Duodenal mucosae of uninfected lambs and lambs inoculated at least 16 days earlier with 85000–140000 Trichostrongylus colubriformis larvae were examined with the scanning electron microscope. Normal duodenum had tall spatulate villi with surface folds upon which goblet cells and a regular pattern of hexagonal enterocytes were seen. Micro villi on normal enterocytes were closely packed and imparted a granular surface texture. In heavily infected areas of gut the villi were atrophic, the mucosa sometimes being composed of irregular masses and ridges, with crypt mouths, often surrounded by collars of cells, opening into the surface. More severely affected mucosae were flat, with protuberant collars of cells surrounding crypt mouths. There were rounded bodies, interpreted as sloughing enterocytes, or inflammatory cells, on the mucosal surface. Apices of enterocytes were domed and microvilli were sparse and irregular. Micro-organisms were numerous on cell surfaces. Nematodes were located in sinuous thin-walled tunnels in the epithelium. The mucosal microtopography is compared with that of coeliac disease of humans, nippostrongylosis in rats and with villus atrophy in pigs.

Semi-defined and defined media for the growth of culture forms of Trypanosoma brucei sspp. have been developed by enrichment of tissue culture medium 199 with additional vitamins, amino acids, salts and other compounds. The semi-defined medium contains an acid hydrolysate of casein: in the empirically devised defined medium the casein requirement has been circumvented by inclusion of additional vitamins and amino acids. Both media are very hypertonic. Control of pH was found to be particularly critical for growth. The optimum temperature for growth in the semidefined medium was between 25°C and 28°C, but cells would undergo one or two division cycles at 37°C.

The histology and ultrastructure of the salivary gland in Dermacentor andersoni are presented with particular emphasis on those aspects relating to fluid secretion. We suggest that the group III acinus contributes most of the fluid portion of the saliva (i.e. water and small molecules) and that the main cell-type involved is what we name the ‘water-cell’. The granule-cells possibly secrete the cement by which the tick secures its mouthparts to the host, and the ‘vacuolar cell’ possibly produces a protein-rich secretion. The function of the group I acinus remains obscure.

Juvenile hormone and its analogues inhibited growth of Panagrellus redivivus and of the free-living stages of Haemonchus contortus. Substances extracted from nematodes had similar actions and also showed the activity of juvenile hormone in insects. Partly purified material from 1 g of freezedried juveniles of H. contortus contained about 200 Tenebrio units.

The effects of Trypanosoma (Trypanozoon) brucei infection have been studied in actively growing connective tissue in rabbits.

Groups of mice were exposed to Schistosoma mansoni cercariae in a large volume of water. A factorial design was used to investigate the effects of cercarial concentration and length of exposure on infection rates and worm burdens. Low exposure times and cercarial concentrations gave no infections, but prolonged exposure to high concentrations gave high infection rates and worm burdens. Prolonged exposure to low concentrations gave low worm burdens and moderate infection rates: short exposure to high concentrations gave moderate infection rates and worm burdens. Statistical analysis showed that both infection rates and mean worm burdens were significantly related to the two main factors, but the relationship was complicated in each case by curvilinear effects and by a significant interaction between the main factors. Field cercarial concentrations are generally low on St Lucia, a fact suggesting that brief human water contacts, such as fording and filling domestic water containers, play little part in transmission. Prolonged contact during swimming, bathing and washing clothes may produce significant infection rates accompanied by low worm burdens. However, on the rare occasions when high cercarial concentrations occur, even the briefest exposure may produce significant infection rates and moderate worm burdens.

Daily infection with doses of approximately five oocysts of Eimeria tenella produced an infection with an extended patency which ceased by the time the birds had received about 140 oocysts. Total oocyst production was comparable with that in birds given the same number of oocysts in a single dose, but the immunity to subsequent heavy challenge was significantly greater. Continuous exposure to low-level infections may be more comparable to the field situation and the present results suggest how birds can acquire a strong immunity without showing evidence of clinical disease.

Bucephalus haimeanus is shown to be an estuarine species. The cercaria from Cardium edule is briefly redescribed to include details of the nephridial system. The metacercaria is described for the first time, having been obtained experimentally in Pomatoschistus microps and Pleuronectes platessa. In Pomatoschistus microps it survives at least 10 months, development within this host being completed within 2 months. The main site of infection is the liver. Migration is completed within 1 h and in some instances within 10 min. During this period the metacercaria actively feeds on host tissue, the gut being greatly distended with food on encystment. A hyaline cyst wall is maintained throughout the remaining life of the metacercaria. ‘O’ group plaice are highly susceptible to invasion by B. haimeanus during early summer and 100% infections were recorded in catches from Ynys-las, Dovey Estuary, in June. Experiments showed that only 2% of the metacercariae survived more than two weeks and that ‘l’ group plaice were non-susceptible to infection. Plaice are therefore considered accidental hosts. The metacercaria was linked with the adult stage from Morone labrax on the basis of comparative morphology and the ecology of the hosts, the bass entering the estuarine habitat during the summer months. The adult is considered synonymous with Bucephalus minimus Stossich, 1887.

Samples of approximately five wild rabbits were obtained each week over the 4-year period 1967–70, and their intestines examined for adult tapeworms. Pour species of anoplocephalinae were found, Cittotaenia pectinata, C. denticulata, C. ctenoides and Andrya cuniculi. C. pectinata was found in 29% of the 968 rabbits examined, C. denticulata in 14%, C. ctenoides in 12% and A. cuniculi in 6%. There were 63 double infections, of which 44 involved A. cuniculi, and three triple infections. The most frequent number of worms per infection was one for C. pectinata and A. cuniculi and two for C. denticulata and C. clenoides, although the mean numbers for these species were respectively 7·2, 5·3, 2·7 and 1·8. A. cuniculi, and to a lesser extent C. ctenoides, were very restricted in distribution within the study area, occurring only on the higher, chalk downland (250–550 ft A.S.L.). This finding implies that individual rabbits usually spend their lives within relatively small areas. Considering all the material a seasonal trend in host infection rate was apparent only with C. denticulata, which increased in abundance from July to a peak in September and then declined gradually to a low level, lasting from April to June. Infections, including small specimens of any of the four species, were rare from February to June and it is presumed that infected intermediate hosts were correspondingly rare during this period. Except for C. denticulata, which was found more frequently in male rabbits than females, the sex of the host had no influence on its likelihood of infection. However, except for C. pectinata, the age of the host was important. Thus, C. denticulata and A. cuniculi were significantly more frequent in juveniles than adults whilst the reverse was true for C. ctenoides. Small (‘young’) specimens of C. denticulata and A. cuniculi were more frequent in juvenile than adult rabbits, but the difference was not significant for the other two species. It is concluded that only C. ctenoides survives for more than a year and that this species and C. pectinata are more likely to infect rabbits that are adult than are the other two species.

Prophryxus, a new genus of hemiarthrinid bopyrid from Kenya, is described. The only species, P. globicaudatus, is parasitic upon the shrimp Coralliocaris graminea (Dana). Prophryxus is considered to be most closely related to the genus Hemiarthrus Giard & Bonnier, from which it differs in the morphology of the abdominal appendages. It is most remarkable for the presence of a sucker-like organ on the dorsum of the cephalon, a feature unique in the Bopyridae.

Worms of secondary infections of Raillietina cesticillus established in 10-week-old birds but failed to grow mature strobilae. This was taken as an indication of resistance to the cestode. The resistance was inhibited by the immunosuppressant and anti-inflammatory drug dexamethasone, which prevented the local inflammation around attached scolices characteristic of secondary infections of R. cesticillus. Mast cell hyperactivity and eosinophil infiltration in intestinal tissues and immunofluorescent antibodies in sera of infected birds were also demonstrated. Scolices without strobilae from refractory hosts with both primary and secondary infections regrew their strobilae when transplanted into susceptible hosts.