Two species of chondracanthid copepods Acanthochondria platycephali Heegaard, 1940 and Pterochondria alatalongicollis Heegaard, 1940 are described. The latter was described by Heegaard as Acanthochondria platycephali f. alata-longicollis. However, it is placed in a new genus, based on the studies of type specimen and new material. A discussion on the other species of Acanthocondria parasitic on the flathead is given. It is suggested that A. bulbosus Heegaard, 1943, is synonymous with A. tchangi Y¨, 1935, and A. diastema Kabata, 1965, with Pterochondria alatalongicollis.

Two new species are described from New Guinea pythons, i.e. Ophidascaris niuginiensis and O. papuanus. The former was from Chondropython viridis and Liasis albertisi, the latter from L. amethistinus. Development of O. niuginiensis in mice involved a primary stage in the liver, a secondary stage in the mesenteric blood vessels and a tertiary stage in the skin, where growth occurred to a length of 50 mm or more. Initial growth, up to 10 mm, of O. papuanus occurred in the liver and body cavity of mice; a secondary growth phase occurred in the body cavity of the python host.

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.

1. The in vivo growth of Schistocephalus solidus plerocercoids was investigated by surgical implantation of worms into the body cavity of uninfected, recipient sticklebacks. 2. Burdens of one, two and five worms were used. 3. Results show a reduction in parasite growth with both increasing size and increasing numbers of parasites. 4. Reasons for the decrease in growth rate of multiple burdens are discussed and reference is made to the significance of burden size in completion of the life-cycle under natural conditions.

The growth of the three free-living stages of N. dubius was measured in terms of dry and fresh weight. Changes in body water content during moulting were demonstrated by variations in dry weight when expressed as a percentage of fresh weight. The respiration rate of the larvae increased until they became infective, after which time it decreased until five days later no oxygen consumption could be recorded. The inability of all larval stages to withstand anaerobic conditions indicated that their metabolism was essentially aerobic. The relationship between body size and metabolic rate was established for each stage and its significance in relation to the life-cycle discussed.

The biology of the life-cycle of Trichuris suis of the pig is described and discussed together with aspects of the hosi-parasite relationship. Development of the infective L. 1 larval stage within the egg was shown to be influenced by temperature. Following ingestion of infective ova by the pig, all subsequent larval development to the adult stage occurred in the mucosa of the caecum and colon. Eggs hatched in the distal region of the small intestine and throughout the large intestine. Larvae then penetrated the caecum and colonic mucosa via the crypts of Lieberkühn, where they entered the cells lining the crypts. The ensuing histotrophic phase lasted 13 days, during which time a gradual larval migration occurred from the deeper regions of the lamina propria to areas immediately beneath the surface mucosal epithelium. Luminal development was initially seen on day 16 when the posterior extremities of larvae were protruded into the gut lumen; from day 20 the entire posterior body region was exposed, while only the filamentous anterior region of the parasite remained embedded in the mucosal surface. The prepatent period varied from 41 to 47 days. Four moults were observed during development within the host and these occurred on days 10, 16, 20, 32 and 37 (to form the L. 2, L. 3, L. 4 and L. 5 or adult stage respectively). It is suggested that although T. suis may not be an important pathogen in its own right, its activities in the caecal and colonic mucosa may cause sufficient damage to enable secondary pathogenic invaders to become established.

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.

Two strains each of Eimeria acervulina and Eimeria mivati were examined for their ability to develop in the chorioallantoic membrane (CAM) of chicken embryos and the caeca of chickens. It was found that between 100 and 1000 times more sporozoites of E. acervulina were needed to produce infections in the caeca and the embryo CAM respectively. The reproduction of both species in infections of chickens was similar and a high degree of cross-protection occurred.

It was found that oocysts of E. mivati differed in size and shape depending upon whether they were produced from infections of embryos or chickens. When maintained by passage in chickens they assumed size and shape characteristics of E. acervulina.

These findings, with the known similarity of the life-cycle stages, pathogenicity and pathology, indicate that E. mivati is not sufficiently different from E. acervulina to be a distinct species. It is suggested that it is best referred to as E. acervulina var. mivati.

The egg and larval stages of Trichuris suis can be briefly characterized as follows: The egg: barrel shaped, possesses a thick shell consisting of three thick outer layers and an inner thin vitelline membrane, is operculate at each end and is unsegmented and unfertilized when freshly deposited. L. 1 within the egg: presence of an oral spear, a poorly denned oesophagus and an intestinal tract consisting of undifferentiated granulated material. L. 1 within the host: initial differentiation of an oesophagus, cell body, intestine and rectum. L. 2: further differentiation of the body organs and the appearance of the rudiments of the reproductive system. L. 3: initial development of reproductive system and development of a cloaca in the male thus distinguishing the sexes. L. 4: differentiation of reproductive system into vagina, uterus, oviduct and ovary in the female, and testis, vas deferens, ejaculatory duct, spicule and spicular muscle, sheath and tube in the male. L. 5 or adult stage: completed development of the sexual organs including formation of the vulval orifice and eggs in the female and seminal vesicle in the male.

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.

The results of experimental infections of Trichuris muris in wild field mice (Apodemus sylvaticus) and laboratory-bred wild house mice (Mus musculus) showed that the parasite elicited an immune response similar to that previously described in strains of laboratory mice. Experiments in laboratory mice showed that the parasite was able to become sexually mature only when small single infections or repeated low-level infections were given. A survey of a population of 43 wild house mice naturally infected with T. muris showed that the pattern of small worm burdens in the majority of mice was consistent with a situation of repeated low-level infection, except in the case of six female mice which harboured larger mature worm burdens. It is suggested that in these mice pregnancy and/or lactation may have suppressed the immune response, allowing the accumulation of a worm burden in excess of the threshold for worm expulsion.

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 ultrastructure of the reproductive system of mature (54-day-old), immature (32-day-old) and females from unisexual infections of Schistosoma mansoni is described in detail. The uterus is tegumentary in structure but the vitelline duct and oviduct are complex and possess cilia as well as lamellae on their luminal surfaces. The characteristics of the cells forming the walls of the ducts suggests that they may have a digestive function. The posterior portion of the oviduct of the adult worm contains sperm which become enveloped by lamellae. The vitelline cells of the adult contain vitelline droplets, much lipid and little glycogen. A second type of body derived from endoplasmic whorls is also present. Mehlis's gland contains only one type of gland cell and these cells pass through the ootype wall and open into its lumen. The female from unisexual infections has an incompletely developed Mehlis's gland, an ovary in which the Golgi complexes do not produce typical cortical granules and has vitelline cells which remain immature. The oviduct, ootype and uterus are well developed in contrast to the vitelline duct. A comparison with young, but not inseminated worms, suggests that the presence of sperm in the oviduct is not the major stimulus which induces maturation of the female worm.

Experiments using chicks of specified strain, age and sex raised under identical conditions on the same diet and infected with known strains of coccidia are described. The relationships between the infection rates and resulting oocyst productions of Eimeria acervulina and E. tenella are presented graphically and are used to demonstrate a crowding effect. Possible contributory factors to the crowding effect and possible reasons for the differences between the E. acervulina oocyst production of unmedicated birds or birds medicated with decoquinate are discussed. It is suggested that standard curves for normal infection rate — reproductive potential relationships under strictly specified conditions may be of value in choosing appropriate infection rates for critical experimental work to assess the effects of anticoccidial compounds on oocyst production.

Surface aminopeptidase (APase) in the acanthocephalan, Moniliformis dubius, was studied using leucylleucine, leucylglycylglycine, glycylglycine, alanylalanine, tri-alanine and tetra-alanine as substrates. In the presence of intact worms all peptides, except glycylglycine, were hydrolysed liberating amino acids and/or peptide subunits into the incubation medium. In 5 min incubations with 5mM leucylleucine, 93% of the liberated leucine was absorbed by the worms indicating a kinetic advantage for absorption of the leucine. In media with leucylleucine plus 10 mM methionine as an inhibitor of leucine uptake, the liberated leucine was not absorbed by the worms, but accumulated in the incubation medium. The inhibitory effects of leucylleucine and alanylalanine (or products of hydrolysis) on the uptake of 0·1 mM [14C]leucine in 2 min incubations were examined. Inhibition of [14C]leucine uptake by these peptides was non-linear up to 5 mM inhibitor concentration. Concentrations of either peptide greater than 5 mM did not produce further inhibition. A significant portion of [14C]leucine transport was not inhibited by these peptides. Inclusion of 0·5 mM Pb2+, an APase inhibitor, blocked the inhibition of [14C]leucine uptake by leucylleucine indicating that the inhibition is caused by the liberated leucine alone, and that interaction of the intact dipeptide and the leucine transport system is negligible. It is concluded that the surface membrane of adult worms has APase which can hydrolyse peptides in the ambient medium. The spatial arrangement of the APase and the leucine transport system is such that the hydrolysis of a peptide confers a kinetic advantage for absorption of the liberated amino acids. Encysted or mechanically excysted cystacanth larvae from the haemocoele of the cockroach showed no APase activity. Activation of the APase required a 30 min treatment in lipase, [Na+]taurocholate or other surface active agents. Since the APase in adult worms was unaffected by washing, the data strongly suggest that this enzyme is of parasitic origin.

Alteration of the free amino acid pool of Hymenolepis diminuta was observed following incubation of worms with a single exogenous amino acid in vitro, recovery from which depended upon the initial magnitude of alteration. The free amino acid pool of both rat small intestine and H. diminuta was rendered imbalanced after feeding a single dietary dose of proline. Recovery was more rapid in the host than in the parasite tissues. The quantitative dynamics of amino acid change with time were examined. The effects of amino acid variation upon the uptake and incorporation of lysine-C14 into worm protein were examined in vitro. Four amino acids altered lysine incorporation; aspartate stimulated incorporation while ornithine, arginine and histidine reduced variously the absolute amount of lysine uptake but produced relative stimulation of lysine incorporation. These data indicate that, in the system examined, short term variation of the free amino acid pool is unlikely to affect protein synthesis in H. diminuta. Data were obtained suggesting the possible occurrence of certain amino acid inter conversions in H. diminuta.

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.

Biochemical studies on the non-specific phosphomonoesterases have demonstrated the presence of acid phosphomonoesterase with maximum activity at pH 4·0 in Gastrodiscus aegyptiacus (enzyme I) and at pH 4·5 in the case of Fasdolopsis buski (enzyme II). The Km for ρ-nitrophenyl phosphate hydrolysis was 0·66 mM for enzyme I and 1·1 mM for enzyme II. Different concentrations of fluoride, arsenate, tartrate, tartaric acid, cysteine and copper brought about inhibition of both enzymes and magnesium, iodoaeetate, iodoacetamide and EDTA had no influence on either enzyme activity. Cobalt activated both enzymes while zinc inhibited enzyme I and strongly stimulated enzyme II.