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.

By combining a number of well-known but scattered results, a theoretical model has been constructed to explain the observed quadratic increase in sample variance of egg counts over sample mean with increasing egg concentration. Our contention is that the over-dispersion arises because of inherent variation in volumetric deliveries of faecal suspension onto the counting slide. Even though the observed variation of volumetric deliveries appears to be small, we have shown that it is adequate to cause a considerable increase in egg count variance over mean at not unreasonably high concentrations.

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.

(1) Cultures of Panagrellus redivivus increased and decreased in acidity as population increased and decreased.

(2) Comparison of the sex ratio of the mature worms present in the culture medium and, at the same time, on the walls and lids of the culture vessels, indicated a shift towards maleness in the sex ratio with distance from the culture medium.

(3) The results are discussed in relation to migratory behaviour.

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.

The paper summarises the cases of cysticercosis on record at the Central Histology Laboratory, Salisbury, and describes two unusual cases of cysticercosis recently found.

1. The intake of microfilariae of Onchocerca volvulus in two series of females of Simulium damnosum fed on an infected human volunteer in West Africa and dissected after staining in London was from 0–171 microfilariae per female in one series and from 0–152 microfilariae per female in the other series. The distribution of microfilariae per female became more normal when plotted on a geometric scale.

2. The migration of the microfilariae was followed in the two series of flies by comparing the geometric (Williams) mean numbers of microfilariae in the stomach, abdomen, thorax and head, from 2 minutes to 48 houis after engorgement on blood. Microfilariae left the blood meal rapidly after engorgement, 40–50% leaving the stomach within the first 60 minutes.

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.

1. There is a slow but definite loss of infective forms of B. pahangi from A. togoi maintained on honey and water alone and denied access to a host.

2. During the first blood meal after maturation of the filarial larvae there is a highly significant loss of infective forms from the mosquitos. On the 13th day, when they concentrate in the head of the mosquito, there is an unusually high (96·2%) loss after bloodfeeding.

3. The infective larvae migrate to and from the head and proboscis, and the thorax. There is also a migration to and from the head and the proboscis. This shows itself as a rhythm with 8 day oscillations.

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.

1. Maritrema apodemicum sp. nov. from the long tailed field mouse, Apodemus sylvaticus sylvalicus (L.) on Skomer Island is described and compared with other species of the genus.

2. 14·6% of the mice were infested, the % infestation being greater in the males, 20·3%, than the females, 5·4%.

3. A brief discussion of the genus and of other species occurring in mammals is included.

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.