Of the three species of fish which live in Afon Terrig (Salmo trutta, Cottus gobio and Nemacheilus barbatula), only S. trutta was infected by Cyathocephalus truncatus. The parasite has a clear annual cycle and hence a periodicity of occurrence in the brown trout.

No age resistance of fish to infection by C. truncatus is found. The increase of incidence with age among l+—3+ year-old fish and decrease in the older age groups are correlated with the variation in the food and feeding habits of trout with age.

The details of the post-embryonic development of Echinorhynchus truttae in the intermediate host, Gammarus pulex, and the final host, Salmo truttae, are described.

The cystacanths of this species are sexually mature and are formed about 82 days after infection at room temperature, ca. 17°C.

Copulation takes place in the definitive host soon after the worms enter the pyloric region of the intestine. About 10 weeks after infection, mature eggs are passed out with the faeces of fish.

In the limited period available Mermis was found to be influenced by light, in activity, orientation and oviposition. The peak would appear to be in green light, with a peak at 540µ, corresponding closely to the β absorption band of Mermis oxyhaemoglobin.

A topographical distribution of Ostertagia spp. lesions in the abomasum of sheep has been observed under certain field conditions which is the reverse of that described by Sommerville (1953, 1954) and also seen by this author to be characteristic of a primary Ostertagia spp. infection.

This “reverse distribution” has been demonstrated experimentally under conditions in which a heavy primary Ostertagia infection has been acquired (in the field or artificially) and naturally eliminated; the “reverse distribution” is then characteristically acquired by a challenge infection.

The planorbid snail Helicorbis coenosus (Benson) has been found experimentally to serve as the intermediate host of Gastrodiscoides hominis.

The cercaria of G. hominis is described. It is characterized by the presence of a pair of well-developed oral pouches, an alimentary tract having an oesophagus with a muscular bulb and two simple intestinal caeca, an excretory system with a cross-connection between the two main trunks and a reproductive system represented by rudimentary cell groups arranged in a manner similar to that found in the adult fluke.

A new species of filarial worm, Paronchocerca mansoni, a cardiac parasite of Pica pica sericea (Gould) and Cyanopica cyana interposita Hartert, is reported from Peking, China. The thread-like adults of both species taper towards anterior and posterior ends. The cuticle exhibits superficial rugae, with multiple transverse striations underneath. The lipless mouth is surrounded by 4 paired submedian papillae and one lateral pair of amphids. The posterior end of the body is curved ventrad; the post-anal region is short. The male measures 17 mm. long and 0·14 mm. in diameter; the female, 35·8 mm. long by 0·23 mm. in diameter. In both sexes the anterior muscular oesophagus is short, the posterior glandular portion much longer. In the male, there are two pairs of pre-anal and one pair of post-anal papillae, likewise one pair of subterminal caudal papillae. There are neither caudal alae nor gubernaculum. The longer left spicule and the shorter right one have distinct species-characteristic morphological patterns. In the female, the vulva opens approximately 2·0 mm. from the anterior end. The microfilariae are sheathless; immature ones preponderate in heart blood; mature ones, present in heart blood and exclusively in circulating blood, measure 147 to 184 by 6·0 to 6·5 microns.

Groups of helminth-free weaner sheep were equilibrated on a ration containing almost no cobalt for 3 months. Cobalt supplementation was given orally thrice weekly to provide the minimum requirement for sheep. Infective larvae of Haemonchus contortus, Trichostrongylus colubriformis and Ostertagia spp. were given at two dosage levels to each of three groups, respectively, for 18 days, followed after a lapse of 30 days by small daily dosings of a mixed suspension of these helminths. Serum vitamin B12 was determined for a month before parasitization and for up to 12 weeks thereafter for every sheep. Sheep parasitized with higher numbers of T. colubriformis and Ostertagia spp. were significantly affected with loss of weight and in three cases, death, although there were no changes in the serum levels of vitamin B12 which remained fairly constantly at the lower end of the normal range during most of the parasitic stage. Sheep dying from these infestations showed terminal rises of serum vitamin B12 whilst those surviving showed falls in the last few weeks of the trial associated with significant decreases in liver cobalt levels. Morphological changes of some severity were found in the abomasum and intestines of the sheep receiving T. colubriformis and Ostertagia spp. and appeared to limit the uptake of vitamin B12. It is concluded that mild to moderate infestations of intestinal trichostrongyles and to a lesser degree Ostertagia spp. will interfere with the absorption of vitamin B12 and that these helminths may precipitate cobalt deficiency syndromes if cobalt is at or near the critical level in the feed.

The acanthocephalan parasites of seals, Corynosoma strumosum (Rud.) and C. semerne (Forssell) were found in one mink farm in the south western archipelago of Finland, where the minks suffered from a bloody and often fatal diarrhoeal anaemia. C. strumosum was found in the two victims of the disease examined, whereas C. semerne occurred in 75·3 per cent of the surviving minks. In a highly anaemic group of minks the mean incidence of C. semerne was 2·9 specimens per animal, whereas the incidence was 1·5 in a mildly anaemic group. The epidemiology of the disease is discussed.

Amongst the unidentified material in the nematode collections of the British Museum (Natural History) was the remainder of a collection, made by Dr. D. R. R. Burt from reptiles in Ceylon. One new species is now described and a list of seven previously known species is given below. In addition it is convenient to include the description of a new species of the genus Kalicephalus based on specimens obtained from a Varanus bengalensis which died at the Zoological Gardens, London, since the normal geographical distribution of this host is Ceylon and India.

During a study of the larval trematodes infecting the fresh-water molluscs of Llangorse Lake, South Wales, twenty-one species of cercariae have been encountered. The present paper deals with the Furcocercariae. Six new species are described in detail and the remaining two compared with the description of previous workers.

Information on the incidence of larval trematodes infecting the fresh water molluscs of Llangorse Lake, South Wales, has been collected over a period of three years.

The percentage infection of the molluscs occurring within the habitat has been assessed and comparisons made with the findings of other workers.

The percentage of active and passive parasite stages composing this infection has been considered.

Observations on infection and the development of F. gigantica (W. African strain) in the susceptible L. natalensis and in the less susceptible mature L. rufescens (from Pakistan) and the histological study of the two species of snails at various stages of development of the contained parasite, revealed that,

The miracidia appeared to take a longer time to start penetrating the less susceptible host.

There was no significant tissue reaction even in L. rufescens to the development of the sporocysts. The development of the sporocysts which were embedded in denser tissues of the snails was apparently retarded in both the species of snail.

The genus Galebiella Basir, 1941, has been recorded from Hydrous aculeatus Sol. (Coleoptera: Hydrophilidae) in the U.A.R. Female nematodes only were found, in the hindgut of the adult beetles.

Worms were especially abundant close to the pyloric valve and were found free in the gut lumen; a few of them were loosely attached to the gut wall.

The reaction of the hind- and midgut was almost the same yet the infection was restricted to the hindgut.

In many cases of infection the peritrophic membrane in the hindgut region became fragmented into longitudinal fibres. The intima, epithelium and muscle layers showed no changes at all.

The original description of Schistosoma rodhaini was based on the examination of one adult male, two adult females and one young male (Brumpt, 1931). Fain et al. (1953) reported that the measurements of worms from natural infections in Ruanda-Urundi did not correspond to those given by Brumpt in 1931. They maintained that, in experimental infections, the variations in the length of the worms were more notable; being generally smaller than those collected from natural infections. Also they reported similar differences in the measurements of eggs.

The material comprises three complete male worms in good condition and some male fragments; there are no females.

The worms are small, cylindrical and greyish yellow in colour. The body is partially covered with spines.

The material comprises two immature females found in a baboon in Rhodesia. So far as I can gather from the available literature, they appear to be the first record of the genus Gigantorhynchus Hamann, 1892, emend. Yamaguti, 1963 in monkeys; moreover, they are a new locality record of this genus in Africa, since all the hitherto known species occur only in South America (Brazil, Venezuela and Peru).

The adult of Clinostomum tilapiae n.sp. obtained from the buccal cavity and oesophagus of Bubulcus ibis 7½ days after experimental infection with metacercariae is described.

The metacercaria of C. tilapiae n.sp. from Tilapia zilli, T. heudeloti and T. galilaea is described.

Anatomical differences between metacercariae and adults of the species are listed.

The experimental infection of young cattle egrets with metacercarial cysts of Clinostomum tilapiae Ukoli, 1966 from Tilapia spp. is described.

A table showing the duration of infection, the number of parasites recovered, the percentage of infection and the location of the parasites within the host is constructed and the results discussed.

A graph of mean length and breadth of body, oral and ventral suckers, cirrus pouch, ovary and anterior testis, is plotted against the duration of infection in days. Most of these dimensions are found to attain a peak two days after infection. It is also found that while the ovary increases in size with age, the cirrus pouch remains constant, so that in mature adults, both are about equal in size,

It is shown, by plotting length of organs against length of body and by expressing mean measurements of certain dimensions as percentages of body length, that apart from the testes, all the other organs in both the metacercariae and the adults maintain a constant relationship both with one another and with body length as they grow older.

The metacercariae of Euclinostomum helerostomum (Rud., 1809) from Tilapia zilli and T. heudeloti and immature adults recovered from the oesophagus of the African darter and the long-tailed shag, three days eighteen hours after experimental infection with metacercaria are described.

It was found that the number of diverticula from each intestinal caecum varies within species, hence Jaiswal's (1957) three species, E. bhagavantami, E. channai and E. heptacecum are proposed as synonyms of E. heterostomum.

The process of attack and penetration of the snail hosts by miracidia is an important stage in the life history of most digenetic trematodes. This paper is concerned with the mechanism of penetration, and further development within the snail, of Schistosoma mansoni as revealed in serial sections.