A description is given of the male, female, nymph and larva of Rhipicephalus carnivoralis sp.nov., a parasite of carnivores in East Africa, and its affinities within the genus are discussed.

Its developmental periods under laboratory conditions are given and its hosts and distribution in the field are recorded.

The author wishes to thank the Director of the East African Veterinary Research Organization for permission to publish this paper. She is also most grateful to all who made field collections of this species for her; to the British Museum (Natural History), London, for the loan of specimens from their collection; to J. P. J. Ross for the loan of specimens from his collection and to D. W. Brocklesby and K. P. Bailey, who carried out the experiments on the transmission of East Coast fever. Dr G. Theiler, Mr G. H. Yeoman, Mr G. M. Kohls, Dr C. M. Clifford and Dr H. Hoogstraal kindly checked the manuscript before publication and made helpful suggestions. Finally, she would like to thank Professor P. C. C. Garnham and Dr Charles Wilcocks for their advice on the name of this tick.

The gregarine Stylocephalus mesomorphi has a diploid chromosome number of 8. The diploid stage is represented only by the zygote nucleus before the metagamic divisions start. The other stages in the entire life history of this gregarine are haploid.

The mitotic chromosomes are four in number, one being the longest, two of medium size and the fourth the smallest.

I am grateful to Professor J. C. Uttangi, Head of the Zoology Department, Karnatak Science College, Dharwar, for the encouragement he gave me throughout this work. I am also greatly indebted to my colleague Dr M. J. Devadhar, for having given me many valuable suggestions.

The adult stage and nymph 2 of Hoplopleura johnsonae sp.nov. and the nymphal stages of H. captiosa Johnson are described. The morphology of Hoplopleura nymphs and the infraspecific variations of H. captiosa Johnson are discussed, and a key to the seven species of Hoplopleura Enderlein known in Thailand is also presented.

I am grateful to Dr K. C. Emerson, Arlington, Virginia, and Dr Zofia Wegner, Gdansk-Wrzeszcz, Poland, for the loan of materials on which this work was based. I am also indebted to Dr Phyllis T. Johnson, University of California at Irvine, and Dr Edwin F. Cook, University of Minnesota, for their suggestions as to this species complex and reading the manuscript.

There was no difference between the worm burdens or the lengths of the worms recovered from sexually immature male and female mice infected with Amplicaecum robertsi.

In mice older than 70 days there were fewer larvae recovered from the female than the male host. The larvae were also longer in the male than in the female mouse.

The suckling mouse harboured fewer larvae than the weanling; the susceptibility of the mouse continued to increase with increasing age until the one-hundredth day in the males and the seventy-fifth day in the females. In animals older than this an age resistance was apparent. It is suggested that the much lower susceptibility of the suckling mouse is due to the small gut and villi size reducing the establishment of the larvae.

Worm growth also varied with host age, the longest larvae being recovered from the suckling mice and successively smaller worms from each older age group up to the seventy-fifth day, beyond which there was no significant change in worm growth with age of the host. There was no difference between the worm burdens and the lengths of the worms recovered from 90-day-old mice. The injection of testosterone had little or no effect on the host–parasite relationship of gonad-ectomized animals. Larvae from gonadectomized mice were significantly shorter than those from the intact hosts.

The biology and life cycle of Apatemon gracilis minor is briefly described.

The morphology of the cup–shaped forebody with the small lappets, the pear-shaped subcuticular cells and the very flexible finger–like adhesive organ lobes is considered in some detail.

An extensive description of the body musculature is given and the mode of attachment of the parasite to the host mucosa is studied.

The main results of the histochemical tests are: (a) a relative absence of enzymes in the adhesive organ and a greater activity in the lappets; (b) the presence of two types of esterase, a non-specific esterase of B-type in the caecal cells and a non-specific esterase of resistant type, possibly a non-specific cholinesterase, in the rest of the reacting sites in the parasite; (c) a relatively small activity for leucine aminopeptidase; (d) the presence of RNA at all sites of enzyme formation; and finally, (e), the presence of enzymes and carbohydrates in the cuticle.

The activities of the parasite result in a local disruption of the host intestinal mucosa at the site of attachment. It is suggested that this is a result of the activities of the enzymes secreted by the parasite.

The absorption of nutrients and the circulatory function of the excretory system are discussed.

I should like to express my sincere thanks to Dr D. A. Erasmus for helpful discussions and advice during the progress of the work and to Professor J. Brough for giving me the opportunity to work in his department. The study was conducted during the tenure of a grant from Svenska Vetenskapliga Centralrådet i Finland.

Adults of Nematospiroides dubius recovered from female mice were smaller than those from male mice. In general, a similar result was obtained for infections in rats. Longer worms were recovered from gonadectomized rats than from intact animals; the difference between the growth of the worms in male and female hosts was still apparent.

Treatment of castrate male rats with testosterone was more favourable to the growth of the male than the female worm. Oestradiol treatment of spayed female rats caused a stunting of both sexes of the nematode. However, this effect was least noticeable among the female worms.

An increase in the age of the rat resulted in a decrease in the lengths of the worms recovered. The worms grew to greater lengths in 25-day-old mice than in rats of the same age and sex.

It is suggested that the sex hormones may have two effects on worm growth. First, an indirect effect involving the nutrition of the worm, and secondly, a direct effect of the hormones themselves on the tissues of the worm.

This work was done during the tenure of a Department of Scientific and Industrial Research Studentship. My thanks are due to Dr E. T. B. Francis for his help and criticism, and to Professor I. Chester Jones, in whose department the work was done, for the facilities he provided.

R. carnivoralis has been shown to be capable of transmitting T. parva under experimental conditions and stages of the protozoon have been found in sections of salivary glands of the tick.

The commencement and duration of haemolysis and the length of time the erythrocytes remain intact in engorged virgin and fertilized females and in male Ornithodoros savignyi were investigated by means of red cell antigens.

There were no differences between fertilized and unfertilized females, haemolytic tests were possible in both groups up to 120 h after engorgement.

In the male group haemolytic tests were possible only up to 24 h after engorgement.

In both female groups inhibition of the in vitro haemolysis could be observed until the fifth day, after feeding on a calf with erythrocyte mosaicism, indicating the loss or masking of antigens due to the damage of cell walls.

The authors wish to thank Dr G. Theiler for her interest and advice during this work.

Ten-month-old Blackface sheep double vaccinated with X-irradiated larvae of H. contortus were shown to be highly resistent to individual challenge with 50000 larvae. Compared to unvaccinated sheep, the percentage reductions in the numbers of worms established 6, 9, 12 and 16 days after challenge were 83, 90, 99 and 100 respectively. The immune response was directed against the 3rd and 4th larval stages.

The author wishes to express his thanks to his colleagues at the Wellcome Laboratories for Experimental Parasitology for their co-operation and help during the period of this experiment.

This work was supported by a grant from Allen and Hanburys Ltd., Ware, England.

Two new, nine little known species and nine unnamed ‘species’ of Echeneibothrium Beneden, 1850, have been investigated and observations have been made on the ‘related’ genera, Discobothrium Beneden, 1870, and Pseudanthobothrium Baer, 1956. Brief descriptions of the species are given, but a discussion of the history of each differs greatly from most previous accounts in that few or no synonyms have been listed for the species and in that nine forms are left unnamed; this approach differs greatly from that in a large number of taxonomic papers in helminthology. A detailed discussion of the reasons for adopting this procedure is, therefore, given. A provisional key to nineteen ‘species’ of Echeneibothrium is included. E. minutum sp.nov. closely resembles E. variabile var. exiguum of Euzet (1959), described in this paper as ‘Echeneibothrium sp. of R. clavata’, but occurs only in R. batis and differs in its very small size, in having only about ten proglottids, long peduncles to the bothridia and a myzorhynchus which remains evaginated in fixed specimens. It differs from E. demeusiae Euzet, 1959, mainly in the number of proglottids, testes and loculi. E. elongatum sp.nov. resembles E. dubium from which it differs in the length and form of the strobila, in having only six clearly visible loculi in each bothridium, about twenty testes and in that it occurs in R. circularis. It has, however, more characters in common with a species referred to in this paper as ‘Echeneibothrium sp. from Raja naevus’ and which possesses eight loculi. A list is given of twenty-seven species wrongly allocated by various authors to the genus Echeneibothrium. The comparative morphology of some species of the genus, their ecology and speculations on their life-histories, are described.

It is shown for the first time that Echeneibothrium from species of Raja caught off the British Isles, and presumably from rays of other localities, can be separated into two distinct biological groups. One group includes species which possess shallow open bothridia covering comparatively large areas of the host's mucosa, a variable myzorhynchus which may be either rudimentary or very large and spherical eggs laid singly or in capsules; these occur mainly in rays from shallow waters and in which the mucosa of the intestine lacks prominent villi. The other group includes species in which each bothridium possesses a small opening adapted for attachment to a single villus, the myzorhynchus is consistently cylindrical, the eggs have long polar filaments and the species occur in deep water rays with well-defined villi on the intestinal mucosa. Studies on variation in the form of the eggs in different species of Echeneibothrium in relation to the behaviour and feeding habits of the various host-species suggest that the eggs are eaten by arthropods which are most likely to form part of the diet of the final host. A general trend towards an increase in the complexity of the bothridium and a decrease in the size of the myzorhynchus in Echeneibothrium is thought to be of considerable advantage to the species and an indication that Rhinebothrium, which is restricted to the Myliobatoidea, has evolved from a form like Echeneibothrium which is restricted to the Rajoidea. This supports the view that the Myliobatoidea have evolved from the Rajoidea. The results from this study of Echeneibothrium illustrate the following general rule which can be applied to the Tetraphyllidea, namely, those species which are abundant in any given host are very well adapted for attachment to the host's gut and cause little, if any, damage while rare species are often highly pathogenic.

This work would not have been possible without generous financial aid from the Department of Scientific and Industrial Research and various kinds of other aid and encouragement from a number of persons, in particular Dr Gwendolen Rees.

It was begun in 1958 at the University College of Wales, Aberystwyth, the British Museum (Natural History), University of Montpellier, France, University of Neuchatel, Switzerland, the Plymouth Marine Laboratory and the Aberdeen Marine Laboratory during my tenure of a D.S.I.R. Fellowship. I wish to record my gratitude to Dr Rees who has also suggested improvements to the manuscript and to the following persons: the late Professor T. A. Stephenson, F.R.S., Dr E. E. Watkin, Mr S. Prudhoe, Dr L. Euzet, Professor Jean G. Baer, The Director, Dr F. S. Russell and Staff, in particular Mr J. Green and Mr A. Mattacola, of the Plymouth Marine Laboratory, and the Director and staff, in particular Dr B. B. Rae and Dr Z. Kabata, of the Aberdeen Marine Laboratory.

The work was later continued at the University College, Cardiff, and I am most grateful to Professor James Brough for providing excellent research facilities and to Mr W. O'Grady for technical assistance.

At the Bureau of Helminthology, St Albans, much encouragement from Professor R. T. Leiper, C.M.G., F.R.S., enabled me to put the work together while having free access to his invaluable collection of books and reprints on helminths; it became unnecessary to search elsewhere for the literature. Mr G. Dimmock gave technical assistance for which I am most grateful.

Male mice harboured more third-stage larvae of Amplicaecum robertsi than females; these larvae also grew longer than did those in female mice. Gonadectomy removed the differences, evident between the sexes, in both the numbers recovered and the growth of the third-stage larva, between male and female mice. The worms recovered from the gonadectomized hosts were smaller than those from the intact male and female host.

Pregnant female mice harboured more worms than either the male or the non-pregnant female mouse. These worms were also smaller than those from the male and non-pregnant females. There was no difference in the growth of the larvae from gonadectomized and pregnant hosts.

The treatment of spayed female mice with progesterone resulted in an increase in the size of worm population as compared with the numbers of worms recovered from intact female mice. The worms from the progesterone-treated spayed females were also longer than those from the spayed female hosts.

Treatment of normal female mice with progesterone resulted in an increased recovery of worms compared with the numbers of worms recovered from normal female animals. The worms were stunted but they were of a size comparable to those recovered from pregnant female mice.

It is suggested that the increase in the size of worm populations and the stunting of the worms recovered from pregnant female mice is associated with the effects of progesterone in relation to the hormone balance associated with the ovary at the time of pregnancy.

A strain of Trypanosoma avium isolated from Corvus frugilegus in England was readily cultivated in vitro in diphasic blood agar, or blood nutrient agar, media at 28 °C.

In both media, small trypanosomes appeared which morphologically resembled the metacyclic forms from the insect vector and which were infective to canaries. They were more numerous, and developed more regularly, in the medium with the nutrient agar base.

At 40–41 °C a few of these small trypanosomes apparently developed into large trypanosomes similar to, but not identical with, those seen in the blood of infected birds.

The method of attachment of the cattle tick Boophilus microplus (Canestrini) has been investigated on cattle of different breeds and susceptibility to infestation.

Despite their differing sizes, the larval, nymphal and adult mouthparts penetrate to a similar depth towards the base of the Malpighian layer. Penetration may occur within 5 min of the arrival of the tick on the host.

Attachment is accomplished by the secretion of a cement substance in which the mouthparts are embedded and which adheres firmly to the hosts skin.

The cement consists of two main components: a cortex of carbohydrate-containing protein, stabilized by quinone tanning and disulphide linkages, and an internum which is lipoprotein in nature.

The start of the secretion of cement and the initial cutting of the host tissues by the chelicerae occur simultaneously. Final rapid engorgement of each stage is preceded by a secondary secretion of cement into a fluid-filled cavity which forms directly beneath the mouthparts and provides additional support.

It is concluded that attachment is an entirely mechanical process by an inert cement which does not provoke the development of host-parasite factors inimical to the tick.

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

The cercaria of Fasciola hepatica has four types of cystogenic cells which can be characterized by their position and by their histochemical properties. On the basis of their histochemical reactions, each type of cell was related to a specific layer in the cyst wall of the metacercaria.

The tanned protein cells occupy almost all of the ventral half of the body and contain large granules consisting of basic protein and phenols. Although the presence of a phenolase could not be demonstrated, it is considered that the granules are composed of tanned protein. Before the cercaria leaves the redia, the granules are secreted to the exterior to form a layer contained by a thin, bounding membrane. The tanned protein cells form layer I of the cyst wall.

The mucopolysaccharide cells are concentrated at the dorsal and dorso–lateral surface except for a few around the ventral sucker. They contain acid and neutral mucopolysaccharides and contribute to layers II and IIIb and c. Some of the granules are secreted to the exterior before the cercaria leaves the redia, in a similar manner to the tanned protein granules.

The mucoprotein cells are few in number and lie centrally between the ventral sucker and the pharynx. They give reactions for proteins and carbohydrate-protein complexes and probably help to form layers II and IIIa of the cyst wall.

The keratin cells fill almost the entire dorsal half of the body and contain numerous rod-like granules. These rods are composed of a protein containing sulphydryl groups and disulphide bonds and give rise to layer IV. After secretion of the tanned protein granules to the exterior, some of the keratin cells move to the ventral part of the body formerly occupied by the tanned protein cells.

The outer cyst wall exists in a preformed state in the free swimming cercaria.

I am grateful to Professor J. D. Smyth and Dr J. A. Clegg of this department for advice and encouragement during this investigation and in the preparation of the manuscript. The work was done during the tenure of a Commonwealth Post-Graduate Scholarship.

When infected with equal numbers of eggs of Amplicaecum robertsi normal male mice harboured more larvae than normal females. Treatment of the mice with thiouracil and thyroxine eliminated the differences between the sizes of the worm populations shown between the sexes in normal mice.

Thiouracil treatment increased the susceptibility of mice to A. robertsi infection, but caused a stunting of the larvae. Thyroxine treatment had no effect on the host–parasite relationship.

It is suggested that the differential ability of the larvae to hatch, penetrate the tissues of the host and migrate to the liver in thiouracil- and thyroxine-treated mice was responsible for the differences in the sizes of the larval populations observed.

This investigation was carried out during the tenure of a Senior Research Fellowship from the Wool Research Board of Australia. I should like to thank Professor J. F. A. Sprent for his continued interest and Mr C. Wilkinson for his careful assistance.

A flagellate morphologically similar to Polymastix melolonthae (Grassi, 1879) was found inhabiting the colons of three out of over 200 cockroaches (Periplaneta americana) examined. A morphological description of the flagellate is given.

I wish to express my thanks to Professor H. P. Moon, in whose department this work took place, for his help and advice; to my supervisor, Dr Marjorie G. Guthrie, for her advice, encouragement and constructive criticism, and also to Dr Ann Bishop, F.R.S., and Dr Elspeth W. McConnachie for their advice.

The ultrastructure of the parenchyma and interstitial material and the interrelations between them are described.

The interstitial material, composed of a granular matrix containing fibres, is shown to ramify as a network between parenchymal cells and around organ systems. It is postulated that this structure is a ‘skeleton’.

In certain localized areas the interstitial material between parenchymal cells is absent and at these points adjacent cells are united by attachment plaques (desmosomes) without tonofibrils.

The possible functions of the parenchyma are considered and it is suggested that these cells are responsible not only for secreting the interstitial material, but also store glycogen and act, in the absence of a circulatory system, as a transport system for metabolites and excretory products.

Excystment of the metacercaria of Fasciola hepatica is an active process and occurs in two stages—activation and emergence. Activation is initiated by high concentrations of carbon dioxide, reducing conditions and a temperature about 39 °C. The reducing conditions increase the rate of action of the other two stimuli. The carbon dioxide stimulus need only be applied for 5 min, but the exposure time to the reducing conditions has to be of the order of 30 min. Changes in the order of application of the stimuli carbon dioxide and redox potential have no effect.

The second phase, emergence, is triggered by bile. Metacercariae were held in an activated condition for 24 h, and when bile was added emergence took place normally.

During excystment the metacercariae exhibit a complex behaviour pattern. After activation there is an initial period of rotatory activity, but after about 20 min a quiescent phase ensues when the metacercariae contract away from the cyst wall at an imperceptible rate. This behaviour occurs in response to stimulus from a high concentration of carbon dioxide and a temperature about 39 °C. When the metacercariae are exposed to bile the second phase of activity is initiated, consisting of antero-posterior thrusting movements directed against the ventral side of the cyst wall. Within about 15 min the juvenile flukes escape through a small circular hole in the ventral surface of the cyst wall which corresponds to the ventral plug region.

A twofold increase in resistance to glycarbylamide was induced in a strain of Eimeria tenella in chicks. This strain remained susceptible to amprolium, nicarbazin, nitrofurazone, zoalene, 3,5-dinitrobenzamide, 2-chloro-4-nitrobenzamide (M & B 5921) and spiramycin.

At least an eightfold resistance to 2-chloro-4-nitrobenzamide (M & B 5921) was developed in another strain of E. tenella. This strain was also resistant to nitrofurazone, zoalene and 3,5-dinitrobenzamide, but not to glycarbylamide, amprolium, nicarbazin and spiramycin.

A single test showed no transfer of drug-resistance when the two resistant strains were given simultaneously to the same birds.

When a small number of parasites of a glycarbylamide-resistant strain of E. tenella was introduced into a larger inoculum of the normal parent strain, the resistant individuals appeared to diminish in number during passages through untreated chicks.

I wish to thank Mrs B. M. Mitchell, Miss C. A. Hitchcock and Miss J. Watkins for technical assistance at various stages of the work.

An examination with light and electron microscopes has been made of the cell type which is considered by some authors to be a sporozoan parasite, Rhabdospora thelohani, and by others to be a tissue cell of fishes and amphibians.

The cell type was found in the minnow Phoxinus phoxinus in many tissue sites, including olfactory and pharygneal epithelia, kidney, eyes and brain. In some specimens it could not be found in any tissue.

The cell has a thick fibrous wall, a basal nucleus, an apical mitochondrial zone, a Golgi body, and from 8 to 50 characteristic refractile rodlets.

The rodlets give a negative reaction to the Feulgen test for nuclear material, but are positive to the periodic acid–Schiff stain, a test for polysaccharide. Glycogen does not appear to be present in the rodlets.

Under certain circumstances the rods rupture the cell wall and may protrude in the apical region of the cell.

The structures described are discussed with the evidence for and against a parasitic interpretation of the cell. It is concluded that Rhabdospora is a protozoan parasite, whose exact functional and taxonomic status is as yet unknown.

I am grateful to Professor G. E. H. Foxon and to Professor P. C. C. Garnham for their encouragement, advice, and helpful criticism of the manuscript. I am further indebted to the National Spastics Society for the use of the electron microscope housed in Guy&s Hospital Medical School, and to Mr I. D. Bradbrook for his assistance with the histological techniques.