The locomotion of two species of cercariae has been studied by cinematography. The ability of the tail to generate bending waves providing the force to drive the cercaria forward has been demontrated. The waveform of the tail and its relation to the pattern of movement has been described and evidence is presented that the tail is capable of propagating complicated swimming movements in the absence of the body. The pattern of propulsion is related to the functional organisation of the tail musculature of the cercaria.

Mice immunized by single pyrimethamine terminated infections of Plasmodium berghei berghei, strain NK65 or the Nigerian P. berghei-like parasite, N67, were immune to challenge by P.b. berghei, P.b. yoelii strain 17X, P.b. killicki strain 194ZZ and N67. Mice similarly immunized against P.b. yoelii were only immune or N67 resulted in infections comparable to those found in normal mice. Mice immunized against P.b. killicki were similar except that they also possessed some protection against challenge by N67. Evidence was obtained which indicated that the difference between P.b. yoelii and N67 was not associated with the virulence of the parasites. Prolonged exposure to P.b. yoelii infection slightly increased homologous and heterologous immunity. Two lines of parasites were crossed; one of these was derived from P.b. yoelii and the other from N67. They differed in pyrimethamine sensitivity, glucose phosphate isomerase type and the ability to survive in mice immunized against P.b. yoelii. Ten lines of parasites showing the P.b. yoelii characters of pyrimethamine resistance and GPI-1 were isolated in drug treated mice immune to P.b. yoelii challenge. Twenty-one clones were isolated without drug or antibody selection from the parasites resulting from the cross between P.b. yoelii and N67. Sixteen of these clones were classified according to the markers which they possessed and six were found to be recombinant in character. The experiments showed that genetic recombination occurred as a frequent event in P. berghei and involved factors which control the cross-immunity produced following infection with these parasites.

Ultramicroscopic features of the ookinete/oocyst transformation in Plasmodium berghei are described. The apical complex of organelles and some pellicular components, believed to be responsible respectively for cell penetration and body form were resorbed into the cytoplasm shortly after the ookinete came to rest under the basal lamina of the midgut wall. Within a single digitate nucleus, spindles at different phases of division were observed with kinetochores in early and late anaphase position. From the number of kinetochores the chromosome complement was estimated at 5–10.

Bloodmeal volumes and haemolysis rates were determined in male Argas (Persicargas) arboreus and A. (P.) persicus fed on pigeons, domestic fowl, and adult and fledgling herons. Erythrocyte osmotic fragility curves were prepared for the host species.

Ancylostoma tubaeforme infective larvae have been tracked in agar and the dominant features of their tracks subjected to a numerical analysis. Very few of the features are uniformly random, most follow a well described normally random frequncy distribution. The mean size of an ‘are’ was 3·61 mm in radius and subtended an angle of 123° at the centre. The length of track per unit time declined with larval age and reversals were the main features to disrupt the pattern of tracks.

The development of larvae of Baylisascaris tasmaniensis to the adult stage is described, using laboratory mice and the Tasmanian devil as experimental hosts. The first moult occurred in the egg, the second moult occurred in mouse tissues at 1–2 weeks after ingestion of embryonated eggs. Larvae migrated to liver, lungs, brain, eyes and kidneys, but most larvae were found in the mesenteric tissues and wall of the intestine. Larvae grew to a length of 0·5–1·0 mm in mice, although some attained a length of 2 mm or more in infections over a year in duration.

The cysticercoid of Tatria octacantha Rees, 1973 from the haemocoele of damsel-fly nymphs consists of an outer and inner cyst. The tegument of the outer surface of the outer cyst bears long slender microvilli which increase the surface area presumably for absorption. The tegument on the inner surface bears electron-dense microvilli and contains vesicles embedded in an electron-dense material. The contents of the vesicles resemble those of the central cavity in which the inner cyst floats freely. Nutrients absorbed by the outer cyst pass into the central cavity where they are available to the inner cyst.

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.