Experiments were constructed to assess the ellects or changes in the diet of Periplaneta americana on Thelastoma attenuatum. Synthetic diets depressed parasitaemia although apparently adequate for the host. However, adult worms were supported best by high carbohydrate levels although protein was necessary for the final moult. Little effect was observed on the distribution of worms within the htndgut although excess roughage appeared to result in a slight backward migration. Egg output per worm remained fairly constant but rose slightly under conditions of extreme stress. Dietary changes affected the size of adult female worms differentially but had little apparent effect on food reserves. Possible reasons for the changes are discussed

Microfilariae of Onchocerca cervicalis were injected subcutaneously into jirds, Meriones unguiculatus. At 72 hours post-inoculation the microfilariae had redistributed and the distribution pattern remained stable for approximately 100 days. Live active microfilariae were recovered from jird skin 168 days post-inoculation.

Fifty nine per cent of the microfilariae recovered at 72 hours were from the skin of the tail and inguinal region. The inguinal region was the preferred site in male hosts and the tail in females, the difference in distribution being attributed to temperature differences in the inguinal region of the hosts. It is suggested that the microfilariae migrate along a thermal gradient rather than at random.

The redia, cercaria and metacercaria of Opisthodiscus nigrivasis from Ancylastrum fluviatilis are described. Observations were made on the behaviour of the cercaria and experimental infections with metacercariae have been carried out in laboratory-raised frogs of the species Rana ridibunda. Some features of the morphology of these juvenile stages and aspects of the behaviour of the cercaria are compared with those of others related species.

The best known biological cycles in the Diplodiscinae are those of Diplodiscus subclavatus (Pallas, 1970) Diesing, 1836, and Megalodiscus temperatus (Stafford, 1905) Hanvood, 1932. The first was described by Looss (1892), who showed that the molluscs Planorbis nitidus, Pl. vortex, Pl. rotundatus, Pl. spirorbis and Pl. contortus acted as intermediate hosts. More recently Milka (1970) found young forms of D. subclavatus in Pl. planorbis and gave a brief description of the redia and cercaria of this species.

Five Macaca mulatta were each inoculated with 200 larvae of Brugia pahangi. One monkey showed no microfilariae and the other 4 only low and transient microfilaraemias. Another group of 5 monkeys were each given an original 200 larvae and 11 further infections with 50 larvae but no better microfilaraemias were obtained. These monkeys were killed between 176 and 185 days later and no adult worms could be found. A few adult worms were found in two further monkeys killed 60 days after infection.

Brugia pahangi infects mammalian hosts of several orders but the only primate found naturally infected is Nycticebiis coucang (Laing et al., 1960, Ash and Riley, 1970). Edeson et al. (1960) tried to infect Macaca inis, M. nemestrina, M. mulatta and N. coucang but were only able to detect microfilariae in N. coucang. On the other hand, B. malayi (sub-periodic strain) infects primates much more readily (Laing et al., 1960) in nature. Fredericks and Ramachandran (1968) successfully infected 26 of 27 M. mulatta with B. malayi.

Twelve sheathbills, Chionis alba, 12 South Georgian diving petrels, Pelecanoides georgicus, and 5 common diving petrels, P. urinatrix, collected at Bird Island, South Georgia, were examined for helminth parasites. These appear to be the first helminthological examinations of birds from South Georgia. Eleven of the 12 sheathbills were infected with helminth parasites and the pattern of infection of adult male and female birds was similar. Five species of helminths were found in sheathbills, namely Gymnophallus dellciosus, Notocotylus chionis, Paramonostomum signiensis, Lateriporus australis and Corynosoma hammani. Two species, namely Tetrabothrius sp. and Stegophorus heardi, were found in both Pelecanoides georgicus and P. urinatrix.

The helminth parasites of whales and seals in the Antarctic and Subantarctic have been extensively studied, while in comparison those of birds from these regions have been neglected. As far as we are aware there are no previous reports on helminth parasites from the sheathbill, Chionis alba (Gmelin), the South Georgian diving petrel, Pelecanoides georgicus (Murphy and Harper), and the common diving petrel, P. urinatrix (Gmelin), from South Georgia.

The structure and affinities of the progenctic larva of Echinobothrium reesae Ramadevi, 1969, are described and discussed.

Eight species of Monogenea (Dactylogyridae) are reported from the gills of freshwater fishes from Colombia as follows: Anacanthonis colombiamis sp. n. from Salminus affinis Steindachner and Tilapia mossambica (Peters); A. cuticulovaginus sp. n. from S. affinis; Cichlidogyrus sclerosus Paperna and Thurston, 1969, and C. tilapiae Paperna, 1960, both from T. mossambica; Urocleidoides costaricensis (Price and Bussing, 1967) Kritsky and Leiby, 1972, U. hcteroancistrium (Price and Bussing, 1968) Kritsky and Leiby, 1972, and U. strombicirrus (Price and Bussing, 1967) comb. n. (all) from Astyanax fasciatus (Cuvier); and U. anops sp. n. from Characidium caucanum Eigenmann. C. sclerosus and C. tilapiae are recorded for the first time from the western hemisphere.

The life-cycle of the cestode Proteocephalus percae (Müller), a parasite of the perch Perca fluviatilis L., involves two hosts and was studied both experimentally and by field observations in Hanningfield Reservoir, Essex. The hexacanth embryo is bilaterally symmetrical, with three pairs of hooks and paired glands. The copepods Cyclops (Eucyclops) agilis, C. (Mesocyclops) leuckarti and C. (Acantftocyclops) viridis were infected experimentally with P. percae eggs. The egg hatches in the intestine, the embryo penetrates the intestinal wall by means of its hooks and possibly by secretions from its paired glands, and the larva develops within the haemocoel. Development took 3–4 weeks at 14°C in C. viridis, but the rate of development varied at different temperatures and copepod species differed in their suitability as hosts for P. percae larvae. The adult cestode showed a yearly cycle of occurrence and maturation in perch. Egg production occurred in the spring, after which adult worms were lost from the fish to be quickly replaced by juvenile worms of the succeeding generation. Increase in length of the adult cestode population occurred in two stages, a period of rapid initial growth commencing immediately after establishment in the perch, and a second stage closely associated with maturation of the worms.

Culicoides nubeculosus, the vector of Onchocerca cervicalis, was found to have two daily peaks of activity when attacking horses in South Hertfordshire. The evening peak occurred just before sunset and was 2–2.5 times as great as the morning peak. Most of the attacking midges (85 %) landed on the ventral mid-line of the horse in an area stretching from the front legs to the sheath or mammae. The attractiveness of the ventral surface of the host was found to be related to illumination and to the arrangement of the host's body hair. 42.1 % of the C. nubeculosus landing on the host were successful in obtaining a blood meal.

Allocreadium sudanensis sp. nov. is described from a cyprinid fish (Barbus bynni) from the White Nile in the Sudan. The new species is compared with other related species of Allocreadium.

A key for identification of five African species of the genus Allocreadium is given.

The present material was collected by the senior author in January, 1969 from the intestine of a cyprinid fish, Barbus bynni (Forskal), caught from the White Nile at Rabag near Kosti (about 200 miles to the south of Khartoum) in the Sudan. Eighteen trematodes, collected from a single infected fish, were fixed in hot 70% alcohol. Examination of these specimens in whole mounts stained in aceto-alum carmine and in sectioned material revealed that they belong to a hitherto unknown species of trematodes belonging to the genus Allocreadium, Looss (1900) which is described here as Allocreadium sudanensis sp.

A study of the distribution and population of Lymnaea gedrosiana in relation to the transmission of Ornithobilharzia turkestanicum in various habitats was carried out in Khuzestan.

Populations were higher in canals and swamps than in ponds, with peaks in spring and autumn and low densities in summer and winter.

The reproductive capacity of L. gedrosiana was higher in running water than in stagnant water. The peak reproduction rates occurred in spring and autumn and reproduction continued at a low level in summer but was nil in winter.

Infection with O. turkestanicum was higher in large than in small snails (0.1 %, 0.5% and 1.1% in snails measuring 0.6 mm, 6–10 mm and 10–14 mm respectively). In canals and swamps transmission occurred throughout the year, with a peak in late summer in the former and early summer in the latter. In ponds, most transmission probably occurred in spring and autumn. Drains played a very minor role in transmission.

Pelecitus galli n.sp. is described from the Malayan jungle fowl Gallus gallus spadiceus. It differs from other species of the genus in the size of the spicules, number and arrangement of caudal papillae in the male, and the relative position of the vulva. It is also the first species of Pelecitus described from the genus Gallus.

Three types of microfilariae were seen in blood and lung smears of two jungle fowls trapped in Tasek Bera in Pahang State. One of these microfilariae is indisguishable from that described by Dissanaike (1963) from the Ceylon jungle fowl. One of the other two resembles the microfilaria of Pelecitus ceylonensis described from Ceylon (Dissanaike, 1967) and adults were found between the tendons at the bases of the legs of one of the jungle fowls examined.

A comparative study on the pathogenicity of two strains of Schistosoma mansoni one from Bor District and the other from the Gezira in the Sudan, using Cercopithecus aethiops monkeys as experimental hosts. The results, which were based on the assessment of various clinical, parasitological and pathological parameters, indicated that Bor strain was responsible for a more severe type of disease than its Gezira counterpart. Monkeys infected with Bor parasite generally revealed higher worm and egg loads, more marked changes in Hb content and body weight gain and more extensive lesions in the liver and two monkeys died.

In the Sudan, it has often been noted that the disease produced by Schistosoma mansoni, as observed among patients from Bor District in the Southern Region, is far more severe than that usually encountered in those from the Gezira in the northern part of the country. These two areas which are about 500 miles apart differ widely in their climate, indigenous population, and social and economic status. It has been suspected that differences in the pathogenicity of the local S. mansoni strains may be one of the important factors determining the clinical presentation of the disease. Accordingly, a comparison of these two strains was undertaken, using the green monkey, Cercopithecus aethiops, as an experimental model. These animals varied in their response to the schistosomal infection, irrespective of the strain used, but the group infected with the Bor strain generally suffered from a more severe illness than their counterparts infected with the Gezira form of the parasite. This was evidenced by the higher worm and egg loads, and consequently the more severe clinical and pathological effects shown by the former group.

An immature parafilarial worm recovered from the anterior chamber of the eye of a buffalo (Bubalus bubalis) is described. On the basis of characteristic cuticular ornamentation at the anterior extremity, an undivided short oesophagus and unequal spicules, the specimen has been identified tentatively as a male juvenile of Parafilaria bovicola. This is the first record for P. bovicola as an accidental infection of the eye of a buffalo.

The laboratory infection of Lymnaea gedrosiana with 1,2,5,10 and 20 miracidia of Ornithobilharzia turkestanicum, resulted in infection rates of 54.5%, 57.1%, 62.5%, 84.0% and 100% respectively, with a prepatent period of 18–21 days.

The numbers of cercariae shed daily by single snails exposed to one or 2 miracidia were significantly lower than from those exposed to 5,10 or 20 miracidia.

Few cercariae were shed during the early patent period, but the number increased with the duration of infection. All infected snails died at the peak of cercarial shedding, and no infected snails survived more than 60 days after exposure to miracidia. The differences between the mean life-span of infected snails and non-infected snails in the control group were statistically significant (P < 0.001).

A comparative study was made of the occurrence of the metacercariae of Diplostomum spathaceum, Tylodelphys clavata and T. podicipina in the eyes of brown and rainbow trout, perch, ruffe, roach, ten-spined stickleback, eel and stone-loach, from Hanningfield Reservoir, Essex between January 1968 and March 1969. D. spathaceum was found in all fish species and T. clavata in all except eel and stone-loach. The degree of infection varied considerably between different host species. T. podicipina occurred mainly in young perch but was also found in rainbow trout and ruffe. D. spathaceum normally occurring in the lens was also found in considerable numbers in the humor of the eye in brown and rainbow trout, perch and ruffe. Infection with D. spathaceum and T. clavata increased with length and age of the host although in some host species there was a reduction in the largest fish examined. Newly introduced rainbow trout became infected with D. spathaceum and T. clavata during their first summer in the reservoir.

Metacercariae of two species of trematode (Clinostomum tilapiae, Postodiplostomum nanum) excysted in the stomach of birds, while those of three species (Parorchis acanthus, Posthodiplostomum sp., Postliodiplostomoides leonensis) excysted in the duodenum. Differences were related to the structure of the cyst wall. All could excyst in birds which were not the definitive host and the speed of excystment depended on the speed of movement of food in the gut. All, except P. acanthus, also excysted in the body cavity of the mouse.

There have been few previous reports on the site of excystment of metacercarial cysts in vivo and most indicate that the duodenum is the site for most species studied, e.g. Clonorchis sinensis (Faust and Khaw, 1927), Parorchis avitus (Stunkard and Cable, 1932), Cryptocotyle lingua (Smyth, 1962) and Fasciola hepatica (Smyth, 1966). In their study of the migratory route of Paragonimus westermani in rats, cats and guinea-pigs Yokogawa et al. (1962) found that excystment occurred in the small intestine where the pH range was 5.0–6.0. Also, although the site of excystment has been established for some species, very little quantitative work has been reported about the percentage excystment in vivo and results of work on these lines is reported in this paper.

Distinct morphological differences were found between microfilariae of Onchocerca cervicalis in the uterus of the adult and those in the skin of the horse, suggesting that development occurs during migration from the adult worm to the skin.

Uterine microfilariae can be divided into two types which represent stages of development not embryonic male and female worms.

Skin microfilariae of O. cervicalis were readily distinguishable from those of O. volvulus and O. gutturosa. Morphological comparisons between adult and larval O. cervicalis collected during this project with published descriptions of O. reticulata show that there is insufficient evidence for their specific separation.

The first two papers in this series have dealt with the prevalence of Onchocerca cervicalis in British horses and with the pathology caused by the parasite to the definitive host. The present paper is concerned with the morphology and taxonomy of the parasite, particularly the microfilarial stage.

Histological and gross changes in the lymphatics of cats singly or repeatedly infected with Brugia pahangi were studied chronologically over a period of 5 years. Lymphatic dilatation occurred within 2 weeks of injection and an initial acute inflammatory reaction in the lymphatic wall and lumen was followed by chronic inflammation within 4 months. In some long-term repeatedly infected cats, the lymphatics became non-functional fibrous cords and conditions of oedema and early elephantiasis, similar to those seen in early human filariasis, were produced. The main points of contention in the study of filariasis which were cluciaated in this system were: (1) that living worms cause lymphatic damage, not exacerbated by their death; (2) that lymphatic damage is not progressive after a certain peak of reaction is reached, except in repeatedly challenged animals; (3) that microfilariae do not appear to cause lymphatic damage.

Adults of Hepatojarakus malayae live in the bile duct of many species of Rattus in Peninsular Malaysia, ine life cycle of this parasite was studied in laboratory white rats. Eggs were passed out with the faeces at the early morula stage and hatched within 15 hours, giving rise to the first stage larvae. These developed to the third stage in about 36 hours and these were given orally to new rats in experimental infections. The migratory route of the larvae from the gut to the liver was traced. Penetration into the host appeared to be confined mainly to the fundic wall of the stomach. The larvae presumably followed the portal route to the uver. Here the final moult occurred before the young adults moved into the biliary passages.