The species described in this paper were found in Bithynia tentaculata from the Wentloog level, near Cardiff, South Wales. The larval stages of Psilotrema oligoon are redescribed and the taxonomy of the adults discussed. C. frondicola sp.nov. is a psilostome cercaria which has the probable flame-cell formula 2 [4 + 4 + 4 + 4 + 3 + 3] = 44. It emerges at night or during early morning, is positively phototactic and will not normally encyst on anything but vegetation. C. granocutis sp.nov. is also a psilostome cercaria; it is very small and has the probable flame-cell formula 2 [3 + 3 + 3 + 3 + 3] = 30. It emerges during the afternoon and will encyst freely on a variety of substrata.

I thank Professor J. Brough of the Zoology Department, Cardiff, for the facilities provided, Dr D. A. Erasmus for supervising and encouraging this work and Dr S. M. Willmott, Director of the Commonwealth Bureau of Helminthology, for providing library facilities. This study was carried out during the tenure of a D.S.I.R. research studentship.

Arthur & Chaudhuri (1965) have reviewed the literature dealing with the taxonomic status of Nosomma monstrosum (Nuttall & Warburton, 1908). They have also redescribed the adults and have given the host and geographical distribution of this species. There have, however, been no descriptions or records of immature stages of this species. They are described and illustrated here from laboratory-reared and field-collected material. The parent females of the laboratory-reared material were compared with the female specimen in the Indian Museum collection, reg. no. 2172/17, on which the description of the female was based (Warburton, 1918).

Experiments were performed to determine at what phase or phases of its parasitic development Boophilus microplus becomes infected with Babesia bigemina. Problems due to Boophilus microplus being a one-host tick were overcome by artificially transferring ticks from one host to a second just prior to a moult. In several experiments, a babesiacide was used to eliminate parasites so that the exposure of ticks to infection could be restricted to one phase of their development. Further information was obtained by correlating the presence or absence of patent parasitaemia in the bovine with the presence or absence of infection in ticks which fed on it.

It was found that ticks were susceptible to infection for approximately the last day of their parasitic life. Infection at other times, that is, during larval, nymphal and the major part of the adult stages was not usual. Four of five attempts to infect larvae and all five attempts to infect nymphs were negative.

Infection of ticks always resulted when a patent parasitaemia coincided with the last day of parasitic life. Ticks were infected in all thirteen instances when these conditions existed but in only seven of eighteen instances when the animal was a carrier but was not showing parasitaemia.

Stage-to-stage transmission did not occur, although suitable conditions for this existed on nine occasions.

Phyllobothrium piriei sp.nov. (Cestoda: Tetraphyllidea) from the intestine of Raja naevus in the North Sea resembles P. dagnallium, P. radioductum and P. britannicum more closely than any other known species of the genus but differs from these mainly in its host, in having distinctly bifid bothridia with faint marginal loculi and about 150 testes in each proglottid. Brief comments are made on the preference shown by the adult for the posterior region of the intestine and on a modification of its bothridium for attachment to up to 12 villi.

This work was supported by generous financial aid from the Natural Environment Research Council. I wish also to record my gratitude to Professor V. C. Wynne-Edwards and Dr P. A. Orkin for reading and suggesting improvements to the manuscript and to the Director and staff Marine Laboratory, Aberdeen, in particular Dr B. B. Rae and Mr Stuart Pirie, after whom this species has been named, for providing live rays. Alasdair McVivar of this department, who has now begun an independent study of the intestine of Raja naevus as a habitat for helminth parasites, kindly provided information for Fig. 9.

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.

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).

The cellular and syncytial components of the mature uterine bell of the palaeacanthocephalan, Polymorphus minutus are described, and compared with previous accounts of the histology of uterine bells. Each uterine bell always contains 17 separately distinguishable nuclei. This situation provides a good illustration of the phenomenon of organ eutely, common in Acanthocephala. The luminal spaces of the bell are described and their relevance to the translocation of eggs discussed.

I should like to thank Dr D. W. T. Crompton for his help and encouragement during the course of this work and Dr P. Tate for the provision of facilities. The work was carried out during the tenure of an S.R.C. Research Studentship.

An evaluation programme is presented for determining activity of unknown compounds on Ascaris suum larvae migrating into pulmonary tissues of animals. Data on gross lung lesions due to migrating ascarid larvae were obtained in a series of 44 screening tests consisting of 223 group observations from 1115 mice orally infected with A. suum. Lesion scores were graded in ascending order from 0 to 5 depending upon number and extent of pulmonary haemorrhages. In general, there was no significant difference in lesion scores between untreated mice and mice treated with unknown compounds in their ration. The programme is based on an initial 95% rejection of compounds with a 5% ability to retest compounds in groups of mice.

The grand mean score for 44 tests was 2·88. Ninety per cent confidence limits for means among tests established scores at 2·21 and 3·55, and among groups of mice at 1·76 and 4·00, When the test mean was less than 2·2, the ascarid ova used for infection were considered non-virulent. Compounds selected as active were in groups of mice having a mean lesion score of 1·76 or less. Banminth, Styquin and Tetramisole showed larvicidal activity. A reasonable compromise exists in this system wherein false leads are tolerated to avoid screening out effective materials. The host-parasite relationship is proposed as a valuable tool for anthelmintic evaluation.

The authors wish to thank Mr W. Henry and Mr M. Jackley of this laboratory.

Studies have been undertaken to examine the alternative hypotheses of a Poisson or a negative binomial distribution of the numbers of strongyloid nematode eggs in deposits of faeces produced by flocks of grazing sheep, which were proposed in certain mathematical models for the distribution of strongyloid infective larvae on pastures.

Observations were made on the distribution of the weights of faecal deposits produced by flocks of ewes and lambs. In all cases the distribution was found to be significantly positively skewed. A possible fundamental basis for this skewness has been suggested.

The distribution of strongyloid egg concentration in random samples of faecal deposits collected from pasture, and the distribution of egg concentration for the single species N. battus and N. filicollis in rectal samples of faeces collected from a lamb flock, have both shown highly significant departures from a Poisson distribution. This, coupled with the fact that the weights of individual deposits vary widely, provide strong empirical grounds for rejecting the Poisson distribution as a model for the distribution of egg numbers per deposit.

An examination of the distribution of egg counts for N. battus and N. filicollis in samples of faeces collected from a lamb flock at weekly intervals through the spring and summer has suggested that the distribution tends to become more overdispersed with the passage of time and as the mean egg count is falling.

Fundamental grounds for preferring a more general model, such as the negative binomial, to describe the distribution of strongyloid egg output in flocks of sheep have been discussed.

These studies were carried out under the supervision of Dr H. D. Crofton, to whom I am deeply grateful for his stimulating encouragement and constructive criticism. My thanks go also to Professor J. E. Harris, C.B.E., F.R.S., for the provision of facilities in the Department of Zoology, and to Professor T. K. Ewer and Mr M. R. McCrea for the provision and handling of pastures and sheep at the School of Veterinary Science, Langford. This work was undertaken during tenure of a C.S.I.R.O. Overseas Research Studentship.

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.

A method for rearing blowfly larvae giving good synchronization of growth is described. Electron microscope studies showed that the lateral lamellae of the pharyngeal ridges each have a swelling at the tip, and that the lamellae from adjacent ridges are interdigitated in a regularly alternate pattern. Formation of the ridges in the second-instar larva begins 8 h before the moult when the four rows of partially syncytial epidermal cells lying beneath the floor of the pharynx begin to form nine dorsal projections. These lengthen and gradually take up the form of the ridges, the fine divisions which are the lateral lamellae being the last feature to develop. After a two-layered epicuticle has been formed the cytoplasm rapidly withdraws from the ridges leaving them, and the new floor of the pharynx, strengthened by a network of fibres. At the moult a further zonse of cuticle, showing parallel striations, is added to the base of the ridges. The lateral lamellae are epicuticular structures. The importance of the intracellular formation of cuticle is discussed.

I should like to thank Dr P. Tate under whose supervision this work was carried out for helpful advice, and wish to acknowledge financial support from the Agricultural Research Council in the form of a Postgraduate Studentship.

Third-generation rediae and escaped cercariae of Philophthalmus gralli are found primarily in the interacinar spaces on the periphery of the hepatopancreas of its molluscan host, Tarebia granifera. The presence of these stages of P. gralli causes both mechanical and physiological damage to the adjacent host cells. Mechanical damage results from ingestion by rediae and pressure exerted by motile rediae and cercariae. Histochemical tests involving two different substrates L-leucyl-α-naphthylamide and L-leucyl-4-methoxy-β-naphthylamide, have revealed the occurrence of aminopeptidase activity associated with the body surfaces of both rediae and cercariae. This exopeptidase is believed to be responsible for the lysis of the cytoplasm of surrounding host cells during migration and to be associated with extracaecal digestion. The intensity of the enzyme activity is correlated with the ages of the rediae and cercariae. Young rediae did not reveal aminopeptidase activity and cercariae within redial brood chambers revealed little or no activity.

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

Chick embryos have been infected with sporozoites of Eimeria tenella, but not with E. brunetti, and died from coccidiosis 5 days after infection.

Chick embryos can be protected from death due to coccidiosis by some but not all drugs which give a therapeutic response in chickens. The system is therefore not satisfactory as a screening tool, but may have applications in studies on the nature of drug activity.

Splenectomy, either alone or in conjunction with hormonal bursectomy, did not appreciably affect E. tenella infections as measured by oocyst output.

Operated birds became resistant to re-infection as readily as the controls and it seems unlikely that the spleen in chickens plays an essential role in the host's defence against the Eimeria.

Thanks are due to my colleague, Mr P. L. Long, for his advice and interest throughout the work. Mrs J. Simpson gave valuable technical assistance.

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.

Studies based on the mixed antiglobulin reaction have shown that γ-globulin is adsorbed from normal human sera by the cuticle of parasitic nematodes. Using antiglobulins specific for IgA, IgM and IgG, it was possible to demonstrate uptake to titres of 4, 64 and 128, respectively. Adsorption continued for at least 24 h, and the responsible immunoglobulins could be absorbed from the sera by nematode preparations.

A comparison of normal human sera with sera from cases of ascariasis and visceral larva migrans revealed that there was no significant difference between the titre of anti-cuticular immunoglobulins in normal sera or sera from helmin-thiases. It is suggested that these immunoglobulins adsorbed by the nematode cuticle represent cross-reacting, naturally occurring antibodies.

I am sincerely grateful to Professor R. R. A. Coombs, F.R.S., for his help, advice and encouragement, and to Mr M. J. Eburne for splendid technical assistance.

The adult and two nymphal stages of Hoplopleura kitti sp.nov. from Rattus berdmorei Blyth, and the adult stage of Polyplax pricei sp.nov. from Rattus niveiventer Hodgson are described and illustrated.

I thank Dr K. C. Emerson, 2704 N. Kensington Street, Arlington, Virginia 22207 for making these specimens available to me for this study. I am grateful to Dr Edwin F. Cook of the University of Minnesota for reading the manuscript.

Morphological features of the bladder wall of Cysticercus fasciolaris and carbohydrate analysis of the contained fluid are described. The bladder fluid was found to have a higher concentration of glucose than the plasma of the respective host animal. The bladder wall has a prominent duct system with numerous cytoplasmic extensions and interconnections. It is suggested that the bladder may function in the nutrition of the developing cysticercus by providing a reservoir of raw material which may be utilized by the growing strobila.

The authors wish to thank Dr Theodor von Brand for many helpful discussions, and Dr Harley G. Sheffield and Mr Ned M. Etherington for their advice and technical assistance in the preparation of the electron micrographs.