Initial work on the fractionation of Schistosoma bovis adult worms is described. Both male and female worms were homogenized and sonicated before being passed through Sephadex G200. Five peaks were obtained with male fractionation (designated Ml to M5) and four with female (designated Fl to F4). Using the complement fixation test S. bovis antigen activity was detected primarily in peaks Ml and Fl. With the indirect haemagglutination and indirect haemagglutination inhibition tests S. bovis antigen activity was detected primarily in peaks Ml, M2, M3, Fl and F2.

An indirect haemagglutination test has been developed for the detection of Schistosoma bovis antibody. Fresh, formalin and glutaraldehyde fixed sheep erythrocytes as well as fresh and formalin fixed human erythrocytes were tested. Tanned glutaraldehyde fixed sheep erythrocytes sensitized with an adult worm extract were the most sensitive and remained stable for at least 8 weeks at 4°C. With such cells 98% of a group of S. bovis infected cattle were positive while negative results were obtained from cattle infected with other helminths.

A description of the male and a redescription of the female of Philometra cylindracea, a parasite of yellow perch (Perca flavescens), are presented.

Philometra cylindracea has a one-year developmental cycle starting as infective larvae in June and becoming mature, larvigerous worms at the end of next June. Cyclops vernalis was found to be a suitable intermediate host under experimental conditions.

Microfilariae in whole uncentrifuged cat blood were transfused from infected to normal cats. The recipient cats were bled frequently and the life-span of the microfilariae in the peripheral circulation was determined. The life-span of microfilariae in different cats was very variable. Microfilariae were detected for 2–136 days after inoculation. In immunized cats microfilariae could not be detected 18 hours after inoculation. Any attempt to concentrate or clean the microfilariae caused them to disappear from the circulation more quickly.

Colonies of Culicoides nubeculosus and C. variipennis were established at Winches Farm Field Station, St. Albans.

Both species of midge were found to be susceptible to infection with Onchocerca cervicalis microfilariae. Infection was achieved either by engorging through a chick skin membrane on a suspension of microfilariae in blood, or by feeding upon a horse naturally infected with O. cervicalis microfilariae.

A large proportion of the microfilariae ingested by the midges penetrated into the haemocoel and migrated first to the thoracic flight muscles and then to the head. Larval development occurred during migration and 3rd stage (infective) larvae of O. cervicalis reached the head of infected midges (kept at 23°C.) 14–15 days after engorgement.

Mice were immunized to the intestinal stage of T. spiralis by using infections terminated with methyridine before production of newborn larvae had commenced. The muscle larvae which encysted following a normal complete challenge infection were reduced by 87 and 95% in immunized mice. No statistically significant reduction in a challenge infection of intravenously injected parenteral larvae was produced (8% and 15% actual reduction). Previous work has shown that adult worms in a challenge infection are stunted and expelled earlier as well as haying a reduced fecundity; it is concluded that the immunity generated by the intestinal stage is largely specific in its action to that phase in a challenge infection.

Four species of anoplocephaline cestodes were found in wild rabbits collected throughout Britain in 1962 and 1972, i.e. since the great reduction in rabbit numbers following the introduction of myxomatosis in 1953. They were Cittotaenia pectinata (Goeze, 1782), C. denticulata (Rudolphi, 1804), C. ctenoides (Riehm, 1881) and Andrya cuniculi (Blanchard, 1891). C. pectinata and C. denticulata were relatively common with a respective prevalence of 25% and 8% in two samples totalling 442 rabbits and were widely distributed throughout Britain. C. ctenoides was rare and only recorded from seven localities, although these were spread throughout Britain. A. cuniculi was also rare being known from four counties in England and five islands off southern England and Wales. C. pectinata was the only species found in hares and its prevalence was low at 6%. The records are shown plotted on to 10 km square distribution maps.

2 678 naturally infected cataleptic ants of the species Formica pratensis were divided into three categories depending upon their size viz., large, medium and small, and were dissected to elucidate the intensity of infection with Dicrocoelium dendriticum. 2 233 (83.4 percent) were positive for metacercariae. The maximum number of metacercariae isolated in the three categories were 443 252 and 176 respectively. The average number of metacercariae varied greatly in the 3 categories, though no appreciable difference was observed in the percentage of infected ants. The presence of even a large number of metacercariae in the abdomen of ants seemed to cause few harmful effects.

The rate of escape of the third-stage larvae of Brugia pahangi from Aedes togoi which were allowed to probe on a cat and a mouse at time intervals of 5, 10, 20. 30 and 60 seconds was studied. The rate of escape of third-stage larvae at all time intervals was greater during probing on the cat than on the mouse, and was in a logarithmic linear relation to the length of probing time by the mosquito host. The greatest loss (91.35%) of third-stage larvae was in mosquitoes which fed on a cat until fully engorged. There was a remarkable rate of escape (57.41%) within 5 seconds. This striking rate of escape of third-stage larvae may have important implications on filariasis transmission. Most larvae migrated towards the proboscis and head of mosquitoes during these feeding periods. Nearly equal numbers of third-stage larvae escaped from mosquitoes which fed to repletion for more than 60 seconds on a mouse and from those which probed for more than 60 seconds on the same mouse but did not engorge. This confirmed our view that filling up of the stomach with blood does not constitute the single factor in causing the release of third-stage larvae from the mosquito host.