This paper records the presence of a new species of trypanosome in the lizard Uranoscodon superciliosa L. (family Iguanidae), caught near Codajaz, Amazonas, Brazil, in August 1964 during the Guy's Hospital Expedition to the Lower Amazon.

Examination of a methanol-fixed and Giemsa-stained smear of blood taken from the heart of the lizard showed a heavy infection of trypanosomes. Camera lucida drawings of twenty were made, measurements being determined with dividers and a map-measuring wheel. The animal was preserved in 10% formalin, portions of liver, spleen, brain, heart, and lung being later extracted. Sections 5 μ in thickness were cut and stained in Ehrlich's haematoxylin and eosin, and in Giemsa's stain.

The chief distinguishing feature of the trypanosomes was their comparatively enormous size, up to 124 μ in total length, including the free flagellum, and 19 μ in width. The cytoplasm stained deep blue in Giemsa's stain, there being little indication of any vacuoles or inclusions. The posterior end was generally less intensely stained, and in certain cases pale, narrow, channel-like extensions from this region forward into the main body of the organism could be detected (Fig. 1). The nucleus, elongated and rather variable in shape, was distinguished by being less deeply coloured than the surrounding cytoplasm; it lay slightly posterior to the mid-point of the body, its longest diameter being parallel to the longitudinal axis of the animal. The kinetoplast, situated slightly posterior to the nucleus, was usually of circular shape, staining deep red; from it arose the flagellum, which passed forward along the margin of an undulating membrane and terminated in a free portion at the anterior end. Measurements of the organisms are given in Table 1.

Unidentified helminth larvae in the eyes of the North Sea whiting, Gadus merlangus L., were recorded in an unpublished survey of parasites of gadoid fish by Dr Z. Kabata of the Marine Laboratory, Aberdeen, in 1957. Since then these larvae have been observed frequently and during the first 6 months of 1964 an effort was made to identify them. They proved to be the plerocercoids ofa trypanorhynch cestode.

The plerocercoids are usually free in the aqueous or vitreous humour, but occasionally one is found attached to the lens. Very often both eyes of the same fish are infested, the largest number of larvae recorded from one eye being ten, from a fish taken in Shetland waters. The other eye of the same fish contained eight larvae.

In several plerocercoids examined the proboscides were evaginated, thus enabling detailed drawings to be made of the armature at a magnification of × 900. A number of specimens were fixed in Gilson's fixative; transverse and longitudinal sections were cut and stained with Mallory's triple stain; whole mounts were stained with borax carmine.

Early larval stages are completely undifferentiated; they develop, later, to the stage shown in Fig. 1. A plerocercoid with a fully developed scolex measures 3·5–8·0 mm long by 0·7–1·6 mm broad.

The larva is composed mainly of faintly staining tissue resembling the parenchyma of adult cestodes. The scolex is withdrawn into a cavity, the receptaculum scolecis, in the anterior half of the plerocercoid. At the anterior extremity is a deep invagination from which, in early larval stages, the receptaculum scolecis begins to develop.

The genus Acanthobothrium van Beneden, 1850, seems to be in a state of slight confusion due, possibly, to some inadequate descriptions which have led to subsequent misidentifications of some of the species. The type species A. coronatum was first recorded and very briefly described by Rudolphi (1819) as Bothriocephalus coronatus from ‘Squali stellaris, Squali squatinus and Torpedinis marmoratae“. Since then specimens have been assigned to this species which probably belong elsewhere; the list of synonyms and the host records are extensive. Baer (1948) divided the species of the genus into two groups, namely, those parasitic in sharks and those in rays. This seems to be a reasonable distinction as specificity is very marked in cestodes and especially in those of elasmobranchs. It was thought that a detailed study of the type species, presented here, would be a useful preliminary to a consideration of the genus as a whole.

Specimens of A. coronatum were obtained from the spiral valve of Scyliorhinus stellaris (L.) caught in Cardigan Bay in July 1956 and at Plymouth in August 1958 and August and September 1959. The number of worms, complete with scoleces varied from 6 to 10 per fish and in one instance 14. Many fragments of two to three proglottids and many individual proglottids were also present. The scoleces were attached in the first turn of the spiral valve and the strobila adhered feebly along the whole length, sometimes as far back as the rectal gland, leaving on removal a distinct groove in the mucosa.

In the course of work designed to measure the extent to which methionine absorbed in one region of a tapeworm became distributed throughout the strobila, it was observed that, whereas, in saline, Hymenolepis diminuta lost previously absorbed methionine slowly, in the intestine of a rat the methionine was lost very rapidly. The fact that two worms containing initially the same amount of free methionine should, after a short period in different environments, contain utterly different quantities of methionine indicated that the quantity of a free amino acid present at any time is not simply dependent on the amount previously absorbed less the amount metabolized.

This observation has a bearing on several aspects of tapeworm physiology. Do tapeworms normally absorb amino acids from the intestine during periods of high concentration and release them when the concentration falls? If they do, the presence of tapeworms in the intestine could be beneficial to the host by extending the period over which an amino acid is available to the host, an important point as a mammal is unable to store amino acids for more than a few hours (Gitler, 1964). A knowledge of the environmental conditions which influence the level of free amino acids in a tapeworm, and thereby its ability to synthesize proteins, is obviously also of critical importance to workers attempting to grow worms in vitro.

Relatively little is known of the way in which the populations of monogenean parasites are related to the behaviour and physiology of their hosts or how such populations vary in composition over the year. Bychowsky (1957, trans. Hargis, 1961, p. 108) has described the results of studies upon six different fish hosts and parasites, while Llewellyn (1962) has studied two other species of Monogenea living on one host species. In all these investigations, the various ecological factors which influence the life cycles of the parasites have been determined.

Dogiel, Petrushevski & Polyanski (1961, p. 14) referred to a previous population study of Discocotyle sagittata on a host Coregonus lavaretus in Lake Ladoga, Russia. The parasite was said to breed in July and August, while in September broods of young and old parasites overlapped. The large individuals disappeared in October and November and this ‘death of the older generation’ was taken to indicate that the parasites had a life span of only one year.

The only relevant work available when the present study was commenced was the population study of the monogeneans Gastrocotyle trachuri and Pseudaxine trachuri by Llewellyn and as this concerned a marine host, it was of obvious interest to investigate the population dynamics of a parasite of a freshwater fish. Discocotyle sagittata was chosen because the biology of the British host, the brown trout (a different host from that in the Russian study of Discocotyle), has been intensively studied for many years. It was thought that this would be of advantage in attempting to relate any seasonal fluctuations in the parasite population to the biology of the host.

At present many laboratories throughout the world are studying the chemotherapy and immunology of Schistosoma mansoni in laboratory hosts. Many workers judge the success or failure of their attempts to cure or immunize these hosts from the ratio of the number of living adult worms recovered to the number of infecting cercariae. This ratio is affected, however, not only by the efficacy of any treatment, but also by the methods used to infect the animals and to recover the worms. If these methods result in widely varying worm recoveries amongst the animals in any experimental group, then small but significant effects of treatment might well be missed. Alternatively, such large experimental groups must be used that the work becomes tedious to perform and depends upon the availability of a great deal of technical assistance. This paper describes techniques which are rapid and do not require great skill in their performance. More important, in our hands they have given very consistent results. In this respect, particularly, we believe that these techniques have advantages over others which are currently practised.

The techniques described here are those which were used in other investigations reported in this journal (Smithers & Terry, 1965a, b).

The strain of S. mansoni used throughout this work was isolated in Puerto Rico and was obtained through the courtesy of Dr W. B. DeWitt of the National Institutes of Health. The parasite is maintained in an albino strain of Australorbis glabratus (Newton, 1955). Snails are exposed individually to ten miracidia overnight at 27 °C.

In recent years there has been a steadily growing interest in the immunology of schistosomiasis. Much work has been carried out using a variety of experimental hosts and many attempts have been made to vaccinate these hosts against schistosomes, both by exposing them to irradiated cercariae and by injecting them with various antigens derived from the parasites. These attempts have been attended by varying degrees of success. The ultimate object of much of this work has been its possible application to the disease in man. We believe, however, that work of this kind cannot really be profitably undertaken unless there already exists a sound understanding of the basic host-parasite relations between the schistosomes and their hosts. This knowledge is essential in order to decide whether a finding in one host is likely to be applicable in others. With this idea in mind, we report here our findings on naturally acquired resistance to Schistosoma mansoni in the rhesus monkey.

The host–parasite relationships of Schistosoma mansoni in the albino rat have been studied recently by Ritchie, Garson & Knight (1963) and by Sadun & Bruce (1964). The general findings of these and other workers are that, in rats, the worms are always stunted, although they may pair and non-viable eggs may be found in the liver. The worms remain in the liver and seldom, if ever, migrate to the mesenteries. Ritchie et al. (1963) found that the majority of the worms were eliminated between the 4th and 8th week after infection; this is much sooner than in other experimental hosts. Sadun & Bruce (1964) suggest that rats are particularly suitable and convenient for studies on acquired resistance to S. mansoni; this suggestion is based mainly on the grounds that acquired resistance is more easily demonstrated in animals which show a relatively great degree of innate resistance.

The present work has been undertaken in order to establish whether the immune response in the albino rat is at all similar to that in the rhesus monkey (Smithers & Terry, 1965b). Two features of the host–parasite system have been studied in detail; the elimination of the worms which follows an initial infection and a comparison of the development of acquired resistance following exposure to X-irradiated cercariae with that following exposure to normal cercariae.

A Puerto-Rican strain of S. mansoni, and Sprague–Dawley rats weighing 100–200 g, were used in all experiments. The methods of exposing the rats percutaneously to infection and the recovery of the worms by perfusion have been fully described (Smithers & Terry, 1965 a).

The rate of development of sterile 2nd-instar beet eelworm (Heterodera schachtii Schm.) larvae to the adult stage on excised sterile roots of sugar beet (Beta vulgaris L.) was studied.

Culture methods were as previously described (Moriarty, 1964). Sterile excised sugar-beet roots were placed on White's medium gelled with 0·75 % agar, inoculated with about 0·1 ml of an aqueous suspension containing several hundred sterile 2nd-instar eelworm larvae, and kept at 25 ± 0·5 °C. After 24 h the roots were transferred to liquid White's medium. Two roots were stained in acid fuchsin lactophenol (Goodey, 1963) every 24 h, for 19 days. Later, the length of main root axis and total length of laterals were measured, the number of laterals counted, the eelworms dissected out and the larval instars identified (Raski, 1950).

When roots were removed for staining, the liquid medium was examined for eelworms. Only adult males were ever found, and these are included in the counts in Table 1.

The rate of development of larvae varied greatly, about half did not develop beyond the 2nd instar (Table 1) and from the fifth day onwards some atrophied. One root in which many adults developed was kept 41 days before killing and staining: there were still some 2nd-instar larval cuticles, devoid of contents except for the buccal stylet, and presumably dead. The average number of all instars found per root did not decline during the 19 days of observations: therefore few of the atrophying larvae could have been missed. The percentage of larvae that entered the roots was variable and small.

Acquired resistance to some nematode parasites can be suppressed by daily administration of cortisone acetate to the host. Cortisone treatment completely suppressed previously acquired resistance of mice to Trichinella spiralis (Coker, 1956) and suppressed, at least partially, the acquisition of resistance to T. spiralis by rats during initial infection (Markell & Lewis, 1957).

A previous report (Weinstein, 1955) suggested cortisone acetate treatment was less effective in the suppression of acquired resistance of rats to Nippostrongylus brasiliensis. Weinstein showed that daily treatment with 2 mg cortisone acetate throughout five immunizing infections and continued during the challenge infection increased the number of worms in the intestine and had a marked effect on the cellular response in the skin and lungs. However, there was no significant effect when daily cortisone treatment commenced only on the fifth day before the challenge infection. This result suggested that acquisition of immunity to N. brasiliensis was partially overcome by cortisone treatment, but the same level of drug treatment had no effect on immunity already acquired.

In the experiments reported here, previously acquired resistance to N. brasiliensis was suppressed completely and the initiation of immunity stopped, either completely or at a very early stage, by treatment with the cortisone derivatives prednisolone or betamethasone. The complete suspension of all manifestations of acquired resistance obtained by treatment with these drugs was used to investigate the fate of larvae migrating in an immune host.

The rats and strain of parasite, and the methods of handling them, have been described previously (Ogilvie, 1965).

The Oxyuridae parasitic in Primates have a restricted host range with, in the wild, one species of parasite characteristic of one genus of host (Inglis, 1961). Under such conditions one would expect the hosts and their parasites to show parallel evolutionary trends. While this is not established in detail there is a broad correlation between the trends that can be established in the morphology of the parasites and the phylogenies of the hosts (Inglis, 1965).

Recently some parasites were reported which suggested that the Hapalidae could be considered primitive monkeys of the superfamily Ceboidea rather than specialized (Inglis & Dunn, 1964), but it was then stressed that, because few parasite records were available, the suggestion must be tentative. However, two further samples of pin-worms from Hapalidae have now become available which also support this suggestion. One sample is from Oedipomidas oedipus (reported by Menschel & Stroh (1963) as Enterobius minutus) and the other is from Callimico goeldii. Both samples represent new species which are described below.

The specimens from C. goeldii are particularly interesting because they represent a species which is clearly con-generic with those from the Hapalidae that have been studied. This suggests that Callimico should be referred to the family Hapalidae rather than to the family Cebidae or even, as is suggested by some authors, to a distinct family Callimiconidae.

Both the new species are referable to the genus Trypanoxyuris and the opportunity is taken to publish an illustration of the lateral view of the male tail of Trypanoxyuris callithricis (Fig. 1).

The specific composition of the parasitic helminth fauna of wild ruminants in Britain has not been examined for 30 years, and the series of surveys to be described were undertaken to provide data on this aspect of helminth epidemiology. With the increase in interest in conservation of wild stock, and especially ruminants, in recent years, information on the epidemiology of their helminth infections is an essential adjunct to any schemes for their protection and husbandry.

The common roe deer, Capreolus capreolus capreolus, is distributed throughout Europe and Asia, the other subspecies, G. c. pygargus, the Siberian roe, G. c. bedfordi, the Manchurian roe, and C. c. melanotis, the Szechwan roe, being limited in range. It is indigenous to Britain, and over the centuries its populations have undergone great numerical fluctuations. Though at one time nearly extinct in England except in the counties on the Scottish marches it appears at present to be in a period of resurgence, and the range is extending from dense foci in the south and south-east to join the northern population. It has always been numerous in mainland Scotland and a few of the Western Isles, but is extinct in Wales and Ireland (Whitehead, 1964). The roe is the smallest of our indigenous deer and differs from the others in its breeding habits, not forming herds, but grouping as family units of buck, doe and offspring. On the mainland of Europe, however, herding does take place, and a limited migration has even been observed in Russian roe (Flerov, 1952). Its habitat is essentially woodland, but it grazes open areas to some extent and, not-withstanding its timid character, lives in close proximity to man in agricultural and even in urban areas.

Periodicity of occurrence in the final host has been observed in only a few of the known Acanthocephala of fish (Van Cleave, 1916; Steinstrasser, 1936; Komarova, 1950; Shulman & Shulman-Albova, 1953). The periodicity appears to be due to the simultaneous operation of a complex of physiological, developmental and ecological factors.

In the present investigation a detailed study has been made of both the occurrence and the developmental cycle of Echinorhynchus truttae in its hosts in a small trout stream, Afon Terrig, in North Wales. An attempt has also been made to ascertain to what extent some of the various and varying ecological and physiological factors influenced the incidence, degree of parasitization and the development of the worm in nature.

Samples of the intermediate host, Gammarus pulex pulex L., and the final host the brown trout, Salmo trutta L., were taken monthly at three points or stations where the stream was readily accessible. Station I was at Rhydtalog as far upstream as practicable. Station III was at the opposite end of the stream near Caegwydd and station II was about mid-way between the other two sampling points. To ensure that each host sample was examined in as fresh a condition as possible, autopsy of the intermediate host was completed before the definitive host was taken.

Within the first week of each month from November 1961 to January 1963, shrimps were taken from over a stretch of about 30 m at each station.