, as significant amounts of egg-shell protein, sperm, and apparently normal ova were present.

The results of culturing E. serratum are compared briefly with those of D. phoxini.

I should like to record my sincere thanks to Professor J. D. Smyth for his advice and comments on the manuscript.

Mitotic metaphase chromosomes of the tsetse fly Glossina palpalis R.-D. have been investigated.

The chromosomes studied were in circumoesophageal nervous tissue from young pupae, stained with aceto-orcein and spread by squashing.

The diploid number of chromosomes was shown to be 6, consisting of 2 long pairs and 1 short pair at metaphase.

This finding is discussed briefly in relation to previous descriptions of the chromosomes of G. tachinoides West. and G. morsitans morsitans West. and to accepted systematic divisions of the genus Glossina into subgeneric groups.

I wish to thank Mr H. Dickson for assistance with photography. I thank Mr D. A. T. Baldry for advice and suggestions concerning the manuscript. Mr T. M. Leach has also made suggestions concerning the manuscript, and as Director of the Nigerian Institute for Trypanosomiasis Research, has given his permission to publish this paper.

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.

Five strains of Entamoeba histolytica isolated from man and capable of growth at room temperature were tested for virulence by inoculation into the caeca of young rats. The results showed all strains to have a low infectivity and none produced caecal ulceration. Ten laboratory strains of E. histolytica were examined for growth at 25 °C, but none were established at this low temperature.

Myxidium oviforme is described from Irish salmon Salmo salar. Its close relationship with M. folium, M. moxostomatis and M. aplodinoti, and its possible economic importance are discussed.

Attempts to establish infections of M. oviforme in young, parasite-free salmon are described, and the reasons for their negative results discussed.

This work was carried out during the tenure of a Medical Research Council Scholarship for Training in Research Methods between October 1964 and September 1966, and forms part of a thesis submitted for the Ph.D. Degree of the University of London. Grateful acknowledgement is due to Dr J. G. Ross and Dr G. Lawson of the Veterinary Research Division of the Ministry of Agriculture for Northern Ireland for information on salmon infections in Ireland, to the Ministry of Agriculture and Fisheries for the provision of young salmon, and to Messrs Barnetts of Frying Pan Alley Ltd., London, for the provision of salmon livers.

A combination of histochemical and electron microscope techniques have demonstrated, in Cyathocotyle bushiensis, alkaline phosphatase activity in the matrix of the tegument, in the distal and basal plasma membranes of the tegument, in the wall of the ducts extending from the adhesive organ gland cells and in the wall of the adhesive organ microvilli. Acid phosphatase activity was much stronger and was present in the tegument matrix and in the granular component of the secretion from the adhesive organ gland cells. Strong acid phosphatase activity was also present in the cisternae of the endoplasmic reticulum of the adhesive organ gland cells.

I am greatly indebted to Professor Brough for the excellent facilities available within this department. I also wish to thank Professor J. Sinclair (Department of Mining) for electron microscope facilities extended to me in the early stages of this investigation, and to Mr W. Henderson, Mr T. Davies and Miss M. Williams for their invaluable assistance. The purchase of the Huxley ultramicrotome, coating unit and an AEI EM 6 electron microscope was made possible by a grant from the Science Research Council.

The presence of three types of cystogenous gland cells, designated as protein, mucopolysaccharide, and mucoprotein cells, in P. gralli cercariae has been demonstrated.

The protein cells are PAS-negative but positive for tyrosine-, histidine-, and arginine-containing proteins. No tryptophane is detectable in this type of cell. The mucopolysaccharide cells are positive for acid mucopolysaccharides and are gamma-metachromatic. The mucoprotein cells are PAS-positive and diastaseresistant.

The mechanism of metacercarial cyst formation is described. The fully formed cyst consists of three walls designated inner, middle and outer walls. The outer wall is subdivided into a basal and a peripheral layer.

Histochemical studies on the cyst walls have shown that the outer and middle walls are PAS-negative but the inner wall is PAS-positive and diastase-resistant. All the walls include proteins but differ in their amino acid contents.

By comparing the chemical composition of the cyst walls with that of the three types of cystogenous gland cells, it is evident that each cyst wall is formed from the secretions of two or more types of cells. The outer and middle walls appear to be formed from the secretions of both protein and mucopolysaccharide cells, and the inner wall from protein, mucopolysaccharide, and mucoprotein cells.

This research was supported in part by a grant from the American Cancer Society.

A hypothesis is developed to explain how the nematode propels itself around in the egg before hatching. The normal reactions at the ends of the egg to the pressure exerted by the nematode are each equivalent to a force propelling the nematode around inside the egg and to a displacement force. A diagram of forces that satisfies the requirements for undulatory locomotion has an asymmetrical egg with ends of variable curvature. In such an egg the only effective forces acting on the nematode are the propulsive forces along the longitudinal axis of the nematode and frictional forces between the nematode and egg shell. A steady glide occurs when these two forces are equal. As the nematode moves around the ends of the egg, the muscles in contact with the shell come under tension and owing to the change in curvature of the shell they contract and release the potential energy necessary for propulsion.

Measurements on the shape of eggs, the configurations of actively moving nematodes in the egg, ciné film of eggs and a model of a nematode in an egg do not disprove the hypothesis.

Prior to hatching the surface area of the egg increases and increased force by the head of the nematode at one end of the egg produces a protuberance which eventually bursts under the influence of the mouth stylet which punctures the shell and the pressure from the nematode's head. Propulsive forces within the egg enable the larva to hatch.

Nematodes at a root surface form waves of large amplitude with the result that the head and stylet often meet the root at right angles. The nematode then attaches itself to the root and active use of the mouth stylet makes the initial puncture in the plant's epidermis. Penetration to a depth of 100 μm occurs under the influence of propulsive forces developed by that part of the body outside the root. Thereafter, the section of the body within the root develops the necessary forces and the posterior part outside the root remains almost stationary. The nematode penetrates the root intermittently to a depth of 40–60 μm every 20–40 min corresponding to the penetration of a series of cell walls.

The relationships between egg shape, movement in the egg, mode of hatching and site of hatching present a further interesting problem because it is possible that nematodes that hatch into an environment outside the host require some pre-hatch movement to bring the muscular system to a high level of efficiency. Nematodes that hatch within the host may not need such an adaptation.

Thanks are due to Mr I. R. Dick for his help and useful discussion, to Mr K. W. J. Crocker for technical help and to Miss Colleen Hill who made the drawings.

Syphacia (Syphatineria) oceanica sp.nov. is described from the squirrel Sundasciurus steerii juvencus. It is closest to S. transafricana Chabaud & Biocca, 1955, differing from it in having a cephalic vesicle, an isthmus between oesophagus and bulb, and in characteristics of the gubernaculum. Syphacia (Syphacia) critesi sp.nov. is described from S. steerii juvencus and the flying squirrel Hylopetes nigripes. It is closest to S. thompsoni Price, 1928, differing from it in lacking cephalic vesicle, alae, and cervical papillae; in having a long oesophagus and shorter gubernaculum Syphacia (Syphacia) magnispicula sp.nov. is described from H. nigripes and S. steerii juvencus. It is characterized by having a spicule 312–338 μm long, much longer than any species yet reported. Syphacia (Syphacia) coli sp.nov. is described from H. nigripes and the rat Rattus exulans luteiventris. It is closest to S. critesi sp.nov., differing from it in sizes and shapes of oesophagus and gubernaculum, in having lateral alae, and in egg size. Syphacia sp. is reported from Rattus exulans luteiventris; Blattophila sp. is reported from the skunk Mydaus marchei; and Allodapa sp. is reported from Sundasciurus steerii juvencus.

The authors wish to express their appreciation to Dr D. S. Rabor, Silliman University, Dumageute, Negros Oriental, Republic of Philippines, for general support in field activities and for tentative host identifications; Mr Max Thompson, Bishop Museum, Honolulu, for assistance in collection of hosts and Dr David H. Johnson, Research Curator, Division of Mammals, U.S. National Museum Washington, D.C., for final host identifications. Thanks are extended to Dr W. G. Dyer and Dr P. D. Leiby, Minot State College, for technical assistance during the course of this work, and to Dr W. W. Becklund, Beltsville Parasitological Laboratory, for the loan of specimens for comparative purposes. Special thanks are due to Mrs MayBelle Chitwood, whose efforts greatly improved the quality of this work.

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.