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.

An experiment was performed to test whether the larvae of the sciomyzid fly Dichetophora biroi are able to ‘recognize’ and reject Lymnaea tomentosa snails infected with Fasciola hepatica.

The analysis of the results indicates that the larvae do not show any obvious preference when given the simultaneous choice of non-infected and infected snails, and also that, under laboratory conditions, the latter are not more vulnerable than the former to the larval predation.

I wish to express my sincere gratitude to Dr R. P. Herd for his help and encouragement during this work. I am also grateful to Professor C. O. Berg, Cornell University (U.S.A.); Dr J. J. Lynch, C.S.I.R.O. Pastoral Research Laboratory, Armidale (N.S.W.) and Dr M. D. Rickard, University of Melbourne, for valuable advice and fruitful discussions. Dr J. A. Thomson, University of Melbourne, critically read the manuscript.

Cordonema gen.nov. is proposed for C. venusta sp.nov. (type species), C. longifuniculata (Sobolev, 1952) comb.nov. and C. solonitzini (Sobolev, 1943) comb.nov. The genus differs from Skrjabinoclava Sobolev, 1943, in lacking laterally directed loops of the cordons. Cordonema venusta sp.nov. from Cinclus pallasi from Taiwan, differs from Cordonema longifuniculata in its spicule ratio of 4:1 compared to 2:1. It differs from C. solonitzini in having longer cordons in proportion to body size and in spicule ratio, which is 2:1 in C. solonitzini.

Skrjabinoclava cincli (Yamaguti, 1935) Sobolev, 1943, is redescribed from males and females from the type host, Cinclus pallasi, from Taiwan. Skrjabinoclava decorata (Solonitzin, 1928) Sobolev, 1943, is redescribed from Lonchura fuscans from Borneo.

Skrjabinoclava rallae sp.nov. from Rallus striatus from Palawan differs from S. horrida in its spicule ratio of 4.7:1 compared with 3.6–4:1, and in the structure of the right spicule. It differs from S. cincli in having shorter cordons and spicules. Skrjabinoclava amaurornae sp.nov. from Amaurornis phoenicurus from Palawan differs from S. alii Ali, 1968, in having longer cordons, shorter pharynx, and in the absence of a sclerotized bar connecting the first spines of the lateral rows. It differs from S. cincli in having larger body spines and a right spicule of different shape.

Keys to the genera in Echinuriinae and the species in Cordonema and Skrjabinovlava are included.

We wish to acknowledge the field support by Dr D. S. Rabor, Department of Biology, Silliman University, Dumaguete City, Negros Oriental, Republic of the Philippines, and the technicians of the Parasitology Department of Naval Medical Research Unit No. 2 for general assistance in procurement and examination of hosts. Dr John M. Kinsella kindly read the manuscript and improved it with his advice.

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 quantitative study has been made of the relationship between Moniliformis dubius and Periplaneta americana.

1. Eggs removed from the body cavity of the worm hatch at a higher rate after dessication and after a short period of time following removal.

2. There is an exponential decline in the additional number of cystacanths recovered as the dose is increased linearly.

3. Female cockroaches are more susceptible to high levels of infection than males.

4. Direct injection into the haemocoele produces a similar recovery rate to that from oral infection.

5. Previous infection does not seem to affect the success of a superimposed infection.

6. Rates of development and growth are described.

7. The effect of the parasite on the concentration of free amino acids in the haemolymph was found to be negligible.

I would like to thank Miss S. Arnold and Mr D. Barnard for technical assistance, Mr E. Walters for help with statistical analysis, Dr D. W. T. Crompton for many helpful discussions and Dr P. J. Whitfield for reading this paper. This work has been carried out during the tenure of a Science Research Council Studentship.

Young cercariae were covered with a thin nucleated primitive epithelium which was lost when the true tegument appeared beneath it. The tegument was at first similar to the primitive epithelium in that it was a nucleated, cytoplasmic syncytium but it could be distinguished from the primitive epithelium by its thickened outer membrane and by the layer of interstitial material beneath its basal membrane. The tegumental nuclei became pycnotic and disappeared and, at about the same time, nucleated subtegumental cells became continuous with the tegument. Two types of small, dense bodies were formed in the subtegumental cells and passed into the tegument. Later in development the tegument became filled with dense, granular material and spines were formed. The fully developed cercarial tegument was covered with a surface coat of fibrous material which was specifically attached to the outer membrane of the tegument.

The observations described in this paper formed part of a thesis approved by the University of London for the Degree of Ph.D.

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 ability of various mammals to transmit Dracunculus medinensis has been investigated. The most suitable definitive host for laboratory transmission was the rhesus monkey (Macaca mulatta) and, in 11 out of 14 of these animals female worms emerged 321 to 371 days after first infection. The parasite has now been maintained in monkeys for four laboratory cycles. Five of 11 dogs and 17 of 30 cats had developing parasites in their tissues when autopsied, but no worms emerged from two dogs left for over a year and only a single worm from one of nine cats. Monkeys showed a seemingly haphazard pattern of susceptibility to infection and reinfection, although none of the 17 animals exposed was completely refractory. Cyclops vernalis americanus (Marsh) was an easily maintained and efficient intermediate host; a 90% infection rate with an average of two infective larvae per Cyclops was obtained.

This work was supported by a grant from the Tropical Medicine Research Board through the Ministry of Overseas Development. Thanks are due to Mrs Vivian Duckett for technical assistance.

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.

The structure and ultrastructure of the excretory system of Panagrellus redivivus, Ditylenchus myceliophagus, D. dipsaci and the second-stage larvae of the Heterodera rostochiensis are described. Panagrellus has two lateral ducts, a median duct and a gland. The two lateral ducts are joined over the anterior part of the oesophageal bulb to form a loop. Anteriorly this loop continues as a median duct, which opens to the exterior in an excretory pit, part of the system lies free in the pseudocoelom. The lumen of the lateral excretory duct and the greater part of the median duct is surrounded by capitate tubules, which open into the lumen of the excretory duct. Capitate tubules develop by the invagination of the hypodermal membranes and lie embedded in thick cytoplasm surrounded by mitochondria. Ensheathed in cell membranes the excretory duct forms an anastomosis in the loop and at three other places along the length of each lateral excretory duct. At these regions there are nerve endings. The excretory gland opens posteriorly into the loop and is full of Golgi complexes, endoplasmic reticulum and secretory granules.

In the system of Ditylenchus and the second-stage larva of Heterodera the right lateral duct is absent while the left lateral excretory duct continues anteriorly past the median excretory duct; a true loop is not formed. The median excretory duct lies embedded almost throughout its length in the excretory gland. Capitate tubules are present along the length of the lateral excretory duct, but, unlike Panagrellus, are not present around the median excretory duct. Anastomosis is not formed in the excretory ducts. In other respects the system of the species studied is similar to that of Panagrellus.

The capitate tubules form a system of fine microtubules. Their ultrastructure and, particularly, their association with large numbers of mitochondria, is very reminiscent of structures thought to be concerned with an active transport role, related to ionic and osmoregulation in other phyla.

The excretory system is almost certainly hypodermal in origin. Differences between the morphology and relations of the median duct of Enoplus (Narang, 1970), on the one hand, and that of the other forms studied suggest that these ducts may have different origins: the presence of separate nuclei in the lateral duct and gland portions of the system would be consistent with this view. It is considered that the two parts may have originated separately and have become joined during evolution. It is also shown that the excretory system of Ditylenchus cannot be derived either from an H-shaped system or from a primitive gland system.

I wish to thank Professor C. Ellenby and Mr L. Smith for their helpful criticism.

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.

Viktorocara acholonui sp.nov. is described from a babbler, Alcippe brunnea, from Taiwan. It differs from V. charadrii Belopolskaja, 1959, and V. guschanscoi Leonov, 1958, in having a longer pharynx and in shape of tip of left spicule, and from V. tenuis (Maplestone, 1932) in having 6 rather than 10–13 pairs of preanal papillae.

Smetaleksenema gen.nov. is proposed for Skrjabinobronema pileati Smetanina et Alekseev, 1968, which becomes Smetaleksenema pileati (Smetanina et Alekseev, 1968), comb.nov. It differs from Ancyracanthopsis Diesing, 1861, in having serrated cephalic processes. The species is redescribed.

Ornithostrongylus vetterlingi sp.nov. is described from emerald doves, Chalcophaps indica, from Borneo and Palawan. It differs from all other species in the shape of the gubernaculum and in possessing a striated, common spicule sheath which binds the spicules tightly together.

Also reported and briefly discussed are: Viguiera dicrurusi Gupta, 1960; V. buckleyi (Yeh, 1954) Chabaud, 1957; Cyrnea (P.) excisiformis Yamaguti, 1935; C. (P.) leptoptera (Rudolphi, 1819) Chabaud, 1958; C. (C.) eurycerca Seurat, 1914; Physaloptera alata Rudolphi, 1819; Ornithostrongylus quadriradiatus (Stevenson, 1904) Travassos, 1914; O. travassosi Maplestone, 1932; Amidostomum skrjabini Boulenger, 1926; and Epomidiostomum anatinum Skrjabin, 1915.

We wish to acknowledge the field support by Dr D. S. Rabor, Department of Biology, Silliman University, Dumaguete City, Negros Oriental, Republic of the Philippines, and the technicians of the Parasitology Department of Naval Medical Research Unit No. 2 for general assistance in procurement and examination of hosts, and to Mr H. G. Deignan (deceased), U.S. National Museum, for identification of birds.

Initial work for this study was supported by funding under Public Law 480, section 104(c), by funds provided by the Bureau of Medicine and Surgery, Navy Department Work Unit MR 005.20-0098, by contract no. NR 103-690/N 0014-66-C0094, between the Office of Naval Research, Department of the Navy, and the Southwest Foundation for Research and Education, and research grant HE-5-P01-6M-13252-02 from National Institutes of Health, USPHS.

Final efforts were sponsored by Department of the Army, contract no. DADA17-68-C-8094.

Maximum levels of protective antibody activity were reached in the circulation of rats given a primary infection or one or two re-infections of Plasmodium berghei at the time the infection was finally eradicated. This association of maximum protective antibody activity with complete clearance of the parasite was also found in recipients of lymphoid cells from immune donor rats and suggests that a high level of protective antibody activity is one essential factor in complete elimination of the parasite.

Excellent technical assistance was given at different times by Mrs J. Page, Mr A. J. Edwards and Miss D. Leader.

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.

Upon stimulation, following a period of ambient conditions, infective A. tubaeforme larvae follow a committed characteristic pattern of activity, after being released by short-term mechanical or continuous photic stimulation. For the photic response this is stimulated by an increase in the intensity of stimulation, and for non-dark-adapted larvae a sudden fivefold increase in illumination is required, irrespective of previous stimulation.

Acetylcholine chloride, adenosine triphosphate, γ-amino butyric acid, histamine diphosphate, 5-hydroxytryptamine, neostigmine bromide, physostigmine (eserine), potassium hydroxide, succinyl choline chloride and d-tubocurarine chloride have been added to larvae and their subsequent postures and activity recorded. It is concluded that the typical activity pattern of larvae may be altered by the use of drugs which interfere with neuromuscular phenomena, and therefore the activity responses of infective A. tubaeforme are based on sensory and neurosecretory rather than energetic considerations.

We thank Mrs Helen Foreman for maintaining the larvae and the Medical Research Council of Great Britain for their generous support.

Development of cercariae within intramolluscan germinal sacs is recognized to be in seven stages; in brief, these stages are: 1, germinal cell; 2, naked cell aggregate; 3, germ ball prior to elongation; 4, elongating germ ball; 5, tail bud stage; 6, tail elongation stage; and 7, fully developed cercaria.

Schistosoma mansoni cercariae at each of the developmental stages is described.

The dimensions of both germinal and somatic cells comprising the bodies of developing S. mansoni cercariae decrease with maturation.

The surfacial membrane of Stage 3 cercarial embryos is formed by a number of small somatic cells which migrate to the surface and coalesce.

The chronologic and partially synchronized development of S. mansoni cercariae is presented.

The body-tail ratio during S. mansoni cercarial development is presented.

Twelve rabbits were dosed with infective larvae of a sheep parasite Nematodirus battus and killed in a serial manner over a period of 32 days. The percentage of worms which became established was 10–36% over the first 24 days after infection. The minimum period of development of the parasitic stages was similar to that in sheep, although adult worms recovered from rabbits were on average smaller than worms normally found in sheep. The course of migration followed by the parasitic larvae was the same as in sheep. The distribution of fourth-stage larvae and fifth-stage worms along the small intestine was that of a normal frequency distribution. N. battus was still infective for lambs and rabbits after one passage through the rabbit.

I would like to express my appreciation for the advice and encouragement given in the course of this work by Mr M. G. Christie.

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.

Thirty-five lambs (14 weeks old), the progeny of Border Leicester rams mated with Border Leicester × Merino ewes, were divided at random into two groups. Seventeen lambs in Group A received 3500 Haemonchus contortus larvae weekly and 18 lambs in Group B received 500 larvae each day: the dosage was decreased to 1400 larvae weekly and 200 larvae per day after 8 weeks.

Pathogenicity was found to be higher when the lambs were infected with a small number of larvae daily (daily group) than when the same number of larvae were given in one dose at weekly intervals (weekly group). The period of survival was consistently shorter in the former group.

No significant difference in faecal egg counts was observed between the two groups.

Reduction in food intake per head per day and in live weight were more pronounced in the ‘daily group’ than in group dosed weekly. The discrepancy in food consumption and live weight between these two treatments was more apparent at the end of the experiment.

Some resistance was observed in both groups but the level of resistance was not high.

Accumulation of inhibited larvae was apparent after 104 days in the ‘weekly group’ and after 78 days in the ‘daily group’. An infection arising from a large number of larvae given at weekly intervals induced a mild form of resistance leading to an accumulation of inhibited larvae at the end of the experiment. This was less apparent in lambs infected with the same number of larvae given each day.

Interference with ovulation in adult females was recorded in both treatments. Sex discrimination against the female population both in the extent of elimination of adults and in the retardation of development of fourth-stage larvae was recorded and the intensity of discrimination was more pronounced with the weekly regime of larger doses than with the same number of larvae but given in daily doses. The worms were eliminated sporadically and not continuously. A challenge infection of 10000 larvae given to two lambs in the ‘weekly’ regime treatment on the 107th day initiated a partial selfcure reaction demonstrated by an immediate fall in faecal eggs per gram (i.e. Epg) but the egg count returned to the original value in 28 days.

Nippostrongylus brasiliensis of either sex, 216 h old, were injected directly in the intestinal lumen of 10-week-old laparotomized male rats in the duodenum or near the ileocaecal valve and their position ascertained 24 h later. Males migrated anteriad farther when females were placed in the duodenum than when they were alone or when 32P tagged males were in the duodenum. Females migrated anteriad similarly when they were alone or when males were in the duodenum or when 32 P tagged females were injected in the duodenum. The findings are consistent with the idea that females attract males anteriad at a distance.