Four groups of guinea-pigs were infected with a range of doses of T. colubriformis. The infections were followed by egg counts and weight measurements, and the adult worms were recovered from the animals post mortem. A multivariate analysis, details of which are given in an appendix, showed that the sensitivity of the measures used was, in descending order, final weight, total egg count and worm burden. The course of the infection is discussed in view of the apparent self-cure mechanism. Precautions are outlined for the experimental use of this hostparasite relationship.

The author is grateful to Professor B. G. Peters for his advice on this work, to Dr P. Silverman of Allen and Hanburys Limited for a supply of T. colubriformis infective larvae and to Dr R. E. Blackith for his advice on the statistical treatment of the data.

1. A plerocercoid of ‘Acanthotaenia’ has been found in large numbers in ‘cysts’ in the pancreas of Rana occipitalis (Günther) in Ghana.

2. ‘Cysts’ containing plerocercoids were fed to Varanus niloticus (L.). Adults of Proteocephalus niloticus (Beddard) were recovered from the intestine 3 weeks later.

3. It is suggested that the life cycle involves three hosts, the first being a copepod.

4. The morphology of the larva and adult is described.

I wish to express my sincere gratitude to the authorities of the University of Ghana for inviting me to spend some time in the Zoology Department there. I am most grateful, also, to Professor R. D. Purchon for his kindly interest and for the facilities which he placed at my disposal. It is a pleasure to thank Dr J. D. Thomas and the technical staff for their assistance in the collection of material.

The status of Trypanosoma suis was held in doubt from the time it was first seen in 1905 until it was re-discovered and carefully studied in the Belgian Congo in 1954.

A description is given of the morphology of single and dividing forms of T. suis as seen in stained thin films made from the blood of infected pigs, and a selection of these is illustrated by line drawings. Briefly this trypanosome is short and stumpy with a free flagellum.

A biometrical study was made on 200 organisms, showing a normal length distribution with a range from 8·5 to 18·5μ, and mean = 14·43μ.

The monomorphism of the trypanosome is verified, and—because of its development in the salivary glands of Glossina—its systematic position as a monomorphic subgroup of the Brucei group is confirmed.

I am much indebted to Dr C. A. Hoare, F.R.S., for the loan of the blood films used in this study and for his interest in the work. I am also grateful to Professor P. C. C. Garnham for providing me with accommodation and equipment at the London School of Hygiene and Tropical Medicine.

Caraphractus cinctus Walker is a parasitoid of the eggs of Dytiscidae. The entire development of this Mymarid takes place in eggs immersed in water and attached to, or embedded in, plant tissue. The winter is passed in diapause as a full-grown resting larva (prepupa) in the host egg.

Diapause of Caraphractus has been studied in the eggs of Agabus bipustulatus. The eggs of this Agabus do not undergo diapause and since the shell is transparent, the larvae of Caraphractus (usually two to three in each egg) are clearly visible during their later stages, so the time of pupation is easily determined.

Experiments were made of chilling the maternal generation of Caraphractus at various stages of development, but this did not lead to diapause in the larvae of the chilled generation, or to any increase in the diapause in the offspring.

When the Mymarid was bred in a north room exposed to natural daylight and darkness, some diapausing larvae occurred in mid-September and by October all were in diapause.

When larvae were reared in long photoperiods (16½–24 hr. light) development was direct, but with short photoperiods (2–15 hr. light), diapause occurred. The critical period lies between 14 and 16 hr. of light.

The stage sensitive to photoperiod is the full-grown larva, and when larvae are reared to this stage under short photoperiod and then transferred to continuous light, direct development is determined within 3 days. Conversely, larvae reared under continuous light and removed to short photoperiod before reaching the sensitive stage, go into diapause.

The larvae are sensitive to light of very low intensity, developing direct with a ‘night’ of 0·03–0·05 f.c. Larvae becoming full grown in the end of August and beginning of September do not diapause and must respond to 2–3 hr. of twilight.

Diapause induced, under artificial photoperiods at any time of the year, usually lasts about as long as the normal winter diapause. If however the prepupae are subjected to temperatures below freezing for about a fortnight (provided they have already been about 15 weeks in diapause) pupation occurs as soon as the temperature is suitable. In cold weather the pupal stage may be greatly prolonged.

I am much indebted to Professor H. G. Callan for his kind permission to use the constant temperature rooms at the Natural History Department of St Andrews University. I have received most valuable help from Dr C. Muir in conducting the various photoperiod experiments, especially in regard to light measurements, and I am most grateful to him for discussing with me many of the problems that arose in the course of this research and for commenting on the typescript of this paper. To Dr H. E. Hinton I am indebted for useful advice, and to Dr Seliga of St Andrews University for his translation of Russian papers. Professor and Mrs Stibbs have been most kind in providing me with information regarding the duration of astronomical darkness in the latitude of St Andrews. I am especially grateful to Dr George Salt for his kindness in reading over my typescript and for his helpful criticisms.

The life cycle of Entobdella soleae, a monogenean skin-parasite of a marine bottom-living flatfish (Solea solea) has been described and related to the habits of the host, which buries itself in the sediment for some time each day and when not buried rarely moves more than a few centimetres from the sea bottom.

The eggs of the parasite are laid by specimens attached to the lower surface of the host and are anchored to sand grains on the sea bottom by an egg stalk bearing sticky droplets. The anchoring device may prevent the eggs from being carried by water currents vertically or laterally out of the region inhabited by soles.

The free-swimming oncomiracidium which hatches from the egg invades the anterior part of the upper surface of the fish, which is the only part exposed when the fish is buried in the sand. After a short period of development on the upper surface the parasite emigrates to the lower surface where sexual maturity is reached.

Adult parasites, which are distributed randomly on the lower surface, are orientated with the adhesive organ upstream with respect to water currents produced by the forward locomotion of the host, but the parasites are capable of moving from place to place on the lower surface of the fish. This movement of the parasite may be connected with the nature of the food.

I wish to thank the Director and Staff of the Plymouth Laboratory and in particular Mr J. E. Green, for invaluable assistance. I am also very grateful to Dr J. Llewellyn for advice and criticism. The work was conducted during the tenure of a Fishery Research Training Grant from the Development Commission.

1. Mice were given a supplement of nicotinic acid, riboflavin or B complex from 1 to 6 months.

2. One mouse of each group was then infested with Myocoptes musculinus for a period of 1 week or 8 weeks. At infestation the supplement was discontinued. Alternatively infestation lasted 8 weeks, the supplement being continued until death.

3. The mitotic rate was estimated for the epidermis of clean and infested mice and the rates compared.

4. Other mice were fed cysteine for periods of three months, one was then infested for a period of 8 weeks before being killed and the mitotic rates of the clean and infested mice compared.

5. It was found that after supplementing the feed of the mice by members of the B group vitamins, quite large numbers of mites (M. myocoptes) could be carried without deleterious effect to the host and without signs of mange.

6. With cysteine supplementation, no gross signs of mange were seen but the mite affected the skin by raising the mitotic rate in the malpighian layer.

I wish to thank Vitamins Limited for supplying the vitamin supplements; and the Royal Free Hospital School of Medicine for facilities for carrying out the work; also Dr A. M. Hughes for her helpful guidance at all stages of the work and especially for reading the paper.

In the Ascaroidea the germinal vesicle, the pronuclei and the nuclei of all the blastomeres prior to chromatin diminution are strongly Feulgen positive. The nuclei of the somatic cells, which become suddenly Feulgen negative upon chromatin diminution, gradually become strongly Feulgen positive again during subsequent development. The nuclei of the germ track cells which are not subjected to chromatin diminution remain strongly Feulgen positive during the whole development. In all the other metazoa, including the nematodes where chromatin diminution does not occur, the germinal vesicle, the synkaryon and the nuclei of the blastomeres during the earliest cleavage stages are Feulgen negative. The latter, however, become gradually strongly Feulgen positive again during the subsequent development. The nuclei of the female germ cells and the synkaryon of protozoa and plants have also been reported to be Feulgen negative. Thus, the Feulgen-positive nuclei of the definitive somatic cells always originate from Feulgen-negative nuclei, in the Ascaroidea from the Feulgen-negative nuclei of the blastomeres and in all other forms of life from the Feulgen-negative nuclei of the eggs. The Feulgen-positive nuclei of the germ cells also originate from Feulgen-negative nuclei except in the Ascaroidea, where they originate from Feulgen-positive nuclei. In the somatic track the sequence of Feulgen-positive nuclei is interrupted in all forms of life and during the germ track it is also interrupted in all forms of life except the Ascaroidea, where it is uninterrupted. These biologically important phenomena are discussed.

These investigations have been supported by a grant from the Knut and Alice Wallenberg stiftelse. The author is indebted to Mrs. M. Wahlström and E. Nowak for their valuable technical assistance.

1. Three new species of Myxosoma (Sporozoa, Cnidosporidia, Myxosporidia) are described from freshwater fish of the genus Tilapia in East Africa.

2. Two of these, M. heterospora and M. brachyspora spp.nov., inhabit the abdominal viscera: the former was found in 41 of 43 fish examined, while the latter was less common. The third species, M. homeospora sp.nov., produces small oval or circular ‘cysts’ in the subdermal muscle and was found in two very young fish only. Spores resembling those of the first two species were also found in one Haplochromis sp.

3. The spores of M. heterospora are roughly ellipsoidal but are very variable in shape, and range from 8·5–17·0 μ in length and 6·3–11·0 μ in breadth; the two anterior polar capsules measure from 2·0–9·5 by 1·5–3·5 μ. Those of M. brachyspora are flattened antero-posteriorly, measuring from 7·0–7·5 μ long and 12·0–13·5 μ broad; their polar capsules are from 2·5–3·8 by 2·3–2·5 μ in size. M. homeospora has ovoid spores with the anterior end narrowed, measuring from 13·5–17·0 by 8·5–11·0 μ; the polar capsules measure 4·0–6·0 by 2·0–4·0 μ.

4. It is suggested that M. heterospora, at least, is pathogenic and may play a considerable part in reducing the availability of fish as food in this part of Africa.

5. A check-list is given of all species of the genus Myxosoma.

I thank Mr R. S. A. Beauchamp (then Director of E.A.F.R.O.) and his staff, also Mr G. Bowser (Manager of TUFMAC), for facilities and assistance in the examination of fish; also Dr G. D. Fryer and Dr D. J. Garrod for sending material to me in London, and Dr P. H. Greenwood for supplying the Haplochromis and checking the names of fish; also Messrs G. D. Lomax and P. E. Nesbitt for the preparation of sections. This work was commenced while I was employed at the East African Trypanosomiasis Research Organization.

The presence of Ellobiopsis chattoni is recorded on Undinula vulgaris var. major for the first time.

The presence of this parasite in shallow tropical water, within a temperature range of 25·92–26·28° C. (salinity range 35·43–36·38‰) is recorded for the first time.

It is noted that the parasite was completely species specific to its host.

Table l analyses the incidence of the parasite in a population of Undinula vulgaris.

It was found that the parasite affected egg production in the ovaries. The suggestion is that it produces a starvation effect on the copepod, this effect being reversible.

1. Thirty-six of 70 Microtus agrestis captured near Oxford, England, between January and July, 1961, were infected with blood parasites—9 with Trypanosoma microti Laveran & Pettit, 1909, 18 with Babesia microtia (França, 1912) and 19 with Grahamella microti Lavier, 1921: some had more than one species.

2. Morphologically indistinguishable parasites were found in 6 of 20 Clethrionomys glareolus (Babesia in 3, Trypanosoma in 2, and Grahamella in 1) and 2 of 4 Apodemus sylvaticus (Grahamella only). Hepatozoon sp. indet. was found in one C. glareolus.

3. It is probable that the proportion of M. agrestis with patent infections of G. microti increased, and possibly that due to T. microti fell, during February–April, 1961.

4. M. agrestis often have very enlarged spleens and it appeared that B. microtia (sometimes associated with T. microti) was commoner in the animals with the largest spleens.

1. Experimental systems are described for studying the interaction of compounds with various species of trichomonad. In vitro systems have been used to study the effects of compounds on trichomonads growing in culture and to determine the speed of action of compounds on non-dividing populations. In vivo experiments have utilized vaginal infections in hamsters and subcutaneous, intraperitoneal, intra-muscular and caecal infections in mice. In vitro assays have also been carried out on serum and urine obtained from non-infected rats or monkeys dosed with compounds showing in vitro activity.

2. The types of activity which can be obtained experimentally are illustrated by reference to a number of local remedies already available and to representatives of a number of chemical types, notably acridines, quinoxaline N-oxides, anthrapyrimidines, nitrofurans, thiazoles, imidazoles and pyrazoles.

We thank Dr R. F. Jennison and Mr H. Francis for clinical trial results, Drs J. K. Landquist, G. V. McHattie and D. Richardson for synthesis of some of the compounds mentioned, Dr G. E. Paget for toxicity data, Dr W. M. Duncan for data on the metabolism of 5667, Dr J. M. Pryce for pK determinations and Mrs M. Ryley, P. Ward, A. Fletcher, D. Wood and Miss V. Rowe for technical assistance at various stages in the work.

Observations are reported on the life history of Amplicaecum robertsi, in relation to the mode of infection as it occurs under natural conditions. Some of the natural intermediate hosts are listed, as compiled from observations on natural infection with third-stage larvae in Queensland mammals. Various natural intermediate hosts were experimentally infected by means of eggs, and observations on the growth and development of the larvae are described.

It was found that the second-stage larvae have a wide range of hosts, including earthworms, snails, fish, tadpoles, reptiles, birds, and mammals. Development to the third-stage was only observed to occur in birds and mammals. Third-stage larvae exhibited a wide variation in the degree of growth attained in different animals. In birds, growth was slight, not extending beyond 3–4 mm.; in mammals, growth varied considerably in different species; it was greater in the indigenous species, reaching 70–80 mm. No development beyond the third-stage occurred, except in reptiles.

Second-stage larvae in the tissues of invertebrates and lower vertebrates could be transferred by feeding to reptiles, birds and mammals. Development proceeded in these hosts to the same extent as occurred following egg infection.

Third-stage larvae could be transferred to certain snakes and lizards by feeding liver of infected rodents, but third-stage larvae over 3 mm. could not be transferred to mammals. Third-stage larvae were found to be uninfective at all stages of growth for birds.

The third moult occurred in the carpet snake when fed with third-stage larvae in the liver of Trichosurus caninus, Rattus assimilis and Melomys cervinipes infected 1 month previously. This was in contrast to previous findings with laboratory rodents, in which maturation of the third-stage larva took considerably longer.

Besides the carpet snake, the third and fourth moult was observed to occur in the goanna (Varanus spp.), the blue-tongued lizard (Tiliqua scincoides) and the bearded dragon (Amphibolurus barbatus). No growth in length was observed and no eggs were evident. As far as is known, none of these lizards is a definitive host of A. robertsi.

The results are discussed in relation to the food chain involved in the natural habitat of the carpet snake. The snake is depicted as the apex of a food pyramid, whose base comprises a variety of animals ranging from earthworms to herbivorous mammals. It is concluded that A. robertsi has adapted its life history in such a way as to enable the parasite to ascend the pyramid by transference through a series of predatory episodes, which culminate in the infection of the natural prey of the snake.

The life history is thus regarded, not as a life cycle, but as a life pyramid; development proceeds according to a pattern of diminishing host-specificity. Host-specificity is wide at the base of the pyramid, so that second-stage larvae occur in a wide variety of paratenic hosts. Host specificity narrows at the second moult which may occur in birds and mammals. It narrows still further in the third stage, because this larva, though it will survive in reptiles, birds and mammals, will not grow to a length at which it is capable of further development in the snake, except in certain mammals. At the third moult, host specificity shifts to certain reptiles, but becomes eventually restrictive to the carpet snake, because this host alone appears to provide a suitable environment for maturation of the eggs.

This work was financed by a research grant from the University of Queensland. The writer's sincere thanks are due to Miss Ann Pritchard and Mr J. Ballantyne for their valuable assistance.