It has been demonstrated that under prolonged experimental conditions lipid is utilized most quickly under optimal conditions of tonicity, gaseous exchange, pH and sensory stimulation. There is good evidence that activity may be an appreciable energy-consuming process. It has been deduced, however, that the low Reynold's number means viscous forces dominate locomotory energy consumption, and work done is proportional to the square of the velocity. Osmoregulation in hypotonic media and tolerance of hypertonic media do not require appreciable energy.

Locomotion is only possible in limited environmental conditions, and these may also be conditions of peak basal metabolism. Larvae are able to enter quiescence which is not energy-demanding, in poor conditions. Larvae can survive anaerobiasis, but finally die without reduction in lipid and cannot convert lipid to carbohydrate for anaerobic metabolism.

The help of Mrs Helen Foreman in staining the larvae and for statistical analyses, and of Mr J. M. Smith is greatly appreciated. I would like to thank Dr Elizabeth U. Canning for kindly providing the microdensitometer and Professor G. S. Nelson and Dr D. A. Denham for enabling us to establish A. tubaeforme in our cats. The generous support of the British Medical Research Council is much appreciated.

The growth curve, rate of neutral unbound lipid synthesis, and relationship between morphogenesis and lipid reserve have been studied at 30 °C. The feeding process, including a theoretical calculation of bacterial requirements of preinfective larvae, is presented, together with some measurements of the most important variables in ingestion, expulsion of water through the anus, and its dependence on larval posture is described.

Larval stages have been tracked on agar; L1 are so inactive that no tracks were obtained; L2 show short, irregular tracks, and infective larvae strong, long and straighter tracks. The locomotory activity of L2s is primarily for feeding, whereas L2s are adapted for dispersion and host location.

I thank Mr J. M. Smith for tracking the larvae and Mrs Helen Foreman for staining them, Dr Elizabeth U. Canning for making available the scanning microdensitometer and Professor G. S. Nelson and Dr D. A. Denham for enabling us to establish A. tubaeforme in cats. Finally the generous support of the British Medical Research Council is appreciated.

During 2 min incubations of Trypanosoma gambiense (bloodstream form) with [U-14C]glucose (1 mM) over 60% of absorbed label was detected in free alanine. In the presence of 12·5 mM unlabelled alanine, the amount of alanine synthesized from glucose was reduced by less than 10%. These data support previous observations on the high level of transaminase activity in African human trypanosomes.

Alanine, aspartate and glutamate were metabolized to various other free amino acids whereas a significant amount of label derived from [14C]arginine could not be accounted for by amino acid assay.

The sulphur containing amino acids, cysteic acid and taurine, were apparently synthesized from alanine, glutamate and arginine. The significance of these syntheses is poorly understood.

Following incubations of trypanosomes for 2 min in exogenous amino acids the internal free pool became imbalanced due to accumulation and metabolism of the substrate amino acid.

Evidence obtained indicated that the level of free endogenous glutamate may be rate limiting for the glutamate-pyruvate transaminase system.

The results of several experiments that included variation of the pH and concentration of the extracts and analysis of the role of enzymes separated from midgut fluid by electrophoresis indicated that hatching involved two or more proteolytic enzymes that digested the cytoplasmic layer and embryophore. Amylases from T. molitor and other sources were shown to play no part in hatching. A defined medium based on analyses of midgut fluid and containing trypsin, chymotrypsin and peptidases was shown to digest the embryophore and effect the release of hexacanths in a time comparable to that obtained with T. molitor extracts. The specificity of the enzymes attacking the cytoplasmic layer remains unknown.

Over 90% of Hymenolepis diminuta cysts administered by stomach tube become established in CFLP, and Porton strains of mice. The rate of growth of single worm infections in terms of dry weight and length was determined. The rate of growth of H. diminuta in mice is slower than in rats even in worms only a few mm long. In most mice growth ceases abruptly on day 10±1 day when the worm is 4–30 cm long, destrobilation usually occurs leaving a scolex and neck often 0·5–2 mm in length. Destrobilated worms can survive for at least 47 days but little if any regrowth occurs unless the worms are surgically transplanted into rats or previously uninfected mice. Normal growth appears to be resumed within hours in both recipient hosts. The cause of destrobilation is probably not physiological; position of establishment and forward migration during growth of the worm in mice is similar to that in a rat. Destrobilation occurs well before the worm fills the small intestine lengthwise. Strong evidence of an immunological response being involved is given by the fate of a secondary infection given 22 and 28 days after the primary. Lower % recoveries were recorded in secondary infections killed 6–9 days later, and the worms were severely stunted. The various lines of evidence are discussed and it is concluded no reasonable doubt exists that H. diminuta is rejected by CFLP and Porton mice as a result of an immunological response.

Worm counts, faecal egg counts and erythrocyte losses are recorded for lambs which were exposed on a naturally infected pasture for different periods in different years. After each exposure period the lambs were kept under conditions in which no further infection could occur; at varying times, usually after the infections had had time to maturo, the lambs were killed and examined. A detailed analysis of the results is given. It is concluded that the negative binomial distribution of worms among sheep within a flock is not a reflexion of the pasture distribution of infective stages but is the result of a combination of Poisson distributions, these distributions being generated by genetic subsets within the flock. There is a remarkable correlation between the numbers of Haemonchus present and the numbers of worms of the other genera. It is suggested that there are host-mediated common elements in the biomass regulating parameters of mixed trichostrongyle infections and that there is a resource-allocating device. Three main hypotheses are proposed. The hypotheses are: (1) The dimensional constraints on the host-parasite system are the results of various kinds of pace-setters or biological clocks. In each annual cycle the parent worms programme the rate of development through each generation. (2) The rate of development of the worms is tied stochastically or deterministically to the rate of senescence and death. (3) The rate of development and death for each trichostrongyle is set at the start of each season by a host factor which acts on a comparable area of the genome in each trichostrongyle. Methods of testing these hypotheses are discussed and the work related to other systems.

Groups of Rhipicephalus appendiculatus ticks were given single doses of irradiation (range 0·25–16 krad) at different stages in their life-cycle: unfed nymphs, engorged nymphs, moulting nymphs and unfed adults. The effects of irradiation were assessed by evaluating the subsequent performances of the ticks when fed on rabbits. Observations were carried through until the viability of egg batches from surviving females had been recorded. Irradiation of unfed and engorged nymphs produced similar effects on the ticks, whilst irradiation of moulting nymphs and adults produced effects which were different from those produced on the other two groups but similar to each other. Ticks were in general unaffected at irradiation doses below 2 krad, but at this level and above, survival rates, mean engorged weights, percentage egg weights and viability of eggs were reduced, and feeding times were extended. Male ticks appeared to be more susceptible to the effects of irradiation than female ticks. Males irradiated at 4 krad were sterile, but since they survived doses considerably higher than this they might well prove suitably competitive in further trials should a sterile male release be considered feasable. The possibility is also considered of irradiating Theileria parva parasites in ticks and thus altering the parasites in some way that could be used in studies of immunisation of cattle against East Coast fever.

A study was carried out to determine if snail nutrition influences infectivity of Schistosoma mansoni cercariae for mice. The percentage of worms recovered after infection was the chief criterion used to determine infectivity. Six groups of Biomphalaria glabrata were raised on separate diets of (1) a standard formula with and without lettuce, (2) ‘Gaines Meal’ dog food (compressed pellets), (3) a commercial chicken feed, (4) Romaine lettuce, (5) squash, and (6) the rhizome of a Caladium plant. At 6 weeks the snails were infected and the cercariae resulting from the different snail infections were used to infect mice. Seven weeks later the mice were sacrificed and worms were recovered by perfusion. Snails raised on squash, lettuce and the Caladium rhizome were only one-half the size of those receiving either the standard formula or the ‘Gaines Meal’ at the time of infection, and produced fewer than one-fifth as many egg clutches. However, the percentage parasitemia on all six groups of mice only varied from 49 to 55%, and there were no apparent differences in the size or development of the worms from the different groups of mice.

A new species of phryxid (Isopoda, Bopyridae) found attached in the pterygostome region of a pontoniid shrimp, Periclimenes grandis (Stimpson), is described. The only specimen, found at Mazizini, Zanzibar, has been placed in a new genus, which is defined here. The parasite, Orophryxus shiinoi gen.nov., sp.nov., is the only bopyrid which has been found attached in the pterygostomial region.

The development and survival of the eggs and larvae of O. circumcincta was studied by spreading the daily faecal output of a sheep over a 2 m square grass plot for 1 week. Observations were carried out for 3 years on material spread at 4-weekly intervals and broadly similar results were obtained in each year. Development time was long in eggs placed outside in January, February, March, November and December. Yields of larvae were small and all were dead within 5 months. During the rest of the year development time was about 2 weeks, yields of larvae were high and larvae survived until July or August of the following year. The significance of these findings in devising systems of grazing management to control parasitic gastroenteritis is discussed.

Observations have been made on the development and survival of the free-living stages in faeces deposited out of doors at different times of year, and on the migration of infective larvae to the surrounding herbage. Laboratory experiments were performed to assist in the interpretation of the field observations. Studies were made on the rate of development to the infective stage in faeces kept at different temperatures. The rates at which eggs and larvae of Strongylus vulgaris, S edentatus, S. equinus and Trichonema nassatum developed on faecal-agar cultures at different temperatures were compared. Studies were also made on the effect of desiccation of faeces on the development and survival of the free-living stages. The results of these observations are discussed in relation to the development of herbage infestations on British pastures.

A laboratory strain of Eimeria acervulina was found to develop in the caeca when large numbers of excysted sporozoites were injected into that organ. Both schizonts and gametocytes were formed, but parasitization of the caeca was never heavy and did not increase with serial passage. The infection was not increased by the simultaneous injection of betamethasone.

A quantitative assessment of the effect of larval Caryophyllaeus laticeps upon its intermediate host, Psammoryctes barbatus, was obtained by comparing the energy budgets of infected and uninfected tubificids from the same natural populationm throughout the course of a year. Measurements of the energy transformations during growth, reproduction and respiration of tubificids indicated some of the effects of the parasite.

Infection had no influence upon the life-span of the host, but progressively decreased its growth and prevented reproduction. By contrast no significant differences were detected between the respiration rates of infected and uninfected animals. Decrease in the production of infected host tissue became apparent as soon as the parasite was detectable. Over the first 6 months loss in production due to the parasite was 50%, and over the whole life-span 59·9%. The production: respiration ratio of infected tubificids was also lower, but differences in assimilation were probably only small. The overall effects of the parasite upon its host population are slight, and the loss in tubificid nutriment available for fish food due to the parasite is less than 5% and of little economic importance. The way in which the parasite actually influences its host's physiology is discussed, and the effect of C. laticeps upon its host's energy budget compared with that of a plerocercoid larva on its fish host.

I should like to thank Dr M. Palmer for the loan of her Warburg flasks, Mr J. Harris for taking samples for me when I was unable to do so,'and Mr G. G. Vickers for many helpful comments and discussions on ecological energetics. I am also grateful to Mr G. Baileyfor combusting the samples for me.

Attempts to repeat the isolation of an ecdysone-like steroid from Biomphalaria glabrata revealed that some of the manipulations described by Muftic (1969) were physically impossible to repeat. With modified procedures no ecdysone-like steroid was found. The original publication gives scant attention to certain experimental details. Some sections of the text bear very close resemblance to earlier publications by different authors. The amount of substance claimed to have been isolated, and the long survival period claimed for Schistosoma mansoni larvae in vitro, are claims which, amongst others, seem highly unlikely a priori. All attempts to contact Muftic have proved to be futile. It is suggested that the paper is, at least in part, erroneous and that any future reference to it should clearly indicate its suspected invalidity.

Despite these results, it is considered likely that future investigations will demonstrate physiological roles for steroids in snails.

I wish to acknowledge the stimulating communications of Drs E. L. Hansen, M. Voge, R. E. Thorson, C. S. Richards, J. N. Kaplanis, G. Nace, R. Monroe, and of E. Chernin, who first brought this matter to my attention. Theanalytical steroid work could not have been done nor interpreted without the considerable time and effort willingly given by Drs F. Kohen and R. Counsell of the University of Michigan College of Pharmacy. My snail populations were supplemented with snails from the tanks of Mrs B. Caveny. Technical help was given by E. Perisho, G. Lindsay and P. LoVerde. Financial support was kindly provided by Dr J. B. Burch. This investigation was supported in part by the United States-Japan Cooperative Medical Science Program administered by the National Institute of Allergy and Infectious Diseases of the National Institutes of Health, Department of Health, Education and Welfare, grant N.I.A.I.D. AI-7364, and in part by NSF grant GB-29315. Improvements were made to the first draft of the manuscript after it was critically read by Drs E. L. Hansen, F. Kohen, M. Voge, E. Chernin, R. E. Thorson and J. N. Kaplanis.

Forty-five cattle, which had recovered from EOF and been kept free from reexposure to infection for periods of 1–43 months, were given a single uniform lethal challenge using a stabilate prepared from triturated infected ticks. All withstood the challenge which killed the five controls. There was an increase in the incidence of mild febrile reactions with time since last exposure to T. parva, indicating a gradual loss of immunity in the absence of reinfection. The duration of the immunity was not related to the severity of the initial reaction.

We are indebted to our colleagues on the Immunological Research on Tickborne Cattle Diseases and Tick Control Project, with whom we designed and carried out the experiment.

An analysis of the course of infection of mixed oral infections of 12 cystacanths of Moniliformis dubius in 174 male and 179 female Wistar rats has been undertaken.

There was a marked decline in the average recovery rate of worms of both sexes from hosts of both sexes during the course of the infection.

Female worms from both male and female rats showed, on average, a greater power of survival than male worms from the third period (10–13 weeks) onwards.

Male rats were found to retain, on average, a greater number of worms of both sexes than female rats.

We wish to thank Miss Susan Arnold and Mr David Barnard for excellent technical help.

A large Babesia species was found in a leopard (Panthera pardus) in Kenya. It was established in domestic cats but no other animal was found to be susceptible. The parasite has been compared with other piroplasms of felids and it was found to differ from them in some significant characters. It was established as a new species and named Babesia pantherae.

We would like to thank Miss B. O. Vidler for her assistance, Dr S. F. Barnett for many helpful discussions and Professor N. D. Levine for pointing out the need for this description.

The parasite was isolated when we were working at the East African Veterinary Research Organization at Muguga in Kenya and we are most grateful to that organization for facilities.